Alloy composition mass transport coupled

Moffat [80] reported the electrodeposition of Ni-Al alloy from solutions of Ni(II) in the 66.7 m/o AlCl3-NaCl melt at 150 °C. The results obtained in this melt system are very similar to those found in the AlCh-EtMcImCI melt. For example, Ni deposits at the mass-transport-limited rate during the co-deposition of Al, and the co-deposition of Al commences several hundred millivolts positive of the thermodynamic potential for the A1(III)/A1 couple. A significant difference between the voltammetric-derived compositions from the AlCl3-NaCl melt and AlCl3-EtMeImCl melt is that alloy composition is independent of Ni(II) concentration at the elevated temperature. Similar to what has been observed for room-temperature Cu-Al, the rate of the aluminum partial reaction is first order in the Ni(II) concentration. Moffat s... 

NiCit] to the cathode surface. Because the deposition rate of the two metals is coupled, the alloy composition does not vary with rotation rate. In contrast, if the concentration of Ni in solution is comparable to or higher than that of MoO4 , the rate of formation of the Ni-Mo intermediate is limited by the transport of molybdate, while Ni can be deposited in parallel—its rate of deposition being independent of the rate of mass transport. Increasing either the rotation rate or the molybdate concentration—the partial current density of Mo deposition will also increase, while that of Ni deposition will not be affected. Thus, it was proven beyond any doubt that the induced codeposition of Mo with Ni and other iron-group metals was dependent on the existence of the iron-group metal ions in solution. 

For the present system the magnitudes of the calculated effective diffu-sivity, taking account of volume and composition constraints, do not differ by large factors from the diffusivity of aluminum in nickel. In order to test the coupled diffusional analysis it would be desirable to increase the aluminum concentration sufficiently and suppress the oxygen solubility in nickel. According to theoretical predictions the effective diffusivity for the mass transport process should then approach that of oxygen in nickel. Similar experiments with Ni-Al alloys as the metal phase are reviewed elsewhere ( ). 

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See also in sourсe #XX -- [ ]

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