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Review

A Comprehensive Review of the Influence of Sensitizers on the Detonation Properties of Emulsion Explosives

by
Andrzej Maranda
1,
Dorota Markowska
2,
Bożena Kukfisz
3,* and
Weronika Jakubczak
4
1
Łukasiewicz Research Network, Institute of Industrial Organic Chemistry, Annopol 6 Street, 03-236 Warsaw, Poland
2
Faculty of Process and Environmental Engineering, Lodz University of Technology, Wolczanska Street 213, 90-924 Lodz, Poland
3
Institute of Safety Engineering, Fire University, Slowackiego Street 52/54, 01-629 Warsaw, Poland
4
Internal Security Institute, Fire University, Slowackiego Street 52/54, 01-629 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(5), 2417; https://doi.org/10.3390/app15052417
Submission received: 7 January 2025 / Revised: 3 February 2025 / Accepted: 20 February 2025 / Published: 24 February 2025
(This article belongs to the Special Issue Advanced Blasting Technology for Mining)
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Abstract

:
Emulsion explosives are extensively utilized in the global mining industry due to their superior water resistance, high safety standards, cost-efficiency, and robust performance. The basic component of these explosives is a water-in-oil emulsion matrix, which, in its initial state, lacks the capacity for detonation. The sensitization process, achieved through either physical or chemical means, is a critical step that enhances the emulsion’s sensitivity to detonation, thereby improving its operational efficiency in blasting applications. This review presents a comprehensive and systematic analysis of the current scientific literature and experimental investigations concerning the impact of key sensitizing methods and agents on the detonation characteristics of emulsion explosives. Particular emphasis is placed on the classification of sensitizers, their physicochemical properties, and their interactions with the emulsion matrix. By examining various sensitization mechanisms, this study provides insights into the role and efficacy of both established and emerging sensitizing agents. The findings of this review highlight the pivotal role of sensitizer selection in defining the detonation performance of emulsion explosives, with implications for enhancing safety standards and ensuring the protection of both industrial operations and public safety. The most optimal sensitization method is chemical, utilizing cost-effective components that generate gas bubbles within the matrix. A key advantage is the in situ production of emulsion explosives, which eliminates the need for their transport on public roads, thereby enhancing safety and reducing the risk of terrorist threats.

