Influence of irradiation on the thermal decomposition of some perchlorates

1829

Notes J. inorg, nud, Chem.,1975,

Vol.37.pp.1829-1830.PergamonPress.PrintedinGreatBritain

Influence of irradiation on the thermal decomposition of some perchlorates (Received 1 January 1975) ALTHOUGH a considerable amount of work has been done on the thermal ecomposition of chlorates and perchlorates[1], the influence f irradiation[2] on the decomposition has not received much attention except in the case of ammonium perchlorate. It has been found that when irradiated chlorates[3] and perchlorates [4] re gently heated, the chemical damage fragments and other lattice defects generated by irradiation undergo recombination (annealing) reactions which tend to annul the effects of irradiation; heating in these experiments is done necessarily at temperatures at which there is no thermal decomposition of the substances. The present work deals with the influence of irradiation on the thermal decomposition of barium perchlorate which decomposes in the solid state and of lithium perchlorate which undergoes decomposition after fusion.

EXPERIMENTAL Lithium and barium perchlorates of AR grade were dried to constant weight, the former at 200°C and the latter at 250°C. Samples of these salts sealed in glass ampoules were irradiated with different doses up to 500 Mr of 6°Co y-rays. The decomposition apparatus and the procedure employed were the same as those already described [5]. About 10 mg portions of the I

i

i

substances were heated in a thermostated electric furnace at temperatures in the range 400-470°C (-+I°C) and the pressure of oxygen developed at different time intervals was measured at each temperature with a cathetometer.

RESULTSANDDISCUSSION Representative sets of plots of fractional decomposition {c~l against time (t) at different temperatures for normal lithium and barium perchlorates and for the substances irradiated with 100 Mr of y-rays are given in Figs. 1 and 2 respectively. Figures 3 and 4 record the influence of irradiation dose on the decomposition of the perchlorates, each at a given temperature. In the case of the normal salts, decomposition is characterized by initial gas evolution, more pronounced for barium than for lithium perchlorate, followed by an induction period which becomes shorter at higher temperatures. Subsequently, the substances decompose through a short acceleratory followed by a long decay stage. Irradiation increases initial gas evolution and shortens the induction period as well as the acceleratory stage, the effect increasing with irradiation dose. The data for both the perchlorates, normal and irradiated. 1.0

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ITHIUMPERCHLORATI NORMALtO0Mr 0 • 40o*c • 420 "

A

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I00 150 TIME, min.

200

I'O

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250

Fig. 1. Thermal decomposition of lithium perchlorate, normal and irradiated with 100 Mr'°CO y-rays, at different temperatures.

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50

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TIME, rain,

150

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200

250

Fig. 3. Effect of 6°CO y-irradiation dose on the thermal decomposition of lithium perchlorate at 410°C.

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0"9

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~

0~

~0'7 °0.6 20"5 cl ~ 0"4 ~ 0'3 0'2

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50 75 TIME, rain.

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Fig. 2. Thermal decomposition of barium perchlorate, normal and irradiated with 100 MR 6°CO y-rays, at different temperatures.

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25

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TIME, min.

75

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125

Fig. 4. Effect of 6°Co y-irradiation dose on the thermal decompositionof barium perchlorate at 430°C.

1830

Notes

analyse best according to the Prout-Tompkins equation[6] ~t

Jo~ 1 - a =

.1.2,

The data show that whereas the activation energy for the acceleratory stage is diminished by irradiation that for the decay stage is unaffected. The rate constants for both the substances increase with the irradiation dose.

+c

with different constants k, and k: for the acceleratory and the decay stages respectively. The rate constants increase with temperature and yield linear Arrhenius plots. Values for the activation energy in kcal mole-1, E, for the acceleratory stage and Ea for the decay stage, determined from the temperature dependence of the Prout-Tompkins constants k, and kz are recorded below.

