## 2 Review of Influence of Sensitizers on Detonation Properties of Emulsion Explosives
### Addition of Substances with Very Low Bulk Density
The matrix was sensitized with GMs and their mixtures with TiH\({}_{2}\) and titanium. GMs had a bulk density of 0.25 g/cm\({}^{3}\) with an average grain size of 55 \(\upmu\)m. In contrast, the other additives had significantly higher bulk densities of 3.91 g/cm\({}^{3}\) (TiH\({}_{2}\)) and 4.5 g/cm\({}^{3}\) (Ti), and average grain sizes of 48 \(\upmu\)m. Underwater energy, detonation velocity, and aggregability were determined for the EEs tested. In the underwater test, [PERSON] et al. [PERSON] _et al._ (2018) detonated EE charges of 10 g. In the first phase of their tests, they determined the pressure changes (\(p\)) at time (\(t\)) for mixtures containing different amounts of GMs (Figure 2). They obtained a maximum pressure value of 20.58 MPa at a GM content of 4%, which was used in the subsequent EEs tested. They then determined \(p=\) f(t) for EEs containing different amounts of TiO\({}_{2}\) (Figure 3, Table 6). The estimation of shock wave energy, gas bubble energy, and total energy (Figure 4) was estimated according to the methodology presented in the paper [PERSON] _et al._ (2018); [PERSON] _et al._ (2018). For the two selected \begin{table}
\begin{tabular}{c c c c} \hline \hline
**GMs Size [\(\upmu\)m]** & **GMs Content [\%]** & **Density [g/cm\({}^{3}\)]** &
\begin{tabular}{c} **Detonation** \\ **Velocity [m/s]** \\ \end{tabular} \\ \hline \multirow{4}{*}{153} & 5.359 & 0.909 & 3891 \\  & 3.874 & 1.003 & 4218 \\  & 2.135 & 1.100 & 4214 \\  & 1.724 & 1.210 & 3754 \\ \hline \multirow{4}{*}{108} & 8.985 & 0.900 & 3837 \\  & 6.645 & 0.998 & 4165 \\  & 4.586 & 1.103 & 4374 \\  & 3.014 & 1.202 & 4120 \\ \hline \multirow{4}{*}{82} & 9.916 & 0.895 & 3779 \\  & 8.289 & 0.992 & 4203 \\  & 5.870 & 1.097 & 4551 \\  & 3.876 & 1.205 & 4615 \\ \hline \multirow{4}{*}{64} & 11.972 & 0.891 & 3781 \\  & 9.030 & 0.999 & 4244 \\ \cline{1-1}  & 6.544 & 1.112 & 4695 \\ \cline{1-1}  & 4.321 & 1.204 & 4711 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: EEs’ detonation velocities as a function of GM content and dimensions [PERSON] _et al._ (2017). These results show that at a certain content of T\({}_{\text{i}}\)H\({}_{2}\), the EEs have higher parameters (maximum shock wave pressure, explosion energy, detonation velocity, and brisance) than EEs sensitized with GMs alone. In contrast, the addition of titanium powder causes a decrease in maximum shock wave pressure and a slight increase in explosion energy compared to EEs sensitized with GMs alone. These results may suggest that hydrogen generated by the decomposition of T\({}_{\text{i}}\)H\({}_{2}\) is involved in the chemical reactions of the detonation wave. CSs formed during the combustion of lignite coal are another additive studied in terms of EE sensitization. They have a higher bulk density (0.3 g/cm\({}^{3}\)) than typical GMs. In the work of [PERSON] et al. [34], the same qualitative dependence of the critical diameter of detonation on CS content was obtained as in the work [30] for GMs. However, the determined critical detonation diameter was much higher (16 mm) and occurred at a higher sensitizer content (18%). The results of studies of the effect of the content and dimension of CSs on the detonation parameters of EEs are presented in works [35; 36]. [PERSON] et al. [35] tested EEs with matrices containing ammonium nitrate (76.9%), industrial oil (6.9%), emulsifier (1%), and water (15.3%), sensitized with CSs of several grain sizes and differing in bulk density. The dependence of the detonation velocity on the grain size of CSs is illustrated in Figure 4 [35]. A maximum value of the velocity of detonation of 5.5-5.6 km/s was obtained, in charges of 55 mm in diameter, for a narrow fraction of CSs with sizes in a range from 70 to 100 \(\upmu\)m (bulk density of 0.36 g/cm\({}^{3}\)) and an EE density of 1.18-1.20 g/cm\({}^{3}\). The mass content of CSs was 8-10%. The critical diameter was 35-40 mm. Increasing the size of CSs to 200 \(\upmu\)m resulted in a decrease in the velocity of detonation by 1.0-1.3 km/s.