Rapid Oxidation of Adsorbed Organic Impurities on Stainless Steel by Treatment with Diluted Peroxynitric Acid

TL;DR

A new method using diluted peroxynitric acid rapidly removes organic impurities from stainless steel while preserving its protective oxide layer.

Contribution

An innovative, eco-friendly method for rapid stainless steel surface cleaning using peroxynitric acid is introduced.

Findings

PNA treatment reduces organic impurities on stainless steel surfaces within a minute.

PNA selectively removes iron oxide while preserving the chromium oxide protective layer.

The method is faster and more environmentally friendly than traditional cleaning techniques.

Abstract

Stainless steel forms a native film of mixed metal oxides, and organic impurities are likely to adsorb on the surface upon exposure to ambient conditions. For many applications, oxides and impurities should be removed, and several techniques have been used for decades. An innovative method is presented in this paper. The organic impurities were oxidized using a water solution of 1 M peroxynitric acid (PNA). Stainless steel samples were immersed in the solution, and the oxidation of organic impurities was evaluated by the ultra-thin depth profiling using secondary ion mass spectrometry (SIMS). A minute of treatment with PNA caused oxidation of organic impurities and a decrease in the SIMS CN– signal over an order of magnitude. Prolonged treatment caused the selective removal of the native iron oxide film, leaving a protective film of chromium oxide. Removal of the iron oxide film was also observed when stainless steel was treated with 1 M HNO3. The PNA method is useful for routine cleaning of stainless steel to remove the organic contaminants from the surface and keep the passive chromium oxide film intact. It is ecologically friendly and enables rapid decomposition of the traces of organic impurities likely to be adsorbed on the metallic surfaces.

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