Reaction Bonded Silicon Carbide

Reaction bonded silicon carbide (RBSC) is an exceptionally hard and strong ceramic material with superior mechanical strength, impact resistance, chemical stability and formability, making it suitable for various applications.

RB-SiC offers lower hardness compared to sintered silicon carbide but is easier and less costly to manufacture, while boasting excellent thermal shock resistance properties.

Physical Properties

RMI process utilizes a-SiC particles incorporated in a porous carbon preform (G0), before infiltrating with liquid silicon to achieve reaction-bonded silicon carbide. Unfortunately, however, liquid silicon may cause the pores to clog due to infiltration process and therefore in this study multiphase carbon was used as an antidote against this problem and to enhance mechanical properties of RB-SiC.

Multiphase carbon was composed of fine amorphous carbon black and coarse micro-spherical carbon. When infiltrated with liquid silicon, micro-spherical carbon is consumed while the amorphous carbon can escape pores to prevent pore-filling reactions clogging them up – thus, when observed on specimens P10F90, P20F80, and P30F70 the characteristic peak was not present, suggesting the multiphase carbon helped avoid this problem and improve bending strength as infiltration temperature and soak time increased.

Mechanical Properties

RB silicon carbide is produced by infiltrating molten silicon into a porous carbon or graphite preform, where it reacts with carbon to form SiC and creates an outstanding wear, impact and chemical resistant ceramic material that comes in various shapes and sizes ranging from simple cone and sleeve shapes to larger engineered parts for mining or processing industries.

The composition of a composite precursor, especially its ratio of PF to FA, influences the reaction rate between carbon and liquid silicon during high-temperature pyrolysis. Multiphase carbon enhances liquid silicon penetration through pores in porous preforms; graded carbon sources help control both content of b-SiC and free Si.

Flexural strength and elastic modulus of RB silicon carbide can be substantially increased through careful grading of its carbon source, due to eliminating smooth black and white block grain surfaces which cause intergranular fracture during bending.

Thermal Properties

Thermal properties of reaction bonded silicon carbide ceramics depend on their type and proportion of bonding. Reaction-bonded silicon carbide (RBSC), infiltrated with metallic silicon particles, infiltrated into carbon or graphite preforms that do not shrink during this process; parts with very precise dimensions can thus be created.

After being infiltrated with RBSC, it is then subjected to high temperature nitriding at high temperatures. This transforms metallic silicon into SiC nitride and fills any remaining pore spaces with silicon carbide network material. XRD shows that this form contains diamond, a-SiC, b-SiC, Si and SiO2, while SEM shows graphite layers as well as amorphous carbon.

Due to the graphite layer present, RBSC exhibits lower k values than sintered SiC, yet outshone those of NSIC. Furthermore, it significantly outperformed SiO2-based ceramics in terms of corrosion resistance, high temperatures resistance, thermal shock resistance, and thermal shock absorption capacity.

Electrical Properties

Reaction bonded silicon carbide offers great electrical properties, such as low specific resistance and high thermal conductivity. These attributes make it an excellent material choice for electrical heating elements. In addition, its chemical inertness and resistance to oxidation make it suitable for furnace thermocouples, burner tips, checker bricks and muffles in furnaces; its superior thermal shock resistance also make it suitable as furniture in kilns.

Reaction Bonded SiC can be created through the process of mixing finely divided intimate mixtures of sic and carbon with plasticizer, then shaping and burning off the plasticizer before infiltrating it with liquid or gaseous silicon. This reaction allows silicon to bond with carbon to produce more silicon carbide which then reacts with original silicon carbide to form composite consisting of a-SiC, b-SiC and residual Si.

At infiltration time, it is claimed that a-SiC granules and b-SiC formed during reaction are evenly dispersed throughout the porous preform without lumping, likely attributed to capillary channels not being blocked by newly formed b-SiC particles.