IndIan Journal of ChemistryVol. J6A. May 1978. PI'- 406-409

Kinetics of Catalysed Thermal Decomposition of AmmoniumPerchlorate

GURDIP SINGH & RAM RAJ SINGHDepartment of Chemistry, University of Gorakhpur, Gorakhpur

Received 11 1uly 1977; revised 4 November 1977; accepted 9 February 1978

The kinetics of thermal decomposition of ammonium perchlorate (AP) in the presence ofbasic copper carbonate and chromium carbonate as catalysts have been investigated. Prout-Tompkins and Contracting-Cube equations have been found to fit the isothermal TGA data ofcatalysed AP decomposition. The mechanism of the catalysed thermal decomposition of AP hasalso been discussed in the light of electron transfer process,

AMMONIUM perchlorate (AP) hr s been foundto play a key role in the combustion ofcomposite solid propellants-'". It he s also

been observed that decomposition and burningproperties of AP ca n la rgely be improved by usingva rious ca talysts2•4-8, The effect of cata lysts on thecombustion of composite propellants h: s oIso beendealt with in many papers9-12, Recently Solymosi-"hrs reviewed the effect of different oxides ad saltson the slow and fast decomposition of AI'. Prout-Tompkins. Avra mi-Erofeyev and Contracting-Cubeequations have been found to fit the data. Further,the two rote constants for the catalytic AP decom-position in the r cceleratory and decelera tory periodshave been also reported by some workers14-15•

We have studied the kinetics of the thermaldecomposition of AP and polystyrene (PS)-APpropellants in the presence and absence of catalysts.Basic copper carbonate (BCe) end chromium carbo-nate (CC) were used ,'S the ca ta lysts. IsothermalTGA studies on AP and propellants were undertaken,Prout-Tompkins and Contracting-Cube (n = 2) equa-tions were found to fit the da.ta of the ca ta lysedthermal decomposition of AP. The mechanism ofthe catalysed thermal decomposition of AP hr s beendiscussed in the present communication,

Materials and MethodsAmmonium perchlorate (AP) obtained from CECRI,

Kara ikudi, was used 25 such. Crystals of AP weregrounded in a mortar and sieved to 100-200 mesh.Bo sic copper carbonate (BDH, LR grr de). chromiumcarbonate (USSR), CuO (BDH, LR grade), Cr203

(USSR) were used in the form of fine powderswithout any purification and grinding. The styrenemonomer (Synthetics & Chemicals Ltd, Ba reillv)was purified-and polymerized 2S reported earlier-".The propellant samples with and without catalystswere prepared in the same manner-".

Isothermal TGA of AP (powder form) and pro-pellants (pellet form) - Decomposition studies onAP + BCC (4% by wt) and AP + CC (4% by wt)were undertaken, using a TGA instrument assembledby us, in the temperature ranges 225-55° and 240-70°

406

respectively, whereas decomposition of AP sr mpleswas studied in the range 255-325°. The highesttemperatures for AIl + BCC and AP + CC sampleswere selected to be 255° and 270°, because thesesa~ples deflr grata without undergoing appreciableweight loss a bove these tempera tures. The pro-pella n t S8 mples were run at 2700 because a bove thistempera ture the propellant samples defle gra te. Thesample (--100 mg) under investigation was takenin a platinum crucible hanging in a tube furn: cewhich was cont~olled within ± 1°. The weight losswas recorded WIth the help of a sensitive balance,

A combined TGA and DTA study 011 basic coppercarbonate and chromium carbonate W2S made at aheating rate of 10° mirr ' using alumina r s thestandard.

