## 3 Results and Discussion  
### Thermal Analysis of Single Component  
The TG process of boron was studied with a nitrogen atmosphere. As shown in Figure 2, a weight loss of approximately 3.3% is observed from heating to 117.5 \({}^{\circ}\)C, which reflects the loss of moisture and volatiles in boron powder. Until 500 \({}^{\circ}\)C, the quality of boron powder samples increases gradually, and the speed increases after 650 \({}^{\circ}\)C. The total mass increases to approximately 118% at 1000 \({}^{\circ}\)C. It is speculated that the reaction in this stage is the slow reaction of boron powder and nitrogen, and the final product is BN. The reaction equation is  
\[2\text{B}+\text{N}_{2}=2\text{BN}, \tag{1}\]  
The DSC curve of KNO\({}_{3}\) has two endothermic peaks. The first endothermic peak (peak temperature 132.6 \({}^{\circ}\)C) corresponds to the conversion temperature of KNO\({}_{3}\), which is the phase transition of KNO\({}_{3}\) from rhombic to trigonal. The second endothermic peak (peak temperature 332.0 \({}^{\circ}\)C) corresponds to the melting point of KNO\({}_{3}\). [9] The DSC curve shows that the decomposition of KNO\({}_{3}\) occurs at more than 500 \({}^{\circ}\)C. Combined with the TG curve, the mass change of KNO\({}_{3}\) is 5.1% at 545 \({}^{\circ}\)C, indicating that KNO\({}_{3}\) is melting but is not decomposed or gasified from the melting point (332.0 \({}^{\circ}\)C) to the temperature of 500 \({}^{\circ}\)C. Therefore, the physical stability of KNO\({}_{3}\) changes within the temperature range of 332-500 \({}^{\circ}\)C, but the chemical stability is not affected.  
A weight loss of KNO\({}_{3}\) of 88.1% mainly occurred between 545 \({}^{\circ}\)C and 765 \({}^{\circ}\)C. According to [PERSON] [17], the decomposition of KNO\({}_{3}\) took place at this stage, generating nitrite, followed by the  
\begin{table}
\begin{tabular}{c l} \hline \hline
**Analysis Method** & **Content** \\ \hline Thermogravimetry & Measure the weight of loose sample before and after high temperature test with precision balance. \\ Appearance & Scanning microscope, optical digital microscope used to observe the color, \\  & particle size, etc. \\ DSC analysis & Analyze the initial decomposition temperature and peak decomposition \\  & temperature of samples. \\ Content analysis & Ion exchange method for determination of KNO\({}_{3}\) contentMannitol complex \\  & titration method for determination of boron. \\ output performance & P-t curve pressure peak and rise time to evaluate the power capacity of samples. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Analysis methods for BPN thermal analysis and high temperature stability analysis.  
Figure 2: **(a)** Thermogravimetric-Differential Scanning Calorimetry (TG-DSC) curve of boron powder; **(b)** TG-DSC curve of KNO\({}_{3}\) (in nitrogen atmosphere).  
decomposition reaction of potassium nitrite, and the product K\({}_{2}\)O was reported to evaporate (m.p. 380 \({}^{\circ}\)C) [10]. The equation of weightlessness in this stage is [8]  
\[2\text{KNO}_{3}\to 2\text{KNO}_{2}+\text{O}_{2}, \tag{2}\]  
\[4\text{KNO}_{2}\to 2\text{K}_{2}\text{O}+4\text{NO}+\text{O}_{2}, \tag{3}\]  
Compared with the operating condition of 180 \({}^{\circ}\)C, the melting temperature of KNO\({}_{3}\) at 336.5 \({}^{\circ}\)C is about 156 \({}^{\circ}\)C higher. No obvious chemical reaction occurs before the peak temperature of decomposition (i.e., more than 545 \({}^{\circ}\)C). It can be qualitatively concluded that the boron powder and KNO\({}_{3}\) components are stable at a high temperature of 180 \({}^{\circ}\)C. It should be noted that this result is obtained according to the reaction temperature of DSC, and the stability of samples at constant temperature needs to be verified.