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1.
High Yttria–Zirconia and Yttria Ceramics for Petrochemical Reverse‐Flow Reactor Applications
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ChangMin Chun Sanket Desai Frank Hershkowitz Trikur A. Ramanarayanan 《International Journal of Applied Ceramic Technology》2015,12(3):585-597
Reverse‐flow reactors achieve the desired hydropyrolysis reaction of natural gas and other hydrocarbon feeds at very high temperatures of up to 2000°C, which enables the production of many high‐value chemicals. To identify refractory ceramic materials suitable for constructing key components of the reactor, the full range of solid solutions between zirconia and yttria having 18 to 100 mol% yttria have been tested in a laboratory reactor. Conventional yttria‐stabilized zirconia (YSZ) materials having 8 mol% Y2O3 appear to accommodate reactor thermal severity, but are prone to a new form of corrosion termed ceramic dusting that is observed when pyrolysis and oxidation cycles are alternated under reverse‐flow conditions. Yttria and high yttria–zirconia ceramics having ~80 mol% or more yttria suppress ceramic dusting corrosion in steam‐free pyrolysis environments. The addition of low levels of steam of ~5% to the pyrolysis gas stream increases the stability of YSZ materials substantially, so that the stability threshold is closer to 40 mol% Y2O3 in the yttria–zirconia system. The two approaches can be combined to optimize reactor performance. Key experimental results are presented and discussed taking into account the thermodynamic phase stability of the different phases. 相似文献
2.
S. Giese F. Kern C.A. Macauley S. Neumeier M. Göken 《Journal of the European Ceramic Society》2019,39(13):3830-3836
Yttria stabilized tetragonal zirconia polycrystal (Y-TZP) owes its high toughness to transformation toughening, a mechanism that requires the development of a process zone. It is important to measure if and to what extent the size of components can be reduced. In this study, tests were carried out using focused ion beam or picosecond milled pre-notched, 3 mol percent Y2O3 (3Y-) TZP micro-cantilever (10–250 μm) beams. The tests show clearly that the maximum fracture resistance is size dependent and the plateau toughness was not reached in any of the small-scale samples. A correlation between transformability of the tetragonal phase and the measured fracture resistance became visible only for the largest micro cantilever but did not reach the values measured in macroscopic samples. Based on these results, it is not advantageous to use very tough zirconia materials in components with dimensions smaller than ~0.25 mm, as the high toughness is not fully realized. 相似文献
3.
Y.X. Kang Y. Bai W. Fan T. Yuan Y. Gao C.G. Bao B.Q. Li 《Journal of the European Ceramic Society》2018,38(7):2851-2862
La2Ce2O7 (LC) is receiving increasing attention due to its lower thermal conductivity, better phase stability and higher sintering resistance than yttria partially stabilized zirconia (YSZ). However, the low fracture toughness and the sudden drop of CTE at approximately 350?°C greatly limit its application. In this study, the LC/50?vol.% YSZ composite TBC was deposited by supersonic atmospheric plasma spraying (SAPS). Compared to YSZ or double layered LC/YSZ coating, the thermal cycling life of LC/50?vol.% YSZ coating with CMAS attack increased by 93% or 91%. The latter possessed higher fracture toughness (1.48?±?0.26?MPa?m1/2) than LC (0.72?±?0.15?MPa?m1/2) and better CMAS corrosion resistance than YSZ owing to the formation of Ca2(LaxCe1-x)8(SiO4)6O6–4x with <001> orientation perpendicular to the coating surface. The sudden CTE decrease of LC was fully suppressed in LC/50?vol.% YSZ coating due to the change of temperature dependent residual stresses induced by YSZ. 相似文献
4.
