Vacuum Sintering Furnaces for Ceramics

Observing the sintering phenomenon at the macro and micro levels, it can be seen that at the macro level, the volume of the product after vacuum sintering shrinks, the density increases, and the strength increases. Microscopically, the shape of the pores changes, the crystals grow, and the composition changes (doping elements). According to the changes in the sintering process, vacuum sintering is mainly divided into the following stages:
1. Early stage of vacuum sintering
(1) Removal of binders, etc.: For example, paraffin wax completely vaporizes and volatilizes at 250~400℃.
(2) As the sintering temperature increases. The diffusion of atoms intensifies, the gaps shrink, the point contact between particles changes from point contact to surface contact, the gaps shrink, and the connected pores become closed and distributed in isolation.
(3) Small particles appear first at grain boundaries, and the grain boundaries move and the grains become larger.
2. Vacuum sintering later stage
(1) Elimination of pores: Materials on the grain boundaries continue to diffuse into the pores, gradually eliminating the pores.
(2) Grain growth: The grain boundaries move and the grains grow.
The sintering methods that can be used for ceramics usually include:
Hot press sintering
Hot press sintering uses a special hot press machine to complete single-phase or two-phase pressure at high temperatures. The interaction between temperature and pressure strengthens the viscosity and plastic flow of the particles, which is conducive to the densification of the blank, and can obtain almost pore-free products. At the same time, the sintering time is short, the temperature is low, the grain growth is suppressed, and the product performance is improved. .
However, hot-pressing sintering can only produce products with simple shapes. At the same time, the microstructure after hot-pressing sintering is anisotropic, resulting in anisotropic performance, which limits its scope of use.
High vacuum sintering
High vacuum sintering is a sintering technology that sinters ceramic bodies in a high vacuum state. Vacuum sintering has attracted the attention of many scholars in the preparation of low-porosity, small-size grain ceramics due to its advantages such as reducing the heating rate, inhibiting abnormal grain growth, and reducing irregular porosity.
High vacuum sintering can not only enhance some properties of high-purity alumina ceramics, but also reduce impurities at grain boundaries and pores in the sintered body. During the process of preparing high-purity alumina ceramics by vacuum sintering, oxygen ions in the alumina crystal lattice are easily lost, forming a large number of oxygen ion vacancies, and the aluminum ion concentration is relatively increased, which accelerates the aluminum ion diffusion process and is conducive to sintering.

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