The Electrodeposition of an Aluminum‐Manganese Metallic Glass from Molten Salts

Abstract

The electrodeposition of binary aluminum-manganese alloys from chloroaluminate molten salts is reported. The manganese content of the electrodeposit varies from 7 to 30 w/o and is dependent upon deposition potential and the relative concentrations of A12C17 and Mn++ in the melt. At small cathodic overpotentials the deposition process, with respect to alloy composition, is kinetically controlled. At larger cathodic overpotentials, it becomes mass transport limited in Mn + § and then A12C17-. The most uniform and brightest deposits are obtained at a constant potential of -0.3V with respect to an aluminum wire in the same electrolyte. The potential dependence of alloy composition allows one to create homogeneous, graded and modulated structures from a single electrolyte. The structure of the as-deposited alloy appears to be that of a metallic glass above 27 w/o manganese and a mixture of glass and supersaturated aluminum below 27 w/o. Heating to 400~ converts the deposit containing less than 26 w/o Mn to a mixture of the orthorhombic A16Mn intermetallic and aluminum. The ability to electrodeposit intermetallic compounds on a near atomic scale presents interesting possibilities for high temperature alloys.

Electrodeposited Al–Mn alloys with microcrystalline, nanocrystalline, amorphous and nano-quasicrystalline structures

“…Stafford carried out linear sweep voltammetry in a 2:1 mole ratio AlCl 3 -NaCl electrolyte and found that as the content of MnCl 2 in the electrolyte increases, the cathodic overpotential becomes more negative [7]. A similar trend was also observed in AlCl 3 -NaCl-KCl electrolyte by Hayashi [40].…”

“…Interestingly, a great many of these phases can be produced by a single technique, i.e. electrodeposition from acidic chloroaluminate salts [1][2][3][4][5][6][7][8][9][10][11][12][13]. While phases predicted by the equilibrium phase diagram have been electrodeposited in the temperature range of 250-425°C [6,8], non-equilibrium phases, such as the quasicrystalline phases, amorphous phase and supersaturated face-centered cubic (fcc) phase, have been deposited at lower temperatures from 150 to 325°C [3,4,6,7,[9][10][11].…”

“…Despite the significant number of works conducted on electrodeposited Al-Mn alloys [2][3][4][5][6][7][8][9][10][11][12][13][14], only a few studies have provided detailed characterization of the deposited structure. In 1966, Read and Shores presented transmission electron diffraction patterns of Al-Mn alloys electrodeposited from a chloroaluminate molten salt electrolyte (AlCl 3 -KCl-NaCl-MnCl 2 ), presumably at 200°C [10].…”

Electroplating of Amorphous Aluminum-Manganese Alloy from Molten Salts.

“…(a) [Mn2+]=0mass'/., AH=2.1x 104J/mol (b) [Mn2+]=0.3mass"/., AH=5.1x 104J/mol (c) The excess Cl~which is formed on the cathode surface by reactions (5) and (6) deposits as the solid NaCl or KCI if it does not quickly form AICl~according to the reaction (4 Therefore, it is necessary that the electrodeposition proceed by the reaction (7). ExcessC1-should be removed from the cathode surface by the reaction (4) even if the electrodeposition proceeds by the reaction (5) or (6 between amorphousstructure and fine crystalline structure. As is shown in Fig.…”

Electrodeposition of Al, Mn, and Al–Mn Alloy on aluminum electrodes from molten salt (AlCl3–NaCl–KCl)

“…Stafford [21] has studied the co-deposition of Al-Mn in a acidic chloroaluminate molten salt at 150°C where it is claimed that deposition of Mn occurs cathodic of the deposition of Al 2 Cl 7 -species on account of no peak appearance. The onset of co-deposition has been reported to be at -0.3 V/Al.…”