Thermodynamic Properties and Detonation Characterization of 3,3

Oct 3, 2013 - Conservation Technology Department, The Palace Museum, Beijing 100009 ... synthesis, crystal structures, and non-isothermal kinetic anal...
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Thermodynamic Properties and Detonation Characterization of 3,3Dinitroazetidinium Hydrochloride Biao Yan,†,‡ Hongya Li,†,‡ Ningning Zhao,‡ Haixia Ma,*,‡ Jirong Song,‡,§ Fengqi Zhao,∥ and Rongzu Hu∥ †

School of Chemistry and Chemical Engineering, Shaanxi Key Laboratory of Low Metamorphic Coal Clean Utilization, Yulin University, Yulin 719000, Shaanxi, China ‡ School of Chemical Engineering, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Xi’an 710069, Shaanxi, China § Conservation Technology Department, The Palace Museum, Beijing 100009, China ∥ Science and Technology on Combustion and Explosion Laboratory, Xi’an Modern Chemistry Research Institute, Xi’an 710065, Shaanxi, China ABSTRACT: The thermal behavior of 3,3-dinitroazetidinium hydrochloride (DNAZ·HCl) was studied at a nonisothermal condition by differential scanning calorimetric and thermogravimetric/differential thermogravimetric methods. The results show that there is only one intense exothermic decomposition process. Its kinetic parameters of the intense exothermic decomposition process are obtained from analysis of the DSC curves. The apparent activation energy (Ea), pre-exponential factor (A), and the mechanism function ( f(α)) are 155.72 kJ·mol−1, 1015.84 s−1 and 3α2/3, respectively. The specific heat capacity (Cp) of DNAZ·HCl was determined with a continuous Cp mode of microcalorimeter. The specific molar heat capacity (Cp,m) of DNAZ·HCl was 205.10 J·mol−1·K−1 at 298.15 K. The selfaccelerating decomposition temperature (TSADT), thermal ignition temperature (TTIT), and critical temperatures of thermal explosion (Tb) were obtained to evaluate the thermal stability and safety of DNAZ·HCl. The detonation velocity (D) and detonation pressure (P) of DNAZ·HCl were estimated using the nitrogen equivalent equation according to the experimental density. The stability, safety, and detonation performance of DNAZ·HCl were compared with that of 3,3-dinitroazetidinium 3,5dinitrosalicylate (DNAZ·HClO4).

1. INTRODUCTION

dinitrosalicylate (DNAZ·HClO4, Figure 1) through the frontier orbital energy by a theoretical calculation, the thermal behavior, and the thermal safety temperature. The detonation characterization for DNAZ·HCl was also performed and compared with that of DNAZ·HClO4 to deepen the study of structure−activity relationship.

Dinitro- and trinitro-derivatives of azetidine contain a strained ring system, and this structural feature makes them good candidates for energetic materials (propellants or explosives). Initial reports of 1,3,3-trinitroazetidine (TNAZ) and 3,3dinitroazetidine (DNAZ) concentrate on their synthesis.1−3 DNAZ (pKb = 6.5) is the most important derivative of TNAZ; it can prepare a mass of solid energetic DNAZ salt.3−12 3,3Dinitroazetidinium hydrochloride (DNAZ·HCl, Figure 1) is a novel insensitive high energy explosive. Presently, there is no literature reported about the thermal and detonation characterization of DNAZ·HCl. The thermal stability and safety of DNAZ·HCl were compared with 3,3-dinitroazetidinium 3,5-

2. EXPERIMENTAL SECTION 2.1. Materials and Analytical Instrument. The DNAZ· HCl was synthesized and purified according to a reported method. A colorless single crystal of DNAZ·HCl (CCDC 907770)12 was obtained. The purity of the single crystal was above 0.998 as determined by HPLC. The differential scanning calorimetric (DSC) and thermogravimetric/differential thermogravimetric (TG/DTG) analyses of DNAZ·HCl were conducted using a Q600SDT (TA, USA) instrument under a nitrogen atmosphere (purity, 99.999 %) at a flow rate of 100 cm3·min−1 with the sample mass of about 1.346 mg, and the heating rates were (2.5, 5.0, 10.0, and 15.0) K·min−1. The temperature and heat were calibrated using pure indium Received: May 15, 2013 Accepted: September 20, 2013 Published: October 3, 2013

