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81.
《Journal of the European Ceramic Society》2014,34(11):2687-2694
The spallation resistance of an air plasma sprayed (APS) thermal barrier coating (TBC) to cool-down/reheat is evaluated for a pre-existing delamination crack. The delamination emanates from a vertical crack through the coating and resides at the interface between coating and underlying thermally grown oxide layer (TGO). The coating progressively sinters during engine operation, and this leads to a depth-dependent increase in modulus. Following high temperature exposure, the coating is subjected to a cooling/reheating cycle representative of engine shut-down and start-up. The interfacial stress intensity factors are calculated for the delamination crack over this thermal cycle and are compared with the mode-dependent fracture toughness of the interface between sintered APS and TGO. The study reveals the role played by microstructural evolution during sintering in dictating the spallation life of the thermal barrier coating, and also describes a test method for the measurement of delamination toughness of a thin coating. 相似文献
82.
Various zinc oxide nanostructures were synthesized using thermal decomposition of zinc acetate dihydrate in a single process. The characterization of samples using powder X-ray diffraction, scanning electron microscope and FT-IR measurements revealed that the pure phase of different morphologies such as nanoparticles, nanowires and nanodisks had been synthesized successfully. Surprisingly some synthesized ZnO nanostructures were dark gray. The results showed that the reason may have been related to the oxygen deficiency and strong asymmetric stretching mode of wurtzite ZnO nanostructure. Using such samples, the photodegradation of Methylene blue was performed by UV–vis absorption measurement and the effect of morphology on the photocatalytic properties of different ZnO nanostructures was examined. The results showed that the nanodisks had the best photocatalytic performance among the other morphologies. The reason was attributed to the presence of specific crystal planes such as (0001) facets in nanodisks which can improve their photocatalytic performance. 相似文献
83.
Contrarily to conventional sintering (CS) method where longer cycles and high temperature (1400–1500?°C) are applied to sinter yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics, this work presents a faster and low temperature (1175?°C) way through hot pressing (HP) to produce full densified zirconia with good mechanical and tribological properties. This work is concerned with the influence of sintering pressure on the microstructure and tribological properties of hot-pressed Y-TZP. For this purpose, four sintering pressures 5, 20, 60 and 100?MPa were tested. The wear tests were carried out by reciprocating ball-on-plate as a simplified test for tooth-to-restorative material contact under 37?°C using artificial saliva to mimic oral conditions. The results demonstrated that density, hardness and tribological properties are strongly influenced by the sintering pressure, namely an improvement with pressure increase was achieved. The highest density, hardness values and wear resistance were achieved for Y-TZP samples produced at P?=?100?MPa. Furthermore, it was revealed that a smaller grain size for Z100 samples (full densification condition) was achieved comparatively to conventional-sintered Y-TZP. This work proves that it is possible to produce dense Y-TZP materials under low sintering temperature and faster cycles with reduced grain size without compromise mechanical and tribological properties. 相似文献
84.
Two-step sintering behavior of titanium-doped Y2O3 ceramics with monodispersed sub-micrometer powder
Two-step sintering of titanium-doped Y2O3 was carried out using monodispersed sub-micrometer powder. The effect of titanium dopant concentration on the sinterability and kinetic window of constant grain-size sintering were examined. The titanium doping improves the sinterability of the Y2O3 powder, which broadens the sintering kinetic window and lowers sintering temperature. The Vickers hardness was also enhanced as the doping concentration of titanium was increased, assuming the same grain size. 相似文献
85.
In this study, the effect of sintering parameters on densification and fracture toughness of spark plasma sintering ZrB2-SiC nanocomposites was evaluated. For this purpose, ZrB2-??30?vol% SiC nanocomposites in the conditions of ?1600?°C-4?min, 1700?°C-4?min, 1800?°C-4?min, 1800?°C-8?min, 1800?°C-12?min? were sintered.? Scanning Electron Microscopy (SEM) was used in order to investigate the ?microstructural variations. The bulk density was measured accoring to ASTM C 373–88. Single edge notch beam (SENB) method was used to ?determine the fracture toughness of samples. Microstructural observations showed that ?an increase in sintering temperature led to slight ?increase in SiC grains size but no sensitive variation in ZrB2. However, increasing the sintering time resulted to increase both ZrB2 and SiC grain size. Also, it was found, temperature and time ascent always increases the relative density. In addition, it was concluded that optimal temperature and time to reach the highest fracture toughness are 1800?°C and 8?min, respectively. Investigation of SEM images of the Vickers indent and their path propagation showed that the deviation and branching of crack are the most important toughening ?mechanisms in ZrB2-SiC nanocomposites.? 相似文献
86.
