A Li-Garnet composite ceramic electrolyte and its solid-state Li-S battery

The effect of nanoscale SiC particles on the microstructure of Al2O3 ceramics

Trace SiO2 and MgO additive distributions in sintered alumina have been studied using high-resolution scanning secondary ion mass spectrometry (SIMS) When doped with each additive individually, evidence is seen for both strong silicon segregation to grain boundaries (Cgb/Cgrain similar/congruent 300) in SiO2-doped alumina and strong magnesium segregation to grain boundaries (Cgb/Cgrain similar/congruent 400) in MgO-doped alumina When codoped with both SiO2and MgO, segregation of both ions to grain boundaries is reduced by a factor of 5 or more over single doping The additive concentrations increase proportionally in the grains, and both dopants become more uniformly distributed throughout the bulk It is concluded that codoping with these additives increases their mutual bulk solid solubility and decreases their interfacial segregation over single doping The beneficial effect of MgO additions in controlling microstructure development in alumina and improving corrosion resistance to aqueous HF stems from its ability to redistribute silicon ions from grain boundaries into the bulk

Silica and Magnesia Dopant Distributions in Alumina by High-Resolution Scanning Secondary Ion Mass Spectrometry

High-purity Al 2 O 3 compacts were doped with 0-350 ppm (by weight) of MgO using a liquid immersion technique and equilibrated at temperatures between 1700° and 2000°C under hydrogen. The solubility limits of MgO in Al 2 O 3 at temperatures of 1720° and 1880°C were very low, ∼75 and 175 ppm, respectively. Variation of MgO solubility with temperature could be represented by the equation, In Mg/Al = 3.80 - 2.63 x 10 4 /T. The small MgO solubilities were understood by the high enthalpy (326 kJ/mol) of solution. The results of this study suggested that previous investigations on sintering and grain-growth mechanisms in MgO-doped Al 2 O 3 were probably not done in single-phase Al 2 O 3 solid solutions. However, the conclusions on sintering and grain-growth mechanisms in prior research work in MgO-doped A 2 O 3 may be correct. The effects of SiO 2 impurity and grain size on MgO solubility are discussed. Previous grain-growth experiments in MgO-doped Al 2 O 3 are described that demonstrate the clearest evidence for grain-boundary mobility controlled by a solid-solution mechanism.

Solubility of Magnesia in Polycrystalline Alumina at High Temperatures

The effects of MgO doping and specific surface area of powder on microwave sintering behavior of -Al2O3 were investigated. A comparative study was simultaneously achieved in conventional and microwave heating with an identical thermal process. The experimental results show that both MgO and particle size have significant influence on microwave enhancement in the densification of the alumina samples. It is found that an amount of MgO surrounding the solubility limit in Al2O3 or leading to second phase precipitation of MgAl2O4 spinel induces more significant microwave enhancement. A significant microwave gain in densification is also observed while powder has a high specific surface area. These results indicate that the enhancements during microwave sintering processes are associated with the formation of lattice defect and with the increase in concentration of grain-boundary region.

Comparison of the Microwave and Conventional Sintering of Alumina: Effect of MgO Doping and Particle Size

Small amounts of additives can have a great influence on the sintering of ceramic powders. The most extensively studied example is, without doubt, the effect of dopants especially MgO, on the sintering behaviour of Al2O3. In spite of all these studies many questions are still unsolved since Coble1 reported that the addition of 0.25 wt % MgO inhibits discontinuous grain growth and allows nearly theoretical densities to be achieved.

J. G. J. Peelen

Papers

Influence of MgO on the Evolution of the Microstructure of Alumina