Energetic Materials Based on W/PTFE/Al: Thermal and Shock-Wave Initiation of Exothermic Reactions

: The parameters of combustion synthesis and shock-wave initiation of reactive W/PTFE/Al compacts are investigated. Preliminary thermodynamic calculations showed the possibility of combustion of the W/PTFE/Al system at high adiabatic temperatures (up to 2776 ◦ C) and a large proportion of condensed combustion products. The effect of the Al content (5, 10, 20, and 30 wt%) in the W/PTFE/Al system on the ignition and development of exothermic reactions was determined. Ignition temperatures and combustion rates were measured in argon, air, and rareﬁed air. A correla-tion between the gas medium, rate, and temperature of combustion was found. The shock initiation in W/PTFE/Al compacts with different Al content was examined. The extent of reaction in all compacts was studied by X-ray diffraction. The compositions with 10 and 20 wt% Al showed the highest completeness of synthesis after combustion and shock-wave initiation.


Introduction
Reactive materials (RMs) are powder mixtures that are inert under normal conditions but are capable of releasing energy when heated or subjected to high-velocity impact [1][2][3][4]. RMs are more stable under external impact and have greater strength than explosives, which allows them to be mechanically processed [5]. Therefore, RMs can be used in the arms industry, namely, in rocket artillery [6], in shaped charges [7], and as structural components of warheads [8,9]. However, the use of RMs is not limited to the arms industry. For example, the focused heterogeneous jet of solid, liquid, or gaseous products obtained through RMs can be used to cut or perforate structural materials. Moreover, with RMs, this can be done in underwater and high-pressure conditions, for example in through-tubing and throughcasing perforation [10]. RMs include intermetallic compounds [11][12][13], thermite [14][15][16], and metal/polymer mixtures [17][18][19][20]. The metal/polymer mixture based on aluminum (Al) and polytetrafluoroethylene (PTFE) is most promising due to its sensitivity to highvelocity impact, the high proportion of gaseous products, and energy concentration [21]. The thermal effect of the chemical reaction in the Al/PTFE mixture (with a ratio of 26.5:73.5) is 8.53 MJ/kg, which is twice as high as that of trinitrotoluene (4.18 MJ/kg). The adiabatic temperature of this reaction can reach 4000 K [22,23]. A large number of recent works are devoted to the study of shock-wave initiation of the Al/PTFE system under quasi-static [24] and dynamic loading [5,[25][26][27][28][29].
The main disadvantage of Al/PTFE composites that limits their use as structural components of special-purpose products in comparison with metals is their low density and strength [30]. High-density powder additives such as tungsten (W), nickel (Ni), etc., increase density and strength [31,32]. It was shown in [33][34][35] that increasing the W and Ni content in the Al/PTFE mixture increases the strength of the composite but decreases the thermal effect of the reaction and the sensitivity to shock-wave initiation. The strength and shock-wave initiation of the Al/PTFE mixture is significantly affected by the particle size of initial powders. For example, Wu [17] and Zhang [36] report the studies on the effect of the initial Al and W particle size on the strength and shock-wave initiation of the Al/PTFE mixture. It was found that the smaller the aluminum particles, the lower the initiation threshold and the higher the strength, while the decrease in the tungsten particle size leads to the decrease in the strength and sensitivity to shock-wave initiation.
In [37], the effect of porosity on the delay time and duration of the exothermic reaction under dynamic loading was investigated. It was found that increasing porosity reduces the duration of the exothermic reaction and does not affect the initiation time. There are a large number of works devoted to studying the effect of the proportion of different components in Al/PTFE and Al/PTFE/W systems. In [38], it was found that the addition of Mg to the Al/PTFE/W system increases the rate and intensity of combustion, as well as the destructive potential of incendiary bullets. Hydrides of titanium [39,40], magnesium [41] and zirconium [42], as well as oxides of copper [43], molybdenum [44], and manganese [45] can be used as additives introduced into the Al/PTFE system to significantly increase the rate and heat of energy release.
This study focuses on the reactive W/PTFE/Al materials with different Al contents. W/PTFE was used as the base system. The combustion and ignition parameters were investigated depending on the gaseous atmosphere. The effect of Al content on the shockwave and thermal initiation sensitivity of the W/PTFE/Al system was investigated.

