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High temperature and high pressure corrosion of titanium in hydrometallurgical applications

University of British Columbia

The corrosion characteristics of titanium (ASTM Grade 2) in copper pressure leaching environments are determined from room temperature and pressure up to high temperatures and pressures (230 °C, 430 psi). Anodic oxidation and controlled chemical oxidation methods are used to improve the corrosion resistance of Ti. Electrochemical and mass loss measurements are performed to evaluate the corrosion resistance of pre-oxidized titanium, compared to that of titanium with no prior oxidation, to generate a best practices guide for the hydrometallurgical industry. The results at low temperature showed that H₂SO₄ solution is very corrosive for Ti with a freshly polished surface. The corrosion rates (CRs) of Ti are obtained using mass loss and electrochemical measurements in H₂SO₄ with Cl-, Cu²⁺ and Fe³⁺ additions up to 175 °C. It is found that the CRs of Ti are unaffected by the presence of Cl− ions in H₂SO₄ solutions. CRs obtained from mass loss and electrochemical measurements confirm that Cu²⁺ and Fe³⁺ ions are good corrosion inhibitors for Ti. Iso-corrosion diagrams, with 0.1, 0.5 and 1 mm yr−1 lines for Ti in 3-50 wt.% H₂SO₄ solutions with Cu²⁺ and Fe³⁺ additions from room temperature to 175 °C are constructed from immersion test data. The effects of temperature (100-230 °C) and SO₄²− concentration (0-0.5 mol L−¹) on the pitting corrosion of Ti are studied in neutral Cl− containing solutions using cyclic potentiodynamic polarization and linear-sweep thermammetry measurements. A metastable pitting temperature threshold (MPTT) is defined for Ti as a function of sulfate to chloride mole ratio using linear-sweep thermammetry measurements. iii Anodic oxide films (AOFs) are potentiostatically formed on Ti in 0.5 M H₂SO₄ solutions at various anodizing voltages (up to 80 V) at 25 °C. A new method is developed to fabricate chemically oxidized films (COFs) with high corrosion resistance by controlled chemical oxidation with H₂O₂ solutions at 90 °C. The corrosion behavior of the as grown AOFs and COFs is investigated in copper sulfide leaching solutions. It is confirmed that chemical oxidation with 2 M H₂O₂/0.1 M HCl solution leads to the best improvement of the corrosion resistance of Ti.

Text

2015-03-11

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52353

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/