Phase composition and morphology of products of combustion of ferrosilicon in nitrogen

Abstract

The results of a study of silicon nitride phase formation in combustion of ferrosilicon in gaseous nitrogen are reported. It was shown that formation of a-or b-modifications of silicon nitride is basically determined by the composition of the batch for self-propagating high-temperature synthesis. When ammonium chloride was added to the initial ferrosilicon, a combustion product with a high (up to 80%) a-Si 3 N 4 content is formed, while dilution with the final product and magnesium fluoride results in predominant (more than 95%) formation of b-Si 3 N 4 . The particle size and shape are a function of the conditions of synthesis and are primarily determined by the temperature and the additives incorporated in the initial alloy.Silicon nitride, which has unique performance properties (high strength, crack resistance, resistance to high-temperature oxidation, corrosion resistance in aggressive media, heat resistance, etc.), is increasingly widely used in modern technology. Furnace synthesis and plasma chemical methods are the basic industrial methods of manufacturing silicon nitride. These methods are distinguished by high energy capacity and the use of expensive equipment and initial materials, which is reflected in the cost of the silicon nitride powders obtained with these technologies.The method of self-propagating high-temperature synthesis (SHS), which allows attaining high reproducibility with minimum power consumption since no external sources of heat are used, occupies a special position. The SHS method does not introduce contaminants in the synthesis process, so that the purity of the product is determined by the purity of the initial silicon. To obtain pure silicon nitride powders by the SHS method, silicon wastes of semiconductor purity are used as the raw material [1,2]. The combustion products are in the form of cake and must be ground. One available method of dispersing the powders is still grinding in a mill with steel balls, but the silicon nitride is contaminated with iron, and chemical treatment in hydrochloric acid solutions is required to remove it.We showed (RF Patent No. 2257338) [3] that silicon nitride can be obtained from ferrosilicon, which is manufactured by domestic industry in large amounts, since it is used as a hardener and scavenger in smelting steel. Ferrosilicon is a brittle material, and when ground, it forms a large amount of fine fraction (dust) which is removed by the ventilation system and is finished feedstock for high-temperature synthesis of silicon nitride. The product of combustion of ferrosilicon in nitrogen is a composite of silicon nitride and iron. After acid concentration in hydrochloric acid solutions, silicon nitride powder with a 0.05% residual iron content is obtained. 2 The results of a study of the effect of the basic synthesis parameters on the phase composition and morphology of silicon nitride particles are reported.PUD-75 powdered ferrosilicon wastes -polydisperse powder with a particle size less than 160 mm and 79.0% silicon content -was used as feedstock....

Microstructure and Mechanical Properties of Si3N4-Fe3Si Composites Prepared by Gas-Pressure Sintering

“…%) and a small amount of un-nitrided Fe 3 Si (~15 wt. %) [16,17]. With the main phase being Si 3 N 4 , Fe-Si 3 N 4 inherits the excellent comprehensive properties of pure Si 3 N 4 .…”

Research on High Performance Fe3Si-Si3N4-SiC Composite Used for Blast Furnace

“…Si 3 N 4 -SiC materials with uniformly dispersed metallic plastic phase is expected to have higher thermal conductivity and thermal shock resistance in favour of enhancing blast furnace cooling rate. At present, the research on Fe 3 Si-Si 3 N 4 -SiC materials is rarely reported in domestic and oversea research [11][12][13][14], this research hopes to provide some useful reference.…”

Chemically and thermally conjugate synthesis of silicon nitride based compositions using ferrosilicon

“…The basic mechanisms of this process are described in [3,4]. For the interaction of ferrosilicon with nitrogen in a combustion regime heat is released as a result of the interaction of silicon with nitrogen:…”