Thermal Dehydration of Magnesium Acetate Tetrahydrate: Formation and in Situ Crystallization of Anhydrous Glass

Abstract

The kinetics and mechanism of the thermal dehydration of magnesium acetate tetrahydrate were investigated as a typical example of the glass formation process via the thermal decomposition of solids. Formation of an intermediate fluid phase was identified as the characteristic phenomenon responsible for the formation of anhydrous glass. Thermal dehydration from the surface fluid layer regulates the zero-order-like rate behavior of the mass-loss process with an apparent activation energy E(a) ≈ 70-80 kJ mol(-1). Because of variations in the mechanism of release of the water vapor with changes in the reaction temperature range, the mass-loss behavior is largely dependent on the particle size of the sample and heating conditions. The formation of hollow anhydrous glass is the novel finding of the present study. The mechanism of formation is discussed in terms of complementary interpretations of the morphological changes and kinetic behavior of the thermal dehydration. On further heating, the as-produced anhydrous glass exhibits a glass transition phenomenon at approximately 470 K with an E(a) ≈ 550-560 kJ mol(-1), and subsequently crystallizes via the three-dimensional growth of nuclei controlled by diffusion. The crystallization process is characterized by an E(a) ≈ 280 kJ mol(-1) and an enthalpy change ΔH = -13.3 kJ mol(-1), resulting in the formation of smaller, rounded particles of crystalline anhydrate.

Alkaline Metal Reagent-Assisted Synthesis of Monodisperse Iron Oxide Nanostructures

“…The decomposed acetylacetonate and acetate anions can enable reduction to aldehyde and alcohol as oxygen resource with a high reduction potential of alkaline metal ions in the reductive environment. For alkaline metal reagent-assisted magnetite nanoparticles formation, we choose magnesium acetate based on the following considerations: (1) alkaline metal reagent can be decomposed at a lower temperature than that of iron (III) reagent; (2) species with relatively small ionization energies is preferred; and (3) higher reducing potential than that of iron reagent is crucial to avoid precipitation of alkaline metal oxide or alloy [25,26].…”

A Combined 25Mg Solid‐State NMR and Ab Initio DFT Approach to Probe the Local Structural Differences in Magnesium Acetate Phases Mg(CH3COO)2 ⋅ nH2O (n=0, 1, 4)

“…[19] The Mg sites are both 6-coordinate (MgO 6 ); Mg1 coordinates to one water molecule, three monodentately bridged acetate groups and one chelating acetate group, whereas Mg2 coordinates to one water molecule, and five monodentately bridged acetate groups [ Figure 1]. [20] Additional peaks may also relate to other partial hydration states. The 13 C CPMAS NMR spectrum, shown in Figure 2(b) contains sharp resonances with broader underlying components.…”

“…The tetrahydrate phase is readily available and several reports of the 25 Mg NMR parameters appear in the literature, of a single MgO 6 site with a relative modest quadrupolar constant (C Q~2 .5 MHz), with the most recent higher field studies providing the most accurate values and were in good agreement. [20,21] No single crystal structure has been reported for this second anhydrate phase, but the NMR data can help determine the number of different sites present. For the latter compound the challenge of evaluating the NMR parameters of the superimposed signals from two MgO 6 and one MgO 7 coordination [ Figure 1] is possible by comparing a high-quality distortion-free one-dimensional MAS spectrum at 20.0 T with the DFT calculated parameters.…”

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

“…When the mutual interactions of the component reaction steps are negligible, the overall rate behavior of the oxidation reaction is expressed by the cumulative kinetic equation of the two reaction steps [35][36][37][38][39][40][41][42].…”

“…The aim of this study is to establish a test method for characterizing the compositional and structural properties of a carbon/carbon composite through kinetic analysis of its thermal oxidation process. Kinetic deconvolution analysis of the thermoanalytical data recently used to gain a detailed understanding of the various types of multistep solid-state and solid-gas reactions [35][36][37][38][39][40][41][42] was applied as the most suitable approach to describe the kinetic phenomena of the thermal oxidation process with the aid of the results of fundamental kinetic calculations and morphological observations of the samples during the reaction. This article reports a detailed comparison of the kinetic characteristics of the thermal oxidation processes of two different mechanical pencil leads manufactured by different companies as the first part of our study, which is expected to provide the necessary information to establish the methodology of kinetic analysis as a test method that is generally applicable to various carbon/carbon composites.…”