ABSTRACT
MO + ()2-;: Mo~- (6.37) then complex ion formation can take place and the metal oxide gets dissolved in the melt as a complex anion. This is referred to as basic fluxing. Figure 6.30 further demonstrates that from a minimum solubility of NiO corresponding to activity of Na20 as 10-10·3, the solubility goes on increasing with the increase of aNa~ (i.e., decreasing pso) according to the reaction:
(6.38)
(6.39)
which corresponds to acid fluxing. Such solubility behavior in Na2S04 is also reported for other oxides, such as Co30., Fe203, Ab03, and Cr20 3, which are of principal interest in high-temperature alloys and coatings. The reported solubility curves for the different oxides maintain the same nature but with different minima values and are displaced to the left or the right of each other. The differences in magnitude of -log aNa~ values as observed for the solubility minima between the different types of oxides further emphasize that the local chemistry within a fused salt film is important. The terms acidic and basic are relative and refer to the reaction that occurs rather than the condition of the melt.