1. Introduction

Emulsion explosives (EEs) have become the most widely used blasting agents in the mining industry and for various other industrial applications, primarily due to their exceptional water resistance, insensitivity to mechanical stimuli facilitating the mechanical loading of blast holes, and remarkable chemical and physical stability, particularly in cartridge form. The basic component of EEs is a water-in-oil emulsion, referred to as the matrix, with densities typically ranging from 1.3 to 1.4 g/cm3. This phase acts as the medium within which water droplets are suspended, forming a theoretically homogeneous material with continuous mechanical properties. However, such mixtures, in the absence of chemical compounds classified as explosives, exhibit only minimal detonation capability.
Following the relatively short era of slurry explosives, emulsion explosives have become one of the primary blasting agents used in the mining industry. A notable example is the Polish mining sector, where in 2022, bulk emulsion explosives (chemically sensitized) accounted for 75% of all blasting agents used in open-pit mines, with ANFO being the second most common choice. The observed decline in ANFO consumption is attributed, among other factors, to the rising cost of ammonium nitrate and the transition to water-bearing deposits. Similarly, in underground mining, both cartridge and bulk forms of emulsion explosives have dominated as the primary blasting agent (90%), gradually replacing dynamite. The widespread adoption of emulsion explosives is driven not only by their previously mentioned advantages, such as water resistance and minimal sensitivity to mechanical stimuli, but also by their detonation parameters, which position them slightly below dynamite yet significantly above ANFO.
EEs are recognized for their comparatively lower environmental impact relative to conventional explosives. Their detonation produces fewer toxic fumes, which benefits both the environment and the health of mine workers. By adjusting their formulation, it is possible to further reduce the emission of harmful gases, such as nitrogen oxides (NOx), enhancing their environmental friendliness [1]. However, despite their environmental advantages, the production and use of emulsion explosives still contribute to various environmental impacts. Maranda et al. [2] stated that the greatest contribution to marine aquatic ecotoxicity potential occurs during the raw material extraction and production stages of emulsion explosives, while their detonation has the most significant impact on acidification and particulate matter emissions with inorganic compounds. Process contribution analysis indicates that ammonium and sodium nitrates are the primary contributors to the overall environmental burden. Bulk emulsion explosives have a 65% lower environmental impact compared to cartridge emulsion explosives.
The primary method of initiating a high-energy process in explosives is to act on it with suitably intense shock waves generated by the detonation of a blasting agent. The initiation of a rapid chemical reaction is associated with the high temperature generated by the shock wave’s rapid adiabatic compression of the explosive. However, the impact of even a very intense shock wave causes a small average increase in the temperature of the loaded homogeneous material. Therefore, it is necessary to make structural changes to the explosive that will cause local foci characterized by increased energy to form behind the front of the initiating shock wave. These points (areas) are called hot spots. If the energy at such a point is high enough, then it can become the focus of a chemical reaction. If it develops according to the thermal mechanism, the point is an active hot spot, and if it disappears, it is an inactive hot spot. The phenomenon of hot spot formation in energetic materials remains incompletely understood, with multiple mechanisms proposed to explain their generation. These include the formation of matter streams during collisions between crystals and grains, and medium heating due to pore reduction, which is influenced by the viscosity or viscoelastic properties of the deformed material near pore surfaces or by the development of microfluidic flows during pore surface deformation and their interaction with explosive material. Other mechanisms involve local heating of the medium from the shock compression of entrapped gas bubbles, shock wave interactions near inclusions with high wave impedance, frictional heating from relative movement between explosive crystals and grains, and internal friction generated on slip planes within explosive crystals [3,4,5,6,7]. The dominance of any particular mechanism in the hot spot formation process may vary depending on the specific conditions, or multiple phenomena may act simultaneously. Based on these theoretical premises and the outlined mechanisms, various sensitization methods have been developed to enhance the explosive properties of the emulsion matrix. These methods include the following:
  • The reduction in matrix density through chemical means;
  • The introduction of low-bulk-density substances to decrease overall density;
  • The incorporation of solid inhomogeneities to promote localized energy release;
  • The addition of high-energy explosives, such as 2,4,6-trinitrotoluene (TNT), pentrite, nitrocellulose, smokeless powder, complex rocket fuels, hexogen, octogen, and their mixtures.
A co-occurrence analysis of the keywords “emulsion explosives”, “sensitizers”, and “detonation parameters” was conducted to elucidate the relationships and thematic connections between key research areas. The sizes of the circles and labels represent the relative weights of keyword co-occurrences. The network map was constructed using bibliometric data from 30 articles indexed in the Scopus database, published between 2004 and 2024. The visualization of the co-occurrence network was generated using VOSviewer software (version 1.6.20). The analysis identified 26 key elements, which were categorized into three distinct clusters (Figure 1). Our findings indicate a growing research emphasis on the production of emulsion explosives (EEs) through the chemical sensitization of various matrices. This trend is driven by the pursuit of a deeper understanding of how different sensitizing additives influence critical detonation parameters, such as detonation velocity and detonation pressure. The clustering of keywords highlights the interconnected nature of studies focusing on matrix composition modification, the development of novel sensitizers, and their subsequent impact on the energetic and physical properties of EEs.
The purpose of this review is to present a comprehensive synthesis of theoretical, practical, and application-oriented research on the sensitization of emulsion explosives. This review not only enhances our understanding of the underlying mechanisms of sensitization, but also lays the groundwork for the development of more effective sensitization strategies.

