Anodizing mechanism

The formation of an anodized coating on a Mg alloy is a result of electrochemical and chemical reactions between the Mg alloy and an anodizing bath solution 

To further illustrate the anodizing mechanism and the reactions involved in Mg anodization, an anodizing process of a Mg alloy in a silicate containing bath is analyzed as an example (Shi, 2005 Shi et ah, 2003, 2005, 2006a,b,c). 

The anodizing voltage increased linearly with time. Dissolution of Mg, formation and deposition of Mg(OH)2 and MgSi03 and oxygen evolution occur. The possible detailed reactions include  

The anodizing voltage further increases to about 190 V. Within this potential range, evolution of some tiny gas bubbles was observed. There was no sparking. It is postulated that in addition to anodizing reactions (16.1), (16.2), (16.3) and (16.4), another reaction starts to take place  

This is an electrochemical reaction resulting in coating formation directly. Mg is directly electrochemically oxidized into MgO. 

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Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

In the following discussion, the anodic mechanism is described in detail. Figures 34(a and b) schematically illustrate the galvanic element with respect to the current potential curves for anodic metal dissolution in the head and oxygen reduction at the back of the head. SKP measurements clearly show that the head of the filiform exhibits a more negative potential than the tail (Fig. 35). 

As for the anodic mechanism, a similar study on the nucleation of the PPP was undertaken in the case of the reductive coupling of 4,4 -dibromobiphenyl (M) on ITO electrodes in a mixture of THF + hexamethyl phosphoramide with LiC104. The catalyst (C) was NiCl2 bis(l,2-diphenylphosphinoethane) and different [M]/[C] ratios were investigated [172]. 

It is usual to consider that various classes of anodic mechanisms exist depending on the range of potential with respect to the passivity domain. Active dissolution taking place at potentials preceding the passivation on a film-free surface is of major importance for the homogeneous corrosion in weakly oxidizing media such as acidic solutions of stable anions (e.g. sulfuric, perchloric, phosphoric, hydrochloric). Localized corrosion in pits, crevices, cracks, etc. is also assirmed to proceed through active dissolution stabilized at passive potentials by ohmic drops and/or local chemistry. 

Beyond the mechanics of scale-up and refueling, important areas of research concern anode mechanisms at open circuit and under moderate loads (0.05-0.4 A/cm ). The balance of CO- and C02-producing... 

N. Ryckelynck, H. Stecher and C. Reimers, Understanding the anodic mechanism ot a seafloor tuel cell Interactions between geochemistry and microbial activity. Biogeochemistry 76, 2005, 113-139. 

Ryckelynck, N., Stecher, H.A.I. and Reimers, C.E. (2005) Understanding the anodic mechanism of a seafloor fuel cell interactions between geochemistry and microbial ability. Biogeochemistry 76, 113-139. 

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