Preparation and Formation Process of HfB_2 Fine Powders by Mg-Thermite Method

Preparation conditions and formation process of HfB_2 fine powders from HfO_2, amorphous B and Mg under an argon flow were examined. Fine powders of single phase HfB_2 were prepared by heating powder mixtures of HfO_2: amorphous B: and Mg in molar ratios of 1:2:7-10 at 800℃ for 1 h. The HfB_2 powders had particle sizes of 0.03-0.3μm. The formation process of HfB_2 was composed of the following reactions: (1)650℃〜: HfO_2+2Mg→α-Hf+2MgO, (2)550-750℃: Mg+2B→MgB_2, (3)750℃〜: MgB_2→Mg+2B, (4)800℃〜: α-Hf+2B→HfB_2 and (5)850℃〜: 2MgB_2→MgB_4+Mg. MgB_2 did not interfere the formation of HfB_2 because it decomposed above 750℃, whereas MgB_4 interfered the boridation of α-Hf above 850℃ because it is thermally stable. For the preparation of single phase HfB_2 powders, it is most important to suppress the formation of MgB_4 by controlling the reaction temperature below 850℃.rights: 社団法人日本セラミックス協会rights: 本文データは学協会の許諾に基づきCiNiiから複製したものであるrelation: IsVersionOf: http://ci.nii.ac.jp/naid/110002290337