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Thermal Behavior, Non-Isothermal Decomposition Reaction Kinetics and Thermal-Safety Evaluation on 3-Amino-4-chloroximidofurazan.

Byline: BIAO YAN, HONGYA LI, HAIXIA MA, JIRONG SONG AND FENGQI ZHAO

Summary: 3-Amino-4-chloroximidofurazan (ACOF) is an important precursor of synthesizing new furazanon (furoxano) energetic compounds. Its thermal behavior was studied by the differential scanning calorimetry (DSC) method.

The results of this study show that there are three exothermic decomposition processes. Its kinetic parameters of the intense exothermic decomposition process were obtained from the analysis of the DSC curves. The apparent activation energy, pre-exponential factor and the mechanism function are 153.54 kJmol [?]1 , 10 14.34 s [?]1 and f((alpha)) = 2(1-(alpha))[-ln(1-(alpha))] 1/2 , respectively. The specific heat capacity of ACOF was determined with a continuous C p mode of micro-calorimeter. Using the relationship between C p and T with the thermal decomposition parameters, the time of the thermal decomposition from initialization to thermal explosion (adiabatic time-to-explosion, t TIAD ), the self-accelerating decomposition temperature (T SADT ), thermal ignition temperature (T TIT ), critical temperatures of thermal explosion (T b ) and period of validity (t 0.9 ) were obtained to evaluate its thermal safety.

Key words: 3-Amino-4-chloroximidofurazan (ACOF), thermal behavior, Non-isothermal kinetics, Thermal safety.

Introduction

Many studies show that furazan ring is a perfect structure unit for constructing new high energy density material [1-10]. Most of the energetic compounds containing furazan ring (such as 3,4-bis (nitrofurazano) furoxan (BNFF) [3, 4], 3,4-bis (4'- azidofurazano-3'-yl) furoxan (DAZTF) [6], and, 4- amino-3-(5-tetrazole) furazan(HAFT) [7], etc.) have common characteristics such as high standard enthalpy of formation ((delta)H f Th ), high nitrogen content, high energy density, good thermal stability, and low melting point. Theoretical calculations show that when a nitro group is displaced by a furazan group in energetic compounds, the density and detonation velocity can increase by about 0.06 - 0.08 gcm -3 and 300 ms -1 , respectively [2].

Thus furazan compounds have received much attention worldwide. 3-Amino-4- chloroximidofurazan (ACOF) (Fig. 1) is an important precursor of synthesizing new furazano (furoxano) energetic compounds, such as 3,4-bis (nitrofurazano) furoxan (BNFF) [3, 4], 3,4-bis (aminofurazano) furoxan (BAFF) [3, 5], 3,4-bis (4'-azidofurazano -3'- yl) furoxan (DAZTF) [6], 4-amino-3-(5- tetrazole)furazan(HAFT) and its energetic salts [7], 3,3'-Dicyanodifurazanyl Ether(FOF-2) [8], Oxidative cyclocondensation of 4,4'-diamino-3,3'-bi-1,2,5- oxadiazole and isomeric 3(4)-amino-4(3)-(4-amino- 1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole 2-oxides [9] and 3,6-bis(3'- aminofurazan-4-yl)-1,4-dioxa-2,5- diazacyclohexa-2,5-diyne (BADDD) [10]. So, it is significant to study the chemicophysical properties of ACOF. However, there're no reports on its thermal behavior. The purse of the article is to describe its thermal decomposition processes, non-isothermal decomposition kinetics and thermal safety.

Result and Discussion

Thermal Behavior

The DSC heat flow curve for ACOF at the heating rate of 10 Kmin -1 is shown in Fig. 2. The DSC curve indicates that the thermal decomposition of ACOF can be divided into three stages. The first stage is an intense exothermic decomposition process, the extrapolated onset temperature (T e ) and peak temperature (T p ) obtained at a heating rate of 10 Kmin -1 are 470.26 K and 485.89 K, respectively. The second stage is a mild exothermic decomposition process with T e and T p are 509.35 K and 541.32 K, respectively. The third stage is also a mild exothermic decomposition process with T e and T p are 589.40 K and 616.83 K, respectively. The basic data for the intense exothermic decomposition process are listed in (Table-1).

Table-1: Basic data for the intense exothermic decomposition process of ACOF.

