Thermal decomposition of ethylene diamine diperchlorate

C O M B U S T I O N A N D F L A M E 37: 155-162 (1980)

155

Thermal Decomposition of Ethylene Diamine Diperchlorate T. J. THOMAS* and U. S. NANDI Department of Inorganic and Physical Chemistry. Indian Institute of Science. Bangalore--560 012 India

Thermal decomposition of ethylene diamine diperchlorate (EDDP) has been studied by differential-thermal analysis (DTA), thermogravimetric analysis (TGA), isothermal weight-loss measurements and mass-spectrometric analysis of the decomposition products. It has been observed that EDDP decomposes in two temperature regions. The low-temperature decomposition stops at about 35 to 40 percent weight loss below 250 ° C. The reason for the low-temperature cessation may be the adsorption of excess ethylene diamine on the crystal surface of EDDP. An overall activation energy of 54 kcal per mole has been calculated for the thermal decomposition of EDDP. Mass-spectrometric analysis shows that the decomposition products are mainly CO2, H20, HC1 and N 2. The following stoichiometry has been proposed for the thermal decomposition of EDDP: (-CH2NH3CIO4) 2 ~ 2CO 2 + 4H20 + 2HC1 + N2.

INTRODUCTION Studies on the thermal decomposition and combustion of organic amine perchlorates have assumed an important position in recent years [ I - 8 ] mainly because o f their similarity with composite solid propellants based on ammonium perch/orate (AP). Typical nonmetallised propellant compositions, for example, contain about 8 0 - 8 6 percent of AP which is similar to the perchlorate content, calculated as NHaC104, in methyl amine perch/orate (MAP) or EDDP. (The percentage o f perch/orate calculated as NH4C1Oa in these compounds is about 89.) Proton-transfer dissociation into NHa and HC104 is believed to be the initial step in b o t h the thermal decomposition and combustion o f AP and propellants based on AP [ 9 - 1 1 ] . The subsequent steps which lead to ignition and combustion o f an AP monopropellant, or an Ap-based * Present address: Propellant Engineering Division, Vikram Sarabhai Space Centre, Trivandrum-695 022 India. Copyright © 1980 by The Combustion Institute Published by Elsevier North Holland, Inc.

composite propellant, are very complex and still remain a fascinating problem. The analogous simple systems like MAP or EDDP, on the other hand, may provide valuable information which can shed some light on the decomposition and combustion o f propellants. One of the least studied and understood phenomenon o f the pyrolysis o f polymers in a high oxidizing environment at high heating rates and at high pressures is thus eliminated. These considerations motivated us to undertake a study o f the thermal decomposition o f EDDP.

EXPERIMENTAL Materials EDDP is prepared by treating ethylene diamine with an excess o f 70% perchloric acid. The temperature o f the reaction mixture is kept below 10°C by surrounding the container with crushed ice. The precipitated salt is filtered through a sintered

0010-2180/80/020155+08501.75

156 crucible, washed with cold water, and recrystallised three times from distilled water. The crystals of EDDP hemihydrate thus obtained are dried in an air oven at 60°C for 8 hr and then kept over P205 in a desiccator. The compound is analysed for HC104 content after passing through an ionexchange column containing Zeocarb 225 resin [obtained from Ion Exchange (India) Limited] and for chlorine by fusion with sodium carbonate and titrating with silver nitrate solution. Water content is estimated by Karl Fischer Reagent. The sample is found to correspond to the formula (-CH2NHaC104)2"½H20 and the percentage purity is 99.5.

App~ams DTA experiments have been carried out with a Fischer instrument. Thermogravimetric analysis and isothermal weight-loss measurements have been recorded by an apparatus similar to that described by Nambiar and Jain [12]. Mass spectrometric investigation of the decomposition products is carried out with an Associated Electrical Industries MS I0 mass spectrometer. The tube containing the sample is connected to the system and evacuated to a pressure of I0 - 9 mm of Hg. After taking the background readings, the tube is surrounded by a tubular furnace which has attained the required temperature. The decomposition products are led into the "ion-source cage" and the ion intensities are recorded. The background values are subtracted from the corresponding m/e values.

