Corrosion of titanium and its alloys in sulfuric acid in the presence of chlorides

Titanium alloys (ASTM Grades 1, 2, 7, 12, and 18) are employed as the liner and internal components of autoclaves during the high-pressure acid leaching (HPAL) of nickel laterite ores. This paper summarizes the corrosion behavior of these alloys in sulfuric acid and the effect of the addition of chlorides (NaCl). New thermodynamic E _h-pH diagrams for the Ti-H ₂O, Ti-SO ₄-H ₂O, and Ti-Cl-H ₂O systems are presented. Micrographs are also presented and the corrosion morphology is discussed. Long-term immersion tests were carried out to determine corrosion rates. Electrochemical techniques were used to provide insight into the corrosion chemistry. The shortcomings of accelerated corrosion testing of Ti alloys are addressed. Pd enrichment on the surface of Ti-18 was confirmed by a combination of open-circuit potential measurements and chronoamperometric measurements.