2. Review of Influence of Sensitizers on Detonation Properties of Emulsion Explosives

2.1. Chemical Density Reduction

This process involves the addition of substances into the matrix that decompose to release nitrogen or other gases in the form of microbubbles. These substances include N N,N-dinitrosopentaethyl-ethylenetetramine; hydrogen peroxide; azodicarbonamide; sodium, potassium, and barium inorganic peroxides; bicarbonates of alkali metals and alkaline earth metals; nitrates (III) of alkali metals or chemical systems of sodium nitrate–urea; alkali hydroborides–urea [8,9]; or a mixture of potassium manganate (VII) and hydrogen peroxide [10]. The encapsulated gas microbubbles act as “hot spots”, facilitating the initiation and propagation of the EE detonation process.
The aeration of the emulsion using the sodium nitrate (III)–urea chemical system occurs due to the release of gases (carbon dioxide and nitrogen) according to the following reaction (Equation (1)):
3NaNO2 + 3HNO3 + 2(NH2)2CO → 3NaNO3 + 2CO2 + 4H2O +3.5N2↑
The nitric acid (V) involved in the reaction acts as a pH-regulating agent. If NaNO2 alone is used to sensitize the matrix, it will react with ammonium nitrate (V) according to Equations (2) and (3):
NaNO2 + NH4NO3 → NH4NO2 + NaNO3
NH4NO2 → 2H2O + N2↑
In total,
NaNO2 + NH4NO3 → NaNO3 + 2H2O + N2↑
In practice, if NaNO2 is used as a stand-alone gassing agent, compounds containing thiocyanate anions are additionally dosed to increase the decomposition efficiency of the sodium derivative. The decomposition of NaNO2 in the presence of ionic thiocyanate compounds follows Equation (5):
H+ + SCN− + HONO → NOSCN + H2O
NOSCN is formed, which is more active than nitric (III) or nitric (V) acids, and reacts in solution with amines or inorganic ammonium salts.
Another aerating substance is sodium bicarbonate. It already decomposes easily at 65 °C, and at 270 °C, carbon dioxide is released completely. The decomposition reaction is more intense under humid conditions. The aqueous solution of sodium bicarbonate has a slightly alkaline pH, and when acetic acid is added, decomposition occurs with the release of carbon dioxide. Therefore, in order to gasify the EE matrix, sodium bicarbonate and acetic acid are dosed simultaneously.
The effect of the degree of gasification, achieved through the application of sodium nitrate (III), on the density and detonation velocity of EEs was determined by Mishra et al. [10]. Experiments were performed for 30 min at different temperatures (31 °C, 47 °C, and 70 °C) and at five concentrations of gassing agent solution (2%, 4%, 6%, 8%, and 10%). At 31 °C, there was a monotonic decrease in density for 25 min, followed by stabilization for another 25 min. At temperatures of 47 and 70 °C, density stabilization occurred after 20 min. The minimum densities for temperatures of 3 °C 1, 47 °C, and 70 °C, reached values of 1.14, 0.92, and 0.94 g/cm3, respectively. The density of the EE (1.15 g/cm3) at which the maximum detonation velocity of 4381 m/s was achieved was determined. The maximum density at which the process disappeared was 1.27 g/cm3.
An original gassing agent was proposed by Kramarczyk et al. [11,12], through the addition of sodium perchlorate to an aqueous solution of ammonium nitrate (sensitizers BK-1 and BK-2, Table 1). They were used to sensitize the commercial EE Emulinit 8L. Compared to the standardly aerated Emulinit 8L (using the EE sensitizer without the addition of sodium perchlorate), the resulting EE exhibited higher detonation velocity, brisance, and air blast parameters, lower content of harmful detonation products, and a shorter density reduction time (Table 2).