Results and DiscussionThe rate of decomposition (30% decomposition) for

AP ,:n? the propellanr with and without catalystsat various tempera turas hr s been calculated fromTGA plots (Figs. 1-4) arid the data are given inTa ble 1. The ca ta lytic activity (CA) of the ca ta Iystshr s also been estimated using Eg. (1) and theresults a re given in Ta ble 1.c = Rate of decomposition of catalyst AP/propellant

A Rate of decomposition of uncatalysed Ap/propellanC·(l)The do ta of decomposition of AP, AP + BCC

and AP + C\ have been fitted in Prout-Tompkinsand Contr<]ctlrg-Cube equa tior s (Eqs. 2 arid 3).Log (11./1-11.) = K1t+c (2)1-(I-rx)'=Kzt (3)where 11. is the fraction decomposed, t is the time.a r d Kl and Kz are the rate constants, whichdepend upon temperature. Rr te constants obte ir edat various temperatures in er ch cr se ere giver: inTable 2. The typical plots, usirg Eqs. (2) 2Ld (3)fO,r AP + BCC ar d AP + CC systems, ere given inFIgS. 5 and 6 respectively. The c ctivation energies(AE) for the thermal decompositior: of AP andAP + catalysts have been calculated and vc lues aregiven in Table 2. Many previous investigators havealso calculated the kinetic pars-meters for therme l

SINGH & SINGH: KINETICS OF CATALYSED THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE

X PURE AP• Ap+ CHROMIUM CARBONATE(4°/0)o AP + BASIC COPPER CARBONATE (4°/0)

4 • AP+CUPRIC OXIDE (4°/.)

5 ~ AP + CHROMIUM OXIDE (4 °/0)

1eo 2

3

zQ 60•..in:?:Iou~ 40•..ZWU0:WI\. 20

50 150100TIME,mln

Fig. 1- Thermal decomposition of AP and AP + catalystsat 255°

3

80 o (PS/AP"/3)t BASIC COPPER CARBONATE (4'1. BY WI)• (PS/AP "/31 +CHROMIUM CARBONATE (4". BY WI)a (PS/AP"/31 + CHROMIUM OXIDE (4.,. BY WI)• (PS/AP, '/3H-CUPRIC OXIDE (4". BY WII{J. PURE PROPf.LLANT (PS/AP, 1/3)

zoE 60<floII.I8W 40o•..zWU[f, 20II.

4

2

5

100 200TIME,min

300 400

190Fig. 4 - Thermal decomposition of propellants with and

without catalysts (4% by weight) at 270°

TABLE1 - EFFECTOF CATALYSTSON THE THERMALDECOMPOSITIONOF AP ANDPROPELLANTS

(Catalyst cone. 4% by wt)

55 Temp. Sample Rate (for 30% Catalytic(OC) decomposition) activity

z min'? (CAla~ 40 255 AP 0'40a 255 AP + BCC 0'97 2'420..

240 AP + BCC 0·49l:a 225 AP + BCC 0·15u 270 AP+ CC 0·75UJa 255 AP + CC 0'53 1·33•.. 20 240 AP + CC 0·43zUJ 255 AP + CuO 0·71 1·77u 255 AP + Cr.03 0'27 0·680:UJ 270 PS + AP 1-150..

