Search

Nano-porous SiO2 insulation material was made from foamed aqueous slurry of nano-silica powder by filter-pressing. The foamed aqueous slurry mainly consists of hydrophobic SiO2 nano-particles, xonotlite whiskers and glass fiber. The latter two will enhance strength of the insulation material. Rheological properties of the foamed slurry with varying solid mass concentration were studied. The effect of forming pressure on the density and pore size distribution of the nano-porous silica material was investigated. It was found that the foamed slurry with solid concentration less than 17% behaves pseudoplastic as decreasing its apparent viscosity with increasing of shear rate during rheological testing. Homogeneous foamed slurry can be obtained when solid concentration in it is below 7%. Such slurry should be dewatered into solid concentration being of 10-15% before filter-pressing. Rigorously stirring of the concentrated slurry is required before pouring it into a mould, which leads to reducing the viscosity of the slurry and helps uniformly filling mould. During pressing the loading speed should be strictly controlled in order to reaching designed pore size distribution in SiO2 insulation material. The SiO2 insulation material with apparent density about 0.45g/cm3 and pore size mainly ranging from 10 to 50nm was obtained.

Porous Si3N4/SiO2/BN composite ceramics with high strength and low dielectric constant were prepared by dry-pressing process and pressureless sintering at 1750°C for 1.5 h in flow nitrogen. The influences of BN content on microstructure, porosity, mechanical and dielectric properties of the porous Si3N4/SiO2/BN composite ceramics were discussed. The results showed that the porous Si3N4/SiO2/BN composite ceramics with porosity ranging from 29% to 48% were fabricated by adjusting the content of BN. The flexural strength of the porous Si3N4/SiO2/BN composite ceramics was 78215 MPa. The dielectric constant of the porous Si3N4/SiO2/BN composite ceramics was 3.9~5 at 1 MHz.

Porous SiO2 insulation material was made by wet process. Fibrous xonotlite crystal and glass fiber were used as reinforced fibers, and graphite, zirconia and titania powders were added as infrared scattering materials into the porous SiO2 insulation material. The density of the SiO2 insulation material was about 0.3g/cm3. The porosity was about 85%, and the pore size was mainly ranged from 20 to 60 nm in diameter. Heat transfer due to solid conduction and gas convection was reduced greatly because of the existence of larger amount of nano pores. Thermal radiation was partly blocked by the infrared scattering powders. Thermal conductivity of the porous SiO2 insulation material added with graphite powder as infrared scattering powder can reach as low as 0.04W/m.K at 700°C. The type and amount of added infrared scattering powders had important influence on the thermal performances of insulation materials.

BiFeO3-based single-phase multiferroics have been widely studied in both ceramics and films. However, the macroscopic magnetic properties of BiFeO3 ceramics were now most very weak. In this work, MnO2 and Co2O3 were used as B-site substitutes in BiFeO3 ceramics in order to the enhancement of magnetic properties. The change of magnetization was analyzed based on the phase composition and the microstructure of ceramics.

Extrusion gelation freeform fabrication (EGFF) is a new solid freeform fabrication technique to fabricate ceramic parts. The study of ceramic suspensions rheological behavior is essential to a better understanding of parts fabrication through EGFF process. In this paper, the effects of dispersant concentrations, solids loading and binder composition on the rheological behavior of alumina suspensions were examined. The optimal amount of dispersant was found to be about 0.1 wt.%. The suspensions with 50 vol.% alumina and 1wt.% sodium alginate show shear thickening behavior. Such behavior is unfavorable for extrusion gelation freeform fabrication. By addition of PVA or styrene-acrylic latex, the rheological behavior of suspensions was changed. The addition of PVA or latex has a great effect on the viscosity of the suspensions and the type of their rheological behavior. The ceramic suspensions with PVA or latex were found to be shear thinning more suitable for EGFF.

As a good binder for aqueous Al2O3 suspensions tape-casting process, a commercial styrene-acrylic latex binder had been investigated. This paper studied on the rheological behaviors of the suspensions and drying process of aqueous slurries with latex binder system, and the research results indicated the rheological behaviors was affected by pH value, solid loading and dispersant (PAA-NH4) additives; and the drying speed of slurries was most decided by drying temperature and slurry coating thickness.

Piezoelectricity of composite was simulated by employing Dilute Model and Limit Unit method. The analogizing results recommend that the particle stackers influence the properties of piezo-composite. While fabricating piezo-composite, particles stack different with different routine. For thermo-pressing proceeding, stackers trend to take on higher D33 than that processing from forging-membrane.

Extrusion gelation freeform fabrication process is an extrusion-based freeforming technique capable of fabricating complex shaped monolithic ceramic prototypes by the sequential deposition and solidification of ceramic suspensions from a computer aided design model. In this process, ceramic parts are produced using an extrusion nozzle suitable for extruding ceramic suspensions. In this study, the processing parameters influencing on manufacturing Al2O3 parts were discussed. Air pressure on top of suspensions, rotating speed of screw, nozzle diameter and scan speed are the main factors to influence the dimensional precision of ceramic bodies. By optimizing these processing parameters, the green bodies were fabricated with high precision. The sintered samples with homogenous microstructure and ~97.6% relative density could be prepared by sintering of these green bodies at 1600oC for 2 hours.

By means of a finite element method model, the effects of property parameters of refractory on thermal stress of injection lance have been studied. The results show that the maximum thermal stress increases with the improvement of thermal conductivity and elastic modulus of refractory, while it decreases at first and then increases with the improvement of the coefficient of expansion of refractory.