Microstructure and Mechanical Properties of 2024-T3 and 7075-T6 Aluminum Alloys and Austenitic Stainless Steel 304 After Being Exposed to Hydrogen Peroxide
ProQuest, 2008 - 191 pages
The effect of hydrogen peroxide used as a decontaminant agent on selected aircraft metallic materials has been investigated. The work is divided into three sections; bacterial attachment behavior onto an austenitic stainless steel 304 surface; effect of decontamination process on the microstructure and mechanical properties of aircraft metallic structural materials of two aluminum alloys, i.e. 2024-T3 and 7075-T6, and an austenitic stainless steel 304 as used in galley and lavatory surfaces; and copper dissolution rate into hydrogen peroxide. With respect to bacterial attachment, the results show that surface roughness plays a role in the attachment of bacteria onto metallic surfaces at certain extent. However, when the contact angle of the liquid on a surface increased to a certain degree, detachment of bacteria on that surface became more difficult. In its relation to the decontamination process, the results show that a corrosion site, especially on the austenitic stainless steel 304 weld and its surrounding HAZ area, needs more attention because it could become a source or a harborage of bio-contaminant agent after either incidental or intentional bio-contaminant delivery. On the effect of the decontamination process on the microstructure and mechanical properties of aircraft metallic structural materials, the results show that microstructural effects are both relatively small in magnitude and confined to a region immediately adjacent to the exposed surface. No systematic effect is found on the tensile properties of the three alloys under the conditions examined. The results of this investigation are promising with respect to the application of vapor phase hydrogen peroxide as a decontaminant agent to civilian aircraft, in that even under the most severe circumstances that could occur; only very limited damage was observed. The results from the dissolution of copper by concentrated liquid hydrogen peroxide showed that the rate of copper dissolution increased for the first 15 minutes of the reaction time with an activation energy of 19 kJ/mol, and then the fraction of copper dissolved became constant. This constant dissolution was expected to be due to the formation of copper hydroxide, which was observed to precipitate after the solution settled for some time. However, because the final consumption of hydrogen peroxide was not controlled, the exact reason for this constant dissolution cannot be determined at this time. The value of activation energy is within the range of activation energy found in the literature for other dissolution process. The low activation energy for dissolution of pure copper correlates with the observation of dissolution of copper from intermetallic particles in the aluminum alloys.
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SUGGESTIONS FOR FUTURE WORK 157
OBJECTIVES OF THE RE SEARCH
RESULTS AND DISCUSION
2024-T3 aluminum alloy 7075-T6 aluminum alloy activation energy aircraft metallic structural aircraft structural materials airliner and/or as-polished as-received ASTM International Auburn University austenitic stainless steel Bacillus anthracis bacterial attachment basically bio-contaminant chemical compositions chlorine dioxide chromium composite materials concentration contact angle copper dissolution Coupon series decontaminant agent decontamination process decontamination technology different surface diffusion dip testing dislocation dissolved effect of decontamination electron images Equation exposure and dip fatigue fraction of copper hardening higher wettability hydrogen peroxide vapor intergranular corrosions intermetallic intermetallic particles investigators liquid hydrogen peroxide magnesium major alloying elements materials compatibility McMaster-Carr mechanical properties metallic materials metallic structural materials monocytogenes needed number of bacteria oxide film phase of hydrogen pitting corrosion polishing precipitates precipitation hardening reaction run VHP samples silicon stainless steel 304 standard deviations strength surface area surface finish surface roughness temperature tensile testing vapor phase Vernon Hills VHP exposure weight change weld zinc