The finding that electrode gap distance is inversely proportional to coating http://www.selleckchem.com/products/CP-690550.html thickness is in line with previous reports which found that when gap between electrodes is narrow the intensity of electric field increases and electrolyte resistance between anode and cathode decrease [10, 12]. These result in increasing metal deposition rate or thicker coating within a certain period of time. This study adds that the relation in particular settings is linear. Regarding the linear effect of deposition time to coating thickness, it is in agreement with Faraday’s law in which deposition rate (or in this case the coating thickness resulted within a certain period) is proportional to the plating current and time [13, 14].3.2. Layer UniformityThe layer thickness variations between the substrate face and its circumference are shown in Figure 5.

The combination between the electrode gaps and plating time used in this study can generate coating layer with up to a maximum of 26.5% thickness variation. The increase of both electrode gap and plating time tend to produce more uniform nickel coating on the hard metal substrate.Figure 5Thickness uniformity versus plating time at various electrode gaps.In developing the empirical model for coating thickness uniformity as function of gap distance and plating time, similar steps used to develop model for coating thickness was employed. A preliminary diagnosis was conducted to determine the appropriate power transformation for the model. This was assessed by diagnosing Box-Cox plot of coating thickness uniformity.

The lowest point of the plot that might result in the minimum residual sum of square in the transformed model (��) was 0.61. Accordingly, a logarithmic transformation (�� = 0) was selected as the closest value to the actual one and as the most appropriate power transformation. Next step was determining the suitable regression model. The probabilistic value, Prob > F, was calculated, and linear model was selected for having the least probabilistic value. Then, analysis of the variance was performed in order to test the significance of the selected regression model and its coefficients (Table 3). In the same way as before, the maximum probabilistic value of 5% was set for the model, and its coefficients were to be considered significant.Table 3Analysis of variance for the coating thickness uniformity.

The empirical model equation which relates coating thickness uniformity (k) to gap distance (d) and plating time (t) was found to beln?k=4.48?0.05d?0.08t.(3)This AV-951 model can be represented by the graph of contours (Figure 6). The model’s high coefficient of determination (R2 = 0.92) and adequate precision (of 14.56) indicated that the model is adequately representative. At any combination of gap distance and plating time, the model’s predicted coating thickness uniformity is within the range of 95% confidence interval.