# Studies on Influencing Factors of Ammonium
## 3 Results and Discussion
### Influence of Centrifugal Speed  
The ammonium rhenate was crystallized with the same amount of aqueous ammonia and at the same centrifugal temperature (25 \({}^{\circ}\)C) but at different centrifugal speeds. The relationship between purity, aging time, and centrifugal speed is shown in Figure 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Concentration of NH\({}_{3}\)** & **FWHM (101\({}^{\circ}\))** & **FWHM (112\({}^{\circ}\))** & **Area (101\({}^{\circ}\))** & **Area (112\({}^{\circ}\))** \\ \hline
10 wt \% & 0.1181 & 0.1375 & 4564.15 & 6100.02 \\
15 wt \% & 0.1376 & 0.1406 & 3663.07 & 3156.45 \\
20 wt \% & 0.1378 & 0.1574 & 2289.86 & 3091.68 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: XRD information of NH\({}_{4}\)ReO\({}_{4}\) crystals at different NH\({}_{3}\) wt %. FWHM, full width at half maximum. Figure 3: XRD patterns of NH\({}_{4}\)ReO\({}_{4}\) crystals at different NH\({}_{3}\) wt %: (**a**) 10%, (**b**) 15%, (**c**) 20%. It was found that crystallization time decreased with increased centrifugal speed, as shown in Figure 4. Moreover, the purity of NH\({}_{4}\)ReO\({}_{4}\) was 98.5% at centrifugal speeds of 500-1000 rpm; when centrifugal speed was higher than 1000 rpm, the purity of NH\({}_{4}\)ReO\({}_{4}\) began to decrease. Therefore, centrifugal speeds above 1500 rpm have no significance. When centrifugal speed was 500 rpm, the NH\({}_{4}\)ReO\({}_{4}\) particles formed many large agglomerated crystals, as shown in Figure 5a. Since the NH\({}_{4}\)ReO\({}_{4}\) particles could not collide or break into the secondary nucleation stage at low centrifugal speed, the particles gathered together and formed large agglomerated crystals under Van der Waals force. When centrifugal speed was 1000 rpm, the NH\({}_{4}\)ReO\({}_{4}\) particles formed many complete rhombic crystals, as shown in Figure 5b. This suggests that the large particles collided and broke into the secondary nucleation stage at an appropriate centrifugal speed; the particles gathered together and formed integrated crystals. When centrifugal speed was 1500 rpm, the NH\({}_{4}\)ReO\({}_{4}\) particles formed many smaller rhomboid crystals, as shown in Figure 5c. The reason is that the larger particles collided and broke into secondary, and the secondary nucleation became the main source of nucleation in the system at an excessive centrifugal speed. Due to the excessive speed, the crystals broke up into many smaller crystals before they grew, and the collision probability and intensity increased, which enhanced the growth rate of the crystals and caused the formation of many smaller crystals. The XRD patterns of the samples at different centrifugal speeds are shown in Figure 6, and the XRD information is given in Table 4. It was found that the main diffraction peaks were ammonium rheate, and other crystal items were not observed. When the centrifugal speed was 1000 rpm, the characteristic peaks in the XRD patterns were highest, FWHM was minimum, and relative crystallinity was the ideal. If the relative crystallinity of the samples prepared at 1000 rpm was treated as 100%, according to the amorphization formula A = (1 \(-\) Area\({}_{\rm x}\)/Area\({}_{\rm 0}\)) \(\times\) 100%, the relative crystallinity of the samples at 500 rpm and NH\({}_{3}\) 1500 rpm was 69.2% and 47.8%. According to Table 4, the selectivity of crystal growth direction on (101) crystal plane and (112) crystal plane at different centrifugal speeds can be calculated by the Scherrer formula, D = K\(\lambda\)/(B cos \(\theta\)), and the results are given in Table 5. From Table 3 it can be seen that the growth of (101) crystal plane and (112) crystal plane was promoted at an appropriate centrifugal speed, and was promoted with increased ammonia content. Figure 4: Centrifugal speed—conversion relation of crystallization time and purity. Figure 5: SEM images of NH\({}_{4}\)ReO\({}_{4}\) particles at different centrifugal speeds: (**a**) 500 rpm, (**b**) 1000 rpm, (**c**) 1500 rpm.