Abstract: 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 ℃ for 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.

Key words: lanthanum hexaboride, thermodynamic, solid-state reaction, reaction mechanism