Thermodynamics and surface properties of liquid Cu-B alloys

The study of the thermodynamic and the surface properties of liquid Cu-B alloys can help better understanding of a complex interfacial chemistry related to liquid Cu-brazes in contact with boride substrates. Despite a simplicity of the Cu-B phase diagram, only a few thermodynamic data are available in the literature, while in the case of the surface properties a complete lack of data is evident. The quasi-chemical approximation (QCA) for the regular solution has been applied to describe the mixing behaviour of liquid Cu-B alloys in terms of their thermodynamic and surface properties as well as the microscopic functions. In view of joining processes related to liquid Cu-brazes/solid boride systems a particular attention is paid to the surface properties of the Cu-rich part of the system and the calculated values are substantiated by the new surface tension experimental data of liquid Cu and Cu-10 at.% B alloy. The tests have been performed by the sessile-drop method under the same experimental conditions. Considering the experimental uncertainties, the effect of oxygen on the surface tension of liquid Cu and Cu-10 at.% B alloy has been analysed by simple model that combines the physical property data included in Butler's equation with the oxygen solubility data and it gives the same results as Belton's adsorption equation.