Materials and Methods
The compositions were selected based on preliminary calculations in the ISMAN-THERMO software (Version 4.3, Company ISMAN, Chernogolovka, Russia) [46]. This software is developed for thermodynamic equilibrium calculations in complex multi-element heterophase systems and is designed to analyze the possible composition of inorganic synthesis products (condensed and gaseous) and the adiabatic combustion temperature of the system. The ISMAN-THERMO software includes a data bank of thermodynamic information, a program for calculating the coefficients of thermodynamic functions for new compounds and including them in the data bank, and a program for calculating equilibrium characteristics.
The equilibrium characteristics were calculated by minimizing the thermodynamic potential of the system, taking into account the contributions of thermodynamic potentials of all compounds in the system, as well as the concentrations of the compounds. The algorithm for minimizing the thermodynamic potential is based on the gradient descent method. The calculation results are the adiabatic combustion temperature as well as the amount and phase composition of solid, liquid, and gaseous synthesis products. It is obvious that the processes of combustion and shock-wave initiation are far from equilibrium, nevertheless, the calculations performed can be used to limit the number of experiments and select the most promising compositions.
Five W/PTFE/Al compositions were prepared. Table 1 shows the ratio of the components and their theoretical maximum density (TMD)-actual and relative. The powders were mixed in a tumbling drum mixer for 2 h at 30 rpm with a ball-to-powder weight ratio of 5:1. The powders of tungsten (PV2 grade, particle size < 50 µm, Polema Co., Tula, Russia), PTFE (F-4NTD-2 grade, particle size < 50 µm, HaloPolymer Co., Kirovo-Chepetsk, Russia) and aluminum (ASD-1 grade, particle size < 50 µm, Valkom-PM Co., Volgograd, Russia) were used as initial components. The particle size distribution of the initial powders is shown in Figure 1.
To measure the combustion rate, the parallelepiped-shaped specimens with dimensions 5 mm × 5 mm × 20 mm and a relative density of 0.95 (Table 1) were prepared using a manual hydraulic press (PRG-10, Lab Tools, St. Petersburg, Russia). The density of the specimens was determined from their geometric dimensions (micrometer Dasqua, Cornegliano Laudense, Italy) and weight (CAS XE-300 analytical balance, CAS Corporation, Seoul, South Korea). The relative density was calculated as the ratio of the actual to the theoretically possible [47]. Two holes 0.3 mm in diameter and 2 mm in depth were drilled  To measure the combustion rate, the parallelepiped-shaped specimens with dimensions 5 mm × 5 mm × 20 mm and a relative density of 0.95 (Table 1) were prepared using a manual hydraulic press (PRG-10, Lab Tools, St. Petersburg, Russia). The density of the specimens was determined from their geometric dimensions (micrometer Dasqua, Cornegliano Laudense, Italy) and weight (CAS XE-300 analytical balance, CAS Corporation, Seoul, South Korea). The relative density was calculated as the ratio of the actual to the theoretically possible [47]. Two holes 0.3 mm in diameter and 2 mm in depth were drilled on the side surface of the specimens for WR5/WR20 thermocouples 100 μm in diameter. The distance between the holes was 14-15 mm (Figure 2a).
The specimens were placed in a 20 L reactor [48]. The experiments were conducted in argon and air at atmospheric pressure, as well as in vacuum at 2 × 10 4 Pa. A flat graphite heater was used to create a flat combustion front. Thus, the whole edge surface of the specimen was heated producing a flat combustion front (Figure 2b). The distance from the ignition point to the first thermocouple was about 3-4 mm. The signals from the thermocouples were recorded with a frequency of 250 Hz through QMBox analog-to-digital converter-ADC (R-Technology, Moscow, Russia). The combustion process was recorded with a video camera (HC-VC770, Panasonic, Osaka, Japan) at a frame rate of 50 fps.  The specimens were placed in a 20 L reactor [48]. The experiments were conducted in argon and air at atmospheric pressure, as well as in vacuum at 2 × 10 4 Pa. A flat graphite heater was used to create a flat combustion front. Thus, the whole edge surface of the specimen was heated producing a flat combustion front ( Figure 2b). The distance from the ignition point to the first thermocouple was about 3-4 mm. The signals from the thermocouples were recorded with a frequency of 250 Hz through QMBox analog-to-digital converter-ADC (R-Technology, Moscow, Russia). The combustion process was recorded with a video camera (HC-VC770, Panasonic, Osaka, Japan) at a frame rate of 50 fps. The specimens with a diameter of 3 mm and a height of 1.5-2 mm were used to measure the ignition temperature. The ignition of the specimens was conducted in the reactor (Figure 3a). The specimens were placed on a 50 μm thick WR5/WR20 thermocouple in a boron nitride crucible [49] and heated at 60-80 °C/s using a graphite heater to create thermal explosion conditions (Figure 3b). The specimens with a diameter of 3 mm and a height of 1.5-2 mm were used to measure the ignition temperature. The ignition of the specimens was conducted in the  (Figure 3a). The specimens were placed on a 50 µm thick WR5/WR20 thermocouple in a boron nitride crucible [49] and heated at 60-80 • C/s using a graphite heater to create thermal explosion conditions (Figure 3b). The specimens with a diameter of 3 mm and a height of 1.5-2 mm were used to measure the ignition temperature. The ignition of the specimens was conducted in the reactor ( Figure 3a). The specimens were placed on a 50 μm thick WR5/WR20 thermocouple in a boron nitride crucible [49] and heated at 60-80 °C/s using a graphite heater to create thermal explosion conditions (Figure 3b). The shock-wave initiation ability of the compounds was determined through 1 km/s oblique impact of a steel plate (100 mm in diameter and 2.5 mm in thickness) at a matrix (100 mm in diameter and 20 mm in thickness, Figure 4a) with the specimens (Figure 4b).
The cylindrical specimens with a diameter of 10 mm, a height of 10 mm, and a relative density of 0.98 were used. The same loading conditions for all specimens were provided by the initiation of the explosive detonation from the center of the assembly. The phase composition of the products was characterized by X-ray diffraction (XRD, DRON-3M, Burevestnik, St. Petersburg, Russia). The specimens were scanned from 20° to 80° (2Θ) with a scanning step of 0.02°. The shock-wave initiation ability of the compounds was determined through 1 km/s oblique impact of a steel plate (100 mm in diameter and 2.5 mm in thickness) at a matrix (100 mm in diameter and 20 mm in thickness, Figure 4a) with the specimens (Figure 4b).
The cylindrical specimens with a diameter of 10 mm, a height of 10 mm, and a relative density of 0.98 were used. The same loading conditions for all specimens were provided by the initiation of the explosive detonation from the center of the assembly. The phase composition of the products was characterized by X-ray diffraction (XRD, DRON-3M, Burevestnik, St. Petersburg, Russia). The specimens were scanned from 20 • to 80 • (2Θ) with a scanning step of 0.02 • .

Results
Calculations in the THERMO software showed that the adiabatic combustion temperature and the proportion of condensed products (most of which are tungsten carbide W2C) in the W/PTFE system depend significantly on the component ratio. Thus, the peak adiabatic temperature (Tad) is reached at a tungsten content of 60 wt% and is 2317 °C, while the proportion of condensed products (graphite with the small amount of W2C) is minimal-about 10 wt% ( Figure 5). The gaseous phase in this case consists mainly of heavy gases such as tungsten fluorides WF6 (15 wt%), WF5 (43 wt%), WF4 (29 wt%). Besides this, the disadvantage of this composition is the difficulty of uniform mixing of the components due to big differences in their specific volumes. Thus, the composition with an 80 wt% tungsten content is optimal and demonstrates the high combustion temperature (2115 °C) with a high proportion of condensed products. The main calculated prod-

Results
Calculations in the THERMO software showed that the adiabatic combustion temperature and the proportion of condensed products (most of which are tungsten carbide W 2 C) in the W/PTFE system depend significantly on the component ratio. Thus, the peak adiabatic temperature (T ad ) is reached at a tungsten content of 60 wt% and is 2317 • C, while the proportion of condensed products (graphite with the small amount of W 2 C) is minimal-about 10 wt% ( Figure 5). The gaseous phase in this case consists mainly of heavy gases such as tungsten fluorides WF 6 (15 wt%), WF 5 (43 wt%), WF 4 (29 wt%). Besides this, the disadvantage of this composition is the difficulty of uniform mixing of the Metals 2021, 11, 1355 5 of 12 components due to big differences in their specific volumes. Thus, the composition with an 80 wt% tungsten content is optimal and demonstrates the high combustion temperature (2115 • C) with a high proportion of condensed products. The main calculated products of this composition are condensed products, such as tungsten carbide W 2 C (53 wt%) and graphite (3 wt%), as well as gaseous tungsten fluorides WF 6 (14 wt%), WF 5 (20 wt%), WF 4 (9 wt%).