Between 2013 and 2016, five studies by Cheng et al. [13,14,15,16,17] were published, in which the authors proposed the use of magnesium dihydride (MgH2) as a sensitizing agent for EEs. The sensitizing agent was dihydrogen microbubbles formed during MgH2 decomposition. Publications [17,18] present the results of studies on the parameters of emulsion explosives (EEs) containing matrices with a density of 1.31 g/cm3. These matrices consisted of ammonium nitrate (75%), sodium nitrate (10%), paraffin wax (4%), diesel oil (1%), emulsifier (2%), and water (8%). The performance of EEs sensitized with magnesium dihydride (MgH2) (98% purity, average particle size of 3 μm, and bulk density of 1.45 g/cm3) was evaluated and compared to that of EEs containing glass microspheres (GMs) (average particle size of 55 μm, bulk density of 0.25 g/cm3), a GM/Al mixture, and sodium nitrite (NaNO2). The compositions and parameters of the EEs are shown in Table 3.
The high detonation capability of EEs is due to their structure consisting of the maximum homogenization of oxidants and combustible components, ensuring the maximum degree of rearrangement in the chemical reaction zone of the detonation wave, as well as gassing additives forming “hot spots” in the non-explosive matrix. The shock wave propagation in the EE, which does not initiate the detonation process in the loaded material, can cause its partial or complete desensitization, as a result of emulsion reversal (crystallization of oxidants [18]) or the deformation (destruction) of hot spots. The aforementioned phenomena may occur during blasting operations as a result of the “channel effect”.
Therefore, Cheng et al. conducted studies of the effects of shock waves of different intensities on EEs sensitized with MgH2 and, comparatively, with GMs [14,15] or sodium nitrite [15,16,17]. They placed 30 g EE samples in a container filled with water at various distances from a 10 g hexogen booster (hexogen/wax 95/5, density-1.45 g/cm3). The EE samples were subjected to the shock wave generated by the detonation of the booster. The unloaded and loaded samples were then initiated with the detonator and the overpressure course was determined using the underwater test method. Starting from the obtained magnitudes of maximum overpressures, the authors of papers [18,19,20] estimated the degree of desensitization (Sd) (Table 4) of loaded EEs based on Equation (6):
Sd = (P0 − P1)/(P0 − Pd)
where P0—peak overpressure of unloaded EE, P1—peak overpressure of loaded EE, and Pd—peak overpressure of the booster.
The data summarized in Table 3 clearly demonstrate that EEs sensitized with MgH2 exhibit the highest energy parameters. This result is attributed to the contribution of hydrogen, generated during the decomposition of MgH2, to high-energy reactions within the detonation wave zone. Additionally, when assessing the degree of desensitization of EEs with different sensitizers, Cheng et al. [13,14,15,16,17] (Table 4) observed that EEs containing MgH2 displayed the highest resistance to non-initiation shock waves. However, it is puzzling that the authors of studies [13,14,15,16,17] reported identical desensitization values for EEs despite using two different MgH2 contents.
Based on the observed relationship between the degree of desensitization and the type of EE, Cheng et al. [13,14,15,16,17] concluded that the process affecting the value of this parameter is not the phenomenon of matrix demulsification. Instead, it is attributed to changes occurring in the “hot spots” formed by individual sensitizers. Under the influence of the shock wave, some of the GMs are crushed and lose their sensitizing properties. In contrast, in the case of MgH2, the hydrogen bubbles are flexible and can return to their original form when squeezed. The authors also believed that when added to the matrix, only part of the MgH2 reacts. The remaining MgH2 can react only as a result of exposure to a strong shock wave (temperature increase), in which case, we would be dealing with so-called “dynamic sensitization”.
The gasification method is now increasingly used in the production of EEs, due to the cumbersome handling of either glass or polymer microspheres and their high prices. However, this yields EEs with lower physical stability, due to the greater possibility of gas bubbles migrating from the explosive mixture. Chemical aeration in particular should be used for in situ EE fabrication.

