DECOMPOSITION OF ALKALIAND ALKALINE EARTH PERCHLORATES
a small amount of C103. Good stoichiometry has been obtained. Acknowledgment. The authors wish to extend their thanks to Rlr. I. H. S. Fraser, Dr. W. Forgeng, and associates, Union Carbide Corporation, Metals Division,
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Niagara Falls, N. Y., for their assistance in obtaining the infrared, ultraviolet, and X-ray diffraction data. We also wish to express our appreciation to the Union Carbide Corporation, Linde Division, for many courtesies, including provision of the apparatus and gases employed in the high pressure radiation experiments.
The Radiation-Induced Decomposition of the Alkali and Alkaline Earth Perchlorates. 11. Mechanism of the Decomposition’”
by L. A. Prince and E. R. Johnson1b Chemistry Department, Stevens Institute of Technology, Hoboken, N e w Jersey
(Receioed August 6 , 1964)
The mechanism of the radiation-induced decomposition of the alkali and alkaline earth perchlorates is discussed. Evidence is presented to show that c103-, C1-, C102-, C102, and oxygen are the primary prcducts and that CIO- is not, its appearance being concomitant with a decrease in the yield of ClOz and ClOz-. The yields of (ClOz C102-) arid C1are related and appear to originate from a competitive primary reaction. Data are presented on the thermal decomposition of the products in the irradiated crystals. I t is showii that C102- and C10- thermally decompose to yield C1-, whereas C102 undergoes a neutralization reaction.
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In a previous conimunication,lc we have reported on the products and stoichionletry of the radiation-induced decomposition of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium, and strontium perchlorates. The results and discussions were confined to establishing the products, methods of analysis, and C: values. It was shown that C103- and O2 are always the principal products, followed by C1,- C102, or ClOZ-, depending upon the particular salt, then CIO-. Evidence was also given for the presence of a minor product found only in the alkali perchlorates, tentatively identified as c103, and also for the presence of a metal oxide. In this conimunication, we discuss the kinetics and mechanism of the decomposition.
Experimental The radiation source and methods of analysis have been discussed previously. There were no other excep-
tional experimental methods employed which require further discussion other than that which is found in the text. Kinetics. In Figure 1 is shown a semilog plot of undecomposed C10,- us. dose for the alkali and alkaline earth perchlorates. The dashed lines represent a firstorder plot and the solid lines experimental values. For low percentages of decomposition, all the perchlorates appear to follow first-order kinetics. This seems to he true for most radiation-induced inorganic solid decomp o s i t i o n ~ . ~ -The ~ degree of departure from first-order kinetics varies considerably aniong the different per(1) (a) Research supported by A.E.C. cotitr:ict AT-30-1 -1824: (bj N:itional S t a n d a r d Referenre D:itn I’rogr:um. N:ltion:d Bure:lu o f St:uid:irds, Washington 25, D. C . ; (-1 L. A. I’riiice :uid E. 11, .Johrlsorr. J . Phys. Chrm.. 69, 350 (1965).
( 2 ) T. Chen :itid E. 11. Johtison, i t i d . , 66, 2249 (1962). (3) J. Cutiiiiiigh:iin, itlid.. 65, 028 ( l O O l j .
L. A. PRINCE AND E. R. JOHNSON
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I2
I6
20
a2
24
O O l f , E L L C T I O l VOLT X I O ' l l t L R
BAAM
Figure 1. Semilog plot of undecomposed Clod- concentrations in irradiated alkali and alkaline earth perchlorates as functions of dose.
chlorates, and there is good evidence to indicate that this is due to the different degrees of back reaction which occurs. E$td of Temperature. I n Table I are summarized the results for the decomposition of KCIO, irradiated at different teniperatures. The effect of temperature on the radiation-induced decompositions of the other perchlorates was not studied. As can be seen froiii Table I, the appearance of hypochlorite as a product is concurrent with a decrease in the G value for CIOzand CIOz-. It appears also that, within experimental error for analysis at these low concentrations, the sum of the concentrations of CIOz C10- is approximately constant up
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The Journal of Physical Chemistry
to about 20'. At the higher temperatures, C10- is no longer observed as a product. GOcI- is relatively constant up to 72' where there is an abrupt increase due, as will be shown later, to the thermal decomposition of CIOz-and C10- to CI-. Both -GOclo,- and G0clo,- remain relatively constant except a t 72 and 260'. Whether or not any significance can be attached to the increases at these temperatures cannot be deterinined a t this writing. Certainly, stoichiometry is good a t 7 2 O , as there is ex(4) G . E. Boyd, E. W. G r a h a m , and 66,300 (1962).
&. \'. Larson, J . Phys. Chem.
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DECOMPOSITION OF ALKALIAND ALKALINE EARTH PERCHLORATES
Table 11: Thermal Decomposition of the Reaction Products of the Alkali Perchlorates Irradiated and Stored at Room Temperature
Table I : GO Yields of KClOa Irradiated a t Various Temperatures and Atmospheric Pressure Temp., O C .
-196 -80 -16 -8 0 19 20 72 260 295
-Goc104-
4.0 4.0 3.7 3.5 3.4 3.7 3.7 4.1 4.9 3.8
0 0 ~ 1 0 ~ -
2.7 2.8 2.8 2.6 2.6 2.9 2.9 3.3 4.2 2.9
G ~ c I o ~ - GOCIO,
0.58 .49 .26 .26 .20 .20 .19 .19
0.18 .17 .06 .09 .70 .10 .09 .09
.OO .OO
.OO 00
Gocio-
0.00 .OO .06 .06 .06 .06 08
.oo .oo .oo
GOCl-
0.5 .6 .5 .5 .5 .5 .5 .5 .7 .9
Goo,
3.0 2.7 2.4 2.6 2.2 2.5 2.7 2.0 1.0
cellent agreement between the experimental O2 value and O2 calculated from the radiolytic fragments. ( - GOCl0,- values are determined by difference.) The G values for Clot- and CIOz show the widest variation with temperature. At - 196O, G°C102-is 0.58 and G0c1oi is 0.18; a t room temperature G0c1o2-is 0.19 and GOclo, is 0.09. The fact that C10- is not a product a t -196' and that its appearance is acconipained by a decrease in CIOzand CIOz-, suggest that its origin may be associated with some reaction or reactions of these molecules. This will be discussed in more detail later. Thermal Decomposition of Reaction Products. A comparison of the data in Tables I1 and I11 shows the relative stability of C10-, CIOz-, and C102 in thedifferent lattices. llore extensive data on the thermal decomposition of the perchlorates can be found by consulting ref. 5 . I t is seen, for instance, that CIO- is generally more stable in the alkaline earth lattices than in the alkali lattices, and that CIOz- and C102 are least stable in the cesium and rubidium lattices. A kinetic plot of the thermal decomposition of C10-, CIOz-, and CIOz in irradiated perchlorate lattices does not reveal any simple order. There is a very complicated concentration dependence of these components for thermal decompositions a t room temperature and a t elevated temperatures. The kinetics of the thermal decomposition of these species are such that it has not been possible to obtain even a crude number for an activation energy for decomposition of any of the species. In Table IV are summarized the results of annealing irradiated I
