Conclusions
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1.
A study, based on kinetic investigation and metallographic examination, was made of the high-temperature oxidation of lanthanum hexaboride in air in the temperature range 500–1200°C.
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2.
On the basis of thermodynamic calculations of the equilibria in the systems LaB6-oxygen (nitrogen) at temperatures of 298–2000°K, it was established that, from the thermodynamic point of view, LaB6 is unstable in oxygen and nitrogen atmospheres. It was also found that, in the process of oxidation of LaB6, the most probable are the reactions resulting in the formation of La2O3 and B2O3. The reactions yielding lanthanum and AI 3 and also La2O3 and free boron are also thermodynamically probable.
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3.
On the internal scale/LaB6 interface, the existence was detected of the lower lanthanum boride LaB4, which constitutes an intermediate oxidation product of the starting hexaboride.
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4.
It is shown that, during the oxidation of LaB6, an unknown phase — possibly LaB6 of increased boron content — is formed.
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Literature cited
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Translated from Poroshkovaya Metallurgiya, No. 2 (122), pp. 71–75, February, 1973.