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Herein, the Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) ceramic with low sintering temperatures were prepared via the traditional solid-state method, and the Mg2SiO4/LMZBS ceramic composite was prepared by adding Mg2SiO4 ceramic, and the results showed that the properties of LMZBS ceramic was improved upon addition of Mg2SiO4 ceramic. The sinterability, microstructure, dielectric properties, mechanical properties and coefficient of thermal expansion (CTE) of composite were determined. The crystal structure was determined using X-ray diffraction, and Mg2SiO4, Mg3B2O6, Mg2B2O5 were the main phase. The 20 wt% Mg2SiO4 ceramic sintered at 900 °C exhibited superior performance: ε r of 6.97, Q value of 1732 at 10 GHz and flexural strength of 206 MPa, and CTE value of 10.06 ppm/°C. The composite was also found to match well with the Ag electrode in an investigational study. These properties have made the Mg2SiO4/LMZBS ceramic composite great candidates in low-temperature co-fired ceramics technology. [ABSTRACT FROM AUTHOR]

In this study, CaO–Al2O3–B2O3–SiO2(CABS) glass/MgAl2O4 composite for low-temperature co-fired ceramics (LTCC) applications was prepared. The sinterability, microstructure, dielectric properties, mechanical properties, and coefficient of thermal expansion (CTE) of composite were determined. MgAl2O4 as ceramic filler improves the dielectric properties of the composite, mechanical properties, and density. The 45 wt% CABS glass contents composite sintered at 900 °C exhibit superior performance, which have relatively high bulk density, dielectric constant = 6.51, dielectric loss = 3.1 × 10–3 (10 GHz) and CTE = 4.51 ppm/°C, flexural strength = 261 MPa. [ABSTRACT FROM AUTHOR]

Abstract: Alumina matrix composites containing 5 and 10wt% of ZrO2 were sintered under 100MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600nm and yttria-stabilized zirconia with 16at% of Y2O3 and with a particle size of 40nm were used as starting materials. The influence of ZrO2 content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400°C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66–0.79μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO2 content, and the samples containing 10wt% of ZrO2 had the highest Vickers hardness of 18GPa (5kg load) and fracture toughness of 5.1MPam1/2. [Copyright &y& Elsevier]

Abstract: The preparation of ultrafine-grained alumina ceramics by the fast sintering technique Self-propagating High-temperature Synthesis plus Quick Pressing (SHS-QP) method and spark plasma sintering (SPS) technique was reported. The effects of different heating rates (SHS-QP-1600°C/min, SPS-200°C/min) on the preparation of ultrafine structure were compared. The densification and grain growth as a function of sintering time and temperature were discussed. Within a short sintering time (<3min), the full-dense alumina with ultrafine-grained structure was obtained by SHS-QP at 1550°C under 100MPa. By SPS, the sintering temperature was lower (1200°C) than that of SHS-QP. The differences in densification parameters were explained by analyzing the thermodynamics of sintering process. [Copyright &y& Elsevier]

Fast sintering processes offer promising new routes for the fabrication of bulk ceramics but it is not clear that the microstructural details and properties resulting from a very short, rapid densification procedure are the same in all respects as those resulting from traditional sintering. Here, not fully relaxed grains and their weak mechanical properties of as-prepared nanoscale alumina are described. It was found that low temperature annealing did not cause grain growth but allowed normal boundaries to develop. [Copyright &y& Elsevier]

Abstract: Experimental sintering studies on Al2O3 powder (200nm and 600nm) were done at a heating rate of 1600°C/min. The microstructural changes of specimens were examined and corresponding detailed data on the densification and grain size as a function of sintering time were presented. The grain-growth transition behavior during sintering was discussed. The results showed that the neck growth caused principally by surface diffusion could be negligible within 2min. With subsequent increases of sintering time, grain growth promoted by grain boundary and lattice diffusion occurred. [Copyright &y& Elsevier]

Abstract: Fine-grained alumina was obtained in 2min by a new densification method based on Self-propagating High-temperature Synthesis plus Quick Pressing (SHS/QP). The sample was densified to more than 99% of theoretical density under a large mechanical pressure (100MP) and a fast heating rate (1600°C/min). Compared with the alumina sample obtained by spark plasma sintering (SPS) at lower heating rates (100 or 500°C/min), almost no grain growth was found in the sample obtained in this work. The microstructure and mechanical properties were studied. Hardness value of 18.6±0.4GPa and fracture resistance value of 3.4±0.3MPam1/2 were measured for fine-grained alumina of this work. The densification mechanism was discussed. [Copyright &y& Elsevier]

0.9(Zn 0.9 Mg 0.1 )TiO 3 -0.1TiO 2 (ZMT-TiO 2 ) ceramics doped with BaO-B 2 O 3 -ZnO(BBZ) glass were prepared by conventional solid-state routes. The effects of BBZ glass on the phase evolution, microstructure, sintering mechanism and microwave dielectric properties have been investigated. The BBZ glass as a sintering agent can effectively reduce the sintering temperature of ZMT-TiO 2 ceramic below 1000 °C. The XRD patterns indicate that the ZMT-TiO 2 ceramic consisted of ZnTiO 3 , Zn 2 TiO 4 and TiO 2 phases. Added BBZ glass inhibit the decomposition of the ZnTiO 3 into Zn 2 TiO 4 and TiO 2 . In addition, SEM results showed that BBZ significantly improved the grain growth and densification, this is due to the fact that the BBZ glass liquid sintering mechanism. The sintering mechanism was analyzed through the wetting behavior and the activation energy(Ea). When added 3 wt% BBZ glass, the activation energy reduced from 614.79 KJ/mol to 417.49 KJ/mol. This result indicate that the BBZ glass can promote the sintering process. Typically, the ZMT-TiO 2 ceramic with 3 wt% BBZ sintered at 950 °C for 4 h has shown excellent microwave dielectric properties of ε r = 24.46, Q × f = 47500 GHz and τ f = -14.68 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline Ba(Mg1/3Nb2/3)O3 (BMN) powders were successfully synthesized through a modified combustion synthesis method by using Ba(NO3)2, Mg(NO3)3·6H2O and Nb2O5 as starting materials. Gel precursor and calcined powders were characterized by thermogravimetric (TG), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrate that pure perovskite Ba(Mg1/3Nb2/3)O3 powder formed at 800°C for 2h. And the crystallite size was about 40nm. The specimen sintered at 1550°C for 12h shows 96.3% of the theoretical density and gave the excellent microwave dielectric properties: ɛ r =31.3 and Qf =71,800GHz. [Copyright &y& Elsevier]

Dense silicon nitride ceramic was sintered by hot pressing at 1800 °C for 3 h under the uniaxial pressure of 40 MPa in N 2 atmosphere using CeO 2 –MgO as sintering aid. In this study, the effect of the addition of CeO 2 –MgO on the sintering of silicon nitride ceramics was investigated. The equiaxed α-Si 3 N 4 was transformed into a rod-shaped β-Si 3 N 4 completely by using XRD and SEM analysis. The sample reached a maximum density of 98.2% and a high flexural strength (872 ± 65 MPa). The range of dielectric constant is 10.79–11.06 (12.4 GHz), and the dielectric loss is in the order of 10 E−3. The highest thermal conductivity achieved in all samples is 45.5 W/mK. [ABSTRACT FROM AUTHOR]