## 3 Results and Discussion
### Thermal Exposure Test at 180 \({}^{\circ}\)C and Analysis  
After drying at 60 \({}^{\circ}\)C for 4 h, the samples of BPN, boron powder and KNO\({}_{3}\) were placed in a temperature environment testing instrument for a thermal exposure test. The temperature settings were 180 \({}^{\circ}\)C for two and five days. The apparent morphology, DSC parameters, weight loss ratios and output performance of samples before and after the test were compared and analyzed. Apparent Morphology  
The apparent morphologies of KNO\({}_{3}\), boron and 4#BPN samples before and after different temperature storage are shown in Figures 4-6. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **First Endothermic Peak (\({}^{\circ}\)C)** & **Second Endothermic Peak (\({}^{\circ}\)C)** & **Exothermic Peak (\({}^{\circ}\)C)** \\ \hline
1\#BPN (15:85) & 133.6 & 332.0 & 547.4 \\
2\#BPN (25:75) & 134.8 & 331.3 & 534.6 \\
3\#BPN (33:67) & 136.5 & 332.6 & 526.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Peak temperature of DSC with different ratios of BPN. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Samples** & \begin{tabular}{c} **Weight Ratio @** \\ **100 \({}^{\circ}\)C (\%)** \\ \end{tabular} & \begin{tabular}{c} **Weight Ratio @** \\ **200 \({}^{\circ}\)C (\%)** \\ \end{tabular} & \begin{tabular}{c} **Weight Ratio @** \\ **400 \({}^{\circ}\)C (\%)** \\ \end{tabular} & \begin{tabular}{c} **Weight Ratio @** \\ **500 \({}^{\circ}\)C (\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Weight Ratio @** \\ **500 \({}^{\circ}\)C (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Weight Ratio @** \\ **650 \({}^{\circ}\)C (\%)** \\ \end{tabular} \\ \hline
1\#BPN (15:85) & 99.3 & 98.3 & 94.8 & 88.6 & 57.5 \\
2\#BPN (25:75) & 99.9 & 98.5 & 93.2 & 92.7 & 75.7 \\
3\#BPN (33:67) & 100.0 & 99.1 & 97.4 & 94.2 & 72.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Weight statistics of potassium boron nitrate samples at different temperatures. After observing the boron powder, KNO\({}_{3}\) and 4#BPN samples before and after high temperature, it is found that the color of the KNO\({}_{3}\) sample changes slightly from white to yellow, and the particle size and shape do not change. The particle size, shape and color of boron powder and 4#BPN are not observed to change. In addition, there is no change in appearance quality, such as expansion of fractures, loose pits, shrinkage or melting residue. DSC test  
The DSC curves and DSC parameter comparison of 4#BPN sample are given in Figure 7 and Table 5 respectively. Figure 4: The apparent morphology of KNO\({}_{3}\) compared before and after different temperature tests. Figure 5: The apparent morphology of boron compared before and after different temperature tests. Figure 6: The apparent morphology of 4#BPN compared before and after different temperature tests. According to the DSC analysis of the variation of the peak temperature, the temperature difference between the first endothermic peak and the second endothermic peak is very small, comparing the samples at 180 \({}^{\circ}\)C for two days, 180 \({}^{\circ}\)C for five days, and 60 \({}^{\circ}\)C for 4 h; \(\Delta\)T \(<\) 1 \({}^{\circ}\)C. The exothermic peak temperature variations of the samples at two days and five days are \(-\)6.51 \({}^{\circ}\)C and \(-\)2.77 \({}^{\circ}\)C, respectively, but the failure rates of the agents are 1.01% and 3.26%, respectively. This indicates that the exothermic peak temperature of the sample is advanced, but the energy is not consumed. It can be preliminarily concluded that BPN containing KNO\({}_{3}\) and boron powder has good thermal stability at 180 \({}^{\circ}\)C for two days and five days. * Weight loss ratio  
The weight loss ratios of BPN samples in 180 \({}^{\circ}\)C test are given in Table 6. Furthermore, the component variation of BPN samples within 180 \({}^{\circ}\)C test are given in Table 7.  
Figure 7: DSC curves of 4#BPN 60 \({}^{\circ}\)C,4 h samples and 180 \({}^{\circ}\)C samples (heating rate 5 \({}^{\circ}\)C/min).