The effects of a superimposed magnetic field B on the structure of nickel electrodeposits prepared from a quiescent Watts solution were studied by scanning electron microscope and transmission electron microscopy investigations. It was observed that B can induce a change of the surface morphology and of the preferential growth direction of the nickel grains. In the absence of organic inhibitor, it is shown that these effects result from an inhibition of nickel electrocrystallization in relation to the mass‐transport enhancement of ions promoted by the magnetic field. The phenomenon is much more important in the presence of a strong inhibitor such as 2‐butyne‐1,4‐diol, the activity of which is also under mass‐transport limitation. The presence of the magnetically induced convective flow is directly illustrated by the perturbations of the relief of the deposit in the vicinity of attached bubbles. These results demonstrate that most structural modifications of nickel electrodeposits observed in the presence of a magnetic field are consequences of convection phenomena induced by a magnetohydrodynamic effect.

The effect of uniform, vertically oriented high magnetic fields up to <mml:math display="inline"><mml:mrow><mml:mn>13</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">T</mml:mi></mml:mrow></mml:math>13T on the electrodeposition of Co has been investigated in dependence on the cell and electrode geometry as well as the orientation and strength of the magnetic flux density by means of cyclic voltammetry, chronoamperometric measurements, and atomic force microscopy investigations. In the majority of cases, the limiting current density <mml:math display="inline"><mml:msub><mml:mi>i</mml:mi><mml:mi>lim</mml:mi></mml:msub></mml:math>ilim increases with increasing magnetic flux densities independent of the cell geometry and orientation. The current efficiency of Co increases with increasing magnetic flux densities only in magnetic fields aligned parallel to the electrodes due to the magnetohydrodynamic (MHD) effect. The morphology of the deposits exhibits randomly oriented round-shaped grains. The electrochemical behavior of horizontal electrodes with magnetic fields oriented perpendicular to the surface is strongly dependent on the electrode geometry. The current efficiency of the Co deposition on flat electrodes increases for low magnetic flux densities and keeps constant for high magnetic fields. In contrast, for wall electrodes the current efficiency decreases strongly even for low magnetic fields. These results are caused by overlapping effects of two types of convection, macro-MHD- and micro-magneto convection due to gradients of the concentration and the magnetic susceptibility. This leads to a modified morphology.

A very recent paper, referred to below as Paper I, had been devoted to the description of magnetic field effects on the structural features of nickel electrodeposits grown from a Watts solution, either pure or in the presence of small amounts of a primary brightener and leveling agent such as 2‐butyne‐1,4‐diol (BD). The conclusions of Paper I stressed the major effect of the magnetic field which was supposed to come down to a magnetohydrodynamic forced convection close to the cathodic interface. This convection enhances those among the cathodic reactions which are likely to be mass‐transport controlled, which is the case for the hydrogen electrode reaction as well as for the catalytic hydrogenation undergone by BD on the cathodic surface. The aim of this paper is to describe the results of electrochemical studies which have been carried out with the same system so as to check the validity of our assumption.