The Influence of Platelet‐Like LaMgAl11O19 on the Toughness of 3 mol% Yttria Partially Stabilized Zirconia Ceramic
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Xin Min Zhaohui Huang Minghao Fang Yan'gai Liu Yuanfei Gao Fengjiao Liu Meiling Hu Chao Tang Tingting Qian 《International Journal of Applied Ceramic Technology》2015,12(1):176-183
LaMgAl11O19‐3 mol% yttria partially stabilized zirconia ceramics were successfully prepared by pressureless sintering at 1550°C for 3 h. The ceramic's mechanical properties were measured, and the phase composition and microstructure observed using X‐ray diffraction and scanning electron microscopy. The results show that the mechanical properties of the ceramic were initially improved on addition of LaMgAl11O19, but further additions were detrimental. When the amount of LMA added was equal to 2 wt.%, the bending strength and fracture toughness reached 812 ± 37 MPa and 14.0 ± 0.3 MPa·m1/2. This equates to an increase of 8.0% and 6.9% compared with untreated 3 mol% yttria partially stabilized zirconia (3YSZ) ceramic, respectively. However, the bending strength and fracture toughness both decreased when the amount of LaMgAl11O19 added was 4 and 6 wt.%. A crack propagation and force analysis of the crack tips in LaMgAl11O19‐platelet‐reinforced 3YSZ ceramic were also carried out. The results indicate that phase transformation and crack deflection were the dominant toughening mechanisms in the LaMgAl11O19‐3YSZ ceramic. At the same time, energy dissipation by the LaMgAl11O19 platelets also helps to restrain crack propagation in the matrix, which improves toughness more effectively. 相似文献
5.
Gopal Dwivedi Vaishak Viswanathan Sanjay Sampath Amit Shyam Edgar Lara‐Curzio 《Journal of the American Ceramic Society》2014,97(9):2736-2744
Fracture toughness of thermal barrier coatings (TBCs) has gained significant interest in recent years as one of the dominant design parameters dictating selection of materials and assessing durability. Much progress has been made in characterizing and understanding fracture toughness of relevant TBC compositions in their bulk form, but it is also apparent that the toughness is significantly affected by process‐induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma‐sprayed TBCs has been carried out. Yttria partially stabilized zirconia (YSZ) coatings were fabricated under different process conditions inducing different levels of porosity and defect densities. Fracture toughness was measured on free‐standing coatings in as‐processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative composition, Gd2Zr2O7 which, as anticipated, shows significantly lower fracture toughness compared to YSZ. The results not only point toward a need for process and microstructure optimization for enhancing TBC performance, but also a framework for establishing performance metrics for promising new TBC compositions. 相似文献
6.
La2Ce2O7 (LCO) is a promising candidate material for thermal barrier coatings (TBCs) application because of its higher temperature capability and better thermal insulation property relative to yttria stabilized zirconia (YSZ). In this work, La2Ce2O7 TBC with segmentation crack structure was produced by atmospheric plasma spray (APS). The mechanical properties of the sprayed coatings at room temperature including microhardness, Young's modulus, fracture toughness and tensile strength were evaluated. The Young's modulus and microhardness of the segmented coating were measured to be about 25 and 5 GPa, relatively higher than those of the non-segmented coating, respectively. The fracture toughness of the LCO coating is in a range of 1.3–1.5 MPa m1/2, about 40% lower than that of the YSZ coating. The segmented TBC had a lifetime of more than 700 cycles, improving the lifetime by nearly two times as compared to the non-segmented TBC. The failure of the segmented coating occurred by chipping spallation and delamination cracking within the coating. 相似文献
7.
Bensheng Huang Sheng Fu Shunshun Zhang Anna Lin Zhongyi Guan 《International Journal of Applied Ceramic Technology》2020,17(3):1183-1193
The effects of zirconia and yttrium oxide addition on microstructure, bulk density, microhardness, flexural strength, and wear resistance of high alumina ceramics (>97 wt% Al2O3, MSA ceramics) composed of MgO–SiO2–Al2O3 system have been investigated. The results show that the addition of zirconia makes the mechanical properties and wear properties of ceramics composed of MgO–SiO2–Al2O3–ZrO2 (MSAZ ceramics) system have been greatly improved compared with MSA ceramics. In addition, the ceramics composed of MgO–SiO2–Al2O3–ZrO2–Y2O3 (MSAZY ceramics) system have better mechanical properties and wear properties than MSAZ ceramics. With the contents of zirconia and yttrium oxide increase, the bulk density, microhardness, and flexural strength of MSAZ and MSAZY ceramics increased at first and then decreased. However, the wear rate shows the opposite. When 0.4 wt% ZrO2 and 0.6 wt% Y2O3 were added to the matrix, the wear rate of MSAZY ceramics reached a minimum of 0.042%, and the wear resistance was improved by about 73.8% compared with MSA ceramics with a wear rate of 0.16%. In addition, the optimum additions of zirconia and yttria are 0.4% and 0.6%, respectively. 相似文献
8.
