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Samples of Fel7Cr, Fe15Cr4Mo, and a commercial 304 stainless steel were passivated in 0.1M sulfuric acid solution at constant potentials. The alloying effects of Mo and Ni on the corrosion property were studied in relation to their potentiodynamic polarization curves. A revolutionary new method of analysis in analytical chemistry, the inductively coupled plasma-source mass spectrometry (ICP-MS), was used to analyze the corrosion products in passivating solutions so as to explore the ion selectivity during dissolution and film formation processes. The selectivity factor S was defined and used to characterize the selective dissolution of Fe and/or Ni from the steels. The dissolution behavior of the Ni bearing steel changes with polarization time, from the initial selective dissolution of Ni to the final selective dissolution of Fe. Surface analyses of the passive films by x-ray photoelectron spectroscopy (XPS) were also conducted in conjunction with ion beam sputtering to obtain depth distributions of alloying components. The selective enrichment of ions in the passive films were characterized by the enrichment factorf. A model based on the selective ionization was proposed t0 explain the enrichment of Ni in the metallic phase underneath the passive film. The dissolution kinetics as well as the film formation kinetics are discussed in terms of the charge balance during 69h polarization. Results from surface analyses of passive films by XPS are complementary with those from solution analyses by ICP-MS.

A study has been made of the surfaces of Immaculate 5, En58AM and Nimonic 105 materials by X-ray photoelectron spectroscopy, (a) after cleaning using simple washing methods and (b) after contamination in the laboratory environment for periods of up to 156 days, using filtered and unfiltered laboratory air. All surfaces are covered by a thin oxide and this is further covered by a thin layer of carbonaceous contamination of atmospheric origin. Some of the contamination is removed by surfactants contained in various proprietary cleaners or by boiling water (used to mimic steam-cleaning methods). The first exposure to boiling water increases the chromium content of the oxide. Exposure to the environment causes the carbonaceous contamination thickness to grow at a rate described by either simple diffusion theory or by a "logarithmic" theory such that the increase in mass of a kilogram artefact is around 15 μg/year after five years. If the laboratory air is filtered and moves at a low rate the carbonaceous contamination growth is low, but if the filter is removed and the flow rate raised, the carbonaceous contamination rate increases. It is recommended that masses made from these materials are initially subject to a wash in boiling water for 5 minutes to develop a stable oxide thickness, stored in static filtered air to reduce the carbonaceous contamination and are cleaned using a dilute aqueous solution of gentle surfactant cleaners or possibly by a steam-cleaning method. Some further work confirming this by weighing is required.