## 2 Review of Influence of Sensitizers on Detonation Properties of Emulsion Explosives
### Addition of Substances with Very Low Bulk Density  
Dosing substances containing occluded air or other gases is another method of reducing the density of the matrix, causing an increase in its detonation ability. Several materials may be used, including glass or plastic microspheres, cenospheres (CSs), glass or polystyrene beads, glass capillaries, and various grades of perilites. The addition of GMs as sensitizing agents for EEs was already proposed in the first patents for EEs, such as those of EE inventors [PERSON] [19] and [PERSON] [20]. Detailed results on the effect of the content and dimensions of GMs on the detonation velocity of EEs have been reported by [PERSON] and [PERSON] [21] and in [PERSON]'s monograph [22]. The EEs tested in the paper [21] contained ammonium nitrate (66.91%), calcium nitrate (14.59%), water (12.0%), light mineral oil (5.0%), and the emulsifier SPAN 80 (1.5%). They were sensitized with QCel GMs made by the PQ Corporation. The cracked GMs were separated with isopropyl alcohol. The results of detonation velocity tests in 23.6 mm diameter charges are summarized in Table 5. The study [21] was conducted on EEs containing glass microspheres with diameters of 33 \(\upmu\)m, 54 \(\upmu\)m, and 125 \(\upmu\)m. It was found that as the size of the glass microspheres increased, the detonation velocity decreased. The maximum detonation velocities recorded were 4620 m/s (125 \(\upmu\)m), 5260 m/s (54 \(\upmu\)m), and 5500 m/s (33 \(\upmu\)m). Additionally, with decreasing microsphere size, these maximum velocities were observed at progressively higher densities--1.15 g/cm\({}^{3}\), 1.24 g/cm\({}^{3}\), and 1.27 g/cm\({}^{3}\), respectively. From the data presented in Table 5, it can be seen that the dimensions of GMs have a significant effect on the detonation speed of EEs. Moreover, the sensitizer content, by adjusting the density, is the main factor determining the detonation velocity of EEs. The density dependence of the detonation velocity is of the same nature for EE as for other ammonium-salt explosive mixtures not sensitized with individual explosives. With increasing density, the detonation velocity initially increases until it reaches a maximum, and then decreases until the detonation process disappears. A similar characteristic of dependence of the detonation velocity on GM content was observed by [PERSON] et al. [PERSON] _et al._ (2017). According to the breakdown proposed by [PERSON] (1984) under experimental conditions, EEs behave like secondary explosives (e.g., ammonium nitrate (V), ammonium chlorate (VII), dinitrotoluene), defined as \"non-ideal\". The non-ideality of EEs sensitized with microspheres is further supported by the relationship between the critical diameter and GM content [PERSON] _et al._ (2017). As the GM content increases, the critical diameter initially decreases, reaching a minimum, after which it begins to increase. The lowest critical diameter was observed at a GM content of 3%. Other studies have shown that the size of GMs affects the properties of EEs, including detonation ability and generated pressure, after prior dynamic loading [PERSON] _et al._ (2017); [PERSON] _et al._ (2018). Additionally, it influences the degree of crystallization [PERSON] _et al._ (2017) and the density, which is crucial for producing EEs with low detonation velocity for high-energy cladding applications [PERSON] _et al._ (2017). Further sensitizers that have ben used in EEs are binary systems of GMs with titanium dioxide or titanium [PERSON] _et al._ (2018). The choice of TiO\({}_{2}\) as a system component was dictated by its resistance to oxidation and active water interaction [PERSON] _et al._ (2018); [PERSON] _et al._ (2018), ensuring the stability of Ti\({}_{1}\)H\({}_{2}\) in the EE matrix. [PERSON] et al. [PERSON] _et al._ (2018) studied the properties of EEs containing matrices with a density of 1.31 g/cm\({}^{3}\) consisting of ammonium nitrate (75%), sodium nitrate (10%), paraffin wax (4%), diesel oil (1%), emulsifier (2%), and water (8%).