Papers by Keyword: Porous Ceramics

Abstract: Porous ceramics composite was prepared with mixed powders (Al, TiO₂ and B₂O₃) by SHS (Self-propagating High-temperature Synthesis) method. The effects of the particle size of aluminum power, the additives of SiC and the compacting pressure on the product properties and the pore size, as well as the combustion process in the Al₂O₃-TiB₂ system were researched. The effects of all factors on properties of the product were tested in this paper. The microstructure and mechanical properties (density and compressive resistance strength) were reported. It is learnt from the study that the relation between the open porosity and the pore size does not exist, the former depends on the green density, and the latter depends on the particle size of the aluminum powder. The porous ceramic composite with porosity is ranged from 45% to 68%, pore size is ranged from 1um to 400um, and the compressive strength is about 9.5 MPa. SEM observations of fracture surface suggest that the fracture mode is brittle fracture, and the microstructures of the porous of ceramic composite is very homogenous.

Abstract: Porous potassium niobate (KNbO₃, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g₃₃ constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Abstract: Porous ceramics were produced by mixing clay and ash of sago waste from the sago processing industry in Indonesia. The composition was prepared by adding an amount from 0 to 40 wt% of ash into the clay, and then the samples were milled for 6 h. The samples were dry pressed and sintered in the temperature range between 900°C and 1300°C. The influence of the ash content and the sintering temperature on the bulk density, firing shrinkage, and porosity was studied in detail. The results show that an amount of 10 wt% ash can be incorporated into the clay material without any appreciable effect on the bulk density and porosity of the samples sintered at 1000°C. It was found that if the amount of ashes is greater than 20 wt% and the sintering temperatures are lower than 1100°C, then the percentage of the porosity is greater than 30%. These results are important for optimization of the parameters of the technological processes for production of porous ceramics for various applications, each of which requires a specific porosity.

Abstract: Using tetraethoxysilane, aluminum nitrate and aluminum fluoride as raw materials, the precursor of mullite was prepared by sol-gel process. When the precursor sintered at 1200°C, mullite ceramic was obtained. Differential thermal analysis, X-ray powder diffraction and scanning electron microscope were used to characterize the dried mullite gel and ceramic blocks. The results suggest mullite is synthesized by solid-phase reaction mechanism. X-ray powder diffraction indicates mullite is the main crystals phase in the ceramic specimen. SEM micrograph shows the mullite grains in the shape of short rod with length of 20 um when sintered at 1200 °C for 2 h and the grains grown up to acicular with length of more than 50 um when the treating time under 1200 °C achieved to 4 h.

Abstract: In order to develop porous ceramics with high strength and corrosion resistance as the support for the preparation of asymmetric ceramic membranes, porous ZrO₂-Al₂O₃ composite is designed and fabricated by adding Zr(OH)₄.as sintering aid. The content of Zr(OH)₄, the sintering temperature and the bending strength before and after corrosion of the composite are discussed. The results shows that 10wt% ZrO₂-10wt% Zr(OH)₄ -80wt%Al₂O₃ composite bar fabricated by cold press with the porosity of 32% can be fabricated in 1550°C for 4 h. The bending strength of the composite is 111.2MPa. After corrosion, the quality lose and the bending strength lose is no more than 1%. The tubular composite is suit for the preparation of micro-filtration membrane.

Abstract: This paper presents the results of synthesizing porous Si₃N₄-glass composite with Y₂O₃ as additives by combustion synthesis. The effect of glass content on the final morphology was investigated in detail. The results reveal that the final morphology of products is depended on the glass content. With the increasing glass content, the porosity of the composite is decreasing and the highest strength is obtained when the glass content is 2wt%.

Abstract: Biomorphic silicon carbide (bioSiC) was prepared by high temperature pyrolysis and sol-gel and carbothermal reduction processing at 1600 oC. The morphology and microstructure of carbon-silica composites and purified bioSiC samples were characterized by scanning electron microscopy. The phase composition of the resulting sample was analyzed by X-ray diffraction. The results suggest that the bioSiC mainly consists of cubic ß-SiC, and principally replicates the shape and microstructure of the carbon template.

Abstract: The object of the research was to compare the corrosion resistance of three types of multioxide technical ceramics in hydrofluoric acid containing aqueous media according to a full factorial experimental plan with pH and fluoride ion concentration as variables. The samples were a silicon carbide doped aluminum silicate material, and two membrane coated aluminum silicates with one containing a membrane on both sides of the ceramic plate. The substrates contained more additives on alumina, while the membrane coats were of higher grade aluminum oxide. The samples were shaken in containers for up to two weeks, and their remaining hardness and weight losses were measured. Daily samples drawn from the liquid phase were analyzed for dissolved components. With respect to all measured properties, fluoride concentration affected the materials more detrimentally than alterations in pH.

Abstract: High performance porous structural ceramics have been widely studied. Silicon nitride is an interesting material for this application because bodies with high mechanical strength, achieved as a result of “in situ” anisotropic grain grown, can be obtained. In this study, Si3N4 bodies with different porosity related aspects (percentage, morphology, etc.) are made using the sacrificing template method, by changing the percentage (vol%) and the drying method of the mixture as well as the sintering time. The porosity, apparent density (Archimedes method), microstructure (SEM) and the mechanical strength (in compression) of these bodies were determined. It was thus possible to relate the type and amount of starch with the porosity and mechanical properties of the bodies.

Abstract: This work deals with the preparation and characterization of macroporous alumina ceramics and permeable laminates with a stepwise (layerwise) porosity gradient in the range of approx. 20–50 %. Layered structures are made by sequential casting and draining of ceramic suspensions containing corn starch (median size approx. 14 micrometers), using both traditional slip casting (TSC) and starch consolidation casting (SCC). In both techniques starch acts as a poreformer, which is eliminated during firing. The influence of the alumina concentration and starch content in the suspension on the porosity, pore size and pore connectivity in the individual layers is studied. It is shown that differential shrinkage of the layers in the case of SCC, caused by the different starch content, may be avoided by controlling the alumina content. The distribution of pore throat diameters (cell window sizes) is determined by mercury porosimetry, whereas the distribution of pore cavity diameters (cell sizes) is measured by microscopic image analysis.