270 PS + AP + BCC 0·60 0'520 270 PS + AP + CC 0·44 0'38

TIME,min270 PS + AP + CuO 0·49 0·43270 PS + AP + Cr.O. 0·42 0·37

Fig. 2 - Thermal decomposition of AP + basis coppercarbonate at (1) 225°, (2) 240° and (3) 255°

~~~----------------------~----~~~~~·zoi= 40

~l:

8UJ020I-zWU0:WI\.

50 100TIME,min

150

Fig. 3 - Thermal decomposition of AP + chromium carbo-nate at (1) 240°, (2) 255° and (3) 270°

BCC, CC, CuO and Cr.03 have been used as catalyst andAP+ PS as propellant.

decomposition of AP using Prout-Tompkir.s andContracting-Cube equa tionsU,16,18,19.

A slight broadening in IR absorption bends ofAP was observed when the material w, s heatedwith catalysts. The combined DTA and TGA plotsin the range 100-420° for besic copper carbonateand. chromium carbonate <'re given in Fig. 7.B~SlC copper carbonate gives two endotherms in thetemperature r2rges 100-200° and 200-250° whereaschromium carbonate gives only one broz d endothermin the temperature range 90-380°. The formercat~lyst shows an exotherm in the range 250-420°while latter hr s an exothermic peak in the range380-460°.

Table 1 clearly shows that the rate of thermaldecomposition of AP is increased in the presenceof BCC, CC ?nd CuO where, s it is inhibited byCr203 at 255°. The propellant decomposition rate

fQ7

INDIAN J. CHEM., VOL. 16A, MAY 1978

TABLE2 - KINETICPARAMETERSFORTHERMALDECOMPOSITIONOF AP, AP + BCC AND AP + CC

Sample Temp. min? (Eq. 2) kcal/mole (Eq. 2) min' (Eq. 3) kcal'mole (Eq. 3)(0C) _ _

255 1·76 0·09 0·47275 2·72 0·09 12'83 20·93 0·67300 7·14 0·18 2·00325 7·14 0·37 2·00225 1·42 0·13240 3'30 0'20 32'30 0·48 0·05255 8·00 0·22 0·90 0·05

240 4·00 0·11 0'38 0·02255 6·00 0·26 24·15 25·07 0·44 0·07270 14·00 0'36 1·00 0·09

Ka" Ka" Ka, and Kd, are rate constants using Eqs. (2) and (3) in the acceleratory and deceleratory (decay) periods.Eat' Ea" Ed, and Ea, are activation energies in the acceleratory and deceleratory periods using Eqs. (2) and (3).

Ka, X 102 Kd, X 10'AP

AP+BCC

AP+CC

Ea, x.; x 10' Ea,Kd, X 10'0·030·030·050·14

13·12 20·93

32'20

23'00 27'32

2·0

C\I+

1·6

(2) (1)\:l '·2I<,

\:log 0·8

o~ ~~ ~~ ~~ ~o 50 100 150 200

TIME,min

Fig. 5 - Kinetic analysis of (1) AP + basic copper carbon~teand (2) AP + chromium carbonate by the Prout- Tompkins

equation

0·3

~0'2

\:l.!

r0·'

J;L....L---;5:l;0:;----~1~O;rO:;------,:;1~-::-O---::;:2-;::O-:f.-

TIME,min

Fig. 6 - Kinetic analysis of (1) AP + basic copper carbonateand (2) AP + chromium carbonate by the Contracting-Cube

equation

408

Fig. 7 - TGA and DTA of (1) basic copper carbonate and(2) chromium carbonate at the heating rate of 10° min'?

was lowered by BCC, CC ar.d CuO initially but thedecomposition WeS four.d to be enhanced at laterstages. Cr203 W2 s a lwa ys fou.nd to decrer se therote of decomposition at 2700 (Fig. 4). The orderof catalytic r ctivity (CA) in AP decomposition wasfound to BCC>CuO>CC (Table 1).

The kinetic p2 r<meters reported in Ta ble 2 showthat the rate constants for AP + BCC and AP + ccsystems increase with the increase in temperaturein both the a ccelera tory and decelera tory periods.The reported values of energy of ectivation (AE)for catalysed AP are higher than those of pure AP.Many previous investigators2.14.19 have also reportedthe increase in AE in the use of catalysed APdecomposition. Further, the AE values have beenestimated for catalysed and uncatalysed decomposi-tion of AP using Jacobs-Kureishy technique also.

SINGH & SINGH: KINETICS OF CATALYSED THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE

The time (.it) for 5-25% decomposition w, s r.otedand log (l/.it) was plotted, gairst liT. The AEvalues for AP (255-325°), AP + BCC (225-55°) andAP + CC (240-70°) come out to be 20'41, 34·50and 17·50 kcal/mole. The A E values obtained usingJacobs- Kureishy technique are not compare ble withthose calculated using Prout-Tompkins and Con-tracting-Cube equations which r.re nearly the sz me(Table 2).

