Corrosion of alumina/titanium diboride composites in neutral and acidic chloride solutions

Abstract

This research concerns the study of the corrosion behaviour of monolithic titanium diboride and the composites 50%Al2O3/50%TiB2 (50/50) and 70%Al2O3/30%TiB2 (70/30) in 3.5% NaCl solutions, at pH 7 and 3 (adjusted by HCl additions). The test temperature is 45 ± 1°C. Both electrochemical and chemical techniques are applied. Scanning electron microscope (SEM) observations are also used to investigate the corrosion attack morphology. Polarization curve recording evidences that at short immersion times both composites exhibit a passive behaviour. The stability of these passive conditions decreases at increasing volume fractions of titanium diboride in the material and is minimum in the monolithic material. The analyses of the aggressive solutions during 30 days of immersion of 50/50 under free corrosion conditions are in agreement with the hypothesis that at both pH values passivity is due to the presence of a titanium‐containing insoluble surface film, probably constituted by hydrated titanium oxide. SEM observations evidence the presence of a third phase in the composites, beside titanium diboride and alumina, that is constituted by an aluminum borate, formed during sinterization. This phase undergoes a chemical attack during exposures to the aggressive solutions, under free corrosion conditions. The relative importance of chemical towards electrochemical corrosion, as assessed by coupling potentiostatic tests and chemical analyses, increases when passive conditions are maintained.

Electrochemical and DFT studies of laser-alloyed TiB2/TiC/Al coatings on aluminium alloy

“…4a) indicates a feature of Warburg impedance. This effect can be attributed to a diffusion control of ions from the electrode to the bulk solution [15]. Bode plots in Fig.…”

“…The corrosion resistance mainly depends on the general coating integrity and quality based on the aspects such as but not limited to adhesion, porosity, roughness, coating passive film, kinetics of the passive film formation and its resistance. When titanium diboride is immersed in NaCl solution at room temperature, it behaves like a passive metal due to the formation of a surface oxide film (hydrated titanium dioxide), whose protectivity decreases with the temperature and completely vanishes at 65 °C [15], [38]. In salt rich ocean water, a white film of tetravalent oxide titanium TiO2-H2O is formed, which hinders the material dissolution [13], [38].…”

“…However, there are only few reports concerning the corrosion behaviour of Ti3AlC2 [14] and Al2O3/TiB2 [15]. Covino et al [16] reported significantly higher corrosion resistance of Ti + TiC composites in reducing mineral acid solution compared to the Ti + TiB2 composites.…”

Corrosion behaviour of hafnium diboride in aqueous solutions

“…The electrodes were prepared according to the procedures described elsewhere [19], with a surface area of 1 cm 2 . After polishing down to 1 m by diamond paste, degreasing by acetone and drying, they were exposed to the following aqueous solutions at 45 ± 1 • C, under natural aeration conditions: For the electrochemical experiments a three-electrode cell was used, equipped with a Pt auxiliary electrode and a saturated calomel reference electrode (SCE).…”

Effect of sintering temperatures on the properties of in-situ copper-niobium-titanium di-boride composites

“…The addition is expected to enhance the mechanical properties as well as the corrosion resistance of the composites. There are research works that have shown that titanium-diboride behaves like a passive metal in acid and salt environments, due to the formation of a surface oxide film, whose protective power, decreases with temperature [16,17].…”