Formation of Titania/Hydroxyapatite Composite Films by Pulse Electrolysis

The aim of this study was to examine the formation of titania (TiO 2 )/hydroxyapatite (HAp) composite films on a titanium substrate using anodic-cathodic pulse electrolysis. The TiO 2 /HAp composites were coated on commercially pure titanium plates (surface area: 1.0 cm 2 ) using pulse electrolysis in an autoclave in an aqueous solution that consisted of 0.3 mM Ca(H 2 PO 4 ) 2 and 0.7 mM CaCl 2 and pH ¼ 5:5 at 120 C. The pulse potentials were applied at þ8:7 V vs. Ag/AgCl sat. KCl as anodic potential and À9:3 V as cathodic. The total electrolysis time was 1800 s. We examined the effects of the electrolysis cycle (60 $ 600 s) and duty ratio on such properties of the coatings as the surface morphology, the amount of precipitated HAp, and the size of the HAp crystals. Prior to the pulse electrolysis, cathodic and anodic electrolysis experiments were also conducted. With pulse electrolysis, we could obtain TiO 2 /HAp composite films with fine HAp particles dispersed uniformly on a thin TiO 2 coating

Osteoconductivity and Hydrophilicity of TiO2 Coatings on Ti Substrates Prepared by Different Oxidizing Processes

Various techniques for forming TiO2 coatings on Ti have been investigated for the improvement of the osteoconductivity of Ti implants. However, it is not clear how the oxidizing process affects this osteoconductivity. In this study, TiO2 coatings were prepared using the following three processes: anodizing in 0.1 M H3PO4 or 0.1 M NaOH aqueous solution; thermal oxidation at 673 K for 2 h in air; and a two-step process of anodizing followed by thermal oxidation. The oxide coatings were evaluated using SEM, XRD, and XPS. The water contact angle on the TiO2 coatings was measured as a surface property. The osteoconductivity of these samples was evaluated by measuring the contact ratio of formed hard tissue on the implanted samples (defined as the RB-I value) after 14 d implantation in rats' tibias. Anatase was formed by anodizing and rutile by thermal oxidation, but the difference in the TiO2 crystal structure did not influence the osteoconductivity. Anodized TiO2 coatings were hydrophilic, but thermally oxidized TiO2 coatings were less hydrophilic than anodized TiO2 coatings because they lacked in surface OH groups. The TiO2 coating process using anodizing without thermal oxidation gave effective improvement of the osteoconductivity of Ti samples

Formation of Anodic Films on Mg-Al Alloys in NaOH solutions at Constant Potentials

The formation behavior and corrosion characteristics of anodic oxide films on pure magnesium and on Mg-Al alloys were investigated, focusing on the effects of anodization potential, aluminum content, temperature, and NaOH concentration. Pure magnesium and Mg-Al alloys were anodized for 600 s at 3, 10, 40, and 80 V in NaOH solutions. It was found that the anodic film formed at 3 V had the best corrosion resistance, regardless of temperature, NaOH concentration, or aluminum content. An especially high current density was observed at applied potentials of 3-7 V on anodization in alkaline NaOH solutions. XRD analysis detected Mg(OH) 2 and MgO peaks in the films on the anodized specimens. The relative intensity of the Mg(OH) 2 XRD peaks decreased with increasing applied potential, while those of MgO increased. Mg(OH) 2 was generated by an active dissolution reaction with high current density at the specimen surface. Generation of Mg(OH) 2 increased with increasing temperature, while that of MgO increased with NaOH concentration. Moreover, the current density after anodization for 600 s at a constant potential decreased with increasing aluminum content in Mg-Al alloys