Adsorption systems at temperatures below the freezing point of the adsorptive

Adsorption systems at temperatures below the freezing point of the adsorptive

Adumues in Cbiloid 0 Elaevier Seientiik ARKMPTION C.C. end khterfeee Seienee, 9 (1978) 288-882 Publishing Company. Amsterdam - Printed in The Netbe...

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Adumues in Cbiloid 0 Elaevier Seientiik

ARKMPTION

C.C.

end khterfeee Seienee, 9 (1978) 288-882 Publishing Company. Amsterdam - Printed in The Netberhmds

SYSTEMS AT TEMF’EtUTURES BELOW TllE FREEZING

POINT

25s

OF TllE ARSORPTIVE

LITVAN

Division

of

Building

Research,

National

Research

Council

of

Canada.

Ottawa,

KIA OR6

CONTENTS I

.......................................................

Introduction Theoretical

II

I11 1V V VL VII

Experimental Length tleat

Methods

Change

Vapour

and

and

Area

of

Temperature

.

Length

-

Freezing

Aqueous

. X

Cycles

Anomaly or

. X1 XI I XIII XIV xv

Action

Testing

of

Frost in

Mechanism

of

xvi1

Permeability

.

Viscosity

-

Minimiring Salt

Action

ConcLuslon

in

Non-equilibrium

of

267

O°C ...........................

Isosteres Adsorbed

ChaAges

27

....................... in

Porous

Silica

Agents

De-icing

279 283

Cement.. on

the

..................... Freezing

........................................ Systems

...................................

........................................

.................................................. ....................................................

Ap ................................................... .................................................. Agents

....................................

.........................................................

274 276

................................

of

I

273 Glass..

..................................

Concrete

Resistance

Resistance

Cryoprotective

267

..............................................

Cryoprotection

Bufferiag of

265

Obtained

.......................................................

-

261

..................................

Extension

and

Biological

Rare..

.

of

Solutions

Frosr

Effect

. Cooling

XV!

Failure

Aggravating

Curves

Vicinity

the

Cerneat

Affecting

Cryoinjury

the

Lengrh

and in

............................

.........................................

Extension

Chloride

Mechanical

Factors

Isotherms

260

................................................

in

of

Sodium

256 259

..................................

Low Temperatures..

Thermograms

Frost

Extension

the

. Interpretation IX

Changes..

Determination

Interpretation

254

..............................................

Length

Pressure

154

.........................................

...............................................

Studies

Contenr

Surface

VIII

Considerations

,of

285 Cement

Paste

288 239 292 296 296

296 297 297 297 298 308

ABSTRACT Isothermal below in

the

bulk

are

pressure

adsorptive

or

matter

adsorbate

and

shis

cement

an

some problems explanation

of for

ro

foodstuff.

the the

for

is

arwined.

nor

surface

action

of

for

porous

area

has

building

cryoprotective

bulk

process;

the

of

process

glass. such

led

the

the

formatioa.

co

the

cannot

aninral

and

development

of

clarification

method

and

be

hydrated

as

materials,

determination

of

the

pressure

this

silica

substances

of

that

desorption

when

adsorbed

between

vapaur

meniscus

then,

understanding

durability

BET

through only

a

the

changes

substances

and

by

while

biological

This

the

resolved

valid

that

adsorbate

occurs

be

dimensioaal

The difference

system

&creases

and even

testing

is

of

indicate

unfrozen

system

srace

found

measurement

in situ.

of the

system

equilibrium

and for

adsorbate

the

pores

the

was

the

porous

the

of

the

of

outside

bricks,

tissue,

new methods

the

in

mechanism

paste,

plant

of

breakdown

completed

of

and

to freeze

energy

freezes

remaining

Mechanical

point

unable

free

outside

&sorbed

studies

freeting

solids

porous

vapour

adsorption

it

of

suggests

an

agents.

I!CPTRODUCT1ON

I.

Adsorption of

the

systems but

of

substance on

the

perhaps of

2)

features

Answers

the

are

the

are

two

of

most

phase not

of

plants,

and

Kumerous

inherent

links

This

is

II.

TIEORETICAL

the

in

of

are

to

the

the

interest.

concerned

satisfy

of

temperature been

widely

present

with:

in

heaving

adsorbed

state.

freeze-thaw

~011s. brick. of

for

foodstuff

not

practical

stone).

clarify

have

modifiand

but

to

fields

potential

adsorbate.

curiosity

preservation

diverse

arise,

of

(concrete.

undertaken

the

the

the

triple-point solid-adsorbate

questions

1) of

theoretical

materials

bulk

Several

substances

frost

the

by porous

to solidification for

have

the

phase

two phases

phases

coexist

and the

curved

instead

of

and,

low

below

exhibited

winter and

various been

biological

aspects,

bur

considered.

review.

CONSIDERATIONS

to

Ibe

great

due

fields

stuaies

among

purpose

According

surfaces

of

relations

only

temperatures

behaviour

of porous building

materials.

valid.

at

important forces

in the diverse

hardiness

solids

phenomena

adsorption

susceptibility

present

anomalous

sought

application

the

on

cooling

cation the

vapours and

vapour

rule.

such

as

system

planar pressure

therefore,

pure

water

and

vapour.

invariant.

If

1 iquid is

surfaces, of

bulk

the

curved

equilibrium

phase

At the

rule

surfaces annng

has

the

is

in

one

degree

the

are

phases

when

three

separated

usual

different

three

free&m

triple-point

phases its

of

form

is

by no

from

that

of

single-component

a

of

Loflger planar

266 substance

can be achieved

radii of

curvature

of

The dependence

‘at temperatures

the

iaterfares

other

of the triple-poiat

both

surroundedby

each phase, eliminating

In this equation bulk

comprising

the the

A$

temperature,

heat of fusion,

rhe

Various of

the

T and

dropler

coexistence pg

(Figure

the

can

curves 1) _

The

of

best

be

surveyed

liquid-vapour

value

of

T at

To the triple-point of the system c2.g radius of the droplet, r s.g

point.

Such

a shift

by

and the

A shift of eirher or both

freezing

for

toasion.

The aeu tripleon the relative

crystal.

possibilities

freezing point. alters

and

and a

of the Laplaee

point of the system may be either below or above To, depending sire of

equation

the relation

V the volus~ and a the surface

that of the crystal,

was derived

of a droplet

the Gibbs-Duham

yields

if the

values.

terms by the substitution

and iaregraring

denotes

Y

phases,

system eoasisting

By writing

the pressure

simplification

equation,

vapour.

the triple-point

on the radii of curvature

by Befay et al [l] for a siegle-eompoaent crystal,

than

assume the appropriate

means

a schematic

solid-vapour

intersection curves

occurs

of

to if

in of

higher

the

the or

surface

the

illustration

coordinates

curves

is

the

lower pg values of

the

condensed c

Fig. 1.

Schematic

phase diagrams

of

water

with

planar aad eurved

surfaces.

is either

phase a

new constituent early

and

increases

even

observarion

at

at

or

solutions. could

the

but

not

solids

or

unequivocal

for

solve

the

to

the

Vapour important phase

techniques

Unfortl the

ligroin care

is has

to

experimentally

In

sink. but

the

c3n

As

as

will

oe

from

heat

state. ever,

capacity

on is

of

capacity

the

be

the

not

freeze of

strength

coeeept.

theory,

the

however. ia

porous

Neither

it.

but

could

this

may be

applied.

calorimetry in

In

avoid

bulk

of

of

of

the

phase,

the

the

solidified

mst

conven-

such

vapour

rnsrimum

the

adsorbate In

fluid

determining

the

of

perhaps

study

difficulties.

condensation as

are

the

system

so

as

pressure,

substance

vapour

on

pressure

validity

the

adsorbent adsorbent

from

IOU

of

the

adsorbare

can

in

the

is

is

is

perturbed. altered

It by

the

is

heat

of

in

experiment.

in

low

Calorimetric state

period

of

time

chaage

is

so

but

capacity to

be

ef

its

measure’ments

very

probable of

required

slow

and

from that eaused

such

presence

the

equilibrium

rate

assumed

during

operated

it.

indistinguishable the

to

hysteresis

long

tie

always

observable

&fined

1:4.

cooling

thus

behaviour.

reach

tie

was

prior

ande a heat

than

in

literature,

marked

extremely

calculating

adsorbent

is

to

temperatures, it

the

as

greater

calorimeter

in

dimensional

a uniquely

that

seldom

is

acts

operated

the

exhibit

adsorbare

which

remperarures

followed by

is

reported

their

presented

small

masses

systems to

the

calorimerers

work to

of

133~s of

uncertainty,

path

low

the

adsorbent Because

the

not

changes

determination

cooled

the

Moreover,

Dimension31

of

all

At

effect

the

in

commence

drift.

that

the

serious

adsorbent.

to

respect

equilibrium.

calorialeter

ionie

by

techniques

adsorption

the

heat the

adsorption with

&pen&

observable

explain does

phenomenon

caused

and

pressure

1:20.

systee

difficulty

attain

the

thus

that

Another

the

3s

manner

cycles

one

of

considerable

of

the

of

adsorbate

described,

measurements

to

that

specific

sa;;rll

conventional

temperature

to

of

that

to

the

This

employed

Furthermre.

elevated

presence

results

requiring

of

support

undesirable.

is

rhe

the

be

yield

of

sssessed.

The-ratio it

mode

coaeentration

plants

freering

the

suffer

the

exercised

the

calorimetry, by

in

cooling.

concerning

difficult

be

during

directly

all

:lately.

presence

obviobly

realizable be

to

of

dilatometry

wslls

the

found

difficulties

the

eoneept or

basis

problems

experleental

hypothesis never

of

engineering be

the

if

value. this

temperature.

lower

measurements.

dr

cell

on

features

evidence

or

concrete,

pressure

particular the

soils,

predicted

many

fiaite

utilized

classical

dilatometry,

tolueng

a

planar.

.MElllODS

transitions.

tional

of

to [2]

in

other

inherent

EXPERiMENTAL

III.

the

experimental

attributed

water

a significaatly

account

[3]

that

zero

work

temperature

at

instead

from

eontemporary

weLI-known 0’2,

or concave

cmvex

an

that

the

value

in

indicate, the

adsorbate

by

adsorbate the

pure

how-

heat but.

beeause

257 the

magnitude

of

Common to content,

the

all

effect

methods of

i.e.,

maintaining

measurements,

may cause

evaporation

container

during cooling. to

rate of cooling,

rate

i.e.,

the

at

constant-temperature cases

inert

course,

gas

is

The

inherent

can hardly

vapour

adsorbate

content

branch

of

the

relation

follows

on

of

be

to to

is

as being

transfer

that

is

in the

directly

only at infinitely this

incremeets

re-esrablish

retard

Ia

created

on the walls of the

avoided

small

adsorbate

is cell tempera-

certainty.

To minimize

very

imposed

effect

and

a

in

long

equilibrium.

distillation;

low

In

this

some

addition.

of

measurement.

carrying

out

with

the

in

the

the is

high

adsorbate

care.

With

decreases the

the

dead

so

opposite

the

the

described

the

content that

in

the

occurs

of

excess

cell,

by

the

the

adsorption

desorption.

effect, by

however.

lowering

that

space

system

expressed

change

measurenent.

isosteric

cell in

variables

temperature

an

greatest

sstsll

On warming,

relatively

sign

by

resulting

increases,

at

ran

mass

temperature.

However

isotherm.

the

and

changed

pressure

beween.the

that

depend

cooling

even

of

of

cell

thus be described

of

adsorbent.

with the

can

¶he rate

to the cell

the

out

across

system

pressure

the on

rulej

The

is

circumvented

condenses

the

added

be

change

during chaage

condensation

is

difficulty

be

temperature,

conditions

gradient

constant

vapour

neglected.

and

period

precludes

be

sample

of

temperature

to

preventing

the

from

the

has of

isosteric

branch of the isotherm.

proportional

it

difficulty

a temperature

isosteric

practice,

unknown,

the

if ever, can mass transfer

tures; seldom,

desorption

is is,

desorption

of

dimensions a

when

occurs

branch. the

particular

and It

system state

is

reached. In order With

r31. rod

was

are

lowered

or

shown

in

in

to

those

I.

the

where

points Nos. 6 ad &sorption It

information

branch

of

exercised remeebered a rule

because can

of be

to avoid that

the

may be

same

temperature the

extension

that the

from

misinterpreratioa. systems

the

length

that

of

the

as

in

about

was

restored

the

points AL/L

=

of

Nos.

below

In

the

of

measurements,

subjected

with

assessing to

restored The

but results

temperature

as

results was rep-

8 and

11.

units

shorter

(adsorption

the

rod than

branch).

the fact that the adsorption

branch.

experiments the

glass

changed

temperature

1.4. -5

the isosteric

shortcomings

was

out

silica was

again.

