Electrolytes titanium alloys

The occurrence of pitting seems to stem from the differential stabiUty of the passive film that forms on the titanium alloy. This film does not break down uniformly even when the electrolytes are fluoride and bromide based. The pitting can be so severe that special measures are needed to counteract it. 

Coulometric determinations can be carried out in which no physical separation occurs but simply a quantitative change in oxidation state. For example, MacNevin and Baker determined iron and arsenic by anodic oxidation of iron(II) to iron(III) and arsenic(III) to arsenic(V). The reduction of titanium(IV) to titanium(Hl) and the reverse oxidation have been used for the analysis of titanium alloys. Conversely, the output current from a cell made from a silver-gauze cathode and a lead anode with potassium hydroxide electrolyte can be used to measure low concentrations of oxygen in inert gases. ... 

Wang J, van Apeldoom A, de Groot K (2006) Electrolytic deposition of calcium phosphate/ chitosan coating on titanium alloy growth kinetics and influence of current density, acetic acid, and chitosan. J Biomed Mater Res A 76(3) 503-511... 

Titanium and titanium alloys Sodium bromide (NaBr), sodium chloride (NaCl), mixed electrolyte, e.g., sodium chloride (NaCl) - - sodium nitrate (NaN03)... 

N. Qu, X. Fang, W. Li, Y. Zeng, Di Zhu, Wire electrochemical machining with axial electrolyte flushing for titanium alloy. Chin. J. Aeronaut. 26 (2013) 224-229. 

The Ti02 film, being an n-type semiconductor, is electronically conductive. As a cathode, titanium permits electrochemical reduction of ions in an aqueous electrolyte. On the other hand, very high resistance to anodic current flow through the passive oxide film (i.e., significant anodic polarization) can be expected in most aqueous solutions. Elevated anodic pitting (breakdown and repassivation) potentials can also be expected with many titanium alloys. 

FIG. 6—Typical examples of laboratory cell setups for cathodic charging tests on titanium alloys, (a) Typical cell setup for short-term cathodic charging of titanium samples at constant current In hot acidic electrolytes, (b) Typical cell setup for longer-term cathodic charging of titanium samples at constant potential in seawater and brines. 

Plasma electrolytic oxidation (PEO) is an efficient method for production of functional ceramic surface layers on non-ferrous metals, such as aluminium, magnesium, zirconium and titanium alloys. During PEO process the electrochemical reaction of anodic oxidation on the metal surface is assisted by micro-discharge events to promote formation of thick, hard and well-adhered oxide ceramic surface layers with specific morphologies and phase compositions, exhibiting superior protective performance and other useful electro-physical and chemical properties. ... 

Hackett et al. (2007) reported experiments with DCFCs where rods prepared from different carbon materials were used as the anodes. The cathodes were made from iron-titanium alloy. Melts of NaOH at temperatures in the range 600 to 700°C were used as the electrolyte. The most stable operation with high performance figures was obtained with graphite anodes. The OCV value was 0.788 V. At the optimum temperature of 675°C, the voltage was 0.45 V at a current density of 140 mA/cm. Anodes made of other carbon materials had higher OCVs (up to 1.044 V), but exhibited inferior and less stable performance when current was drawn. The equation for the anodic reaction in NaOH melt can be written as... 

Impressed current anodic protection is of Little importance in comparison to cathodic protection. It has been applied successfully to the protection of stainless steel and titanium alloys in the presence of acidic electrolytes. As in the case of impressed current cathodic protection, it is essential to control the electrode potential within suitable limits. Figure 10.35 indicates the application of anodic protection to a simple tank and to a more complex tube-and-shell heat exchanger. When anodic protection is commissioned, the current must be large enough to exceed icurr order to passivate the surface. The current then falls to fpAss current is increasingly deflected to more remote parts of the structure which passivate in turn. Once established, the current drain is minimal and is approximately equal to ipASs ... 

CEC BITAC 800 Electrolyzer. The Chemical Engineers Corporation (CEC) bipolar BITAC electrolyzer was jointly developed with Tosoh Corporation. The design follows the filter-press principle. Up to 80 bipolar electrode frames are clamped together by end plates and spring-loaded tie rods. The frames are made of special titanium alloy for the anode and nickel for the cathode. The electric current flows along the nickel pans, since the electrical conductivity of nickel is six times higher than that of titanium. Gas and electrolytes leave the cell compartment in overflow mode with little pressure fluctuation. Transparent PTFE tubes are attached at the electrolyte inlet and outlet nozzles of each element. Anolyte recirculation takes place through an external loop. 

Table 2 Electrolytes and voltages for electropollshing of titanium and titanium alloys...

For long lengths of anode it is sometimes necessary to extrude one material over another to improve a particular characteristic. Thus titanium may be extruded over a copper rod to improve the longitudinal conductivity and current attenuation characteristics of the former lead alloys may be treated similarly to compensate for their poor mechanical properties. It should he noted that these anodes have the disadvantage that, should the core metal be exposed to the electrolyte by damage to the surrounding metal, rapid corrosion of the former will occur. 

Pure vanadium can be obtained from the electrolytic reduction of fused salts, such as VC12, to produce a metal similar to titanium that is steel gray, hard, and corrosion-resistant. Often the pure element is not required for alloying. For example, ferrovanadium, produced by reducing a mixture of V2Oj and Fe203 with aluminum, is added to iron to form vanadium steel, a hard steel used for engine parts and axles. 

Up until now, there has been little interest in electrolytic deposition of iron metals and chromium from nonaqueous solutions, because such deposits are easily obtained from aqueous electrolytes. On the other hand, adhesive layers can be applied to reactive metals like titanium, beryllium, and magnesium, for example through nickel deposition from nonaqueous solutions. By depositing such metals out of nonaqueous solutions, hydrogen sensitive materials, such as low-alloy high-strength steel, can be coated without danger of embrittlement. Materials coated in this way with a compact poreless metal layer can be further coated in an aqueous electrolyte. 

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