| Abstract |
| The mechanism of electrolytic pickling in a neutral sodium sulfate solution as well as the correlation between oxide scale and the pickling has not been clearly understood in spite of the vast use of the pickling method. Hence, AES, thin film x-ray diffraction (TFXD) and calculation of phase equilibria for scale analysis, and the electrochemical tests such as galvanostatic test and potentiodynamic test for electrochemical analysis were employed finally to propose the mechanisms of pickling two types of stainless steels(type 430 and type 304).The electrolytic pickling of the stainless steels in a neutral sulfate solution begins with the preferential dissolution of the oxide consisting chromium and manganese placed in the outer layer of the scale. However, the differences in the characteristics of oxide scale between type 430 and type 304 such as thickness and constitution make next pickling step depend on type of stainless steel. Mter the preferential dissolution, the residual scale on type 430 being as thin as 30 nm and mainly consisting of iron oxide is proposed to separate by accumulation of vacancy at the interface between the scale and the matrix, according to point defect model and surface charge approach. On the other hand, the residual scale on type 304 being as thin as 600 nm and consisting of iron and chromium oxide and silicon oxide is proposed to be separate by the dissolution of chromium metal and iron metal at the matrix/scale interface. |
|
|
| Key Words |
| Oxide scale, Thin film X-ray diffraction, Selective oxidation, Galvanostatic test, Auger electron spectroscopy, Surface charge approach, Point defect model |
|
|
 |
|
