抄録
The self-regulation of sulfate concentration by the addition of Sr2+ to a chromium plating bath saturated with SrSO4 was studied. The following results were obtained: (1) Since SrSO4 is a strong acid salt, the solubility of SrSO4 in low pH solution such as a chromium plating bath was not much higher than that in its aqueous solution. (2) The SO4 concentration could freely be regulated by the addition of SrCO3 to the chromium plating bath. (3) The decrease in the solubility of SrCO3 conformed to “common-ion effect” in the chromium plating bath, but not in the aqueous solution. It would be more clear by assuming activity instead of concentration. Namely, the ionic strength was higher and steady in the chromium plating bath and was supposed to be proportional to CrO3 concentration; but it was changeable in the aqueous solution. (4) For example, the solubility of SrSO4 (as SO4) was 1.4g/l in chromium plating bath containing 50g/l of CrO3 at 55°C. When SrCO3 of 6.0g/l was added to the bath, the SO4 concentration became 0.5g/l, by which the plating bath for self-regulating SO4 was prepared.
