Surface pretreatment of austenitic stainless steel and copper by chemical, plasma electrolytic or CO2 cryoblasting techniques for sol–gel coating

The surface pretreatments of the austenitic stainless steel and copper surfaces for the sol–gel coating were carried out by chemical, plasma electrolytic or CO2 cryoblasting techniques. With the austenitic stainless steel the smoothest surfaces were obtained with plasma electrolytic cleaning, after which the measured contact angles of water were clearly decreased revealing improved hydrophilicity. As well with the copper samples the smooth surface and improved hydrophilicity was obtained with the plasma electrolytic cleaning, but oxide layer formed to the copper surface immediately after the treatment. CO2 cryoblasting provided rough surface with wetting properties close to the original surface both for austenitic stainless steel and copper surfaces. CO2 cryoblasting provided best appearance for the copper surface because no oxidation happened with that treatment. XPS and SIMS studies showed that with the plasma electrolytic treatment the surface layer of the austenitic stainless steel enriched of chromium and the oxide layer formed on the surface was less than 10 nm thick. With the chemical cleaning and CO2 cryoblasting, the chromium enrichment to the stainless steel surface was less. However XPS and SIMS studies showed that chemical treatment provided thinner oxide layer to copper surface than plasma electrolytic treatment.