Silicon nitride is an important structural ceramic material. It is a super-hard substance that is inherently lubricating and wear-resistant. It is an atomic crystal and resists oxidation at high temperatures. Moreover, it can also resist hot and cold shocks. It can be heated to more than 1000°C in the air and will not break even if it is rapidly cooled and then heated rapidly. Precisely because silicon nitride ceramics have such excellent properties, people often use it to manufacture mechanical components such as bearings, turbine blades, mechanical seal rings, and permanent molds. If silicon nitride ceramics, which are resistant to high temperatures and are not easy to conduct heat, are used to make the heating surfaces of engine components, it will not only improve the quality of the diesel engine, save fuel, but also improve thermal efficiency. Our country, the United States, Japan and other countries have developed this kind of diesel engine.
What is the production process of silicon nitride ceramics?
The process flow for preparing silicon nitride ceramic products generally consists of raw material processing, powder synthesis, powder processing, forming, green body processing, sintering and ceramic body processing.
The types of silicon nitride ceramic preparation processes are mainly distinguished by different methods and sequences of synthesis, shaping and sintering.
[Silicon nitride ceramic molding process]
Commonly used molding methods for ceramics include dry pressing, casting and Injection, among which dry pressing molding is the most widely used molding process and is also the mainstream of mobile phone ceramic backplanes One of the molding processes, the ceramic back covers of Xiaomi MIX series are all dry-pressed. Today, we will take a closer look at the ceramic dry pressing molding process.
1. Dry pressing
Dry press molding, also known as compression molding, is one of the most commonly used molding methods. Dry press molding is to put the granulated powder with good fluidity and suitable particle gradation into the metal mold cavity, apply pressure through the indenter, and the indenter moves in the mold cavity, transmits the pressure, and makes the powder in the mold cavity The bulk particles are rearranged, deformed and compacted to form a ceramic blank with a certain strength and shape.
2. Process principles and influencing factors of dry press molding
1. Process principle
The essence of dry press molding is that under the action of external force, the particles are close to each other in the mold, and the particles are firmly connected with the help of internal friction to maintain a certain shape. This internal friction acts on thin layers of binder on the periphery of the particles that are close to each other.
As the pressure increases, the blanks will change their shape, slide against each other, reduce the gap, gradually increase the contact, and stick to each other. As the particles get closer together, the force between the colloidal molecules and the particles is strengthened, so the green body has a certain mechanical strength.
2. Influencing factors
(1) Powder properties: particle size, particle size distribution, fluidity, moisture content, etc.;
(2) Selection of binders and lubricants;
(3) Mold design;
(4) Pressing force, pressurizing method, pressurizing speed and pressure holding time during the pressing process.
In summary, if the blank particle gradation is appropriate and the binder is used correctly,The pressing method is reasonable, and the dry pressing method can also obtain a relatively ideal density of the green body.
[Silicon nitride ceramic sintering process]
High-purity silicon nitride powder basically does not shrink when hot pressed at 1700 C. There are three main sintering methods for silicon nitride: reaction sintering, conventional sintering and hot press sintering.
Finally, let me share with you the application of silicon nitride ceramics
The initial application of silicon nitride ceramics was mainly used in machinery, metallurgy, chemical industry, aviation, semiconductor and other industries as parts of certain equipment or products, and achieved good expected results. . In recent years, with the development of manufacturing processes and testing and analysis technologies, the reliability of silicon nitride ceramic products has continued to improve, so the application areas have continued to expand. What is particularly commendable is that silicon nitride ceramic engines are being developed and great progress has been made, which has become a major event that attracts worldwide attention in science and technology.
1. In the metallurgical industry, it can be used to make crucibles, muffle furnaces, burners, heating element fixtures, casting molds, aluminum liquid conduits, thermocouple temperature measurement protection sleeves, aluminum electrolytic cell linings and other thermal equipment components.
2. In the machinery industry, it can be made into high-speed turning tools, bearings, supports for heat treatment of metal parts, rotor engine scrapers, gas turbine guide vanes and turbine blades, etc.
3. In the chemical industry, it can be made into ball valves, pump bodies, sealing rings, filters, heat exchanger components, fixed catalyst carriers, combustion boats, evaporation dishes, etc.
4. Used in the semiconductor, aviation, atomic energy and other industries to manufacture switching circuit substrates, film capacitors, electrical insulators that can withstand high temperatures or drastic changes in temperature, radar radomes, missile tail nozzles, Supports and isolation parts in atomic reactors, carriers of nuclear fission materials, etc.
5. Artificial joints can be made into medical engineering.
6. The silicon nitride all-ceramic engine under development will replace the same type of metal engine.
