Part I: Basic Principles: Introduction.- Principles of Photoelectrochemical Cells.- Photoelectrochemical Measurements.- Part II: Materials Properties and Synthesis: Nanostructured alpha-Fe2O3 Photoanodes.- Mixed Metal Oxide Photoelectrodes and Photocatalysts.- Combinatorial Identification and Optimization of New Oxide Semiconductors.- Part III: Devices and Device Characterization.- Multijunction Approaches to Photo-electrochemical Water Splitting.- Part IV: Future Perspectives.- Economic and Business Perspectives.- Emerging Trends in Water Photoelectrolysis.

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Photoelectrochemical hydrogen production

Effect of grain size and twins on corrosion behaviour of AZ31B magnesium alloy

This paper reviews various aspects of anodizing of magnesium alloys, such as the basics, processes, properties and applications. It systematically summarises the existing fundamental studies and technical developments of anodizing of magnesium alloys, and concludes that new anodizing processes based on electrolytic plasma anodizing that convert the surface of a magnesium alloy into a hard ceramic coating in an electrolytic bath using high energy electric discharges can offer improved wear and corrosion resistance. These new anodized coatings are often claimed to perform better than the traditional ones obtained through older anodizing processes, such as DOW17 or HAE. The new anodizing techniques are chromate free and hence environment friendly. It is expected that more cost-effective, environment-friendly and non-toxic anodizing techniques will be developed and applied to magnesium alloy components in the future.

Anodizing Treatments for Magnesium Alloys and Their Effect on Corrosion Resistance in Various Environments

Effect of electrolyte additives on performance of plasma electrolytic oxidation films formed on magnesium alloy AZ91D

Electrochemical corrosion behaviour of plasma electrolytic oxidation coatings on AM50 magnesium alloy formed in silicate and phosphate based electrolytes

Anodization of die-casted AZ91D magnesium alloy was performed in 3 M KOH+0.21 M Na 3 PO 4 +0.6 M KF base electrolyte with and without Al(NO 3 ) 3 addition. The anodic film was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the various anodized alloys was then evaluated in 3.5 wt % NaCl solution using electrochemical impedance spectroscopy (EIS) and immersion testing. The results showed that the anodic film was mainly composed of MgO. The addition of Al(NO 3 ) 3 into the base electrolyte results in the formation of Al 2 O 3 and Al(OH) 3 in the anodic film. The maximum amount of Al 2 O 3 was found in the anodic film when the alloy was anodized in the electrolyte containing 0.15 M Al(NO 3 ) 3 . The results of EIS analysis and morphological examination showed that the MgO anodic film modified with Al 2 O 3 exhibited the superior corrosiom resistance for AZ91D Mg alloy.

Characterization of anodic films formed on AZ91D magnesium alloy

The anodic films formed on AZ91D magnesium alloy after heat treatment were analyzed and their electrochemical properties were investigated. The results showed that the cooling rate had a significant influence on the microstructure evolution of the AZ91D magnesium alloy after solution heat treatment at 440 °C for 20 h in N2 atmosphere. A single-phase microstructure was observed when the alloy was quenched in water after solution heat treatment. However, a duplex structure consisting of both a and s phases was found if the solution-annealed alloy was cooled in air. The differences in microstructure of the heat treated AZ91D magnesium alloy gave rise to a significant change in the property of the anodic film formed in 3 M KOH + 0.21 M Na3PO4 + 0.6 M KF + 0.15 M Al(NO3)3 electrolyte. During the early stage of anodization, for the as-cast alloy, inhomogeneous anodic films were formed exhibiting relative rough surface appearances. A rather smooth anodic film was formed for the solution-annealed AZ91D magnesium alloy either followed by air cooling or water-quenched. The surface and cross section appearance was almost the same regardless of the prior heat treatment after anodizing for 20 min. The corrosion resistances of the various anodized AZ91D magnesium alloy were evaluated and compared by employing electrochemical impedance spectroscopy (EIS). The results demonstrate that the anodic film formed on the water-quenched AZ91D magnesium alloy had a slightly higher polarization resistance than that formed on the as-cast alloy. The highest polarization resistance of anodic film was found for that formed on annealed and air-cooled alloy. The presence of Al-rich s phase on the surface gave rise to the formation of a more protective anodic film which consisted of a great amount of Al2O3.

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Houng Yu Hsiao

Papers

Characterization of anodic films formed on AZ91D magnesium alloy

Effect of heat treatment on anodization and electrochemical behavior of AZ91D magnesium alloy