Quantitative Analysis of the Relative Basicity of CaO and BaO by Silver Solubility in Slags

The solubility of silver in molten CaO-B(2)O(3) and BaO-B(2)O(3) slags at high temperatures was measured to seek a new measure of the basicity of slags. The B(2)O(3)-bearing fluxes, which have wide range of liquids at the temperature of interest, have been applied to investigate the effects of flux composition on the solubility of silver from the saturation of acidic or basic components. The solubility of silver in slags has a minimum value as a function of flux composition, and it is suggested that silver behaves as an amphoteric substance and dissolves by different mechanisms in acidic and basic fluxes. The solubility of silver decreased with the increasing temperature and content of basic oxides in the acidic region, and vice versa in the highly basic region. In the acidic region, BaO is more basic than CaO by, at most, about 33 pct, based on the difference of the solubility of silver in both slags, indicating that BaO is not a much-stronger basic oxide than CaO in the acidic slags. In the highly basic region, BaO is about 5 times more basic than CaO. The solubility of silver in slags was compared to the nitride capacity, showing that the dissolutions of silver and nitrogen into the melts are similar to each other. The relationship between Ag solubility and theoretical optical basicity was also discussed.