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Characteristics of Ferro Silicon Nitride

Ferro Silicon Nitride(FeSiN), when used in refractory materials, appears as a gray-white (or tea-brown) powder, while the Ferro Silicon Nitride used in steelmaking is in the form of gray-white granules. Ferro Silicon Nitride is a mixture of silicon nitride and iron, typically containing 75% to 80% (w) Si3N4, 12% to 17% (w) Fe, and free Si not exceeding 1% (w). In Ferro Silicon Nitride, Si3N4 exists in two crystal types, α and β, both of which are hexagonal crystals, and iron elements exist in the form of α-Fe or (and) iron silicides.

Ferro Silicon Nitride, due to the presence of Si3N4, exhibits excellent properties such as high refractoriness, good erosion resistance, high mechanical strength, good thermal shock resistance, a lower thermal expansion rate, and higher oxidation resistance. Additionally, its plasticity phase (Fe) contributes to good sintering performance. Moreover, compared to pure silicon nitride, Ferro Silicon Nitride has a lower cost, making it suitable for industrial promotion and production. Therefore, it has been used as a raw material for refractory materials, high-temperature bonding phases, and high-temperature structural materials, and is widely applied in blast furnace iron trough casting materials and gun mud. In recent years, there has been a growing focus on research on Ferro Silicon Nitride materials and their applications in refractory materials.

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Synthesis Methods of FeSiN:

Various methods are used for the synthesis of Ferro Silicon Nitride, including direct nitridation, carbon thermal reduction nitridation, vapor deposition, thermal decomposition, self-propagating high-temperature combustion synthesis, flash combustion synthesis, microwave synthesis, silicon-iron melt nitridation, etc. The composition and structure of Ferro Silicon Nitride vary with different synthesis methods and processes.

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  1. Flash Combustion Synthesis: This method, also known as vertical continuous combustion synthesis, was initially applied in the field of metal nitrides and later introduced to refractory materials for Ferro Silicon Nitride In the process, fine powder particles of silicon-iron alloy react with rising nitrogen gas flow, releasing a large amount of heat to sustain the self-sustaining reaction. Flash combustion synthesis has high efficiency, resulting in Ferro Silicon Nitride without free silicon, high product purity, low cost, and suitability for large-scale continuous production.
  2. Self-Propagating High-Temperature Combustion Synthesis: Also known as combustion synthesis or SHS, this method utilizes the high exothermic chemical reaction between reactants for self-heating and self-conduction to synthesize materials. FeSiNproduced through this method contains β-Si3N4, α-Si3N4, Si2N2O, FexSi, and other components. The microstructure consists of dense silicon nitride blocks, covered with Si2N2O film on the surface, and small crystalline silicon nitride embedded in the dense blocks. While this method has the advantages of low production cost and suitability for industrial production, it has strict operational processes, complexity, difficulty in controlling nitridation reactions, high nitridation pressure, demanding equipment requirements, and challenges in continuous production and low yield.
  3. Carbon Thermal Reduction Nitridation: Researchers from China University of Geosciences use iron ore powder, quartz powder, and coke powder as main raw materials (with particle sizes all below 0.3mm), along with a room temperature binding agent. These are mixed in certain proportions and subjected to carbon thermal reduction nitridation sintering at an appropriate temperature regime. After cooling, the resulting product is crushed and ground to obtain high-performance Fe-Si3N4 refractory raw materials applicable to various gun mud refractory materials.
  4. Direct Nitridation: This traditional preparation method involves directly using silicon-iron powder for nitridation reactions at high temperatures. It is a relatively simple and widely used experimental method due to its simplicity, minimal equipment requirements, and low reaction temperature. However, its drawbacks include low nitridation rate, long nitridation time, and high energy consumption. Additionally, achieving high β-Si3N4 content requires prolonged high-temperature nitridation, leading to increased energy consumption.

Application of FeSiN in Refractory Materials:

Currently, Ferro Silicon Nitride is primarily used in casting materials, gun mud, and composite refractory materials.

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  1. Casting Materials: Ferro Silicon Nitride is mainly used in casting materials such as Al2O3-SiC-C iron trough casting materials, magnesia casting materials, and high-alumina casting materials.
  2. Gun Mud: Gun mud is an essential refractory material used to block the iron tap of a blast furnace, allowing slag and iron to be discharged simultaneously during iron tapping. With advancements in blast furnace technology, such as large-scale operation, extended service life, high-temperature air injection, and high-pressure techniques, higher requirements have been placed on the performance of gun mud, including high resistance to chemical, slag, and molten iron erosion, good sintering and filling properties, excellent thermal shock resistance, high-temperature volume stability, minimal environmental pollution, easy opening, extended iron tapping time, and furnace protection. Gun mud containing Ferro Silicon Nitrideexhibits stable iron flow during practical use, with no abnormal phenomena like splashing or red spots. It has high-temperature flexural strength, strong resistance to molten iron scouring, achieves stable iron tapping for over 60 minutes, completely seals the iron tap, and avoids issues like wind drill running.
  3. Composite Refractory Materials: Composite refractory materials consist of two or more different types of refractory raw materials that, through physical or chemical methods, form refractory materials with new properties. The application of Ferro Silicon Nitride in composite refractory materials primarily focuses on carbon-containing and non-carbon-containing composites.

 

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