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Applications of Silicon Carbide in Refractory Materials

Release Date:

2022-05-20 17:08

Author:

Originating from the internet

1. Wear Resistance: Silicon carbide ranks second only to diamond in hardness and exhibits excellent wear resistance, making it an ideal material for wear‑resistant pipelines, impellers, pump chambers, hydrocyclones, and liners for mining buckets. Its wear life is 5 to 20 times that of cast iron or rubber, and it is also one of the preferred materials for aircraft runways. By applying silicon carbide powder to the inner surfaces of turbine blades or cylinder blocks using a specialized process, its wear resistance can be significantly enhanced, extending service life by a factor of 1 to 2. 2. Corrosion Resistance: In silicate‑bonded silicon carbide materials, the SiO₂ contained in the bonding matrix readily forms low‑melting-point compounds upon contact with certain substances, making the material susceptible to erosion by molten slag. Consequently, this type of silicon carbide…

1. Abrasion resistance

Silicon carbide ranks second only to diamond in hardness and exhibits excellent wear resistance, making it an ideal material for wear‑resistant pipelines, impellers, pump chambers, hydrocyclones, and liners for mining buckets. Its wear life is 5 to 20 times that of cast iron or rubber, and it is also one of the preferred materials for aircraft runways. By applying silicon carbide powder to the inner surfaces of turbine blades or cylinder blocks using a specialized process, its wear resistance can be enhanced, extending service life by a factor of 1 to 2.

2. Corrosion Resistance

Within the binding matrix of silicate-bonded silicon carbide, the SiO2 present readily forms low-melting-point compounds upon contact with certain substances, making the material susceptible to slag erosion and thus resulting in relatively poor chemical resistance. Since most metal melts do not wet silicon nitride or oxynitride, these materials exhibit superior corrosion resistance compared to silicate-bonded silicon carbide.

3. Thermal Shock Resistance

Due to silicon carbide’s high thermal conductivity and low coefficient of thermal expansion, this silicon carbide refractory material exhibits excellent resistance to thermal shock. The thermal shock resistance of silicon carbide products is also closely related to the type and properties of the binding matrix. Tests have shown that when a sample is rapidly heated in an electric furnace at 1200°C for 20 minutes, then removed and cooled in air, the change in its elastic modulus can be measured. For silicate-bonded silicon carbide products, the elastic modulus displays a relatively gradual decline with increasing numbers of thermal–cold shock cycles. In contrast, nitride‑bonded silicon carbide products behave differently: prior to the 30th thermal cycling test, their elastic modulus changes only slightly with the number of thermal shock cycles, remaining fairly constant. However, after the 31st thermal shock cycle, the sample’s elastic modulus drops sharply, leading to sudden failure. Silicon oxynitride‑bonded silicon carbide products, similar to silicate‑bonded ones, do not exhibit abrupt failure; instead, their elastic modulus decreases gradually as the number of thermal shock cycles increases. In practical applications, because silicate‑bonded silicon carbide products show noticeable swelling, cracking, and deformation before failure under thermal shock, their service life can be readily predicted.

4. High thermal conductivity

Due to the excellent thermal conductivity of silicon carbide itself, refractory materials with a high SiC content generally exhibit high thermal conductivities, most exceeding 14.4 W/(m·K). During service, the thermal conductivity at the particle surfaces of silicon carbide products tends to decrease gradually. The nature of the binder also exerts a significant influence on the thermal conductivity of silicon carbide products: silicon nitride–bonded and silicon nitride‑bonded SiC materials display relatively high thermal conductivities, whereas silicate‑bonded SiC shows lower thermal conductivity.

5. Antioxidant Activity

The oxidation resistance of silicon carbide refractory products also varies significantly depending on the type of bonding phase. Silicon nitride‑bonded silicon carbide exhibits relatively poor oxidation resistance, which can be attributed to its microstructural characteristics. In these materials, the bonding phase adopts an interwoven fibrous morphology, resulting in high porosity and limited protective coverage over the silicon carbide particles. By contrast, in silicate‑bonded and oxynitride‑bonded silicon carbide, the silicon carbide grains are enveloped by a continuous matrix, thereby conferring superior oxidation resistance. Although the oxidation resistance of silicate‑bonded and oxynitride‑bonded silicon carbide demonstrated similar behavior in the aforementioned tests, their differences become more pronounced during prolonged service.

6. Anti-slag adhesion property

Slag resistance refers to the ability of silicon carbide bricks to withstand the erosive and scouring effects of furnace slag at high temperatures. Here, “slag” is understood in a broad sense to encompass metallurgical slags, fuel ash, fly dust, various materials—including both solid and liquid substances such as sintered cement blocks, calcined lime, iron filings, molten metals, and glass melt—and gaseous species like coal gas, carbon monoxide, fluorine, sulfur, zinc, and alkali vapors that come into contact with silicon carbide bricks under high‑temperature conditions. The reason silicon carbide refractory castables are difficult to wet by slag lies in the intrinsic properties of silicon carbide itself: SiC exists in two crystalline forms, α‑SiC and β‑SiC, with β‑SiC exhibiting a hexagonal crystal structure. Among the α‑SiC polymorphs, approximately 120 variants are known, including 4H, 15R, and 6H; the 6H polymorph is the most widely used in industrial applications. In 6H‑SiC, silicon and carbon atoms are arranged in alternating layers, with interlayer distances of 2.5 Å between Si layers or C layers, and an Si–C bond length of about 1.9 Å. There is a certain thermal stability relationship among the various SiC polymorphs, and the α‑ and β‑forms can interconvert. Below 1600 °C, SiC predominantly exists in the β‑form; when the temperature exceeds 1600 °C, β‑SiC gradually transforms via recrystallization into several α‑SiC polymorphic variants (such as 4H, 15R, and 6H). The α‑to‑β transformation requires relatively high pressures, whereas the reverse β‑to‑α transformation can occur under lower pressures. Moreover, these phase transitions do not involve significant volume changes. Silicon carbide is a compound characterized by strong covalent bonding. Even at elevated temperatures, it maintains high bond strength, resulting in exceptional hardness, a high elastic modulus, and excellent wear resistance; it is also resistant to attack by most acidic and alkaline solutions. Furthermore, its slag penetration and the low‑melting‑point compounds formed upon reaction with slag confer markedly superior slag resistance compared to oxides and similar materials.

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