(Beta)/(Kmin-1)###Te/K###Tp/K###(Delta)H/(Jg-1)

2.5###454.58###469.19###746.1

5###464.77###477.46###722.3

10###470.26###485.89###760.3

15###472.90###491.38###790.4

Non-Isothermal Decomposition Reaction Kinetics

To explore the reaction mechanism of the intense exothermic decomposition process of ACOF and obtain the corresponding kinetic parameters [apparent activation energy (E a /kJmol [?]1 ), pre- exponential constant (A/s [?]1 )] and the most probable kinetic model function, the DSC curves at the heating rates of 2.5, 5.0, 10.0 and 15.0 Kmin [?]1 were dealt with the mathematic means, and the temperature data corresponding to the conversion degrees ((alpha)) were found. Six integral methods (MacCallum-Tanner, Satava-Sestak, Agrawal, General integral, Universal integral, Flynn-Wall-Ozawa) and one differential method (Kissinger) were employed [11-15]. The values of E a were obtained by Ozawa's method from the isoconversional DSC curves at the heating rates of 2.5, 5.0, 10.0 and 15.0 Kmin [?]1 , and the E a -(alpha) relation is shown in Fig. 3. One can see that the activation energy slightly changes in the section of 0.15-0.70 ((alpha)), and the ranges were selected to calculate the non-isothermal reaction kinetics in Fig. 3.

Forty-one types of kinetic model functions and the basic data were put into the integral and differential equations for calculation. The kinetic parameters and the probable kinetic model function were selected by the logical choice method and satisfying the ordinary range of the thermal decomposition kinetic parameters for energetic materials (E = 80-250 kJmol -1 , lgA = 7-30 s -1 ). These data together with their appropriate values of linear correlation coefficient (r), standard mean square deviation (Q) and believable factor (d, where d = (1[?]r)Q), are presented in (Table-2). The values of E a and logA obtained from a single non-isothermal DSC curves are in good agreement with the calculated values obtained by Kissinger's method and Ozawa's method. Therefore, we conclude that the reaction mechanism of the intense exothermic decomposition process of ACOF is classified as Avrami-Erofeev equation G((alpha)) = [-ln(1-(alpha))] 1/2 , f((alpha)) = 2(1-(alpha))[-ln(1-(alpha))] 1/2 . Substituting f((alpha)) with 2(1-(alpha))[- ln(1-(alpha))] 1/2 , E with 153.54 kJmol -1 and A with 10 14.34 s - 1 Eq. (1),

Table-2: Kinetic parameters for the intense exothermic decomposition process of ACOF.

Method###(Beta)/

###Kmin-1 Ea/kJmol-1 log(A/s-1)###r###Q###d

###2.5###148.66###14.05###0.9999###7.36x10-5###7.52x10-9

MacCallum-Tanner###5###168.47###16.25###0.9998###1.39x10-4###2.67x10-8

###10###157.43###14.95###0.9993###5.36x10-4###3.99x10-7

###15###142.06###13.23###0.9986###1.00x10-3###1.39x10-6

Satava-Sestak###2.5###148.54###14.07###0.9999###7.36x10-5###7.52x10-9

###5###167.24###16.15###0.9998###1.39x10-4###2.67x10-8

###10###156.82###14.92###0.9993###5.36x10-4###3.99x10-7

Agrawal###15###142.31###13.31###0.9986###1.00x10-3###1.39x10-6

###2.5###148.48###14.08###0.9999###3.82x10-4###4.22x10-8

###5###167.99###16.24###0.9998###7.26x10-4###1.51x10-7

General integral###10###156.88###14.94###0.9992###2.87x10-3###2.38x10-6

###15###141.52###13.23###0.9984###5.35x10-3###8.39x10-6

###2.5###148.48###14.08###0.9999###3.82x10-4###4.22x10-8

Universal integral###5###167.99###16.24###0.9998###7.26x10-4###1.51x10-7

###10###156.88###14.95###0.9992###2.87x10-3###2.38x10-6

Mean###15###141.52###13.23###0.9984###5.35x10-3###8.39x10-6

Flynn-Wall-Ozawa###2.5###146.83###12.67###0.9999###3.95x10-4###4.62x10-8

Kissinger###5###166.57###14.81###0.9998###7.40x10-4###1.60x10-7

Mean(EeO,EpO, EK)###10###155.67###13.56###0.9992###2.83x10-3###2.36x10-6

###15###140.44###11.91###0.9984###5.30x10-3###8.35x10-6

###153.54###14.34###

###162.05(EeO)###0.9813###1.31x10-2###

###147.78(EpO)###0.9999###5.88x10-5###

###147.43(EK) 13.94###0.9999###3.23x10-4

Mean(EeO,EpO, EK)###152.42

Note: E with the subscript of eO and pO is the apparent activation energy obtained from the onset temperature (Te) and the peak temperature (Tp) by Ozawa's method, E with the subscript of K is the apparent activation energy obtained from the peak temperature (Tp) by Kissinger's method.

The kinetic equation of the intense exothermic decomposition reaction may be described as:

Thermal Safety Studies

The values (T e0 and T p0 ) of the onset temperature (T e ) and peak temperature (T p ) corresponding to (Beta)-0 are obtained by Eq. (2), and the self-accelerating decomposition temperature (T SADT ) is obtained by Eq. (3) [11-14]. The values (T SADT and T p0 ) are 436.03 K and 456.64 K, respectively.

