EFFECT OF CORROSION ON THE ISOELECTRIC POINT OF STAINLESS-STEEL

The recently developed adhesion method for determining the isoelectric points (IEP) of conductive metal surfaces was applied in studying the corrosion processes of stainless steel (SS). This technique allowed f or characterization of the charge on the metal oxide surface as a func tion of pH. The magnitude of IEP was found to correlate with the struc ture of the oxide layer. The exposure of SS to air at 1,000-degrees-C reduced the original pH(IEP) from 4.15 to 2.8 as a result of the prese nce of magnetite. Treatment at lower temperatures yielded a significan t portion of hematite in the oxide layer and pH(IEP) shifted to 3.3. T he corrosion of SS in aqueous sodium chloride (NaCl) solution at room temperature, as examined by the proposed electrokinetic method, result ed in the formation of magnetite in the early stage of the process, wh ile hematite and/or lepidocrocite was detected as a final product.