Figure 1. Molecular structure of DNAZ salt. Left, DNAZ· HCl; right, DNAZ· HClO4. © 2013 American Chemical Society

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(purity, 99.99 %) and tin (purity, 99.99 %) particles under a nitrogen atmosphere at a flow rate of 100 cm3·min−1, and the heating rate was 10.0 K·min−1. The melting point of In (156.61 °C) and Sn (231.89 °C) are 156.56(0.27) °C and 231.95(0.33) °C, respectively. The melting enthalpy of In (28.4 J·g−1) and Sn (60.6 J·g−1) are 28.6(0.2) J·g−1 and 60.8(0.3) J·g−1, respectively. All results indicate that the accuracy of tests is satisfactory. The specific heat capacity (Cp) of DNAZ·HCl was determined by a continuous Cp mode on a Micro−DSCIII apparatus (Setaram, France) under a nitrogen atmosphere (purity, 99.999 %) in the temperature range from (283 to 353) K at a heating rate of 0.15 K·min−1 and the sample mass of 260.56 mg. The mircocalorimeter was calibrated with α-Al2O3 (calcined), its mathematical expression was Cp (J·g−1·K−1) = 0.1839 + 1.9966·10−3T, and the standard specific molar heat capacity was 79.44 J·mol−1·K−1 at 298.15 K, which is in an excellent agreement with the reported value (79.02 J·mol−1· K−1).13 2.2. Standard Deviation. The standard deviations of data except that for ΔG⧧ were calculated with the eq 1.14 σ = [Σ(X i − X mean)2 /n]0.5

Figure 2. DSC curve of DNAZ·HCl at 10.0 K·min−1.

(1)

The standard deviation of ΔG⧧ was calculated with the eqs 2 and 3. when N = X ± Y , when N = XY

σ ( N ) = σ ( X ) + σ (Y )

(2)

σ(N )/N = σ(X )/X + σ(Y )/Y

(3)

Figure 3. TG/DTG curves of DNAZ·HCl at 10.0 K·min−1: black line, TG; red line, DTG.

3. RESULTS AND DISCUSSION 3.1. Frontier Orbital Energy. The density functional theory (DFT) method of the Amsterdam Density Functional package (ADF 2005.01) was used to perform geometry optimization and frequency calculation.15−17 There is no imaginary frequency in the result of the frequency calculation, this indicates that our optimized geometry is the stable one. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have a great impact on the chemical properties of a compound; the HOMO can provide electrons, the LUMO can have a priority to accept electrons, and energy gap between the HOMO and LUMO can be used to characterize the chemical stability of a compound. The frontier orbital energy of DNAZ·HCl and DNAZ·HClO4 are listed in Table 1. ΔEL‑H of the DNAZ·HCl is smaller than that of DNAZ·HClO4, which indicates that DNAZ·HClO4 has better chemical stability than DNAZ·HCl.

of DNAZ·HClO4 (465.24 and 473.99 K),7 which indicates that DNAZ·HClO4 has better thermal stability than DNAZ·HCl. The TG/DTG curves show that the stage begins at 457.11 K and completes at 496.50 K with a mass loss of 67.74 %. The basic data on DSC for the decomposition process are listed in Table 2. Table 2. Basic Data for the Intense Exothermic Decomposition Process of DNAZ·HCl βa/K·min−1 2.5 5.0 10.0 15.0

EHOMOa/eV

ELUMOb/eV

ΔEL‑Hc/eV

DNAZ·HCl DNAZ·HClO4

−5.850 −6.841

−4.836 −5.001

1.014 1.840

442.46 450.55 458.35 463.08

± ± ± ±

0.53 0.56 0.55 0.82

Tpc/K 453.34 462.53 467.80 472.20

± ± ± ±

0.39 0.58 0.37 0.60

ΔHd/J·g−1 1590 1599 1625 1579

± ± ± ±

54 58 66 68

a

The heating rate. bThe onset temperature of DSC. cThe peak temperature of DSC. dThe decomposition heat of DSC.