10

by cooling is

system

reference

11 *

is consistent

isotherm

was carried

a porous

Z.SO’C,

reeaeured

when

and

these

of

temperature

the

seen

and

length

temperature,

and

the results

problems

obtained

adsorption

isesferie.

the

branch)

length

experiment

following

original

0.5’C)

It

the

a&orbed,

13. This differeace

is not suggested

dismissed

as

both),

(desorption

of

eases

water After

(within

Table

be

assumption

+l.SO°C.

possible

by heating

appears

this

anwwnt of at

as

stored

test

fixed

measured

(raised, closely

to a

method. great it

care has

cycling

should

be

Valuable has to

to be

be

are

not

26%

.

=rABLE

I

Length changes Point Number

due to temperature Temperature. 2.50 l25.0 - 6.5 + 2.58 +30.0 + 2.07 -31.5 + 2.85 +22.0 0.0 + 2.92 +20.0 + 2.02

1

l

2 5 4 5 6 7 8 9 10 11 12 15

OC

variation

with

fired amunt

of water

[3]

AL/L x lo-' 0

- 1.01 +15.33 - 3.60

- 0.12 +lO.ZS

I-

I -

l-

I

-tal-

Fig. 2_ Expansion isostere of porous silica glass containing 8.8839 g/g wafer (Reproduced by permission of the Narieaal Research eomeil of tinada adsorbed. from the Camdian 2ournal of C%emistry. Volume 4. pp. 3095-3107. 1963) (31.

IV.

lJ3Kml

ment

of

constant

cycle until

seen

phase

changes At

changes.

knows

anmunts

between

changes

extensometer.

I inear

of

dimensional

containing

temperature

be

STIJDIES

in the field

Work

rod

CHANCE

ia

the

manner.

length Ia

first

of

adsorbates [SJ

water

+5 and

-165%.

At

length

were

curves

of

the

several

uas each

‘96~per taken

shown

in

the

with Figures

adsorbent-adsorbate

temperature

ia

stage

not detectable are

system

regions,

uith

cotinced

a porous,

adsorbed

Representative

that

of

anomalous

&e

measure-

cent.

silica-glass

steps

through

temperature

a was

kept

a’ capacitance

type

2 to

4.

it

does

not

where

changes

change

my in

a

in dimension

occurred. important

The

mst

1.

No length

than

that

¶his

condition

2.

If

The

occurs

be

ineeptioa

of

the

is

changes exact

adsorbate

is

greater

the

two

if

the

uhieh

-7-C

two

-7

be

ef

swmnarired

of

water

as

follows:

adserbed

the adsorption

is

less

isotherm_

layers.

layers

and

the

can aaxwnt

loop

adsorbed

than near

at

temperature

experilaents

hysteresis to

observable

for

the

detected

equivalent

are

content at

of

can

concentration

length 3.

at

findings

anomaly

on

cooling,

anomalies

in

-22-C.

anomaly

transition.

but

o&curs the

depeads

other

upon

anomely

the

always

-12OC.

+4cl

0 l

COOLING WARMING

+30

a0 +20 SECOND

CYCLE

-i. 2 +I0

6

FIRST

CYCLE P-

-10

*

I

,

.

-I50

- 175

-I25

-160 T.

Fig. 3_ adsorbed_ from the

l+ansion

isostere

(Repreduced

Canadian

ef

Journal

of

silica

~rous

by permission

of

Chemistry,-

+

I

-75

-50

1

-25

t

0

‘c glass

containing

the Nat&~saJ Volume

41.

6.13g9 g/g water Council of Canada 3099-3lD7.* 1963.1 [3]

Research

pp.

if anonralies can be accepted

tinsitions.

4.

but take piace between 5.

Anomalies

6.

All isosteres

7.

After completion

its iaitial

anomalies

are mt

sharp

during warming exhibit

occur at higher temperatures

than during cooling.

hysteresis. the length of the adsorbent

of a cycle.

is different

from

length.

These results. understanding

as indicaters.

5 and 10°C.

of

are in themselves

though interesting, the low temperature

cannot be interpreted

behaviour

insufficient

of adsorption

in terms of physical

to provide

systems.

Ihe

events with any degree of

confidence.

HEAT

V.

CON-t-EM

AND

LWCTH

In order to establish and to learn mOre about heat content originally

the link between

was utilized.

length anomalies

the nature of the latter,

and dimensional

developed

CHANCES

ehanges were

by Antoniou

simultaneous

IBeasuremeat of

A caleriareter design

undertaken.

I-l] that incorporated

Results of the experiments

and phase changes,

an optical

with porous

strain

silica glass-water

gauge system,

+20

+10 ?R 5-

0

4 -10

-20 0

COOLING

.

WARMING

,

-30

I

I

I

I

I

-175

-150

-125

-100

-75

I

-50

I

-25

I

0

I. 'c Expansioa isostere of porous silica glass eontaiaiag 0.1754 g/g u_ater (Reproduced by-permission of the Natienal Research Council of tZaw&t from tie Canadian Journal of Ctiemistry, Volme 41. pp. 3095-3107, 1963.) [3] t Fig.

4.

adsorbed.

-25

-30

-15

-20

-5

-10

TEMPERATURE.

0

UC

Fig. 5. Specific heat of water adsorbed OR porous silica l;lass as a function temperature _ Nmerical values indicate the water eontent of the adso;bate. (Reproduced by permission of the National Research Council df Canada frola the Canadian Journal of Chemistry, Volume 44, pp. 2617-2622. 1966.) IS]

in Figure 5. in addition

shown yielded

the

following

1.

Length

2.

The

-ll’C,

anomalies

specific

do

heat

consistently

(0.45

eal

deg -‘)

‘Ke heat

3.

content

is

extent

of

the

and

to

unfrozen

whm

present

concentrations

vary

length

sigaifieaatly

adsorbed 7.7 of

ft

is

clear

ghis sittitien

that

listed above

[S].

changes.

is,

below

tmre

than

No. in

ia

monolayers.

the

melring

that

of

cal

g

1 (Settion

only

show

good

be

is ~~s~~ unfomte

in

IV), but

the

anosmly

at

bulk ice

value the

the

-1

when

the warer

is uncertain

transition

first

two

behaviour

is

to the

not

?ayers

kmwn.

remain

of these layers at

surmised.

reproducibility

a quantitative

Sesterif

55.5

yhis

invelved

themselves,

can

curves

is

warer

water

VAPOUR PRESSURE AND EXTENSIOAl

VI.

the findings

phase

significantly

quantity

concl&on

Wle

signify adsorbate

the

fusion of

to

higher

confirming

.

According

4.

indeed

of

equivalent

that

to

eonelusioas:

ia

a qualitative

sense,

but

sense.

ISO¶IlERM

adsorptiee

studies

because

suffer

the mhIanism

frem of

uncertaimfies. frost-

action

etiot

of

be

understood

bulk

surprising As

in

without

freezing

point

the

Although

heat

of of

this

In

silica

glass-xenon

To clarify

due

arrangement small

construction

is

is.

in

[6].

at

in-this

system

shown the

question,

of

this

temperatures

field

in

Figure

is

below

heightened

the

above

the

pressure

by

The

results

this

sirultaneoltsly

the

of

had

low

were

walls.

with

a quartz to

be

used

temperatures

and bake-out

I

300 I

-

121.58 ‘C

I

I

extension

avoided balance. for

length

necessitated

to

reduce

triple-

adsorptive isotherms

with

the

isetherms

of

porous

point.

pressure

quantity

bulk

extension

obtained

determined

the

and

results

increase.

decreased and

were

specimen

1

an

vapour

on

equipment

temperature about

indicate

vapour

6 illustrate

concerning

at

in

bring

temperatures

temperature

lowered.

gravimetrically

pressures

increase

should

at

the

of

is

system

condensation

a companion vapour

found

fact,

temperature

any

ccoling

shapes

Uncertainties

content

exothermic,

below

the

glass-water

potential

adsotbate

The

as

the

silica

to

properties

Interest

capacity;

deterrained addition,

distorted

O°C

adsorption

behaviour

become

below

adsorptive

of

adsorbate.

adsorptive

isotherns

capacity.

porous

the

observations.

diminution

point,

knowledge of

at

adsorbed by

water

measuring

Because change all

degassing.

the

temperatures vapour. the

of

this

measurements. metal

and

The

glass

isotherms

600 1

-I-

--I

0

-c 16 -C )6

:

-c b4

P I

II -.-

-+i

;

:

:

: -t I5

IIO 5 --0-v

fB

1. STP

ml ADSORBED

Fig. 6. Adsorptien and expansion isotherma of the porous glass-xenon (Reproduced by penuissien of the National Research Council of Canada Canadian Journal of Chemistry, Volume 41, pp. 3095-3107, 1963.) [3]

system. from the

are shown for relative

pressurs'6~$e~d-&

kk& ";[email protected]

liquid

Py in Figures 7 and 8(a) and for relative I I pressure of iee pi is Figure S(b). 11 'We following conclusioas are valid: 1.

If the relative

adsorbate. 2.

pressure

a. decreases

The isotherms

pip”

is

expressed

with deceasing

can be superimposed

p&ss&'bf pressure

as p/p:.

~.._~_ -.. super-cooled based on the vapour

the amount of

temperature. if the relative

pressure

is

based

on

py.

0.16

0 0.08 5 cp d 0 0.08

0 0.08

0

B-2

Fig. 7. Vapom press-6.4. -14.6. -25;4 and (-m-d by pedssion Faraday Society [a]).

0.4

isoh-

O-6

0.8

1.0

of the porous glass-water system at t1.5, t0 bottom). Adsorption 0. &sorption SoeCety from Transactions of the

-s5.3oe cfrw top of The ek~~af

0.

0.16

0.16

0.08

I

I

II

I

I

I

f

I

I

Y-

0

0.2

0.4

Vapour pressure Fig. 8. +1.5; -----. P/P:. -. (Reproduced by permission Faraday Society (61).

These like

conclusions

non-frozen

The

decrease

agreed

that

is

condensation can

never an

be

On terms

the

the

is

achieved

at

margin

adsorbate

adsorbate by

the

with

capacity

the

on the walls

increasing

termiflated than

of

governed

of pz. this value by

consistent

adsorptive

because

adsorption

0.8

1.0

isotherms superimposed (a) 2 against p/p: -6.4; -----, -14.6; ---, -25.1 and --of The Chemical Society from Transactions

are

state in

0.6

upper

as

at the

the

suggested

known

magnitude

prevents

except

below was

is

previous

of

to

be

p in

findings net-ma1 to in

only

the

of

to pz

the elperilaentally

bulk

temperature

freezing is

[7

values of p/p: that become progressively

-

131. was

state, 0 p,.

rmt

As

above the value

Because the

liquid-

It

realirable

point.

lowered.

the

apparent.

a liquid-like

relation

against -35.3-C. the

of

triple-point

be

a

concerning

the rise of vapour pressure

limit

(b) ---,

p: pz

isotherms

0

Pi

and

exceeds

pz

are

lover and always

less

unity.

rhe 0th~ of

hand_

if a, the aemunt

p/p:. the limiting

relative

of

adsorbed

pressure

substance,

is

expressed

is made equal TV unity.

in

implying

eomplete constructed when

a

The by

isotherm

is

plotted

but

was

at

the

the

a

to

the

specimen.

the

isotherm

is

IUJ reason

warming/cooling

cycles

were

subsequently obtained

on

vertieal

line

all

in

at

it

are

carried

should

on

the

as caused

found

(point

cell

By

water

were

the

hysteresis

loop,

as

in

this

work.

but

be

achieved

if

a sufficient

not

9he

&sorption

(at

-35.3’)

points

can

be

in

number

obtained

and were

above

Khe adsorption that

pressure

in

desorption. B).

of

,#alls.

expected,

attained

eondirions.

maximum relarive

water

S(a)).

obtaining

not

out.

of

Aeeordingly.

