Two Methods for Low Temperature Sintering of Ceramics

Additive action machine

Preparing ceramics at the lowest possible temperature can reduce energy consumption and reduce product costs. Low temperature sintering methods mainly include the introduction of additives, pressure sintering, and the use of easily sintered powders.

(1) Introduction of additives

This method can be divided into two categories according to the action mechanism of additives: the introduction of additives increases the Vacancy defect, which is easy to diffuse and accelerates the sintering rate; The introduction of additives leads to the formation of the liquid phase at lower temperatures, and after the liquid phase appears, the crystals can undergo viscous flow, promoting sintering. When there is no liquid phase present, ceramic powder is usually sintered through diffusion mass transfer. In fact, an ideal crystal does not exist. There is always a certain number of vacancies in the crystal. The vacancy concentration in the neck is high, while the vacancy concentration in other parts is low. The existence of a vacancy concentration gradient leads to the diffusion of the high vacancy concentration part (usually the neck at the contact of two particles) towards the low vacancy concentration part, while the particle (ion) diffuses in the opposite direction, causing the material to sinter. The introduced additives are solidly soluble in the main crystal phase, increasing vacancies and promoting diffusion, making the material easy to sinter. For example, adding TiO ₂, MgO, MnO, etc. to chemical Al203 significantly promotes sintering. When additives are introduced, a liquid phase can be formed at a lower temperature, and after the liquid phase appears, the crystals can flow with viscosity (migration in particles), promoting sintering. Adding MgO, Y ₂ O Å, Al ₂ O Å, etc. to Si3 N4 can accelerate the sintering rate.

In short, additives can display new functions in materials, such as improving strength, inhibiting grain growth, and promoting sintering.

(2) Using powder that is easy to sinter

The preparation methods for easily sintered powder can be roughly divided into general powder preparation processes and special powder preparation methods, with their main difference being the differences in preparation process. The preparation process referred to here includes the chemical composition of the mother salt, the preparation conditions of the mother salt, the calcination conditions, and the crushing conditions. Due to changes in these technological processes, the sintering properties of the prepared ceramic powder undergo subtle changes. For example, the average Granularity of TiO ₂ powder made from tetra Titanium isopropoxide is 0.08 μ m. After sintering, the material density reaches 99% of the theoretical density. The grain size of the sintered body is about 0.15 μ m. The sintering temperature is 800 ℃, which is 500~600 ℃ lower than the sintering temperature of TiO2 ₂ powder prepared by traditional processes (usually the sintering temperature of TiO2 ₂ is 1300~1400 ℃); The average particle size of Ti02 powder synthesized from titanium tetraethyl alcohol is 0.3 μ m. The density of the sintered material is 99% of the theoretical density, and the grain size of the sintered body is about 1.2 μ m. The sintering temperature is 1050 ℃. In summary, with the refinement of powder particles, the microstructure and properties of the powder will undergo significant changes, especially for submicron to nanoscale powders, which have unexpected performance in terms of internal pressure, surface activity, melting point, and other aspects. Therefore, powders that are easy to sinter can accelerate the dynamic process, lower the sintering temperature, and shorten the sintering time during the sintering process.

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