《粉末冶金学》2013,56(2):154-159
AbstractIn order to optimise process variables during the synthesis of tin nanophase particles in an inert gas condensation (IGC) chamber, a two-dimensional finite difference method (FDM) simulation on convection gas currents is proposed and calculated for various boundary conditions. The convection gas velocity and temperature for the 95×105 positions in the chamber were calculated by simulation and compared with experimental results. In the FDM simulation, the governing equations consisted of continuity, momentum, and energy equations. The effects of convection gas pressure, evaporation temperature, position of the evaporation source, and chamber size on the formation of convection currents were investigated by the FDM simulation and experiments. It turned out that among various process variables, the convection gas pressure played the most important role in the formation of the convection gas current that gave rise to an impact on the shape and size of synthesised tin nanophase particles. 相似文献
87.
《Journal of the European Ceramic Society》2021,41(13):6559-6566
This paper reports on a method for producing ceramics from a high-purity, submicron InGaO3(ZnO)2 powder synthesised using a PVA-assisted gel combustion method, as well as an experimental study of the thermophysical properties of the ceramic materials obtained. The platelet-like crystallites of the InGaO3(ZnO)2 obtained were several microns long and up to several hundred nanometres thick. Layered ceramics obtained by sintering compacted InGaO3(ZnO)2 powders at temperatures of 1373–1773 K had a bulk density that was 68–96 % of the theoretical density. The temperature dependence of heat capacity in the range 306–1346 K was studied experimentally for InGaO3(ZnO)2 using the DSC method. It was found that, in the range 323–1173 K, layered InGaO3(ZnO)2 ceramics had a low thermal conductivity, which decreased from 2.0–1.3 W/(m K. The results obtained make it possible to consider this material as a promising thermal barrier coating. 相似文献
88.
E.N. Lysenko V.A. Vlasov A.V. Malyshev E.A. Sheveleva A.P. Surzhikov 《Ceramics International》2021,47(17):23935-23941
The effect of dry and wet ball milling of LiFe5O8 ferrite powder on the microstructure and electromagnetic properties of ferrite ceramics was studied using XRD analysis, scanning electron microscopy, dilatometry, thermogravimetry, calorimetry, and measurement of specific magnetization and electrical resistance. The sintering temperature was 1050 °C; the sintering time was 2 h. It was found that ferrite fabricated from dry-milled powder exhibits an ordered α-LiFe5O8 phase with bulk density of 91%. Its saturation magnetization and Curie temperature are 55 emu/g and 628°С, respectively. Specific electrical resistance is 4?106 Ω cm. Wet milling in isopropyl alcohol causes formation of a disordered β-LiFe5O8 phase. Ceramics produced by this method shows higher bulk density (97%) and low porosity, and an order of magnitude lower resistivity. Its saturation magnetization and Curie temperature are 51 emu/g and 607°С, respectively. 相似文献
89.
Nan Wu Xiaodong Li Mu Zhang Yi Ren Qi Zhu Haijun Peng Hongqiang Ru Xudong Sun 《Journal of the European Ceramic Society》2021,41(4):2898-2907
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density. 相似文献
90.
D. Kherifi H. Belhouchet S. Ramesh K.Y. Sara Lee A. Kenzour S. Djoualah M.K.G. Abbas Y.H. Wong S. Ramesh 《Ceramics International》2021,47(12):16483-16490
In this work, the sintering behaviour of fluorapatite (FAp)–silicate composites prepared by mixing variable amounts of natural quartz (2.5 wt% to 20 wt%) and FAp was studied. The composites were pressureless sintered in air at temperatures from 1000 °C to 1350 °C. The effects of temperatures on the densification, phase formation, chemical bonding and Vickers hardness of the composites were evaluated. All the samples exhibited mixed phase, comprising FAp and francolite as the major constituents along with some minor phases of cristobalite, wollastonite, dicalcium silicate and/or whitlockite dependent on the quartz content and sintering temperature. The composite containing 2.5 wt% quartz exhibited the best sintering properties. The highest bulk density of 3 g/cm3 and a Vickers hardness of >4.2 GPa were obtained for the 2.5 wt% quartz–FAp composite when sintered at 1100 °C. The addition of quartz was found to alter the microstructure of the composites, where it exhibited a rod-like morphology when sintered at 1000 °C and a regular rounded grain structure when sintered at 1350 °C. A wetted grain surface was observed for composites containing high quartz content and was believed to be associated with a transient liquid phase sintering. 相似文献