A quantitative assessment of the influence of voltage on the formation of oxide layers on the surface of titanium by anodization.

Abstract

Statement of problem: Restorations based on titanium and its alloys form weak connections with veneering ceramics. It is unclear if anodizing the titanium surface with different voltages leads to improved bonding.

Purpose: The purpose of this in vitro study was to obtain an oxide layer of an appropriate thickness (0.5 to 0.8 µm) and determine its bond strength.

Material and methods: Titanium specimens were anodized in a mixture of 1 M H₂SO₄ and H₃PO₄ at 120 V, 160 V, and 200 V. The surface was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface roughness testing, and contact angle to determine the surface free energy (SFE). The obtained results contact angle, and SPE were analyzed using the Friedman test, Dunn-Bonferroni post hoc test, and the Page trend test (α=.05). Statistically significant test value was P<.05 and highly significant P<.01. The adhesion of anodized layers to the surface of titanium specimens was determined according to the Verein Deutscher Ingenieure (VDI) 3198 norm (destructive quality test for coated compounds, Rockwell hardness).

Results: In the diffraction diagram, the oxide layer has an anatase crystalline structure with thicknesses of 0.61 µm for 120 V, 1.25 µm for 160 V, and 2.30 µm for 200 V. The secondary electron (SE) and backscattered electron (BSE) images provide an indication of the topography and geometric structure pores, as well as their size and shape. Anodic coatings obtained with higher voltages demonstrate higher roughness profiles. The highest SFE value was obtained for 160 V anodization voltage, the smallest for 120 V. No significant differences in contact angles were observed (P>.05) between different voltages or between different electrolytes. No significant differences between voltages were observed for the dispersive component values (P>.05); however, significant differences were observed for polar components (P<.05). Higher values were noted for 160 V than for 120 V. All indentations were within the range indicated by models HF1 and HF2 (acceptable adhesion), which differ only in the density of the fractures.

Conclusions: The voltage applied during anodic oxidation using a mixture of 1 M H₂SO₄ and H₃PO₄, influenced the thickness and structure of the obtained layers. The oxide obtained had a thickness of 0.6 to 2.3 µm and an anatase crystal structure.