Biswanath Mondal Nilrudra Mandal Biswanath Doloi 《International Journal of Applied Ceramic Technology》2014,11(2):228-239
The nanocomposite CeO2/Y2O3 partially stabilized zirconia (Ce‐PSZ/Y‐PSZ)‐toughened alumina was prepared by wet chemical simultaneous coprecipitation process. The thermal stability of phases and morphology of powders were characterized by TG‐DTA, FTIR, and FESEM. The microstructure, stabilization of phases and compositional analysis with different mol% CeO2/Y2O3‐doped zirconia in alumina are characterized by FESEM, XRD, and EDAX spectra. Significant improvement in fracture toughness and flexural strength has been observed in 10 vol% of partially stabilized zirconia (2.5 mol% Y2O3 in ZrO2/9 mol% CeO2 in ZrO2)‐toughened alumina, which is suitable for high‐speed machining applications. 相似文献
9.
R. Lach K. Haberko M.M. Bu?koM. Szumera G. Grabowski 《Journal of the European Ceramic Society》2011,31(10):1889-1895
The preparation technique of the particulate composite materials in the alumina/YAG system was elaborated. Within alumina particles suspension yttria precursor was precipitated with ammonium carbonate. Drying and calcination at 600 °C resulted in the mixture of alumina and yttria particles, the latter being much finer than alumina particles. This mixture was additionally homogenized by short attrition milling in an aqueous suspension. Sintering of such powders results in the materials composed of YAG inclusions of sizes smaller than shown by alumina grains and evenly distributed within the matrix. YAG particles result from the reaction of Y2O3 with Al2O3 during heat treatment. YAG inclusions limit effectively grain growth of the alumina matrix. Hardness, fracture toughness, strength, Young modulus and wear susceptibility of composites and pure alumina were measured. Composites show higher hardness and in some cases higher fracture toughness and wear resistance than pure alumina polycrystals. 相似文献
10.
《Ceramics International》2017,43(13):10224-10230
Whiskers and nanoparticles are usually used as reinforcing additives of ceramic composite materials due to the synergistically toughening and strengthening mechanisms. In this paper, the effects of TiC nanoparticle content, particle size and preparation process on the mechanical properties of hot pressed Al2O3-SiCw ceramic tool materials were investigated. The results showed that the Vickers hardness and fracture toughness of the materials increased with the increasing of TiC content. The optimized flexural strength was obtained with TiC content of 4 vol% and particle size of 40 nm. The particle size has been found to have a great influence on flexural strength and small influence on hardness and fracture toughness. It was concluded that the flexural strength increased remarkably with the decreasing of the TiC particle size, which was resulted from the improved density and refined grain size of the composite material due to the dispersion of the smaller TiC particle size. SEM micrographs of fracture surface showed the whiskers to be mainly distributed along the direction perpendicular to the hot-pressing direction. The fracture toughness was improved by whisker crack bridging, crack deflection and whisker pullout; the TiC nanoparticles in Al2O3 grains caused transgranular fracture and crack deflection, which improved the flexural strength and fracture toughness with whiskers synergistically. Uniaxial hot-pressing of SiC whisker reinforced Al2O3 ceramic composites resulted in the anisotropy of whiskers’ distribution, which led to crack propagation differences between lateral crack and radical crack. 相似文献
11.
Dense zirconia-toughened alumina (ZTA) ceramic composites with ZrO2 = 0, 5, 10, 15, 20, 30, 60 and 100 wt.% have been prepared by sintering green compacts obtained by dry powder pressing of freeze dried granules consisting of α-alumina and a yttria partially stabilized zirconia (YPSZ) at various temperatures ranging from 1450 to 1650 °C for 1-2 h. The characteristics of sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes principle, Vickers indentation method and by 3-point bend test. Characterization results revealed that adding YPSZ increased the 3-point bend (flexural) strength, fracture toughness and homogeneity of the microstructure, but slightly decreased the hardness and the sintering ability of alumina. A 20 wt.% YPSZ was sufficient to increase the fracture toughness and flexural strength of specimens sintered for 2 h at 1600 °C from 2.5 to 4.6 MPa m1/2 and 150 to 400 MPa, respectively. The XRD results revealed that there is no solid-solution formation between zirconia and alumina constituents of ZTA ceramic composites upon sintering. 相似文献
12.