RESULTS AND DISCUSSION The DTA and TGA traces of EDDP are shown in Figures 1 and 2. During a study of the phase transitions in methyl-substituted amine perchlorates, Stammler [3] has investigated EDDP by DTA and reported a reversible phase transition in the range of 95°C and dehydration of ½H20 at 120-130°C (at a heating rate of 20°C/min). The anhydrous material is reported to have a reversible phase

T.J. THOMAS and U. S. NANDI transition at 52°C and decomposes at about 290°C. Hemihydrate: Phase II 120°C 1

95°C

~ Phase I

Phase I(anhydrous).

-H20 2 Anhydrous: Phase II 290°C

52°C

~ Phase I

Phase I (decomp.).

The present study shows that the thermal decomposition of EDDP takes place in different stages as evidenced from the DTA and TGA traces. The amount of the low-temperature decomposition varies with the sample weight and the heating rate, probably due to self.heating. However, taking sample weights of around 10-15 mg and using a heating rate of 5-10°C/min, the decomposition of EDDP ceases at about 35-40 percent in the temperature range of 150-250°C. Isothermal weight-loss experiments confirm this conclusion. EDDP is a diperchlorate similar to hydrazinium diperchlorate (HP-II). One is therefore tempted to conclude that the decomposition mechanism of the two salts follows a similar pattern. HP-II is reported [13, 14] to decompose first into hydrazinium monoperchlorate (liP-I) and perchloric acid at temperatures below 140°C: N2H6(C104)2 ~ N2H5C104 + HCI04 • Similarly, EDDP is expected to decompose into ethylene diamine monoperchlorate (EDMP) and perchloric acid. (-CH2NH 3 C104)2 H2N CH2CH2NHa C104 + HCI04 The corresponding weight loss is 37 percent, almost the same as the value observed in our isothermal weight-loss experiments in the temperature range of 150-250°C. To corroborate the above mechanistic approach, we have analysed the

ETHYLENE DIAMINE DIPERCHLORATE

157

c) x taJ

i--

n~

100

200

300

400

TEMPERATURE('C) Fig. 1. DTA trace o f EDDP at a heating rate o f 10°C/min. Sample weight: 15 mg.

low-temperature decomposition products of EDDP in a mass spectrometer. The results are reported in Table 1. These data show that the low-temperature decomposition of EDDP is not only a mere proton-transfer dissociation into ethylene diamine monoperchlorate and perchloric acid, but a complex reaction involving oxidation of the organic part of the molecule by HC104 or its decomposition products, similar to the low-temperature decomposition of AP. This again shows that the cessation of the low-temperature decomposition is not confined to AP alone, but is also exhibited by other ammonium salts and amine perchlorates. Ammonium oxalate, for example, has recently been shown [15] to decompose in two temperature regions.

The reason for the cessation of the low-temperature decomposition of AP is not yet clear even though there have been many attempts made to explain this phenomenon [10]. A reasonable speculation based on adsorption-desorption equilibrium of the primary decomposition products on the surface of the crystals has been put forward by Jacobs and his collaborators [16]. Maycock and Pai Vemeker [17], on the other hand, explained this phenomenon on the basis of changes in point defects when the crystal undergoes a reversible phase transition from the orthorhombic to the cubic-crystal system. Based on Jacobs' explanation [16] for the cessation of the low.temperature decomposition of AP, we put forward the following reasoning for the 40 percent decomposition of EDDP in the temperature range of 150-250°C.

158

T.J. THOMAS and U. S. NANDI

25

A I,--

g

0-50 v

03

"r-

LO

75

100

*

100

,

,

200

I

300

TEMPERATURE (*C) Fig. 2. T G A trace of EDDP at a heating rate of 10°C/min. Sample weight: 15 mg.

