Engineering ceramics
Engineering ceramics, also called silicon nitride ceramics or high-strength ceramics, are made of silicon powder as a raw material by two processes, reaction sintering and hot pressing. It has almost all the advantages of the modern ceramic family, the strength is generally very high, it has extremely good wear resistance and chemical corrosion resistance, and it is also a very good electrical insulating material.
Advantages of engineering ceramics
high strength
Engineering ceramics have almost all the advantages of the modern ceramic family, and their strength is very high, especially for hot-pressed silicon nitride, the room temperature bending strength is generally in the range of 8000～10000 kg/cm2. If you add yttrium oxide and alumina hot-pressed silicon nitride, the room temperature bending strength can reach 15000 kg/cm2, making the strength of the ceramic material exceed the 10,000 kg mark, which can be said in ceramic materials It is among the best. It is also very hard and is one of the hardest substances in the world. It is extremely resistant to high temperatures and does not melt into a liquid when heated, but does not decompose into silicon and nitrogen until 1900°C. At the same time, the ability to withstand rapid changes in cold and heat is also very good. When they are suddenly heated from room temperature to a high temperature of over 1,000 degrees, and then suddenly thrown into water, they will never crack. For this reason, they are most suitable for manufacturing high-temperature gas turbine blades. , High temperature crucible, etc. Because of its high hardness, it is used to make metal cutting tools, even in the case of rapid friction and high heat will not soften or oxidize, so it is very suitable for high-speed cutting and cutting such as barrels, brake cylinders and other hard Quality steel parts. It can do things that metal can't do. The use of silicon nitride ceramics to make gas turbine turbine blades has a wide range of uses. Because the gas turbine is an advanced power machine, it is used in jet aircraft, thermal power stations, locomotives, and trucks.
Wear and corrosion resistance
Engineering ceramics have excellent wear resistance and chemical corrosion resistance, and are good materials for manufacturing various corrosion-prone parts. It can withstand almost all inorganic acids (except hydrofluoric acid) and caustic soda solution below 30%. It is also resistant to the erosion of many organic substances. It is also resistant to corrosion by many molten non-ferrous metals, especially molten aluminum. Liquid aluminum is non-wetting to silicon nitride, so there is no risk of contamination by using it to make structural parts that contact liquid aluminum.
insulation
Silicon nitride ceramics is also a good electrical insulating material, and its electrical insulating properties can be compared with alumina ceramics. It also has microwave permeability and can be used as a radome. Its dielectric properties change very little with temperature, and can be used up to 550°C at high temperatures. Its thermal shock resistance is superior in all kinds of ceramics, which makes it possible to use it at six Mach (that is, six times the speed of sound), or even at a flying speed of seven Mach.