Table 1. Some Frontier Orbital Energy Data of DNAZ·HCl and DNAZ·HClO4 compound

Teb/K

3.3. Nonisothermal Reaction Kinetics. To obtain the kinetic parameters [apparent activation energy (Ea/kJ·mol−1) and pre-exponential constant (A/s−1)] and the most probable kinetic model functions of the intense exothermic decomposition process of DNAZ·HCl, six integral methods (MacCallum−Tanner, Šatava−Šesták, Agrawal, general integral, universal integral, and Flynn−Wall−Ozawa) and one differential method (Kissinger) were employed.4−8,18 The corresponding temperature data of DSC curves at the heating rates of (2.5, 5.0, 10.0, and 15.0) K·min−1 to the conversion degrees (α) were found. The corresponding temperature data to the conversion degrees (α) on DSC curves at the heating rates of (2.5, 5.0, 10.0, and 15.0) K·min−1 were found. The values of Ea were obtained by the method of Flynn−Wall−Ozawa from the isoconversional DSC curves, and the corresponding Ea−α

a

Energy of highest occupied molecular orbital. bEnergy of lowest unoccupied molecular orbital. cΔEL‑H = ELUMO − EHOMO.

3.2. Thermal Behavior. Typical DSC and TG/DTG curves of DNAZ·HCl are shown in Figures 2 and 3. The DSC and TG/DTG curves indicate that the thermal behavior of DNAZ· HCl consists of only one intense exothermic decomposition process. The extrapolated onset temperature (Te) and peak temperature (Tp) at a heating rate of 10.0 K·min−1 are 458.35 K and 467.80 K, respectively; they are all lower than those values 3034

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obtained from a single nonisothermal DSC curve are in very good agreement with ones obtained by the methods of Kissinger and Flynn−Wall−Ozawa.4−8,18 The final results are listed in Table 3. According to the above rules, the Mampel power law (G(α) = α1/3, f(α) = 3α2/3) is most suitable for the intense exothermic decomposition reaction of DNAZ·HCl. Substituting f(α) = 3α2/3, Ea with 155.72 kJ·mol−1, and A with 1015.84 s−1 into eq 4,

relations are shown in Figure 4. From the results, it can be seen that the Ea slightly changes in the range of 0.025 to 0.400 (α),

da A = f (α)e−Ea / RT β dT

(4) −1

where β is heating rate (K·min ), R is the gas constant (8.314 J·mol−1·K−1), and T is temperature (K), the kinetic equation of the intense exothermic decomposition reaction of DNAZ·HCl was described as (dα/dT) = (1016.32/β)α2/3 exp(−1.87·104/T). 3.4. Specific Heat Capacity. The Cp of DNAZ·HCl obtained using a continuous Cp mode of Micro-DSCIII apparatus is shown in Figure 5. It is found that the Cp of DNAZ·HCl presents a good cubic equation relationship with temperature in the temperature range from (283 to 353) K, and the Cp equation of DNAZ·HCl is

Figure 4. Ea vs α curve of DNAZ·HCl by the method of Flynn−Wall− Ozawa.

and this range was selected to obtain the nonisothermal reaction kinetic parameters. Forty-one types of kinetic model functions and the original data were put into the five integral equations (MacCallum− Tanner, Šatava−Šesták, Agrawal, general integral, and universal integral) for calculation of the parameters. The determination of Ea, A, and the most probable mechanism function of thermal decomposition must follow a few rules: (1) The values of Ea and A must in the range of the kinetic parameters of thermal decomposition for energetic materials (E = (80 to 250) kJ mol−1, log A = 7 to 30). (2) The linear correlation coefficient (r) must be greater than 0.98. (3) The standard mean square deviation (S) must be less than 0.3. (4) The values of Ea and A

