In this work, we study physical and mechanical properties of oxide films formed on AZ91D magnesium alloy by plasma anodization at different temperatures. It is found that the higher the electrolyte temperature, the lower is the breakdown voltage of oxide layer. This is probably because films formed at higher temperatures are thinner and denser. Moreover, electrolyte temperature plays an important role in the physical properties of the films. As the electrolyte temperature increases from 20 to 50℃, the hardness of the oxide layer increases. Friction test against steel balls indicates that wear scars become narrower for films formed at higher temperatures because the films are harder, as indicated by the Vickers hardness. The thinner and denser nature of the oxide film formed at 50°C is also advantageous for heat transfer when film is used as a heat sink. Laser flash test results show very fast heat transfer for AZ91D with plasma anodized oxide layer formed at higher temperatures.

The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from 0.9 μm to 0.1 μm and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

This study was carried out to investigate the characterization of iron oxide nanotubes (INTs) by anodization method and applied adsorption isotherms and kinetic models for phosphate adsorption. SEM analysis was conducted to examine the INTs surface formation. Further XRD and XPS analysis were performed to observe the crystal structure of INTs before and after phosphate adsorption. AFM analysis was conducted to determine of Fe foil surface before and after anodization. Phosphate stock solution for adsorption experiment was prepared by KH2PO4. The batch experiment was conducted using 20 ml phosphate stock solution and 40 cm3 of INTs in 50 ml conical tube. Adsorption isotherms were applied Langmuir and Freundlich models for adsorption equilibrium test of INTs. Pseudo first order and pseudo second order models were applied for interpretation of adsorption rate by reaction time. The determination coefficient (R2) values of Langmuir and Freundlich models were 0.9157 and 0.8876 respectively.

Electrochemical surface treatment is commonly used to form a thin, rough, and porous oxidation layer on the surface of titanium. The purpose of this study was to investigate the formation of nanotubular titanium oxide arrays during short anodization processing. The specimen used in this study was 99.9% pure cp-Ti (ASTM Grade II) in the form of a disc with diameter of 15 mm and a thickness of 1 mm. A DC power supplier was used with the anodizing apparatus, and the titanium specimen and the platinum plate (3mm×4mm×0.1mm) were connected to an anode and cathode, respectively. The progressive formation of TiO2 nanotubes was observed with FE-SEM (Field Emission Scanning Electron Microscopy). Highly ordered TiO2 nanotubes were formed at a potential of 20 V in a solution of 1M H3PO4 + 1.5 wt.% HF for 10 minutes, corresponding with steady state processing. The diameters and the closed ends of TiO2 nanotubes measured at a value of 50 cumulative percent were 100 nm and 120 nm, respectively. The TiO2 nanotubes had lengths of 500 nm. As the anodization processing reached 10 minutes, the frequency distribution for the diameters and the closed ends of the TiO2 nanotubes was gradually reduced. Short anodization processing for TiO2 nanotubes of within 10 minutes was established.

목적: 본 연구에서는 양극산화방법을 이용하여 착색된 티타늄 안경테의 산화막 두께에 따른 색상을 광 반사 스펙트럼을 통해서 규명하고자 한다. 방법: 양극산화 방법 제조 장치를 자체 제작하여 사용하였다. 연구에 사용한 티타늄 안경테원재료 조성은 EDS로 측정하였고, 구조분석은 XRD를 사용하여 X선 회절선으로부터 구하였다. 광 반사 측정은 UV-VIS-NIR spectrophotometer에 부착된 적분구를 사용했다. 결과 및 고찰: 조성 분석한 결과는 티타늄(Ti)이 97.09%와 탄소(C)2.91%로 합성된 합금으로 해석되었고, 구조는 Hexagonal이었다. 티타늄 안경테 재료에 인가 시간을 조정하여 산화막(TiO2) 두께를 변화시킴으로서 다양한 색상을 얻을 수 있었다. 광 반사 스펙트럼을 측정해 보면 양극산화 방법으로 착색한 티타늄 안경테는 양극산화 초기단계에서는 청색영역의 파장에서 하나의 넓은(broad)피크를 갖는 광 반사 스펙트럼이 관측되었고, 양극산화 시간이 진행되어 두께가 두꺼워 질수록 붉은색 영역에서 광 반사가 크게 일어나고, 피크도 분리되는 것을 알 수 있다. 결론: 티타늄 안경테의 색상은 양극산화에 의해 형성된 산화막의 굴절률과 두께에 의존한 광의 간섭효과에 의해서 변화는 것을 알 수 있다.