Effects of boron addition on the formation of MoSi 2 by combustion synthesis mode

Abstract

The combustion synthesis behavior of Mo–Si–B powder was investigated. Test specimens with nominal compositions including MoSi 2, Mo(Si 0.975B 0.025) 2, Mo(Si 0.95B 0.05) 2, Mo(Si 0.925B 0.075) 2 and Mo(Si 0.9B 0.1) 2 were employed. The combustion mode, propagation velocity of combustion wave, combustion temperature and combustion product structure were studied. The results showed that the combustion wave propagated along a spiral trajectory till reaching the bottom of the compacts. The combustion temperature was increased by the addition of boron, to as high as 1922 K in the case of the Mo(Si 0.95B 0.05) 2 sample. However, the flame-front propagation velocity decreased as a result of the addition of boron. The X-ray diffraction results showed that the combustion products of the Mo(Si 0.975B 0.025) 2 and Mo(Si 0.9B 0.1) 2 samples were composed of MoSi 2 with minor MoB. Those of the Mo(Si 0.95B 0.05) 2 and Mo(Si 0.925B 0.075) 2 samples were composed of MoSi 2 with minor MoB and MoB 2. And traces of Mo 2B 5 were identified in the Mo(Si 0.95B 0.05) 2 sample.