Characteristics and Optimization Points of Silicon Carbide Wear-Resistant Refractory Castables

Silicon carbide wear-resistant castables possess the dual advantages of wear resistance and corrosion resistance. The most prominent property of silicon carbide castables is wear resistance, followed by corrosion resistance. The manufacturing process still uses traditional refractory castables as the framework, introducing a certain proportion of silicon carbide particles to form a composite structure of "refractory aggregate + silicon carbide".

Rongsheng Silicon Carbide Wear-Resistant Castables

Silicon carbide itself has high hardness and high grain boundary strength, allowing it to preferentially bear stress under erosion and friction conditions, thus slowing down matrix wear. Therefore, the overall wear resistance coefficient decreases, and the service life can typically be extended by one to two times. At the same time, silicon carbide has a large wetting angle with molten metal and slag, making it difficult to be wetted. Acidic and alkaline media also have difficulty corroding its surface, allowing the furnace lining to remain intact in multiphase corrosive environments involving solid, liquid, and gaseous states.

Mechanism of Improved Thermal Shock Resistance

Silicon carbide has high thermal conductivity and low thermal expansion. Its addition reduces the internal temperature gradient of the castable, buffering thermal stress caused by rapid heating and cooling. When silicon carbide is combined with silicon nitride, an interwoven fibrous silicon nitride network forms in the matrix, further absorbing thermal shock energy and improving thermal shock resistance by approximately two times.

Furthermore, its high thermal conductivity rapidly homogenizes the furnace lining surface temperature, reducing localized hot spots. This inhibits slag crusting or nodulation on the surface, maintaining furnace internal stability and reducing cleaning intensity.

Oxidation Challenges Arising from High Silicon Carbide Content

As the proportion of silicon carbide increases, the thermal conductivity of the castable also increases. While this is beneficial for heat dissipation, it is accompanied by a significant tendency to oxidize. When the temperature exceeds 1000 degrees Celsius, the silicon carbide surface easily reacts with oxygen to form silicon dioxide. This, along with volume changes, leads to microcracks, thus weakening the strength.

To suppress oxidation, manufacturers commonly introduce metallic silicon powder. At high temperatures, metallic silicon preferentially combines with oxygen to form a dense glassy phase that covers the surface of silicon carbide particles, blocking oxygen diffusion channels and thus slowing down the oxidation rate.

The Influence of Different Bound Phases on Oxidation Resistance

The microstructure of the bound phase determines the difference in oxidation resistance. In silicon nitride-bonded silicon carbide castables, the matrix is interwoven with fibers, resulting in high permeability. Oxygen can still diffuse along the micropores, offering limited protection to the silicon carbide particles. In contrast, in silicate-bonded or oxynitride-bonded products, the silicon carbide particles are encapsulated by a continuous matrix, leading to a tortuous oxygen diffusion path and slow oxide layer thickening, thus exhibiting superior oxidation resistance.

When designing formulations, a balance between thermal shock resistance and oxidation resistance is often achieved by adjusting the type and proportion of the bound phase.

High-Temperature Strength and Chemical Stability

Silicon carbide maintains high hardness and high flexural strength at high temperatures, without significant softening due to temperature increases. Its chemical stability is outstanding; it is inert to most acid and alkali solutions, except for strong alkalis. In non-ferrous and ferrous metal smelting environments, it exhibits good resistance to corrosion from molten iron, steel, copper, and high-calcium and high-iron slags.

Thanks to the synergistic effect of low expansion and high thermal conductivity, the furnace lining can maintain its structural integrity during long-term operation with frequent start-ups and shutdowns and rapid temperature changes, reducing maintenance frequency and improving operational efficiency.

Application Selection and Construction Tips

In actual selection, a comprehensive consideration should be given to the furnace type, operating temperature, corrosiveness of the medium, and thermal shock frequency. High-silicon carbide wear-resistant grades should be prioritized in heavily eroded areas. In areas with strong oxidizing atmospheres, metallurgical silicon micropowder modification or silicon oxynitride bonding systems are recommended. For areas with extremely high thermal shock requirements but low oxidation, the silicon nitride bonding ratio can be appropriately increased. During construction, the amount of water added and the vibration time must be strictly controlled to ensure uniform dispersion of silicon carbide particles and avoid local enrichment or sedimentation, so as to fully utilize its combined advantages of wear resistance (https://rongshengrefractory.com/wear-resistant-refractory-castable/), corrosion resistance, and thermal shock stability.