The Reactivity between Aluminum Powder and Liquid Phase of Fuel-air Explosives

XING Xiao-ling, ZHAO Sheng-xiang, LI Wen-xiang, FANG Wei

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

The Reactivity between Aluminum Powder and Liquid Phase of Fuel-air Explosives

XING Xiao-ling, ZHAO Sheng-xiang, LI Wen-xiang, FANG Wei

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

In order to study the reactivity of solid phase component (aluminum powder )and liquid phase components isopropyl nitrate (IPN) and hydrocarbon fuel MC10 in fuel-air explosive, the decomposition process of aluminum powder with IPN and MC10 under nitrogen atmosphere conditions was measured by high pressure DSC . The results show that there is an oxidation process of MC10 before the decomposition of IPN. Compared with the pure liquid MC10, the oxidation process of MC10 with IPN is more obvious and the oxidation temperature is much lower than that of the pure MC10. The aluminum powder can verify the high temperature pyrolysis process of MC10. The coexistence system of Al/IPN/MC10 has more stable status under high temperature conditions, which is favorable to improve the performance of FAE.

fuel-air explosive;FAE; reactivity; aluminum powder; liquid phase; high pressure DSC;IPN;MC10

Received date:2015-07-25； Revised date:2015-11-24

Foundation:Basic Technology of National Key Project

Biography:XING Xiao-ling(1982-),female,Ph.D.Research field: Applied chemistry.E-mail:arrling@126.com

Introduction

Aluminum is one of the important components for the fuel-air explosives(FAE)[1-3]. The main aim of adding aluminum powder to propellants, pyrotechnics and explosives is to boost their energetic density, and so it is in FAE[4]. The liquid phase in FAE is usually fuel with energy, and sometimes is mixture of different constituents. Both of the aluminum powder and the liquid phase have meaningful effects in FAE. The main trend of understanding for this is that the aluminum particles are coated by liquid and the interface energy of aluminum particles is reduced compared to pure aluminum particles, the reaction between the solid and liquid phases can be improved under the required conditions. The other understanding is that the liquid phase can make aluminum more sensitive once the explosion begins. In this study, we studied the reactivity between the aluminum powder and liquid phase of FAE by using high pressure DSC[5-6]. The liquid phase was the mixture of isopropyl nitrate (IPN) and hydrocarbon fuel MC10. The aluminum can verify the pyrolysis process of MC10. The Al/IPN/MC10 system containing three components has unique advantage on the stability performance of FAE.

1 Experiment

1.1 Materials and equipments

The aluminum powder (Al) used in the experiment with purity of over 85%was from Dongqing Company of Harbin, and the surface of the particles is coated by alumina. The isopropyl nitrate(IPN) and MC10 were prepared by Xi′an Modern Chemistry Research Institute with purities of over 98.3% and 97.9%, respectively.

The HP204 DSC employed in the experiment is from NETZCH Company of Germany, and the field emission scanning electron microscopy from FEI Company.

1.2 Performance test

The HP204 DSC from NETZCH Company of Germany was employed to obtain the heat flow curves of the systems. The crucibles were able to endure high pressures even 10MPa. The heating rate was 10℃/min, and the experimental pressure was 3MPa. The decomposition processes were completed in nitrogen atmosphere and the gas-flow was 25mL/min.

The field emission scanning electron microscopy was used to obtain SEM image of aluminum.

2 Results and discussions

2.1 The decomposition process of MC10

The decomposition curve of MC10 under experimental conditions is shown in Fig.1. From Fig.1, one can see a small exothermic peak at the temperature of 200.2℃. This can be attributed to the oxidation of MC10 by the dissolved oxygen. The products are the peroxides of alkyl groups and kinds of free radicals come from the peroxides of alkyl groups[7-10]. The alcohols, acids, ketones and ethers are formed after the following hydrogen abstraction reaction or the degeneration reaction of side chains. The unsaturated structures produced by pyrolysis processes show endothermic peaks at about 350-500℃. The unsaturated structures appear because of the limited oxygen in MC10. The final products of the pyrolysis are deposition with high carbon contents in it. We can see from Fig.1 that the pyrolysis does not finish during the experimental temperature, and the products may change accordingly with the higher temperature.