2.2. 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 perlites.
The addition of GMs as sensitizing agents for EEs was already proposed in the first patents for EEs, such as those of EE inventors Bluhm [19] and Wade [20]. Detailed results on the effect of the content and dimensions of GMs on the detonation velocity of EEs have been reported by Lee and Persson [21] and in Xuguang’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 μm, 54 μm, and 125 μm. 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 μm), 5260 m/s (54 μm), and 5500 m/s (33 μm). Additionally, with decreasing microsphere size, these maximum velocities were observed at progressively higher densities—1.15 g/cm3, 1.24 g/cm3, and 1.27 g/cm3, 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 Deribas et al. [23]. According to the breakdown proposed by Price [24] 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 [25]. 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 [26,27]. Additionally, it influences the degree of crystallization [28] and the density, which is crucial for producing EEs with low detonation velocity for high-energy cladding applications [29].
Further sensitizers that have ben used in EEs are binary systems of GMs with titanium dioxide or titanium [30]. The choice of TiO2 as a system component was dictated by its resistance to oxidation and active water interaction [30,31], ensuring the stability of TiH2 in the EE matrix. Cheng et al. [30] studied the properties of EEs containing matrices with a density of 1.31 g/cm3 consisting of ammonium nitrate (75%), sodium nitrate (10%), paraffin wax (4%), diesel oil (1%), emulsifier (2%), and water (8%). The matrix was sensitized with GMs and their mixtures with TiH2 and titanium. GMs had a bulk density of 0.25 g/cm3 with an average grain size of 55 μm. In contrast, the other additives had significantly higher bulk densities of 3.91 g/cm3 (TiH2) and 4.5 g/cm3 (Ti), and average grain sizes of 48 μm. Underwater energy, detonation velocity, and aggregability were determined for the EEs tested.
In the underwater test, Cheng et al. [30] 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 TiO2 (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 [32,33]. For the two selected EEs, the authors determined the velocity of detonation in charges placed in PVC pipes with a diameter of 40 mm, and the brisance using the Hess method (Table 7).
These results show that at a certain content of TiH2, 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 TiH2 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/cm3) than typical GMs. In the work of Maranda 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]. Anshits 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].
Applsci 15 02417 g004
Figure 4. Dependence of EE detonation velocity on grain size of microspheres in charges of a given diameter: 1—CSs (d = 55 μm); 2—GMs (d = 55 μm); 3—GMs (d = 36 μm); 4—GMs (d = 23.6 μm) [35].
Figure 4. Dependence of EE detonation velocity on grain size of microspheres in charges of a given diameter: 1—CSs (d = 55 μm); 2—GMs (d = 55 μm); 3—GMs (d = 36 μm); 4—GMs (d = 23.6 μm) [35].
Applsci 15 02417 g004
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 μm (bulk density of 0.36 g/cm3) and an EE density of 1.18–1.20 g/cm3. The mass content of CSs was 8–10%. The critical diameter was 35–40 mm. Increasing the size of CSs to 200 μm resulted in a decrease in the velocity of detonation by 1.0–1.3 km/s. EEs containing an unseparated mixture of CSs had a detonation velocity of 4.2 m/s and a critical diameter of 45 mm.
Fang et al. [36] presented the content of the main components of the CSs in comparison to GMs. They were as follows: SiO2 (52.32% and 74.96%), Al2O3 (30.09% and 0%), and CaO (9.42% and 0%). For EEs containing a matrix composed of ammonium nitrate (75.0%), sodium nitrate (10.0%), paraffin wax (4.0%), diesel fuel (1.0%), emulsifier (2.0%), and water (8.0%), they conducted tests of detonation velocity (in 32 mm diameter charges) and crushability, among others. The variables were the content and grain size of CSs and GMs. The test results are summarized in Table 8 and Table 9.
The results of Fang et al. [36] showed that the optimum content of CSs compared to GMs is much higher, with values of 12% and 4%, respectively. Moreover, EEs containing GMs exhibited higher detonation parameters.
Another type of EE sensitizer is microballoons made from plastics [37,38,39,40,41,42,43,44,45]. A detailed study of the effect of microballoons made of acrylonitrile/vinylidene chloride with a bulk density of 0.027 g/cm3 on the detonation velocity of EEs is presented in [37]. The variables were the degree of aeration (the matrix had a density of 1.39 g/cm3) and the dimensions of the microballoons. Detonation velocity measurements were made in charges of 50 mm in diameter. With increasing aeration (decreasing density), the detonation velocity initially increased, followed by a subsequent decrease. Similarly to glass microspheres, the smaller the microballoons, the higher the maximum detonation velocity, which shifted towards a lower degree of aeration.
Similar results were reported by Mendes et al. [41]. Meanwhile, Yunoschev et al. [44] observed a critical diameter–density relationship of a similar nature to that described for GMs in [25]. It is worth noting that plastic microballoons, in addition to their sensitizing effect, also serve as combustible components, which should be considered when formulating EE compositions. The effect of perlite on the properties of EEs can be found in papers [22,28]. Yan et al. [28] studied EEs containing 2, 3, and 4% perlite. The degree of crystallization of the matrix caused by the influence of shock waves generated in water increased with increasing perlite content and was higher than for the same content of GMs. On the other hand, the dependence of aggregability on perlite content, shown in the monograph in [27], was of the same nature as the effect of GMs or microballoon content on the velocity of detonation. The maximum measured value of this parameter was 16 mm at a perlite content of 6%.

