Key Engineering Materials Vol. 633

Abstract: Ceramic supports were prepared by isostatic pressing, and were compared with commercially available ceramic support by extrusion molding process. Results show that structures of section, inner surface and outer surface keep uniform, and the pore is obvious in section, also on the inner surface and outer surface. While supports by extrusion molding process show great differences between internal and surface in structures. During the extrusion molding process, the orientation and rearrangement phenomenon of particle and powder occur obviously under the action of friction and boundary effect, which make pores on the surface blocked seriously. The ceramic support prepared by isostatic processing technology will show better filtration efficiency relatively compared to that by extrusion molding process.

Abstract: Nb₂O₅-7.5La₂O₃-Al₂O₃ composite ceramics were prepared by microwave sintering. The influence of Nb₂O₅ and La₂O₃ proportion on the microstructure and mechanical properties of Al₂O₃ ceramics was investigated. The results show that when the Nb₂O₅ content was lower than La₂O₃, the columnar LaAl₁₁O₁₈ grains were generated by the reaction of La₂O₃ with Al₂O₃. When the Nb₂O₅ content was higher than La₂O₃, the surplus Nb₂O₅ induced the formation of columnar Al₂O₃ grains. The growth of columnar Al₂O₃ grains were promoted synergistically by LaNbO₄ formed in-situ and Nb₂O₅. The 5Nb₂O₅-7.5La₂O₃-Al₂O₃ composite ceramic exhibited excellent comprehensive properties: ρ_r=99.3% (relative density), HV=11.2GPa (microhardness), K_IC= 6.4MPa·m^1/2 (fracture toughness), σ=304.3MPa (bending strength).

Abstract: Al-Si₃N₄-Al₂O₃ composite was prepared using tabular corundum, white fused corundum,α-Al₂O₃ fine powder and Si₃N₄ fine powder as raw materials and phenolic resin as low temperature binder under nitrogen atmosphere at 1 300 °C for 8 h. The results show that the main reinforced phase of Al-Al₂O₃ is Al₄O₄C in Al-Al₂O₃ specimens without Si₃N₄ fine powder adding,the main reinforced phase of Al-Si₃N₄-Al₂O₃ is SIALON while small quantity of Al,Si plastic phase presents in Si₃N₄ adding Al-Al₂O₃ specimens. Si₅AlON₇(Z=1) is formed in Al-Si₃N₄-Al₂O₃ specimens at low temperature (1 300 °C), which presents good comprehensive properties.

Abstract: TiN-Sialon-Corundum composites were synthesized from rutile and quartz by aluminothermic reduction nitridation (ARN) method. The effects of aluminum contents on the phase behavior and properties of products were investigated. At 1500 oC, the main phases of products ARNed for 4 h were large granular corundum, TiN and hexagonal columnar Si₃Al₃O₃N₅. In addition, small TiN crystal particles distributed around the Si₃Al₃O₃N₅. It suggested that TiN-Sialon-Corundum composites were successfully fabricated by ANR method at 1500 °C for 4h. With increases in the amount of aluminum contents, the compressive strength ,the flexural strength and the bulk density of the composite refractory increased while the apparent porosity decreased. When the the aluminum contents increased to 48.90%, the composites had the highest compressive strength (47.34MPa) ,flexural strength (27.70MPa), bulk density (2.27 g/cm³) and had the lowest apparent porosity (27.57 %).

Abstract: Cordierite samples were prepared using quartz sand tailings, industrial alumina and magnesite tailings as raw materials by high-temperature reaction. The influence of mineral composition and sintering temperature on the final phase composition and physical properties of cordierite were studied. The results shown that a large number of cordierite generated at 1300 °C. When the ratio of Al₂O₃/SiO₂ equals to 1.08, the flexural strength of samples increased to 27.66 MPa.

Abstract: Mullite material was prepared from quartz (SiO₂) and industrial alumina (γ-Al₂O₃). The effects of mineral composition and sintering temperature on the final phase composition and physical properties of mullite were investigated. The results shown that a large number of mullite phase was emerged in samples when the ratio of alumina to silica (A/S) was 2.55. At 1500 ^oC and 1600 ^oC, the flexural strength of the samples reached to 87.13 MPa and 89.50 MPa, respectively. Consider the environmental protection and energy saving, the optimal sintering temperature was 1500 °C.

Abstract: A rapid sintering densification treatment was performed on the surface of silica ceramic by using hydrogen-oxygen flame. The effects of surface densification processing on the phase composition, microstructure and bending strength of the silica ceramic were studied. Results showed that, after the densification processing, there was no obvious change in the phase composition of the silica ceramic but gradual transition structure happened. The transition structure not only prevents the abrupt structural change from the densification layer to porous layer of the silica ceramic but also guarantees the strong interface bonding between adjacent layers, leading to the improved bending strength. The present densification processing could realize the integrated fabrication of silica material with different density.

Abstract: We prepared a series of organic acids pillared layered rare earth compounds Y_2-xEu_x(OH)₅X·nH₂O (X= Organic acid) by hydrothermal reaction, The distance of layers was determined by X-ray diffraction, and discussed the relationship between the intercalated organic anion and the distance between the layers, In addition, the layered rare earth compound we prepared exhibited good fluorescence properties, being excited by ultraviolet light, the layered compound exhibited characteristic fluorescence spectra of Eu³⁺ ions. But the fluorescence intensity of the layered compound changed with different intercalated organic anions, by the ratio of the electric dipole transition and magnetic dipole transitions (⁵D₀-⁷F₂)/ (⁵D₀-⁷F₁), we studied the coordination environment of the luminescent center. And discussed the relationship between intercalated organic anions and fluorescence intensity.

Abstract: The Ce_0.5Zr_0.5O₂ nanocomposites (CZ) were prepared by co-precipitation(CP), fractional precipitation (FP) and fractional precipitation with hydrothermal treatment (FP-HT). The samples were characterized by X-ray diffraction (XRD), Brunauer-Emmet Teller method (BET), H₂-temperature programmed reduction (H₂-TPR), and thermogravimetric analysis (TG) under H₂-N₂. XRD results displayed that all samples formed a single solid solution-like ceria-zirconia phase. BET results revealed CZ prepared by FP-HT (CZ-FP-HT) had the highest surface area. H₂-TPR and TG analysis under H₂-N₂ showed CZ-FP-HT exhibited the strongest redox ability and oxygen storage capacity. Moreover, three-way catalysts of Pd-Rh supported on CZ -FP-HT and commercial CZ with same composites were prepared, and their three-way catalytic activity were also studied by engine evaluation. Pd-Rh/CZ-FP-HT showed a bit of higher oxygen storage capacity, catalytic activity and better thermal stability than Pd-Rh/CZ-commercial.

Abstract: The present review will try to sum up the research on the microstructure and properties of the Ti(C,N)-based cermets materials in recent years. Firstly, the development history, the microstructure and mechanical properties of Ti(C,N)-based cermets, and the relationship between Ti(C,N)-based cermets microstructure and their properties were introduced respectively. Secondly, Compared with different microstructure and properties of Ti(C,N)-based cermets material which were made by different composite constituent. Furthermore, the relationship between mechanical properties of Ti(C,N)-based cermets and sintering method was introduced. Results show that the high performance products can be produced by means of fast sintering techniques at low temperature successfully, such as spark plasma sintering technology. However, the most widely used way is vacuum sintering method. Lastly, the development trend of Ti(C,N)-based cermets were included.