Due to the nature of the process, obtaining high degree of coating uniformity via electroplating technique is practically difficult. The ability of producing uniform coating thickness over a surface by electroplating process is associated with current distribution on that surface [1]. Current distribution is usually determined by the shape of cell assay the surface and its relative position with respect to the anode [15]. Edges and recesses on a surface often receive more current and this consequently results in thicker deposits on them [16]. Placing the electrodes at an adequate distance relative to one another might reduce the thickness variation of an electroplated coating by making the current distribution on the surface to be nearly uniform [10].This study, in which 3% to 26.

5% layer thickness variations were obtained, found that the nickel coating was more uniform when the hard metal substrate is placed at longer distance from the anodes. The result is in good agreement with a previous report that found that short electrode gap produces high offset voltage which causes larger current to be concentrated at the edges and the corner of the electrode [10]. Under this condition, reduction of reactant on the electrode surface is faster, and variation in reactants diffusion between the electrode edges and center region surface could increase [10]. When the distance between electrodes is increased the offset set voltage decreases and plating current lowers. Consequently, the current distribution at the surface area is improved [10].

Electroplating duration is also believed to have a positive effect in acquiring uniform distribution of the coating over the substrate surface. The result obtained from this study showed that plating time is significant in producing uniform coating thickness distribution. This could be explained by the fact that deposited atoms occupy the defect sites (edges, corners, steps, and kinks) on substrate surface after either direct or lateral diffusion. When atoms reach the defected sites they start to back themselves in the form of atoms lines across the substrate surface forming the crystalline structure of the deposit [17]. This action mainly depends on local lattice energy (incorporate more atoms to metal matrix at the cathode) and the plating time, as short time does not allow the completion of this deposition mechanism and could be the reason for nonuniform coating distribution.

3.3. Optimum ConditionGenerally, nickel coating for Entinostat industrial applications must be obtained with an acceptable degree of quality and uniformity. The empirical model developed here revealed the possibility of producing electroplated layer thickness with minimum degree of nonuniformity along the substrate surfaces by setting the electrode gap and plating time. In practice, it is difficult to obtain 100% uniform electroplated coating over a surface.