Alkali Metal Perchlorates as Bases at Elevated Temperatures: The Depolymerization of Alkali Metal Condensed Phosphates

Abstract

The normal course of pyrolysis of L1CIO4, NaClOt, and KClCh to the metal chlorides is altered to varying degrees to yield effectively the metal oxides in the presence of the corresponding metaphosphates. This behavior reflects an acid displacement reaction which is accompanied by depolymerization of the metaphosphates to simpler anionic species. In this respect the perchlorates are bases relative to the isopolyphosphate anionic acids. The extent of metaphosphate depolymerization is found to be a function of the cationic environment such that for perchlorate-metaphosphate mixtures the order of extent of depolymerization is Li > Na K. NaCICh and KCIO4, unlike LÍCIO4, do not depolymerize their corresponding pyrophosphates to orthophosphates. Of interest is the fact that these elevated temperature reactions do not involve mutual oxidation and reduction of the perchlorate and condensed phosphate reactants. The stoichiometry and course of the reactions were studied by means of thermogravimetry, differential thermal analysis, Cl2 evolution measurements, and chemical and X-ray analyses.

A Thermoanalytical Study of Lithium Chlorate.

“…LiClOs-Condensed Phosphate Mixtures. It was thought that as in the instance of LiC104 (44), LiClOs might prove effective as a depolymerizing agent for condensed lithium phosphates (e.g., Li4P20-and the polymeric LiPOs) through its decomposition as per Reaction 1 which yields O-2 ions. Total Cl2 evolution and preliminary DTA and TGA studies showed reaction to become measurable at about 250°for the mixtures of Table II which also summarizes the extents of conversion of the LiClOs contents to Li20.…”

“…Thermoanalytical Techniques. DTA experiments to about 700°were performed in a closed muffle furnace with equipment previously described (35,39,44) in conjunction with calibrated chromel-alumel thermocouples (24 B. and S. gage) and quartz sample tubes (3 The pyrolysis of LiClOs was studied by differential thermal analysis and thermogravimetry at a heating rate of 4°/min., and by isothermal experiments at 339°. The decomposition was shown to follow the sequence: (rapid; ca.…”

“…TGA determinations were made with apparatus already detailed (33, 44) using Vycor sample tubes. Appropriate corrections were applied to all measured temperatures (34) to approximate the sample temperature from the furnace temperature.…”

“…The total CL evolved from various reacting samples was determined by absorption in KI solution as described previously (44).…”

Effect of lithium content on the kinetics of pyrophosphate degradation in molten nitrates

“…1 In every case the net reaction with respect to the NOg-ion was 2N03-2N02(g) + 0.5O2(g) + [02i (1) in which [O2-] denotes the effective donation of an oxide ion to a phosphate acid, and does not imply the existence of any appreciable O2-concentration in a nitrate melt.1,2 In all cases studied degradation of any phosphate species did not yield a product simpler than the P2O74-ion, whose double end-group structure apparently represented a stable form in molten NaNOg and nitrates of the heavier alkali metals. However, it was observed that if molten LiNOg was used as the reaction medium, degradation to PO43occurred, indicating a distinct cation effect.1 This is not unexpected in view of work by Markowitz et al, 3 and by other workers cited in extenso in the work of ref 1. The present work constitutes a study of the kinetics of the reaction P2074-+ 2NOg-->-2P043" + 2N02(g) + 0.5O2(g) (2) Li+ with respect to P2074-in excess molten alkali nitrate solvents (55:1 mole ratio of NOg~t o P2074-) as functions of Li+ concentration from 0.6530 to 0.9323 catiop mole fraction, and of temperature over a fairly small range from 610 to 625 K. Lithium content in the molten nitrates was controlled by mixing appropriate quantities of LiNOg and NaNOg.…”