Rare-earth element desorption from tungsten surface

Rare-earth element desorption from tungsten surface

Classified abstracts 495-624 Classified abstracts 495-504 on this page Editor's note The label immediately following the title of each item denotes ...

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Classified abstracts 495-624 Classified abstracts 495-504 on this page

Editor's note

The label immediately following the title of each item denotes country or origin of publication, and that at the end of each abstract indicates country or origin of work (where known).

I. General v a c u u m science and engineering 14. KINETIC THEORY O F GASES 14 495. The viscosity and thermal conductivity coefficients of dilute neon, krypton and xenon. (USA) The coefficients of viscosity and thermal conductivity for dilute neon, krypton and xenon were examined by a method which selects a suitable potential function, and its parameters, which is then used to correlate the theory with experimental data, given the kinetic theory expressions for the transport coefficients. Tables are given between 100 and 1000°K. H J M Hanley and G E Childs, Rep NASA-CR-87416, NBS-TN-352, March 1967, 31 pages (Sci Tech Aerospace Reps, 5 (19), 3554, N6733538). 14 496. Gas-kinetic computation of the thermal gliding velocity of a gas in the vicinity of a solid surface. (USSR) Using the exact computation of the impact integral in the Boltzmann equation, the true expressions of the thermal gliding velocity of a gas were derived. Yu I Yalamov et al, Dokl Akad Nauk SSSR, 177 (1), 1st Nov 1967, 74-76 (in Russian).

15. FLUID DYNAMICS 15 : 33 497. Dense supersonic hydrogen stream in high vacuum. (USSR) The influence of the hydrogen source temperature on the parameters of neutral hydrogen atom streams, used as a backing for ion beam charge/discharges, was investigated. A t lower temperatures the beam density is higher, the optimal beam being obtained at 20°K for 6 times less hydrogen than at 300°K. By the same method, a hydrogen stream of density 10z7 cm -2 with a pressure difference at the boundary of 7 orders of magnitude may be produced with the nozzle and hydrogen reservoir cooled to 20.4°K. E S Borovik et al, Zh Tekh Fiz, 37 (12), Dec 1967, 2209-2212 (in

Russian).

16. GASES AND SOLIDS 16 : 18 Models for electron emission from metals with adsorbed monolayers. See abstract number 514. 16:32 The surface potential of metal surfaces under electron bombardment in high vacuum. See abstract number 592. 16:47 Outgassing of materials at very low pressures. See abstract number 623. 16 498. Rare-earth element desorption from tungsten surface. (USSR) The temperature dependence of the lifetime of some rare-earth elements adsorbed on a tungsten surface was measured by means of a modulated atomic beam. The following values for the desorption energy of these elements on tungsten were measured: La-6.3 eV, Nd-5.6 eV, Sm-4.2 eV, Eu-3.4 eV, Tb-5.6 eV, Dy-5.0 eV, Ho-5.3 eV, Er-5.1 eV, Tm--4.2 eV. N I Alekseev, Zh Tekh Fiz, 37 (12), Dec 1967, 2224-2228 (in Russian).

16 499. On the problem of maximum and optimum concentrations of adatoms in mono-atom layer systems. (USSR) The definition of optimum concentrations of adsorbed atoms is discussed with regard to surface roughness. N D Konovalov et al, Radiotekh Elektron, 12 (10), Oct 1967, 1861

(in Russian). 16 500. Oxygen adsorption and the reaction of the adsorbed oxygen with molecular hydrogen on silver films. (USSR) Silver thin films were evaporated in oil-free residual atmosphere at 5 × 10-s torr and their surface area was measured using krypton at 78°K. At 300°K adsorption of O2 with subsequent adsorption of H~ was investigated. The H2 adsorption occurs in two stages: at the beginning H~ reacts with sorbed O forming the OH group (high-speed phase) and after adsorbing about 10 per cent of a monolayer, hydrogen reacts with the OH groups producing water which is desorbed when the chamber is again pumped down to 10-7 torr. G K Boreskov and A V Khasin, Dokl Akad Nauk SSSR, 177 (1), 1st Nov 1967, 145-148 (in Russian). 16 501. Surface hydroxyls and hydrogen chemisorption on magnesium oxide, as investigated by means of infrared spectroscopy. (USSR) Dehydrated magnesium oxide was heated up to 800°C and exposed to hydrogen and deuterium. Investigating this process by infrared spectroscopy it was found that at temperatures up to 180°C only OH and OD groups are formed by chemisorption and at higher temperatures these hydroxyl groups are transformed to H=O and D20. A t temperatures above 180°C chemisorbed deuterium in OD group or in D20 is substituted by hydrogen. A A Lisachenko and V N Filimonov, Dokl Akad Nauk SSSR, 177 (2), 1lth Nov 1967, 391-394 (in Russian). 16 502. Consideration of energy loss in the electrostatic model of film adsorption. (USSR) As a contribution to the theory of the work function of thin film systems based on the electrostatic model of adsorption, the process of producing the second adsorbed film on the first one is theoretically analyzed taking into account the first film energy losses due to polarization of the second one. V A Kmmetsov et al, Fiz Tverd Tela, 9 (12), Dec 1967, 3649-3651

(in Russian). 16 503. The enhancement by inert gases of the field desorption of oxygen from tungsten. (Great Britain) Field desorption of oxygen from initially field-evaporated tungsten surfaces has been investigated to determine the extent to which the adsorbate is retained on the surface under the conditions for imaging in a field-ion microscope. Desorption of oxygen occurs in vacuum for electric fields greater than half the field needed to evaporate the tungsten substrate, probably by the desorption of oxide ions. The extent of desorption is greater the higher the electric field. Desorption is greatly enhanced by the presence of the inert gases used in imaging. D W Bassett, Brit J Appl Phys, 18 (12), 1967, 1753-1761. 16 504. Study of some of the parameters affecting Knudsen Effusion. Eft. The vapour pressure of gold. (USA) Vapour-pressure data for gold were obtained during a study of the spatial distributions of molecular beams diffusing from Knudsen

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