Corrosion Behavior Of Pure Titanium Research Articles

Nondestructive Evaluation of Corrosion Progression on Titanium and Its Alloy Surface by Wetting Method

The corrosion behavior of pure titanium and Ti-6Al-4V alloy in NaF solutions and the wettability of pure water on the specimens after corrosion were investigated. The relation between the change of surface chemistry and roughness of specimens after corrosion and the wettability of pure water droplets on such surfaces were discussed.

純チタンおよびチタン合金の NaF 水溶液浸漬による水濡れ性の変化

Titanium is used as an implant material for dentures. However, the corrosion caused by fluoride and the low wettability of titanium by saliva are still problems. In this study, the corrosion behavior of pure titanium and its alloy was investigated in aqueous NaF solutions, and the macro-wettability change of pure water on these specimen surface after corrosion is discussed. The passive current density of pure titanium and its alloy tended to increase with increasing NaF concentration. The potential distribution nearby pure titanium surface slightly changed after immediate immersion in the solution, then the value soon became relatively stable. The contact angle ratio ψ, which is the ratio of the contact angle before immersion θ0 to that after immersion θi, decreased with increasing immersion time. Higher surface wettability was observed after more active corrosion, indicating that the progression of corrosion significantly influenced the wettability of these surfaces by pure water. The surface roughness Ra was larger after immersion in 2.0% NaF solution than in 0.1% solution, which might also have influenced its wettability by pure water.

Corrosion Behavior of Pure Titanium and Titanium Alloys in Various Concentrations of Acidulated Phosphate Fluoride (APF) Solutions

The corrosion behaviors of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys, and an experimentally produced Ti-0.5Pt alloy in 0.05% to 2.0% concentrations of Acidulated Phosphate Fluoride (APF) solutions (corresponding to 226 to 9,050 ppm fluoride at pH 3.5 or 3.6) were examined. While the corrosion of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys might occur easily even in a diluted 0.05% APF solution, dissolution of Ti from the Ti-0.5Pt alloy was observed only in test solutions with APF concentration exceeding 0.2%. When Ti-6Al-7Nb and Ti-6Al-4V alloys were immersed in 2.0% APF solution, their surfaces were entirely covered by compact corrosion products of Na3TiF6 due to severe corrosion. As a result, Ti dissolution was prevented and the amount of Ti dissolved decreased. However, since Ti was covered by porous, large-sized corrosion products of Na3TiF6 and that Ti-0.5Pt alloy was not covered with any corrosion product, the amount of Ti dissolved increased in the 2.0% APF solution.

Effects of fluoride and dissolved oxygen concentrations on the corrosion behavior of pure titanium and titanium alloys.

The effects of dissolved-oxygen concentration and fluoride concentration on the corrosion behaviors of commercial pure titanium, Ti-6Al-4V and Ti-6Al-7Nb alloys and experimentally produced Ti-0.2Pd and Ti-0.5Pt alloys were examined using the corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. A decrease in the dissolved-oxygen concentration tended to reduce the corrosion resistance of Ti and Ti alloys. If there was no fluoride, however, corrosion did not occur. Under low dissolved-oxygen conditions, the corrosion of pure Ti and Ti-6Al-4V and Ti-6Al-7Nb alloys might easily take place in the presence of small amounts of fluoride. They were corroded by half or less of the fluoride concentrations in commercial dentifrices. The Ti-0.2Pd and Ti-0.5Pt alloys did not corrode more, even under the low dissolved-oxygen conditions and a fluoride-containing environment, than pure Ti and Ti-6Al-4V and Ti-6Al-7Nb alloys. These alloys are expected to be useful as new Ti alloys with high corrosion resistance in dental use.

Corrosion Behavior of Pure Titanium and Titanium Alloys in Fluoride-containing Solutions.

The effects of fluoride concentrations and pH on the corrosion behavior of pure titanium, Ti-6Al-4V, Ti-6Al-7Nb alloys and a new Ti alloy adding palladium, which is expected to promote a repassivation of Ti were examined by anodic polarization and corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. The surface of the specimen was analyzed by X-ray photoelectron spectroscopy before and after the measurement. Pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys were easily corroded even in a low fluoride concentration in an acidic environment. The corrosion resistance of Ti-0.2Pd alloy was greater than those of pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys in the wide range of pH and fluoride concentrations. The high corrosion resistance of Ti-0.2Pd alloy was caused by the surface enrichment of Pd promoting a repassivation of Ti. The Ti-0.2Pd alloy is expected to be useful as a new Ti alloy with high corrosion resistance in dental use.