The copper sulfate test is used to detect the presence of metallic iron and iron oxide on the surface of materials.
Question - What solution strength is needed to copper sulfate solution can be used to determine if a metal is stainless steel or just steel ?
Answer - Copper sulfate (CuSO4*5H2O) + H2SO4 (anywhere from 1% to 50% is specified in various test methods).
How does copper sulfate test for passivation work?
ANSWER : Chromium and nickel will not be replaced with the Copper sulfate test solution (which also contains sulfuric acid), only the Fe or other less noble metals. If there is free iron on the surface it will be replaced by the copper, forming the distinctive copper color on the surface in this 6 minute test. Of course, this test should only be used on austenitic stainless steel. Some people use it on other grades, but you can get false failures.
Spray the surface with a solution of copper sulfate in water. If free iron is present, a copper film will form. In this test, the chemical reaction is:
Fe + CuSO4 = FeSO4 + Cu
The copper film is immediately visible.
Ferroxyl test: causes coloured iron compounds to appear as specks.