Silicon Infiltrated Silicon Carbide

Silicon carbide (SiC) is one of the hardest and lightest ceramic materials. Used primarily as an electrical insulator, SiC can also be doped with nitrogen, phosphorus or boron to create conductors of various kinds.

SEM cross-section images of porous carbon preforms manufactured using various mass fractions and particle sizes of TIMREX KS 25 graphite powder infiltrated with near eutectic Si-Zr alloy at 1500 degC are displayed here. Banding of Zr-rich phase observed within these preforms confirms with analytical predictions.

High Specific Rigidity

Silicon infiltrated silicon carbide (SiSiC) is an industrial ceramic material, distinguished by high specific rigidity, low coefficient of thermal expansion and exceptional chemical, oxidation and heat shock resistance. Furthermore, this material boasts excellent tribological properties. SiSiC is produced by infiltrating porous carbon preforms with molten silicon in order to initiate exothermic reaction between carbon molecules and silicon molecules forming dense composite.

Below are various micrographs of fully infiltrated preforms at different magnifications, using polished optical microscopy. In the case of SiCp/C, unreacted carbon can be seen along with reaction-formed Si, as well as unreacted carbon that has yet to react, while most of the preform remains covered by an uninterrupted layer of Si.

Cf/C preforms differ significantly by having almost all amorphous carbon replaced with an even layer of Si, leaving only small amounts of carbon fibers remaining; this fact is evidenced by slower infiltration kinetics and enhanced pore diameter reduction capabilities.

Low Electrical Resistance

Silicon carbide (SiC) is widely utilized in semiconductor electronics due to its high melting point, low sintering temperature and high conductivity properties. Furthermore, it offers stability at high temperatures without experiencing oxidation. Silicon infiltrated silicon carbide (SiSIC), an alternative material with similar physical properties yet lower sintering temperatures that produces fewer pores enables production of larger and more complex-shaped parts and is also more cost-effective than traditional powder sintering technology.

At 1500 degC and 1700 degC, porous carbonaceous preforms with various graphite powder mass fractions and particle sizes were infiltrated with near eutectic Si-Zr alloy to produce dense Si-Zr-SiC structures. HR-SEM cross sections showed that infiltration depth depended not only on capillary forces pulling infiltrating melt into preform pores but also upon chemical reaction between silicon molten at 1500degC and graphite powder that reduced network permeability reducing infiltration depth for given porosities. Therefore as graphite mass fraction increased so should infiltration length increase accordingly for given porosities.

Izturība pret augstām temperatūrām

Silicon carbide excels at resisting corrosion, abrasion and erosion – making it the ideal material choice for high temperature applications. Furthermore, its low thermal expansion rate and hardness properties make it suitable for large components like thermocouple sensors.

Infiltrated RCs have proven highly successful in several scientific experiments. Notable examples include Herschel Space Telescope’s use of SiC mirror disks; due to their high resistance properties they are suitable for temperatures reaching 1,400 degC.

At 1500-1700 degC, porous carbonaceous preforms containing various amounts of graphite powder were infiltrated with liquid silicon at 1500-1750 degC for infiltration. SEM cross sections showed that pore blocking occurred primarily by precipitating solid zirconium silicides at the infiltration front; when increasing graphite mass fraction and/or decreasing infiltration temperature both improved the infiltration significantly, while still leaving some central areas with large quantities of uninfiltrated porosity that couldn’t be filled by liquid silicon alone.

Augsta izturība

Silicon carbide (SiC) is an inorganic hard chemical compound with wide band gap semiconductor properties, commonly found naturally as the gem moissanite; however, mass-produced powder and crystal forms for use as an abrasive are widely produced commercially as an abrasive. SiC boasts superior mechanical strength and fracture toughness as well as good tribological properties at higher temperatures; additionally it offers good chemical and oxidation resistance resistance properties that make it suitable for high temperature usage.

Liquid silicon infiltration of porous SiC-C preforms is an innovative technique used to produce dense ceramics with higher compressive and flexural strengths than can be achieved through traditional reaction bonded SiC (RBSC). To accomplish this feat, various parameters must be modified, such as porosity distribution, pore structure and carbon source usage. Engineering multimodal particle gradation and using nanocarbon black additives are used to achieve this result (Fig.). SEM cross-section images of infiltrated samples show their efficiency (Fig.). At 5-30% graphite mass fraction, samples with uniform distribution of Zr-rich phase and minimal residual porosity could be achieved. Samples with graphite mass fraction of 30 have core areas that remain infiltrated with near eutectic Si-Zr alloy alloy.