The corrosion behaviour of Ti3SiC2 in common acids and dilute NaOH

Abstract

Hot isostatically processed bulk, fine (3-5 lm) grained samples of Ti3SiC2 were immersed in concentrated and dilute hydrochloric, HCl, sulphuric, H2SO4, nitric, HNO3, dilute hydro-fluoric, HF, acids and sodium hydroxide, NaOH, solutions at room temperature. Based on six-months weight changes the dissolution rates of Ti3SiC2 in concentrated and dilute HCl, H2SO4 and dilute NaOH were found to be negligible (<2 μm/yr). In dilute HF and concentrated HNO3 the corrosion rates were, ≈5 μm/yr and 13 μm/yr respectively. In contrast to Ti metal, the weight losses of Ti3SiC2 in dilute HNO3 were ≈250-320 μm/yr) and depended on concentration. Post-immersion scanning electron microscopic micrographs of samples immersed in HNO3 indicated that an oxygen rich Si-based layer forms on the surface of the samples. This implies that the Ti atoms are leached out into the HNO3 solution, leaving behind a Si-rich layer that is ultimately oxidized. Cyclic polarization and potentiostatic i-t transients in dilute HCl and H2SO4 acids, strongly suggest that a thin irreversible electrically insulating layer forms on the surface of Ti3SiC2. Exposing a sample to a constant current density of 0.6 mA/cm2 for two days resulted in the formation of a 5 μm thick SiO2-based layer on the surface. The presence of such a layer would explain the excellent corrosion resistance of Ti3SiC2 in these acids. © 2003 Elsevier Science Ltd. All rights reserved.