- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Density
- Solubility
- Chemical properties
- Other properties
- Obtaining
- Applications
- In the field of electronics
- In ceramic materials
- As a biomedical material
- How Silicon Nitride for Biomedicine is Made
- In various applications
- References
The silicon nitride is an inorganic compound consisting of nitrogen (N) and silicon (Si). Its chemical formula is Si 3 N 4. It is a bright gray or light gray material of exceptional hardness and resistance to high temperatures.
Due to its properties, silicon nitride is used in applications where high resistance to wear and high temperatures is required. For example, it is used to make cutting tools and ball bearings.
Silicon nitride sphere Si 3 N 4. Lucasbosch. Source: Wikimedia Commons.
It is used in pieces of machinery that must resist high mechanical forces, such as turbine blades, which are like large cylinders where the blades must rotate at high speeds with the passage of water or gases, producing energy.
Silicon nitride ceramics are used to make parts that must come into contact with molten metals. They can also be used as a replacement for human or animal bones.
Si 3 N 4 has electrical insulating properties, that is, it does not transmit electricity. Therefore it can be used in microelectronics applications or in very small electronic devices.
Structure
In silicon nitride each silicon atom (Si) is covalently bonded with the 4 nitrogen atoms (N). Vice versa, each nitrogen atom is attached to the 3 silicon atoms.
Therefore, the bonds are very strong and give the compound high stability.
Lewis structure of silicon nitride Si 3 N 4. Grasso Luigi. Source: Wikimedia Commons.
Three-dimensional structure of silicon nitride Si 3 N 4. Gray = silicon; blue = nitrogen. Grasso Luigi. Source: Wikimedia Commons.
Silicon nitride has three crystalline structures: alpha (α-Si 3 N 4), beta (β-Si 3 N 4) and gamma (γ-Si 3 N 4). Alpha and beta are the most common. Gamma is obtained at high pressures and temperatures and is the hardest.
Nomenclature
- Silicon nitride
- Trisilicon tetranitride
Properties
Physical state
Solid bright gray.
Molecular weight
140.28 g / mol
Melting point
1900 ºC
Density
3.44 g / cm 3
Solubility
Insoluble in water. Soluble in hydrofluoric acid HF.
Chemical properties
This is a very stable compound, due to the way the silicon and nitrogen atoms are bonded in Si 3 N 4.
Silicon nitride has excellent resistance to hydrochloric (HCl) and sulfuric (H 2 SO 4) acids. It is also very resistant to oxidation. It is resistant to cast aluminum and its alloys.
Other properties
It has good resistance to thermal shock, high retention of hardness at elevated temperatures, excellent resistance to erosion and wear, and excellent resistance to corrosion.
It has exceptional hardness that allows the application of thin thicknesses of material. It maintains its properties at high temperatures.
Silicon nitride films are excellent barriers to the diffusion of water, oxygen and metals, even at high temperatures. They are very hard and have a high dielectric constant, which means that they conduct electricity poorly, thus acting as an electrical insulator.
It is for all these reasons that it is a suitable material for high temperature and high mechanical stress applications.
Obtaining
It can be obtained starting from the reaction between ammonia (NH 3) and silicon chloride (SiCl 4), in which the silicon amide Si (NH 2) 4 is produced, which when heated forms an imide and then the silicon nitride Si 3 N 4.
The reaction can be summarized as follows:
Silicon chloride + Ammonia → Silicon nitride + Hydrochloric acid
3 SiCl 4 (gas) + 4 NH 3 (gas) → Si 3 N 4 (solid) + 12 HCl (gas)
It is also manufactured by treating compact powdered silicon (Si) with nitrogen gas (N 2) at temperatures of 1200-1400 ° C. However, this material has 20-30% microporosity that limits its mechanical strength.
3 Si (solid) + 2 N 2 (gas) → Si 3 N 4 (solid)
For this reason, the Si 3 N 4 powder is sintered to form denser ceramic, this means that the powder is subjected to high pressure and temperature.
Applications
In the field of electronics
Silicon nitride is often used as a passivation or protection layer in integrated circuits and micromechanical structures.
An integrated circuit is a structure that contains the electronic components necessary to perform some function. It is also called a chip or microchip.
Silicon nitride Si 3 N 4 is used in the manufacture of microchips. The original uploader was Zephyris at English Wikipedia.. Source: Wikimedia Commons.
Si 3 N 4 has excellent resistance to the diffusion of water, oxygen and metals such as sodium, which is why it serves as an insulating layer or barrier.
It is also used as a dielectric material, this means that it is a poor conductor of electricity, so it acts as an insulator for it.
This serves for microelectronic and photonic applications (generation and detection of light waves). It is used as a thin layer in optical coatings.
It is the most common dielectric material used in capacitors for dynamic random access memory or DRAM (Dynamic Random Access Memory), which are the ones used in computers.
DRAM memory used in computers or computers. May contain silicon nitride. Victorrocha. Source: Wikimedia Commons.
In ceramic materials
Silicon nitride ceramic has properties of high hardness and resistance to wear, which is why it is used in tribological engineering applications, that is, uses where a lot of friction and wear occurs.
Dense Si 3 N 4 exhibits high flexible strength, high resistance to fracture, good resistance to dragging or sliding, high hardness and excellent resistance to erosion.
Ball bearing spheres of various sizes made with silicon nitride. They are used to be used in machinery. Lucasbosch. Source: Wikimedia Commons.
This is obtained when silicon nitride is processed by sintering in liquid phase by adding aluminum oxide and yttrium oxide (Al 2 O 3 + Y 2 O 3) at temperatures of 1750-1900 ° C.
Sintering consists of subjecting a compound powder to high pressures and temperatures to obtain a denser and more compact material.
Silicon nitride ceramic can be used for example in aluminum smelting equipment, i.e. very hot places where molten aluminum is present.
Tube for sealing made of Si 3 N 4 ceramic and used in processes with cast aluminum. Hshkrc. Source: Wikimedia Commons.
The structure of silicon nitride ceramic provides a great opportunity to optimize properties for specific applications according to the demands of engineers. Even many of its potential applications have yet to materialize.
As a biomedical material
Since 1989 it was established that Si 3 N 4 is a biocompatible material, which means that it can replace a part of a living organism without causing damage and allowing the regeneration of the tissue around it.
It is used to manufacture components for the replacement or repair of load-bearing bones and also intervertebral devices, that is, small objects that allow repairing the spine.
In tests carried out on human or animal bones, the union between the bone and the implants or Si 3 N 4 ceramic pieces occurred in a short time.
The bones of the human body can be repaired or replaced with parts of silicon nitride. Author: Com329329. Source: Pixabay.
Silicon nitride is non-toxic, it favors cell adhesion, normal proliferation or multiplication of cells and their differentiation or growth by cell type.
How Silicon Nitride for Biomedicine is Made
For this application, Si 3 N 4 is previously subjected to a sintering process with additives of alumina and yttrium oxide (Al 2 O 3 + Y 2 O 3). This consists of applying pressure and high temperature to the Si 3 N 4 powder plus the additives.
This procedure gives the resulting material the ability to prevent bacterial growth, reducing the risk of infection and favoring the body's cellular metabolism.
Thus, it opens the possibility of promoting faster healing in bone repair devices.
In various applications
It is used in high temperature applications where resistance to wear is required, such as bearings (parts that support rotational movement in machines) and cutting tools.
It is also used in turbine blades (machines formed by a drum with blades that rotate when passing water or a gas and thus generate energy) and incandescent connections (joints at high temperatures).
Turbine or aircraft engine, its blades may contain silicon nitride. Author: Lars_Nissen_Photoart. Source: Pixabay.
It is used in thermocouple tubes (temperature sensors), molten metal crucibles, and rocket fuel injectors.
References
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- US National Library of Medicine. (2019). Silicon Nitride. Recovered from pubchem.ncbi.nlm.nih.gov.
- Dean, JA (Editor). (1973). Lange's Handbook of Chemistry. Eleventh Edition. McGraw-Hill Book Company.
- Zhang, JXJ and Hoshino, K. (2019). Fundamentals of nano / microfabrication and scale effect. In Molecular Sensors and Nanodevices (Second Edition). Recovered from sciencedirect.com.
- Drouet, C. et al. (2017). Types of ceramics. Silicon nitride: an introduction. In Advances in Ceramic Biomaterials. Recovered from sciencedirect.com.
- Kita, H. et al. (2013). Review and Overview of Silicon Nitride and SiAlON, Including their Applications. In Handbook of Advanced Ceramics (Second Edition). Recovered from sciencedirect.com.
- Ho, HL and Iyer, SS (2001). DRAMs. Node Capacitance Issues. In Encyclopedia of Materials: Science and Technology. Recovered from sciencedirect.com.
- Zhang, C. (2014). Understanding the wear and tribological properties of ceramic matrix composites. In Advances in Ceramic Matrix Composites (Second Edition). Recovered from sciencedirect.com.