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Sintered Silicon Carbide ( SiC ) Properties and Applications

Background

Sintered alpha silicon carbide (SiC) is produced by initially mixing fine (sub-micron) and pure silicon carbide powder with non-oxide sintering aids. The powdered material is formed or compacted by using most of the conventional ceramic forming processes such as die pressing, isostatic pressing and injection moulding. Following the forming stage the material is sintered in an inert atmosphere at temperatures above 2000°C. The sintered silicon carbide can then be machined to precise tolerances using a range of precision diamond grinding or lapping techniques. As with most advanced ceramics the cost of the component is reduced if the amount of diamond grinding is reduced i.e. either the material manufacturer can achieve the required tolerances “as sintered” or the designer removes unnecessary tolerances.

Key Properties

  • High hardness (second only to diamond)

  • Low density 40% the density of steel – approximately the same as aluminium

  • Low porosity

  • Good wear resistance in sliding and abrasive environments

  • Excellent corrosion resistance in most chemical environments

  • Low thermal expansion and high thermal conductivity leading to excellent thermal shock resistance.

Applications

Automotive Components and Seal Faces

Due to their greater resistance to both wear and thermal shock, sintered silicon carbide seal faces for automotive water pumps are replacing seal faces made of materials such as aluminium oxide. In many cases the material has proven more suitable in meeting the performance demands of U.S. and European vehicles – i.e. lasting the lifetime of the vehicle without leaking. These components are manufactured by conventional high volume pressing and injection moulding methods to meet the economic constraints of the application.

Armor

Sintered Silicon Carbide has demonstrated an excellent performance record as ceramic material in composite armor protection systems. The properties of sintered silicon carbide, such as its high hardness, compressive strength and elastic modulus, provide superior ballistic capability when confronted with high-velocity projectiles. The low specific density of the material makes it suitable in applications where weight requirements are critical.

Heat Exchanger Tubes

Sintered Silicon Carbide tubes are used in shell and tube heat exchangers in the chemical process industry. The tubes used in these applications are often over 4 m in length.

Mechanical Seals

Pumps must operate in an infinite variety of demanding environments. Sintered Silicon Carbide offers a high performance seal face material that has proven successful in such diverse pumping applications as chemical processing, refining, mining and pulp and paper processing. The material provides superior corrosion and abrasion resistance; shock resistance; and low sliding friction against a wide range of mating materials.

Bearings

For state-of-the-art magnetically driven pumps, sintered silicon carbide is particularly suited for thrust and journal bearing components. Excellent corrosion resistance provides optimum performance in many chemical environments. High thermal conductivity minimizes the likelihood of failure due to thermal shock, and its specific strength makes it safe to use at high rotational speeds. Bearing components are usually produced as tight tolerance precision ground parts.

Blast and Atomization Nozzles

Sintered Silicon Carbide is probably the most popular ceramic alternative to tungsten carbide for blast nozzle applications. Typically providing long life (50% over WC) due to excellent wear and corrosion resistance. The low wear rate maintains the internal nozzle geometry and provides maximum blasting effectiveness, minimum compressor requirements and reduced downtime due to replacement. Sintered silicon carbide is also about one fifth the weight of Tungsten Carbide, so the blasting operation is also easier for the operator. Nozzles are often produced as semi finished (non-ground) components thereby reducing costs.

Process Industry Valve Applications

The outstanding corrosion resistance of sintered silicon carbide, particularly in acids, makes it an ideal candidate for valve and valve trim applications. Typical demanding applications such as slurry flashing, HF acid handling and rare earth processing use sintered silicon carbide valve components.

Paper Industry Applications

The excellent corrosion and wear resistance of sintered silicon carbide provides hard surfaces that can be machined to smooth, highly polished finishes. These finishes offer low coefficients of friction and compatibility with forming fabrics. Tiles, inserts and palm guides are available in finished and semi-finished forms.

Centrifuge Tiles and Wear Parts

Often used in applications where tungsten carbide and alumina fail to provide optimum lifetime performance.

Semiconductor Production

The benefit of using silicon carbide for semiconductor components includes; the thermal expansion match to silicon, the resistance to wear and chemical corrosion which leads to reduced maintenance and component recycling. The material is well suited as a structural material for low mass silicon wafer handling components and rigid, dimensionally stable platforms due to its lightness in weight and high elastic modulus. Typical applications include vacuum chucks, chemical mechanical polishing blocks, wafer carriers, and thermocouple protection tubes.

Comments

  1. RAVALIYA KANU RAVALIYA KANU India says:

    What is the basic differnece between Self Sintered SiC and reaction Bonded SiC used in mechanical seal?
    Give some examples.
    Please reply ASAP

    • Gary Thomas Gary Thomas United Kingdom says:

      Hi Ravaliya,

      Thanks for the questions. The following information may be of use to you:

      Reaction bonded silicon carbide is produced by adding molten silicon to a mixture of silicon carbide and carbon. A reaction between the silicon and carbon bonds the structure while the excess silicon metal fills the majority of the pits left in the resultant material. There is almost no shrinkage during the process.

      Reaction bonded silicon carbide has proven to be more chip resistant than the sintered version.

      Self sintered silicon carbide begins as a mixture of silicon carbide grains and a sintering aid which is pressed and subsequently sintered as its name implies. Unlike Reaction bonded SiC, there is no free silicon present. These direct sintered materials have no metal phase and are therefore more resistant to chemical attack.

      Self sintered silicon carbide carries a slight price premium compared to the reaction bonded version and although the preferred seal face material, it is sometimes too brittle for some designs.

      Source: http://www.mcnallyinstitute.com/05-html/5-2.html

  2. John Stephen John Stephen Trinidad and Tobago says:

    Besides Carbon and Silicon, what is the material of composition of silicon carbide? In particular, what % of Aluminium is used when making this product(for a mechanical seal face)?

  3. Jeff Peters Jeff Peters United States says:

    Is this product considered brittle, ie, sensitive to chips and cracks when shipped?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

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