Effect of phase transformation during high energy milling on field activated synthesis of dense MoSi2

The effect of mechanical activation through high-energy ball milling of reactant powders on the subsequent synthesis of MoSi2 by field activation was investigated. Field activated synthesis of this silicide was made through the use of the spark plasma sintering (SPS) method using a pulsed DC current. Milling (0-6 h) produced significant changes in the dispersion and crystallite size of the reactants initially, and resulted in the;partial formation of the product in both the low-temperature (alpha) and high-temperature (beta) modifications when longer milling times were employed. The sequence of phase evolution during milling was determined from XRD, EDX and SEM analyses. Subsequent field-activated synthesis resulted in the formation of alpha-MoSi2 only. The initiation of the synthesis reaction required a threshold power level (equivalent to the level of the current), with the threshold decreasing with increased milling time. However, the initiation time increased when milling resulted in the formation of a significant amount the product phase, with the increase being markedly significant at low power levels. (C) 2002 Elsevier Science B.V. All rights reserved.