The silicon nitride It is an inorganic compound formed by nitrogen (N) and silicon (Si). Its chemical formula is Si3N4. 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 manufacture cutting tools and ball bearings.
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 also serve to be used as a replacement for human or animal bones.
He does3N4 It 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.
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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 gives high stability to the compound..
Silicon nitride has three crystalline structures: alpha (α-Si3N4), beta (β-Si3N4) and gamma (γ-Si3N4). Alpha and beta are the most common. Gamma is obtained at high pressures and temperatures and is the hardest.
Solid bright gray.
140.28 g / mol
1900 ºC
3.44 g / cm3
Insoluble in water. Soluble in hydrofluoric acid HF.
This is a very stable compound, due to the way the silicon and nitrogen atoms are bonded in Si3N4.
Silicon nitride has excellent resistance to hydrochloric (HCl) and sulfuric (HtwoSW4). It is also very resistant to oxidation. It is resistant to cast aluminum and its alloys.
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 an exceptional hardness that allows the application of thin thicknesses of material. 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..
It can be obtained starting from the reaction between ammonia (NH3) and silicon chloride (SiCl4), in which silicon amide Si (NHtwo)4 that when heated forms an imide and then silicon nitride Si3N4.
The reaction can be summarized as follows:
Silicon chloride + Ammonia → Silicon nitride + Hydrochloric acid
3 SiCl4 (gas) + 4 NH3 (gas) → Yes3N4 (solid) + 12 HCl (gas)
It is also manufactured by treating compact powder silicon (Si) with nitrogen gas (Ntwo) at temperatures of 1200-1400 ° C. However, this material has 20-30% microporosity that limits its mechanical strength..
3 Si (solid) + 2 Ntwo (gas) → Yes3N4 (solid)
Therefore, the Si powder is sintered.3N4 to form denser ceramic, this means that the powder is subjected to high pressure and temperature.
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.
He does3N4 it 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 of this.
This serves for microelectronic and photonic applications (generation and detection of light waves). Used as a thin layer in optical coatings.
It is the most common dielectric material used in dynamic random access memory (DRAM) capacitors. Dynamic Random Access Memory), which are those used in computers or computers.
Silicon nitride ceramic has properties of high hardness and resistance to wear, therefore it is used in tribological engineering applications, that is, uses where a lot of friction and wear occurs..
He does3N4 denso exhibits high flexible strength, high resistance to fracture, good resistance to dragging or sliding, high hardness and excellent resistance to erosion.
This is obtained when silicon nitride is processed by sintering in liquid phase by adding aluminum oxide and yttrium oxide (AltwoOR3 + YtwoOR3) 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 there is molten aluminum.
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..
Since 1989 it was established that the Si3N4 it 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, in a short time, the union between the bone and the implants or ceramic pieces of Si3N4.
Silicon nitride is non-toxic, it favors cell adhesion, normal proliferation or multiplication of cells and their differentiation or growth by cell type.
For this application the Si3N4 is previously subjected to a sintering process with additives of alumina and yttrium oxide (AltwoOR3+YtwoOR3). This consists of applying pressure and high temperature to the Si powder.3N4 plus 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..
Therefore, it opens the possibility of promoting faster healing in bone repair devices..
Used in high temperature applications where wear resistance 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).
Used in thermocouple tubes (temperature sensors), molten metal crucibles, and rocket fuel injectors.
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