Abstract
Titanium has been used as a lining material for ductwork and chimneys in power and flue gas desulphurisation plants. In these environments the metal will be exposed to both condensed acids and pulverised fuel ash. Experience on a pilot plant indicated that the resistance of titanium to corrosion by condensed acids was significantly enhanced by the presence of ash. The corrosion of titanium in aerated hydrochloric acid solutions at 50°C containing varying amounts of ash was investigated by potentiodynamic scans and electrochemical impedance spectroscopy. In the absence of ash the titanium corroded freely, an active peak was observed in the potentiodynamic scans and semi-circles in Nyquist plots of the impedance spectra. Modelling of the impedance spectra gave corrosion rates between 0.8 and 1.0 mm y −1. With additions of ash to the solution of greater than 1%, the corrosion rate was reduced by two orders of magnitude. It was found that a minium level of ash was required to inhibit corrosion. An unusual potential cycling effect was observed in the presence of low levels of ash. A mechanism involving anodic inhibition of the titanium by metal ions leached from the ash is proposed.
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