What is the toughest substance inside the international? Everyone usually thinks of diamonds. But you in no way believe that ceramics may also be the toughest substance within the globe. Here we introduce to you silicon nitride ceramics (Si3N4 ceramics), which have excessive strength, especially warm-pressed silicon nitride ceramics. That’s one of the hardest materials within the world. It has excessive power, low density, and excessive-temperature resistance.
Si3N4 ceramic is a covalent bond compound. The basic structural unit is silicon nitride tetrahedron. The silicon atom located in the center of the tetrahedron. There’re four nitrogen atoms around it, which can be located at the four vertices of the tetrahedron. The tetrahedrons proportion the form of an atom, forming a non-stop and solid network structure in 3 dimensions.
Many houses of silicon nitride are due to this shape. Natural Si3N4 is 3119 and has two crystal systems, α, and β, each of which might be hexagonal crystals. The decomposition temperature is 1800 °C in air and 1850 °C in 110MPa nitrogen. Si3N4 has a low thermal enlargement coefficient and excessive thermal conductivity, so its thermal surprise resistance is superb. The hot-pressed sintered silicon nitride will no longer crack even after being heated to 1000 °C. At a now not too excessive temperature, Si3N4 has better electricity and effect resistance.
Nonetheless, it’ll spoil with the boom of the service time above 1200 ℃, with a purpose to reduce its strength. It is going to be more prone to fatigue harm above 1450 ℃, so Si3N4 The working temperature normally does now not exceed 1300 ° C. due to the fact the theoretical density of Si3N4 ceramics is low, it’s far lots lighter than metal and engineering splendid heat-resistant alloy steels. Consequently, it is appropriate to update Si3N4 ceramics with alloy steels in those locations that require materials with excessive strength, low density, and high-temperature resistance. However, that is it.
As a super high-temperature engineering cloth, Si3N4 ceramic cloth has the most blessings in its application in excessive-temperature fields. It is incredibly proof against high temperatures, and its energy can be maintained up to 1200 °C without reducing. It’s going to not soften into melt after being heated. It’ll now not decompose till 1900 °C. It has severe chemical resistance and may withstand almost all Inorganic acid and caustic soda answer underneath 30% can also withstand the corrosion of many natural acids; it’s miles a high-overall performance electrical insulation cloth as nicely.
The future development course of Si3N4 ceramics is:
1. Make full use of the remarkable characteristics of Si3N4 itself;
2. studies and manage the excellent composition of current flux when Si3N4 powder is sintered;
three. enhance the milling, forming and sintering strategies;
four. Broaden composites of substances which includes Si3N4 and SiC with a purpose to make extra excessive-overall performance composite materials.
Silicon nitride ceramics makes use of silicon powder as a raw cloth. It’s miles first formed into the favored shape with the aid of everyday molding techniques. Initial nitriding is achieved in nitrogen at an excessive temperature of 1200 ° C, and a part of the silicon powder reacts with nitrogen to form silicon nitride. At this time, the complete body has selected energy. Then a second nitriding is carried out in a high-temperature furnace at 1350 ° C to 1450 ° C to react to shape silicon nitride. Hot-urgent sintering may be used to supply silicon nitride with a theoretical density of 99%.
Si3N4 ceramic has the characteristics of lightweight and robust hardness, which may be used to make ball bearings. And it has better accuracy than steel bearings, generates less warmth, and might function in higher temperatures and corrosive media. It has better performance than metallic bearings, generates much less heat, and may paintings in better temperatures and corrosive media.
The steam nozzle made of Si3N4 ceramic is with the characteristics of wear and tear resistance and warmth resistance, and it has no visible damage after being utilized in a 650 ℃ boiler for several months, while different warmth-resistant and corrosion-resistant alloy metal nozzles can best be used for 1-2 months under the same situations.
The Si3N4 ceramic glow plug evolved via Chinese scientists solves the hassle of the bloodless beginning of engines, and is suitable for direct injection or non-direct injection engines. This glow plug is the maximum superior and best ignition tool for engines today.
Eastern researchers have efficiently advanced a new hard pump with a rotor in the pump casing along with 11 Si3N4 ceramic rotors. Due to the fact the shoe uses a Si3N4 ceramic rotor with a small thermal growth coefficient and precision air bearing, it is able to function typically without lubrication and cooling media. If this pump is combined with an ultra-vacuum pump such as a rapid molecular pump, a vacuum gadget suitable to be used in a nuclear fusion reactor or semiconductor processing equipment can be fashioned.
The above are only some utility examples of Si3N4 ceramics as structural materials. It is believed that with the development of Si3N4 powder manufacturing, molding, sintering, and processing technology, its overall performance and reliability will hold to improve, and silicon nitride ceramics could be extra broadly used.
Due to the development of the purity of Si3N4 ceramic uncooked materials, the rapid development of the molding era and the sintering generation of Si3N4 ceramic powder, and the non-stop growth of the software subject, Si3N4 is taking an increasingly more vital function in the enterprise as a structural engineering ceramic.
Si3N4 ceramic has splendid comprehensive houses and considerable sources, is a great excessive-temperature structural material, has a huge application discipline and market, and international locations around the arena are racing to investigate and improve. Si3N4 ceramic substances have the traits of wear resistance, corrosion resistance, high-temperature resistance, oxidation resistance, and low specific gravity that are incomparable for well-known metallic materials.
Silicon nitride ceramic has become the crucial primary material to support the pillar enterprise of the 21st century after metallic materials and polymer substances and has grown to be one of the maximum active research fields. These days, international locations around the world attach exquisite importance to their research and development.
As an essential member of the high-temperature structural ceramic own family, Si3N4 ceramics have higher mechanical homes, thermal houses, and chemical balance than different excessive-temperature structural ceramics, which include oxide ceramics and carbide ceramics. Therefore, it’s far taken into consideration to be the most promising cloth in excessive-temperature structural ceramics.
It’s expected that with the continuous development of fundamental research and new era development of ceramics, especially the increasing number of a sophisticated era for the coaching of complex and huge components, Si3N4 ceramic could be more broadly used as engineering materials with extremely good performance.