Papers by Keyword: Porous Ceramics

Abstract: Highly porous silica ceramics were prepared by in-situ gelation of an aqueous suspension with well dispersed silica particles and N’N-dimethylacrylamide (DMAA) monomer, followed by lyophilization and pressureless sintering. The gelcasting process was imparted by polymerization of DMAA. The silica raw materials used in this experiment are the dusts collected from the exhaust fumes of silicon industry. The as-obtained porous silica ceramics had three-dimensional and hierarchical pore structure and the porosity ranged from 75 to 88 % as the sintering temperature varied from 850 to 1050 °C. In addition, the porous silica ceramics appeared to have strong mechanical strength. Compressive strength of the porous silica ceramics was as high as 3.2 MPa even when the porosity was nearly 80%. The gelcasting-lyophilization method was proved to be a novel and promising route for the preparation of highly porous and mechanically strong materials.

Abstract: Magnesium aluminate spinel (MgAl₂O₄) porous ceramics were in-situ synthesized by heating the mixture of Al₂O₃ and MgCO₃ with MgCl₂ salt at 1400~1600 °C for 3 h, and then characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The morphology of as-prepared MgAl₂O₄ porous ceramics was dependent on the addition of MgCl₂, and it indicated that the MgCl₂ molten salt not only acted as a template for pore formation of the porous ceramics, but also provided a liquid environment for the synthesis of MgAl₂O₄.

Abstract: In this work, Ti₂AlN porous ceramics was made by the organic foam impregnation. High-purity Ti₂AlN powder was sintered at 1300 °C for 2 h of Ti/1.1Al/TiN in stoichiometric proportion. The slurry solids of organic foam impregnation method was 60 %, using 2 % polyacrylamide as dispersant, 0.5 % polyvinyl alcohol as a binder and 0.5 % ethanol as defoaming. The polyurethane sponge was pre-treatment for 6 h with 15 % NaOH solution and soak for 24 h with 4 % of carboxymethyl cellulose (CMC) solution. Through the pre-treatment, the polyurethane sponge hangs pulp quantity is higher, and the percentage of plugged hole is the lowest. The Ti₂AlN porous ceramics is relatively uniform open holes with three-dimensional skeleton structure. This study can generate to the studies of the preparation of the mesh structure products and the preparation of ceramic matrix composites by pressureless infiltration process.

Abstract: Yttrium aluminum garnet (YAG) with a chemical composition of Y₃Al₅O₁₂ is an important advanced structural and functional material due to some excellent properties. The porous YAG ceramics were prepared via vacuum sintering technology, the effect of sintering aids on the properties of porous YAG ceramics were investigated in this paper. Through an analysis and discussion, the conclusions are that the porosity increases with the increasing sintering temperature from 1300°C to 1500°C, the pore is moved to the surface of sample, which forms the open pore to make the porosity increase, the more and bigger sintering neck is increased. Porous YAG ceramics are sintered at 1500°C, the regular outside shapes of porous YAG ceramic are kept using CaO and MgO as sintering aids, the outside shape of porous YAG ceramic is wrecked using Al₂O₃ as sintering aids, which shows the over fired phenomenon.

Abstract: It is shown that the organization of co-current flow of the reacting gas during combustion synthesis of porous oxynitride materials leads to intensification of the process. The flow creates favorable conditions for directed heat and mass transfer in reacting media. It results in super-adiabatic heating of the products in the area of the combustion wave. Thus, macrokinetic parameters of the combustion synthesis exceed 10 % than the ones that had been obtained without forced filtering of gaseous reactant. Organization of the process in flowing of the reacting gas allows us to obtain materials with conversion ratio up to 0.95 under the combustion rates up to 0.8 mm/s and maximum temperature in the combustion wave up to 1900 °C.

