Sintered Silicon Carbide As a High Performance Material
Silicon Carbide is an extremely hard material with exceptional resistance to corrosion, oxidation and thermal shock. Additionally, this self-lubricating material features low coefficient of friction.
Machineable in the green or biscuit state, ceramic can be difficult to machine when fully densified due to shrinkage in sintering processes causing around 20% shrinkage of its ceramic body. Reaction sintering offers an effective solution.
Resistance to Corrosion
Corrosion resistance is an essential characteristic for any material intended for use in an acidic environment. Sintered silicon carbide stands out among available materials as being particularly reliable in this regard.
Pressureless sintered (HPSIC) and hot isostatic pressed (HIPSIC) SiC products are virtually por-free, making them even more resistant to corrosion.
Reaction bonded silicon infiltrated SiC (RBSiC) is produced by injecting liquid silicon into a porous carbon or graphite preform. RBSiC typically features coarser grain structure than HPSIC or HIPSIC but offers lower production costs and good corrosion resistance.
Corrosion behavior of ceramics is affected by several factors, including impurities, sintering aids, the type and crystallinity of oxide layer structures and historical reactions. When dealing with SiC materials that exhibit aggressive corrosion rates, short-term corrosion experiments may provide valuable insight into possible changes in mechanisms and corrosion rates.
High-Temperature Stability
Sintered silicon carbide’s exceptional temperature stability enables it to be used in various extreme environments, from oxidation and thermal shock resistance, through strength, hardness and wear resistance to being an excellent combination.
Hot pressing and reaction sintering are two effective sintering processes used to produce dense SiC products, and two of the more popular techniques for doing this are hot pressing and reaction sintering. Hot pressing involves mixing fine SiC powder with oxide-free sintering aids to form a paste before compacting it through forming.
Reaction sintering involves infiltrating molten silicon into a porous carbon or graphite preform, where it then bonds the existing a-SiC to form b-SiC before being sintered to form an accurate product with maximum hardness and strength.
Thermal Shock Resistance
Silicon carbide is one of the strongest ceramic materials ever discovered, boasting five times harder surface area than tungsten and offering great wear resistance, corrosion protection, thermal shock resilience up to 1600degC temperatures while still remaining strong and wear-resistant.
Plywood is an extremely versatile material, capable of being machined in its green or biscuit state into highly complex geometries. When sintered fully, however, its dimensions shrink by 20% during sintering and require the use of precision diamond tools in order to meet tight tolerances.
There are two forms of fully dense sintered SiC, reaction bonded (Refel) and direct sintered (SSiC). Reaction bonded SiC is made by infiltrating compacts with mixtures of SiC grains and liquid silicon before it is sintered using conventional ceramic forming processes at 2000degC.
High Strength
Sintered silicon carbide offers one of the highest strengths among ceramic materials, retaining its hardness and strength at elevated temperatures while boasting excellent wear resistance. Furthermore, its strength can be maintained without suffering the degradation typical of conventional metals.
Production can occur either through reaction sintering or pressureless sintering. Reaction sintering involves processing fine particles of a-SiC with additives into granulation powder and pressing blanks before placing it into a vacuum sintering furnace where its crystals grow. Pressureless sintering involves simply filling an oven without creating pressure, while reaction sintering requires creating heat by melting its material within it, which creates the material.
Ceramic is denser and harder than stainless steel while remaining lighter, offering unique combinations of hardness, thermal conductivity, resistance to corrosion and temperature excursions, thermal conductivity measurements, as well as dimensions accuracy testing for use across a range of applications. Caldera engineers select materials based on site process conditions to ensure equipment longevity while quality control includes scanning electron microscopy testing of strength/hardness/thermal conductivity/dimensional accuracy verification procedures.
Wear Resistance
Sintered silicon carbide boasts superior wear resistance compared to other ceramic materials, making it the go-to material for mechanical seals and process equipment applications. Morgan’s CORESIC SP silicon carbide can also be found in aircraft components due to its chemical and heat resistance as well as thermal conductivity features.
Both pressureless sintered silicon carbide and reaction bonded silicon carbide provide excellent corrosion and oxidation resistance; however, the former is preferred due to its higher strength/hardness/thermal stability characteristics.
Production of silicon carbide ceramics involves mixing powder with binder, shape forming using extrusion (tubes) or cold isostatic pressing (plates and blocks), sintering at high temperature and grinding; pressureless sintering offers superior product density and fracture toughness compared to reaction sintering methods.