# Studies on Influencing Factors of Ammonium
## 3 Results and Discussion  
### Influence of NH\({}_{3}\) (wt %)  
The NH\({}_{4}\)ReO\({}_{4}\) crystals were crystallized at the same centrifugal rate and temperature (25 \({}^{\circ}\)C), but different amounts of aqueous ammonia were added. The relationship between purity, aging time, and amount of aqueous ammonia is shown in Figure 1. \begin{table}
\begin{tabular}{c c c c} \hline
**NH\({}_{3}\) (wt \%)** & **NH\({}_{4}\)ReO\({}_{4}\) (V/mL)** & **Centrifugal Speed (rmp)** & **T (\({}^{\circ}\)C)** \\ \hline
1 & 1000 & 1000 & 25 \\
5 & 1000 & 1000 & 25 \\
10 & 1000 & 1000 & 25 \\
15 & 1000 & 1000 & 25 \\
20 & 1000 & 1000 & 25 \\
10 & 1000 & 1500 & 25 \\
10 & 1000 & 2000 & 25 \\
10 & 1000 & 4000 & 25 \\ \hline \end{tabular}
\end{table} 
Table 1: Experimental parameters at different experimental conditions. Figure 1: NH\({}_{3}\) (wt %)—conversion relation of crystallization time and purity. It was found that crystallization time decreased with the increase of aqueous ammonia; however, the amount of aqueous ammonia had a smaller influence on the purity of NH\({}_{4}\)ReO\({}_{4}\), as shown in Figure 1. When the amount of aqueous ammonia was 1-5%, the result did not have research significance, because the crystallization time reached 48 h, which consumed excessive energy. When the amount of aqueous ammonia was 10%, the NH\({}_{4}\)ReO\({}_{4}\) particles formed many complete rhombic crystals; the surface structure of these crystals was smooth, as shown in Figure 2a. This suggests that the NH\({}_{4}\)ReO\({}_{4}\) particles combined compactly and the surface structure of these crystals grew integrated. When the amount of aqueous ammonia was 15%, the crystallization time reduced from 24 h to 20 h and many NH\({}_{4}\)ReO\({}_{4}\) particles formed near spherical crystals; the surface structure of these crystals was coarse, as shown in Figure 2b. This suggests that the combination of NH\({}_{4}\)ReO\({}_{4}\) particles was insufficient and the surface structure of these crystals grew half-baked. The reason for that phenomenon is that the increase of ammonia ion promotes reverse dissolution equilibrium, which breaks between crystal nucleus growth and crystal growth. This means that the growth rate of NH\({}_{4}\)ReO\({}_{4}\) crystals is too fast and therefore the growth is incomplete. When the amount of aqueous ammonia was 20%, the crystallization time reduced to 18 h and the NH\({}_{4}\)ReO\({}_{4}\) particles formed many large agglomerated crystals, as shown in Figure 2c. The reason for that phenomenon is that the increase of ammonia ion promotes further reverse dissolution equilibrium. The growth of crystal nucleus is incomplete, while the growth rate of NH\({}_{4}\)ReO\({}_{4}\) crystals is too fast. The XRD patterns of the samples with different amounts of aqueous ammonia are shown in Figure 3, and the XRD information is given in Table 2. The main diffraction peaks of ammonium rhenate and other crystal items were not observed. When the amount of aqueous ammonia was 10%, characteristic peaks in the XRD patterns were the highest, full width at half maximum (FWHM) was minimal, and relative crystallinity [14] was the ideal. If the relative crystallinity of the samples prepared  
Figure 2: SEM images of NH\({}_{4}\)ReO\({}_{4}\) particles at different NH\({}_{3}\) wt %: (**a**) NH\({}_{3}\) 10 wt %, (**b**) NH\({}_{3}\) 15 wt %, (**c**) NH\({}_{3}\) 20 wt %. at NH\({}_{3}\) 10 wt % is treated as 100%, according to the amorphization formula A = (1 - Area\({}_{\rm x}\)/ Area\({}_{0}\)) \(\times\) 100%, the relative crystallinity of the samples at NH\({}_{3}\) 15 wt % and NH\({}_{3}\) 20 wt % is 63.9% and 50.5%. According to Table 2, the selectivity of crystal growth direction on (101) crystal plane and (112) crystal plane at different aging times can be calculated by the Scherrer formula, D = K\(\lambda\)/(B cos \(\theta\)), and the results are given in Table 3. From Table 3 it can be seen that with increased ammonia content, the growth of (101) crystal plane and (112) crystal plane was restrained.