Metal finishing Q&As since 1989

-----

Surface treatment detection

Where can I buy detection sticks or kits for determining the surface treatment of galvanized steel sheet? Specifically, I need to confirm the presence or absence of:

1. Chromate
2. Phosphate
3. Oil

Roy Rantilla
- Burghill, Ohio, USA
2002

---

Roy, there is a test for chromate on galvanized surfaces that uses an acidic solution of diphenylcarbizide. If chromate is present a reddish purple color appears when this material has been on the surface for several minutes. There is also a method that measures chrome on the surface using a xray fluorscence method but this require the purchase the instrument.

If a phosphate coating has been applied, you should be able to mark on the surface by dragging you fingernail across the surface. The mark appears as a white line. Phosphate coating can also be measured using a weigh strip weigh method using ammonium dichromate as the stripping solution. If oil has been applied, a weigh strip weigh method can be used to determine how much oil has been applied per unit of surface area stripped. In this stripping procedure, a solvent is used to remove the oil. These tests are probably not as simple as you would like, but they will provide the data you are looking for.

Roy Nuss
Trevose, Pennsylvania, USA
2002