INVESTIGATIONS INTO THE PREPARATION AND DECOMPOSITION OF SAMARIUM TETRABORIDE AND SAMARIUM HEXABORIDE

Thesis/Dissertation · Sun Dec 31 23:00:00 EST 1961

OSTI ID:4774732

Galloway, G L

Attempts to prepare pure samarium tetraboride either by the reaction between samarium sesquioxide and varying amounts of boron or by utilizing the direct reaction between the elements were shown to result only in mixtures of the tetra- and hexaborides. No evidence whatsoever was obtained to suggest the stable existence of a lower boride such as samarium diboride or a higher one such as samarium dodecaboride. The extent of contamination of the products of any reaction used to prepare a preponderance of one or the other of the borides was shown to be a function of the starting composition of the reactants, the temperature and duration of the heating, and, in some cases, the nature of the heating cell used to confine the reactions. Changing only the starting composition of mixtures of samarium sesquioxide and boron examined at 1650 deg in a crucible of boron nitride resulted in a smoothly continuous variation in the ratio of boron to oxygen lost on heating. This result, coupled with accompanying weight data, was irterpreted as evidence of the non-validity of any single equation to describe the reaction simply. A survey was made of some of the materials suitable for use as crucibles at these high temperatures and details of this study are presented. The apparent stability of samarium tetraboride and samarium hexaboride at various temperatures wasshown to be dependent upon the matrix material with which these borides were in contact. The existence of the equilibrium 3 SmB/sub 4/(s) = 2 SmB/sub 6(s) + Sm(l,g) was ultimately verified as a result of observations on the diffusion and evaporation phenomena occurring within the system. When samarium tetraboride-hexaboride mixtures were heated in a crucible of boron nitride, the top surface of a sintered compact was observed to become depleted in samarium tetraboride and rich in samarium hexaboride; complete conversion was brought about by continued heating. However, when in contact with a matrix capable of absorbing boron into its interstices at a sufficiently high rate, a sintered mixture of samarium hexaboride was found to contain samarium tetraboride on its top surface after being heated at temperatures higher than those at which this tetraboride is normally unstable with respect to the hexaboride. These observations are explained in terms of a competition between equilibrium, rates of evaporation of samarium from the heating cell, and rates of diffusion of samarium to evaporation sites. (Dissertation Abstr., 23: No. 3, 1962)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-001509
• OSTI ID: 4774732
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ADSORPTION
BORON
BORON NITRIDES
BORON OXIDES
CHEMICAL REACTIONS
CHEMISTRY
COMPACTING
CRUCIBLES
DECOMPOSITION
DIFFUSION
EVAPORATION
HEATING
HIGH TEMPERATURE
IMPURITIES
LOSSES
MEASURED VALUES
MIXING
OXYGEN
PREPARATION
SAMARIUM
SAMARIUM BORIDES
SAMARIUM OXIDES
SINTERED MATERIALS
SINTERING
STABILITY
SURFACES
TEMPERATURE
WEIGHT