(Figure

resulred,

increments

the

p/p:.-

After

temperature

limit was

Khese

excess

of a uas

equilibrium

Under

the

upper

a giwea

of

superimposed

which

original

distortion

interest.

successive

+l.SOC.

why

a for be

with

A,

inerease

The

in

special

3 deg.

the

net

at

of

can

ef

process,

stable

adsorption.

is

marked

of

ing

by

there

point

pressure

uarming/eool

transferred theory

7)

Restoratios

results

isotherms

approximately

established

of

plotting

reduction

the

(Figure

raised

original this

of

apparest

p/p:

adsorption

adsorption.

repeating

an

-35.3OC

at

temperature

further

and

against

isotherm

isothermal

the

method

This

saturation.

those

isorherm

is

a

i red

real

experimentally. Behaviour KO thaK

described

With

way. at

leading

hys reres i s cooling &o

like;

shape

(Figure

portion

Cines

cell

bur

if

/ py bulk

the

is

SySKeta

curve

(path

be

ice in

isotherm

explained

in

an

the in

following

it

on

of

a and

in

On

will.

boundaries

increase

unity

in a.

region

extreme an

similar

becoming

increase

Khe hysreresis

resulKs

is

the

eventually

causes

within

cycle

-35.3’C

increases,

containing

a warming

Thus,

the

and can

[9]

pz

of

the

a

a decrease. lend

rhe

further

support

isosteres

of

a phase

as

those

KO the from

constructed and

change.

above

this

the

conclusion the

extension

temperature

the have

isotherms

below

that

SO

that

iso&-

they

can

be

adsorbare

is

no break 0-C

point

are

of

the

superimposed

9).

SURFACE AREA DETERMINATION

VII. The

fact

point

hus

using

gases

are

aad

a scanning

.

in

findings

indicative same

loop)

cycle

liquid-

of rhe

follow

desorption.

vertical

temperature.

a decreases,

eool ing.

the

by Emmett

increasing

Warming

OOC.

to

Khar direct other

usually

adsorbare

t&in

carried

convenience. justified

ia areas

adsorption.

The

this of

computing

that

is fer

the the

the

in a the for

nitrogen.

OUT at

Because

applieatioa

krypton,

surfaee

the

consequences

liquid-like BET

example

boiling

point

temperature vapour results,

is

pressure ¶%is

differ significantly

stare

surface

area

krypton of

below

solid

ED&Z of

bulk

for

the the

experiments

sake

triple-point

krypton.

pz.

replaced

by

from pt.

of for

would

however.

ealculatioa.

rripleWhen

the

from ?Aose calculated

discrepancy vanishes when pz is

tie

argon.

or

nitrogen

39 deg of

below

determination.

be yields

nitrogen

ealeulated

by

.,

1 c , ,

16U

I

I 20

40

40

0 40

0 0

a. 24

Fig. 9. Extension isotherms at temperatures of +1.5, -6.4, -14.6. -25.4 and -S5.3°C (from top to bottom). Adsorption 0. desorption l . For sake of clarity of presentation the measured points of the isotherm at -35.3°e are sot shown. Arrows indicate direetion of adsorption path, broken lines presumed path between measured points. (Reproduced by permission of the Chemical Society from the Transactions of the Faraday Society [6]). an

extrapolation,

meter whose value quantities

which quantity is identical

was thought

is considered

to that of pt.

to be fortuitous

that the use of pi is not

only warranted

to be merely The close

[14, IS]. for

an adjustable

agreement

If is important

pragmatie

between

parathese

to realize

reasons but is also

267 theoretically

corqxzt.

adsorption

krypton

Consequently,

but

is

required

It should

be

noted

normal melting

conclusions;

for

greater

unity,

than

in

events

obtained

out

non-equilibrium

in

in

differeutial

measured for

Length The

extension

show

that

aa

-0.2

and

-8-C.

cation ice

of

the

was

on

(b)

the

established

(c)

on

Vicinity and

at

0-C

the

sudden

ice

crystals,

the

outer

that

water

could

not

migrated The discussed freezing adsorbate

the

the

eause

the

content,

'PBe onset

of

the

at

that

as

where

experiments

were

heat

effects

is

in

Figure

a, exceeds

a_,

ceaditioa

carried

measured

were

results

10.

saturated

samples

in heat. It

sample

warmed

at the

water

in

12).

the This

the

is

beeause

the

temperature ice.

the

liquid-like at

which on

the

giass

the

was

colder

of

becomes

temperature

shape

cannot

formed

suggest where O°C

it

the

adsorbate. uhieh

as

the

acrual

content-determined of

the

water

for

available at

with be

ice

pores than

the

by

contact

undercooling)

state water

in

(that in

Watser

indicated

point

located

became

111.

O°C.

as

facts of

was

ice.

the surrounding

-0.4°C.

maximum adsorbate oa

(Figure

freezing

absence

foreed

depeods

the

louer

it

was

about

that

state

with

to

established

0-C.

the

at

bulk

covered

cooled.

only

and

depends

system

solidifi-

concluded

O’C

10)

between

proves

the

in

was

(Figure

region

msy be

-8.6-C

and

Because

that

temperature

surface

were

Representative

of

formed

solidified

the

it

some of

end,

water.

the

Experimentally O’C,

identify

change

1161.

release

ice

heat

indicates

‘Ike

this

to

dimensional

occurring

-10°C.

immersed

mechanism

exteraal

this

of

adsorbed

of

released

below

previously. on

point

was

result

this

at

(Figure

surfaee

of

sudden the

length

also.

the

p/p:

the

surface of the speciaren and was

to solidify

freeze; to

of

shove

dimensions,

water

surface.

are

thermograms

by

undercooling.

failed

by

O°C

surface

in

this to

indieated

1N NON-EQUILIBRIUM

possible

in which

system

inspection

sample

it

To

cycles

of

melting

change

attributed on

visual

but

below

and silarltaneously, the length changes

in

a fraction

glass

the cycles.

of

change

freezing,

When the

out

to

the

solidified.

OBTAINED

linear transformer

accompanied

least

(a)

froze

anomalies

- water

glass

formed on the outside

and

makes

for

and lead to erxtxwous

be

to be

is assumed

for

analysis,

isosteres

because

regard

carried

distorted will

studies

temperature

anomalous

at

be

supersaturation

cooling/uarmieg

silica in

will

CURVES

with a differential

Anomaly

adsorption

EXTENSION

isothermal

thermal

a porous

a0

studies

of

adsorbate

responsible

curves

by

with

CYCLES

Insight gained physical

THE

of p: is not restricted

gases.

results

the

apparent

OF

other

the experiment_

if the adsorbate

¶EMPERATURE

the

the

of

ewle.

IN‘iERPRJZTATION

VIII.

0 p,.

that

point

application all

to the tfgnperature of

relation of their triple-point the

tb

with

adsorption

*by

isotherm.

If a = amx is

decreased

or

remains

specimen

in is

at

below

O°C, migration this

value.

a supercooled

partly

state

saturated

of

water

When it

at

will

start

reaches

(Figure

the

12).

+ > 0-C.

then

c -2

as

On the at

soon

as

external

Y = 0,

the

other hand, a (

temperature

surface.

a

BUX

it if

and

freezes

the a exeeeds

0

0%

-200

--40

-20

TEMPERATURE,

lC

0

Fig. IO. Dimensional changes and thermograms of the porous glass-water system (a) 2-mm thick glass,-water saturated, cooling rate O.Z!i’C/min; (b) 5.RJJIIthick water saturated, 0.2S°C/rin; glass, (c) S-mm thiek glass. water saturated. 0. JS’C/i!lin. (Reproduced by permission of the Aeademie Press fro= Journal of Colloid and Interface Science [ 161) _

269 uhea

a lllsix enly

exceed

a5_

surface

T c 0%.

If

rater

ezateat

is very

tow, a << a,,,

a does xmt

in the region between 8 and -2D'C and no freezing occurs on the

(Figure II).

Below

the bulk

triple-polat.

shows values of the limiting With

@e

pz is the limiting

relative

the aid of the adsorprioa

&sorb-,

TEMPERATURE,

pressure, which

value of p.

Figure

14(a)

pz / pz as a functioa of T. is the relation between

_

adsorbed

=‘C

Fig. II. Dimeasional chaages and thexmograms of S-mm thick porous glass saturated with water awing a +S to -lS°C temperature cycle (0.33°C/min). (Reproduced by permission of rhe Academic Press from Journal of Colloid and Interface Science [16]).

.

01 -40

t 30

I

I

-20 TEMPERATURE,

-io

0

I 10

-C

Fig. 12, Dimensional eh&wes af a S-mm thick porous glass sample immzrsed in water. (~ZV&E& by perm&sion of the Academic Press from Jouraal of _f&lloid and Interface Se%emree f16J). -- I --

amxmt

and relative

derivative

that because only

freezing

This result temperature

In view of the dynamic expeeted

to T is also given

of the shape of the isotherm.

below -5°C.

surface

amax can be related

pressure.

of a wirh respeet

[17] at a coosing

rate of O.O417Y/min.

chloride,

in fact, was

water as the adsorbate. adsorbares

benzene

seen that in every of the anomaly

system

exhibit

there

found with

The suggested

The extension

such as cyclohexane,

and octanol

at the higher

observed

expansion,

rate is very slow, no anomalous

This effect,

containing

tho previously

nature of the factors causing

that, if the cooling

to

The

It can be seen

amount of water

a significant

agrees well with

this system.

moves

exteraal

of -7*C.

can be observed. specific

to P for

[Figure 14(b)).

explaaatioa

features

studies because of either experimental

remained

difficulties

is not

tarbon

(Figure

15).

ranges.

undetected

changes

system

of porous

xylene.

are at least two freezing

temperature

dimensional

the cement-water

"isosteres"

chloroform,

similar

it is to be

glass

tetraIt may be

The existence

in most former

or erroneous

interpretation.

rb)

_!!q

_;q_

-40

-20 TEMPERATURE,

0 =‘C

of (a) 2-mm and Fig. 13. Dimensional cheages and the-grams (b) S-mm thick glass samples partly saturated with water. (Reproduced by permission of the Academic Press from Journal of Colloid and Interfaee Science 1161).

Tke values

exhibit

remarkably

bekaviour.

uniform

freezing

0~ the external

the bulk

freezing point of the adsorbate

mechanism is occurs

at

at

Freezing -

T

supported

Low

occurring

The process

the gradusl

S-EUIIthick

by

the

It

0.92

in degrees that

fact

appears

that

first

and 0.98 To, where To is Kelvin.



Yhe wuggesred

meliciag of the adsorbate

always

Temperatures

porous

at lower

is associated

both extending

expasioe,

Despite

al4

OEWPS between

0'

For transitions

the pores.

surface

over

temperatures,

a temperature

nature of the traasitioa

glass),

the inception

the adsorbate

with an exothermic

range of approximately for a given

temperature

of

(*Cl. 3OC) _

solidifies

I5 degrees.

type of specimen

the process

is

(e.g.,

constant

.

(a)

-I

-40

-30

-20

TEMPERATURE.

-10

in

and

heat effect

0.6

0

OC

(a) Maximum realizable vapour pressure of water as a fumtion Fig. 14. of temperature; @> adaT zx $00 ~3 T for 5-m thick porous glass-uater system based oa isotherm of +t?.S'C. tiReproduced by permission of the Aeademie Press from Journal ef Coileid aad Lnterfaee Seienee [16JI-

(a)

chloroform. -63.5-C:

(b)

a-rylene

(c)

mp

-47.9OC;

carbon Letrachloride, -22.96-C;

QP

(d) octanol.

mp

-16.7°C;

(e)

benzene.

qp +5.SmC:

(f)

cyclohexane

-80

J

0

mp +6.5*C.

-20

-“I+

3

-40

-53 TEMPEAAIuAE.

0 Y

Dimensional ehanges and thenmgrams of 5-u Fig. 15. various adsorbates. (Reproduced by permission of the Journal of Colloid and Iaterfaee Science [161).

rhiek

porous glass with Press from

Academie

¶he

sign

of

on

the

bearing occurred the

all

that

expands

the

a

= 0.12

g/g.

eZ

at

the

other

[S]

and

about in

or p/pi

&and. even

sole

cause

which

is

defined

is

of

freezing

pressure

reduction.

value

a,

of

the

however,

in

into

the

partly

pressure of

the

leave

the

porous

temperature blocked

melting the ice;

points

melting

On the

saturated of

tie

occurs

This low cae

the

is

to

Point

this

only

that

magnitude

the

the of

vapour for

OR desorption freezing

place

theory

the

g/g

brings

takes

of

OS

a = 0.12

conclusion:

pressure a higher

remains

the

vapour

a

given

than

point.

vapour

preceding

point

0,

At

the

the

B reveals

is

siufaee

a nef

of

-15%. is

to

the

probably

pressure.

on

She

(being

drains

high

of

ice

so

differesee Le

expeeted to

transported the

The of

and

the

tie

freering

in which

characteristics

this

condi-

freezing

it

low

water

equilibrium

between

to

partly

trapped

that

rise

has at

because

a pore

sharp

water

possible

viscosity, if

to

ccoling

relative

amount seldom

tirneble

on

adsorbate.

however.

that

then

by

state it

a large

attained,

can

liquid

the maximum realizable

depletion

be

the

pressure

below

determined

causing

in

adsorption),

when

pressure

Extension

effect. OR

with

lhe

are

-13.5OC.

cooliag

effect,

because

diameter

as

freezing

extent

solidi-3S9C.

relative 6&

high

isotherm.

by

isothermal

that

adsorbate

point

of

the

that

meniscus

vapour

in

surprising

than as

that

the

achieve either

cooling

KO the

have

¶he well-established

Y 5 O’C,

zhermal

freezing

tPe.

the

the

preeesses at

pores

vapour

the

of

basis

physical

larger

at which water

Interpretation

the

the

of

temperature the

water on

than

of

attained.

lower should

point

imply

contradicted

filled

Equilibrium

reducing

be a

indicates

because

are

to

Expansion

to

of

less

hypothesis

the

no

substance

at are

value of

“isosteric”

proportional

latter

sysrem.

pores.

freezes, tions

filled

curve

this

of

is

only

glass

results

freezing

branch

the

possible

porous

pores

the

has

system.

is

not

at

findings

lowering

because it

becomes less As/AT

These

on

state

true.

that

pores.

the

g/g.

