Titanium anodized surface

Plate anodes were used for corrosion protection in order to avoid damage due to erosion and cavitation. These consisted of enamelled steel bodies in which a metal oxide-coated titanium anode 1 dm in surface area was fitted. The enamel... 

In aqueous chloride where it is necessary to use platinised titanium anodes coated over only part of their surface, e.g. titanium rod tipped with a thin platinum film, it may be necessary to limit the applied voltage to 12 V. 

Smooth platinum, lead dioxide and graphite are anode materials commonly used in electrooxidation processes. All show large overpotentials for oxygen evolution in aqueous solution. Platinum coated titanium is available as an alternative to sheet platinum metal. Stable surfaces of lead dioxide are prepared by electrolytic oxidation of sheet lead in dilute sulphuric acid and can be used in the presence of sulphuric acid as electrolyte. Lead dioxide may also be electroplated onto titanium anodes from lead(Il) nitrate solution to form a non-porous layer which can then be used in other electrolyte solutions [21],... 

It is known from decades, particularly for Al, that porous oxide layers can be grown by anodization typically in acidic electrolytes, while anodization in neutral electrolytes typically leads to a compact oxide layer. However, Masuda et al were the first who showed that a very high degree of order can be achieved for these porous geometries. Zwilling et first reported the porous surface of titania films electrochemically formed in fluorinated electrolyte by titanium anodization, but only a decade later Grimes et al. showed that the nanostructure is constituted by uniform titania nanotube arrays. 

Beck and Schulz have been working since 1984 on titanium anodes on whose surface chromate is anchored by the usual baking process, which produces dimensionally stable anodes tor chloralkali elektrolysis (e.g., (185, 196, 197)]. 

Fig. 32. Schematic of the redox reaction of chromium species attached to the surface of titanium anodes...

The transition states of the latter are therefore more sensitive to stereochemical and electronic influences, which also leads to a higher selectivity than in analogous electrochemical conversions. At some oxide electrodes, such as the Ni(OH)2 electrode [13], the oxidation occurs as inner sphere electron transfer by hydrogen atom transfer. Also at doped titanium anodes this seems to be partially the case [14]. It cannot be definitely excluded that also in some oxidations at platinum anodes, higher valency oxides at the surface act as inner sphere electron transfer agents. Electrochemical" inner sphere electron transfers are intentionally used in indirect electrochemical conversions where selective chemical oxidants or reductants are regenerated by electron transfer from the electrode [15]. They are also immobilized by attaching polymer-bound electrocatalysts as mediators to the electrode surface [16]. 

In many cases the surface of the anode is oxidized to lead oxide, which thus is the real anode material. Titanium anodes coated with lead oxide have been found to have a long lifetime [154,155]. In some cases the lead dioxide, a strong oxidant in acid solution, reacts chemically with the substrate [156] and is continuously regenerated whereas it acts as an inert electrode in other oxidations. A review of the basic electrochemistry of Pb02, mainly in relation to the lead battery, has been published [157]. 

Tokuyama Soda Co., Ltd. has developed a large bipolar electrolyzer that has an electrolysis area of 2.7 m per unit. The cell bodies are metallic. The anode chamber is lined with titanium plating and the cathode chamber and structural frame are carbon steel. The anode surface is titanium mesh with an... 

Anodic acidification. At the anode surface, the anodic process of oxygen evolution takes place 2H2O —>62 + 4H + 4e . In the presence of chlorides, even chlorine develops 2Cr —> CI2 + 2e . Such processes may directly or indirectly produce acidity and may thus lead to destruction of the cement paste in contact with the anode [34]. Experience shows that such deterioration is negligible for activated titanium mesh anodes if the anodic current density does not exceed 100 rtiA/m (or values 3-4 times greater for brief periods). Design of the anodes for cathodic prevention and cathodic protection must respect these hmits. 

Oxide film laser lithography (OFLL) replaces the UV patterned photoresist of TMEMM by laser ablated patterned oxide mask, which is grown anodically on the titanium surface. OFLL can be appUed precisely to nonplanar complex surface and it also allows multilevel patterning. Fig. 12.11 shows that titanium cylinder surface consists of hemispherical cavities which are electrochemically micro-structured using OFLL. However, the process is serial and slower compared to TMEMM. 

Anodized surface of titanium with porous oxide fiim exhibits submicrometer size pores [26]. 

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