COMPARISON CHARACTERIZATIONS OF Cr (III) AND Cr (VI) CONVERSION COATING ON ZINC ELECTROPLATING SUBSTRATE

Tóm tắt

Some of characterizations of Cr (III) conversion coating have been compared with that of Cr (VI) conversion coating. The comparison was made on the base of conversion coating color, anticorrosion ability, and effect of drying temperature. The obtained results indicated that the color of Cr (VI) conversion coating was darker than that of Cr (III) conversion coating. However, the color of Cr (VI) conversion, more or less, depended on the drying temperature. The color of conversion coating the darkest if the drying temperature was at 50^oC. Moreover, the characterizations of Cr (VI) depended significantly on the drying temperature. The drying temperature had a significant effect on anticorrosion ability of Cr (VI) conversion coating, especially for samples dried at higher temperature than 110^oC. In contrast, the Cr (III) conversion coating showed more stable and insignificantly depended on drying temperatures. In addition, the surface of Cr (III) conversion samples was smooth, no crystalline structure. Conversion coating was layered fibrous. The Cr (III) sample had no crash while the Cr (VI) had. Hence, the obtained results indicated that Cr (III) conversion solution can creat the conversion coating which has anticorrosion ability, which can replace Cr (VI) based conversion coatings.