Abstract: YAG is an important advanced structural and functional material. The mechanism of controlling pore microstructure of YAG porous ceramics were investigated in this paper. Through the porosity and SEM result analyzing, the conclusions are shown as follows, the porosity and the pore size of YAG porous ceramics are decreased with increasing the sintering temperature, the pores of YAG porous ceramics show a regular and well-distributed structure as lower sintering temperature, the porosity of YAG porous ceramics is increased with increasing the foaming agent content, but the increasing tendency is few after adding content more 15wt%, when the foaming agent content is less than 15wt%, the big pore is more and the pore microstructure is better. So the sintering temperature at 1500°C for 1 hour and the foaming agent content for 15wt% are better controlling conditions for obtaining better porosity and pore microstructure.

Abstract: Porous ceramics was successfully fabricated by a sacrificial porogen leaching method using in-situ synthesised aluminium based binders by reaction bonding at low sintering temperatures of 600-1000°C. Porous ceramics with porosity in the range of 27 to 65% were obtained by leaching technique. Interconnected bimodal pores were produced by both stacking of starting particles and leach out of salt. During sintering, the aluminium binder experienced metal to ceramic transformations and act as good binder.

Abstract: This study examined the feasibility of utilizing lignite bottom ash as a partial substitute for ball clay in an insulating brick composition. Lignite bottom ash is a waste byproduct that is high in alumina and silicates and is therefore a candidate material for replacing aluminosilicate minerals such as clay. The lignite bottom ash powder was obtained from the Mae Moh power plant, Thailand. Small brick specimens were produced by die pressing a mixture of lignite bottom ash, ball clay and aluminum hydroxide. The composition of the mixture contained a fixed amount of aluminum hydroxide, while the lignite bottom ash replaced from 30 to 70% of the ball clay. The pressed samples were sintered at 1300 oC for 1 hour in air. The density, porosity, strength and thermal properties of the samples were measured. A microstructural analysis of the sintered brick was also performed. It was found that the porosity of the samples increased from 35 to 45% with increased lignite bottom ash content. The modulus of rupture and the thermal conductivity of the bricks were reduced with increased lignite bottom ash content, likely due to the increased amount of porosity. Dilatometric analysis found that the thermal expansion increased with increased amounts of lignite bottom ash, possibly as a result of an increased amount of glassy phase. Despite the high thermal expansion coefficient at high temperature, the feasibility of using lignite bottom ash in the insulating brick composition was demonstrated.

Abstract: Electrophoretic deposition (EPD) with controlled gas evolution by electrolysis was used for producing ceramic green bodies with unidirectional pore channels. The method was applied to alumina, alumina-toughened zirconia, and mullite. It requires stable aqueous suspensions with sufficiently high particle charge for the electrophoresis and appropriate amounts of electrolyte for the gas bubble formation. An anionic polyelectrolyte and ammonia were shown to be a suitable additive combination for all three oxide powders. The amount of polyelectrolyte was chosen for each of the powders on the basis of electroacoustic measurements of the zeta potential. The addition of ammonia solution was necessary in order to obtain the desired porous structures.

Abstract: The high dielectric constant of Si₃N₄ ceramic limited its application as wave-transparent materials, thus Si₃N₄ ceramics always been prepared as porous ceramics to enhance the properties of wave transparent. While the mechanical properties would be declined in this way, so the BNNTs were used to improve the properties of the composites in this paper. The porous BNNTs/ Si₃N₄ composites were prepared by normal pressure sintering in nitrogen atmosphere. Then the effects of sintering temperature and contents of BNNTs to Si₃N₄ porous ceramics and composites were investigated. The results show that the Si₃N₄ phase was transformed to β-Si₃N₄ completely when the sintering temperature was raised to 1750°C. The BNNTs and rod-like β-Si₃N₄ guaranteed the considerable mechanical properties of the composites, and the mechanical properties increased with the increase of the sintering temperature and the addition of the BNNTs. When the sintering temperature was 1750°C and the content of BNNTs was 0.5wt.%, the porosity and density of the composite are 35% and 2.0g/cm³, respectively. While the flexural strength and the elastic modulus of the composite are 231.8MPa and 62.04GPa, respectively.