Electrodeposition titanium

Titanium owes its great importance due to its excellent mechanical and corrosion performance. Titanium is produced by reduction of TiCl with magnesium (Kroll method) or sodium (Hunter method). As the cost of Hunter method is higher than Kroll method, Kroll method is considered the most efficient method for titanium electrodeposition. 

Mukhopadhyay et al. [98] studied the titanium electrodeposition on a Au(lll) substrate in the l-methyl-3-butyl-imidazolium bis(trifluoromethylsulfone) imide ([BmimJBTA) ionic liquids with 0.24 M TiCl at room temperature. It was found that TiCl is converted to TiCl in a first step, which is subsequently reduced to metallic Ti. Two-dimensional (2D) clusters form preferentially on the terraces in underpotential deposition range. At a potential of -1.8 V, a dense layer of three-dimensional (3D) clusters of titanium of 1-2 nm thickness is formed. The electrochemical reduction of tetravalent titanium species in hydrophobic 1-n-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP]TFSI) room-temperature ionic liquid was studied by Kayayana et al. [182]. It was found that the stepwise reduction from Ti(IV) to Ti(III) and probably Ti(II) in [BMP]TFSI containing TiBr without [BMP] Br. The potentiostatic cathodic reduction gave some deposits at 180°C. The reduction of Ti(rV) species at -2.3 V led to the deposition of some Ti compounds containing... 

There are several studies dealing with the current efficiency of titanium electrodeposition. The summary in Table 4.10.1 demonstrates that high current efficiencies have been found especially in the case of compact or dendritic deposits. 

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

Pt electrodeposits may also be produced from molten salt electrolytes. Such a high-temperature process has the advantage that the deposits are diffusion bonded to the titanium substrate and thus have good adhesion, and, if necessary, thick deposits can be produced. However, they have the disadvantage that because of the complexity of the process there is a limitation on the size and shape of the object to be plated, and the resultant deposits are softer and less wear resistant than those from aqueous solutions... 

Magnetite may also be used in combination with lead or electrodeposited onto a titanium substrate". The latter anode system has been shown to exhibit good operating characteristics in seawater but at present it is only of academic interest. 

Use of low-temperature molten systems for electrolytic processes related with tantalum and niobium and other rare refractory metals seems to hold a promise for future industrial use, and is currently of great concern to researchers. The electrochemical behavior of tantalum, niobium and titanium in low-temperature carbamide-hilide melts has been investigated by Tumanova et al. [572]. Electrodeposition of tantalum and niobium from room/ambient temperature chloroaluminate molten systems has been studied by Cheek et al. [573],... 

Darkowski and Cocivera [94] investigated trialkyl- or triarylphosphine tellurides, as low-valent tellurium sources, soluble in organic solvents. They reported the cathodic electrodeposition of thin film CdTe on titanium from a propylene carbonate solution of tri-n-butylphosphine telluride and Cd(II) salt, at about 100 °C. Amorphous, smooth gray films were obtained with thicknesses up to 5.4 p,m. The Te/Cd atomic ratio was seen to depend on applied potential and solution composition with values ranging between 0.63 and 1.1. Polycrystalline, cubic CdTe was obtained upon annealing at 400 C. The as-deposited films could be either p- or n-type, and heat treatment converts p to n (type conversion cf. Sect. 3.3.2). 

Lead sulfide, PbS, nanoparticulate thin films having pancake-like geometry and exhibiting ID quantum confinement, as controlled by the lowest dimension of the particles, have been synthesized by cathodic electrodeposition on TTO/glass and titanium electrodes from a pH 0.62 solution containing Pb(N03)2 and Na2S203 [162]. 

Gonzalez-Garcia J, Iniesta J, Exposito E et al (1999) Early stages of lead dioxide electrodeposition on rough titanium. This Solid Films 352 49-56... 

S.A. Marzouk, Improved electrodeposited iridium oxide pH sensor fabricated on etched titanium substrates. Anal. Chem. 75, 1258—1266 (2003). 

Electrodeposition of CdjcHgi jcTe films on a titanium [210] and stainless steel substrates [211] from a bath containing CdS04 and Te02 and HgCl2 was investigated. Film composition and band-gap energy were evaluated. 

Ir Ir02 electrodes (commercially available from Cypress Systems, Lawrence, KS) can measure pH in harsh environments or microscopic spaces [S. A. M. Marzouk, Improved Electrodeposited Iridium Oxide pH Sensor Fabricated on Etched Titanium Substrates, Anal. Chem. 2003, 75, 1258 A. N. Bezbaruah and T. C. Zhang, Fabrication of Anodically Electrodeposited Iridium Oxide Film pH Microelectrodes for Microenvironmental Studies, Anal. Chem. 2002, 74. 5726 D. O. Wipf. F. Ge, T. W. Spaine, and J. E. Baur, Microscopic Measurement of pH with Ir02 Microelectrodes, Anal. Chem. 2000, 72, 4921]. For pH measurement in nanoscopic spaces, see X. Zhang,... 

When Bandi and Kuhne studied the reduction of C02 to methanol at mixed Ru02 + Ti02 electrodes (ratio 3 1) produced by coating titanium foil [65], in a C02-saturated KHC03 solution at a current density of 5 mA cm 2, only minimal C02 reduction was observed. However, the addition of electrodeposited Cu led to faradaic efficiencies of up to 30% for methanol at potentials of approximately -0.972V (versus SCE). Trace amounts of formic acid and ethanol were also observed. In this case, the rate-limiting step was surmised to be the surface recombination of adsorbed hydrogen and C02 to yield adsorbed COOH". 

In this section we will show that air- and water-stable ionic liquids can be used for the electrodeposition of highly reactive elements which cannot be obtained from aqueous solutions, such as aluminum, magnesium and lithium, and also refractory metals such as tantalum and titanium. Although these liquids are no longer air-and water-stable when AICI3, TaFs, TiCU and others are dissolved, quite interesting results can be obtained in these liquids. 

Interesting potential applications of molten salts are electroplating and electrorefining of refractory metals and rare earth metals. Electrowinning of titanium has been tested on a pilot scale. Electrodeposition of refractory compounds like TiB2 has also been demonstrated. Due to space limitations these more exotic applications of molten salts will not be treated here. However, short chapters on molten salt batteries and fuel cells are included. 

The kinetics of the electrodeposition and electrocrystallization of titanium were studied in alkali chloride melts by Haarberg et al. [140], The cathodic reduction Ti(III)/Ti(II) was very irreversible, and the Ti(II)/Ti reduction was found to be quasi-reversible, as shown in the voltammogram in Figure 14. In LiCl-KCl... 

---