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...

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...

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