If

these

has

the

of

and

[3].

inversely

is

One may argue freeze

g/g

appears

that

was

pIace

desorptioo

adsorbate

so

opposite.

be

it

equation),

took

point

to

assumed

adsorption,

the

= 0.17

the: bulk

state.

veids

an estiaered

correct,

by

the

in

water

bulk

the

attained,

has

freeriag

although

[6].

in

Kelvin

a = 0.884

desorption

states

was

the

transition

with

the

in

a=x

uhieh

s

adsorbent-adsorbate

studies

= 0.7

water.

of

freezing

water

to

on

15).

-25V.

(aceordiag with

on

adsorbing

-35Y.

filled

changes

change

(Figure

adsorption

of

pressure

volume

systemg

isothermal

fication

sgeeifie

dimensioaal

with

group In

the

and

occurs can

at

form

of the formed

ice.

lsosteres an attempt

hypothesis, anomalies

Figure

in

10(b).

temperature aad

the

the

eontrclets represented

latent

coetraetioe

length

fer

heat this

of

can

be

made

changes.

¶he

on cooling

temperature

specify

specimen

as a result

by A (because freexing

to

warms eyele

a 5 a_,), the

system

resulting

274 from

loss

because the

of

of

pores The

the

on cooling

water

thermal eofmences

large

result of the

the

changed

conditions

presence

to be

of

partly

me1 ting

temperature

is

a measure

recognized,

however, on whether

extension

itself

F

loss

of

when

the

ice

CHLORIDE

mechanism glass

in

impregnation

is

the

with

from

the

were If,

the

smaller

that

one

least

is

th3t

to

the

the

change

may well

low

at

this

must

be

constant state,

appears

the

It

D.

at

in

expansion

length

C and

in

freely

where

of

&sorption

may be

solidified to

This

adsorbent

or

and

take place

between

is

D.

the

increase

water

coverage

according

also

exist

to

for

crevices

is

than

at

were

of

is

glsss that

consistent

the

The

twenty

with

structured

their

on porous

vacuum can

be

from

calculated

values 10 per

calculated the

the

by

reported

cent.

assuming

salt

[2-l. the

of

the

aforementioned

haemoglobin nature

calcula-

(determined

approximately is

salt.

231 and

by

saturation

by

tbar

[18].

glass

of

so

adsorption

prepared

liquid

free

119 -

effect

GLASS

water,

the

solution

adsorbed

completely

analysis

pure water

complete

content

the

This

SILICA

concentrations

impregnation.)

of

increasing

Cy

glass.

POROUS

studying

specimens various

impregnating

porous fact

In

salt

to

IN

rather

solution

the

about

the

melts.

ADSORBED

NaCL. of

brought of

251.

first

which

layer

is

solute.

humidities,

process,

a

Initially,

the

amount

solid

and

saturated

been

the

the

adsorption

has

part.

in

the

salt

of

This

by

salt

net

strength

solutions

due

isotherms.

relative in

response

E on warming.

to adsorption

the

pore

layer

du-‘. to

adsorption

various

3nd

in

C again

the

freezing

glass

situation

interest.

concentration

phenomenon

unavailable The

the

in

and

weight

vanL3h.

presumably

lhis

due

of

the

monomolecular

rejection

of

mechanical

solutions

of

dry

is

great

uptake

than

however,

differences

The

adsorption

9).

with

C.

point

develops. to

suffered

SOLUTIONS

presence

uater

of

increase

an

contain of

NaCe

¶?e concentration ted

in

(Figure

systems

t natural

silica

damage

to

eaanot

strain

contracts

dimensions

is

E and

AQUEOlJS SODIUM Cbs

the

and

between

pressure

freezing

and

At

conditions.

Expansion

IX.

pressure)

completed.

the

it

isotherms

non- isoche-1

manifests

of

the

B and

between

water.

extends

occurring

vapour

pores,

is

that

between

system

of

3ssoeiated

normally

the the

process

depend

relative

in

contracts

loss that

D is

interaction

reversible;

also

IZ and

changes

solids

The system wntinu>us

a process

(temperature.

temperature

the

between

Dimensional

ambient

and

solidify,

to

expansion

adsorbate.

to A.

eontraction

dissolved.

obtained are

changing result of

adsorbatof

water solution water

by

shown

the is

exposure

of

Figure

16.

In

uptake

Distortion

concentration

constant

salt

insufficient are

salt-impregnated

leads

and

to

present.

In w

in

the

varying

dissolve later

dilution

all stages of

the

samples is caused,

course

of

water the

to at

the

eontent. salt.

when

all

solution.

so

that

the Only

276 whes

available

ths

become The

equal

u

water

uptake

pressure

pressure in

the

liquid

has

to be

V81ues.

the

solution

at

the

held

in

ia

p"

hysteresis

loop

reduced

adsorptive

occurs

of

salt. 'fhe experiments

solubility

r

first

- that SALI

OF

lead

salt-free appear

CONlEN

Figure

value.

The

similar

lower

to

the

shape

to lower relative

and

has

similar

governed

by

coseentration

identical

TV that existing

the

adsorption,

eoncentratian relative

saturation

For each

relative

pressure

are

shown

in

Figure

but

c8nnot

be

superimposed

the

horizontal

uarer

content

pore

that

the

properties those I

I

GLASS. s s -0 0000

dtnz to

adsorbed - vapour

of

the

17.

bulk

salt

for

of and

effects

These sixes

expressed

section valUes

of

pressure

pressure

recalculated.

the

pressures.

to

relative

terms of the vapour

in

changing

diminished

conclusion

leonoiayer to be

and

results

in

the

Because

16 were

increases,

shifts

at

rather

tiring

appropriately

calculated

capacity

is not

but

Varies

YIS

pressures

solid

adsorption-

of

does

liquid.

water.

of

results

concentration

by

the

stage

of

filled

a concentration

having

terms the

81-e very

relative

pure

capillaries

concentration

salt

of

current

appropriate

completely

impregnating

terms

the

expressed

as

high

the

been

has

8 salt-impregnated

of a bulk

'Ihe_isotherms

side

of in

the

reasons: at

of

that

.kcordingly.

point,

volume

expressed

pores

the

with

pore

the the

are

the

two curves

caused

presence

out-

solution

pressure,

density,

state.

1. / /

k

1

0

PElAItVE

.e

PRESSURE

Adsarptioa isotherma for water oa porous glass impregn8ted vith HaCL ef various concentrations. Relative pressure is based on the saturatien pressure ef pure water. [Reproduced by perg;;ion ef the Acadearle Press frem Jo1 of Colloid and Interface gcience . Fig. 16. solutions

276 ¶hern~grams

and

Length

¶he extension 18(b).

of

Changes

diagrams,

porous

glass

Figure

samples

concentratiens

show :

(1)

freezing

of

respective

point

temperature

elosely

consistent

with

formation

sf ice

surface The

of

in

A and

tmdercooL2-d

Liquid

between

peaks

the

Significantly, peak In

from

thiB in and

is

if

on

for

18(b))

&sorption

euteetic

indication

of

salt

at

the

by

continuous

solution

freezing,

is

saturated

bulk

on

(18

a

due

to

the point.

and

ice

22 per

in

Exothermic as

at

are

freezing

of

NaCL.

bulk

place

freezing

formation

respectively.

the

results

takes by

various

anomalies

concentration

caused

solid,

impregnating

occurs

high

are

below

Such

followed

Figure

of

on heating,

point.

cooling.

melting

thermograms Figure

solutions

5 degrees

(2)

freezing

container,

on warming.

the

an

the

bulk

the

2 to

and

tbe~grams.

salt

the

effect

expected. only

a single

occurs. the

temperature

dimensional These

ntodel:

specimen:

anomalies

the

of

differential with

solution,

the

wall

and

saturated

cooling,

proposed

on

peaks

marked

on

approaching

the

the

double

cent,

the

18(a).

full;e

range

changes

anomalies the

and

are

heat

-19

to

manifestations

following

-4O’C.

content

of

anolaalies the

SALT

in

the

(Figure

18).

Circumstances.

9

I

GLASS

I

0.0000

-

ooza

-----r)

0

sample

of second freezing and are assumed to result

I

4

were obtained

water-saturated

0

0

0.8099

---0.0218 0..

0.0

l

0.0308

. . . .

0.0402

.-.--

0.063G

0.2

0.4 RELAIIVE

Fig.

0.6

17. Adsorption isotherm for water on pomus solutions of various concentrations. Values explained in text. (Reproduced by permission of of Colloid and Intetiace Science ll81). NaCL

B.8

1 .o

PEESSURE

silica glass impregnated with of Figure 16 replorted as the Academie Press hxu Journal

277 Maximum relative cooling, Figure

the

14).

of

inception

92

ef

desorption

changes froku 0.8 0.08

per cent

the

to

0.6.

of

the

peiat

equal

eapillary-held

causes

significant

disrurbance

seldom

established

owing

slou

cooling In

of

ahother

0.33

the rates

phenomenon compared

experiment

C deg/min

until

to

was

¶he

with the

is the

of

of

on

(see

the ~001ir.g.

the

pressura

reduced

from

aa

0.24

to

uptake

ultimate

of such

water). -lO°C

of

as relative

content

amount

and of

equilibrium conditions. eondimigration

rate.

very much reduced

that

observed

19).

water-saturated

commencement

at

race

cent

inadequate by

0.8

sectien

transfer

under

undercooled of

eoastant

region:

65 per

even the

ef

value

At

water to

demonstrated

(Figure after

in this

a

descending

7).

water.

tions

of

steep,

equilibrium

being

pressure

reaches

(Figure

greatly

the

vapour it

the

of

water

character

oa

until

isotherm

iacreases

differeaee

the

g/g.

(hased

continuously

branch

desorption rate

pressure

decreases

at of

higher

djmamic

expansion

St

rates.

glass

. freeziag

The

was at

cooled

-18-C.

at a rate when

(apart

Porous silica glass samples saturated with NaCE solutions of various (a) dimeasioual ehaages. duriag temperature cycle (0.3S”C/min). (RegFodueed by permissien of the Academ$c Press (h) differeatial thers*rgmums. from Journal of Colloid aed Interfaee Science [ISI].

Fig.

18.

cmncentratioas

from

a drift In

during

freezing

deg/min. to

thar

contrast higher part

this an

was

with of

0.33

for

anomalies suggests

the

a

.s=ses,

(Figure with

pore-held

for

e.33’ItdlN

in

the

of

of

18(a))

exceeds

x 10

_

These

and

COOLING

ar

a

rate

an arxumt

of

0.33

very

of

low

r'reezing,

of

the

temperature

and without

system

of

caused

for C

similar is

in

that

a

by

too-

rate.

the

with

indicate

conditions

diffusion

water

was maintained -5 that occurred

results

non-equilibrium

of

that

cooling place,

400

adsorbent-adsorbate instead

53 x 10

shis expansion C deg/min. -5 usually found at the

0.0417

behaviour

condition

the

desorprion

adsorbate

!

the

temperature

strain

about

permeability

exist

that

by

of

associated given

constant the

cooling

strain

C deg/min is

similariries

thawing

of

expansive

expansion

strongly in both

a rare

of

On resumption of -5 10 took of 70 x

expansion

ar

an

all

recovered.

over-all

rapi'd cooling Great

almost

period.

obtained

rate of

1 C dex)

of approximately

17 h.

when

external

salt.

re-establishes rhe

vapour

freezing This

and fact

equilibrium, pressure

of

crystal.

. . ....