2.3. Introduction of Constant Inhomogeneities

The sensitization (reduction in the critical diameter) of liquid explosives using solid additives, such as aluminum or Al2O3 grains, was first described by Kurbangalina in 1969 [46]. A similar solution in the case of EEs concerns substances characterized by relatively high hardness: grains of ferrosilicon, ferrophosphorus, ferromanganese, or Al2O3 with a grain size of less than 180 μm [47]. The content of such additives, according to patent data, can be up to 50%. However, it seems that their optimal amount should be a few percent. Higher contents of them significantly reduce the detonation and thermochemical characteristics of EEs, due to their inertness in chemical terms, while at the same time taking heat away from the chemical reaction zone, due to the relaxation of thermodynamic parameters between the explosion products described by the additives.

2.4. Sensitization of EE Matrix with Explosives

The use of high-energy substances that exhibit explosive properties (e.g., TNT, pentrite, hexogen, octogen, nitrostarch, and smokeless powder) as ingredients that impart upon the EE matrix the ability to detonate from a standard No. 6 primer was first proposed by Tomic [48]. However, interest in incorporating such additives into EEs grew significantly during efforts to dispose of high explosives and propellants recovered from the decommissioning of munitions [48,49,50,51,52,53,54,55,56,57,58,59,60]. The purpose of their addition to EEs was to get rid of unnecessary explosive stockpiles and, at the same time, to obtain EEs with improved energy parameters. For example, increasing the 50/50 B composition from 30% to 50% resulted in an increase in detonation velocity from 5559 m/s to 6806 m/s [54,55]. Also, the addition of nitrocellulose powder caused an increase in EE detonation velocity. Charges initiated with an HC-14 booster at nitrocellulose powder contents of 15, 20, and 25% had detonation velocities of 4059, 4282, and 4920 m/s, respectively [56].
In addition to studies of the effect of de-elaborated explosives on the detonation parameters of EEs, analogous experiments were performed with several individual explosives [51,52,53,54,55,56]. Renick et al. [56] determined the effect of octogen on the critical diameter and detonation velocity of EEs with a composition of ammonium nitrate (71.5%), sodium nitrate (10.0%), water (12.0%), and oil phase (6.5%). Increasing the octogen content from 20% to 60% resulted in a decrease in critical diameter from 52 mm to 15 mm, and an increase in detonation velocity in a 51.5 mm diameter charge, from ~5300 m/s to ~8000 m/s.
Kűnzel et al. [59] used an EE matrix consisting of ammonium nitrate (V) (62.5%), sodium nitrate (V) (13,5%), water (15%), urea (3%), oil phase (6.5%), and custom explosive-erythritol tetranitrate (V) (ETN) for sensitization. The detonation velocities of EEs, measured in a 37 mm diameter plastic tube containing 10, 15, and 20% ETN, initiated with a booster made of Semtex, were 1900, 3490, and 4960 m/s, respectively. An EE containing 20% erythritol tetranitrate (V) was detonated from a fuse containing 0.72 g of pentrite.
Yang et al. [60] studied the effect of the addition of hexogen, with an average grain size of 90 μm, on the detonation velocity, brisance, and critical thickness of EEs with a matrix composition consisting of ammonium nitrate (75.0%), sodium nitrate (10.0%), and water oil phase-70, containing GMs (25%). An increase in hexogen content, from 0% to 20%, resulted in an increase in the detonation velocity at a layer thickness of 20 mm from 3120 to 3523 m/s, an aggregate from 11.9 to 17.6 mm, and a decrease in the critical thickness from 6.0 to 3.3 mm.
The method of the sensitization of emulsion explosives with explosive crushing and blasting is very rarely used. It uses raw materials that are sensitive to mechanical stimuli, which creates an explosive hazard, and the final product is much less resistant to impact and friction than typical EEs. This causes, among other things, a great limitation and difficulty in the mechanization of blasting work.

3. Conclusions

The presented literature review on the sensitization of emulsion explosive matrices demonstrates that several sensitization methods exist, each differing in its underlying mechanism. These methods are typically classified into two primary categories: chemical and physical. In chemical sensitization, specific chemical compounds are added to the EE matrix. The decomposition of these compounds produces gases that form bubbles, thereby reducing the density of the matrix. These gas bubbles are adiabatically compressed by the propagating shock wave generated by an initiator, leading to the formation of “hot spots” that are critical for the initiation of detonation. In contrast, physical sensitization encompasses several distinct mechanisms. The incorporation of low-bulk-density substances into the matrix similarly results in the formation of “hot spots” analogous to those produced by chemical gas generation. Furthermore, the introduction of solid heterogeneities—particularly materials with high hardness—represents a conventional approach to sensitizing explosives. The interaction of the shock wave with high-impedance inclusions results in localized temperature increases, which, in turn, trigger the exothermic decomposition of active molecules in their immediate vicinity. Additionally, the inclusion of high-detonation-capable explosive materials into the EE matrix leads to an exothermic reaction upon the passage of a shock wave, thereby creating centers that facilitate the propagation of detonation throughout the entire matrix.
An analysis of the described EE sensitization methods suggests that chemical sensitization is the most optimal approach, particularly when inexpensive components are employed to generate gas bubbles within the matrix. Its principal advantages include low cost and the ability to produce EE in situ. Sensitizing the matrix directly in the blasthole obviates the need for transporting explosive materials via public roads, a factor that is critical for ensuring transport safety and mitigating potential terrorist threats.
The broader field of explosive materials represents a highly specialized domain in both scientific research and industrial applications. Examples include the diverse EE formulations currently in use, as well as various explosive mixtures. Black powder, developed in the 9th century by the Chinese, remains one of the most effective ignition agents; nitrocellulose, synthesized in 1846 by Christian Friedrich Schönbein, continues to serve as a fundamental component in gunpowder formulations; and TNT, invented in 1863 by Julius Wilbrand, is the most commonly used low-sensitivity explosive in military mixtures. A similar scenario applies to emulsion explosives. Despite 56 years having elapsed since their initial patenting by Harold Bluhm, EEs are still regarded as the most advanced blasting agents in mining. Compared to the original patents, significant changes in composition have not been observed, with only modifications such as the incorporation of polyisobutylene succinic anhydride as an emulsifier [61,62] or the development of Low-Water-Composition EEs [63], which include additives like ammonium nitrate and aluminum powder.
Based on the current state of knowledge, it is challenging to delineate new research directions for EEs. A potential innovation in this field may be the development of explosive mixtures in which hydrogen peroxide acts as the oxidizer [64], building on the findings of previous studies by Araos et al. [65,66,67,68]. Notably, in the explosives investigated by Araos et al., a matrix based on a concentrated aqueous solution of hydrogen peroxide was sensitized using either glass microspheres or chemical methods.

