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The Influence of Carbon Black Content on the Microstructure and Properties of Reaction-Sintered Silicon Carbide
Release time:
2022-01-06
In mechanical seals, Reaction-sintered silicon carbide Sealing rings are widely used and are primarily manufactured using the SiC+C+Si process. I have been working in this field—engaged in both technical and production roles—for many years, and I often discuss issues with my colleagues and exchange ideas with them. Since, in the course of our work, the contact surfaces of mechanical sealing rings operate under semi-dry friction conditions, the friction surfaces of the sealing rings must possess excellent self-lubricating properties—a feature that the SiC+C+Si process does not inherently provide.
The effect of carbon black content on... Reaction-sintered silicon carbide The influence of slurry process parameters on the sintering mechanical properties was investigated. The causes of high carbon content in the green body, as well as explosions and internal “sandwich” structures during the sintering process, were analyzed. The microstructures and phase compositions of sintered samples with different carbon contents were also examined.
Reaction-sintered silicon carbide ceramics retain the excellent mechanical properties of silicon carbide ceramics, such as high strength, high hardness, and wear resistance. At the same time, they exhibit remarkable thermal properties, including thermal shock resistance, high thermal conductivity, and a low coefficient of thermal expansion, as well as chemical properties like oxidation resistance and resistance to acid and alkali corrosion. This material is an almost fully dense engineering ceramic. The underlying principle is as follows: liquid silicon, which exhibits high-temperature reactivity, penetrates into a carbon-containing green body under the action of capillary forces and reacts with the carbon to form silicon carbide. The newly formed silicon carbide particles bond in situ with the pre-existing silicon carbide particles already dispersed within the green body, further penetrate into the silicon, and fill the remaining pores in the green body, thereby completing the densification process.
Reaction-sintered silicon carbide boasts advantages such as short sintering time, high production efficiency, low sintering temperature, large workpiece dimensions, and complex shapes, and has become the primary method for industrial-scale production of silicon carbide products worldwide.
Beams, nozzles, radiation tubes, seals, and ball mill liners made from reaction-sintered silicon carbide are widely used in high-temperature kilns, machinery, chemical processing, metallurgy, environmental protection, and military applications. However, the presence of free silicon in reaction-sintered silicon carbide limits its application to temperatures below 1350℃. Once the operating temperature approaches or exceeds silicon’s melting point of 1410℃, the free silicon begins to soften or melt, significantly reducing the material’s fracture strength. Therefore, lowering the content of free silicon in reaction-sintered silicon carbide can further enhance its mechanical properties and operating temperature, thereby expanding its range of applications.
This study aims to increase the amount of carbon black in the original formulation to examine its impact on the microstructure and properties of reaction-sintered silicon carbide ceramics.
Analysis of the Causes of “Inclusion” in High-Carbon Sintered Bodies:
When the carbon black content is too high, the excess carbon becomes difficult to disperse uniformly during mixing, resulting in a region within the green body where carbon is excessively concentrated. The expansion effect generated by the silicon-carbon reaction partially blocks the silicon infiltration channels around this carbon-rich area, slowing down the upward movement of liquid silicon and thereby decelerating the silicon-carbon reaction. Consequently, a “sandwich-like” zone forms within the sintered body. Reaction-sintered silicon carbide The flexural strength is reduced.
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