Fig.1 DSC curve of MC10 at a heating rate of 10℃/min

2.2 The decomposition process of Al/MC10

Aluminum powder was added to MC10 to research its effect on the decomposition process of MC10. The mass ratio of Al/MC10 was 1∶2, and the value is exactly from the ratio of the solid/liquid system in FAE ingredient. The DSC curves of MC10 and Al/MC10 system are shown as Fig.2.From Fig.2, one can see that the oxidation peak of MC10 is more obvious and the pyrolysis is very different from that of MC10. SEM image of Al is shown in Fig.3. From Fig.3, we can see that the distribution of Al is flake-like structure with loose part of the surface. The more obvious oxidation peak of MC10 can be attributed to the more oxygen from the Al surface areas. The main difference of pyrolysis process of the system after the addition of Al is the appearance of the exothermic process and the process does not finish during the experimental temperature. We can deduce that the process may be induced by the reaction between Al and MC10. Al can break up the aluminum oxide shell on its surface with rising the temperature, and the exposed Al can react with MC10 and change its thermal behavior under higher temperature conditions. The obvious change of the heat flow is that the endothermic process of MC10 to the exothermic process after the participation of Al. The slow oxidation of Al by the oxidizing products of MC10 can be observed.

Fig.2 DSC curves of MC10 and Al /MC10 at a heating rate of 10℃/min

Fig.3 SEM image of aluminum

2.3 The decomposition process of IPN/MC10

Besides Al, IPN was added to MC10 to research its effect on the decomposition process of MC10. The mass ratio of the two liquid phases IPN/MC10 is 2∶1, and this is also from the selected FAE ingredient. The details are shown as Fig.4.Fron Fig.4,We can see that the decomposition temperature of IPN is about 216.7℃ and the decomposition products experience obvious oscillation under the experimental condition. The oxidation process of MC10 with IPN is more obvious and the temperature is much lower than that of the pure MC10. More oxygen must be from the IPN molecules. The decomposition peak of IPN can be observed but the vibration disappeared. This may indicate that the reaction between the products of IPN and the oxidation process of MC10 takes place. The other phenomenon we observed from the DSC curve is that the endothermic pyrolysis process cannot be seen. The pyrolysis products of the MC10 may trend to kinds of saturated micromolecules under the influence of IPN, so there may be appearance of small exothermal peaks.

Fig.4 DSC curves of IPN, IPN/MC10 and MC10 at a heating rate of 10℃/min

2.4 The decomposition process of Al /IPN/MC10

The decomposition curve of the system composed of Al, IPN and MC10 is shown in Fig.5.The mass ratio of the three components of Al, IPN, MC10 is 1∶2∶1.From Fig.5, one can see that the oxidation of MC10 is more distinct compared to the decomposition of IPN. The more distinct oxidation process of MC10 must be the co-action of Al and IPN. The amount of heat releasing during the process is enlarged under the effect of Al, and the peak temperature is lower because of the IPN in the system. The decomposition peak temperature of IPN here is higher than that of the pure IPN at the same condition, and the reason may be that Al has participated in the decomposition process of IPN[11]and the thermal behavior of IPN may be changed. The unsaturated structures disappear because of the oxygen from IPN. The very significant improvement of the system is the more stable status at the higher temperature conditions and this must be meaningful for improving the performance of FAE[12].

Fig.5 DSC curve of Al /IPN/MC10 at a heating rate of 10℃/min

3 Conclusions

(1)The very significant improvement of the Al /IPN/MC10 system is that the more stable status at the higher temperature conditions and this must be meaningful for the performance improvement of FAE, and aluminum powder can affect on MC10.

(2)Under lower temperature conditions, the aluminum powder can make the oxidation peak of MC10 more obvious, and IPN can lower the oxidation temperature peak. The Al /IPN/MC10 system has meaningful function for improving the performance of FAE.

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燃料空氣炸藥中鋁粉與液相的反應特性

邢曉玲,趙省向, 李文祥,方 偉

(西安近代化學研究所，陜西 西安 710065)

為了研究燃料空氣炸藥中固相組分(鋁粉)與液相組分(IPN和烴類燃料MC10)的反應特性，用高壓DSC測試鋁粉與IPN及MC10在氮氣氣氛中的分解過程。結果表明，在IPN分解之前存在MC10的氧化過程。與純MC10液體相比，MC10在IPN存在條件下氧化過程更明顯，氧化溫度更低，同時鋁粉能夠改變MC10的高溫分解過程。Al/IPN/MC10三組分共存體系在高溫條件下具有更穩(wěn)定的狀態(tài)，有利于提高燃料空氣炸藥的性能。

燃料空氣炸藥;FAE;反應特性;鋁粉;液相;高壓DSC；IPN;MC10

10.14077/j.issn.1007-7812.2016.06.009

TJ55;TQ560 Document Code：A Article ID：1007-7812(2016)06-0055-03

ZHAO Sheng-xiang(1963-),male,Professor, Ph.D.Research field: energetic materials.E-mail:zsx58@sina.com