Abstract
Bi–Cu alloys may potentially be used for thermal energy storage or as a catalyst for methane pyrolysis. For application research and simulations, it is necessary to know the reliable thermophysical properties of liquid alloys. Density of liquid Bi–Cu alloys (25, 50, 75 at. pct Cu) was measured with dilatometric method over the 971 K to 1500 K range. Density decreases linearly with temperature for all compositions. The molar volume calculated from measured densities shows positive excess molar volume. Surface tension was measured with maximum bubble pressure method over the 1125 K to 1500 K range. The data fitted with linear equations show that while the surface tension of 25 at. pct Cu decreases and that of 50 at. pct Cu alloy does not vary with temperature, the surface tension of 75 at. pct Cu alloy increases with temperature. The present results are confronted with literature data and several model calculations, part of which were performed in Pandat, and the reasons for positive excess molar volume and surface tension temperature coefficient are explained in terms of thermodynamics of Bi–Cu solutions.
Highlights
BI–CU system (Figure 1) is a simple eutectic system with a convex shape of liquidus[1,2,3] and eutectic point close to pure Bi
Based on the present density results and thermodynamic calculations, it may be concluded that liquid Bi–Cu alloys exhibit positive excess molar volume
Comparison of mixing enthalpy with excess molar volume revealed that maxima of both occur near the equimolar concentration
Summary
BI–CU system (Figure 1) is a simple eutectic system with a convex shape of liquidus[1,2,3] and eutectic point close to pure Bi (eutectic temperature 543.8 K). The demixing tendency in the liquid is expressed by thermodynamic properties such as exothermic enthalpy of mixing.[4] The above and the fact that the vapor pressure of Bi is much higher (3 orders of magnitude at TM of Cu) than the vapor pressure of Cu[5] makes experimental determination of the thermophysical properties, such as density, surface tension and viscosity, of the Bi–Cu liquid solutions challenging. Considering very limited, or even lack of any, experimental data published for several multicomponent alloys,[9] several researchers moved to modeling using geometrical models, which rely on input data from
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