Influence of water vapor pressure on the induction period during Li2SO4·H2O single crystals dehydration

Abstract

The dehydration of Li 2 SO 4 •H 2 O single crystals at 80°C has been studied by means of both isothermal thermogravimetry at 2.6, 3.6 and 4.6 hPa of water vapor and environmental scanning electron microscope. Thermogravimetric experiments allowed the determination of induction periods. Distributions of these isoconversion induction periods for a large number of single crystals showed that increasing the water vapor pressure produced a longer induction period. Moreover the shape of the distributions of the induction periods over a large number of single crystals changed from one mode at 2.6 hPa to two modes at 3.6 and 4.6 hPa. Using an environmental scanning electron microscope, this result could be attributed to differences in nucleation rates at edges and faces of the single crystals.

Thermodynamic study of MgSO4 – H2O system dehydration at low pressure in view of heat storage

“…The water vapor pressure is maintained constant during each experiment using thermoregulated water bath. The water vapor pressure is imposed by the temperature, the total pressure being that of water vapor [25]. The thermobalance allows to estimate mass change with precision of about 0.001 mg.…”

“…All the results obtained by means of thermogravimetric analysis allow to plot the phase diagram of MgSO 4 -H 2 O system by representing various isosteres ( = constant) in a 2diagram ( Figure 7). Solid lines indicate a phase transition between crystalline phases [9,25] and dash lines represent equilibrium curves for five chosen non-stoichiometric solids obtained in this work. The solid phase is considered as a solid solution of water molecules in the magnesium sulfate skeleton in equilibrium with the gaseous atmosphere.…”

Impact of atmospheric water vapor on the thermal decomposition of calcium hydroxide: a universal kinetic approach to a physico-geometrical consecutive reaction in solid–gas systems under different partial pressures of product gas

“…Therefore, the physico-chemical processes of nucleation on the surfaces of the reactant solid should be considered when looking at the kinetics of the IP process. [63][64][65][66][67][68][69] According to the classical nucleation theory, [12][13][14][15][16]43,45 various heterogeneous processes may take part in the nucleation process on the surfaces of reactant crystals as elementary steps. For the sake of simplicity, one rate-limiting step was selected from these elementary steps, and the other steps were assumed to be at equilibrium by applying rate-limiting step approximation.…”

“…16,52,58 In some cases, a significant induction period (IP) is also observed prior to the surface reaction (SR). [63][64][65][66][67][68][69] Such heterogeneous characteristics of the reaction and any significant impact of the mass and heat transfer phenomena are responsible for the numerous observations induced by atmospheric gases. Therefore, in addition to having a universal kinetic description for these processes under various p(C(g)) conditions, investigation into the impact of p(C(g)) on each component physico-geometrical reaction step must be explored separately in order to gain further insights into the fundamental problems of reaction kinetics that are often encountered in solid-gas systems.…”

New kinetic model of the dehydration reaction of magnesium sulfate hexahydrate: Application for heat storage

“…Thermoregulated water baths were used to fix and kept constant the water vapor pressure, i.e. the water pressure is equal to the liquid/vapor equilibrium of pure water at a given temperature [54]. The first water bath is regulated at 16•C which corresponds to a water vapor pressure of 18 hPa.…”