LI He-qun，AN Chong-wei，DU Meng-yuan，WEN Xiao-mu，WANG Jing-yu

(1.School of Chemical and Environmental Engineering，North University of China，Taiyuan 030051，China;2.Shanxi Lu′an Mining (Group) Co., Ltd，Changzhi Shanxi 046000，China)

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Study on Kinetic Parameters of Thermal Decomposition Reaction and Thermal Stability of 3,4-Bis(3-nitrofurazan-4-yl)furoxan Based on Kissinger Method

LI He-qun1，AN Chong-wei1，DU Meng-yuan2，WEN Xiao-mu1，WANG Jing-yu1

(1.School of Chemical and Environmental Engineering，North University of China，Taiyuan 030051，China;2.Shanxi Lu′an Mining (Group) Co., Ltd，Changzhi Shanxi 046000，China)

Abstract:The thermal decomposition characteristics of DNTF and 2,4,6-trinitrotoluene (TNT) were investigated by means of differential scanning calorimetry at different heating rates. The kinetic parameters of thermal decomposition reaction, critical temperature of thermal explosion and thermodynamic parameters were calculated, contrasted and analyzed by Kissinger methed. The results show that the thermal decomposition process of DNTF is different with TNT, it occurs in two stages and the first acts as the major part. The activation energy of DNTF is 168.85kJ/mol, which is about 58kJ/mol higher than that of TNT, revealing that DNTF has a good thermal stability at low temperature. However, all the other thermodynamic parameters of DNTF are higher than those of TNT except the free energy of activation. The decomposition peak temperatures and critical temperature of thermal explosion of DNTF are lower than those of TNT. So,the thermal stability of DNTF is poorer than that of TNT.

Keywords:DNTF; TNT; thermal decomposition; kinetics; thermodynamics;kissinger method

Introduction

A high energetic compound based on furazan and furoxan (3,4-bis(3-nitrofurazan-4-yl)furoxan, DNTF) has been first synthesized by Xi′an Modern Chemistry Research Institute of China[1]and N. D. Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences[2]. Its energy output is more than that of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) and slightly lower than that of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20). Because of this characteristic, it has obtained wide attention and affirmation in the field of research and application of energetic materials[3]. In order to learn more about DNTF, its crystal structure[4], density function theory[5], specific heat capacity, thermodynamic properties, adiabatic time-to-explosion, thermal sensitivity probability density distribution[6], nuclear magnetic resonance characterization and solubility in common solvents[7]were studied thoroughly. DNTF is an organic matter that does not contain hydrogen element. This provides the possibility of employing in the low characteristic signal propellant. Recent researches indicated that when DNTF was added into a composite modified double-base (CMDB) propellant, both the burning rate and the pressure exponent increased[8]. Meanwhile, the thermal decomposition rate gradually decreased as the DNTF content increased[9]. When the mass fraction reached 20%, the propellant possessed optimal mechanical properties. In addition, DNTF is sensitive to shock wave and its detonation critical diameter is less than micro size. The critical diameter of DNTF/2,4,6-trinitrotoluene (TNT)/ benzotrifuroxan (BTF) eutectic could even reduce to 0.15 mm[10]. As a consequence, the formulations with DNTF can be used in small size groove of explosive network. Beyond that, DNTF is less sensitive to impact and friction. Its melting point is about 110℃ and it can form the eutectic system with pentaerythritol tetranitrate (PETN)[11], 1, 3, 3-trinitroazetidine (TNAZ)[12]and 2,4-dinitroanisole (DNAN), respectively. The energy of melt cast explosive greatly improved with the addition of DNTF.

Thermal decomposition performance is an extremely significant index for assessing the stability of energetic materials. Of course, the thermal properties of DNTF were discussed[13]since it had been synthesized. To further understanding the thermal decomposition properties of DNTF, in this work, the differential scanning calorimetry (DSC) curves of DNTF were tested under the condition of different heating rates. Moreover, the thermal kinetic parameters, critical temperature of thermal explosion and thermodynamic parameters were calculated and investigated. Besides, traditional melt cast carrier TNT was considered as a reference.

1Experimental

DNTF and TNT were purchased from Gansu Yinguang Chemical Industry Co. Ltd. of China.

DSC studies were carried out on DSC 200 F3, which was made by Netzsch of Germany. Samples of about 1mg were put in an aluminum crucible with a hole in the lid under nitrogen atmosphere (50mL/min) at the heating rates of 1, 2, 5 and 10℃/min, respectively. Each test was conducted under the pressure of 2 MPa to prevent sample volatilizing.

2Results and discussions

2.1Results of thermal analysis

The DSC curves and data of DNTF and TNT are presented in Fig.1 and Table 1. It can be found that there is an endothermic peak at about 109℃ in each DSC curve of DNTF. The temperature compares favorably with its melting point. So does TNT at about 78℃. And TNT has one exothermic peak, which is attributed to the thermal decomposition. Unlike that of TNT, the thermal decomposition process of DNTF can be carried out in two stages. Among them, the maximum heat flow of first stage is higher than that of the second stage. The first decomposition peak temperature of DNTF is lower than that of TNT at the same heating rate.

