The Differential Thermal Analysis of Perchlorates. VII. Catalytic Decompositions of the Alkali Metal Perchlorates by Manganese Dioxide

Abstract

The thermal stabilities of the pure alkali metal perchlorates (MCIOI) and of admixtures with 10 mole % RhOz catalyst follow the order Li < Na < K, Rb, Cs. For both pure and catalyst-containing materials, rapid decomposition is preceded by liquid phase formstion. Analyses of molten perchlorates near their fusion temperatures show that fusion is coincident with decomposition except for LiClO, which has a congruent melting point; the simultaneous occurrence of fusion and decomposition is in contrast to the behavior manifested by RIC103 salts, each of which possesses a congruent melting point and a significant range of liquid phase stability. Catalysis of Mc101 pyrolysis by basic substances yielding 02ion, in conjunction with other evidence, suggests the presence of 0 atoms in decomposing perchlorates. A proposed mechanism for Clz evolution from lIC104 melts (order of extent of Clz release: Li >> Xa > K > Rb, Cs = 0) stipulates an autoionization equilibrium of the type C104-4 c103+ + 02-, so that Clz release occurs through the reaction Clod-+ ClO3+ -+ [C1207] -+ Clz + 7/z02. Such a scheme removes acidic oxides (e.g., P206, B203, W03, Moo3, etc.) from consideration as true catalysts inasmuch as they function by removal of oxide ions and hence undergo specific, irreversible reactions with RIC104 salts. In this regard, MnOZ is primarily a true catalytic agent for MC104 decomposition, but it also does appear to undergo a small amount of chemical reaction with LiClO,, in particular, to foster Clz evolution, viz., LiC104 + MnOz 4 Li?tfnOz + l/zClz + 2OZ.(1) "Gmelins Handbuch der anorganischen Chemie," 8 Auflage, System No. 6, "Chlor," Verlag Chemie, G.m.b.h., Berlin, 1926, pp.

Differential thermal analysis of potassium perchlorate

“…The DTA curve of uncompressed KC104 displays the first endotherm at 303 ~ a second endotherm at 573 ~ and a large exotherm at 585 ~ The sharp exotherm at 585 ~ indicates the decomposition of KC1Oa, forming KC1 as the final product. This DTA curve is in qualitative agreement with the DTA curves reported in references [9] and [10]. The DTA curve of KC104 precompressed at 500 kg/cm 2 shows that the endotherms have shifted to 307 ~ and 604 ~ respectively.…”

“…Further, the latter authors attributed the "resolved exotherm" of Anderson and Freeman [8] to the "possible catalytic effect of the chromel-alumel thermocouple". Later work [10] in this laboratory has confirmed the results of Markowitz and Boryta [9]. More recently, while studying the effect of precompressi0n on the…”

“…The first exotherm appears after the "melting endotherm at 606 ~ Its exothermicity decreases as it reaches 636 ~ At 636 ~ a sharp rise in exothermicity occurs, with a peak at 641 ~ followed by the rapid decay of the exotherm. Markowitz and Boryta [9], on the other hand, observed a single exotherm, pointing to a reaction occurring in a single stage. The latter authors used shielded thermocouples and varied the sample size from 3 to 0.1 g, and observed only one exotherm.…”

Absolute isotopic abundance ratio and atomic weight of terrestrial rubidium

“…(To avoid isotopic con· tamination, the decompositions of the 85RbCI04 ( and 87RbCI04 were performed in new, separate furnaces which had not been exposed to rubidium salts.) The decomposition proceeds in the following manner [18].…”

The effect of defect structure due to doping and irradiation on the thermal decomposition of potassium chlorate

“…On the other hand, the nature of the cations of an oxy-chlorine compound affects significantly the stability and reaction path [4,5], In fact, there seems to be a distinct correlation between the polarizing power of the cations [6] or the ionic character of the cation-oxychlorine bond [7,8] and the thermal stability. The less ionic the bond, or the stronger the polarization power of the cation, the less stable is the compound.…”