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Reaction-sintered silicon carbide possesses excellent physical properties.

Release time:

2023-01-12

　　Because Reaction-sintered silicon carbide It possesses excellent physical properties and is therefore widely used as a key chemical raw material. Its applications fall into three main categories: first, it is used to manufacture abrasive tools and grinding materials; second, it is employed in the production of resistive heating components—such as silicon-molybdenum rods and silicon-carbon tubes—and third, it is utilized in the fabrication of refractory products. As a special type of refractory material, it serves as a fire-resistant lining in areas of intense impact, corrosion, and wear within ironmaking blast furnaces and melting furnaces used for steel production. In the smelting of rare metals (such as zinc, aluminum, and copper), it is used as furnace charge, molten-metal transfer pipes, filtration devices, and crucibles. In aerospace technology, it is employed as nozzle linings for rocket engines and as high-temperature gas turbine blades. In the silicate industry, it is extensively used as kiln shelves, charge materials for box-type resistance furnaces, and crucibles for various industrial kilns. In the chemical industry, it is utilized as fuel for gas generators, vaporizers for crude oil, and charge materials for flue-gas desulfurization furnaces.

　　When producing articles solely from α-SiC, due to its relatively high strength, it is extremely difficult to grind it into ultrafine nanoscale powder. Moreover, the particles tend to be flaky or fibrous in shape. Even when these particles are compacted into green bodies and heated close to their decomposition temperature, they do not exhibit significant shrinkage, making sintering impossible. As a result, the resulting articles have low density and poor oxidation resistance. Therefore, in industrial production, a small amount of ultrafine β-SiC powder with spherical particles is added to α-SiC along with appropriate additives to obtain high-density products. Additives used as binders for these articles can be categorized into several types, including metal oxides, nitrogen compounds, and high-purity graphite—for example, clay, aluminum oxide, zircon, zirconium corundum, lime powder, glass frits, silicon nitride, silicon oxynitride, and high-purity graphite. The forming binder solutions can consist of one or more of the following: hydroxymethyl cellulose, acrylic emulsion, wood cellulose, tapioca starch, aluminum oxide colloidal solution, or silica colloidal solution. Depending on the type and dosage of the additive, the firing temperature of the green bodies varies within a range of 1400 to 2300°C. For instance, a mixture comprising 70% α-SiC with particle sizes greater than 44 μm, 20% β-SiC with particle sizes less than 10 μm, 10% clay, and an additional 4.5% aqueous solution of wood cellulose (8% concentration), uniformly blended together, is formed under a pressure of 50 MPa and then fired at 1400°C in air for 4 hours. The resulting article exhibits an apparent density of 2.53 g/cm³, an apparent porosity of 12.3%, and a tensile strength ranging from 30 to 33 MPa. The sintering performance of articles made with various additives is summarized in Table 2.

　　Generally speaking, Reaction-sintered silicon carbide Refractory materials exhibit excellent performance in various aspects—for instance, they possess high compressive strength over a wide temperature range, strong resistance to thermal shock, good wear resistance, a high thermal conductivity, and excellent resistance to solvent corrosion. However, it should also be noted that these materials have poor oxidation resistance, which can lead to volume expansion and deformation under high-temperature conditions, thereby shortening their service life. To ensure the oxidation resistance of reaction-sintered silicon carbide refractories, considerable efforts have been made in selecting appropriate binders. Initially, clays (including metal oxides) were used as binders; however, they failed to provide sufficient buffering effects, and the silicon carbide particles continued to undergo oxidation and corrosion.

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