We have recently reported the production of Al2O3-matrix nanocomposites via solid state precipitation of nanosized FeAl2O4 particles within the matrix grains during aging of Al2O3–10 wt.% Fe2O3 solid solutions in a reducing atmosphere (N2 + 4% H2). In addition to these nanoparticles, however, coarse micron-sized FeAl2O4 particles were present along the matrix grain boundaries. In the present work, we show that the addition of ~250 ppm yttria to the solid solutions suppressed the development of these intergranular particles, reducing their size by a factor of ~2 with optimum aging. A fracture toughness improvement by 45% and flexural strength improvement by 50% with respect to monolithic Al2O3 were recorded with the yttria-containing nanocomposite developed by aging for 20 h at 1450 °C. Aging also improved the hardness with respect to the solid solution. The change in fracture mode in the presence of the nanosized intragranular particles was believed to be the major contributing factor towards the improvement in toughness and therefore the strength. The higher strengths obtainable in the presence of yttria were attributed to the reduction of intergranular precipitate size relative to yttria-free nanocomposites. 相似文献
13.
Jianhua Zhu Xiaojun Yue Dong Wang Xing Jin Songlin Ran 《Journal of the American Ceramic Society》2023,106(1):10-16
Although the addition of other phases into TiB2 matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB2 ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB2–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti3SiC2–B4C–Ti powder mixtures. During the sintering process, TiB2 grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB2 grains was attributed to the evaporation–condensation kinetics induced by the presence of B2O3. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties. 相似文献
14.
《Ceramics International》2019,45(16):19710-19719
Because gas turbine engines must operate under increasingly harsh conditions, the degradation of thermal barrier coatings (TBCs) by calcium-magnesium-alumina-silicate (CMAS) is becoming an urgent issue. Mullite (3Al2O3·2SiO2) is considered a potential material for CMAS resistance; however, the performance of mullite in the presence of CMAS is still unclear. In this study, mullite and Al2O3–SiO2 were premixed with yttria stabilized zirconia (YSZ) in different proportions, respectively. Porous ceramic pellets were used to conduct CMAS hot corrosion tests, and the penetration of molten CMAS and its mechanism were investigated. The thermal and mechanical properties of the samples were also characterized. It was found that the introduction of mullite and Al2O3–SiO2 mitigated the penetration of molten CMAS into the pellets owing to the formation of anorthite, especially at 45 wt% mullite/55 wt% YSZ. Compared with Al2O3–SiO2, mullite possesses a higher chemical activity and undergoes a faster reaction with CMAS, thus forming a sealing layer in a short time. Additionally, the thermal expansion coefficient, thermal conductivity, and fracture toughness of different samples were considered to guide the architectural design. Considering the CMAS corrosion resistance, thermal and mechanical performance of TBCs systematically, a TBC system with a multilayer architecture is proposed to provide a theoretical and practical basis for the design and optimization of the TBC microstructure. 相似文献
15.
《Ceramics International》2016,42(11):12825-12837
The corrosion resistance of micro-and nano-structured scandia and yttria codoped zirconia (nano-4 mol%SYSZ and micro-8.6SYSZ) and yttria doped zirconia (4YSZ) in the presence of molten vanadium oxide were investigated. To this end, duplex TBCs (thermal barrier coatings), composed of a bond coat (NiCrAlY) and a top coat (4SYSZ or 4YSZ), were deposited on the IN738LC Ni-based supper-alloy by atmospheric plasma spraying (APS). The corrosion studies of plasma sprayed TBCs were conducted in 25 mg V2O5 molten salt at 910 °C for different times. The nanostructured coating, as compared to its micro-structured counterpart, in spite of a further reaction with the V2O5 salt, showed a higher degradation resistance during the corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones. Finally, the corrosion resistance and degradation mechanism of SYSZ and YSZ coatings were compared with the presence of molten NaVO3 and V2O5 salt, respectively. 相似文献
16.
Yttria partially stabilized zirconia (~4.0?mol% Y2O3–ZrO2, 4YSZ) has been widely employed as thermal barrier coatings (TBCs) to protect the high–temperature components of gas–turbine engines. The phase stability problem existing in the conventional 4YSZ has limited it to application below 1200?°C. Here we report an excellent zirconia system co–doped with 16?mol% CeO2 and 4?mol% Gd2O3 (16Ce–4Gd) presenting nontransformable feature up to 1500?°C, in which no detrimental monoclinic (m) ZrO2 phase formed on partitioning. It also exhibits a high fracture toughness of ~46?J m?2 and shows high sintering resistance. Besides, the thermal conductivity and thermal expansion coefficient of 16Ce–4Gd are more competent for TBCs applications as compared to the 4YSZ. The combination of properties suggests that the 16Ce–4Gd system could be of potential use as a thermal barrier coating at 1500?°C. 相似文献
17.
