While coating, do well control the amount of ferrous ion in solution. If few ferrous ions in solution , add ferrous sulfate to supple the vacancy. If ferrous appear insufficient, the brightness of coating will be bad; if ferrous content keeps more than l. 5 g/l, the coating surface will take black.
When too few ferrous ion in solution, usually add ferrous sulfate to make up. Because ferrous ion can make the micro leveling effect in zn-based alloying. Sufficient ferrous ion in zinc ferrous nickel lighting solution will help to update the coating's brightness. General content is 0.6 ~ 0.8 g/L.
The right amount of ferrous sulfate is 0.05 ~ 0.1 g/L per 16 hours. And it should be chemical pure grade because industrial grade is not pure enough and also contains copper ion or nitrate radical ion.
Dissolve it it in hot water and complex with sodium potassium tartrate tetrahydrate .Then it’s ready to be add in. Remember the amount of sodium potassium tartrate tetrahydrate is 4 ~ 5 times of ferrous sulfate industry grade.