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Small amounts of oxide impurities in alkali chloroaluminate and fluorochloroaluminate melts can complicate markedly the electrochemical and spectroscopic behavior of other solute species in these melts. A simple method for the removal of oxides from these melts has been developed in our laboratory. This method is based on the reaction of carbon tetrachloride with oxides to convert them to chlorides. Spectroscopic techniques (UV-visible and IR spectroscopy) have shown that addition of carbon tetrachloride results in the complete conversion of oxides to chlorides.Oxide impurities in molten chloroaluminates ~ may have pronounced effects on the behavior of other solute species in these media; 2-4 these impurities are difficult to avoid. Recently we reported on the removal of oxide impurities from a sodium chloroaluminate melt saturated with NaC1 with phosgene (COC12). 8 Prior studies on the determination and removal of oxide species from chloroaluminate melts are summarized briefly in that paper. 5Phosgene is a very poisonous gas and must be handled with extreme caution. In addition, we have found that the removal of oxide impurities from acidic sodium chloroaluminate melts (A1C1JNaC1 mole ratio > 1) using COC12 is not complete. 5We report here a method for the removal of oxides from both acidic and basic alkali chloroaluminate melts, as well as fluorochloroaluminate melts. This method is based on the reaction of carbon tetrachloride with oxide species to convert these species to the corresponding chloride complexes. Using CC14 as a chlorinating reagent is advantageous compared .to the COC12-treatment in that CC14 is much easier to handle. FTS-7 Fourier transform infrared (FTIR) spectrophotometer which was controlled by a microcomputer system. The in situ infrared spectra of the molten salts were obtained using a cell similar to that described by Flowers and Mamantov. 8'~ The cell utilized silicon windows which were torch-sealed to the Pyrex body of the cell. AceThred adapters (Ace Glass Inc.) on the top of the cell provided access for loading and sample addition, and produced an airtight seal when closed. One AceThred adapter on the cell was covered with a septum. An appropriate amount of CC14 was added by injecting it through the septum using an airtight microsyringe (Baxter Diagnostics, Inc.). A furnace with diametrically opposed holes, which was constructed in house, allowed heating of the melt inside the sample chamber of the FTIR instrument. Results and Discussion AICl3-NaCls~ melt at 200~1 shows infrared absorption spectra in the region from 640 to 880 cm 1 for Experimental Aluminum chloride (Fluka, >99.0%) was purified by subliming it twice under vacuum in a sealed Pyrex tube. Sodium chloride (Mallinckrodt, reagent grade) was dried under vacuum (<50 mTorr) at 450~ for at least 48 h. High purity sodium fluoride (AE SAR, puratronic, 99.995 %), niobium pentachloride (AESAR, puratronic, 99.99%), and tungsten oxychloride (WOC14, Aldrich) were used without further purification. Carbon tetrachloride (water 0.001%) w...

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The electrochemical behavior of KWC16 in the A1C13-NaCls~ t melt at 175 to 200~ was investigated using multiple electrochemical methods: cyclic, normal pulse, square wave voltammetries, chronoamperometry, and exhaustive electrolysis. Electronic spectroscopy and x-ray diffraction methods were employed to characterize the products formed at different potentials. The melt was treated with CCI4 to remove oxide impurities. It was found that the reduction sequence of W(V) was dependent on the scan rate, i.e., at fast scan rates three main redox couples were observed, while additional redex couples appeared in low scan rate voltammograms. To reach a better understanding of the mechanism, some low oxidation state tungsten compounds (K2WC16 and W~CI~2) were also examined. The reduction of W(V) to tungsten metal involves several intermediate oxidation states and cluster species, such as W(IV), unstable W(III), dimers W(IV, III) and W(III,II), [W6C18] ~+ and its one-electron reduction product. Partial characterization of some of the intermediate reduction products has been achieved.

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