Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Rare earth metal
Patent
1987-11-13
1991-04-09
Hunt, Brooks H.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Rare earth metal
423263, 23305RF, 23295R, 156623R, 156DIG63, C01F 1700
Patent
active
050063189
DESCRIPTION:
BRIEF SUMMARY
The object of the present invention consists of novel particulate compositions of rare earth oxide, their preparation and their application.
BACKGROUND OF THE INVENTION
It is known that the obtention of high purity oxides in a finely divided form constitutes an important research objective in different technical fields, to prepare for example ceramics, abrasives, catalyst supports, etc. . . .
It is known that rare earths are present in numerous minerals and constitute by-products of the preparation of various metals. Their utilization poses difficult technical and economic problems. In effect, the conventional methods of the processing of oxide particles generally employ either precipitation processes or those of the sol-gel type. In precipitation methods, the addition of the precipitating agent leads to contamination and thus a change in the purity of the oxide obtained. In the sol-gel methods, processing is generally long and the basic products used are expensive.
Furthermore, the calcination processes which generally represent the final stage in the obtention of oxides introduce the risk of additional pollution by the environment and lead to particles the surface whereof are less than favorable for certain applications.
In U.S. Pat. No. 3,098,708, the obtention of particles of oxides of thorium and uranium by a hydrothermal process consisting of heating an acid solution such as a hydrochloric or sulfuric acid solution of oxides of these metals to a temperature of 170.degree. to 250.degree. C., under a pressure of 100 to 400 psi (approximately 6.5.times.10.sup.5 to 2.6.times.10.sup.6 Pa), is described. In this patent, it is indicated that the process is of interest in particular because the rare earths potentially present do not precipitate during the carrying out of this hydrothermal process.
SUMMARY OF THE INVENTION
It has now been discovered that it is possible to obtain fine particles of a rare earth oxide in the form of microcrystallites, the size and morphology thereof may be controlled, by a solvothermal process consisting of heating the solvent medium under conditions of temperature and pressure corresponding to the hypercritical range. This process has made it possible to obtain for the first time rare earth oxides in the form of fine particles with dimensions of the order of microns having good homogeneity of the grain size distribution. These particles have a monocrystal configuration and in particular are free of internal porosity.
DETAILED OF THE INVENTION
It was discovered further that it is possible with the aid of the appropriate additives to direct the reaction so as to obtain grains the morphology thereof may vary as a function of the additive used.
The object of the present invention therefore consists of novel particulate compositions of rare earth oxides, characterized in that the particles are present in the form of single crystals with a homogeneous grain size and morphology, the dimensions whereof are smaller than or equal to 10 .mu.m and greater than approximately 0.05 .mu.m, and that at least 80% of the particles have dimensions varying within a range of x.+-.0.2 x, x being the mean dimension of the particles of the composition involved, it being understood that the range of variation .+-.0.2 x is not less than .+-.0.1 .mu.m.
The latter condition thus signifies that for compositions with particles having mean dimensions less than or equal to 0.5 .mu.m, at least 80% of the particles have dimensions varying within a range of x.+-.0.1 .mu.m. For compositions with particles having a mean dimension greater than or equal to approximately 2 .mu.m, the process described hereinbelow makes it possible to obtain variations within a range of x.+-.0.1 x for at least 80% of the particles.
Due to the process of the invention, the size of the particles may be controlled and it is possible to readily obtain particulate compositions having a mean particles dimension less than for example 2.5 .mu.m, or less than or equal to 1 .mu.m, or even less than or equal to 0.5 .mu.m.
The particles o
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C. B. Finch and G. W. Clark, Journal of Crystal Growth, 12, No. 2, pp. 181-182 (1972).
Demazeau Gerard
Devalette Michel
Martel Olivier
Verdon Eric
Hunt Brooks H.
Mai Ngoclan T.
Rhone-Poulenc Chimie
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