1984 Volume 70 Issue 11 Pages 1605-1611
The conditions of formation of FeF2+, FeF2+ and FeF3 in the pickling solution of HNO3 and HF for stain less steels have been studied.
The types of ferricfluoride ions depend on the ratio of concentrations (g/l) of total fluoric ion to that of ion in the pickling solution. When this ratio exceeds 1.5, FeF2+ion is formed and FeF2+ ion is formed when the ratio is less than 1.5. Precipitates in the pickling solution are FeF3·3H2O and scales formed during annealing of stainless steels. The amounts of precipitates FeF3·3H2O increases with the concentrations of total fluoric ions and ferric ion. When the concentration of ferric ion is less than 15 g/l, precipitate of FeF3·3H2O is not formed.
For the determination of uncomplexed HF in the pickling solution, volumetric titration method with standard H3BO3 solution is employed.