Abstract
The discolouration over time of titanium used for roofs and walls has been studied and the difference in discolouration resistance between pickled titanium and vacuum annealed titanium has been investigated using weathering tests. In addition, the discolouration mechanism has been investigated via surface analysis of the discoloured titanium, via electrochemical analysis, and via an accelerated discolouration test. Moreover, the low temperature oxidation of titanium has been investigated as a means to achieve improved discolouration resistance. The discolouration resistance of vacuum annealed titanium is inferior to that of pickled titanium. The mechanism of discolouration involves the following steps: first, slight corrosion of titanium occurs in the acid water film formed from acid rain or by the condensation of moisture in the air; second, titanium ions precipitate as titanium oxide on the titanium surface; third, growth of surface film of titanium oxide occurs. Oxidation at low temperature is effective in inhibiting the discolouration.
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