Cleanability of stainless steel surfaces as influenced by heat treatment.

The cleanability of heat-treated 316L stainless steel particles treated at various temperatures of 100 to 500 degrees C was studied in a plug-flow column fed by a 0.1M NaOH solution. Bovine Serum albumin (BSA) was used as the model fouling agent. Heat treatment resulted in the enrichment of iron in passive films on stainless steel particles depending on temperature. The degree of surface hydroxylation and the apparent surface charge density (sigma(app)) of stainless steel particles decreased markedly with increasing heating temperatures. The saturation amounts of BSA adsorbed (gamma(sat)) were larger on the particles heated at higher temperatures. No correlation was observed between the gamma(sat) and sigma(app) values. With increasing heating temperatures, the rate of BSA desorption from stainless steel particles decreased gradually in the initial and later stages of cleaning, resulting in larger amounts of BSA remaining on the particles at the end of 120-min of cleaning. The susceptibility to BSA adsorption and the cleanability were found to be correlated with the iron content of the passive films on stainless steel particles. It could be suggested that the decrease in the cleanability was probably due to the formation of iron-enriched passive films with lower degrees of surface hydroxylation of stainless steel particles due to heat treatment.