A spatio-temporal model of anisotropic propagation of the dehydration front in Na3P309 9 6H20 single-crystals is discussed. It is based on the assumption that dehydration proceeds as a periodic displacement of the reaction front from one reacting elementary bloc~k to another, and that experimentally fixed dehydration patterns are composed of a multitude of elementary patterns having the same shape. The model can be applied to other crystals.On the basis of a kinetic investigation of the dehydration front propagation on the surface and into the volume of sodium cyclotriphosphate hexahydrate (NaaP30 9 9 6H20 ) single-crystals in various directions, depending on the temperature and the relative air humidity, an experimental model of this process has been proposed [1][2][3]. It has been shown that in vacuum and air at low relative humidity (r) the process takes place according to a scheme of uniform surface localization. The resulting planar reactant-product interface penetrates into the crystal, and the unreacted tranparent nucleus acquires the form of a parallelepiped which, depending on temperature, contracts homothetically or nonhomothetically. At about 30 ~ homothetic contraction prevails. At 10 ~ the contraction becomes nonhomothetic and the contracting nucleus gradually elongates along the b axis. If dehydration is carried out in humid air at r ~< 25-30% (t = 20-50~ then the (100), (010) and (001) crystal faces react in the sequence of decrease of their activity, according to a scheme of spot surface localization: first the (100), then the (001) and finally the (010) face. The shape of the well-defined dehydration patterns varies from one face to another. However, the linear rate of dehydration front propagation on faces in one and the same direction remains constant.The coincidence of the kinetic parameters of the three stages of the overall process (mass toss, destruction of initial crystal lattice and crystallization of a new phase) obtained by independent experimental methods (gravimetry, microscopy and X-ray techniques) allows identification of the visually observed interface with the reaction zone and analysis of the connection between the Na3P309.6H20 crystal structure and the dehydration patterns which appear in a wet atmosphere [4].
The isothermal and nonisothermal conversions of hydrated and anhydrous forms of cyelotriphosphates of sodium, lithium and ammonium were investigated in different gaseous atmospheres and in vacuum. It was shown that gaseous ammonia in its mixtures with water vapour can accelerate the solid-state splitting of the anionic cycle. A mechanism is suggested for the decycling effect of gaseous ammonia and its mixtures with water vapour.Despite the large number of publications on the transformation of condensed phosphates, the literature contains practically no information on the influence of temperature and the gas atmosphere composition on the process of the solid-phase decyclization of cyclic triphosphate anions. This report describes a study of the topochemical transformations of the cyclic triphosphates of sodium, Na3P309"xH20 (x = 1, 3, 6), lithium, Li3P309"3H20, and ammonium, (NH4)3P309, in an atmosphere of air, in vacuum, in ammonia and in mixtures of ammonia and water vapour.When heated in vacuum, in a water vapour atmosphere or in air, sodium cyclotriphosphate tri-and hexahydrate lose crystalline water, mainly below 100 ~ the hexahydrate under going dehydration without anion ring breakage and without crystallization of the intermediate phases, while for the trihydrate there is similarly no ring breakage, but the intermediate monohydrate undergoes crystallization.When the monohydrate is heated under the same conditions, water is removed at above 100 ~ in two stages, with corresponding endoeffects at 128 and 210 ~ . Within the given temperature range, and especially in the second stage, the dehydration is accompanied by decyclization of the anion, which results in amorphous products. The decomposition degree is comparatively low, the content of phosphorus in the cyclotriphosphate form not falling John Wiley & Sons, Limited, Chichester AkadOniai Kiad6, Budapest
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.