無電解ニッケル−リンめっきへのセリウム化成処理とその高温耐酸化性

概要

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Cerium conversion coatings of 20-70nm in thickness, have been deposited onto electroless nickel-phosphorus substrate by immersion into a simple 0.01mol/L cerium(III) chloride aqueous solution in the temperature range of 298 to 353K. Cerium-rich film was formed by the dissolution of nickel substrate at the anodic sites and the reduction of dissolved oxygen at the cathodic sites on Ni-P substrate. X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) have been used to characterize the cerium conversion coatings. It was found that the cerium-rich films were crystalline cerium (hydr)oxide with CeO2-fluoride structure. The high-temperature oxidation resistance of Ni-P films in air has been studied after cerium conversion treatment. It was found that the cerium oxide layer on the Ni-P alloy improved the oxidation resistance in the temperature range of 673 to 973K. After oxidation tests, XPS depth profiles revealed the cerium concentration maximum in the oxide scale. The good oxidation resistance of cerium-treated Ni-P was attributed to the low ionic mobility of nickel ion in the cerium-rich oxide layer.