R. Z. Yuan

Synthesis and thermoelectric properties of filled skutterudite compounds CeyFexCo4−xSb12 by solid state reaction

Filled skutterudite compounds, CeyFexCo4−xSb12(x= 0–1.0, y= 0–0.15), were synthesized by solid state reaction using Co, Fe, Sb and CeCl3· nH2O powders as source materials. The lattice constants of CeyFexCo4−xSb12increased with increasing substitution of Fe at Co sites and with increasing Ce filling fraction in the Sb-icosahedron voids. All specimens showed p-type conduction. Carrier concentration (p) and electrical conductivity (σ) increased with increasing substitution of Fe at Co sites and decreased with increasing Ce filling fraction. The Seebeck coefficient (α) decreased with increasing Fe content and increased with increasing Ce filling fraction. Thermal conductivity (κ) decreased with increasing substitution of Fe at Co sites and with increasing Ce filling fraction. A maximum ZTvalue of 0.8 was obtained for Ce0.12Fe0.71Co3.29Sb12at 750 K.

Preparation and characterization of two new dielectric ceramics Ba4NdTiNb3O15 and Ba3Nd2Ti2Nb2O15

Two new cation-deficient hexagonal perovskites Ba4NdTiNb3O15 and Ba3Nd2Ti2Nb2O15 were prepared in the BaO–Nd2O3–TiO2–Nb2O5 system by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction and scanning electron microscope (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. Ba4NdTiNb3O15 has a dielectric constant of 38.15, a high-quality factors (Qu×f >18 700 at 5.4422 GHz), and a small temperature coefficient of resonant frequency (τf)+12 ppm °C−1 at room temperature; Ba3Nd2Ti2Nb2O15 has a higher dielectric constant of 46.83 with high-quality factors Qu×f >19 500 at 5.0980 GHz, and τf+28 ppm °C−1.

Pressureless sintering of silicon nitride with magnesia and ceria

Abstract An investigation of the pressureless sintering of Si 3 N 4 with MgO–CeO 2 revealed that MgO–CeO 2 is a much more effective sintering aid for silicon nitride than either MgO or CeO 2 alone. The concentration of MgO–CeO 2 and the MgO/CeO 2 weight ratio have a strong influence on the densification behavior and mechanical properties of the sintered materials. The pressureless sintered silicon nitride with MgO–CeO 2 achieved a relative density of 98.5% and a bending strength of 948 MPa.

Densification and α/β phase transformation of Si3N4 containing MgO and CeO2 during sintering

This paper deals with the densification and phase transformation during sintering of silicon nitride with MgO-CeO2 as sintering aids. For Si3N4-MgO-CeO2 ceramics, the densification occurs rapidly from 1500°C and nearly ends at 1550°C; the phase transformation from α-Si3N4 to β-Si3N4 occurs rapidly from 1550 to 1600°C and nearly ends at 1600°C. The phase-transformation process lags behind the densification process, showing that the solution and reprecipitation do not play a major role in the densification of the Si3N4-MgO-CeO2 system.

Effect of residual stress on the bending strength of ground Al2O3/TiCN ceramics

Abstract The residual stresses on the surface of the differently ground and polished Al2O3/TiCN ceramics are measured using X-ray diffraction method. The effect of the residual stress on the bending strength is investigated. The residual stresses introduced by surface grinder are tensile, while the residual stresses introduced by universal tooling grinder are compressive. Polishing can smooth the residual stress. Residual stresses induced by grinding process have a significant effect on bending strength.