# Concentration Influence of Complexing Agent on Electrodeposited Zn-Ni Alloy
## 3 Results and Discussion
### Microstructure of Zn-Ni Alloy Coating  
The XRD patterns of Zn-Ni plating layers with different TEPA concentrations and current densities are shown in Figure 2. Only phases of Fe and Zn-Ni alloys were detected from the XRD patterns. Fe phase is reflected at 44, 65, and 83, indicating that the thickness of the Zn-Ni coating was not enough to shield the X-ray signal from the steel substrate. Other visible peaks are from Zn\({}_{11}\)Ni\({}_{2}\) crystalline phase, which is a typical \(\gamma\)-phase crystal structure [32]. The reflection of Zn\({}_{11}\)Ni\({}_{2}\) alloy was at 42.9, 62.4, and 78.7 corresponding to lattice planes of (411), (600), and (721), respectively. It was observed that TEPA concentration and current density mainly influenced the crystal orientation along (411) at 42.9 and (600) at 62.4. Current densities lower than 1 ASD adversely affected crystallization, while a high TEPA concentration of 0.07 M and 0.1 M enhanced the intensity of (411) peak at 0.2 and 0.1 ASD and both intensities of (411) and (600) peak at 0.5 and 1 ASD. At 2 ASD, the (600) orientation was predominant regardless of TEPA concentration. With an increase in current density to 5 ASD, the intensity of (600) peaks decreased, while the intensity of (411) peaks increased will all TEPA concentrations. In conclusion, TEPA concentrations over 0.07 M improved the crystallization of the Zn-Ni alloy phase at low current density but did not have a significant effect on crystallization at high current density over 2 ASD.  
The crystallite size was determined using the Scherrer equation, where \(D=\frac{K\cdot\lambda}{B\text{Coat}}\), with crystallite size (D) in nm, the shape factor (K), X-ray wavelength (\(\lambda\)) of 0.15406 nm for CuK\(\alpha\), full width at half maximum (\(\beta\)) in radians, and peak position (\(\theta\)) in radians (Figure 3). As the (660) peaks were the most well-defined with all current densities, the crystallite size was calculated using full width at half maximum of the (660) peaks. The crystallite size decreased with increasing TEPA concentration until it remained constant at TEPA concentrations greater than 0.07 M. In addition, the increase in current density  
Figure 1: (**a**) Appearance of Zn-Ni alloy coatings obtained by Hull cell test with varying TEPA concentrations, and (**b**) glossiness as a function of current density (A/dm\({}^{2}\)) and TEPA concentration, measured in gloss units (GU).  
induced the decline of crystallite size. The crystallite size with 0.07 M TEPA decreased from 37.5 nm to 12.5 nm when current density increased from 0.1 ASD to 5 ASD.  
Figure 4 shows the morphology of coating at 0.07 M TEPA with different current densities and at 2 ASD with different TEPA concentrations. The surface showed fine, nodular grains with good distribution, and no cracks or defects. The absence of porosity and the dense surface suggested hydrogen desorption during electrodeposition. In the case of 0.07 M TEPA, finer grains were observed at higher current densities. Meanwhile, an increase in TEPA concentration resulted in a finer microstructure of the Zn-Ni coating at 2 ASD, which was constant to what was obtained from crystallite size. It appeared that when the decrease in grain size caused by increasing TEPA concentration induced the increase in glossiness (Figure 1b), which agreed with previous studies [33].  
Figure 2: XRD patterns of Zn-Ni alloy coatings with different TEPA concentrations at (**a**) 5 ASD, (**b**) 2 ASD, (**c**) 1 ASD, (**d**) 0.5 ASD, (**e**) 0.2 ASD, and (**f**) 0.1 ASD.  
Figure 3: _Cont_.