The Electrodeposition of Al3Ti from Chloroaluminate Electrolytes

et al. 2004

The electrochemistry of Zr͑IV͒ and Zr͑II͒ and the electrodeposition of Al-Zr alloys were examined in the Lewis acidic 66.7-33.3 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt at 353 K. The electrochemical reduction of Zr͑IV͒ to Zr͑II͒ is complicated by the precipitation of ZrCl 3 ; however, solutions of Zr͑II͒ can be prepared by reducing Zr͑IV͒ with Al wire. Al-Zr alloys can be electrodeposited from plating baths containing either Zr͑IV͒ or Zr͑II͒, but for a given concentration and current density, baths containing Zr͑IV͒ lead to Al-Zr alloys with the higher Zr content. This result was traced to the diminutive concentration-dependent diffusion coefficient for Zr͑II͒. It was possible to prepare Al-Zr alloys containing up to ϳ17% atomic fraction ͑atom %͒ Zr. The structure of these deposits depended on the Zr content. Alloys containing less than 5 atom % Zr could be indexed to a disordered face-centered cubic structure similar to pure Al, whereas alloys containing ϳ17 atom % Zr were completely amorphous ͑metallic glass͒. The chloride pitting potentials of alloys with more than 8 atom % Zr were approximately ϩ0.3 V relative to pure Al.The maximum solubility of zirconium in face-centered cubic ͑fcc͒ aluminum is 0.08% atomic fraction ͑atom %͒. This occurs at the peritectic transformation point at 660.5°C. At room temperature, zirconium has negligible solubility in aluminum. 1 However like most aluminum-transition metal alloys, supersaturated solid solutions greatly exceeding the equilibrium solubility can be obtained by nonequilibrium processing methods. For example, solid solutions containing up to 3.0 atom % zirconium have been produced by rapid solidification 2-6 and vapor deposition. 7 The Al-Zr solid solution, although metastable, shows good thermal stability up to ϳ400-450°C. This observation is consistent with the general trend that the thermal stability of the solid solution is related to the melting point of the alloying addition; i.e., the higher the melting point, the more stable the solid solution. 8 The thermal decomposition of the supersaturated solid solution results in the nucleation of a metastable Al 3 Zr phase having an ordered cubic L1 2 structure (Cu 3 Au-type͒ 5,6,9-13 and eventually the equilibrium Al 3 Zr phase having a tetragonal structure. These two phases, cubic Al 3 Zr and tetragonal Al 3 Zr, have also been observed in supersaturated Al-Zr solid solutions produced by rapid quenching. 14 The properties of aluminum and its alloys are significantly altered by the addition of zirconium. The rapid solidification of binary Al-Zr alloys with more than 0.15 atom % zirconium produces considerable grain refinement, 15,16 resulting in aluminum grain sizes typically less than 10 m. The general explanation for this phenomenon is that L1 2 Al 3 Zr acts as a low-energy nucleation site for fcc Al due to the similar crystal structures. Rapid quenching is required to ensure that the Al 3 Zr solidifies with the metastable L1 2 structure rather than the equilibrium tetragonal structure...

Section: Resultsmentioning

confidence: 99%

Electrodeposition of Al-Zr Alloys from Lewis Acidic Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Melt

Tsuda

Hussey

et al. 2004

“…Ti + xA1CI~ --~ [Ti(A1CI~)=] ~-x + 2e- [8] A peak current is reached at about 0.37 V followed by a sharp decrease in reactivity. This transition is close to the reversible potential for Ti(II)/Ti(III), thus it is reasonable to associate passivation of the titanium electrode with the precipitation of Ti(III).…”

Section: Fig 8 (A) Samp!ed-current Voltammogram For the Oxidation Omentioning

confidence: 99%

Electrochemistry of Titanium in Molten 2AlCl3 ‐ NaCl

Moffat

1995

Self Cite

The electrochemistry of titanium has been examined in 2A1C13-NaC1 electrolyte. Titanium may be oxidized to yield Ti(II), Ti(III), and Ti(IV) complexes. The divalent species may be used to eleetrodeposit A1-Ti alloys, while the trivalent species is sparingly soluble. Cyclic voltammetry on a tungsten electrode in solutions with varying Ti(II) concentration has been used to examine the kinetics of the precipitation reaction associated with Ti(III). The induction time required for precipitation is dependent upon the bulk concentration of Ti(II), in a manner similar to that reported for homogeneous precipitation from aqueous solutions. At higher Ti(II) concentrations and slower sweep rates the electrode is passivated by the Ti(III) precipitation. Slow sweep rate voltammetry suggests that the i-E characteristics of the passivation reaction are dominated by the resistance associated with the precipitate film. The film blocks the electrode preventing oxidation of Ti(II) to Ti(IV). A parallel study of the dissolution kinetics of titanium metal reveals similar passivation phenomena due to Ti(III) precipitation. However, the passive film on titanium is somewhat conductive unlike that associated with the precipitated film formed on a tungsten electrode. This distinction presumably results from the formation of a compact passive film at the interface between the precipitated film and the titanium substrate. At more oxidizing potentials the protective nature of the passive film breaks down with the generation of Ti(IV). A comparison between the Ti(II) concentration determined by voltammetry and that anticipated from dissolution of titanium metal reveals a deviation from Faraday's law at high Ti(II) concentrations. This discrepancy is resolved by adopting a previously postulated model involving the formation of oligomers of Ti(II).

“…13 The electrochemistry of titanium has been studied extensively in Lewis acidic chloroaluminate melts, [18][19][20][21][22][23][24] and it has been determined that Al-Ti alloys can be electrodeposited from solutions of Ti͑II͒ in these melts. 13 The electrochemistry of titanium has been studied extensively in Lewis acidic chloroaluminate melts, [18][19][20][21][22][23][24] and it has been determined that Al-Ti alloys can be electrodeposited from solutions of Ti͑II͒ in these melts.…”

mentioning

confidence: 99%

Electrochemistry of Titanium and the Electrodeposition of Al-Ti Alloys in the Lewis Acidic Aluminum Chloride–1-Ethyl-3-methylimidazolium Chloride Melt

Tsuda

Hussey

et al. 2003

127

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3methylimidazolium chloride (AlCl 3 -EtMeImCl) molten salt at 353.2 K. Dissolved Ti͑II͒, as TiCl 2 , was stable in the 66.7-33.3% mole fraction ͑m/o͒ composition of this melt, but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti͑0͒ did not lead to dissolved Ti͑II͒, but to an insoluble passivating film of TiCl 3 . At high current densities or very positive potentials, Ti͑0͒ was oxidized directly to Ti͑IV͒; however, the electrogenerated Ti͑IV͒ vaporized from the melt as TiCl 4 (g). As found by other researchers working in Lewis acidic AlCl 3 -NaCl, Ti͑II͒ tended to form polymers as its concentration in the AlCl 3 -EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to ϳ19% atomic fraction ͑a/o͒ titanium could be electrodeposited from saturated solutions of Ti͑II͒ in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition.