ZHOU Jing, AN Jing, DING Li, ZHAO Sheng-xiang, FANG Wei

(Xi′an Modern Chemistry Research Institute, Xi′an 710065, China)

Thermal Behaviors of the Main Components in Nano-based Fuel Air Explosive

ZHOU Jing, AN Jing, DING Li, ZHAO Sheng-xiang, FANG Wei

(Xi′an Modern Chemistry Research Institute, Xi′an 710065, China)

The thermal behaviors in non-oxidizing environment and closed environment of isopropyl nitrate(IPN), high-density liquid fuels (HLF) and nanometer aluminum powder (nano-Al), as the main components in nano-based Fuel Air Explosive (FAE), were investigated by using DSC and DSC/TG-FTIR-MS coupled technique. The influence of nano-Al powder on the thermal behaviors of the main components in FAE was compared. The results show that the decomposition process of the main components in FAE is mainly divided into two stages: endothermic gasification and exothermic decomposition. IPN and HLF are the main energy source of FAE. The decomposition products of IPN can react with HLF and produce heat.

fuel air explosive; nano-Al powder; thermal decomposition; FAE;IPN;HLF

Introduction

Fuel air explosive (FAE) is widely researched and applied since its discovery in the 1950s[1]. Significant changes have taken place in conventional weapons with the use of FAE. The salient feature of FAE is that the oxygen needed for detonation come from air around. Thus, the charging efficiency can be greatly improved[2-3]. Intensive attention was paid to FAE due to its high energy, distribution explosion and so on. In recent years, storage stability and explosive power are urgent need to resolve two key issues for FAE.

Major component of FAE is high energy fuel. At the same time, aluminum is added to improve explosive power due to its high energy and adequate sources[4]. Comprehensive studies of the combustion model[5-6], detonation velocity[7], dispersion[8],detonation mode[9-10],thermal radiation[11]and safety performance[12]of FAE have been carried out. However, there are few reports about the decomposition process of FAE and the influence of aluminum on the decomposition of other components in FAE.

The current work was aimed at the FAE composed of high-density liquid fuels (HLF), isopropyl nitrate (IPN) and nanometer aluminum powder (nano-Al). Based on the DSC/TG-FTIR-MS method, a thermal decomposition process was proposed for FAE. Furthermore, the effects of nano-Al on the thermal decomposition of other components in FAE were presented.

1 Experimental

1.1 Samples

Nano-aluminum，with particle size of 5nm, was supplied by Beijing DK Nano technology Co., LTD. 1,3-Dimethyladamantane was chosen as high-density liquid fuels (HLF) and purchased from Alfa Aesar. Isopropyl nitrate (IPN) (purity>99.0%) used in this work was obtained from Jinjinle Chemical Co., LTD. Mixture A (HLF/IPN=50∶50) and mixture B (HLF/IPN/Nano-Al=30∶30∶40) were both prepared by mechanical mixing of the chemicals using laboratory mortar.

1.2 Apparatus and measurements

A TG/DSC-MS-FTIR coupling system composed of a NETZSCH (Selb, Germany) STA449C, NETZSCH-QMS403C, and Nicolet (Madison, WI, USA) 6700 FTIR were used for thermal analysis. The sample was encapsulated in an Au crucible with a pin hole on the lid (i.e., the measurements were realized at atmospheric pressure in non-oxidizing environment). Measurements were performed from 40℃ to 500℃ under similar conditions for both mixture A and mixture B. High-purity argon was used with a gas flow rate of 25mL/min.

The DSC measurements in closed environment were preformed using a differential scanning calorimeter (DSC Q200) from TA in sealed Au pans with nitrogen flow rate of 50mL/min. The temperature was programmed at 10℃/min from 50℃ to 500℃.

PDSC analyses under pressure of 4MPa and 2MPa were performed on DSC 204(NETZSCH, Germany) at a heating rate of 10℃/ min in nitrogen atmosphere from room temperature to 500℃.

2 Results and Discussion

2.1 Thermal analysis of the main components in FAE

Thermal analysis experiments of mixture B under different conditions were carried out to study the thermal behaviors of the main components in FAE. Fig.1 shows the DSC-TG/DTG measurements at a heating rate of 10℃/min. It can be seen in Fig.1, DSC curve for mixture B is consisted of five endothermic peaks, and a multi-stage process was also observed on the TG/DTG curves (Fig.1). It shows that mixture B exhibits at least five stages on TG/DTG curves, which starts at about 40.3℃ and completes at 355.8℃.

Further analysis of the DSC-TG/DTG curves indicates that there exists only endothermic peak on DSC curve, no exothermic peak under such test condition. Perhaps the main reason, however, centers on gasification of some components in FAE.

To find out, DSC curve in closed environment was recorded and showed in Fig.2. As expected, an obvious exothermic peak is observed due to the decomposition of energetic components in FAE. Simultaneously, PDSC were also conducted as shown in Fig.3. It was shown that the endothermic peaks at the temperature below 150℃ disappeared with increasing the pressure. In view of the peak appears at a low temperature, it should be gasification processes.

In conclusion, thermal behaviors of the main components in FAE at a temperature under 500℃ are mainly divided into two stages, which are endothermic gasification and exothermic decomposition.

2.2 Gasification process of main components in FAE

Considering IPN and HLF are subject to gasification under heating, mixture A was employed to disclose the gasification process mentioned above. Fig.4 is DSC-TG/DTG curves of mixture A in non-oxidizing environment. It can be seen from Fig.4 that two sharp endothermic peaks are well formed with peak maximum temperatures of 110.9℃ and 142.9℃ respectively. However, the two endothermic peaks are all disappeared when the DSC experiment was carried out in closed environment (Fig.5). The boiling point of IPN is 101-102℃ around the temperature of 110.9℃. Thus, the endothermic peaks at the temperatures of 110.9℃ should be the gasification of IPN.

Simultaneously, the gases evolved from DSC/TG-DTG furnace were further analyzed by FTIR. The characteristic spectra at the temperature of 110.9℃ was obtained with the TG pattern and showed in Fig.6. IR absorption bands at the temperatures of 110.9℃ locate at 855.81, 1283.58, 1649.27, 2878.29 and 2956.60cm-1assigned to the stretching vibration of NO, asymmetric stretching vibrations of ONO2, dissymmetric stretching vibrations of ONO2, asymmetric stretching vibrations of CH3, and dissymmetric stretching vibrations of CH3, respectively. According to literature report[13], the spectrum at the temperature of 110.9℃ is quite similar to the spectrum of IPN.

The gasification processes were also confirmed by PDSC curves of IPN, HLF and mixture A in Fig.7. It was also shown that the gasification process of IPN and HLF can be inhibited only when there was enough pressure. In fact, the easy or complexity of gasification refer to the main technical indexes of FAE.

Taking into account above results, the two endothermic peaks are due to the gasification of IPN and HLF, where the first one (with the peak temperature approximated 100 ℃) belongs to the gasification of IPN and the second one (with the peak temperature approximated 150℃) belongs to the gasification of HLF.

2.3 Decomposition process of main components in FAE

The experiments data of different conditions under high-temperature side were analyzed to study the decomposition process of main components in FAE. Fig.4 illustrates again that no exothermic peak was observed on the DSC curves due to most of the sample were vaporized and escaped from DSC/TG-DTG furnace under heating. However, the PDSC curves and DSC curves in closed environment refer primarily to decomposition and give off heat.

The reason is the gasification process of IPN and HLF were inhibited obviously under high pressures or a small, confined space, most of the samples are still in liquid state.

DSC curves of IPN, HLF and IPN/HLF in closed environment were recorded and showed in the illustration of Fig.8. The endothermic peak of HLF in the high temperature turned to be an exothermic peak with the addition of IPN. This fact demonstrates that the decomposition products of IPN are able to react with HLF and gave off heat. Especially, HLF is prone to be oxidized by nitrogen oxides, which

have powerful oxidization capacity.

2.4.The effect of nano-Al on decomposition of FAE

The DSC curves of mixture A and mixture B at a heating rate of 10℃ min are shown in Fig.9. The TG/DTG curves for both mixtures A and mixture B are shown in Fig.10, and the characteristic parameters of TG and DTG curves of both two mixtures are summarized in Table 1.

It shows that mixture A exhibits at least five stages on TG and DTG curves, which starts at about 40.3℃ and completes at 355.8℃.

Table 1 The peak temperature (Tp) and mass loss (Dw, ω%) for mixtures A and B

Note:Tp, temperature corresponding to the maximum rate of mass loss;Dw, corresponding mass loss

It can be seen from Fig.9 that after the addition of nano-Al, the gasification temperature of IPN increases from 110.9℃ to 124.6℃ and the gasification temperature of HLF increases from 142.9℃ to 169.2℃, respectively. This phenomenon shows nano-Al will raise the initial volatile temperature and decrease the mass loss rates obviously at low temperature. The effect of nano-Al to the gasification processes of the main components in FAE is probably attributed to the surface adsorption. Nano-Al with a large surface area can adsorb gaseous reactive molecules on their surface. The first thing for IPN and HLF are to release from nano-Al before gasification. This process of desorption is endothermic. Therefore, gasification temperature of IPN and HLF all shifted to the high-temperature side with a more moderate endothermic progress.To learn the influence of nano-Al on the decomposition process, DSC curves of mixture A and mixture B in closed environment were employed (Fig.11).

By comparison, we can find that the temperature of major exothermal peak remains unchanged. However, DSC curve of mixture B has more exothermal peaks than that mixture A, indicating the complex interactions between nano-Al and other components in FAE.

3 Conclusions

(1) Thermal behaviors of the main components in FAE at a temperature under 500℃ are mainly divided into endothermic gasification and exothermic decomposition.

(2) IPN and HLF as the energy source are both released at the initial stage.

(3) Nano-Al can raise the initial volatile temperature and decrease the mass loss rates obviously at low temperature.

(4) The decomposition products of IPN can react with HLF and gave off heat. The influence of nano-Al on the decomposition process is complex.

[1] Jiang L, Bai C H, Liu Q M. Experimental study on DDT process in 3-phase suspensions of gas/solid particle/liquid mist mixture[J]. Explosion and Shock Waves, 2010, 30(6): 588-592.

[2] Zheng C M, Rui Y, Liu Z W, et al. Experimental study on oxygen consumption effect of thermo-baric explosives[J]. Chinese Journal of Explosives & Propellants (Huozhayao Xuebao), 2014, 37(5): 33-36.

[3] Yang L Z, Zhang C Y, Zhang Z C, et al. Selection of fuels of high power FAE[J]. Journal of Nan Jing University of Science and Technology, 1998, 22:15-18.

[4] Si L H. Nano-metal fuel[J]. Chinese Journal of Chemical Education, 2007, 28(1): 11-12.

[5] Gubin S A, Sichel M. Calculation of the detonation velocity of a mixture of liquid fuel droplets and a gaseous oxidizer[J]. Combustion Science and Technology, 2007, 17(3-4): 109-117.

[6] Liu G, Hou F, Cao B, et al. Experimental study of fuel-air explosive[J]. Combustion Explosion & Shock Waves, 2008, 44(2):213-217.

[7] Zhi X Q. Computation on detonation velocity of single event FAE[J]. Chinese Journal of Explosives & Propellants (Huozhayao Xuebao), 2005, 28(3):76-78.

[8] XU X Z,Pei M J,Wang Y H,et al.Dispersion characteristics of single-event FAE[J].Chinese Journal of Explosives and Propellants(Huozhayao Xuebao),2000,23(1):47-49.

[9] Moen I O, Murray S B, Bjerketvedt D, et al. Diffraction of detonation from tubes into a large fuel-air explosive cloud[J]. Symposium (International) on Combustion, 1982, 19(1): 635-644.

[10] Huang L,He Z Q,Li C G,et al.Application of heat flux microsensor in radiation measurement of blasting field[J].Chinese Journal of Explosives and Propellants(Huozhayao Xuebao),2011,34(5):38-42.

[11] Lee J H. Chemical initiation of detonation in fuel-air explosive clouds: US, 5168123[P]. 1992.

[12] Wei G H, Sun Y W, Hui M A. Research on electrostatic safety of fuel air explosive projectile[J]. Journal of Beijing Institute of Technology, 2005, 25: 89-91.

[13] Kan J L, Zeng X L, Chen W H, et al. Study on FTIR and thermal decomposition kinetics of NPN and IPN[J]. Explosive Materials, 2007, 36(4): 1-2.

納米基燃料空氣炸藥主要組分的熱行為

周 靜，安 靜,丁 黎, 趙省向, 方 偉

(西安近代化學(xué)研究所，陜西 西安 710065)

采用DSC及DSC/TG-FTIR-MS聯(lián)用技術(shù)研究了納米基燃料空氣炸藥(FAE)中主要組分硝酸異丙酯(IPN)、高密度烴(HLF)、納米鋁粉在無氧條件和密封環(huán)境下的熱行為。比較了納米鋁粉對FAE中主要組分熱行為的影響。結(jié)果表明，F(xiàn)AE主要組分的熱分解過程主要分為吸熱氣化和放熱分解兩階段；IPN和HLF是FAE的主要能量來源；IPN的分解產(chǎn)物可以與HLF反應(yīng)并放出熱量。

燃料空氣炸藥；納米鋁粉；熱分解；FAE;IPN;HLF

10.14077/j.issn.1007-7812.2017.03.005

date:2016-10-21； Revised date:2017-01-09

DING Li(1970-), female, research field: Thermal analysis for energetic materials. E-mail: dingli403@sina.com

TJ55;TQ560 Document Code：A Article ID：1007-7812(2017)03-0031-05

Foundation:National Natural Science Foundation of China (No.21473131; No. 21473130)

Biography:ZHOU Jing (1987-), female，research field: Thermal analysis for energetic materials. E-mail: zhoujing19872006@163.com