Proton-transfer dissociation of EDDP results in the formation of EDMP and perchloric acid in the first step. In the second step, EDMP loses the remaining perchloric acid molecule and gets converted into ethylene diamine and perchloric acid: (-CH2NHa C104)2 "+ HC104- - -H2NCH2CH2NHa CIO4 -~ HC104 + H2NCH2CH2NHsCIO 4 H2NCH2CH2NH a C104 HCIO 4 +

H2NCH2CH2NH 2

The HCI04 gets desorbed from the crystal surface or gets heterogeneously decomposed. The heterogeneous decomposition is more probable since Levy has shown [18] that the thermal decomposition of HCI04 is heterogeneous below 325°C and homogeneous above this temperature. The decomposition products of HCI04 (oxides of chlorine or oxygen) can then oxidise ethylene diamine, EDMP or EDDP into oxides of C, H, N, etc. Depending on the chemical equilibria prevailing under the conditions of the experiment, the final decomposition products are obtained. The rates of formation and decomposition of HCI04 and ethylene diamine are different. If the rate of formation of

ETHYLENE DIAMINE DIPERCHLORATE

159 TABLE 1

Mass Spectra of Thermal-Decomposition Products of Ethylene Diamine Diperehlorate Hemihydrate Ion intensities

m/e 12 14 15 16 17 18 22 26 27 28 29 30 32 35 36 37 38 44 45 46 52 61

Probable assignment

Low-temperature decomposition

High-temperature decomposition

C+ N+ CH + O+ OH +, NH3 + H20 + CO ++ CN + HCN + CO +, N2 + CH3CH2 + NO + O2 + C1+ HC1+ CI+ HC1+ CO2 +

1.5 0.2 0.1 1.8 0.2 0,6 0.3 0.6 3.56 13,3 0.1 0.05 0,74 2.2 16.6 0.6 5.4 17.2 0.1

7.0 1.4 0.5 10.25 0.5 2.2 1.8 4.0 20,0 55.6 1.0 3.8 0.2 4.5 33 1.4 10 92.4 1.3 0.45 0.8 0.2

NO2 +

I

1600

1400

I

1200

1000

I

800

Low-temperature decomposition residue 7.8 2.4 0.56 11.5 1.0 4.0 2.0 5.0 27,2 67.6 1.1 7.8 7.0 0.6 4.0 0.26 1.38 83.0 1.2 0,4 (1.7

I

700

/

~o

FREQUENCY (cn'T1) Fig. 3. IR spectra of ammonium perchlorate (1) and isothermal weight loss residue of EDDP (2).

160

T . J . THOMAS and U.S. NANDI

O.75

V-

0s0

u.

,

,

= ,.,.

I

200

i

300

i

~00

TIME IN MINUTES Fig. 4. Isothermal weight loss curves of EDDP. 265°C ( - o - o - ) ; 270°C (_,, A_) 280°C ( - D - o - ) and 295°C ( - e - e - ) . TABLE 2 Calorimetric Values* of EDDP and Other Substituted Amine Perchlorates S1. No. Compound 1. APa 2.

AP/PE(89/11) a

Calorimetric value, Cal/g 226 -+5 1018 ± 50 980 +- 20 1038 +-50 1263 ± 10

3. MAPa 4. DMAPa 5. EDDPb a Values taken from [4]. b This value is an average of three individual determinations. * The term "Calorimetric value" refers to the amount of heat release on self-combustion. The term has been used at the suggestion of the referee.

ethylene diamine is more than that of its oxidation by HC104, an equilibrium situation can be envisaged in which the entire crystal surface is covered with adsorbed ethylene diamine and thus the dissociation automatically ceases. An analysis o f the mass spectra o f the decomposition products reveals that the major products are CO2, H 2 0 , HC1 and N2. The overall stoichiometry can be expressed as: (-CHzNHaC104)2 ~ 2COz + 4 H z O + N 2 + 2HC 1 Even though the overall reaction can be expressed as above, the chemical processes leading to the de-

ETHYLENE DIAMINE DIPERCHLORATE composition are much more complex. In our experiments, for example, a residue was invariably found on completion of isothermal weight loss experiments at the high temperature region. Wet chemical analysis and IR spectra of this residue indicated it to be NHaC1Og, (Figure 3 shows the IR spectra of NHgCIOg and the EDDP decomposition residue.) A different route has been therefore suggested to account for the formation o f - A P thus: (-CHgNHaC 104)2 ~ CHz--CH 2 + NH4C10 4

\\ /

N H . HC104

161 stability due to the presence of a carbon backbone between the -NHsC1Og groups has prompted us to undertake a comprehensive study of the thermal decomposition and explosive sensitivity of polymers such as polyethylenimine perchlorate. Our results suggest that the explosive sensitivity decreases in the case of the polymer compared to the model compounds [22, 23]. Calorimetric value for EDDP has also been determined in a bomb calorimeter (Table 2). The value is more than that for MAP or a mixture of AP and polyethylene. EDDP can, thus, be an energetic additive for composite solid propellants.

