2008 Volume 13 Issue 2 Pages 57-63
Type 316L stainless steel particles were pseudo-sensitized by being heated at 700°C for 100 h under a reduced pressure of 1.3×10-3 Pa. Pseudo-sensitization treatment resulted in the formation of chromium-rich precipitates at the outermost surfaces of the stainless steel particles. The curve for the apparent surface charge density (σapp) of the pseudo-sensitized particles showed a more basic character compared with the curve for the σapp of the original particles. There was no significant difference between the amounts of bovine serum albumin (BSA) adsorbed on the original and the pseudo-sensitized particles. On the contrary, the efficiency of BSA removal from the pseudo-sensitized particles during batch-wise and continuous cleaning operations with 0.1M NaOH solution were significantly smaller than that for the original particles. It was indicated that the extremely lowered cleanability of the pseudosensitized particles was caused by a marked increase in the positive a σapp values after the pseudo-sensitization. Solution treatment of the pseudo-sensitized particles at 1, 050°C for 1 h under a reduced pressure of 1.3×10-3 Pa could put again the chromium precipitates into a solid solution, thereby returning the surface chemical composition and the σapp nearly to the original states. In addition, the solution-treated particles showed a good cleanability comparable to that of the original particles. These results demonstrated that solution treatment could improve the lowered cleanability of the pseudo-sensitized stainless steel surfaces.
