Anodization techniques

Using the impressed-current technique the driving voltage for the protec-ive current comes from a d.c. power source. The sacrificial anode technique... 

Metals such as aluminium, steel, and titanium are the primary adherends used for adhesively bonded structure. They are never bonded directly to a polymeric adhesive, however. A protective oxide, either naturally occurring or created on the metal surface either through a chemical etching or anodization technique is provided for corrosion protection. The resultant oxide has a morphology distinct from the bulk and a surface chemistry dependent on the conditions used to form the oxide 39). Studies on various aluminum alloy compositions show that while the oxide composition is invariant with bulk composition, the oxide surface contains chemical species that are characteristic of the base alloy and the anodization bath40 42). 

The sacrificial anode technique appears to be competitive with regard to the other electrochemical methods [19] to create the silicon-silicon bond and is very promising for the replacement of alkali metals in many syntheses, especially when high selectivity is required. 

Galv moaluminum layers precipitated from electrolytes containing alkyl aluminum possess a much lower microhardness (21 HV) than other electrolytically deposited metals or aluminum layers deposited from other electrolyte systems. The soft galvanoaluminum deposits can be hardened considerably by a subsequent anodizing process. Because of the high purity of the aluminum layer, a transparent oxide layer is produced which can be colored as desired for decorative purposes. The obtainable hardness values are dependent on the selected anodizing technique. 

With the direct current-sulfuric acid technique (GS), final hardness values are between 500 and 600 HV. Lower hardness values of 250-400 HV are reached by a special anodizing technique (NS). The latter procedure is preferred in practice, because, contrary to the GS process, it prevents attack on the base metal of pieces that are not completely aluminum plated, such as a hollow form. 

Reductive silylation of mono- and polyhalothiophens has also been achieved using an Al sacrificial anode [Eq. (12)] [59-61]. This reaction provides a convenient method for the preparation of 2,5-bis(trimethylsilyl)thiophene, which serves as a good precursor of poly thiophene. The sacrificial Mg and Al anode technique was also successfully applied to the reductive silylation of bromopyrroles [62]. 

Johnson et al. [81] have developed a pulsed anodic technique at platinum flow-through electrodes and have applied it successfully to the detection of a number of classes of molecules such as alcohols and carbohydrates, amines, and sulphur compounds. The method has also been extended to the detection of analytes at potentials where they are not electroactive. This procedure has been used to detect Cl" and CN [82, 83]. 

Figure 13. Schematic of the photoelectrolytic cell designed for the generation of hydrogen using a light source (UV or visible). The anode is carbon-doped titania nanotubular arrays prepared by the sonoelectrochemical anodization technique and the cathode is platinum nanoparticles S3mthesized on undoped titania nanotubular arrays. (Redrawn from Misra et al. [220] with permission from publisher, American Chemical Society. License Number 2627061508363).

Nanoporous surfaces can be readily fabricated on some metals by potentiostatic or gal-vanostatic anodization of the metals in acidic electrolytes (e.g., H SO, HNO3, HF, etc.). These metals include A1 and several valve metals such as Ti, Ta, and Nb [15]. In a typical anodization cell (as illustrated in Figure 2.4a), A1 or valve metal acts as anode and platinum is usually used as cathode and both are immersed in an acidic electrolyte. When a proper electric field is applied to the electrochemical cell, nanostructured oxide can form on the anodic metal. Specifically, the anodization technique can create uniform nanotubular structures on Ti (as shown in Figure 2.4b) and Ta surfaces with diameters... 

Anodization techniques. Anodization has also been employed to fabricate 3-D nanoporous or nanotubular scaffolds of anodic titanium oxide and aluminum oxide [42,43]. These techniques are essentially the same as the anodization methods introduced in Chapter 2 and, thus, are not expanded upon here. 

The current and potential fields are uniform around the buried pipeline. Thus, the potential and current field gradients are quantitatively determined in either impiessed-cunent or sacrificial anode techniques. This assumption is not realistic since the complexity of real engineering stmc-tures and heterogeneity of the soil or seawater electrolytes preclude exact theoretical calculations. The margin of error between the fteoretical and experimental results depends on the assumptions considered to develop a particular mathematical model... 

It should be noted that anodizing is a hot topic in the area of corrosion and protection of Mg alloys. It is expected that in near future, more corrosion-resistant, low cost, easily operated, enviromnent-friendly and non-toxic anodizing techniques will become available for Mg alloys. 

Although various anodizing techniques have been developed, which differ from one another for their different anodizing phenomena or coating performance, they do share some common characteristics. 

Vrublevsky L, Rarkoun V, Schreckenbach J. and Marx G. (2004), Study of porous oxide film growth on aluminum in oxalic acid using a re-anodizing technique , Appl. Sutf. Set, 111, 282-92. 

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