Effect of Thermal Oxidation on Corrosion Resistance of Commercially Pure Titanium in Acid Medium

This article addresses the characteristics of commercially pure titanium (CP-Ti) subjected to thermal oxidation in air at 650?°C for 48?h and its corrosion behavior in 0.1 and 4?M HCl and HNO₃ mediums. Thermal oxidation of CP-Ti leads to the formation of thick oxide scales (~20???m) throughout its surface without any spallation. The oxide layer consists of rutile- and oxygen-diffused titanium as predominant phases with a hardness of 679?±?43?HV_1.96. Electrochemical studies reveal that the thermally oxidized CP-Ti offers a better corrosion resistance than its untreated counterpart in both HCl and HNO₃ mediums. The uniform surface coverage and compactness of the oxide layer provide an effective barrier toward corrosion of CP-Ti. The study concludes that thermal oxidation is an effective approach to engineer the surface of CP-Ti so as to increase its corrosion resistance in HCl and HNO₃ mediums.     

Effect of thermal oxidation on the corrosion resistance of Ti6Al4V alloy in hydrochloric and nitric acid medium

The characteristics of Ti6Al4V alloy subjected to thermal oxidation in air atmosphere at 650 °C for 48 h and its corrosion behavior in 0.1 and 4 M HCl and HNO₃ medium are addressed. When compared to the naturally formed oxide layer (～4–6 nm), a relatively thicker oxide scale (～7 µm) is formed throughout the surface of Ti6Al4V alloy after thermal oxidation. XRD pattern disclose the formation of the rutile and oxygen‐diffused titanium as the predominant phases. A significant improvement in the hardness (from 324 ± 8 to 985 ± 40 HV_0.25) is observed due to the formation of hard oxide layer on the surface followed by the presence of an oxygen diffusion zone beneath it. Electrochemical studies reveal that the thermally oxidized Ti6Al4V alloy offers a better corrosion resistance than its untreated counterpart in both HCl and HNO₃ medium. The uniform surface coverage, compactness and thickness of the oxide layer provide an effective barrier towards corrosion of the Ti6Al4V alloy. The study concludes that thermal oxidation is an effective approach to engineer the surface of Ti6Al4V alloy to increase its corrosion resistance in HCl and HNO₃ medium.     

Electrodeposition of hydroxyapatite coating on magnesium for biomedical applications

The effectiveness of hydroxyapatite (HA) coating prepared by electrodeposition technique in improving the corrosion resistance of commercially pure magnesium (CP-Mg) in simulated body fluid (SBF) is addressed. The coating formed in as-deposited condition is identified as dicalcium phosphate dehydrate (DCPD) (Brushite), which is converted to HA after immersion in 1?M NaOH at 80°C for 2?h. The XRD patterns and FTIR spectra confirm the formation of DCPD and HA. During electrodeposition, the H₂PO₄ ^? ion is reduced and the reaction between Ca²⁺ ions and the reduced phosphate ions leads to the formation of DCPD, which is converted to HA following treatment in NaOH. The deposition of HA coating enables a threefold increase in the corrosion resistance of CP-Mg. The ability to offer a significant improvement in corrosion resistance coupled with the bioactive characteristics of the HA coating establish that electrodeposition of HA is a viable approach to engineer the surface of CP-Mg in the development of Mg-based degradable implant materials.     

Corrosion behavior of commercially pure Mg and ZM21 Mg alloy in Ringer’s solution – Long term evaluation by EIS

Evaluation of the corrosion behavior of commercially pure magnesium (CP-Mg) and ZM21 Mg alloy immersed in Ringer’s solution for 92 h by electrochemical impedance spectroscopy (EIS) is addressed. The formation of a compact layer of well-developed rod-like aragonitic CaCO₃ crystals and its subsequent thickening with increase in immersion time offers a higher corrosion protective ability for ZM21 Mg alloy. The formation of a mud-crack pattern and a large number of clusters of needle-like crystals offers a relatively lower corrosion resistance for CP-Mg. The study suggests that ZM21 Mg alloy is a promising candidate material for the development of degradable implants.     

Corrosion resistant Ti alloy for sulphuric acid medium: Suitability of Ti–Mo alloys

The corrosion resistance of Ti–Mo (5, 10, 15 and 25 wt% molybdenum) alloys in 5–25% sulphuric acid was evaluated. The Ti–Mo alloys offered a better corrosion resistance than commercially pure titanium (CP‐Ti). The higher impedance values, higher phase angle maximum, ability to reach the phase angle maximum at relatively lower frequencies, ability to exhibit a constant phase angle maximum over a wider range of frequencies, higher phase angle values at 0.01 Hz, have confirmed the formation of a stable passive oxide film on Ti–Mo alloys. The study recommends the use of Ti–Mo alloys, particularly Ti–25Mo alloy, as a suitable material of construction for sulphuric acid medium.