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ZnO-Al2O3-MgO-SiO2-TiO2-CaO (ZnO-based) linear resistance ceramics were prepared by the conventional ceramics method with different amounts of CaO. The impact of CaO doping on the phase composition, microstructures and electrical properties of ZnO-based linear resistance ceramics was investigated in detail. The research showed that CaO doping not only limits the growth of ZnAl2O4 and ZnO grains—in particular, the grain size of ZnAl2O4 decreased from 4.40 μm to 1.38 μm—but also improves the electrical properties. The grain boundary barrier height and nonlinear coefficient decreased with the increase in CaO content, and the resistance temperature coefficient increased from −5.65 × 10−3/°C to 1.04 × 10−3/°C. The 4.00 mol.% CaO-doped ZnO-based linear resistance ceramics were found to possess excellent electrical properties: the resistivity is 44.87 Ω cm, the grain boundary barrier height is 0.011 eV, the nonlinear coefficient is 1.05 and the resistance temperature coefficient is −0.822 × 10−3/°C, a stable resistivity against frequency. [ABSTRACT FROM AUTHOR]

Porous silicon-bonded silicon carbide (SBSC) ceramics were prepared under argon atmosphere, with silicon as pore former and bonding material, simultaneously, sodium dodecyl benzene sulfonate (SDBS) and ZrO 2 as sintering additives, the effects of SDBS and ZrO 2 on the porosity, pore size, mechanical, physical and thermal properties and microstructures were investigated. The results suggested that suitable content of SDBS and ZrO 2 could not only effectively lower the sintering temperature to 1450 °C due to the sticky flow of molten silicon, but also increase the pore structure and improve the bending strength. The reason for this is that SDBS decomposed into Na 2 O which reacted with ZrO 2 and impurity SiO 2 , which was the native oxide film on the surface of SiC particles, to form a bonding phase between SiC particles to improve the bending strength; meanwhile, the disappearances of impurity SiO 2 would benefit the bond of molten silicon and silicon carbide particles, and silicon melt leaving pores in its original position to increase the pore structure. The optimal apparent porosity, bending strength, average pore size, gas permeance and residual bending strength after thermal shock cycles of SBSC porous ceramic sintered at 1450 °C with 5 wt% SDBS and 6 wt% ZrO 2 were 38.33%, 55.4 MPa, 11.3 μm, 106.4 m3/m2·h·kPa and 28.2 MPa, respectively. [ABSTRACT FROM AUTHOR]

(1−x)(Ca0.88Sr0.12)TiO3–x(Bi0.5Na0.5)TiO3 (CST–BNT, x = 0, 0.025, 0.05, 0.075, 0.10) high dielectric constant ceramics were prepared by the solid state reaction method, and the effects of (Bi0.5Na0.5)TiO3 (BNT) on the sintered properties, phase composition, microstructures, and dielectric properties of (Ca0.88Sr0.12)TiO3 (CST) ceramics were investigated as a function of the x-value and sintering temperature. The results showed that: BNT had no obvious influence on phase composition of CST ceramics, and the single phase solid solutions were obtained throughout the studied compositional range. Adding a moderate amount of BNT not only effectively lowered the sintering temperature from 1400 to 1275 °C, but also improved the sintered properties and the dielectric properties, especially that the τf decreased from + 942 to + 639 ppm/°C, which was decreased by about 32%. For x = 0.05, the 0.95(Ca0.88Sr0.12)TiO3–0.05(Bi0.5Na0.5)TiO3 ceramics sintered at 1275 °C for 3 h exhibit an excellent combination of microwave dielectric properties: εr = 185.5, Q × f = 8116 GHz and τf = + 639 ppm/°C, and which could be used as a promising candidate to equalize the materials with negative temperature coefficient of resonant frequency. [ABSTRACT FROM AUTHOR]

The effect of CaO/SnO 2 additives on the sintered properties, phase composition, microstructures, and dielectric properties of 0.6SrTiO 3 -0.4LaAlO 3 (6ST-4LA) microwave dielectric ceramics prepared by conventional solid-state reaction method were investigated. The results showed that CaO/SnO 2 as additives had no obvious influence on phase composition of 6ST-4LA ceramics, and all of the samples exhibited pure ABO 3 perovskite structures. Adding a moderate amount of CaO/SnO 2 not only effectively lowered the sintering temperature from 1550 °C to 1400 °C, but also improved the dielectric properties, due to formation of the perovskite solid solution, and decreased the microstructure defects and intrinsic loss. The 0.25 wt% CaO-doped 6ST-4LA ceramics with 0.50 wt% SnO 2 , sintered at 1400 °C for 3 h had the optimal integrated microwave dielectric properties: ε r =44.87, Q·f =65277 GHz(at 6.5 GHz), τ f =−1.56×10 -6 /°C. [ABSTRACT FROM AUTHOR]

The present study aims to determine the effects of calcium carbonate (CaCO 3) and zirconium dioxide (ZrO 2) on the microstructure and properties of silicon-bonded silicon carbide (SBSC) porous ceramics. The SBSC porous ceramics were prepared by adding CaCO 3 and ZrO 2 as composite additives in an argon atmosphere. Then, the impact of CaCO 3 and ZrO 2 on the properties and microstructure of SBSC porous ceramics was investigated. The results revealed that a proper amount of CaCO 3 and ZrO 2 can be effective for improving porous structures and increasing bending strength. Calcium zirconium silicate (Ca 3 ZrSi 2 O 9) was identified to have a well-grown neck connection phase, which is the result of the reaction of CaO, ZrO 2 and impurity SiO 2. Simultaneously, the disappearance of the impurities of silicon dioxide (SiO 2) facilitated the combination of fused silicon (Si) and silicon carbide (SiC) grains, thereby creating pores in the original location of the Si and optimizing the micropore structure. In conclusion, SBSC materials with 6 wt% ZrO 2 and 4 wt% CaCO 3 sintered at 1450 °C have the best apparent porosity (38.86%), bending strength (68.7 MPa), mean pore size (7.45 μm), and gas permeability (98.5 m3/m2·h1·kPa1). [Display omitted] • The impact of CaCO 3 and ZrO 2 on the properties and microstructure of SBSC porous ceramics was investigated. • Calcium zirconium silicate (Ca 3 ZrSi 2 O 9) was identified to have a well-grown neck connection phase, which is the result of the reaction of CaO, ZrO 2 and impurity SiO 2. • SBSC materials with 6 wt% ZrO 2 and 4 wt% CaCO 3 sintered at 1450 °C have the best apparent porosity (38.86%), bending strength (68.7 MPa), mean pore size (7.45 μm), and gas permeability (98.5 m3/m2·h1·kPa1). [ABSTRACT FROM AUTHOR]