25

---

17 tlOURS

MINUTES

e.33-IMIN

RATE

250

z t i

z

15e 50 I3 -6 i

TEMPERAIURE.

=C

Fig. 19. Changes in dimensions and heat content of porous silica glass saturated cooling rate 0.33°~/~in between 0 and -lB°C: with water during temperature cycle; -18 and 21-C; arrest for 17 h at -2lY; O.J3*C/min rate in O.l2’C/min between reminder of the cycle. (Reproduced by permission of the Academic Press from Journal of Colloid and Interface Science [ 18)).

379

Durability in

ment. create has

small

proved

bubbles

air be

action

in

greatly

the

beneficial

remain.

~0 the

is

a surface-active

to

problems

concrete

of

which

-

IN fXMJ3lT AND CONeRETE

FROST ACTION

a.

The

of

in

most

impaired

agent

is

paste

and

include

mixing

in

the

in

a test

of

to

coacrete.

this,

of bridge

method

encrain-

operation

hardened

spite

deterioration

of

Air

action.

the

practice.

salts and lack

de-icing

freeze-thaw

during

subsequently

engineering

important

by

added

certain

decks due

for evaluating

fresr

resistance_ reached

The conclusions better

defined

neat

to

results

in

higher

has

specimens

W/C ratios

Investigation dependence factors

an age

at

is

1es sened .

For

specimens

to

manner

similar 9he

3.125

mm thick

9he

to

first

differences,

uith as

that

for

a working

examined

of

by

[hat

not

can were

shown

and

met

the

extension

in the

important

glass

hypothesis

for consistency.

be

The

and

the curve

for the present

The

ia

the

case

the

of

to 0.4

same

system and the

in

a

Section

1.25

mm and

curves. notwithstanding

obtained

sample

in

explanation restits

of

cycle in

that.

those K/C

cement

the

changes

the

by

be

hardened

discussed

is

due

caused

for specimens

made

years

difficulty

can

part

on

hydra-

several

problem

dimensiona

[b)

be

of

environmental

difficulties

inqicated

for

by

a corrliag/uarming

glass

are very similar lG(b).

the

cent,

to

cement

low,

of

pumping.

are

effects

samples

10 per

20(a)

in

experiments.

to

during

porous

Figure

due

than

during

added

co continuing

even

the

W/C ratios

the

due

vel-y

certain

avoided.

of

an excess

difficult

properties

becoaes

Figure

Compare ia

less

the

such

the

out

prepared.

Circumvention

obseAation

curves

system.

were

By employing

determined

in

respectively;

porous

of

ratio

is always

of

For

made very

although

OR the

prartice.

properries

concrete

exposing.

applied

are

is

hydration

humidities shrinkage

porous glass-water

paste

irreversibility.

rate

specialens

resulrs

of

In

carried

nor stone.

achieve

distribution,

to 0.6.

I.0

and chemical

formidable,

example,

relative

cement

i/iII.

the

nure

drying

irreversible saturated

of

and

can be minimized.

the fcrmer cause

irreversibility

cement

0.4

to

wafer

presence

W/C ratio. of

0.4

changes

most

which

the

mainly

workabiliry.

size

were

sand

IFI order

of the

in cement and

experiments

dep&ds

The

behaviour

utilized neither

mix.

pore

range

between

physical

an element

have

to the

hardened of

In addition,

tion.

to

of

OR time

paste

as

altered

proportional

the

original

practice

and

in

were

contained

for hydration.

porosity

a W/C ratio

with

cement

the

in

low-temperature

Initially.

in

needed

the

system

samples

hardened

ratio) knowa

directly

are

concrete

old.

of

(W/C

ammnt

the

study of

the

i.e.,

structure

plasticity, of

which

paste,

cement

required excess

the

glass-water

investigations.

c=ent

The pore water

in

silica

durability

concrete with

porous

will

for the Figure

20

IIHY be assumed KUM be

TEMPERATURE,

‘C

400 -

I

200 -

* 300 -

“0 z < -I

500 -

.





8

SPCCIIIEN TNICKNESS, 8 I26 mm







I

I

-60 -40 KMPCRATURE, ‘C

I

!

.20

I

I

0

I

Fig. 20. Fractionallength changes of vacuum-saturatedplain cement specimens in temperaturecycles (0,3YC/mln). Curves have been shifted along the temperatureaxis; starting temperature,each casc,+S°C. (Reproducedby permission of the American Ceramic Society from Journal of the American Ceramic Society 1171).

7NICKNELS, I.tImm

SPECIMEN

(Al

Z81 Ihe anomaly

aear -8Oe in the 1gagth changes

is associated

heat effect and is caused by the freezing of water drivea by the

vapour pressure

water and external which

weight

-2lV.

exothermic system

of

takes place,

pores. On warming,

adsorbed

21.

during a

was kept unchanged

at room temperazure

than that of bulk solid only at water

length

anomaly

corresponding

to

occurred

coasistently

associated

that

to a higher o+der

of

the

the szmi-amorphous

metastable

1

1

I

I

I

I

I

I

I

-20 TEMPERATURE.

at

with an porous

transition

in small pores but is. during cooling.

I

-40

humidity

desorbed

-4OOC. a

at -20°e aad attributed

observed

in Figure samples

surface

pore-held

at high remperatures because the vapour

greater

Freezisg

temperatures,

that was originally

cement

the temperature

relative

an anomaly

beromes

-18'C.

heat effeet

cent

at 84 per

of the adsorbate

At lower

is presented

change of two fully saturated

(Figure 22) failed to exhibit

below

the liquid-like.

had been achieved.

equilibrated

temperatures

for desicrztion

cycle, when at each point

until wnstant

pressure

that exists between

Evidence

ice.

shows the weight

coeling/wamuieg

Samples

differeRce

with an exothermic.

to the external

glass

of the wafer in the larger

iee welts at approximately

-1OOC.

-0 C

specimens vacuum-saturated with water during a Fig. 21 Weight change of cement Results uere obtaiaed in gravimetrie adsorption experiments temperature eyele. (Reproduced by permission of the American and represent ewilibrium values. Ceramic Society frem Journal of the American ceramic Seciety 1171).

-8o

I

*

I

,’

4 D-

ID-

-60

-20

TEMPERATURC,'C

-40

0

-

I -60

--x7 I

0I! 05 r/c,0 IS" -------

40

-20 TEMPERATURE,'C

I -40

0

:,

J

-I

1

Pig. 22. (A) Fractional length changes and (L) thermogramsof plain cement specimensequilibratedat 84% rh. (Reproduced by panlssion of the American Ceramic Society from Journal of the American Ceramic Society [17]).

5 -

a

I

I

4:pi$&b) ’ _’ ‘:i

t

Uechanieal The

r Failure

volume

seldom, other

if hand,

associated (1)

the

0.125-in. frost

of

specimen,

and

little,

can

while

the

full

at

(Figure

The

residual

and

of

severe

aRd

strain

is

uhich

20(b));

per and

by

to cent

(2)

field

damage

resulting

was

maintained, ubile

residual

expansion

destruction

for

a sanpie

value

is

experience from

the

of

ratio,

cycling

direct

strain

0.7

related

(W/C

repeated

provided

of

at

proof -IO’%

are on

kportance.

the

its

structures

concrete

practical that

leads

CO.7

Significantly.

23).

to little

suggest

-8°C

established

saturation

(Figure

temperature

very large as

etc).

a small

observations

be

Thickness

inter-relation

is

dilation

susceptibility

-IO°C.

-40OC.

following the

dilation

of

at

exposed,

with

this

and

change

ever,

the

is cement

paste:

W/C ratio to

the

degree

dimensions between of

+S

the

changes

additive.

600

500

400

u\ % 380 =? A 200

108

c

tl

-10

0

TEMPERATURE.

+ 10 ‘C

Fig, 2J. Fractional length changes of cement specimen during repeated tempea(Reproduced by permission of the Put1 saturation was maintained. tures cycles. American Ceramic Society from .Lsurnal ef the American eeraaie Society [17]]. _

of

3ke

assumption

the

water

samples,

volume

33 and

(Figure

21)

volume

that

than

cooling

of

very

slow

that

freezing

occurred

that

the

of

rate the

evidence, reduction Ibe than is

the

the

in.

and

(b)) .

50

by

thick

must

effective

-44’,

most

to

there

be

the

more of

the

the

water

24.

occurs

on

or

-

freezing. of

20

the the

a

the

specific

= 0.7)

thermgram

15). during

indicates

-4O’C.

suggesting

factor. water

expelled

with

(Fggure

(W/C

of

due

Un this to

cell. water

concestrarion

humidity. the

specimen

the

cooled

uas

found

a controlling expulsion

in if

4 times

above

increase

two slowly

freezing

the

relative

reaches

-40

on

cent

present

was

sample

no expansion is

9 per

uater

3 to

Although

dilation

that

in

volume

prevailing

that,

because total

cement

humidity

than

the

behaviour

in

uas

by

than

mDre

desorption

expansion at

rhe

freezing

Figure

causing

caused

:ccepted

decrease

in

observation

increases As

that

is

of

similar

relative

that value

the

be

a vacuum-saturated

at

is

-8’C

equivalent

process

process

equilibrium

supported

cannot

plotted

are

implication the

0.125 (al

of

is

uater

changes

at

respectively,

Furthermore.

other

length

The

cent,

amount

_ this

expansion

freezing

on

40 per

increase.

adsorbares

the

outer

length 0.050 surface

This of

in. by

is

higher

conclusion

a specimen thick

(Figure

migration

20

along

0

TEhlPCRATllPE. e: Fig. 24. Tllermogram (top) and fractional length changes (bottom) of cement specimen, 3.125 mm thick (W/C ratio = 0.7) during a temperature cycle with slow cooling and heating rate (O.O417’C/ain). (Reproduced by permission of the American Ceramic Society from Journal of the American Ceramic Society 071) -

the

shortest

path

understandably In

occurs.

reduces

must

be

the

with

the

by

determined the

relative having

is

at

essentially

fully

the

solids

surface cooling

on

freezing. the

weak

the

(rate

of

aad

distance dilation

at constant

freezing

non-equiiibritaa

conditions,

and

the

the permeability

of

of

fully

water

relative

degiee

rates,

pores

at

at

where

it

freezes

O°C

If

without

severely

small

the

causing

the

A solid

specimens

when

temperatures

0-C.

only

the

unit

a given

may be

with

in

decrease),

of

saturation

the solid

exuded

for

same conditions. low

of

be

humidity

a solid

at

to

to be emptied

saturated

whereas

only

of

be

Lhree The

its

to

preferable

of

pores not

are

Later

flows

expansion

become

involved

the

with

ice

fissure

of

These are

and

soon

creating

formation

formed

fissures

therefore

break

rate

rhe

saturation

is

there)

located

and on

observations

water

cement

and

matrix

made The

the

stone

Ideally,

medium

size

in

freeriag

under

factors

field

are

conditions

now considered

environment.

and

_‘n any

the

CEMENT

durability.

durability.

ef

extending

OF

the

for

content.

those

and

the outer

unless

degree

cracks.

cooling

the

to

desiccation

causing

assoeiared

RESISTANCE

paste,

affeeting

to

of

diffusion

destruction.

the

water

of

and a high

further

reason

explains

relatiag

degree

freezing,

force

&signing

structure

on

(the

FROST

in

property

ones

to

described

to reduce

order

on

the solid

AFFECTING

groups

important

expands

path

conditions occurs,

migrares

expansive

the

required

normal

expansion

water

leads

utilized

pore

of

dimensions, the

under

water

areas

mechanism

can

achieve

deal

the

cycling

The

to

Thus,

FAC4uRS

small

valm quantity

initial

external

slow.

to which

Here

the

are

long

a great

voids.

