Application of magnesium oxide in transparent ceramics

1) The impact on the relative density.

Adding the right amount of magnesium oxide alumina transparent ceramic relative density will be improved, but it should be noted that with the increase of magnesium oxide doping, its relative density has decreased, this is because too much magnesium oxide additives will cause the increase of pores and is not conducive to the densification of the sample. When the amount of MgO additive is around 0.05%, the relative density reaches 99.5%, and the ceramic samples have very high densities and the highest permeability.

Meanwhile, the relative density of the ceramic samples increased with the extension of the holding time. It means that the ceramic grains were further grown and perfected with the extension of the holding time, and the pores in the ceramic samples were further discharged, which increased the relative density of the samples. Therefore, extending the holding time can obtain transparent alumina ceramics with better density and better light transmission.

2) The effect on the microstructure.

The increase in the amount of magnesium oxide added, the ceramic grain is more fine. This is because the formation of magnesium oxide-Al2O3 spinel phase in the ceramic can impede the movement of grain boundaries, inhibit the growth of grains. However, if the addition of magnesium oxide is too large, the pores also gradually increase. The reason for this phenomenon may be that too much doping can form a discontinuous liquid phase at the grain boundaries, which makes the tiny pores aggregate into larger pores and remain in them. This kind of pore exclusion is slow, so when the amount of addition is too large, the bulk density instead of showing a decreasing trend.

3) The impact of optical properties

When the doping amount of magnesium oxide is low, transparent ceramic light transmission rate is relatively high, which is due to the right amount of magnesium oxide can inhibit the rapid movement of the grain boundary, making the pore discharge more complete, ceramic more dense, higher transmission rate. But with the increase of doping amount, the magnesium oxide content exceeds the solid solution degree in alumina, it will form the second phase locally, forming the light scattering center, causing the decrease of transparent ceramic transmittance.