## 2 Materials and Methods
### Material Characterization  
Figure 4 shows that the particle size of the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor prepared with the three methods was about 40 \(\upmu\)m. Figure 4c shows the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor prepared with the WCSC method. Compared to the original MSA, the composited inhibitor was fully coated, and the pores of the MSA were coated and filled up by NaHCO\({}_{3}\); Figure 4d shows the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor prepared with the DCBM method. There were a few pores on its surface, but the product was well-coated at large; Figure 4e shows the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor prepared with the DCAI method. There were many pores on its surface, and these were obviously filled by NaHCO\({}_{3}\). Accordingly, the SEM diagrams show that the composite powder explosion inhibitor prepared with the WCSC method was the most efficacious. Table 3 shows that the specific surface areas and pore volumes of the three kinds of MSA-NaHCO\({}_{3}\) composite powder explosion inhibitors were smaller than those of MSA, because NaHCO\({}_{3}\) could be effectively compounded to MSA after the compounding process. As shown in Figure 5, the nitrogen adsorption-desorption isotherm curve of MSA shows an IV-H2(a) hysteresis loop in IUPAC classification, indicating that MSA has relatively uniform pores [25; 26]. The WCSC-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor presents a type III isothermal curve. Combined with Figure 4 (SEM), it can be seen that the WCSC-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor was a non-porous material. The isotherm curve of DCBM-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor shows an IV-H2(a) hysteresis loop. In comparison with the III curve of the WCSC-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor, DCBM-MSA-NaHCO\({}_{3}\) contained a certain amount of pores and its composite effect was relatively poor. The SEM analysis revealed that this method could still achieve an ideal composite state. The nitrogen adsorption-desorption isothermal curve of DCAI-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor is characterized by an IV-H3 type hysteresis loop in IUPAC classification, which indicates a flat slit structure, cracks, and wedge structures, as well as broader hysteresis loops compared to the isothermal curve of the DCBM-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor [27]. Considered in tandem with the results in Figure 4 (SEM), it can be concluded that the composite powder produced by DCAI method was less efficacious than the DCBM method. Figure 3: The DCAI compounding method. Figure 4: SEM images of MSA–NaHCO\({}_{3}\) composite powder explosion inhibitors prepared with three preparation methods: (**a**). NaHCO\({}_{3}\); (**b**). MSA; (**c**). WCSC-MSA–NaHCO\({}_{3}\); (**d**). DCBM-MSA–NaHCO\({}_{3}\); (**e**). DCAI-MSA–NaHCO\({}_{3}\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **Specific Surface Area (m\({}^{2}\)/g)** & **Pore Capacity (cm\({}^{3}\)/g)** \\ \hline MSA & 567.6321 & 0.416673 \\ WCSC-MSA–NaHCO\({}_{3}\) & & \\ composite powder & 68.4097 & 0.198494 \\ explosion inhibitor & & \\ DCBM-MSA–NaHCO\({}_{3}\) & & \\ composite powder & 90.0693 & 0.126428 \\ explosion inhibitor & & \\ DCAI-MSA–NaHCO\({}_{3}\) & & \\ composite powder & 220.8976 & 0.288409 \\ explosion inhibitor & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analysis of specific surface area and pore volume of composite powder explosion inhibitors. From the preparation principle of the three preparation methods, the following conclusions could be drawn: the advantages of the WCSC method are that the supporter can fully enter the pores of the carrier and the composite effect is better. The disadvantage is that the supporter must be easily soluble, which limits many insoluble carriers with good performance. The DCBM and DCAI methods lead to the compounding of more carriers and supporters.