Cp(J·g −1 ·K−1) = −2.2831 × 10−7T 3 + 2.1042 × 10−4T 2 − 6.1490 × 10−2T + 6.7970

(5)

The correlation coefficients of the fitting R and the standard deviation result are 0.99802 and 0.00255, respectively. The relative uncertainty of experimental data is 3.11%. The results of the difference curve between the experimental data and the proposed empirical fit indicate that the heat capacity equation can well fit the experimental data. The Cp,m of DNAZ·HCl is 2

Table 3. Calculated Values of Kinetic Parameters of the Intense Exothermic Decomposition Reaction of DNAZ·HCl method MacCallum−Tanner

Šatava−Šesták

Agrawal

general integral

universal integral

mean Flynn−Wall−Ozawa Kissinger mean (EeOb,EpOc, EKd)

βa/K·min−1 2.5 5 10 15 2.5 5 10 15 2.5 5 10 15 2.5 5 10 15 2.5 5 10 15 EeOb EpOc EKd

Ea/kJ·mol−1 173.77 153.31 150.89 147.14 172.25 152.93 150.65 147.10 173.68 153.23 150.69 146.87 173.68 153.23 150.69 146.87 171.59 151.37 149.05 145.36 155.72 141.06 163.03 163.75 155.95

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.43 0.40 0.26 0.39 0.40 0.38 0.24 0.38 0.42 0.39 0.25 0.39 0.42 0.39 0.25 0.39 0.43 0.40 0.25 0.40 10.23 1.15 1.00 1.07 10.53

log(A/s−1)

r

S

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.9858 0.9891 0.9899 0.9847 0.9858 0.9891 0.9899 0.9847 0.9845 0.9880 0.9889 0.9830 0.9845 0.9880 0.9889 0.9830 0.9842 0.9877 0.9886 0.9827

5.53·10−3 4.24·10−3 3.93·10−3 5.94·10−3 5.53·10−3 4.24·10−3 3.93·10−3 5.94·10−3 2.93·10−2 2.25·10−2 2.09·10−2 3.16·10−2 2.93·10−2 2.25·10−2 2.09·10−2 3.16·10−2 2.93·10−2 2.25·10−2 2.08·10−2 3.15·10−2

0.9998 0.9922 0.9918

1.07·10−4 5.48·10−3 2.89·10−2

18.25 15.75 15.44 15.00 18.12 15.75 15.46 15.03 18.29 15.80 15.48 15.02 18.29 15.80 15.48 15.02 16.76 14.35 14.06 13.63 15.84

0.65 0.64 0.65 0.65 0.64 0.64 0.66 0.64 0.65 0.64 0.66 0.64 0.65 0.64 0.66 0.64 0.64 0.64 0.65 0.64 1.37

16.44 ± 0.14

a

The heating rate. bThe Ea was obtained from the Te by Flynn-Wall-Ozawa’s method. cThe Ea was obtained from the Tp by Flynn-Wall-Ozawa’s method. dThe Ea was obtained from the Tp by Kissinger’s method. 3035

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Tbe0(or bp0) =

EO2 − 4EORTe0(or p0)

EO −

(8)

2R

The activation entropy (ΔS⧧), activation enthalpy (ΔH⧧) and activation Gibbs energy (ΔG⧧) of the intense exothermic decomposition reaction of DNAZ·HCl were obtained from eqs 9 to 114−10 corresponding to T = Tb, Ea = Ek (Ea obtained from the Tp by Kissinger’s method) and A = Ak (A obtained from the Tp by Kissinger’s method), and the values are listed in Table 4. The ΔG⧧ is a positive value, indicating that the intense exothermic decomposition reaction of DNAZ·HCl was a spontaneous process under the heating conditions. Figure 5. Determination results of the Cp of DNAZ·HCl. Black line, experimental curve; red line, fit curve; blue line, difference curve.

