Magnesium Acetate Tetrahydrate:Thermal Dehydration and application research

Introduction

Magnesium acetate tetrahydrate (Figure 1) is widely used as the precursor for the synthesis of magnesium oxide and magnesium containing oxides in the forms of thin film, rode, porous particles with high specific surface area, and so on,where ethanol-mediated sol-gel process and subsequent thermal decomposition of the as-prepared gel are the major chemical processes. For example, Bian et al. reported a successful template-free synthesis of mesoporous magnesium oxide via the thermal decomposition of monodispersive crystalline particles of anhydrous magnesium acetate for the application in carbon dioxide adsorption. If the formation process of magnesium acetate anhydrous glass were mediated by an intermediate fluid phase, the glass material in varieties of size and morphology could be produced. In this case, magnesium acetate anhydrous glass can be the possible candidate for the precursor in such synthesis of magnesium ceramics, which realizes the potential applications.

Thermal Dehydration of Magnesium Acetate Tetrahydrate

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. 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 Ea ≈ 550-560 kJ/mol, and subsequently crystallizes via the three-dimensional growth of nuclei controlled by diffusion. The crystallization process is characterized by an Ea ≈ 280kJ/mol and an enthalpy change ΔH=-13.3 kJ/mol, resulting in the formation of smaller, rounded particles of crystalline anhydrate.[1]

Application researches example

SiO₂-MgO coated MWCNTs

In the present publication, multiwalled carbon nanotubes (MWCNT) coated with SiO₂-MgO nanoparticles were successfully fabricated via sol-gel method to facilitate their incorporation into polymer matrices. Magnesium acetate tetrahydrate and tetraethyl orthosilicate were used as precursors. The coated MWCNTs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy methods. These investigation techniques verified the presence of the inorganic nanoparticles on the surface of MWCNTs. Surface coated MWCNTs were incorporated into polyamide (PA), polyethylene (PE) and polypropylene (PP) matrices via melt blending. Tensile test and differential scanning calorimetry (DSC) investigations were performed on SiO₂-MgO/MWCNT polymer composites to study the reinforcement effect on the mechanical and thermal properties of the products. The obtained results indicate that depending on the type of polymer, the nanoparticles differently influenced the Young's modulus of polymers. Generally, the results demonstrated that polymers treated with SiO₂-MgO/MWCNT nanoparticles have higher modulus than neat polymers. DSC results showed that nanoparticles do not change the melting and crystallization behavior of PP significantly. According to the obtained results, coated MWCNTs are promising fillers to enhance mechanical properties of polymers.[2]

A lamellar material preparation

A lamellar material composed of alternating layers of magnesium phosphate sheets and n-hexadecylammonium (n-C₁₆H₃₃NH₃⁺) ions was synthesized by the reaction between magnesium acetate tetrahydrate and phosphoric acid. A composite material of magnesium phosphate sheets and n-hexadecylammonium (n-C₁₆H₃₃NH3⁺ ) ions was prepared through the reaction between magnesium acetate tetrahydrate (Mg(OAc)₂ · 4H₂O) and phosphoric acid (H₃PO₄) in a basic EtOH/H₂O mixed solution.The pH value of the solution was adjusted by the addition of tetramethylammonium hydroxide (TMAOH).The chemical formula of the composite material was determined to be (n-C₁₆H₃₃NH₃⁺)Mg²⁺(HPO₄^2-)(H₂PO₄^-) by ICP, TG, and 31P MAS NMR measurements. The lamellar composite was obtained under basic conditions adjusted with tetramethylammonium (TMAOH) and tetraethylammonium hydroxides (TEAOH), while ammonium ions did not act as an alkali source useful for obtaining the composite material. The formation of crystalline byproducts such as hydrated newberyite (MgHPO₄.3H₂O) and ammonium-type struvite (MgNH₄PO₄. 6H₂O) was suppressed by using the EtOH/H₂O mixed solution and by adding TMAOH and TEAOH to adjust the synthetic condition, respectively. Including the data on calcium, barium and strontium phosphates, we can totally understand the formation of the mesostructured materials composed of ionic frameworks in the presence of n-alkylamines in detail. It is quite important to suppress the formation of crystalline alkaline earth metal phosphates and control the solubilities of reactants and products for synthesizing pure mesostructured materials with ionically crosslinked frameworks.[3]

Preparation of optically transparent magnesium fluoride sols

A synthesis route for the preparation of optically transparent magnesium fluoride sols using magnesium acetate tetrahydrate as precursor is described. The obtained magnesium fluoride sols are stable for several months and can be applied for antireflective coatings on glass substrates. Reaction parameters in the course of sol synthesis are described in detail. Thus, properties of the precursor materials play a crucial role in the formation of the desired magnesium fluoride nanoparticles, this is drying the precursor has to be performed under defined mild conditions, re-solvation of the dried precursor has to be avoided and addition of water to the final sol-system has to be controlled strictly. Finally, strict consideration of these reaction parameters enables the upscaling of the synthesis conditions for optimised MgF2 sols which can be stored and handled for at least 3 to 4 months. Such sols are suitable for coating of glass substrates under industrial conditions. The optical performance is better and the mechanical properties are comparable to the classical SiO₂ coatings as described in.[4]

References

[1] Koga N, Suzuki Y, Tatsuoka T. Thermal dehydration of magnesium acetate tetrahydrate: formation and in situ crystallization of anhydrous glass. J Phys Chem B. 2012;116(49):14477-14486. doi:10.1021/jp3052517

[2] Nemeth K, Varro N, Reti B, et al. Synthesis and investigation of SiO2-MgO coated MWCNTs and their potential application. Sci Rep. 2019;9(1):15113. Published 2019 Oct 22. doi:10.1038/s41598-019-51745-1

[3] Ikawa N, Iwata M, Oumi Y, Kimura T, Sano T. Understanding of the formation of mesostructured alkylammonium-alkaline earth metal phosphates composed of ionic frameworks. J Nanosci Nanotechnol. 2009;9(1):627-633. doi:10.1166/jnn.2009.j072

[4] Scheurell K, Noack J, König R, et al. Optimisation of a sol-gel synthesis route for the preparation of MgF2 particles for a large scale coating process. Dalton Trans. 2015;44(45):19501-19508. doi:10.1039/c5dt02196k

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