perature and the proportion of condensed products (most of which are tungsten carbide W2C) in the W/PTFE system depend significantly on the component ratio. Thus, the peak adiabatic temperature (Tad) is reached at a tungsten content of 60 wt% and is 2317 °C, while the proportion of condensed products (graphite with the small amount of W2C) is minimal-about 10 wt% ( Figure 5). The gaseous phase in this case consists mainly of heavy gases such as tungsten fluorides WF6 (15 wt%), WF5 (43 wt%), WF4 (29 wt%). Besides this, the disadvantage of this composition is the difficulty of uniform mixing of the components due to big differences in their specific volumes. Thus, the composition with an 80 wt% tungsten content is optimal and demonstrates the high combustion temperature (2115 °C) with a high proportion of condensed products. The main calculated products of this composition are condensed products, such as tungsten carbide W2C (53 wt%) and graphite (3 wt%), as well as gaseous tungsten fluorides WF6 (14 wt%), WF5 (20 wt%), WF4 (9 wt%).  The first explosion experiments showed that the double W/PTFE system is difficult to be initiated by shock-wave loading [47]. An increase in the reactivity can be achieved by preliminary mechanical activation [50] and/or by activating additives such as aluminum and magnesium powders [38]. Aluminum powder was chosen as an activating additive.
Thermodynamic calculations were performed in the W/PTFE/Al system with different Al contents. The calculations showed that an increase in the Al content leads to a sharp decrease in the combustion adiabatic temperature ( Figure 6). The calculated adiabatic combustion temperatures, the content of gaseous products, and the composition of condensed products are shown in Table 2. The maximum adiabatic combustion temperature corresponds to composition No. 2 and is equal to 2866 • C with a high proportion of condensed products.  The calculated condensed products of composition No. 1 at 2776 °C consisted of 75 wt% carbide (W2C), half of which was in the liquid state after the reaction and 16 wt% gaseous aluminum fluoride (AlF3). The proportion of melted tungsten carbide (W2C) in composition No. 2 was 74 wt%, and the gaseous phase was represented by aluminum fluorides: AlF3 (11 wt%), AlF2 (5 wt%), and AlF (7 wt%). Compositions No. 3 and No. 4 showed relatively low adiabatic combustion temperatures (1710 °C and 1382 °C, respectively) and low proportions of condensed products such as tungsten carbide W2C (66 wt% and 57 wt%, respectively).
In this study, the ignition experiments were conducted to determine the character of the exothermic reaction (ignition) for each composition and the temperature at which it starts. The experimental studies of the ignition temperature showed that chemical transformations in the specimens proceed relatively slowly, as evidenced by the thermograms The calculated condensed products of composition No. 1 at 2776 • C consisted of 75 wt% carbide (W 2 C), half of which was in the liquid state after the reaction and 16 wt% gaseous aluminum fluoride (AlF 3 ). The proportion of melted tungsten carbide (W 2 C) in composition No. 2 was 74 wt%, and the gaseous phase was represented by aluminum fluorides: AlF 3 (11 wt%), AlF 2 (5 wt%), and AlF (7 wt%). Compositions No. 3 and No. 4 showed relatively low adiabatic combustion temperatures (1710 • C and 1382 • C, respectively) and low proportions of condensed products such as tungsten carbide W 2 C (66 wt% and 57 wt%, respectively).
In this study, the ignition experiments were conducted to determine the character of the exothermic reaction (ignition) for each composition and the temperature at which it starts. The experimental studies of the ignition temperature showed that chemical transformations in the specimens proceed relatively slowly, as evidenced by the thermograms of ignition of the W/PTFE/Al system (Figure 7). Upon reaching the melting point of aluminum, the heating was continued to 800-900 • C, after which the temperature jumped to 1200-1400 • C. The combustion temperature recorded in these experiments was much lower than the adiabatic temperature due to the small size of the specimens and the large number of gaseous products, which destroyed the specimen and did not allow all the heat of the reaction to be transferred to the thermocouple. of ignition of the W/PTFE/Al system (Figure 7). Upon reaching the melting point of aluminum, the heating was continued to 800-900 °C, after which the temperature jumped to 1200-1400 °C. The combustion temperature recorded in these experiments was much lower than the adiabatic temperature due to the small size of the specimens and the large number of gaseous products, which destroyed the specimen and did not allow all the heat of the reaction to be transferred to the thermocouple.  Figure 8 shows the video frames of the combustion for the four compositions in the air (Figure 8a,d,j,e), argon (Figure 8b,e,h,k), and vacuum (Figure 8c,f,i,l). The combustion of the specimens of composition No. 4 in the air was accompanied by the emission of large   (Figure 8a,d,j,e), argon (Figure 8b,e,h,k), and vacuum (Figure 8c,f,i,l). The combustion of the specimens of composition No. 4 in the air was accompanied by the emission of large amounts of gaseous products. After the exothermic reaction was completed, another exothermic reaction took place along the specimen with a delay of 5-10 s, but with a lower rate (about 1 mm/s) and intensity. The effect of prolonged afterburning of the specimen (within 2 min) was also observed. This effect is related to the oxidation of wolfram in the air. After combustion, a white residue was present on the specimens (Figure 9a). Combustion in argon was characterized by the absence of white residue, afterburning effect, and a second exothermic reaction (Figure 9b). Combustion in vacuum was less intensive, burning one-third of the specimen (Figure 9c). The exothermic reaction occurred in a pulsating mode, loosening the specimen, thereby disturbing the heat transfer from the combustion front to the initial reagents. The combustion of the specimens of composition No. 3 in air, argon, and vacuum was identical to that of composition No. 4 but differed by a higher combustion rate (4/5/0.6 mm/s, respectively) and the absence of the afterburning effect.