XI.

in

the

begins

larger

very

sites

repeated

in

too is

filled.

and

rate

cooling

Iarge

specimen

after

of

(number of pores

under

this

mechanism.

diameter

fast

empty

with

is

of

at

large

of

22(a)).

in

are

and

desorption

partly

(Figure

cooling

the

observed

existence

The

invulnerable

saturated,

into

new

of

mderately

the

resistance.

isotherm

leaving

effect

absolute

change;,

many pores

damaged

water

the

the

&sorption

humidity

ef

proposed

that

time

of

amount

an increase

thickness),

relaxation

emphasized

frost

is

the

is prooi of

19)

does not determine shape

case

the

(Figure

consistent

It

this

addition,

temperature

a state

(in

because

perhaps

porosity

very

case,

is

large

mechanism

should

the be

large

and

very

pores

are

seldom

oaly

at

very

mst

very

small full

low pores and

Iw

temperatures. The

during quantity alse

of

of

features

W/C ratio.

the

pore

The amOunt

the traversing depends prime

oa

of

of

system

water a given

porosity.

interest.

fable

of

that

eement has

to

temperature Ease

of

11 [26]

paste be

are

determined

removed

range

is

te of

flow.

ekaracterized

shows

the

maintain importance. by

approximate

mainly by the equilibrium This

permeability.

a-unt

of water

is

Amount of water lest by fulIy saturated cement samples on decrease of relative humidity from 100 te 80% [261 Nen-air-entrained

Air-entrained

W/C Ratio

gram of water per gram of saturated paste

expressed in multiples of 0.0168 (0.4 W/C paste)

gram of water per gram of saturated paste

0.4 0.5 0.6 0.7 0.8

0.0168 0.0291 0.0812 O.OY77 0.1100

1.0 1.7 4.8 5.8 6.5

9.0228 0.0327 0.0581 0.0963 0.1024

TABLE

III

Desorptlon time of half the amunt of water lost by non-air-entrained cement samples on decrease of relative humidity from 100 KO 80% [26] Half-time in seconds

in multiples of 2600 (0.4 W/C)

2600 7056 8300 11200 19600

1.0 2.7 3.2 4.3 7.5

W/C Ratio 0.4

0.5 0.6 0.7 0.8

lost

by

fully

humidity

saturated

is reduced

approximately

equal

pastes of

to these values.

paste with a W/C ratio of 0.8 when times greater

structure

W/C ratios

of water centent damage ensues.

to

water

because

flow,

for

was reduced it gives

to establish

expel when cooled

of water

from 0

that has to leave a

is, of itself. not detrimental:

may- create

from

i.e..

resistance

such a condition. eontent)

100

of to 80

the time neeessary

various

cement

per cent.

Cement

require

In a series of exploratory

desiccation

6.5

but if the process of

greater

experiments

pastes when

the pore

pastes with

permeability

the relative

of half

the

amount required that under U/C ratios

RCW example.

valves

shown

in ?able

is used

the rates of drying of eement pastes of differeat

Ihe

if

the "half-times"

(She term. half-time.

for desorption

large

III indieate

equilibrium.)

these conditions are similar.

amunt

the relative

of water are

it is cooled by 25 C deg is approximately

(owing to their higher water

determined

humidity

specimens

Lou permeability,

damage is to be avoided. were

the

W/C ratios when

The quantities

than that from a paste with a W/C ratlo of 0.4.

Reduction is impeded,

different

to those that saturated

According

to -2s"c.

cement

from 100 co 80 per cent.

paste with a W/C ratia of 0.8 lost 6.5 times the

281 amount had

a

be

of

not

with

exuded

unusual

by

bubbles

U/C

with

of

spaced

cent

RH;

are

so-hat

rate

rate

of

increase

of

large

the aeed for is

and

0.4,

surprising drying

the

half-times

because

would

it

increase

as

uould pore

under normal with

can of

other

hand,

when is

with

is

bubbles

serve

reservoirs

between

external

surfaces. has

It

the

on prolonged

therefore,

is low,

uniformly

than

in

and

exposure

ro

proportionately

concrete

air-entrained

been

plain or air-enrrained,

because

only

The

as

the degree of saturation

water

to

Barring

clear.

durability.

wherber

water

distances

distant

beneficial

field conditions. in

to

of

of

permeability.

paste

Short

affeeting

when concrete,

filled

water

by

water

-unt

increased

escape.

factor

susceptibility

the

cement

provided

water

second

of

protect

cavities

frost

W/C ratio

benefit

Air-entrainment become

explains in

migration

the

OR the

filled

the

is destructive

voids

drying

bubbles

expelled

saturation

fully saturated.

voids

the

without

the

cooling,

iittle damage occurs.

per

of

a W/C ratio is

with

air-entrained

shove that freezing

closely

that

ratios: sharply

which

eliminate

Degree

is

expect

circumstances,

which.

with

fiediag

unchanged

high increases

mechanism

paste

This

increases.

essentially

pastes

from

. I.

to

(porosity)

The

into

dewrbed

of 7;s to

unreasonable

volume

be

water

ratio

100

fewer

non-air-entrained

concrete. Freshly water

placed

content.

desiecste

before

are

remain

and

Relative cannot as

to

the

gives

readily

4he tions

can

most

minimum freezing of but

be

rapid

of

has is

reservoirs

when cement

into

because

unchanged.

and

helpful

by external

high to

the

water

can

f DY

falls below 0-C.

size

voids

the time

in this case also.

which

their

Whether

of

insufficient

the temperature

Paste

determined

of

and

imProve

distribution

are

filled

conditions:

regard

below

mechanism. change.

by only

If

not the

a

by and

few

fully

rate

is

degrees

is

can

be

water

The

after

with

water

relative

Good

the

tie

are

the

the

slow can

is

of

enough. result

the

to

the

alter and

pores

engineering to wazer.

darsag:a.

condi-

of

the

involved

in

of

the

significance can

so

rain,

of exposure value

field

it

by

environmental

desorption in

in

wetting

¶he absolute

fraetion

realized

done

architectural

minimizing

action.

exposed

from

temperature

frost

determines

0-C

Perhaps

to

concrete

nothing

drainage.

humidity

with

which

may contain

durability

relative

to

essentially

Concrete

from inadequate

important

temperature

atmosphere

damage.

or

cooling

the

wdified.

frost

temperature

is

damage

autumn

shape of the structure.

greatly

factors

the

remain

frost

the

Air-entrainment

provides in

to

in

capillaries

empty

the

from groundwater design

occurs.

pores

humidity

prevent

late

bubbles

and

partially

humidity.

vulnerable

smaller

total volume of or

air

neighbouring

hydration

is placed

freezing

of

Incorporation

from

concrete Concrete

take

the rate

place;

ACCRAVATINC

XII. 7he

so-called

departments de-icing direec

chemicals.

of

steel

agents

Figure

_/-

has

results 25.

_e---m_

of

Ihe

but of

a

a

features

.

T



r----

also

CaCEl

awst and

highway

maintenance

ever-increasing

in

smaller

pavements,

and

economic

use

of

quantities.

bridge

decks

Disintegration

technical

been

study

by

large

alarmingly.

serious

yet

in

wncrete

increased

is

adopted

resulted

NaCL.

has

elements

ACENT?G ON THE PREJZZINC OF CEMEMf PASTE

policy

has

deterioration

solution

Representative shoti~ in

pavement” years

primarily

de-icing

no satisfactory

ICUI-

“bare recent

consequence,

embedded action

in

EFFECT OF DE-ICING

due problem

As

to for

the which

found. of

of

salt the

impregnated curves

are

cement

onee

again

samples

[27]

are

similar

to

those

r-

__---=

l5c lCI-

O-

-X I-

IW.P---em---

-x

o-

I-

CI-

-X l5c

3W-

L

Cl-

200-

-x

l-

100-

lx lII l-

Olooo

G ;;

-x

$ i

2

0,

I-

lX l-

6

4

CI-X

l-

*lot

,-

Moo.

mot-

2ooc I

a

and

o-100 -

Fig. 25. (a) Fractional length changes and (b) thermograms of 0.5 W/C ratio _ . cement paste, air entrained and saturated with NaCL solutions of ameesttari~s indicated. during temperature eyclea (0_53°C/miaia) _ S~ecWns 1.27 ms thick. (Reproduced by pertission of the Ame ricaa Ceramic Sosiefy fromJournalef the American Ceratie Society [27]).

. obtained

with

the corrospondiag

be superfluoos.

The mochaaism

liquid and external

that

adsorbate

distills

to

unless

the

as follows: is

be

precautiens

are

amly

when

taken to avoid the creation

In contrast,

substance.

is adsorbed

in the porous body, TU) distillarioa

the vapour

pressure

the

external

of

solution

The

ice or water.

2t'C the vapour

pressure

of

is

usually

following

saturated

NaeL

to 0-C

of a temperature

to a single-component

less

example

of the warm

when cooled

gradient.

the

lowering of the

solid fully saturated

saturated

as opposed

in

of the pore

portion

a

A pornus

partiaily

whea a solution,

for the various agents

the priuary cause of

reduced by the

eold surroundings. will

valid

the vapour pressure

occurs on cooling

wuld

instead of

substance.

effect of de-icing

between

difference

normally

+S’C

say.

special

This

i+e.

content

at,

can he explaiaed

is the difference

adsorbate

rhea,

to be universally

appears

The aggravating

iystems.

action

could be detected

urea. uas used as the impregrating

akent.

concrete and cement paste

with water

difference

of deterioration

adsorbate-adsorbent

freeze-thaw

pornus glass system and their description

No qualitative

NaCL. another de-icing

889

than

takes place because the

vapour

illustrates

solution

pressure

of

this Point: at

is 19.g KPa and that of

in a 100 per cent relative humidity, the system that contains 36.4 salt is exposed to p/p0 = = 1.33. This large excess re3ults not only in 19.8 complete saturation but prevents desorption even if a moderate temperature

water

26.4 KPa.

gradient occur,

in

freeze-thaw

I-ESTlNC

Efforts are

specimens

The decisive

Usually, frequency

than

provide

The

rigorous.

2 and

results

of

water

previously.

5 in.

and

of

of elasticity

agaiast

the uncertainties

seem

is aunitored

KO be

control of cooling

by the

reither easily

between

that cooling 14 and16 by

in.

distillation

rate, degree of

of uhich

ASTM standard

The sample width

desiccation

the cold cooling

frost

that

field perfor=nce.

of the pertinent

length

cycles

of their mechanical

factors the i-rtanee

than 4 hr.

the

of freeze-thaw

impairment

materials

In concrete,

test method.

of this tesr

They require osly

shorter

safeguards w

serious

is due to inadequate

She specifications

3 and

warm sample

22)

does not

importance

of porous building

by the amber

the chaage of the mdulus srethod.

sample sire, and other

(C666) are not

Beyoad

assessed

or fully representative

understood.

durability

by the lack of a reliable

Poor reproducibility saturation,

(Fig.re

dermnstrated

are able to eadure without

reproducible

not

was

the freeze-thaw

hampered

is most commonly

strength. resonant

action

to improve

resistance

between

effeet of desiccation

OF FROST RESISTAXE

seriously

longer

The alleviatiag

in most cases, when salts are present.

content

XIII.

etists on cooling.

is not fully

testing procedure

from 37 to 3-F

is allowed Ihe

must

specifieatiofis

from

be

to vary

the

do

relatively

eoils.

inherent

in the execution

of the test. the results

are

in an+ny eases not representative

performance

suffers

iaherent material

from the widely

property

eeptible or is not.

depends on the ability at an adequate

rate.

of the structure but

the two most important

also

be durable

in one application

difficulty

in testing freeze-thaw

the concrete

example.

the asDunt of personal

that

Once

assessment

these limitations

time is usually

much as 18 months. KO

requirement:

and

can

nature of the For

rill erperieace.

things, on the shape of the from the interior,

not

known

comparative

as to whether

the

in advance.

testing

test is that can

is all

the frost resistance

that proved durable

of

in a similar

of the test are recognized.

useful

can be made.

Testing

means.

One concrete

to the results of a durability

that of an old concrete

and rare.

The intrinsic

in another.

circumstances

can be obtained

of water

and cooling

is the undetermined

aaDng other

Under those circumstances.

ieformation

a new sample matches application.

all

periods.

judgment with respect

still necessary. be achieved:

content

under consideration

depends,

sus-

that perfomco

the required quantity

rain, the extent of condensation

length of sunny and windy so

indicates

by the environment.

durability

is an

not only on the permeability

and susceptible

degree of saturation

object,

clearly

on the initial water

factors determined

conditions

that frost resistance

to expl

depends

of future

a given nraterial is either

discussion

This capacity

porosity of the solid

environmental

held opinion

and that therefore

The foregoing

Prediction

of field perfonmnce.

far too long:

Principally,

shorten

a minimum of six and in some cases as are open

for reducing

the cycle period or to evsluate

¶he former increases

curtails

two ways

the

the time allowed

to

rate of coolin&

an

the time

damage by snre sensitive

excessively

high

they are undesirable the two effects may comoensate for one a.xother, freezing process deviate+ greatly from the course that usually occurs

field conditions. deterioration

and

in Section

VIII that the length increase of the adsorbent

in a cooling/warming

cycle

is a quantitative

inflicted on the system.

This finding

detection

1271.

of frost &laage

Of specimens

with

the

under

preferable.

