Key Engineering Materials Vols. 602-603

Abstract: One of the materials with high potential for application as a refractory material is aluminum oxynitride with spinel-type structure, γ-alon. Alon materials, single-phase or composites, are characterized by good mechanical properties, high thermal shock resistance and a high corrosion and erosion resistance. Another advantage is possibility of usage of SHS method for producing of relatively good sinterable powders of γ-alon, however, are characterized by poor compressibility. This paper describes a method of compaction of SHS-derived γ-alon powder using the hydrolysis reaction of aluminum nitride, which is one of the products of SHS synthesis. The green bodies made from the powder with addition of 10 mas.% of water after two weeks of storage reach a strength level up to 30 MPa and an open porosity of less than 30%. Pressureless sintering of the such compacts allows to achieve 95% of theoretical density at 1700°C in less than one minute.

Abstract: 2.5D and needle-punched performs of silica fiber were studied in the paper,pore structures and slurry diffusion were studied. Mechanical properties of two prefoms composites were different,and influence of pore structures and volume fraction on performance of composites were researched.The results indicated that 2.5D composites had obvious advantages on tensile properties.But needle-punched composites had isotropic properties in their plane ,that were better than 2.5D composites which had anisotropic properties. Needle-punched composites had obvious advantages on compression properties,which overcomed compression strength of was weaker 2.5D composites in some direction.

Abstract: Industrial solid residues and poor quality clay as main raw material were used to prepare porous ceramic balls by ceramics process with coal and wood powder as pore-forming additive to improve the porosity of the ceramics ball. Effect of pore-forming additive on the properties of ceramic ball was investigated. The phase composition and section morphology of the ceramics balls was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The apparent porosity and crushing force of the ceramic balls were tested by Archimedes hydrostatic weighing method and crushing strength tester respectively. The tested results showed that the apparent porosity of the porous ceramic balls mainly influenced by species and addition amount of the pore-forming additive. The apparent porosity increases with the adding of the pore-forming additive. The apparent porosity and crushing force of the optimized porous ceramic balls was 49.68% and 1.17 kN respectively, which is a potential candidate used for waste water filtration.

Abstract: This paper describes the process of fabricating porous carbon preform by casting the camphene based charcoal slurry. Five kinds of slurry with different solid content varied from 20vol% to 40vol% has been prepared, we have studied the rheological behavior of slurries and the sublimation behavior of casted bodies. Porous carbon preform with negligible linear shrinkage (<0.6%), high porosity (>67vol%) and interconnected pore structure has prepared.

Abstract: Using quartz, feldspar as raw material, charcoal as pore-forming agent, adding CaSO₄, Na₂CO₃, kaolin, KCl, LiF and NaF as fluxing agent respectively, quartz micro-porous ceramic matrices were prepared for inorganic salt/ceramic composite phase change energy storage materials. The effect of different fluxing agents on basic performance of porous ceramics and infiltration process were researched. The research shows that NaF can improve the strength of porous ceramics as fluxing agent, and have little impact on high temperature mechanical strength of Na₂SO₄/SiO₂ phase change energy storage materials. When the mass ratio of quartz, feldspar and charcoal is 7:2:1 and NaF is 1 wt% of them, the quartz porous ceramics have good performance as follows: the apparent porosity is 53.74%, the bulk density is 1.19 g/cm³, the compressive strength is 10.1 MPa, the average pore size is 12.53 μm, molten salt infiltration rate is 50.02 %, and the molten salt leakage rate is only 0.42 ‰ after 20 times of thermal loops.

Abstract: In this study, the environment-friendly egg white protein was used as foaming agents and binders to fabricate Al2O3 ceramic foams, owing to its excellent foaming and binding properties. The CaO-SiO2-MgO-ZnO-TiO2-B2O3 composite sintering additive was added into Al2O3 ceramic foam to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering. The modified Al2O3 ceramic foam was investigated on porosity, density, compressive strength, pore morphology and grain size. The investigation revealed that: compared with ordinary Al2O3 ceramic foam, although the samples adding sintering additive had lower porosity, larger density and bigger grain, its compressive strength was significantly much stronger than samples without sintering additive. The XRD result indicated that samples adding sintering additive had spinel, anorthite and a small amount of mullite phase besides the main corundum phase. Adding sintering additive is a new way to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering which can help grain growth, thereby improving the mechanical properties of Al2O3 ceramic foam.

Abstract: Low fracture toughness of SiC ceramics limits their applications for the low reliability. Inclusion of second ceramic phase improves the toughness of SiC ceramics. In this presentation, SiC ceramics with 5wt% TiC was pressureless liquid phase sintered (LPS) with the additives of Al₂O₃ and Y₂O₃ to ~98% theoretical density at the temperature of 1920 °C for 1 hour. The TiC grains were well distributed and good for the uniform distribution of the liquid phase YAG in the SiC matrix, which resulted in the homogeneous microstructure with fine SiC grains. The existence of TiC benefited the formation of elongated α-SiC, which favored the bridging and deflection of cracks so that the fracture toughness was improved to some extent. Because the amount of TiC was so small that the inherent properties of SiC was not degraded. The flexural strength and Vickers hardness maintained similar with the LPS SiC without TiC. The phase compositions detected in the sample were SiC, YAG and TiC. And no solid-solution of SiC and TiC was revealed by the mapping of EDS.

Abstract: The effect of Al₂O₃ and SiC as the sintering additives for pressureless sintering boron carbide (B₄C) was investigated. The aids were 10 wt% Al₂O₃ (10A), 10 wt% Al₂O₃ and 15 wt% SiC (10A15S), 10 wt% Al2O3 and 30 wt% SiC (10A30S), and 30 wt% SiC (30S) (all based on B₄C). The sintering behavior, microstructure evolution and phase compositions of the samples were studied. 10A15S and 10A30S can effectively enhance the densification of B₄C, comparing with 10A and 30S. The linear shrinkage rate of 14% for the 10A15S and 10A30S samples can be reached. The bending strength approaching 400MPa for the 10A30S sample sintered at 2170°C can be obtained.

Abstract: Mesoporous and macroporous mullite ceramics were fabricated from pyrolysis of alumina nanopowders filled silicone resin. The effect of pore-forming agent (carbon nanopowders) on the pore structure and mechanical property of the porous mullite ceramics were investigated. By varying the carbon content, the porosity and flexural strength of the obtained ceramics could be easily tuned. Both of the open porosity and average pore size of the obtained samples increased at elevated carbon content, and reached the maximum value of 61.0%, 225.5 nm respectively when the carbon content got the highest point (40 Vol.%). The flexural strength of nanoporous mullite ceramics changed almost with an opposite trend of open porosity, with the biggest value of 36 MPa when 10 Vol.% carbon was adopted. The microstructure of porous mullite ceramics consists of dense region and loose region when the added carbon content was at relatively low level. However, the dense area gradually disappeared with the increasing of carbon content.

Abstract: The yttria-doped mesoporous zirconia was successfully synthesized by evaporation induced self-assembly (EISA) method, and the microstructure and textural properties of the as-made product were studied extensively. The results showed that the as-made product possessed crystallized framework walls and a worm-like mesopore with a narrow pore distribution. The BET specific surface area and pore volume of the as-made product calcined at 500°C are 111 m²/g and 0.16 cm³/g respectively, and the corresponding data changed to 73 m²/g and 0.052 cm³/g after calcined at 700°C, which indicated that the as-made yttria-doped mesoporous zirconia possess a higher thermal stability.