A=

205.10 J·mol−1·K−1 at 298.15 K. Although the temperature range is only from (283 to 353) K, the Cp equation is stable and continuous, which can provide a reference for the wide range temperature applications. 3.5. Thermal Safety Studies. The values (Te0 and Tp0) of Te and Tp of DNAZ·HCl corresponding to β → 0 were obtained from eq 6, and the self-accelerating decomposition temperature (TSADT) of DNAZ·HCl was obtained from eq 7.4−10 The values are listed in Table 4. Te(or p) = Te0(or p0) + aβ + bβ 2 + cβ 3

a

DNAZ·HCl

DNAZ·HClO4 438.62j 450.02j 448.81j 461.50j 42.26j 154.44j 135.42j 8326.42 ± 5.23 32.30 ± 0.05

(10) (11)

where kB is the Boltzmann constant (1.38066·10−23J·K−1), h is the Plank constant (6.6260755·10−34 J·S), ΔS⧧ is the activation entropy (J·mol−1·K−1), ΔH⧧ is the activation enthalpy (kJ· mol−1) and ΔG⧧ is activation Gibbs energy (kJ·mol−1). From Table 4, one can find that TSADT, Tp0, TTIT, and Tb of the DNAZ·HClO4 are higher than those of DNAZ·HCl, which once again indicates that DNAZ·HClO4 has better thermal stability and is safer than DNAZ·HCl. 3.6. Characterization of Detonation Velocity and Pressure. Detonation velocity (D) and detonation pressure (P) are the most important characteristics for energetic materials. D and P of an explosive can be predicted from the nitrogen equivalent equations (NE equation) 12 to 14.20

b

The self-accelerating decomposition temperature. The Tp corresponding to β→0. cThe thermal ignition temperature. dThe critical temperatures of thermal explosion. eThe activation entropy of the intense exothermic decomposition reaction. fThe activation enthalpy of the intense exothermic decomposition reaction. gThe activation Gibbs energy of the intense exothermic decomposition reaction. hThe detonation velocity. iThe detonation pressure. jObtained from ref 20.

∑ N = e ∑ xiNi/M

(12)

D = (f + hρ0 ) ∑ N

(13)

P = j(ρ0 ∑ N )2 − k

(14)

where e, f, h, j, and k are experimental coefficients: e is 100g· mol−1, f is 690 m·s−1, h is 1.160·106 cm4·s−1·g−1, j is 1.092 GPa· cm6·g−2, k is 0.574 GPa. ∑N is the nitrogen equivalent of the detonation products, xi is the mole number of certain detonation product produced by a mole of explosive, Ni is the nitrogen equivalent index of a certain detonation product, and ρ0 is the density of an explosive (g·cm−3). The nitrogen equivalent indices of detonation products are listed in Table 5. According to the order of Cl2−H2−C−H2O− CO−CO2 in forming detonation products, the detonation products of DNAZ·HCl and DNAZ·HClO4 are calculated as follows:

where a, b, and c are equation coefficients. They were determined by the fitting equation of Te(or p)−β, and where a is in min, b is in min2·K−1, and c is in min3·K−2:

TSADT = Te0

⎛ ΔH ⧧ ⎞ ⎛ ΔS ⧧ ⎞ kBT ⎟ exp⎜ − ⎟ exp⎜ h ⎝ RT ⎠ ⎝ R ⎠

ΔG⧧ = ΔH ⧧ − T ΔS ⧧

(6)

429.96 ± 0.40 436.46 ± 0.24 441.45 ± 0.52 446.63 ± 0.19 66.65 ± 2.68 163.75 ± 1.07 134.66 ± 2.28 6881.40 ± 1.48 20.85 ± 0.01

(9)

A exp( −Ea /RT ) =

Table 4. The Derivative Parameters for DNAZ·HCl and DNAZ·HClO4 TSADTa/K Tp0b/K TTITc/K Tbd/K ΔS⧧e/J·mol−1·K−1 ΔH⧧f/kJ·mol−1 ΔG⧧g/kJ·mol−1 Dh/m·s−1 Pi/GPa

kBT ΔS ⧧/ R e h

(7)

