Effect of the conditions of hydrolysis of tetraethoxysilane on the synthesis of forsterite

Abstract

The sol-gel process for synthesizing forsterite from magnesium acetate and tetraethoxysilane (TEOS) is investigated. The effect of the conditions of hydrolysis of TEOS on the morphology and phase composition of the powders is studied. It is found that a solution of magnesium acetate and TEOS hydrolysate in an acid medium forms a stable sol which transforms into gel. In this case, the yield of forsterite after heat-treatment at 800°C is 97%. Performing hydrolysis in an alkaline medium and combining the hydrolysis and precipitation of magnesium hydroxide makes it possible to obtain a weakly aggregated powder with composition close to monofractional but the synthesis temperature of forsterite increases.Sol-gel technology is now making it possible to synthesize multicomponent oxide compounds (silicates, spinels) as well as controlling the properties of ceramic powders and materials.The sol-gel method is successfully used to obtain forsterite powder, which is of interest for use in electronics and laser technology. For example, in [1] forsterite was synthesized from melts of magnesium salts and amorphous silica in the presence of a solution of polyvinyl alcohol. The authors of [2] propose using an alkoxide precursor -magnesium -silicon cellosolvate. Well-crystallized forsterite powders were obtained only after calcination of hydrolysates at 800°C for 2 h. The 20-nm primary crystallites combine to form large and dense aggregates.Our previous investigations [3] show that magnesium acetate and silicasol -a sol of amorphous silica -are effectively used to synthesize forsterite. However, a temperature 1200°C is required to complete the formation of forsterite. At this temperature dense aggregates of particles up to 20 mm in size are formed. Thus, the problem of obtaining a monofractional forsterite nanopowder was not solved.According to the published data, it is preferable to use tetraethoxysilane (TEOS) to synthesize silicates, in particular, forsterite. As a rule, the hydrolysis of TEOS is conducted in a water-alcohol medium with different values of the pH. By changing the conditions of hydrolysis it is possible to obtain particles ranging in size from 5 to 100 nm. In addition, the tendency of silica to polymerize will promote the formation of Si -O -Mg bonds even at the stage of mixing and hydrolysis.The main problem of our work is to study the interaction of the products of hydrolysis of TEOS and magnesium acetate in order to obtain a highly disperse forsterite powder with composition close to a single phase and monofractional. To this end, it is proposed that different regimes of TEOS hydrolysis in acidic and alkaline media without organic solvents as well as directly in a solution of magnesium acetate, obtained by dissolving analytically pure magnesium oxide with molar ratio MgO : H 2 O : CH 3 COOH = 1.5 : 11.0 : 4.0, be tested.The products of the interaction (precursors) were studied by means of IR spectroscopy, XPA, and microscopic analysis. The content of forsterite was determined by quantitative XPA as a function...

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

“…Magnesium acetate tetrahydrate 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.…”

Non-hydrolytic sol-gel processing of chloride precursors loaded at forsterite stoichiometry

“…As can be seen, the intensity of the magnesia reflections has been increased and, more importantly, the forsterite peaks have disappeared in comparison to Fig. 2, suggesting a more silicon depletion and lack. Considering the promoting role of water in both hydrolysis and condensation sol-gel reactions [30,31], even with the presence of water in the HCl solution used for this exaggerated sample, any improvement in the expected calcined structure was not only achieved, but also the deviation with respect to the expected stoichiometry was enhanced. It suggests the domination of the inhibiting role of HCl and verifies the above described mechanism about condensation inhibited by the severe chelation effect.…”

Thermal plasma sintering of forsterite ceramics

“…Для синтеза форстерита разработаны различные методы подготовки порошков, такие как соосаждение, золь-гель, твердофазная реакция, метод саморастекания и т. д. [6][7][8][9]. Но керамика, полученная на основе порошков, синтезированных указанными выше способами, всегда имеет некоторые ограничения по плотности и механической прочности, которые необходимы для материалов, применяемых в высокотемпературных условиях.…”