It was mentioned occurring

because

of mre sensitive means for earlier detection of thawing leaves the test conditions unaltered

Utilization

due -to freezing

and is. therefore.

level

Although

for x-e-saturatton on thawing in water.

is less for air-entrained

expansion

cycles

increases

than for plain eement

of

the

residual

is shown in Figure

with

increasing

samples,

damage

for the early

Ihe change of the cumulative

the ntssber of freeze-thav

it may be seen that residual

measure

is now being applied

expansion 26, where

W/C ratio and

in aecordanee

with

expectations. Frost resistance coefficient on

24-h

of bricks

[also calTed

submersion

is at present

c/b ratio),

in cold water

assessed

the ratio of

to the quantity

the

by the so-called

saturation

amount of water absorbed

contained

in the specimen

after

5-h

submersion

c/b

ratio

is

that

bricks,

able

to

not

control

and

absence

exposure

to

relative

level

increases

area

decreasing is

from

tricks

used

local

the

the

products that ly _

particular

to

were

had

in

for

the

at

very

low

this

frost

NUMBER

area

constant for

expected the

empty to

great

c/b

space

will of

char

the

avall-

prove

bricks

values.

need

if

assumption

pore

ice.

performance

high

frost

resistance

pores

become

100 per

cent

Some others

resistance in

of per

Ihe

with

method

for

exisrs

plant

service.

depends filled

and

brick unit

total

durable

assumption, [28].

durability

the

durability

service, of

Fig. 26. Change of cumulative number 0f freeze-thaw cycles. AR designates air the curves. from Mterials and Structures

nearly

surface

determined

failed

Large

of

sire

of

The assessment product

the

be

validity

that

pores.

fact.

pore

expected

To determine commercial

In Because

is on

test.

humidities

drops.

have

changes

with the

described

srall

of

those

fulfil

acceptance

mechanism

network.

with

to

and

incorrect,

to

service devised

when water

is

superior

user’s

in

originally

saturated

volume

however,

the

performance was

partly in

hypothesis

normally

the

porous

surface

inerease

from

humidity

Good test

The

become ‘oaly

on

coarse

0.8.

enough.

follows

long

water.

this

is

reliable

primarily

the

which

ratios

quality

It

than

Although

c/b

is

leas

aeeorasodate

durable. low

in boiling

only

empty

is

due

weight

to

of

porosity,

the

after

quickly its

very

material BET

nitrogen

bricks.

the of

curface

the

from

unexposed

was

areas

samples

based

Thus.

of

were or

exposed

or. rhe

products

27

obtained bricks’

reputarion-of were

classified

Of CYCLES

residual expansion of eersent speekas with the The W/e ratio of the specimens is in_dcated on entraiaaent. (Reproduced by permission of RILE t261).

if

20% 7aIu.E

IV

Surface area ef bricks Sample

Iki.

0.21 0.35 0.15

l

0.52 0.57

* *

0.63 60.76 0.78 0.85 0.98 1.01 1.01

t c

6 12 4 2

1.11 1.14 1.25 1.35 1.44

11 22 1 27 25 10 16 5 24 20

1.46 l.SO 1.65 1.68 2.00 2.65 2.88 3.00 5.60 8.25

as durable

It

t

t * l

l

t

*

t t t t l

1 l

. t * t I

and unsound

is apparent

that record

(sample originating in order of

durable

bricks

with XIV.

respect

Several

that

failed

in

surface area values

service).

in Table

IV.

have low surface area and that bricks with a

have high surface area.

It

is not

implied that a threshold'

or that it even exists. but the value

surface area can serve as a good basis

for ranking samples

IN B10LfX1cP.I.SYSTEM5

theories

tion inside and outside solution during

been

kave

[29] suggested

advaeeed

that damage the eel1 that

ice formation.

in the liquid state well below hypotheses.

brick

to their frost resistance_

CRYOINJURY

Lovelock

(some known cases of failure

from

increasing

value for surface area can be established of the BET nitrogen

Unsound

.

results are arranged

poor service

[28]

Questionable

(no incidence of failure) questionable

product).

The

frost durability

Durable

3

of

to

Area r'g-

26 2: 19 13 17 7 18 15 22 9 14 8

related

to explain

increases when water

Wle observation

is higher

of cryoinjury. coscentra-

is resloved from the

that intracellular

fluids

remain

- 15-C [30] served as a basis for several

As the free energy of undercooled

vapour pressure,

the mechanism

is caused by the high elecrmlyte

liquids,

than their solid mdificatioa.

as manifested

by higher

a dehydration

preeess

results.

Injury

the eell.

viz.,

protectiag

was

thought

severe

water

layer

but

relevant

observat$oas.

Perhaps

the

the

agents

to

that mst

systems

molecules.

ineluding

eas

biological

be

polyxxsr [35] surfaces

of

that

weter

vicinity

surfaees

to

st:reng

forces

ie

which

Water

the

is

diameter that

at

main

component

[ 25.

44}

that

the

and has

invariably

at

rhe is

below

No doubt also

bulk

on

surface

is

it

and

energy for Thus

it

with

not

eel1

-

the

has

cells

15-i

been

found

[-IS]

as consonant

reasonable

proteins

431.

64,508).

available

diffusion seems

[S6 blood

wt

in

.

subjected

red

It

is

is

(mol

their

exists

water

out

molecules.

proximity

has

be

cells

viable

to

is

Phe

it

is restricted intracellular

assume

also

for

frozen of

case

subsequent

insect

cells

[49]

while

freezing.

to extracellular

reported.

for&,_

after

tbaving. iee

has

shown

intracellular

freezing Survival

Clycerolated

xx~y be

present

sim.i1ar1y,

formatiea

eoneluded

hypothwis

[52].

that,

in

cytolysis (481

both plant tissues

of the cell membrane. been

to extracellular ice

after

rabbit

cornea1

general.

is based on the

ice,

if

[SO] and

solid, cells

these

intracellular assumption

that

intraeellulal

frog blood

Disregarding

and

and was

af rats [Sl]. frozen to form a translucent

intracellular

time being,

of

every

fcrmed

when

effect occurs

study in

reewtly

formation

cooling.

Phis

_

formed

all,

sarcoma

lethal.

rapid

with destruction

forleation

to

close

16. 16. 171 or

macromoLecule

that

activation

rates, crystal [47]

ice

associated

survive

“bound.”

of

carried

haeroglobin

in

A&orbed

theory.

systems

those

been

interaction. in

Microscopic

cells.

it occurred

te

held

With

ensues

extracellular

proved

is

higher

cycle.

their

from crystallization.

130. 461.

ascites

water

to

the freezing phenomena

forces,

large specific

adjacent

surface

rigidly

At slow cooling

ice

the

water

water

prohibited

ef

according

biological

have

formed

part

of

ehemieals

state at temperatures

is the haemoglobin

by

the action

with inorganic

uncommon in

on the relatively

significant

animal

properties

in

investigations

a&orbed

with

spaces

has

[32]. is

for all the

these

integrated

strong attractive

channels least

solvent

and

extensive

Specifically,

account is

water

experimental

tissues,

concerning

a single,

in a liquid-like

as a result of

the

100 per cent in a freeze-thaw

into two groups

by

triple-point the

to

gocd

phenomena

in elose proximity

remain

in

content

of

membranes.

explained

water,

able

biologieal

of the observatieas

bulk

in

to

are divided

migrate through

biological

is

unexplained

When added

loss

of the protoplnslltle proteins

Each theory has

[3S].

the

[31] and

fre ering of the undercooled

rate from zero to even

the additives

appears

volume

mechanisms

of

[54].

reduction of the water

by eel1

to denaturation

proposed

mast important

the survival

Customarily,

It

the

that intracellular

none of

ery0protectiwe

ability

caused

of

for injury te the cells

support,

increase

be

leading

It was also suggested responsible

to

reduction

that

were

were found

exceptions ice

for

formstian

intracellular

‘4 q

294 ice

does

and

not

cause The

form

cell

water

subsequent a manner

,

This

mechanism

continuous

and [533

temperature

denaruration Df

the

the

cell

allows tion

is

or

salt

solutions.

because

. fashion.

at

out.

rise

creation

system

This

shown

a maximum

that

is

inversely

proportional

“so1 ution

effects”

The

and

freezing

outlised. simultaneously c$cle

lhe

is

WA

1561

The

water.

is

extra-

is

and

establisted

cells

and

the

process

below

the

their

has

eutectic

understandable

that

protective

layer

survival

rate

as

of

cooling.

mechanism

of plant

were

similar

is

changes

of

change

those

the cell

rate

al

that

a potato

applied

the

two

with

protein-water can

the

study

be

other them as and

intraare

mechanism

the

during

a

The

details

of

lethal.

exhibit

factors

the and

sample

extremely

identified

4 C deg/min. in

damaging.

EO desiccation)

themgram

was

[54].

not

curves

the

[56]

been

min

the

for

in

destruc-

has

to

and

consistent

differential

temperature to

et due

suggests

tissues

the

length

of

Mazur

water

per

the

cooling

directly

concentration

destruction.

shows

one

probably

itself

wing

from

versus

latter

in

cell

membrane

the

C deg

values

the

membrane

The

and

transfer

faetors.

of

5000

sudden

p/p0

is

nowever.

total

it.

small is

high

that

salt

in

is

however. at

w

exceeding

leaves

damage

cooling,

either

Ap

of

water

permeability

holes

rate

and

proposed

rate

lea&

pressure

two

desorbed

of cellular

the

of

rate

27 [57]

a

isotherm

result of to

than

value

membrane

curve

The of

on

first

slow,

proposed

cellular

precede

temperature

porous

of

glass

and

least

two

adsorbents.

stages. second

the

well

lose

On rapid

small

at

behaviour

the

experimentation cement

bound

determined

where

freetable

desiccation

it

cause

that

the

(increased

Figure

of

The

small.

chief

numerous

that

the

freezing.

dehydration

Mt

(desorption)

Equilibrium

temperature

molecules

faster

cooled

increase

been

cellular

of

of

has

It

protein

The

t-he adsorption

[SS].

a

did

systems.

Accordingly,

condition

are

release of

cell.

phenomeaoe.

-60DC,

is sufficiently

a rate

emphasized

resulting

steep

the

and

water

dehydration

denaturation.

a

if erythrocytes be

the

consequent

to rhe

the at

water bound

inorganic

severe

observed

it.

of

from in

been

decreases.

of cooling

flow

of

even

released

to

should

The

nature

has

followed

release

for the

proceed

water

and

it

noted It

to

a nondestructive

dehydration

gradual

accounts

it

intracellular

of the free water

msc

rate

where

to that observed

occurs

anmunt

the

gradual

of

and

Tather

but

to

similar

found

cella

non-freezable

leads

been

in

of

excretion

in

If

intact

destruction

coexistence

cellular

the

in

that

cooling

peak

eontinuous the

first

water at -7-C;

crystallization;

indicates

exotheteic

and

that

freezing peak that ice.

this

is

that is

freezing

extending caused triggers

formation

took

place

of

sudden

characteristic

by

over

nucleation

desorption, occurs

a wide

in

at

freezing

temperature

of the transfer,

extracellulariy

and

undercooled and from

the

range.

extra-

finally water

It

that

a95 was

originally The second

large

expaasioa

termiaated The half

ia

when.

main

as

much.

time

The

identical,

but

a wide

range

dZ/L

is

the

at

essentially

instances

ceil

and

is

has

at

of

same.

process

the sharp

bulk

certain at

released

during

as

expeeted.

because

same

of

when

the

a mre

-5

temperature at

It

of

lsay be

second

mentioned

rate

are

of

and

apparent.

of

freezing frozen

continuously

fractional

cases,

freezing

that

probability

water

the

expansion is

-4OOC.

ice

is

presumably

the

phase

aapunt

the

frozen.

cooling

approximately

0-C because

essentially is

(-1.3°C).

even rate both

In

.

is

water

changes

the

with

rate-coatrolling

increase

the

Most significantly,

occurs

properties.

asmmt

temperatures

at

the

temperature

heat

associated

process

quaatitative

sub-zero

of 27 x 10

aad

lhe

same

a higher

proceeds

instead

the

is

is

temperature.

renmifa

but

of temperature.

18 x10m3

in both

no significant

period

the

only

completed

cooling, curves

first.

&sorption

of

initiated

amount

the

function

these

is

foIIws

to -4O'C beeause

2 C deg/mie.

about

be

over

the

of

loager

to

immediately

a

on further

i.e.,

nucleation.

is

is

freezing

the

appeared

tura

features

Extracellular because

which

and extends

which

proeess.

of

in9-aeellular. pnwess.

is

Melting

located

hardy

outside

uiater

plants

-i?

-P

COQL116 wARYINQ LENGTH CHAWXS aT*

-

-

-__

-I-

r’ /

-

I1

--__ -5

c

t --__--__----___ -----____

Y

c!i

-5

.

