The corrosion behavior of Ti3SiC2 in common acids and dilute NaOH

Hot isostatically processed bulk, fine (3-5 mum) grained samples of Ti3SiC2 were immersed in concentrated and dilute hydrochloric, HCl, sulphuric, H2SO4, nitric, HNO3, dilute hydrofluoric, 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 mum/yr). In dilute HF and concentrated HNO3 the corrosion rates were, respectively, approximate to5 mum/yr and 13 mum/yr respectively. In contrast to Ti metal, the weight losses of Ti3SiC2 in dilute HNO3 were higher (approximate to250-320 mum/ 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/cm(2) for two days resulted in the formation of a 5 Pm thick SiO2-based layer on the surface. The presence of such a layer would explain the excellent corrosion resistance of Ti3SiC2 in these acids. (C) 2003 Elsevier Science Ltd. All rights reserved.