Molten chloroaluminates

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],... 

Electrodeposition of Transition Metal-Aluminum Alloys from Chloroaluminate Molten Salts... 

Phase Equilibria and Physical Properties of Chloroaluminate Molten Salts. 277... 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

Although chemically similar, the inorganic and organic chloroaluminate molten salts or ionic liquids, as some prefer to call them, differ greatly with respect to their melting temperatures and physical properties. Figures 1 and 2 show the phase diagrams... 

In many ways, chloroaluminate molten salts are ideal solvents for the electrodeposition of transition metal-aluminum alloys because they constitute a reservoir of reducible aluminum-containing species, they are excellent solvents for many transition metal ions, and they exhibit good intrinsic ionic conductivity. In fact, the first organic salt-based chloroaluminate melt, a mixture of aluminum chloride and 1-ethylpyridinium bromide (EtPyBr), was formulated as a solvent for electroplating aluminum [55, 56] and subsequently used as a bath to electroform aluminum waveguides [57], Since these early articles, numerous reports have been published that describe the electrodeposition of aluminum from this and related chloroaluminate systems for examples, see Liao et al. [58] and articles cited therein. 

Carlin, R. T. and Wilkes, J. S., Chemistry and Speciation in Room-Temperature Chloroaluminate Molten Salts, in Chemistry of Nonaqueous Solutions, G. Mamantov and A. I. Popov, Editors. 1994, VCH Publishers New York. p. 277. 

Ketonate complexes of Ru are reported in a number of papers. The parent complex [Ru(acac)3] has been subject to a polarized neutron diffraction study at 4.18 K, to powder neutron diffraction studies and to single-crystal structure determinations at 293 K, 92 K, and 10.5 K. The structure is disordered at all temperatures. Measurements of the magnetic susceptibilities (at 2.5 K and 300 K) have been made along different crystal axis directions, and the results analyzed. An investigation of the relationships between ionization potentials and half-wave potentials of a series of tris(/3-ketonate)Ru complexes has been reported, and the electrochemical properties of [Ru(acac)3] in chloroaluminate molten salt media have been reported. The reduced species [Ru(acac)3] can react with AICI4 reduction by bulk electrolysis of a small amount of [Ru-(acac)3] in the melt yields [RuClg]. ... 

Thapar R, Rajeshwar K (1983) Mott-Schottky analyses on n- and p-GaAs/room temperature chloroaluminate molten-salt interfaces. Electrochim Acta 28 195-198... 

Haloaluminate ILs are tunable solvents that allow the dependence of the oxidation state of a compound on the solvent acidity to be studied. An example [4] is the characterization of iodine and the iodine species in different oxidation states at widely varied acidities of [C4py]Cl/AlCl3. The variety of the species formed at different solvent acidities reflects the features of the characteristic acid-base interactions in chloroaluminate molten salts as well. Combining electrochemical and spectroscopic data, the electro-active species can be idenhfied as it was done in Ref. 5. 

Wilkes, J. S., Levisky, J. A., Pflug, J. L. et al.. Composition determinations of liquid chloroaluminate molten-salts by nuclear magnetic-resonance spectrometry, Anal. Chem., 54,2378, 1982. 

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