An investigation was made of reactions in the Zr - B - C system. The existence of a eutectic in the quasibinary section B 4 C - ZrB 2 was confirmed. A directionally solidified eutectic alloy was obtained by zone melting. Its composition was precisely determined as (mol. %) 71.5 B 4 C, 28.5 ZrB 2 . The effect of melting parameters on the eutectic structure was studied.

It has been established that hydrochloric acid treatment is an effective means of ridding an industrial lanthanum hexaboride powder of impurities. It is shown that acid treatment of industrial LaB6 powders substantially improves the corrosion resistance of parts made from them by powder metallurgy techniques. A mechanism of rupture of hot-pressed and sintered lanthanum hexaboride parts is proposed.

AbstractX‐ray lineshifts of rare earth elements in the hexaborides of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, and Y relative to the corresponding tri‐ or difluorides are measured by the crystal diffraction method. The experimental shifts are compared with the values obtained in relativistic self‐consistent field calculations in the effective free ion approximation. The hexaborides of La, Ce, Pr, Nd, and Gd are shown to have 4fn‐15d configuration (4d for Y), and those of Eu and Yb, 4fn configuration. The shifts obtained for Sm in SmB6 support the suggestion that Sm is here in an intermediate valence state and is best described by the 4f6−x5dx configuration with x = 0.615 ± 0.007.

Samarium hexaboride of the limiting composition, SmB6, possesses the maximum chemical activity in relation to sulfuric and hydrochloric acids.

The mixed-configuration state of samarium in SmB6 is stable and unaffected by defectiveness of structure and the presence of vacancies of metallic states in the lattice. The introduction of atoms of stable integral valence into the SmB6 crystal lattice alters the valent state of the samarium atoms. The introduction of divalent atoms of atomic radius larger than that of samarium increases the lattice constant of the boride and results in the effective valence gradually growing to the integral value 3. The larger the atomic radius of the addition metal, the lower is the concentration of this addition at which a change in the valence of the samarium atoms is observed. The introduction of trivalent atoms shifts the mixed-configuration state of Sm ions toward smaller values of effective valence, but an integral value is not attained. The effect of substitution of magnetic elements (Eu and Gd) for samarium is the same as that of substitution of nonmagnetic elements (Yb and La).