Determination of Density and Surface Tension of CaO–Al2O3 Molten Slag Using Pendant Drop Method

The pendant drop method is often used to determine the surface tension of liquids. However, in the process of calculating surface tension, corresponding density data are required, which brings a series of problems to the determination of the surface tension of high-temperature slag, especially. So far, there have been few reports on determining the two properties of density and surface tension by the pendant drop method in a single experiment. In this work, CaO–50% Al2O3 slag was taken as the research object, a novel ring-shaped-pendant drop-forming device constructed with Pt–10% Ir alloy was employed, and the outer diameter of the alloy ring at experimental temperatures was determined as a reference scale by pixel analyses of images. The density and surface tension of the slag within the range of 1450 to 1650 °C were simultaneously determined under heating and cooling modes, respectively, and the effect of slag mass on measurement results was also investigated. The results show that the measurement mode (heating or cooling) has little effect under experimental conditions, whereas the slag mass has a certain effect when it is small. The average density and surface tension values obtained both decrease with increasing temperature, and the temperature coefficients are −3.406 × 10−4 g/(cm3⋅°C) and −4.2 × 10−2 mN/(m⋅°C), respectively. The density and surface tension of the slag at 1550 °C are 2.836 g/cm3 and 624 mN/m, respectively. In addition, the combined standard uncertainties of the measured density and surface tension are 0.01 g/cm3 and 4 mN/m, respectively. The density and surface tension values are basically consistent with literature data. This work can provide an experimental basis for the development of a pendant drop method used to determine the density and surface tension properties of molten slag.