Author Contributions

Conceptualization, A.M.; methodology, A.M.; data curation, B.K. and D.M.; writing—original draft preparation, A.M., B.K. and D.M.; writing—review and editing, A.M., B.K., D.M. and W.J.; funding acquisition, W.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Centre for Research and Development (Poland) under the project “Development of integrated knowledge management system for rescue phases: preparedness, prevention, response, and recovery, for fire protection and population safety”, based on agreement GOSPOSTRATEG9/001G/2022 and the work was financed from funds granted to the Fire University, Warsaw, Poland by the Minister of the Interior and Administration, Poland for the maintenance and development of research potential under application RN-1.601.2.2025.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results. The authors declare that they have no involvement in any projects related to military applications or sensitive military research.

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Applsci 15 02417 g001
Figure 1. Co-occurrence analysis of keywords (emulsion explosives, sensitizers, and detonation parameters) in articles published between 2004 and 2024 (keyword co-occurrence threshold of 4).
Figure 1. Co-occurrence analysis of keywords (emulsion explosives, sensitizers, and detonation parameters) in articles published between 2004 and 2024 (keyword co-occurrence threshold of 4).
Applsci 15 02417 g001
Applsci 15 02417 g002
Figure 2. Pressure–time dependence for EE-GMs-TiH2 containing different amounts of GMs [30]: 1—0%, 2—2%, 3—4%, 4—6%.
Figure 2. Pressure–time dependence for EE-GMs-TiH2 containing different amounts of GMs [30]: 1—0%, 2—2%, 3—4%, 4—6%.
Applsci 15 02417 g002
Applsci 15 02417 g003
Figure 3. Pressure–time dependence for EEs-GMs-TiH2 containing different amounts of TiO2 [30]: 1—0%; 2—2%; 3—4%; 4—6%; 5—8%.
Figure 3. Pressure–time dependence for EEs-GMs-TiH2 containing different amounts of TiO2 [30]: 1—0%; 2—2%; 3—4%; 4—6%; 5—8%.
Applsci 15 02417 g003
Table 1. Sensitizer’s components [11].
Table 1. Sensitizer’s components [11].
ComponentSensitizer
EEBK-1BK-2
Component Content [wt. %]
Ammonium nitrate-30.047.1
Water95.4561.641.0
Sodium perchlorate-4.08.0
Sodium nitrite 4.503.03.3
pH modifier0.051.50.7
Table 2. Sensitized EEs parameters when sensitized according to [11,12].
Table 2. Sensitized EEs parameters when sensitized according to [11,12].
SensitizerDetonation Velocity [m/s]Peak Overpressure 1 [kPa]Impulse
ABV 1 [Pa∙s]		Explosive Gas Content [kg/dm3]
NOxCO
EE4233123.7357.200.554.11
BK-14647127.1357.530.332.51
BK-25033131.2058.600.313.45
1 2 m from axis of EE sample.
Table 3. EE compositions and parameters [13].
Table 3. EE compositions and parameters [13].
ComponentSensitizer
GMsGMs/AlMgH2NaNO2
[wt.%]
Matrix96.092.098.099.8
GMs4.04.0--
Aluminum dust-4.0--
MgH2--2-
NaNO2---0.2
Parameter
Density [g/cm3]1.211.241.291.24
Underwater test10.8910.7213.12-
maximum overpressure [MPa]
Energy [kJ/kg]287131873762-
Detonation energy [kJ/kg]
Theoretical3297368435303297
Experimental2728302835742835
Detonation velocity [m/s]443443895552-
Brisance [mm]16.116.219.116.85
Table 4. Compositions and degrees of desensitization of EEs sensitized with various additives [13,14,15,16,17].
Table 4. Compositions and degrees of desensitization of EEs sensitized with various additives [13,14,15,16,17].
Sensitizer
GMsNaNO2MgH2
Component[wt.%]
Matrix96.099.898.099.0
GMs4.0---
NaNO2-0.2--
MgH2--2.01.0
Distance [mm]Sensitization degree [%]
