## 2 Materials and Methods
### Compounding  
According to the literature [20; 21; 22; 23; 24], at present, two methods are generally adopted for material compounding. One is the reverse osmosis method, and the other is the mechanical compounding method. In this study, three methods--the solvent-crystallization wet coating (WCSC), ball milling dry coating (DCBM), and air impact dry coating (DCAI) methods--were used for the comparative preparation of slag-based composite powder explosion inhibitors, and the method with the best composite effect was selected for further study. Slag-based composite powder explosion inhibitors were prepared using each of these three methods and were named as Table 2.  
First of all, MSA-NaHCO\({}_{3}\) composite powder explosion inhibitors were prepared by using the solubility difference between H\({}_{2}\)O and C\({}_{2}\)H\({}_{6}\)O, namely by WCSC, as shown in Figure 1. First, 100 g of MSA were added to 150 mL of C\({}_{2}\)H\({}_{6}\)O, and the mixture was stirred with a magnetic stirrer. Next, 9.6 g of NaHCO\({}_{3}\) were dissolved in 100 mL of deionized water (at a temperature of 30 \({}^{\circ}\)C) to form an NaHCO\({}_{3}\) saturated solution, which was then slowly and uniformly added into the suspension of MSA-C\({}_{2}\)H\({}_{6}\)O (at a temperature of 30 \({}^{\circ}\)C and speed of 700 r/min). Then, 150 mL of C\({}_{2}\)H\({}_{6}\)O were added until the NaHCO\({}_{3}\) crystal was completely precipitated from the surface of the slag matrix. After ultrasonic dispersion for 30 min, the precipitate was filtered out, dried in a vacuum oven for 24 h, and then ground into MSA-NaHCO\({}_{3}\) composite powder explosion inhibitors with the same grain size (\(<\)75 \(\upmu\)m). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Method** & **Process Name** & **Inhibitor Name** \\ \hline Solvent-crystallization & Slag-based-NaHCO\({}_{3}\) & WCSC-MSA–NaHCO\({}_{3}\) \\ wet coating & composite powder & composite powder \\  & explosion inhibitor & explosion inhibitor \\  & Slag-based-NaHCO\({}_{3}\) & DCBM-MSA–NaHCO\({}_{3}\) \\ Ball milling dry coating & composite powder & composite powder \\  & explosion inhibitor & explosion inhibitor \\  & Slag-based-NaHCO\({}_{3}\) & DCAI-MSA–NaHCO\({}_{3}\) \\ Air impact dry coating & composite powder & composite powder \\  & explosion inhibitor & explosion inhibitor \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Name list. Figure 1: The WCSC compounding method. The process flowchart of DCBM is shown in Figure 2. During preparation, the powders of both components were fully ground, and they were embedded and coated with each other under friction and extrusion. The carrier was then embedded into the pores of the supporter and coated over the supporter. DCBM was carried out with the following procedure. First, the particle size of NaHCO\({}_{3}\) was controlled at below 5 \(\upmu\)m with the ball milling screening method. MSA and NaHCO\({}_{3}\) were placed in a vacuum drying oven and dried at 30 \({}^{\circ}\)C for 12 h. Next, 100 g of MSA and 100 g of NaHCO\({}_{3}\) were weighed, placed together into the steel tank, and ground at 500 r/min for 5 min. Then the finished product was taken out, and the excess NaHCO\({}_{3}\) was screened out through a 10 \(\upmu\)m sieve to yield the DCBM-MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor. Samples from the first and second operations were disposed as waste from machine washing; that from the third operation was used as the finished product. The process flowchart of DCBM is shown in Figure 3. Under the intense impact of high-speed air flow, particles of the two components of the composite inhibitor rubbed and collided with each other, and they were coated on each other under mechanical impact. DCAI was carried out with the following procedure. First, the particle size of NaHCO\({}_{3}\) was controlled at below 5 \(\upmu\)m with ball milling and screening.