What are Silicon Nitride Properties?

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Silicon nitride can be considered an essential engineering clay. High temperatures give silicon nitride excellent mechanical properties. These include low density and high bending strength. They also have high fracture toughness. The material has excellent thermal characteristics, can withstand rapid, significant temperature changes and minimizes expansion and contraction. The chemical properties of silicon nitride are excellent, with good stability to most acids, bases, corrosive gases and liquid metals.
The results of rolling contact fatigue (RCF), tests on several ceramic-based materials that were subjected to high performance bearing loads have shown that only fully dense silicon nitride is capable of outperforming bearing steel. RCF has a ten-fold longer service life than high-performance steel bearing steel. This is evident with the compact Si3N4 bearing material. A high-speed rotating body may cause significant centrifugal stresses. Because it is a low-density metal, silicon nitride can be as light as aluminium. This material has an additional benefit. The low density Si3N4 helps to reduce the centrifugal stresses on the outer rings of the high speed rotating body. The high tensile strength and flexibility of silicon-nitride ceramics allows for resistance to elongation as well as the ability to withstand lateral stress. The full density Si3N4 is also extremely resistant to fracture toughness and modulus. This material can withstand severe operating conditions that could cause other ceramic materials such as cracking, deform and collapse.

It is capable of displaying superior mechanical properties and thermal properties. This makes silicon nitride suitable for demanding industrial applications. Thermal conductivity refers to the material’s ability to conduct or transfer heat. The heat transfer coefficient plays a critical role in determining the suitability for industrial applications. Silicon nitride, due to its unique chemical structure and microstructure, has the same low thermal conductivity of metals.

These properties allow silicon-nitride greatly reduces thermal conductivity in extreme temperatures applications. The thermal expansion problem occurs when materials heat up and their volume and size change in small increments. The temperature at which the material is heated affects how much expansion occurs. The ratio of thermal expansion coefficients is a measure of the material’s expansion per 1degC temperature increase. Because of the strong atomic bonds of Si3N4, this material has a low coefficient thermal expansion. It also experiences very little deformation when heated.

The superior thermal properties of silicon nitride make it less sensitive to high-speed applications. Silicon nitride, which has a moderate dielectric constant, is the best material for RF applications. This refers to its ability to store electric energy in an electrical field. It also has low RF losses.

This unique combination of properties has led to further research on silicon nitride’s use in structural ceramics for biomedical applications. In vitro and in vivo studies, as well as later studies involving the injection of silicon dioxide into animals, have established the biocompatibility. An in vitro study from 1999 further confirmed the biocompatibility claim of Si3N4 for functional human bone cell proliferation. These findings support silicon nitride being a promising biomedical material. Additionally to its biocompatibility silicon nitride has surface chemical characteristics that encourage bone formation (osteogenesis), as well as increased bone contact with implants.

Silicon nitride exhibits excellent stability because of its strong Atomic Bonds. This material is highly resistant to corrosion in acidic and alkaline environments at room temperatures. This is important when considering long-term implantation of silicon nitride in a salty and watery environment. This is due to the formation on the material’s surface of an oxide layer. When silicon nitride was subjected to hot gases, molten metals, or other chemicals, the same resistance was observed. The corrosion resistance of materials is affected by the formation of the oxide layer.

Its unique microstructure that self-reinforces, its high strength, toughness and other excellent properties make silicon nitride a desirable structural component for many applications across a range of industries, including biomedical.

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