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Corrosion of Titanium and its alloys at high temperatures and pressures Vaughan, James W.

Abstract

Selected Ti alloys (ASTM Grades 1, 12, and 18) were tested in sulfate media, simulating typical Ni laterite leach liquor. The investigation involved a thermodynamic analysis of the Ti-FbO, T1-S-H2O, and T i - C l - H20 systems. Long-term immersion (ASTM G31), potentiodynamic polarization (ASTM G5), cyclic polarization, and potentiostatic tests were administered to investigate and quantify the corrosion. XRD, SEM, XPS, and AES were used to characterize the uncorroded and corroded surfaces and the nature of the corrosion products. Long-term immersion tests provided real time corrosion rates. Two week moderate temperature immersion tests were implemented to compliment the long-term results. Ti corrosion increased with more acid and higher temperatures. The addition of chlorides led to higher corrosion rates while the addition of Fe, Cu and the presence of Ti ions inhibited the corrosion. Polarization experiments were performed at intermediate temperatures (50-70 °C, 323-343 K) using a water bath and at elevated temperatures (150-250 °C, 423-523 K) using a 2L autoclave. Results from the polarization tests complement the immersion results. Corrosion rates calculated from the polarization tests exaggerated the rate of Ti-18 and underestimated the rate of Ti-12. The Ti-18 accelerated corrosion rates were inflated because there was insufficient time for Pd to become enriched on the surface. Characterization of the samples exposed the different corrosion behaviour of the alloys and provided chemical and depth profile information regarding the thermally induced oxides at simulated HPAL conditions.

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