Fig. 1　Non-isothermal DSC curves of samples atvarious heating rates

β/(℃·min-1)Tp1/℃Tp2/℃DNTFTNTDNTFTNT1108.6276.98251.48266.092108.6377.78258.67283.885108.8578.66272.18303.3910110.3478.95282.29316.59

2.2Thermal kinetic parameters

(1)

whereEis the activation energy in kJ/mol;Ais the pre-exponential factor in s-1;βis the heating rate in ℃/min;Tpis the peak temperature of decomposition reaction atβinK;Ris the universal gas constant (8.314J·mol-1·K-1).

Fig.2　Kissinger′s plots of DNTF and TNT

As shown in Fig.2, the linear fitting of DNTF and TNT is straight lines withR=-0.998 andR=-0.996, respectively, which demonstrates that Kissinger method is applied to calculate the thermal kinetic parameters. From Table 2, the activation energy of DNTF is about 58 kJ/mol higher than that of TNT. Therefore, DNTF has good thermal stability at low temperature.

Table 2　The results of computed parameters

2.3Critical temperature of thermal explosion

The critical temperature of thermal explosion (Tb) acts as the lowest ambient temperature to make energetic materials self-explosion. It is an extraordinarily vital parameter for energetic materials when it comes to insure safe storage and process operations.Tbcan be calculated according to the following equations[15].

(2)

(3)

wherebandcare constants;βiis the heating rate in ℃·min-1;Tpiis the peak temperature of decomposition reaction atβiin K;Tp0is the peak temperature whenβiis zero in K;Eis the activation energy in J/mol;Tbis the critical temperature of thermal explosion in K.

First of all,Tp0is calculated according to Eq.(2). ThenTp0,EandAare brought in Eq.(3), the critical temperature of thermal explosion of DNTF and TNT is obtained and the results are shown in Table 3. It can be clearly seen from table 3 that the critical temperature of thermal explosion of DNTF is lower than that of TNT. However, it is more stable than the conventional nitramine explosives RDX and CL-20.

Table 3　Comparison of critical temperature of thermal

2.4Thermodynamic parameters of activation reaction

The thermodynamic parameters of activation reaction of DNTF and TNT can be calculated in accordance with Eqs.(4)-(6)[18-19]. The results of such calculations are presented in Table 2.

(4)

ΔH≠=E-RT

(5)

(6)

whereΔG≠is the free energy of activation in kJ/mol;ΔH≠is the enthalpy of activation in k/Jmol;ΔS≠is the entropy of activation J/mol;kBis the Boltzmann constant, 1.3807×10-23J/K;his the Plank constant, 6.626×10-34J·s;TisTp0calculated by Eq.(2);EandAare the kinetic parameters obtained by Kissinger method.

It can be seen from Table 2 that all the thermodynamic parameters of DNTF are higher than those of TNT except the free energy of activation. The value of the free energy of activation of DNTF is close to that of TNT , revealing that DNTF has heat-resistance ability level approaching that of TNT.

3Conclusions

(1) The thermal decomposition process of DNTF can be divided into two stages. The first exothermic decomposition peak temperature of DNTF is lower than that of TNT at the same heating rate.

(2) The kinetic parameters, their critical temperature of thermal explosion and thermodynamic parameters for exothermic decomposition reaction of DNTF and TNT were obtained.

(3) The value of the free energy of activation of DNTF is close to one of TNT, realing that DNTF has heat-resistance ability level approaching that of TNT.

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基于Kissinger方法的3,4-雙(4-硝基呋咱-3-基)氧化呋咱的熱分解反應動力學參數(shù)和熱穩(wěn)定性研究

李鶴群1，安崇偉1，杜夢遠2，溫曉沐1，王晶禹1

(1. 中北大學化工與環(huán)境學院，山西 太原 030051;2. 山西潞安礦業(yè)(集團)有限責任公司，山西 長治 046000)

摘要：采用差示掃描量熱法研究了DNTF和TNT在不同升溫速率下的熱分解特性；利用Kissinger方法計算和對比分析了DNTF和TNT的熱分解反應動力學參數(shù)、熱爆炸臨界溫度和熱力學參數(shù)。結(jié)果表明，DNTF的熱分解過程不同于TNT，DNTF的熱分解經(jīng)歷了兩個階段，其中第1階段為主要部分。DNTF的活化能為168.85kJ/mol，比TNT高約58kJ/mol，表明DNTF在低溫下有良好的熱穩(wěn)定性。然而，除自由活化能外，DNTF的其他熱力學參數(shù)均比TNT高。DNTF的熱分解峰溫和熱爆炸臨界溫度都比TNT小。因此，與TNT相比，DNTF的熱穩(wěn)定性差。

關(guān)鍵詞：DNTF；TNT；熱分解；動力學；熱力學；Kissinger方法

DOI：10.14077/j.issn.1007-7812.2016.03.0011

Received date:2015-10-12；Revised date:2016-02-25

CLC number：TJ55;TQ560

Document Code：AArticle ID：1007-7812(2016)03-0058-03

Biography:LI He-qun (1990-), male, Ph.D, research field: explosives and propellants. E-mail:lhq6371630@163.com