Lin Hong

Fabrication of Transparent Polycrystalline Yttria Ceramics by Combination of SPS and HIP

Abstract Transparent polycrystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0 μm and narrow size distribution was selected as the starting material. Transparent polycrystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700 °C for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ∼ 40 μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.

Difference of Mullite Whiskers between Ytterbia-Doped Aluminum Hydroxide-Silica Gel and Mechanochemical Process

Abstract A number of processing routes were developed for the synthesis of mullite whiskers. Mullite whiskers that were derived from ytterbia-doped aluminum hydroxide-silica gel were studied; another process for preparing mullite whiskers from Al2O3-SiO2 oxide mixtures by mechanochemical method was encountered by chance. The method of ytterbia-doped aluminum hydroxide-silica was used to enhance mullite formation from gel. For adding ytterbia, mullite formation can take place at 1000 °C and almost single-phase mullite can be achieved at 1150 °C, which is a significantly lower temperature than mechanochemical method. This enhancement of mullite formation is also attributed to refinement of aluminum hydroxide-silica by gel. Furthermore, well-developed single-crystal mullite whiskers were produced from the gel powder instead of normal-shaped grains. The presence of YbO might have promoted the formation of nanosized Al2O3 particles, which then acted as a template leading to mullite whiskers at higher sintering temperature.