THE ELECTRODEPOSITION OF Al-Cu ALLOYS FROM ROOM-TEMPERATURE CHLOROALUMINATE ELECTROLYTES G.R. Stafford, V.D. Jovic and T.P Moffat Materials Science and Engineering Laboratory National Institute of Standards and Technology Gaithersburg, Maryland 20899, USA Q. Zhu, S. Jones and C.L. Hussey Department of Chemistry University of Mississippi University, Mississippi 38677, USA ABSTRACT The electrodeposition of Cu-Al alloys, as well as the underpotential deposition (UPD) of A1 onto Cu(l 11), were investigated in acidic aluminum chloride/1-methy 1-3-ethylimidazolium chloride ambient temperature molten salt. It was shown that it is possible to produce Cu-Al alloy deposits at potentials positive of that corresponding to the electrodeposition of bulk Al. The onset of Al codeposition was found to occur at approximately 0.30 V versus the A1(III)/A1 couple, and the Cu-Al alloy composition was found to be independent of the Cu(I) concentration, reaching a maximum value of 43 % atomic fraction Al at 0 V. Alloy deposition potentials based on free energy calculations are in good agreement with those observed experimentally for Zn-Al, Cu-Al, Co-Al, and Fe-Al deposited at room temperature and Ni-Al deposited at 150 °C from an aluminum chloride/sodium chloride melt. Cyclic voltammograms recorded on Cu(l 11) clearly indicate that UPD of Al commences at about 0.30 V vs. Al and is characterized by two distinct surface processes. In-situ scanning tunneling microscopy (STM) examination indicates that an ordered ad-layer appears on the C u (lll) surface at potentials positive of the first UPD wave. A possible model representing this structure corresponds to a layer of tetrachloroaluminate ions, oxidatively adsorbed on the C u (lll) surface, with the face of the tetrahedra adjacent to the copper surface. INTRODUCTION Aluminum alloys can be electrodeposited from chloroaluminate molten salts with the addition of the solute metal ions to the electrolyte. This can be accomplished by either anodic dissolution of the solute metal directly into the melt or by the addition of the appropriate chloride salt. The formation of Al-transition metal alloys is also possible even though the deposition potential of the transition metal may be several hundred millivolts more positive than that of Al. The mechanism leading to the formation of these alloys is a variant of underpotential deposition (UPD) phenomena whereby alloy formation proceeds by co-deposition of Al during the mass-transport-limited electrodeposition of the transition metal. Such interesting alloy formation has been demonstrated for Al-Ni (1) from AlCl3:NaCl electrolyte as well as Al-Ni (2-4), Al-Co (5,6) and Al-Cu (7,8) from the room-temperature chloroaluminates. In this article, we describe the electrodeposition of Cu and the underpotential co-deposition of Al with Cu to form Cu-Al alloys from solutions of Cu(I) in the Lewis acidic AlCl3-MeEtimCl melt. Alloy deposition potentials independently derived from the free energy of alloy formation are compared to those observed experimentally for several aluminum alloy systems. In addition we examine the Proceedings of The Electrochemical Society, PV 1999-41, 535-548 (1999) DOI: 10.1149/199941.0535PV © The Electrochemical Society ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 207.241.231.83 Downloaded on 2019-04-28 to IP