Abstract
Surface treatment of stainless steel by ozonized air was investigated over the range of 0.01 to 0.2% (v/v) ozone (O3), using nonporous stainless steel particles. Ozonized air contained nitrogen oxides (NOx) at a NOx/O3 ratio of approximately 0.04. When stainless steel particles were treated with ozonized air, nitric acid was formed on their surfaces depending on the O3 concentration. As a result of ozonized air treatment, the adsorption affinity of water vapor for stainless steel particles decreased and the absolute values of the apparent surface charge density (σapp) of stainless steel particles decreased over the pH range of 3 to 10, resulting in the lower adsorption affinity of bovine serum albumin (BSA). The σapp curves of stainless steel particles treated with ozonized air at 0.15 to 0.2% O3 were very similar to the curves of the particles treated with 10 and 30% HNO3. These results indicated that nitric acid formed during ozonized air treatment brought about the modification of the surface charge of stainless steel particles. Ozonized air pretreatment of stainless steel particles fouled with BSA or calcium hydrogenphosphate markedly facilitated their removal during subsequent alkali cleaning or rinsing through O3 oxidation or descaling with nitric acid.
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