Velocity of ultrasound in molten au-co alloys for the determination of compressibility and partial structure factors

Abstract

The velocity of ultrasound was measured in molten Au-Co alloys containing 0, 10, 20, 27, 30, 40, 50, 60, 70, 80, 90, and 100 at.% Co within the temperature range from 995°C to 1700°C. The temperature coefficient of the velocity versus concentration plot shows a positive deviation from ideal behaviour. The adiabatic compressibility was calculated from the velocity and is discussed. From it the partial structure factors a_ij(o) and S_ki(O) for zero momentum transfer were obtained. According to these results, the melts of the Au-Co system show a weak tendency to segregation, i.e. they show concentration fluctuations. Between zero and 60 at.% Co these concentration fluctuations correspond to Au-enriched regions and Co-enriched regions, these being present to the same extent. Between 60 and 100 at.% cobalt the influence of Co-enriched regions is greater than that of the Au-enriched regions.