Now the problem is what are the species which<' re acting, s ca talysts. TGA plots of BCC ar.d CC(Fig. 7) clearly indicate that both the carbonatesstart changing into oxides, t 100°. The rate ofdecomposition of AP is cffected very little ..t initialst ges (Fig. 1) on .ccount of the fact that carbonatestake some time for conversion to oxide. Theinhibition of propellant decomposition initially maybe due to the in terferer.ce of polymer degradationin AP decomposition in the presence of ca talysts(Fig. 4). Further, the decomposition of carbonateshr s been found to be endothermic (Fig. 7) whichwould further affect the extent of decomposition ofAP and propells.nt ,. t initial stages. It is inferredthat r lthongh carbonates are used r.s catalysts, it isoxide form" tion thr t is the rea I ca use of ca ta lysis.Thus, the freshly available oxides during the thermaldecomposition of AP + catalyst (BCC or CC) mixturewould containL rge number of defects ar.d dis-loca tions in their crystal la ttices. Hence a lagenumber of active centres would be <I vaila ble for theadsorption of the reactants and the rate of APdecomposition would be incret sed in the presenceof carbonates rather than the r ged oxides (Table 1).However, BCC hr s been found to be more effectivethan Cc.

The mechanism of ca talysed AP decompositionmay be understood in terms of the followirg twoeffects: (i) Electron transfer process in AP decom-position which may be cata lysed, s nd (ii) formationof metal perchlora te <' ndlor perchlorr te rmmine.

The present TGA data are recorded below 300°and it is known that AP decomposition takes placeby electron tra nsfer process in this tempera turerange. It is possible thr. t metal oxides (MO) ma yenhance the decomposition of AP on cccount oftheir incre: sed electron-hole density, r s hr s beensuggested by Solyrnosi et al.B•15• '

MO++Cl04 -~ MO+ClO. ...(4)NHt+MO -~ MO++NH. . .. (5)ClO,+NH, -~ CI02+tN2+2H20 ... (6)

Further, the reaction of metal oxides with APto form metal perchlora te/ammine seems to be quiteplausible. A number of workers have proposed thefollowing rea ctiou 7.13.15 (Eq. 7).2NH.ClO.+MO -~ M(CI04)2+2NHd·H20 ... (7)In order to decide between the two alternatives,IR and chemical analyses, of the residue left afterthe decomposition of AP + catalyst mixture werecarried out. No new per k w: s observed in the IR,except a broadenir g of the pea ks. The broa denir gof the IR bands signifies that AP hr s developedimperfectior.s, more likely because the cata lyst hr sdiffused into the crystal la ttice of AP which might

ha ve ; ffected AP decomposition : s reported byKishorc ct af.19. Further, to detect the presence ofCu(II) or Cr(III) iors in the l.ttice of AP, sr.mples(AP + cr.talyst) which were used for IR studies,were dissolved in distilled wa ter. The filtr: te gavepositive tests for the presence of Cu(II) r ndCr(III) iOLS. This does I.Ot completely rule out thepossibility of meta 1 perch lore tel; mmine form: tiondue to the fr ct thr t perchlora tes]: mmines of copper<1nd chromium rre very unsta ble and their decom-position is explosive20-21. It m"y be thrt somesurf, ce perch lor" tes r nd/or perchlora te r mmines ~reformed which immcdi., tely decompose producinghea t "nd cor sequently the rr te of AP decompositionis enhanced. Summrrizir.g, the catalytic decom-position of AP cloes Lot seem to be expl: inedby a single mechanism rnd more work is needed tounderstand the exact mechanism.

AcknowledgementAuthors are thankful to Prof. K. P. Rastogi

for helpful discussions. The financial support fromCSIR, New Delhi, is thankfully acknowledged.Thanks are alo due to Prof. U. G. Ag. rwcl, lIT,Kanpur, for DTA studies.

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