Mechanochemical Synthesis of CrB2-MoB2 Composite Powder

Takeshi SASAKI, Kiyokata IIZUMI*, Katsuya KUDAKA and Shigeru OKADA

Department of Applied Chemistry, Tokyo Institute of Polytechnics; 1583, Iiyama, Atsugi-shi 243-0297 Japan
Department of Civil Engineering, Kokushikan University; 4-28-1, Setagaya, Setagaya-ku, Tokyo 154-8515 Japan

Ball-milling of elemental powder mixtures without external heat application has been utilized as a process for the mechanochemical synthesis of high melting compounds. The mixtures of chromium, molybdenum and amorphous boron elemental powders with atomic ratios Cr : Mo : B= (1−x) : x : 2 (x=0--1.0) were comminuted for 10--40 h in a planetary ball-mill, and a single hexagonal phase (Cr1−x Mox B2) was formed after 40 h of milling using tungsten carbide balls. By annealing at 900--1400 °C, a single hexagonal phase was still observed at the compositions of x =0--0.6. At x = 0.8 and 1.0, the hexagonal phase was observed to be partly transformed to rhombohedral phase by annealing at the temperatures above 1300 and 1000 °C, respectively. The variation in the lattice parameters of the hexagonal phase with x was estimated to differ from Vegard's law because of a tendency toward superlattice formation. The rhombohedral phase was estimated to be Mo2 B5− x type by the determination of lattice parameters.

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