The combustion of the specimens of composition No. 2 in air and argon occurred with the formation of reactive jets and was accompanied by a rapid release of gaseous products at the front of the wave, preventing the transfer of heat from the burned part to the initial reagents. Combustion in a vacuum was less intensive; the specimens did not burn completely.
At the attempt of the reaction initiation by a flat graphite heater, the specimen of composition No. 1 starts burning only in the place of contact. After preheating the specimens to 200-300 • C, the combustion in air, argon, and vacuum was conducted in the same mode as for the specimens of composition No. 2 but with a lower rate (1.6/1.8/0.2 mm/s respectively). Table 3 shows the combustion rates depending on the composition and medium for the W/PTFE/Al system. Composition No. 3 had the maximum combustion rate and compositions No. 1 and 2 had the minimum combustion rate.
It has been experimentally shown that the presence of air or an inert gas (Ar) in the reactor has little effect on the combustion rate. In the air, the reaction products contain tungsten oxide. This indicates that air participates in the reaction. However, the main reactants are still W, PTFE, and Al. When the experiment is done in a vacuum, the main factor affecting the combustion is not a chemical (as in the case of Ar or air) but a physical one, namely, the low pressure. The rarefied air environment affects considerably the combustion rate due to the mechanisms of heat transfer in the specimens. Combustion transfers heat through radiation, conduction, and convection. The burning specimens release a large number of hot gaseous products. In the rarefied air environment, these hot gaseous products are intensively drawn from the combustion front, which decreases the convective heat transfer from the areas of reacted initial reagents. Thus, the combustion front loses heat, which reduces the combustion rate. tungsten oxide. This indicates that air participates in the reaction. However, the main reactants are still W, PTFE, and Al. When the experiment is done in a vacuum, the main factor affecting the combustion is not a chemical (as in the case of Ar or air) but a physical one, namely, the low pressure. The rarefied air environment affects considerably the combustion rate due to the mechanisms of heat transfer in the specimens. Combustion transfers heat through radiation, conduction, and convection. The burning specimens release a large number of hot gaseous products. In the rarefied air environment, these hot gaseous products are intensively drawn from the combustion front, which decreases the convective heat transfer from the areas of reacted initial reagents. Thus, the combustion front loses heat, which reduces the combustion rate     Table 4 shows the ignition and combustion temperatures for the W/PTFE/Al system. The highest combustion temperature of composition No. 2 was 1900-2000 °C, which agrees with the thermodynamic calculations. Composition No. 4 had the lowest combustion temperature in the range of 1400-1500 °C. Composition No. 3 had an average combustion temperature in the range of 1500-1600 °C.   Table 4 shows the ignition and combustion temperatures for the W/PTFE/Al system. The highest combustion temperature of composition No. 2 was 1900-2000 • C, which agrees with the thermodynamic calculations. Composition No. 4 had the lowest combustion temperature in the range of 1400-1500 • C. Composition No. 3 had an average combustion temperature in the range of 1500-1600 • C. According to the XRD analysis of compositions No. 1-4 (with 5, 10, 20, 30 wt% Al, respectively) burned in argon, we can conclude that the combustion of composition No. Compositions No. 1-4 were subjected to shock-wave loading. During the impact, the flyer plate was welded to the surface of the matrix with the specimens, ensuring the safety of the products. Visual inspection of the matrix showed the occurrence of such a violent exothermic reaction in the cell filled with composition No. 2, that the flyer plate was perforated above the 2.5-mm-thick specimen ( Figure 11). In addition, the cell with composition No. 3, which emitted more gaseous products, showed only bloating without decompression. It should be noted that the calculated adiabatic temperature of this composition is more than 830 • C lower than that of the previous one. respectively) burned in argon, we can conclude that the combustion of composition No. 2 left the least amount of unreacted W, and Al was completely consumed, forming gaseous aluminum fluoride (Figure 