2510088.1238.9738.97
4086.4184.4718.8918.89
5079.8271.6312.1112.11
6073.6753.4710.4510.45
7563.3415.5911.7611.76
Table 5. EEs’ detonation velocities as a function of GM content and dimensions [21].
Table 5. EEs’ detonation velocities as a function of GM content and dimensions [21].
GMs Size [μm]GMs Content [%]Density [g/cm3]Detonation
Velocity [m/s]
1535.3590.9093891
3.8741.0034218
2.1351.1004214
1.7241.2103754
1088.9850.9003837
6.6450.9984165
4.5861.1034374
3.0141.2024120
829.9160.8953779
8.2890.9924203
5.8701.0974551
3.8761.2054615
6411.9720.8913781
9.0300.9994244
6.5441.1124695
4.3211.2044711
Table 6. Compositions and parameters of EEs-GMs-TiH2 containing different amounts of TiO2 [30].
Table 6. Compositions and parameters of EEs-GMs-TiH2 containing different amounts of TiO2 [30].
NoComponent [%]Maximum Overpressure [MPa]Energy [MJ/kg]
MatrixGMTiH2SW *GB **Total
1954119.010.6581.632.69
2944220.580.7121.682.83
3924420.720.6951.662.79
4904619.920.6811.642.74
5884819.460.6791.652.75
6964-21.770.7041.502.58
79442 ***19.160.6651.582.63
* Shock wave, ** gas bubble, *** titanium.
Table 7. Parameters of EE with different TiH2 contents [30].
Table 7. Parameters of EE with different TiH2 contents [30].
NoComponent [%]Density
[g/cm3]		 Detonation Velocity [m/s]Brisance
[mm]
MatrixGMTiH2
1964-1.18453416.1
294421.11265923.8
Table 8. Dependence of detonation velocity and brisance on CS (d50 = 58 μm) and GM (d50 = 57 μm) content, according to [36].
Table 8. Dependence of detonation velocity and brisance on CS (d50 = 58 μm) and GM (d50 = 57 μm) content, according to [36].
Content [%]Density
[g/cm3]		Brisance
[mm]		Detonation Velocity [m/s]
CSsGMs
2-1.249.9ND
4-1.2110.7ND
6-1.1813.03027
8-1.1713.33367
10-1.1613.44138
12-1.1514.74616
14-1.1314.44137
16-1.1113.94053
-21.2018.73653
-31.1819.74950
-41.1220.65176
-51.1020.24789
ND—no detonation.
Table 9. Detonation velocity and brisance of EEs as a function of grain size (d50) at optimum CS and GM content, according to [36].
Table 9. Detonation velocity and brisance of EEs as a function of grain size (d50) at optimum CS and GM content, according to [36].
Content [%]Grain Size
[μm]		Density
[g/cm3]		Brisance
[mm]		Detonation Velocity [m/s]
CSsGMs
12-26-1.2311.2ND
12-58-1.1514.74616
12-83-1.1818.34970
12-142-1.2013.83862
-4-181.164.8ND
-4-351.1414.54541
-4-571.1220.65176
-4-1021.0914.74563
ND—no detonation.
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Maranda, A.; Markowska, D.; Kukfisz, B.; Jakubczak, W. A Comprehensive Review of the Influence of Sensitizers on the Detonation Properties of Emulsion Explosives. Appl. Sci. 2025, 15, 2417. https://doi.org/10.3390/app15052417

AMA Style

Maranda A, Markowska D, Kukfisz B, Jakubczak W. A Comprehensive Review of the Influence of Sensitizers on the Detonation Properties of Emulsion Explosives. Applied Sciences. 2025; 15(5):2417. https://doi.org/10.3390/app15052417

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Maranda, Andrzej, Dorota Markowska, Bożena Kukfisz, and Weronika Jakubczak. 2025. "A Comprehensive Review of the Influence of Sensitizers on the Detonation Properties of Emulsion Explosives" Applied Sciences 15, no. 5: 2417. https://doi.org/10.3390/app15052417

APA Style

Maranda, A., Markowska, D., Kukfisz, B., & Jakubczak, W. (2025). A Comprehensive Review of the Influence of Sensitizers on the Detonation Properties of Emulsion Explosives. Applied Sciences, 15(5), 2417. https://doi.org/10.3390/app15052417

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