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Phenolic resin/ZrW2O8 composites were successfully fabricated and their coefficient of thermal expansion (CTE) as well as mechanical properties was investigated. The CTE of the composites decreases from 46 × 10–6 to 14 × 10–6 K?1 when the ZrW2O8 volume fraction increases from 0 to 52 vol %. The CTE of the composites is analyzed by some theoretical models; Schapery's upper bound provides the best estimate of the reduction in CTE. The Barcol hardness of the composites increases with an increase in the ZrW2O8 volume fraction. The bending strength of the composites with 19–25 vol % of ZrW2O8 fillers shows a maximum value of 130 MPa, which is 45% larger than that of phenolic resin without fillers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
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Ikuo Yanase Hiroya Chida Hidehiko Kobayashi 《Journal of the European Ceramic Society》2018,38(1):221-226
Calcined powders of ZrV1.2P0.8O7 (ZVP) and ZrV2O7 (ZV) were synthesized by heating gels prepared from NH4H2PO4, NH4VO3, and ZrOCl2 solutions at 500 and 400 °C, respectively. Dense ZV-added ZVP sintered bodies were subsequently fabricated through heating at 850 °C for 20 h, with the addition of ZrV2O7 as a sintering additive. The resulting material had a relative density of ca. 92%, while the relative density of pure sintered ZVP was ca. 72%. NH4H2PO4 (NHP) was also added to ZVP along with ZV to obtain a molar ratio of P in NHP for V in ZV = 1. Subsequently, a single phase (NHP, ZV)-added ZVP sintered body was obtained by heating at 850 °C. Thermomechanical analysis showed that the dense ZV-added ZVP sintered body exhibited a positive thermal expansion from 25 to 150 °C and a negative thermal expansion from 150 to 500 °C. 相似文献
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《Ceramics International》2017,43(9):6831-6835
Zr2W2P2O15 with larger-negative-thermal-expansion-coefficient (NTEC, −4.01×10−6 K−1, 143–673 K) is developed by controlling reaction process to avoid the intermediate phase of Zr2WP2O12, whose smaller NTEC limits its application. From 1473 K to1573 K, Zr2WP2O12 forms easily but the reaction between Zr2WP2O12 and WO3 to generate Zr2W2P2O15 is difficult even followed by heating up to 1673 K. However, putting raw materials of ZrO2, WO3 and NH4H2PO4 into a pipe furnace at sintering temperature 1673 K directly, the Zr2W2P2O15 is formed avoiding the intermediate phase of Zr2WP2O12. 相似文献
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G. Moskal L. Swadźba M. Hetmańczyk B. Witala B. Mendala J. Mendala P. Sosnowy 《Journal of the European Ceramic Society》2012,32(9):2035-2042
The microstructure of following thermal barrier coatings (TBC) was characterised in this paper: monolayer coatings Nd2Zr2O7 and 8YSZ; a double ceramic layered (DCL) coating. Coatings were characterised by thicknesses that did not exceed 300 μm and porosities of approx. 5%. The chemical and phase composition analysis of the DCL layers revealed an external Nd2Zr2O7 ceramic layer approx. 80 μm thick, a transitional zone approx. 120 μm thick and an internal 8YSZ layer 100 μm thick. For the case of the monolayer coating, the Nd2Zr2O7 pyrochlore phase was the only one-phase component. The surface topography of both TBC systems was typical for plasma sprayed coatings, and compressive stress state had a value of approx. 5–10 MPa. Measurements of the thermal parameters, i.e., thermal diffusivity, point to considerably better insulative properties for both new types of layers when compared to the standard 8YSZ layers. 相似文献
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Different acids were used to prepare ZrW2O8 powders at 570 °C by the hydrothermal method. The products were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, thermogravimetric and differential scanning calorimetry and Fourier transform infrared absorption spectra. The results indicate that among the chosen acids, only HCl and HNO3 can be used to prepare pure ZrW2O8 powders with high crystallinity and rod-like shape. When the hydrothermal temperature reduces to 160 °C, nano-sphere particles with an average diameter of 30 nm is obtained, if prepared by HNO3 addition. The results of in situ X-ray diffraction measurement indicate that ZrW2O8 powders prepared by pure HCl or HNO3 have strong negative thermal expansion. 相似文献
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To explore the effect of negative thermal expansion on the reduction of the coefficient of thermal expansion of polymer with respect to that of chain stiffening, the preparation of polycarbonate composites with ZrW2O8 and ZrW2O7(OH)2·2H2O are attempted. In the process, the dispersion of the filler particles in the polymer needs to be optimized, and the transfer of properties at the interface between the two phases. Therefore, surface modification by in situ polymerization is performed on these two particles. Several parameters of the reaction are optimized to achieve higher surface coverage of oligomer, including reaction time and the amount of monomers and particles. On the basis of the optimized conditions, two modification steps are then used to maximize both recovered amount of modified particles and surface coverage. The composites prepared with modified particles show enhanced dispersion of the particles and interaction at the interfaces. POLYM. COMPOS., 37:1359–1368, 2016. © 2014 Society of Plastics Engineers 相似文献