10). Combustion in the air was distinguished by the formation of tungsten oxide (WO3) and a decrease in the proportion of other products (WC, W2C). The formation of tungsten aluminide (WAl4) and aluminum fluoride (AlF3) is typical for compositions No. 3 and No. 4 in addition to the formation of tungsten carbides (WC, W2C), while the formation of aluminum fluoride (AlF3) is typical for composition No. 1. Compositions No. 1-4 were subjected to shock-wave loading. During the impact, the flyer plate was welded to the surface of the matrix with the specimens, ensuring the safety of the products. Visual inspection of the matrix showed the occurrence of such a violent exothermic reaction in the cell filled with composition No. 2, that the flyer plate was perforated above the 2.5-mm-thick specimen ( Figure 11). In addition, the cell with composition No. 3, which emitted more gaseous products, showed only bloating without decompression. It should be noted that the calculated adiabatic temperature of this composition is more than 830 °C lower than that of the previous one. The conclusions after visual inspection were confirmed by the X-ray diffraction analysis ( Figure 12). The reaction products of compositions No. 2 and 3 practically did not contain the initial components, which indicates the maximum extent of the reaction, while in compositions No. 1 and 4 the exothermic reaction did not take place. Thus, despite the similarity of the calculated combustion temperatures and the proportion of condensed products for compositions No. 1 and 2, in practice, they behaved differently, which confirms the need for experimental testing of compositions. The conclusions after visual inspection were confirmed by the X-ray diffraction analysis ( Figure 12). The reaction products of compositions No. 2 and 3 practically did not contain the initial components, which indicates the maximum extent of the reaction, while in compositions No. 1 and 4 the exothermic reaction did not take place. Thus, despite the similarity of the calculated combustion temperatures and the proportion of condensed products for compositions No. 1 and 2, in practice, they behaved differently, which confirms the need for experimental testing of compositions.
The conclusions after visual inspection were confirmed by the X-ray diffraction analysis ( Figure 12). The reaction products of compositions No. 2 and 3 practically did not contain the initial components, which indicates the maximum extent of the reaction, while in compositions No. 1 and 4 the exothermic reaction did not take place. Thus, despite the similarity of the calculated combustion temperatures and the proportion of condensed products for compositions No. 1 and 2, in practice, they behaved differently, which confirms the need for experimental testing of compositions.
The thermodynamic calculations showed the possibility of combustion in the W/PTFE/ Al system at high combustion temperatures and large proportions of condensed products for compositions No. 1 (2776 • C and 75 wt%), No. 2 (2866 • C and 74 wt%), No. 3 (1710 • C and 66 wt%), and No. 4 (1382 • C and 57 wt%).
All compositions of the W/PTFE/Al system ignited in the thermal explosion mode in the air, argon, and vacuum, and the temperature jump occurred at a temperature of 800-900 • C, which is associated with a large number of gaseous products emitted.
It was found that, under normal conditions, composition No. 1 did not burn in the self-sustaining mode, but burned only after preheating the entire specimen. The main reason why combustion stops in the specimen of composition No. 1 is the lack of heat released when the thin layer of the specimen burns. To solve this problem, the specimen was preheated to 200-300 • C. A self-sustaining reaction occurs in the entire specimen of composition No. 1 when it is heated.
Compositions No. 2, 3, and 4 burned without preheating. These compositions release a large number of hot gaseous products, which sustain the combustion of the specimens. Composition No. 3 had the highest combustion rate (5 mm/s) and the combustion temperature of composition No. 2, which had the highest extent reaction was 2000 • C.
In the shock-wave loading experiments, an intense exothermic reaction in compositions No. 2 and 3 led to the perforation and deformation of the flyer plate. This effect was related to the maximum extent of the reaction. The main products were AlF 3 , W 2 C, and WC, which agrees with the thermodynamic calculations. Data Availability Statement: Data presented in this article are available at request from the corresponding author.