Chemical Vapor Deposition, Reaction Sintering and Sintering of Sintered Silicon Carbide

Silicon carbide is an extremely hard and resilient ceramic material with excellent strength, high temperature toughness and oxidation resistance. It comes in both sintered and reaction bonded forms for production.

Sintered silicon carbide (SSiC) is produced by pressing and sintering silica powder. SSiC boasts low sintering temperatures, easy forming capabilities and exceptional mechanical properties that give it distinct advantages over competing materials.

Chemical Vapor Deposition

Chemical Vapor Deposition (CVD) employs flowing gases to form thin films of high quality that can be used for creating solid materials and coatings, etching and microelectronic device formation.

CVD refers to a family of processes, which includes rapid thermal CVD, plasma-enhanced chemical vapor deposition and laser-induced chemical vapor deposition. Each uses precursor gas to deposit solids onto substrate surfaces while differing processes utilize various methods to initiate reactions and initiate solidification reactions.

Rapid thermal CVD utilizes heating lamps to preheat precursor gas before it reaches the wafer surface, helping reduce unwanted gas-phase reactions and gaseous reactions.

Another method of producing CVD-b-SiC involves inserting a graphite baffle 102 before the mandrel box. This technique preheats reagents, increasing their sweep speed on mandrel walls, and producing dense, good quality b-SiC deposits that are shown in FIGS. 3a and 3b. Other baffles may also be placed before and after the mandrel box to maximize deposition results and provide more uniform and conformal coating of b-SiC on irregular-shaped substrates. This material is highly conductive, chemically and oxidatively stable, hard, scratch-resistant and theoretically very dense – characteristics which make it suitable for many specialized material applications, including wafer boats and furniture for semi-conductor processing, optical telescope structures and end effectors used during wet bench cleanings.

Pressureless Sintering

Sintering is the process of joining together or rearrange particles of ceramic or metal powder into an integrated structure, usually by hot pressing, reaction sintering and pressureless sintering. For centuries this technique has been employed to manufacture nearly all forms of ceramic and metal objects including structural steel parts, porous metal filters for filtering applications, tungsten wiring for self-lubricating bearings and electrical materials among many others. Manufacturing processes usually include hot pressing, reaction sintering or pressureless sintering.

Sintered silicon carbide can benefit greatly from pressureless sintering as an effective way of improving its mechanical properties, particularly its temperature resistance and flexural strength. Grain growth reduction during sintering contributes to this result while increasing tensile strength leads to greater durability and lifespan of material.

Pressureless sintering offers several distinct advantages over other processes, including its ability to create complex shapes with precise dimensions. This makes the pressureless sintering process ideal for manufacturing unique products that would be difficult or impossible to create using other means, making it particularly suitable for high-performance applications like hard-faced seal components and high-temperature work.

Hot Pressing

Hot pressing is an efficient and cost-effective method of producing silicon carbide components with large sizes and complex shapes, such as seals for pumps with demanding applications, quickly. Pressure and high temperature (up to 2000 degC) are applied simultaneously during this process, making for fast production times with cost efficiency.

Sintering processes that produce dense SiC and b-SiC composite ceramics for dry gas seals have proven particularly successful. One such effective sintering method entails mixing a-SiC powder with graphite in certain proportions and heating; during sintering, a-SiC powder penetrates porous steel billets through the use of vapor phase Si to form dense bodies with no size reduction and high density.

Due to its strong covalent bond of Si-C, silicon carbide exhibits low self diffusion rates during sintering processes. As such, its driving force for producing high density silicon carbide is considerably lower than that of other ceramic materials and research into suitable sintering methods and additives has become a primary focus in this field.

Characterizing the microstructure of sintered samples involves employing XRD patterns and selected area electron diffraction (SAED) analysis to characterize their microstructure. We determined an 83:17 ratio in terms of sintered temperature.

Reaction Sintering

Reaction Sintering of Sintered Silicon Carbide (RSSiC) is a process in which liquid silicon is infiltrated into porous carbon or graphite preforms through infiltration of molten silicon, producing ceramic that boasts high strength, excellent wear resistance and thermal stability, along with superior resistance against oxidation, corrosion and etching as well as good electrical properties. Density for RSSC depends on its silicon/carbon ratio which ultimately determines hardness.

Sintering involves mass movements within a porous microstructure that reduce total porosity by repacking and transport along crystal boundaries to smooth pore walls, thus decreasing grain size and leading to dense fine-grained matrix structures with uniform structures.

Reaction sintering allows for the production of large and complex-shaped sintered silicon carbide parts with near net shapes and high precision, using lower temperatures and shorter times compared to traditional methods of sintering. However, it should not be used in environments with strong oxidizing or corrosive influences as this process may cause insufficient silicon penetration and abnormal grain growth, ultimately decreasing mechanical properties of sintered materials. Sintering processes depend heavily on the consistency of starting powders and must be managed carefully for consistent part shrinkage, reduced distortion and to produce components with stable quality. RVS-S vacuum sintering furnace can be used for reaction sintering of SiC products to guarantee quality products.