A method for purifying hundred gram quantities of aluminium chloride

The electrodeposition of Al alloys using chloroaluminate ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium chloride (EMIC)–AlCl₃, has been of significant interest as a surface coating technology. To minimize the contamination of the ILs with water, which can inhibit Al deposition, anhydrous metal chlorides were generally used as metal precursors in the previous studies on Al alloy electrodeposition. However, many anhydrous transition metal chlorides have limited solubility in ILs, making it difficult to obtain Al-based alloy films with a high alloy content at a high current density. This article describes the electrodeposition of Al–W alloy films using W(II) chloride hydrates, W₆Cl₁₂·2H₂O and (H₃O)₂[W₆Cl₁₄]·7H₂O, as W precursors. These hydrated salts were found to have much higher solubilities in EMIC–AlCl₃ ILs than anhydrous W₆Cl₁₂. Therefore, owing to the high solubility of the hydrated salts, Al–W alloy films with a high W content could be electrodeposited even at high current densities. Furthermore, the use of hydrated salts had no negative effect on the quality of the electrodeposited films or the current efficiency. A chemical speciation of the Al and W ions in the ILs was carried out using Raman spectroscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure spectroscopy, and UV-visible spectroscopy. The spectral data conclusively indicated that the dissolved species derived from the hydrated salts were different compared to those derived from the anhydrous salt. The high solubility of the hydrated W salts and the success of Al–W alloy electrodeposition encourage the use of hydrated salts in chloroaluminate ILs.

In recent work we showed that Ziegler-type nanoparticles made from [Ir(1,5-COD)(μ-O₂C₈H₁₅)]₂ plus AlEt₃ are an unusually thermally stable (≥30 min at 200 °C), hydrocarbon-solvent soluble, high catalytic activity nanoparticle catalyst (I.K. Hamdemir, S. Özkar, K.-H. Yih, J.E. Mondloch, R.G. Finke, ACS Catal. 2 (2012) 632–641). As such, they are analogous to—and currently the cleanest and best characterized model system for—Ziegler-type nanoparticles made from Co or Ni precatalysts plus AlEt₃ which are used industrially to hydrogenate ∼1.7 × 10⁵ metric tons of styrenic block copolymers per year (for a review of the area, see W.M. Alley, I.K. Hamdemir, K.A. Johnson, R.G. Finke, J. Mol. Catal.: A Chem. 315 (2010) 1–27). The key question addressed in the present paper is “What is the nature of the AlEt₃-derived stabilizer species?” for the unusually stable and active Ziegler-nanoparticles formed from [Ir(1,5-COD)(μ-O₂C₈H₁₅)]₂ plus AlEt₃. Specifically tested herein are four primary hypotheses for the AlEt₃-derived stabilizer(s) in the Ir(0)_n Ziegler-nanoparticle system: (i) that the key stabilizer is neutral (i.e., uncharged) aluminum alkyl carboxylates following precedent from the work of Shmidt and Bönnemann; (ii) that the key stabilizer is anionic [AlEt₃(O₂C₈H₁₅)]⁻; (iii) that a key stabilizer is the AlEt₃ (or its derivatives) reacting with the Ir(0)_n nanoparticle surface; or (iv) that an important AlEt₃-derived stabilizer is AlOAl containing alkylalumoxanes formed from any water present. The results obtained rule out (ii), but provide strong evidence for (iii), as well as evidence consistent with (i) and (iv), as stabilizers in Ziegler-nanoparticles. A pictorial scheme (Scheme 2) is provided as a working hypothesis for the stabilization mode(s) of Ziegler-nanoparticles and as a way to focus and expedite the needed additional composition and structural studies of Ziegler-nanoparticle stabilizers.

The conductivity (κ) has been determined for the binary molten salt system aluminium chloride/sodium chloride over the range of composition 15–30 wt% of sodium chloride and over the range of temperatures 155–195°C. A three-dimensional empirical equation has been derived from the observed data and shows that over the ranges stated k depends on the first power of T (°C) and on the first and second powers of W (wt% of sodium chloride). The equation is: .