Sintering of Alumina Ceramics
Al2O3 ceramics are one of the ceramic materials with the highest production volume and the broadest range of applications in the world right now. They are extensively used in the machinery, electronics, chemical, aerospace, and other industries. However, since alumina is ionically bound to a cubic crystal structure and has a melting point of 2050 °C, alumina ceramics typically have high sintering temperatures.
On the one hand, appropriately raising the sintering temperature will inevitably lead to an improvement in alumina ceramics' performance across the board. On the other hand, high-temperature sintering is prone to energy consumption and has more stringent equipment requirements. Common 95 porcelain, for instance, sinters at a temperature higher than 1600 °C. Additionally, the required kiln furniture is more expensive than low-temperature ceramics, wears out more quickly, and is more challenging to repair. Thus, lowering the sintering temperature of Al2O3 ceramics not only lowers production costs and conserves energy, but also makes it easier for new applications to be made in other areas.
Influence of Sintering Temperature on Alumina Ceramics
Alumina ceramics are prepared at temperatures of 1500°C, 1550°C, and 1600°C respectively, using calcined alumina powder as the primary raw material. The result shows:
(1) The volume shrinkage of alumina ceramics is significantly influenced by the sintering temperature; the higher the temperature, the greater the volume shrinkage
(2) The bulk density, water absorption, and porosity of alumina ceramics are significantly influenced by the sintering temperature. The bulk density increases with temperature while porosity and water absorption decrease.
(3) Flexural strength and Vickers hardness increase with increasing sintering temperature.
Using ramie fiber fabric as a biological template, polyaluminum chloride as an impregnating solution, and preparing alumina ceramic preforms following impregnation and drying. Then the alumina ceramic preforms were heated at 1350°C, 1400°C, 1450°C, 1500°C and 1550°C respectively, and a erobic calcination was used to make alumina ceramics. The outcome displays:
(1) The real density rises while the porosity falls. This occurs because as the sintering temperature rises, the sample's grains enlarge and the sample's gap narrows, resulting in a decrease in porosity and an increase in real density.
(2) The amorphous structure gradually transforms into a crystalline one as the sintering temperature rises, indicating that Al2O3 has a higher degree of crystallization. Instead, the average grain particle size decreases when the sintering temperature rises above a critical level.
(3) Because the alumina grains in the samples have different morphologies at various sintering temperatures, the sintering temperature likely has a significant impact on how the samples are shaped.
Using alumina nanopowder as the raw material, ZTA composite ceramics were produced by adding different amount of ZrO2 and sintered at various temperatures for three hours. The result shows:
(1) The relative density of the sample increased from 81.73% at 1500°C to 97.48% at 1600°C for the pure Al2O3 sintered sample without adding ZrO2, which is a more noticeable increase.
(2) The sample's flexural strength can be significantly increased by adding ZrO2 additive and raising the sintering temperature.
Furthermore, the sintering temperature influences the electromechanical properties of alumina ceramics. The volume resistivity, bulk density, and breakdown strength of ceramic tiles all increased as the sintering temperature rose. However, the flexural strength first increased and then decreased, and the dielectric constant and dielectric loss tangent both first decreased and then increased.
The following is how temperature affects bulk density:
(a picture)
Conclusion
To summarize, increasing the sintering temperature appropriately has an effect on the density, flexural strength, hardness, water absorption, porosity, and electromechanical properties of alumina ceramics.