Irradiated Normal Substance LiCIO4 Ba(CIO4):

E~

Ea

100 Mr E~

400 Mr

E~

E~

500 Mr

E2

64.1 33.3 54.6 32.8 56.5 41.7 52.4 41.2 51.9 42.8

E,

E2

55.3 33.6 ---

*To whom all correspondence should be addressed.

Acknowledgements--The work was partially supported by the University Grants Commission, New Delhi, to which both S.D.B. and D.K. are also thankful for the award of research fellowships. Nuclear Chemistry Laboratory Utkal University Bhubaneswar 751004 India

S.D. BHATTAMISRA D. KUND S.R. MOItANTY*

REFERENCES 1. F. Solymosi and T. B~insfigi,Acta Chim. Acad. Sci. Hung. 74, 9 (1972). 2. P. J. Herley, C. S. Wang, G. Varsi and P. W. Levy, J. Chem. Phys. 60, 2430 (1974). 3. S. R. Mohanty and V. M. Pandey, Radiochim. Acta 15, 152 (1971); 16, 53 (1971); 19, 22 (1973). 4. B. K. Das and S. R. Mohanty, Rad. Eft. in press. 5. S. R. Mohanty and M. N. Ray, Indian J. Chem. 6, 319 (1968). 6. E. G. Prout and F. C. Tompkins, Trans. Faraday Soc. 40, 488 (1944).

J. inorg, nucL Chem., 1975, Vol. 37, pp. 1830-1831. Pergamon Press. Printed in Great Britain

Formation constants of complexes of N-m-tolyl-benzohydroxamic acid ( m - T B H A ) with some divalent metal ions

(Received 31 January 1975) HYDROXAMICacids have been reported to form complexes with metal ions. Recently metal ligand stability constants of some divalent metal ions with several hydroxamic acids have been reported[l-5]. Additional data on the proton and metal ligand stability constants of complexes of N-m-tolylbenzohydroxamic acid (m-TBHA) with Cu2÷, Zn 2+, Ni 2÷ and Mn 2+ in 70% dioxane-water at 25° and 35o are presented here. The procedure used here for determining the thermodynamic stability constants is an extension of Bjerrum-Calvin pH titration Temp. 25* Cu 1.6

1.2

m

0.8

0.4

method. Calculation of stepwise first and second stability constants K, and K: of the complexes from the results of metal-ligand titrations was accomplished by the method of least squares [4, 6]. The details of reagents and experimental procedure for proton stability constants as described elsewhere[I, 7]. RESULTS AND DISCUSSION No thermodynamic Tpk data in 70% dioxane-water have been reported. The data on thermodynamic ionisation constants and stability constants are given in Table 1-3. Calculation of stepwise first and second stability constants, K, and K2 of complexes from the results of metal ligand titrations also by some other computational methods, viz. interpolation at half-values (H)[ll]. Successive approximation methods (A)[I1] and Goldberg's modified calculation procedure (G)[12] were employed to determine the stepwise metal-ligand stability constants and values are summerised in Table 2. The formation curves are shown in Figs. 1 and 2. There was no evidence of metal ion hydrolysis, polynuclear complexes, protonated complexes or influence of chloride, perchlorate, nitrate and alkali metal cations. The complexes of Mna+, Ni 2. and Zn 2÷ are so insoluble that they are precipitated within five or six stages of the titrations with alkali. Their stability constants were determined by adding free perchloric acid (0.005 M) and by reducing the concentration of metal ions (M:L:::I:50). Table 1. Thermodynamic ionisation constants of N-m-Tolybenzohydroxamic acid in 70% dioxane water media

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7

9

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--z~e &]re 1 AP 1 (]Coall nolo" ~ (KeaA8 mole- ) (Oal.4eg. "t ~10 -I)

pCh-

Fig. 1. Formation curves for the metal ligand stability constants of Cua÷, Zn2+, Ni 2÷ and Mn2+ with N-m-tolylbenzohydroxamic acid at 25° in 70% dioxane-water media.

25e

1~.41

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1~,~1

18Q~4 18.74

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