The thermal ignition temperature (T be0 or T TIT ) are obtained by substituting E eo and T e0 into Zhang et al. equation [Eq. (4)] [16], and the critical temperatures of thermal explosion (T bp0 or T b ) are obtained by substituting E po and T p0 into equation. The values (T TIT and T b ) are 446.25 K and 469.02 K, respectively.

The entropy of activation ((delta)S [?] ), enthalpy of activation ((delta)H [?] ) and free energy of activation ((delta)G [?] ) of the main exothermic decomposition reaction of ACOF corresponding to T = T po , E a = E k and A = A k are obtained by Eqs. (5) - (7) [11-14], are 26.07 Jmol -1 K -1 , 147.43 kJmol -1 and 135.53 kJmol -1 , respectively. The positive values of (delta)G [?] , indicate that the exothermic decomposition reaction of ACOF must proceed under the heating condition. where k B is the Boltzman constant and h the Plank constant.

After the kinetic parameters (E a and A) were obtained, the rate constant (k) for decomposition reaction could be calculated by the following equation:

The period of validity of the ACOF could be determined by the following equation:

where k was the rate constant and could be obtained by Eq.(8), (alpha) is 0.1, G((alpha)) is [-ln(1-(alpha))] 1/2 , E a is 153.54 kJmol -1 , A is 10 14.34 s -1 , T is 298.15 K. The period of validity for ACOF is 37.29 thousand years, indicate that ACOF is very stable under 298.15 K.

The adiabatic time-to-explosion (t TIAD ) of energetic materials is the time of decomposition transiting to explosion under the adiabatic conditions. It is an important parameter for assessing the thermal stability and the safety of energetic materials.

where Q d decomposition heat, 754.78 Jg [?]1 . A, pre- exponential constant, A = 10 14.34 s [?]1 ; C p is the specific heat capacity measured by microcalorimeter in Jg [?]1 K [?]1 , E, activation energy, 153.54 kJmol -1 ; R, the gas constant, 8.314 Jmol -1 K -1 ; f((alpha)), differential

mechanism function f((alpha)) = 2(1-(alpha))[-ln(1-(alpha))] 1/2 .

Substituting the corresponding data into Smith equation Eqs. (10) and (11) [17, 18], The values of t TIAD is 497.96 s. In the calculation process of adiabatic time-to-explosion, a little change in the activation energy located in the integral equation with exponential form can make a great difference in the result, and a small increase of the activation energy can induce t TIAD to rise greatly.

Experimental

Materials and Analytic Instrument

ACOF was prepared and purified by a reported method [3]. The thermal behavior of ACOF was studied using a Q2000DSC (TA, USA) by the DSC method under atmospheric pressure. The sample mass is about 1.580 mg at the heating rates 2.5, 5.0, 10.0 and 15.0 Kmin -1 with nitrogen as the purge and the flow rate is 50 mlmin -1 . The temperature and heat were calibrated using pure indium and tin particles.

The specific heat capacity of ACOF was determined with a continuous C p mode on a Micro- DSCIII apparatus (Seteram, France) under atmospheric pressure, heating rate, 0.15 Kmin [?]1 , sample mass, 285.40 mg; atmosphere, N 2 ; and the specific heat capacity determined for ACOF is C p (Jg - 1 K -1 ) = 1.6041x10 -7 T 3 - 1.6121x10 -4 T 2 + 5.6467x10 - 2 T - 5.6373 (283K less than T less than 354K).

Conclusions

The thermal behavior of ACOF under the nonisothermal condition by DSC methods was studied. The apparent activation energy and pre- exponential factor of the intense exothermic decomposition reaction are 153.54 kJmol [?]1 and 10 14.34 s [?]1 , respectively. The reaction mechanism of the intense exothermic decomposition process of ACOF is classified as Avrami-Erofeev equation G((alpha)) = [-ln(1-(alpha))] 1/2 , f((alpha)) = 2(1-(alpha))[-ln(1-(alpha))] 1/2 .

The specific heat capacity was determined with Micro-DSC method. The specific heat capacity equation is C p (Jg - 1 K -1 ) = 1.6041x10 -7 T 3 - 1.6121x10 -4 T 2 + 5.6467x10 - 2 T - 5.6373. The self-accelerating decomposition temperature, the thermal ignition temperature and the critical temperatures of thermal explosion are 436.03 K, 446.25 K and 469.02 K, respectively. The values of (delta)S [?] , (delta)H [?] and (delta)G [?] of this reaction are 26.07 Jmol - 1 K -1 , 147.43 kJmol -1 and 135.53kJmol -1 , respectively. The period of validity is 37.29 thousand years. The adiabatic time-to-explosion was calculated to be 497.96 s.

Acknowledgments

This work is supported by the National Natural Science Foundation of China (No. 21073141), the education Committee Foundation of Shaanxi Province (No 11JK0564 and 11JK0582) and the Project-sponsored by SRF for AT, YLU (Grant No.09GK019).

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Publication:Journal of the Chemical Society of Pakistan
Article Type:Report
Geographic Code:9CHIN
Date:Jun 30, 2013
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