Editorial Feature
Properties This article has property data, click to view

Nitride Bonded Silicon Carbide (NBSC)

Silicon carbide based materials are used for their good thermomechanical and wear resistance properties. Although heating at high temperature and pressure can densify pure silicon carbide, the process is not a viable commercial process.  High density silicon carbide materials are produced by introducing a sintering aid that produces a second bonding phase.  The thermomechanical properties are then often limited by the bond phase.  For example, the maximum operating temperature of reaction bonded silicon carbide is 1375°C, close to the melting point of silicon.

Production

The nitrogen bonded silicon carbide is made by firing mixtures of high purity silicon carbide and silicon or a mineral additive in a nitrogen atmosphere at high temperature (typically 1350ºC to 1450ºC).  The silicon carbide is bonded by the silicon nitride phase (Si3N4) developed during nitriding.  The maximum operating temperature of the resulting material is around 1750ºC.

Key Properties

The properties of nitrogen bonded silicon carbide suit many severe service conditions:

        Good wear resistance in abrasive environments

        High mechanical strength that is maintained up to 1650°C, beyond the service temperature of common refractories and metals.  NBSC is particularly strong under compressive loading.

        Thermal shock resistance due to high temperature strength, low thermal expansion coefficient and high thermal conductivity.  As a result NBSC can be cycled through large temperature differences without losing strength or developing cracks.

        Good chemical resistance particularly to most acids, molten salts and halogens.  NBSC may be attacked by oxidising agents and strong bases such as iron oxide and sodium hydroxide.

        NBSC resists wetting by non-ferrous metals.

        At high temperature, NBSC is a semiconductor.

Specific values of properties depend on the composition and processing conditions of the material.  A typical composition will contain between 70 and 80% silicon carbide and 20 and 30% silicon nitride. Table 1 provides mechanical properties for such a material.

Table 1. Typical mechanical and thermal properties for silicon nitride (20-30%) bonded silicon carbide (70-80%).

Property

Density (g.m-3)

2.69

Apparent Porosity (%)

14

Young’s Modulus (GPa)

80

Bend Strength (MPa)

38

Thermal Expansion Coefficient (x 10-6/ºC)

2.7

Thermal Conductivity (W/mK)

32

Maximum Operating Temperature (ºC)

1580

Note: Properties can vary widely for nitride bonded silicon carbide materials depending on factors such as composition, porosity, grain size etc. It is strongly recommended that users seek additional information from suppliers/manufacturers.

Applications

Silicon Nitride Bonded Silicon Carbide Bricks

Exploiting the material's excellent stability and mechanical strength, nitrogen bonded silicon carbide bricks are used in a range of process furnaces and kilns such as the side walls of aluminium melting pots, the lower stack of blast furnaces, and as kiln furniture.

Cast Refractories

Nitrogen bonded silicon carbide is commonly found as a cast refractory for use under severe service conditions in place of alloys or other refractory materials.  Near net shapes can be designed to reproduce the metal parts. The high hardness and abrasion resistance of the material means that components should be designed to avoid grinding or other finishing operations.

Applications of cast refractories exploit the physical and chemical properties of the material and the ability to form the material into complex shapes.  Uses include:

        Cyclone liners used in processing minerals and coal and in the chemical and paper industries.

        Slurry pump parts for mineral processing and speciality chemical industries.  Component lives are increased by between two and twenty times compared with metal and elastomeric materials. 

        Coal burner, exhaust and pulveriser parts for use in the power generation industry.  Component life is reported to be increased by between two and eight times compared with other materials.

        Corrosion resistant components for chemical plant.

        Pump components, piping liners, valve liners, spigots and nozzles.

        Non-ferrous metals processing equipment, copper, zinc and aluminium are routinely handled with cast components.

        Kiln furniture with increased life and stability.

Source: Ceram Research

For more information on this source please visit Ceram Research Ltd.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit