Production of Forsterite Powder Using Sol-Gel Technology

Abstract

The effect of initial components, gel-forming additives, and heat-treatment and disaggregation conditions on the completeness of synthesis of forsterite and on powder morphology is considered. The colloid method using silica sol and magnesium acetate solution provides the steadiest and most homogeneous sol and after heat treatment yields highly dispersed powder without additional milling. The technological regimes facilitating complete synthesis are identified. Control of the synthesis temperature makes it possible to obtain powder with particle size ranging from less than 0.1 to 0.2 -0.5 mm and aggregate size from 0.5 to 2 -5 mm.One of the most significant stages in the technology of new generations of ceramics is the production of initial powders. It is this stage that predetermines the shape and size of particles and aggregates dictating the choice of technological regimes and the properties of ceramics.The use of traditional solid-phase synthesis for the production of finely dispersed nonaggregated powders is hampered mainly due to the impossibility of a uniform distribution of initial materials. To ensure a complete synthesis, it is necessary to briquette powders and apply high temperatures and long exposures. In this case strong aggregates are formed and the crystals keep growing. Subsequent milling makes the powder polyfractional and may cause its contamination by the milling bodies. Thus, the temperature at the beginning and the end of forsterite formation in a mechanical mixture of pure magnesium and silicon oxides is within the limits of 1250 -1500°C. The quantity of forsterite produced at 1350°C in briquettes of magnesium oxide and quartz is 58.6% of the theoretical quantity and in briquettes of magnesium oxide and quartz glass it is 64.3% [1].The problem of lowering the temperature of synthesis and producing highly dispersed monofractional forsterite powder with a preset size of particles and aggregates is topical considering the prospects of using forsterite single crystals [2]; therefore, special attention is paid to the chemical methods of synthesizing powders.The methods of precipitation in a liquid phase, usually in aqueous solutions of precipitators, are widely applied. The use of the method of coprecipitation of components in an aqueous medium for the synthesis of silicates is hampered by the absence of water-soluble silicon salts, except for the silicates of alkali metals. The application of special purification methods not only complicates the process, but is frequently ineffective, since alkali metal ions to a large extent are sorbed on the gel. Another version of this method is precipitation on a solid phase, when one of the components has no water-soluble salts. Thus, aluminum hydroxide was precipitated on the surface of highly dispersed amorphous silica in the form of Aerosil in order to synthesize mullite [3]. The distribution uniformity in this case depends on the dispersion of the solid phase and is lower than in coprecipitation. However, the technology of the synthesis of powders beco...

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.…”

Sintering and properties of magnesium orthosilicate ceramic

“…In addition, the quality factor of magnesium orthosilicate was found to degrade substantially in the presence of glass impurity and its ultra high quality factor was only achieved when magnesium orthosilicate is synthesized from high purity raw materials [3]. To date, there are several known magnesium orthosilicate powder preparation methods such as aqueous synthesis [12,13], variants of sol-gel technique with different initial materials such as metal alkoxides and hydrated metal salts [1, 14,15] and solid state reaction [16][17][18]. In spite of the wide array of synthesis techniques available, the production of phase-pure magnesium orthosilicate is a challenge and heat treatment at temperatures ranging from 1200 to 1600°C are often required to obtain pure magnesium orthosilicate [13].…”

Synthesis and fritting of magnesia silicate composite powder

“…Powders were prepared by the sol-gel method based on magnesium acetate and silica sol (colloidal solution of amorphous silicon oxide) by technology developed previously [4]. The magnesium oxide content was varied within the limits from 63 to 37%, including the stoichiometric composition of forsterite (Table 1 and 2).…”