Preparation of Chromium Monoboride by Reaction Between Chromium and Amorphous Boron in the Presence of Halides

Abstract

Chromium monoboride CrB was prepared by reaction between chromium and amorphous boron powders together with halides at 500-4300°C for 2 h in an argon atmosphere, in order to study the influence of halides on the temperature of reaction start and particle size of the system. When the atomic ratios of the starting materials were B/Cr =1.04 and X/Cr =O.02(X = NaC1, KC1 or KI), the formation of CrB began at 600 °C for 2 h, which is 300 °C low er than in the case of no additive. When halides were added, the relative X-ray intensity of CrB at 600-1300 °C became stronger than in the case of no additive. When halides were not added, the product at 1300 °C was coarse sintered particles with a grain size of about 2 pm in diameter. When NaC1 was added, sintered particles with a grain size smaller than 1 pm in diameter were obtained. When KC1 and KI were added, the products obtained were more sintered and, the grain size was larger than in the case of NaC1as additive. The effects of additives on sintering and grain growth of the products obtained by the reaction at 1300 °C was KI>KC1>NaCl. The lattice constants of the CrB formed in the presence of halides are as follows: with NaC1 additive: a =2.9640( 1 ) A, b=7.878 ( 1 ) A, c=2.932 ( 1 ) A, V=68.5 ( 1 ) A; with KC1additive: a = 2.970 ( 1 ) A, b=7.8 71 ( 1 ) A, c=2.928 0( 1 ) A, V=68.4 ( 1 ) A3; with KI a dditive: a=2.970 ( 1 ) A, b=7.865 ( 1 ), c=2.929 ( 1 ) A, V=68.4 ( 1 )A3.