Journal of the Less-Common Metals, 93(1983) 276
normal hydrogen electrode (NHE) in sulphate media to 1.82V (NHE) in perchlorate media. However, a number of workers have reported the use of cerium(IV) to oxidize organic compounds, e.g. 1,Cnaphthoquinone from naphthalene and benzaldehyde from toluene. All these processes have failed because the cerium(IV) salt cannot be regenerated from the cerium(II1) salt after the organic oxidation. Many research groups have investigated the electro-oxidation of cerium, but none of them has been able to develop an industrial process. Therefore an electrolytic cell to solve this problem is being investigated and developed at Rhone-Poulenc. A filter-press electrolytic cell which is compatible with a nitrate or a sulphate electrolyte is used. Cerium is oxidized in the anolyte and the protons are reduced to hydrogen in the catholyte. The two compartments of the cell are separated by a cationic membrane which allows transfer of the protons from the anolyte to the catholyte to form the current. The reactions are Ce3+ + Ce4+ +eH,O + 2H++f0,+2e-
in the anode and
in the cathode. New developments, such as a high anolyte flow rate, are used to increase the mass transfer coefficient of the anbdic reaction and thus to minimize the size of the cell. The investigation is planned in three stages: on the laboratory scale the cell generates 0.1-0.2 equivalents h-i with an anodic current density of about 15 A dm-‘; on the advanced laboratory scale (in progress) the cell generates about 1.5 equivalents h-i with an anodic current density of 20-30 A dm-*; on the industrial scale (designed and in construction) the cell will generate 76120 equivalents h- ’ with an anodic current density of 25-30 A dn-*. In all these steps the electrical yields are better than 90% with oxidation rates of 92%-97x. In summary, work is in progress at Rhone-Poulenc to develop an electrolytic cell which can oxidize Ce3+ to Ce4+ m nitrate, sulphate or perchlorate electrolytes. We believe that this cell will aid organic oxidations using an “oxygen carrier” like cerium(IV).
Rare earth Faraday
M. J. WEBER, E. HILDUM,
S. LEUNG and R. MORGRET
Lawrence Livermore National Laboratory,
of California, Liver-more, CA 94550(U.S.A.)
Optical switches, modulators and isolators based on Faraday rotation are used in various laser systems. Important considerations for Faraday rotator materials in laser applications are the Verdet constant, the transmission (small absorption and scattering losses), the non-linear refractive index (for high power lasers where self-focusing must be controlled) and the cost. The best Faraday rotator materials for most high power lasers operating at visible or near-visible wavelengths are paramagnetic materials consisting of rare earth ions in hosts with low refractive indices. For general use, rare earths with low-lying 5d bands and a large range of transparency are most attractive; ions satisfying these criteria include Ce3+, Pr3+, Tb3+ and Eu*‘. In the search for improved materials the Verdet constants at optical wavelengths were measured for rare earths in many different hosts including oxide and fluoride crystals and glasses. The wavelength dependence of the Verdet constant, the transmission spectra, the linear and non-linear refractive indices and
* Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April l&21,1983. 0 Elsevier Sequoia/Printed
in The Netherlands
of the Less-Common Metals, 93 (1983) 277
other physical properties for 35 diamagnetic elsewhere [l].
crystals and glasses are tabulated
This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W-7405-ENG-48. 1
M. J. Weber, Faraday rotator materials, Rep. M-103, 1982 (Lawrence Laboratory, University of California, Livermore, CA).
The effect of fluoride preparation metals * B. J. BEAUDRY,
P. E. PALMER
on the purity of the rare earth
and K. A. GSCHNEIDNER,
Ames Laboratory, Ames Laboratory and Department State University, Ames, IA 50011 (U.S.A.)
Science and Engineering,
The established process used at the Ames Laboratory to prepare the rare earth metals includes the calcium reduction of high purity rare earth fluorides. The preparation of these high purity fluorides in the past has included melting of the fluorides under a dynamic HF-Ar atmosphere to remove the oxygen quantitatively (the resultant compounds are known as “topped” fluorides). The present research indicates that this melting step is not necessary to prepare fluorides of sufficiently high purity for metal preparation, especially for the light rare earth metals. As an example, the typical oxygen contents of lanthanum, cerium, praseodymium and neodymium prepared from topped fluoride are 34 wt.ppm, 5’7 wt.ppm, 29 wtppm and 40 wt.ppm respectively, while the oxygen contents of the corresponding lanthanides prepared from untopped fluorides are 28 wt.ppm, 59 wtppm, 30 wt.ppm and 55 wt.ppm respectively.
Influence of rare earths on wrinkle formation Fe-Cr-Al alloy * LI BEI, LI PEILIANG
in the scale of
and WANG LIMIN
Baotou Research Institute of Metallurgy, Baotou, Inner Mongolia (China) When Fe-Cr-Al alloys were oxidized in air in the temperature range 800-1300°C the thermal etching pits of the dislocation formed on the alloy surface developed into grooves as a result of the dislocation movement. This led to the formation of numerous wrinkles in the oxide scale. No wrinkles were formed in the presence of rare earths (REs) because they prevented the formation of thermal etching pits on the alloy surface. The REs also inhibited the occurrence of thermal etching at grain boundaries and in the matrix surrounding the inclusions and the carbides on the alloy surface, and hence prevented the formation of voids at the oxide-alloy interface. This behaviour may be due to the interaction of the RE atoms with crystal defects in the alloy.
*Abstract of a paper presented at the Sixteenth Rare Earth Research Conference, The Florida State University, Tallahassee, FL, U.S.A., April l&21,1983. 0022-5088/83/$3.00
0 Elsevier Sequoia/Printed
in The Netherlands