Effect of Zinc Sulfate on the Testing of Chromate Conversion Film on the Surface of Galvanized Steel Sheets

Contents of Cr(Ⅵ) in the chromate conversion film on the surface of galvanized steel sheets were determined by ICP-AES and spectrophotometry.It was found that the presence of zinc sulfate showed significant effect on the values of content of chromium determined,which were inversely proportional to the amounts of zinc sulfate present.It was found that linear relationship between the values of Yt/s and X (the amounts of zinc sulfate present) was found as shown by the linear regression equation: Yt/s=98.809 88=0.233 42 X where Yt/s are the ratio of values of Cr(Ⅵ) found to be the respective values of standard ZnSO4 (count with Zn2+) solution added.As proved by experimental tests,the interference of ZnSO4 on the determination of Cr(Ⅵ) was effectively eliminated by removing the Zn2+ ion by precipitation with sodium carbonate.