Adding Rare Earth Oxides Beo Ceramic Non-pressure Sintering

BeO ceramics is widely applied in special metallurgy, vacuum electronics technology, nuclear technology, and microelectronics and photoelectron technology due to its high thermal conductivity, high melting point, high intensity, high insulation nature, high chemical and thermal stability, low dielectric constant, low dielectric loss and good technology applicability, etc.Gelcasting technology was applied to prepare BeO ceramics. And three aspects of contents related to the sintering of BeO ceramics were investigated:1) the affection of different rare earth oxide on the relative density and the thermal conductivity of BeO ceramics; 2) the affection of different compound sintering additives sintering, microstructure and performance of BeO ceramics; 3) the sintering mechanism of BeO under adding single additive or compound additives. The main results obtained as follows:1) The addition of single rare earth oxide can increase the relative densities and thermal conductivities of BeO ceramics. The relative density of pure BeO ceramic is only 78.78%, whereas the addition of rare earth oxide is 1%(mass fraction), BeO ceramic samples take on higher the relative densities and the highest thermal conductivities in the scope of addition. The relative densities of the samples with 1%CeO2, 1%Pr6O11 and 1%Nd2O3 are 92.17%,85.17% and 91.99%, respectively, and the corresponding thermal conductivities are 197.93W·m-1·K-1, 192.82W·m-1·K-1 and 189.21 W·m-1·K-1, respectively.2) The sintering temperature and holding time have great effect on the relative densities and thermal conductivities of BeO ceramic with single rare earth oxide. Both the relative densities and thermal conductivities increase with the increment of sintering temperature whereas the accretion of relative densities is slowed down when the sintering temperature is above 1600℃. Samples with 1%Pr6O11 take on the highest relative density of 91.02% and the highest thermal conductivity of 234.18W·m-1·K-1. For single additive systems(1%CeO2, 1%Pr6O11 and 1%Nd2O3), the result show that the relative densities and thermal conductivities of all samples increase with the extension of holding time whereas the accretion is slowed down when the holding time is over 90min.3) Different sintering additives have different impacts on BeO ceramics. For compound additive systems, the results show that all the additives can improve the relative densities of BeO ceramics. The order of the effect of acceleration of sintering from strong to weak is (Al2O3-MgO-Fe2O3), (Al2O3-Fe2O3-CaO-Nd2O3), (Fe2O3-E2O3) and AMS or CAS in turn. But samples with AMS (Al2O3-MgO-SiO2) or CAS (Al2O3-CaO-SiO2) have lower thermal conductivities as a result of low thermal conductivity of glass phase. Samples with 1% (Al2O3-MgO-Fe2O3) take on a higher relative density of 93.70% and thermal conductivity of 221.05W·m-1·K-1 after sintering about 120min at 1650℃.4) The sintering additives have impact on the microstructure of BeO ceramics. By comparing the microstructure of samples added single additives with the one adding compound additives, the results show that there are pores at the grain boundaries to the former, but in the intracrystalline to the latter.5) The sintering mechanisms of BeO ceramics with different sintering additives are different. The sintering mechanism is mainly liquid-phase sintering when there are eutectic or glass, otherwise it is mainly solid-phase sintering. The densification of BeO ceramics goes on at 1400～1600℃. The densities of BeO ceramic increase very slowly when the temperature is over 1600℃, as a result of grain growth and small pores vanish.