《Ceramics International》2016,42(5):6072-6079
Due to excellent chemical stability, high rigidity, superior corrosion and wear resistance, aluminum oxynitride (AlON) has been considered as one of most promising candidate ceramic materials in high-performance structural, advanced abrasives and refractory fields. However, it usually exhibited relatively low flexural strength and poor fracture toughness. The study is aimed to develop silicon carbide (SiC) and zirconium nitride (ZrN) nano-particulate reinforced AlON composites with improved mechanical properties and fracture resistance via a hot-press sintering process. It was found that the addition of ZrO2 nanoparticles would be transformed into ZrN during sintering. Due to the pinning effect of SiC and ZrN nano-particles positioned at grain boundaries of micro-sized AlON particles, the presence of SiC and ZrN nano-particles resulted in the reduction of both porosity and grain size, and a change of fracture mode from intergranular cracking in AlON to intragranular cracking in composites. With presence of 8 wt% SiC and 5.2 wt% ZrN nano-particles, the relative density, microhardness, Young’s modulus, flexural strength and fracture toughness increased. Different toughening mechanisms including crack bridging, crack branching and crack deflection were observed, thus effectively increasing the crack propagation resistance and leading to a considerable improvement in flexural strength and fracture toughness. 相似文献
18.
《Journal of the European Ceramic Society》2021,41(15):7771-7782
The relationship between fracture toughness and Yttria content in modern zirconia ceramics was revised. For that purpose, we evaluated here 10 modern Y2O3-stabilized zirconia (YSZ) materials currently used in biomedical applications, namely prosthetic and implant dentistry. The most relevant range between 2-5 mol% Y2O3 was addressed by selecting from conventional opaque 3 mol% YSZ up to more translucent compositions (4−5 mol% YSZs). A technical 2YSZ was used to extend the range of our evaluation. The bulk mol% Y2O3 concentration was measured by X-Ray Fluorescence Spectroscopy. Phase quantification by Rietveld refinement considered two tetragonal phases or an additional cubic phase. A first-account of the fracture toughness (KIc) of the pre-sintered blocks is given, which amounted to 0.4 – 0.7 MPa√m. In the fully-densified state, an inverse power-law behavior was obtained between KIc and bulk mol% Y2O3 content, whether using only our measurements or including literature data, challenging some established relationships. A linear relationship between KIc and the fraction of the transformable t-phase was established within the range of 30–70 vol%. 相似文献
19.
Alumina (Al2O3) ceramic composites reinforced with graphene platelets (GPLs) were prepared using Spark Plasma Sintering. The effects of GPLs on the microstructure and mechanical properties of the Al2O3 based ceramic composites were investigated. The results show that GPLs are well dispersed in the ceramic matrix. However, overlapping of GPLs and porosity within ceramics are observed. The flexural strength and fracture toughness of the GPL-reinforced Al2O3 ceramic composites are significantly higher than that of monolithic Al2O3 samples. A 30.75% increase in flexural strength and a 27.20% increase in fracture toughness for the Al2O3ceramic composites have been achieved by adding GPLs. The toughening mechanisms, such as pull-out and crack deflection induced by GPLs are observed and discussed. 相似文献
20.
《Journal of the European Ceramic Society》2019,39(15):4487-4494
SiC ceramics sintered with yttria were successfully joined without an interlayer by conventional hot pressing at lower temperatures (2000–2050 °C) compared to those of the sintering temperatures (2050–2200 °C). The joined SiC ceramics sintered with 2000 ppm Y2O3 showed almost the same thermal conductivity (˜198 Wm−1 K−1), fracture toughness (3.7 ± 0.2 MPa m1/2), and hardness (23.4 ± 0.8 GPa) as those of the base material, as well as excellent flexural strength (449 MPa). In contrast, the joined SiC ceramics sintered with 4 wt% Y2O3 showed very high thermal conductivity (˜204 Wm−1 K−1) and excellent flexural strength (˜505 MPa). Approximately 16–22% decreases in strength compared to those of the base SC materials were observed in both joined ceramics, due to the segregation of liquid phase at the interface. This issue might be overcome by preparing well-polished and highly flat surfaces before joining. 相似文献