Table 5. Nitrogen Equivalents of Different Detonation Productsa

The thermal ignition temperature (Tbe0 or TTIT) of the DNAZ·HCl was obtained from eq 819 by substituting EeO (Ea obtained from the Te by Flynn−Wall−Ozawa’s method) and Te0, and the critical temperatures of thermal explosion (Tbp0 and Tb) of DNAZ·HCl was also obtained from eq 819 by substituting EpO (Ea obtained from the Tp by Flynn−Wall− Ozawa’s method) and Tp0. The values are listed in Table 4.

detonation product nitrogen equivalent index a

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N2

H2O

CO

CO2

C

H2

Cl2

1

0.54

0.78

1.35

0.15

0.290

0.876

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■

C3H6N3O4 Cl = (0.5)Cl 2 + (3)H 2O + (2)C + (1)CO

REFERENCES

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+ (1.5)N2 C3H6N3O8Cl = (0.5)Cl 2 + (3)H 2O + (1)CO + (2)CO2 + (1.5)N2

According to eq 12, in which MDNAZ·HCl = 183.56 g·mol−1, ρDNAZ·HCl = 1.753 ± 0.001 g·cm−3,12 MDNAZ·HClO4 = 247.56 g· mol−1, ρDNAZ·HClO4 = 1.930 ± 0.002 g·cm−3,7 total nitrogen equivalents of DNAZ·HCl and DNAZ·HClO4 obtained by the nitrogen equivalent indices of the detonation products are calculated and the values are given in Table 5:

∑ NDNAZ·HCl = 100 × (0.5 × 0.876 + 3 × 0.54 + 2 × 0.15 + 1 × 0.78 + 1.5 × 1)/183.56 = 2.53

∑ NDNAZ·HClO4 = 100 × (0.5 × 0.876 + 3 × 0.54 + 1 × 0.78 + 2 × 1.35 + 1.5 × 1)/247.56 = 2.84

D and P can be obtained according to eqs 13 and 14, and these values are listed in Table 4. From Table 4, one can find that D and P of DNAZ·HClO4 are higher than those of DNAZ· HCl, which indicates that DNAZ·HClO4 has a finer detonation performance than DNAZ·HCl.

4. CONCLUSIONS The Ea and A of the intense exothermic decomposition reaction of DNAZ·HCl are 155.72 kJ·mol−1 and 1015.84 s−1, respectively. The most probable kinetic model functions of the intense exothermic decomposition reaction of DNAZ·HCl is Mampel power law G(α) = α1/3 and f(α) = 3α2/3. The Cp equation is Cp(J·g−1·K−1) = −2.2831·10−7T3 + 2.1042·10−4T2 − 6.1490· 10−2T + 6.7970 in the temperature range from (283 to 353) K, and the Cp,m is 205.10 J·mol−1·K−1 at 298.15 K. The TSADT, TTIT, and Tb are 429.96 K, 441.45 K and 446.63 K, respectively. The values of ΔS⧧, ΔH⧧ and ΔG⧧ of the intense exothermic decomposition reaction of DNAZ·HCl are 66.65 J·mol−1·K−1, 163.75 kJ·mol−1 and 134.66 kJ·mol−1, respectively. The D and P are 6881.40 m·s−1 and 20.85 GPa, respectively. The analytical results of ΔEL‑H, Te, Tp, TSADT, Tp0, TTIT, and Tb indicate that DNAZ·HClO4 has better thermal stability and safety than DNAZ·HCl, and the detonation performance of DNAZ·HClO4 is finer than that of DNAZ·HCl.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Fax: +86 2988307755. Funding

This work was supported by the Program for New Century Excellent Talents in University (No. NCET-12−1047), the National Natural Science Foundation of China (No. 21073141, and 21373161), the education Committee Foundation of Shaanxi Province (No. 11JK0564, and 11JK0582), and the Project, sponsored by SRF for AT, YLU (Grant No. 09GK019). Notes

The authors declare no competing financial interest. 3037

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