The atmospheric pressure sintering method is a commonly used technique in the preparation of silicon nitride ceramics, which plays an important role in achieving industrial production of silicon nitride ceramics and expanding their application fields.
Firstly, the molding process is the foundation. Mixing silicon nitride powder with appropriate additives, the selection and dosage of these additives are carefully considered, with the aim of improving the activity of silicon nitride powder during sintering and promoting sintering between particles. Common additives include Y ₂ O3, Al ₂ O3, etc. After mixing evenly, the green body is made using forming methods such as dry pressing and isostatic pressing. During dry pressing, by adjusting parameters such as pressure and holding time, the powder is compacted in the mold to form a billet with a certain shape and strength, suitable for products with relatively regular shapes and small sizes; Isostatic pressure forming uses a liquid medium to uniformly apply pressure, which can make the density of the billet more uniform, especially suitable for manufacturing some billets with complex shapes or high requirements for density uniformity.
Subsequently, it enters the atmospheric pressure sintering stage, where the green body is placed in a regular sintering furnace for sintering within the temperature range of 1700 ℃ -1800 ℃. During this process, as the temperature increases, the atoms on the surface of the powder particles gain sufficient energy to start diffusing, gradually forming necking between the particles, thereby achieving initial densification of the body. However, relying solely on atmospheric pressure sintering may not achieve the desired density of the green body, so subsequent atmospheric pressure sintering steps are often required.
Pressure sintering is usually carried out within the temperature range of 1800 ℃ to 2000 ℃. At this stage, a certain pressure of gas, usually inert gas such as nitrogen, is introduced into the sintering furnace to further promote the densification of the ceramic structure using gas pressure. Gas can fill the pores inside the billet, helping to remove residual pores, further increasing the density of the billet and improving its performance.
The silicon nitride ceramics prepared by atmospheric pressure sintering method have their own characteristics. Compared with the hot pressing sintering method, it has relatively simple equipment and lower cost, and can achieve a certain scale of production. It is suitable for manufacturing silicon nitride ceramic products that do not have particularly extreme performance requirements but require a certain batch size. However, its disadvantages are also quite obvious. The performance of the obtained product is slightly lower compared to the product prepared by hot pressing sintering method, such as slightly inferior strength and density. Moreover, there are certain limitations on the size and shape of the green body during the sintering process, which poses certain difficulties in the manufacturing of complex shaped products. But with the continuous development and improvement of technology, the atmospheric pressure sintering method still has broad application prospects in the production of silicon nitride ceramics, especially playing an important role in some mid to low end markets and cost sensitive application scenarios.

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