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This work provides a novel route for the fabrication of mullite ceramics with excellent mechanical strength using Zircon-Al 2 O 3 -modified SiO 2 as silicon source. The results revealed that silicon sources had significant influences on the grain morphology and properties of the prepared mullite ceramics. A large number of short granular and granular-shaped mullite grains were formed in the mullite ceramics directly prepared using γ-Al 2 O 3 , high-purity quartz and zircon powder, and this is attributed to the very slow diffusion process between the pure Al 2 O 3 and SiO 2 powders under solid state conditions. The melting temperature of the silicon source was obviously decreased after the modification of an appropriate amount of Zr4+ and Al3+ in the SiO 2 lattice. During the sintering process, the Zircon-Al 2 O 3 -modified SiO 2 was transformed into a transient liquid phase with low viscosity at lower temperatures, and this promoted the anisotropic grain growth of the mullite. After sintering at 1650 °C, elongated mullite was formed in-situ while the transient liquid phase was consumed, which enhanced the high-temperature properties of the novel mullite ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Microwave dielectric ceramics of xCaTiO3–(1− x)TiO2–3ZnTiO3 (x =0.05–1.00) were prepared by the solid-state reaction method. The phase relations were investigated using X-ray powder diffraction. In all the studied range, the sintered ceramic was multiphase, which was also verified by scanning electron microscopy (SEM) observation, as well as the energy-dispersive X-ray spectroscopy (EDX) analysis. With the increase of x from 0.05 to 0.25, the amount of rutile phase decreases due to the formation of new Ca2Zn4Ti16O38 polytitanates. And with x increasing from 0.25 to 1.00, rutile phase disappears while CaTiO3 phase increases, accompanying with a slight decrease of Ca2Zn4Ti16O38. Thus, it is considered that the preferential chemical reaction in the system enhanced the formation of the Ca2Zn4Ti6O38 compound, CaTiO3 and rutile phases in the ceramics. Moreover, the microwave dielectric properties of the ceramics were investigated. The simulated dielectric properties of the ceramics were also calculated based on the empirical model. The simulated results and the experimental ones have similar trends, which show that the change of microwave dielectric properties is related to the change of the phase composition in the multiphase ceramics. [Copyright &y& Elsevier]

Abstract: Microwave ceramics of Ba4(Nd0.7Sm0.3)9.33Ti18O54 with 0–3wt% Ag additions were synthesized by a citrate sol–gel method. The BaO–B2O3–SiO2 glass was also added into the sol–gel derived BNST ceramic powders as sintering aids. The undoped, Ag- and BaBS-doped samples can be sintered at 1250°C, 1150°C and 1000°C, respectively. The microstructure and dielectric properties were then controlled by doping Ag or BaBS glass. Near isoaxial grains with about 250nm and typical columnar grains were obtained for the silver-doped and BaBS-doped samples, respectively. For the <1wt% silver-doped samples, the dielectric constant and Q × f retained unaltered but τ f decreased from 9ppm/°C to 1.4ppm/°C. With increasing silver content from 1wt% to 3wt%, the dielectric constant and τ f significantly increased but Q × f decreased. For the BaBS-doped samples, both dielectric constant and Q × f decreased but τ f increased with increasing BaBS content. [Copyright &y& Elsevier]

Abstract: Ceramic bonding phases of non-oxide whiskers can enhance the hot strength and the thermal shock resistance of Al2O3–C refractories. In this paper, the effect of different metals on the microstructure and thermo-mechanical properties of Al2O3–C refractories has been investigated. Thermodynamic calculation of Al–Si–O–C–N systems shows that Al4C3, AlN, SiC and β-Sialon are stable at elevated temperature. AlN with the shape of short column can be generated in Al2O3–C refractories with metallic Al, which leads to high hot modulus of rupture (HMOR) and poor resistance to thermal shock. SiC whiskers formed in Al2O3–C refractories with metallic Si give rise to low HMOR and good resistance to thermal shock. When metallic Si and Al are added together in the refractories, β-Sialon (z=2) with plane structure can be generated under the action of catalyst (nano-sized Ni). The existence of the catalyst promotes the diffusion of Al and O in Si3N4 crystals and contributes to the generation of plane-shaped β-Sialon. The corresponding HMOR and residual cold modulus of rupture respectively increase to about 20MPa and 10.3MPa. The plane-shaped β-Sialon can significantly enhance both hot strength and thermal shock resistance of Al2O3–C refractories. [Copyright &y& Elsevier]