The field of polyoxometalates (POMs), although a mature field, continues to attract significant attention. The number of publications and patents continues to grow. New researchers are entering the field. The scientific communities of fast-growing new economic/technology powers such as Peoples Republic of China and India are becoming important contributors of the total number of worldwide publications on POMs. Figure 1 depicts the growth of the POM literature per year since 1966. In 1996, according to Chemical Abstracts, nearly 600 refereed publications and over 120 patents were issued in reference to the POM chemistry and technology. Figure 2 shows the countries where the most research activity exists based on publications, and Figure 3 lists the 10 largest patent assignee countries in the world. Japan issues 40% of the worldwide patent literature followed by the USA with ∼17%. The applications of POMs are based on combinations of so-called “value-adding properties” which are summarized in Table 1. From the above-listed properties, the applications of POMs are centered primarily on their redox properties, photochemical response, ionic charge, conductivity, and ionic weights. The majority of the patent and applied literature is devoted to the applications of the Keggin type heteropolyacids (HPA) and their salts. Primarily H3PMo12O40, H3PW12O40, H4SiMo12O40, and H4SiW12O40 are used as the main examples for many applications. Their popularity can be attributed to a large extent to the enormous volume of literature over several decades that describes their fundamental chemistry and to their commercial availability, which makes them convenient starting materials. Approximately two-thirds of the applied chemistry/technology literature describes applications that are based on these POMs. Dimitris E. Katsoulis was born in Athens, Greece in 1955. He received a B.S. degree in Chemistry from University of Athens in 1977. He subsequently joined the research group of Prof. Michael T. Pope at Georgetown University and obtained a Ph.D. degree in 1985. He continued with a postdoctoral assignment at Georgetown University, and in 1988 he joined the Science and Technology function of Dow Corporation in Midland Michigan. He is currently an Associate Research Scientist in the Rigid Materials Science Expertise Center (Central R&D) in Dow Corning. His research interests include hybrid materials, with focus on siloxane-polyoxometalate compositions, sol−gel chemistry, silsesquioxanes, gel systems, polymer matrix composites, and nanocomposites. 359 Chem. Rev. 1998, 98, 359−387

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A Survey of Applications of Polyoxometalates

Preparation of bioactive titanium metal via anodic oxidation treatment

Use of XPS in the determination of chemical environment and oxidation state of iron and sulfur samples: constitution of a data basis in binding energies for Fe and S reference compounds and applications to the evidence of surface species of an oxidized pyrite in a carbonate medium

For fundamental studies of the atmospheric corrosion of steel, it is useful to identify the iron oxide phases present in rust layers. The nine iron oxide phases, iron hydroxide (Fe(OH)2), iron trihydroxide (Fe(OH)3), goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), feroxyhite (δ-FeOOH), hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4) are among those which have been reported to be present in the corrosion coatings on steel. Each iron oxide phase is uniquely characterized by different hyperfine parameters from Mossbauer analysis, at temperatures of 300K, 77K and 4K. Many of these oxide phases can also be identified by use of Raman spectroscopy. The relative fraction of each iron oxide can be accurately determined from the Mossbauer subspectral area and recoil-free fraction of each phase. The different Mossbauer geometries also provide some depth dependent phase identification for corrosion layers present on the steel substrate. Micro-Raman spectroscopy can be used to uniquely identify each iron oxide phase to a high spatial resolution of about 1 µm.

Characterization of Iron Oxides Commonly Formed as Corrosion Products on Steel

http://www.eet.bme.hu/~plesz/Gyarmati%20Adam/the%20electrochemical%20oxide%20growht%20behaviour%20on%20titanium%20in%20acis%20and%20alkaline%20electrolytes.pdf

The electrochemical oxide growth behaviour on titanium in acid and alkaline electrolytes

The semiconductive properties of the passive film formed on iron were investigated by measuring the impedance of passivated iron electrodes in neutral borate and phosphate solutions. Mott‐Schottky type of plot was applied to the impedance data to obtain the donor density and the flatband potential as a function of film formation potential, oxidation time, and ion species present in the solution. The value of obtained for the passive film is in the range of and decreases with increasing formation potential and oxidation time, indicating that the structural and electronic defects in the passive film decrease with increasing film thickness. The value of of the passive film formed in phosphate solution is greater than that in borate solution. From the fact that when the electrolyte was changed from borate to phosphate solution increased from the value in borate solution to the value in phosphate solution in a time period of about 103s, it is evident that phosphate ions penetrate into the passive film producing a large number of defects.

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Mott‐Schottky Plot of the Passive Film Formed on Iron in Neutral Borate and Phosphate Solutions

The anodic oxide film on titanium has been studied by ellipsometry and SEM observation. Ex situ multiple‐angle‐of‐incidence and in situ ellipsometric measurements allow the complex refractive index to be estimated at for the titanium substrate and at for the anodic oxide film at wavelength 546.1 nm. The anodic oxide film thickness increases linearly with potential in a range from −0.55 to 7.5V (RHE) at the rate of 2.8 nm V−1 in phosphate solutions of pH 1.6–12.1, 2.5 nm V−1 in solution, and 2.4 nm V−1 in solution. At potentials more positive than 7.5V, the film breaks down, leading to the formation of a thick oxide film probably due to an increased ionic current through the breakdown sites. The film composition is estimated to be or , which suggests the presence of hydroxyl bridge in its bonding structure.

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Ellipsometric study of anodic oxide films on titanium in hydrochloric acid, sulfuric acid, and phosphate solution

Confirmation of a sulfur-rich layer on pyrite after oxidative dissolution by Fe(lIl) ions around pH2

The anodic oxidation and anodic oxide films of cobalt have been studied in borate buffer solutions in the pH range from 7 to 11. The anodic polarization curve shows the active dissolution, primary passivity, secondary passivity, tertiary passivity, and transpassivation. It is also shown that the anodic oxide film is hydrated oxide of in the primary passive region, bilayered oxide in the secondary passive region, and bilayered oxide of in the tertiary passive and transpassive regions. The dissolution current of the anodic oxide film in the secondary and tertiary passive regions is much smaller than that in the primary passive region. By cathodic reduction the outer layer is first converted to and then reduced further to hydrated Co2+ ions before the inner layer is reduced to metallic cobalt.

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Toshiaki Ohtsuka

Papers

Mott‐Schottky Plot of the Passive Film Formed on Iron in Neutral Borate and Phosphate Solutions

Ellipsometric study of anodic oxide films on titanium in hydrochloric acid, sulfuric acid, and phosphate solution

Confirmation of a sulfur-rich layer on pyrite after oxidative dissolution by Fe(lIl) ions around pH2

Anodic Oxidation of Cobalt in Neutral and Basic Solution

Dynamic Ellipsometry of a Self-Assembled Monolayer of a Ferrocenylalkanethiol during Oxidation-Reduction Cycles