Studies of Porosity in Electroless Nickel Deposits on Ferrous Substrates

Abstract

SummaryThe effect of soak and electrolytic alkaline cleaners together with chemical polishing on the porosity of electroless nickel coatings on mild steel substrates was investigated. The porosity of the deposit was evaluated by chemical spot tests using ammonium thiocyanate as indicator, the sulphur dioxide test, Corrodkote, electrochemical corrosion rate measurements and scanning electron microscopy studies. The results showed that the various pretreatments had no significant effect on the porosity of the coating. The overriding factor was observed to be the deposition time hence the thickness of the deposit. All the tests indicated that the percentage porosity decreased exponentially with increase in coating thickness. The relative merits of each of the techniques used in assessing the uniformity of the deposit, are discussed.