--SD-----

_______

___

1

s 1

-60

I

I

-60

_ _

Fractional length [Regrodwed by

. -20

-40 XYPERHME.

Fig. 27. (4-C/miinl.

I

I

----__ ----__ --__

a

g/

I

.+

0

.C

changes of potato during a temperature cycle permissraa of Academic Press from Cryobiglogy

[57]].

shou

multiple

exochermic

_

Process,

presumably

[53]

non-hardy

due

to a

because plants

fragile

the

or

cell

dead

or

metiranes

stems

are

exhibit

al-ready

destroyed

permits

the

intact

and

a single

membrane

freezing

structure.

MECHAN:SE9 UF CRYOPROTECTION

xv.

The

proposed

under

which

Cooling

mechanism

damage

is

that

enough

fast

than at slow

the

to

cryoinjury or

totally

rare

of

dehydration,

the

dehydration

high

Lovelock

[29]

between

-3

5 sec.

The

probably

establishment

of

conditions

avoided.

apply

Sigh

lower

the

in

support

the time

only

by the

than

considerable

cooling

during

these

is

this

period

conditions

large

this

of

required

for

the

the

unfrozen

situation

is aggralrated

diffusfon

is

no reason

to

high

of

small.

occurs t~ore

damage

the

the

than

occurs

water

thawing

is

On warming,

a

of

ice

above

differences

less

crystals,

O°C.

Under

may exist.

temperature,

The

at which water

rapid.

Permeability It of

is

expected

permitting

or.

that

the

alternatively, In

agreement

winter frost

hardiness,

this

protects

the

cell

Williams protected

[60]

extent the

of

of on

has

of

is

rates

the

thar

plants to

been

reported

Es&e&h&z

at

virtue injury

a

given

cooling

during

the

increase

Only

plants

“hardening” [SS]

presumably

cot<.

by

membrane

in, reases.

exposure

also

beneficial

without

damage

observation

permeability

It

permeability

cooling

rate. of whose

temperatures that

by

peptone

increasing

_

grana

Subsequently, by

is

increased

[55,58].

and Meryman spinach

possible.

higher

the

vieu

actually

change

membrane of

reducing this

Tfq bacteriophage

permeability

induced

by with

resistance

showed

increased

application

eryoproteetive

[61] are

demonstrated not

that

injured

Meryman additives

if

suggested as

the

a

winter-hardened reversible

[62]

the

efficacy

influx increased

is

molecules.

same considerations

true.

well

spite is

is

which of

disappearance warm

In

cells

to assume that

pressure

by the relatively

in

may be

can

vapour

red

region

discussed,

complete

injury. in

it

desorption

water

of

mobility

opposite

cells

deleterious

region

been

is

the

damage

because

for

because.

temperature

critical

has

membrane

redistributed

that

this

decreased

There fact,

avoid

of

survival

time available

advantageous

view, in

the

process

In

are

to

mnt

drastically

freezing.

time

rates

optimum

less

enough

spent

value

the

to the warming process.

injurious

slow

of

renders

having

absolute

if

boundary

determined

but

cooling

rate,

found,

velocity

dehydration.

cooling,

rcnJ -_(O°C

Although

intermediate

minimize

avoiding

and

of

minimal

Rate

Lt follows is

peaks

Conversely,

permeable

or

artifically

of

solute

is

permeability

of non-penetrating

agents.

297 TABLE

V

Vapour

pressure

of

aqueous

Solution

solutions

of

Concentration

mnium DMil Glycerine

Acetate

cryoprotective Pressure.

%

36 J9 40

agents

at

O’C

Iklat

torr

3.27 3.48 3.85

ive

[S7] pressure

8.72 0.76 0.81

Viscosity Ia slow

terms

of

cooling

proposal

mainly

may be

achieved

increase

will

solutions

the

by

by

the

particularly

at

least

fluid can

or

low

of

Ap,

increase

property

eertain

damaged

degree

for

This

fluid. that

[glycerine,

noted

during

protectioa

of

intracellular

agents are

acetate)

The

applied

V.

of

pressure in

air.

of

crystalline

represent of

greater

than with

formed

below

substanees belonging recognized

is

p and

p/p0

complete in

the

DWO.

having

aqueous

glycol.

high

viscosity,

low

vapour

pressure

of

three

state is

less

of

the

achieved

by

glass

thermodynamic

those

in

-120°C undergo the

equilibrium

substances

uruier vapour

glass latter

eriterion

formation group

for

are

glass

the

with free

unique

1631.

conditions.

under

almost

all by

are

e.g.. rapidly,

the

pressure

of

do

in

vapour water

relation

to

that

not

configuration

vapour

pressure

Class

but

viscosity.

are

formation

asnrphous

conditions. high

given

because

in

to

form

very

characterized

solid

and

cooled

aqueous

a concentration

energy

is

their

AS glasses

respect

first A

systems,

partial

formation.

erystalline

when

water

than

The

agents. of

deliquescent

extracellular

their

of

biological

are

equilibrium

structure,

the

solutions, of

possible

intracellular solrd.

the

pressure

molecular

extracellular penetrating

vapour

of

theoretically the

known

can

be

the

is of

the

protection

solution

pressure

of

undiIuted

rhe

cryoinjury.

of

one

ice

certain

in

pressure of

the

their

PECLVS

of

saturated

states

changes

vapour

of

vapour

the

additives

for

agenrs

of

cause in

addition

these

their

Increase

the

values

&SC

primary

the

the

common to

solutions.

Salt

the

seems significant

It

cryoprotective

&crease

in by

customarily Table

water.

amine

a

of

are

temperatures.

two ways:

achieved

be

of

viscosity

cells

revieu.

Ap

Elimination

in

flow

trimethyl

at

Minimizing

the

this

Accordingly.

the

penetrating

arnslonium acetate,

in

dehydratioa.

increasing

retard

of

presented

ice

is

other Liquids which

is

a

formation.

Buffering Farrant

coneeatratioa

and

co-workers of

NaCg

164 -

eceurs

at

661

dmnstrated

a lower

temperature

that

the if

harmful

penetrating

threshold cryoprotective

298 agents

of

PVP

protection

XVI.

are

Additives

the

possessing in

additives

that

Is

. protection

that

is

additives

at

as

possess

scetare

obvious

DK50.

[62].

and

provided. which

rate

of

1571 indicate

the

13O’C/min cent

It

concentration

cent

for

good

but

DMX not

freezing

is 1701

to

the

decreased

from The

is

but

vapour

Figtu-e

97

to

p~~_psure

agents

fication

It

have

was

a;so

glycerolated to

the

observation facr,

the

Rapatx

glycerolated

that and

be

of

for

and of

of

in

in

very

PVP [72]

high

97 per of

the

potato

that in

2 to

cent

PVP provided

due

to

good

(60

per

glycerine that

must

recovery

ad&d

was

copper

63 per

cent

absence

of

cent

virtue of

by

absence

and DMSD

exothewic and

of

of

glycerine.

It glass

penetration.

fluid.

containing

formation,

cent in

lack

by

survival

63 per

c2ange.s

the

that found

blocked

the

intracellular

length

glass

in

expected

blood

34 per

[35].

He was

of

concentrations

demonstrated

protection.

acetate

1471.

This

solutions

above

protection

[71]_

in a cooling

glycerine

glycerine

[56].

three

at

asxsonium

wmplete

cent

cells

the

from

reduced

that

the

frog blood

vitreous

cent.

which

established

obtained

forms

compounds.

by

the

thermal

effects

additive. heat

obtained

The

effect.

concomitant

cryoprotec-

i.e.,

changes

solidiia

dtiinished.

is mozt probable

due

the

essentially

have

snd

In

dramatically

28).

glasses

such

means

been

of

[35].

solutions

has

of

MJst

form

of

the

aqueous

ice

that

however.

fractional of

of

(Figure

stem

good

would

achieve

cycle

to

examples

one

glassy

cent when permeation

lowering

the

the

40 per

of

increased

not

known

amamnium acetate

Lovelock

stirviva

29 shows

dimension

view

provide

which

could

of

45 per

for

fowation

63 per

in a eooling/wariding rive

ice

good is

no crystalline

marrow

in

to

cent.

that

formation,

to

pattern

681.

when the concentration was 15 per

and

expected

are

completely

exceed

prorectior

cells

[69]

formation

above

cent

experiment,

red

2 per

suggested

1 .e..

to

are

the [67,

a5uitmiumacetate. PVP

significant

results uere puzzling.

of

instead

DE0

most

31 per

avoid

In a classical penetrate

in is

hamster

to be

required

ions.

and

Chinese is

contributes

affect

co-uorkers

qualities

thermgrams that

required

complete

of

protection cent)

differential

concentration. cent.

is

and

glycol.

concentration

transition

The

37 per

concentration

greatly

Luyet

glass

The

the

by

sucrose

extracellular

laboratory.

above

salt

qualities

stwwn

eryeprotective

this

15 per

redueed

cryoproteetive

Glycerine,

trimerhy1amin.z

the

AGENTS

solutions,

solidification.

It

that

CRYJPROTECTIVE

formation

ice

and

freezing.

AC-t-ION OF

on

present

during

cells

character viability Luyet

blood)

aforementioned

[SO]

with

[50]

of the was

preserved

observed those

during formed

that

obtained

survival

of

intracellular ice.

shis

twmur

[52]

crystallization suspicion

only

if

“tie

similarity

with

aseites

the

solid

non-glyeerolated

is was

was

supported

by

traaslucant.

of the

results

blood

cells

(of

frozes water

at

-150’

cooled

According Ap and fluid

thus and

penetrating external intracellular non-ionic

and

rapidly

recrystallized to

belw

to

the

proposed

the

free

energy.

the

increasing

additives glass

utilizing

such

pressure

(hitherto

not

as

“bound”

glucose

is

It

striking.”

vitreous

penetrating

agents

the

lowering

of

the

solid:

agects water

[ 731 aad.

is

protecr vapour

the

known

that

excludes

eliminating

of

salt, the

the it

of

the

consists

increase

presueebly.

by

pressure

action

satisfactorily) also

uel1

ice.

both

explained

Penetrating

Although

fluid.

-10’ forms

mechanism,

vapour

formation.

species

at -12B°C

mainly

viscosity does

penetrating

the

oonof

of

the

dissolve additives.

1

- 140

-68

-90 TEMPERATURE -t_-2

Differential theraugrams of aqueous Fig. 28. expressed in v/v% and are indicated on the of Academic Press from Cryobiology [57!).

C

433acentratioa.s are DMXI solutions. (Rqwoduced by permission curves.

300 It the

sheuld

be

importance

mechaai sms . eonditioas

emphasized of

the

Rarher

it

this

suggests

which

under

that

these

hypothesis

%inimum

"solution."

the

prisrary

mechanisms

denies

cell

eeither

v01ume.‘~

causes

become

the

and

leading

injurious

operation

nor

“sulfhydryl-disulfide”

to and

creation

the

of

demonstrates

their

compatibility. CONCLUSION

XVII.

1~ appears and

that

consequently

adsorption

of

fraction)

higher

The

system.

desorption

the

substances

have the

system caused

damage

is

cannot

proceed

glassy

solid

applicable

when

forms for

the

than

the its

the

rapidly

to

energy

in

in lowers

unable

energy

adsorhate

crystallizes

porous

free

are free

in

free

to

pore

various

by

decreases

of

at

the This

adsorptive

a rate

energy

(desorbed in

Mechanical that

found

adsorbates

by

remaining

desorption

difference

was

state

the

eliminated,

adsorbate

such

free

and

adsorbed

formation.

mechanism

adsorbents

or the

the

meniscus

eliminate

system.

types

while

the

outside

reduced,

quantity;

space

energy

in

crystals

is

an appropriate

temperature

the

bulk

difference

external

enough

crystallize

to

that

and

a

be were

investigated.

a

5

COOLING -

-

DTA

-

.---

5

2 z

z t:.

’ lOO$J ‘f

__-=

_-----__

I

.

Y

I ,

L__--___

--__

-----_____

--__

-iO

-Go

z

Fig. 29. BSO-water pennissioa

------_________----

--__

-,

.

H

g

4-Y

,/-

__---

--__

4

z

WANWNG

LfNGTH CUANGES

FractConal

length

-40 TEMF’EPATURE.

changes

and

--__

_______-------

--___H

0

-20 lC

thermogram

of

Rate of temperature change was of Academic Press from Cryobiology [57]). solution.

_._--

potato 4°C/min.

presoaked in (R-Troduced

50% by

SO1 This paper Research

is a contribution

Council

of Canada

from the Division

and is published

of Building

with the

approval

Researeb.

National

of the Director

of

the Division.

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