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71.
《Journal of the European Ceramic Society》2020,40(2):417-426
Nacre-like alumina manufactured using spark plasma sintering shows a strikingly different mechanical behaviour compared to conventional alumina. A range of sintering conditions were applied to micron-sized alumina platelet powders to form alumina with different nacre-like microstructures, density, grain size and flexural strength. We show that a microstructure of aligned sintered platelets not only mitigates the typical issue of brittleness, but also has extraordinary energy absorption capabilities. It can withstand an impact with up to three times the kinetic energy required to break monolithic alumina while maintaining structural integrity. The high-rate compressive strength is shown to be more than 50% higher than that of monolithic alumina and we show energy absorption mechanisms such as crack deflection and branching to be present. Our approach provides a fast and effective way of manufacturing aligned nacre-like ceramic microstructures that maintain structural integrity through energy dissipation and interlocking mechanisms. 相似文献
72.
《Journal of the European Ceramic Society》2020,40(14):4837-4843
Fused filament fabrication (FFF), as one of the additive manufacturing technology, provides cost-effective and relatively fast preparation of 3D objects of desired dimensions and design. In this work, a composite filament containing 50 vol. % of sub-micron alumina powder was successfully used for the manufacturing of samples with prismatic design. The influence of the layer thickness (0.1–0.3 mm) on the final bulk density and mechanical properties were investigated. Sintering at 1600 °C for 1 h results in relative densities ranging from 80 to 89 % and the flexural strength reached 200–300 MPa depending on the layer thickness used for the printing. 相似文献
73.
《Journal of the European Ceramic Society》2020,40(13):4536-4538
Single crystal sapphire was synthesized by chemical transport of Al-O generated by the reaction of polycrystalline Al2O3 ceramic and carbon. Using C-axis oriented polycrystalline Al2O3 ceramics as a seed crystal in the deposition temperature range, a C-axis sapphire crystal (Φ5xL35 mm) was grown at a temperature range of 700–1000 °C, and the growth rate in the C-axis direction was about 3.5 mm/h. The transmittance in the visible to infrared region of the synthesized sapphire is a theoretical value (transmission loss is lower than 0.1 %/cm), and the absorption edge was less than 200 nm (the band gap is 6.2 eV), which is shorter than the absorption edge (240 nm) of the commercially available single crystal (band gap 5.2 eV) synthesized by the Czochralski method. The dislocation density in this material was extremely low, and it was confirmed by lattice image observation that it was a high-quality single crystal with very few defects. 相似文献
74.
《Journal of the European Ceramic Society》2020,40(15):5504-5510
Dense alumina ceramics doped with 5 wt% 4CuO-TiO2-2Nb2O5 composite sintering aids were obtained at low sintering temperatures of 950∼975 °C. The ceramic sintered at optimal condition shows good microwave dielectric properties (εr = 12.7, Q × f = 7400 GHz), high thermal conductivity (18.4 W/m K) and high bending strength (320 MPa). TEM and EDS analysis revealed that amorphous Cu-Ti-Nb-O interfacial films with nanometer thickness formed at the grain boundaries, which could provide paths of mass transportation for densification. Al3+ ions may be involved in mass transportation through substitution by Ti3+ and Ti4+ ions near the grain boundary during the sintering process. The accumulation of copper ions at the trigeminal grain boundary was observed. The migration and reaction of copper ions in grain boundaries may also play an important role in promoting mass transportation and low-temperature densification of alumina ceramics. 相似文献
75.
《Ceramics International》2020,46(8):12275-12281
Alumina and zirconia ceramic particles exhibit high hardness and excellent wear resistance at high temperature, and hence are used as ceramic reinforcement phases in some plasma sprayed coatings. In this study, the interface evolution of a zirconia/alumina eutectic ceramic and the phase transition of zirconia in a plasma-sprayed coating were investigated. Scanning electron microscopy and transmission electron microscopy combined with focused-ion beam and energy dispersive X-ray were used to analyze the microstructure and composition of the ceramic interface. The results showed that the eutectic ceramic particles consisted of alumina (outer) and columnar zirconia (inner) before and after the plasma spraying process. The inner zirconia part showed the martensitic transformation of t-type zirconia to stripe-like m-type zirconia. After the plasma spraying, the interface between alumina and zirconia changed significantly, which formed a new oxide layer. The phase transition mechanism in the ceramic particle and oxide layer formation mechanism at the alumina/zirconia interface were investigated. 相似文献
76.
77.
介绍了以烧结刚玉和板状刚玉为原料试制再结合刚玉砖的生产工艺。同时,研究了不同原料、氧化铝微粉、外加物及工艺条件对制品性能的影响。 相似文献
78.
Zinfer R. Ismagilov R. A. Shkrabina Natalia A. Koryabkina 《Korean Journal of Chemical Engineering》1997,14(3):153-161
Fluidized bed catalytic combustion has proved to be very promising for industrial application. The milestone problem is development
of support and catalyst with high mechanical and thermal stability. We have developed a new technology for production of alumina
supports with desired spherical shape, texture and structure. Properties of spherical granules depend on the method of granulation
and most attention has been paid to development and optimization of hydrocarbon-ammonia moulding to produce uniform alumina
spheres. Optimization of high quality spheres production focused on study of effect of initial hydroxide properties and molding
conditions on properties of final product. Modification of spherical alumina with oxides of Mg, La, Ce, and Si proved to be
effective to substantially improve the mechanical and thermal stability. This effect is most pronounced when, pairs of these
dopes are introduced simultaneously. 相似文献
79.
V. Hiremath 《塑料、橡胶和复合材料》2016,45(5):199-206
Nanocomposites were synthesised by dispersing two different types of alumina nanoparticles in epoxy matrix by ultrasonication. Alumina nanoparticles of two shapes, rod and spherical were selected to investigate the effect of particle morphology on viscoelastic and flexural properties of nanocomposites. Specific surface area of both the selected nanoparticles was kept in the similar range. Good dispersion of nanoparticles was observed through transmission electron microscopy. The addition of nanoparticles in epoxy had significant enhancement in the viscoelastic properties and moderate improvement in flexural properties of composites. Composites having alumina nanorods showed higher improvement both in storage modulus as well as in flexural properties in comparison to composites having spherical alumina nanoparticles. Efficacy of Mori-Tanaka method was explored in modelling storage modulus of nanocomposites. Assorted size of alumina nanorods based on particle size distribution was used to model composites with nanorods to see the effect of size assortment on storage modulus. 相似文献
80.
To improve the properties of polyimide (PI), different mass fractions of alumina (Al2O3) nanoparticles, unmodified or modified by KH550, were incorporated into PI matrix to form PI/Al2O3 hybrid films by in situ polymerisation. The effects of Al2O3 additives on the structure, dielectric and mechanical properties of the films were studied. Fourier transform infrared spectroscopy confirmed the successful preparation of PI/Al2O3 hybrid films, and the microstructures of the samples showed a more uniform dispersion of the modified Al2O3 nanoparticles than the unmodified ones in the matrix. The dielectric constant of the films increased with increasing filler content, and the maximum electrical breakdown strength of 311 MV m?1 was obtained with a filler content of 8.0 wt-% modified Al2O3 in the matrix. Both unmodified and modified Al2O3-reinforced PI hybrids demonstrated improved mechanical properties compared with the PI matrix. Moreover, the properties of films with Al2O3 modified by KH550 were better. 相似文献