CH2--CH z -+ CHz--CH 2 + HC104 -~ Products

\

/

NH • HC104 NH

REFERENCES

H2NCHzCH2NH a ClOg ~ CHg.--CHz

'\ /

NH + NHgC104 ~ Products. Distillation of diamine salts has been tried in the preparation o f cyclic compounds [19]. In the case of EDDP the strained aziridine ring that is formed in the above reactions is immediately oxidised by perchloric acid and its decomposition products into stable oxides of C, H and N. The formation of AP as a product in the thermal decomposition of EDDP can thus be explained. Methyl ammonium perchlorate also forms AP as a decomposition product due to the methyl group transfer [5]. The DTA exotherm in the temperature region of 350°C is most probably due to the high-temperature decomposition of AP. Figure 4 shows the isothermal weight-loss curves of EDDP in the temperature region 265295°C. Activation energy for thermal decomposition has been calculated using the JacobsKureishy method [20]. The value thus evaluated is 54 kcal/mole. This value is higher than that reported for MAP (40 kcal) probably due to the insertion of the C-C bond which imparts additional stability for the compound. The reported impact sensitivity values of the two compounds also show such a trend, the values being 20 cms for MAP and 35 cms for EDDP [21] *. This additional • The height at which a 2 kg weight causes 50% explosions in I0 experiments.

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15, 1628 (1972). 8. Fogel'zang, A. E., Svetlov, B. S., Opryshko, V. S., and Adzhemyaw, V. Ya., Fizika Goreniya i Vzryva 8,257 (1972). 9. Hall, A. R. and Pearson, G. S., Oxidation and Combustion Reviews 3,129 (1968). 10. Jacobs, P. W. M. and Whitehead, H. M., Chem. Rev. 69, 551 (1969). 11. Keenan, A. G. and Siegmund, R. F., Quart. Rev. 23, 430 (1969). 12. Jain, S. R. and Nambiar, P. R., lnd. J. Chem. 12, 1087 (1974). 13. Nagaraja Sarma, A., Studies on thermal decomposition of hydrazinium perchlorates, Ph.D. Thesis, Indian Institute of Science, Bangalore, India, 1974. 14. Grelecki, C. J. and Cruise, W., Advanced Propellant Chemistry (R. F. Gould, Ed.) Advances in Chemistry Series, American Chemical Society, Washington, DC, 1966, No. 54, p. 73. 15. Radhakrishnan Nair, M. N. and Pal Verneker, V. R., Combust. Flame 25,301 (1975). 16. Jacobs, P. W. M. and Russel Jones, A., AIAA J. 5, 829 (1967).

162 17. Maycock, J. N. and Pai Verneker, V. R., Proc. Roy. Soc. A 307, 303 (1968). 18. Levy, J. B.,J. Phys. Chem. 66, 1092(1962). 19. Stevens, T. S., in Chemistry of Carbon Compounds (E. H. Rodd, Ed.), Elsevier, Amsterdam, The Netherlands 1957, Vol. IV A, p. 14. 20. Jacobs, P. W. M. and Kureishy, A. R. T., J. Chem. Soc. 4718 (1964). 21. Stammler, M. and Schmidt, W. G., Western States Section, Combustion Institute, paper WSCI 66-26, 1966.

T . J . T H O M A S and U. S. N A N D I 22. Thomas, T. J. and Nandi, U. S., AIAA J. 14, 1334 (1976). 23. Thomas, T. J. and Nandi, U. S., Ind. Eng. Chem. Product R&D 16, 186 (1977).

Received 23 October 19 78; revised 3 July 19 79