Preparation and Reaction Mechanism of LaB6 Powder by Solid―state Reaction at Atmospheric Pressure

The lanthanum hexaboride (LaB6) powders were synthesized under atmospheric pressure using B4C and La2O3 powder as the precursors. The thermodynamic conditions for preparing LaB6 at atmospheric pressure were calculated. The effects of temperature and holding time on the phase composition, morphology, particle size and distribution of LaB6 powders were characterized by X―ray diffraction (XRD), scanning electron microscope(SEM) and laser particle size anslyzer. The reaction mechanism was investigated. The results show that LaB6 powders obtained under atmospheric pressure at 1650 or 2h have cube structure with 99.22% purity after washed by hydrochloric acid. When the particle size of La2O3 powder is much smaller than that of B4C particle, the synthesis of LaB6 starts on the surface of B4C particle, then the residual La2O3 and LaBO3 will diffuse through LaB6 shell onto B4C core until the reaction is completely with the temperature rising and holding time prolonged. The initial shape and particle size of LaB6 powders are depending on that of B4C particles.