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《Journal of the European Ceramic Society》2021,41(15):7752-7761
Three-phase alumina/YAG/yttria-stabilized cubic zirconia (YSZ) composites were fabricated by a solid-state reaction route starting from commercial powders of Al2O3, Y2O3 and monoclinic ZrO2. The final phases Al2O3, YAG and YSZ were obtained after calcination of the powder mixtures at 1400 °C. Dense bulk composites were obtained after sintering, with a homogeneous microstructure of fine and equiaxed grains with sizes of 1 μm. Compressive mechanical tests were performed at 1300–1450 °C in air at constant load and at constant initial strain rate. A brittle-to-ductile transition was found with increasing temperature. Grain boundary sliding is the main deformation mechanism in the ductile regime, characterized by a stress exponent of 2 and by the absence of dislocation activity and changes in grain morphology. Alumina seems to be the rate-controlling phase owing to the improvement in creep resistance by the presence of yttrium and zirconium of the other two phases. 相似文献
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P. Lommens C. De Meyer E. Bruneel K. De Buysser I. Van Driessche S. Hoste 《Journal of the European Ceramic Society》2005,25(16):3605-3610
In this work, a ceramic composite of ZrW2O8 and ZrO2 was synthesized, in order to investigate the possibility of compensating the positive thermal expansion of ZrO2 with the negative thermal expansion (NTE) compound ZrW2O8, tailoring the thermal expansion of these composites. The NTE material was mixed with varying amounts of ZrO2. The thermal expansion coefficients of this series of composites decrease with increasing amounts of ZrW2O8. Nevertheless, a negative deviation from the values expected by the rule of mixtures was found to be most pronounced in the middle of the compositional region. 相似文献
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《Journal of the European Ceramic Society》2014,34(5):1255-1263
(Gd1−xYbx)2Zr2O7 compounds were synthesized by solid reaction. Yb2O3 doped Gd2Zr2O7 exhibited lower thermal conductivities and higher thermal expansion coefficients (TECs) than Gd2Zr2O7. The TECs of (Gd1−xYbx)2Zr2O7 ceramics increased with increasing Yb2O3 contents. (Gd0.9Yb0.1)2Zr2O7 (GYbZ) ceramic exhibited the lowest thermal conductivity among all the ceramics studied, within the range of 0.8–1.1 W/mK (20–1600 °C). The Young's modulus of GYbZ bulk is 265.6 ± 11 GPa. GYbZ/YSZ double-ceramic-layer thermal barrier coatings (TBCs) were prepared by electron beam physical vapor deposition (EB-PVD). The coatings had an average life of more than 3700 cycles during flame shock test with a coating surface temperature of ∼1350 °C. Spallation failure of the TBC occurred by delamination cracking within GYbZ layer, which was a result of high temperature gradient in the GYbZ layer and low fracture toughness of GYbZ material. 相似文献
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《Ceramics International》2022,48(20):30135-30143
In this work, Sc2Mo3O12 has been synthesized via one-pot hydrothermal reaction. The effects of process conditions on the crystal structure, morphology, photocatalytic activity and negative thermal expansion (NTE) behaviors of flower-like Sc2Mo3O12 were systematically investigated. Results indicate that orthorhombic flower-like Sc2Mo3O12 assembled by nano-size flaky crystal grains can be synthesized by one-pot hydrothermal reaction at a temperature as low as 120 °C for 2 h. The hydrothermal reaction temperature and time have no obvious effects on the crystal structure and morphology. However, the photocatalytic property of synthesized Sc2Mo3O12 is sensitive to the above parameters. The sample synthesized at 200 °C for 2 h shows the best photocatalytic degradation of methyl orange, and the degradation rate is 73.32% in 2 h 1The coefficient of thermal expansion (CTE) of Sc2Mo3O12 is ?1.99 × 10?6 °C?1 in 50–500 °C tested using TMA. The high-temperature XRD analysis reveals that Sc2Mo3O12 exhibits anisotropic NTE and the intrinsic CTE is measured to be ?2.09 × 10?6 °C?1 in 25–800 °C. 相似文献
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Thermophysical properties of carbon/carbon composites and physical mechanism of thermal expansion and thermal conductivity 总被引:5,自引:0,他引:5
Five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied. These were three needled carbon felts impregnated with pyrocarbons (PyC) of different microstructures, chopped fibers/resin carbon + PyC, and carbon cloth/PyC. The results show that the X-Y direction thermal expansion coefficient (CTE) is negative in the range 0-100 °C with values ranging from −0.29 to −0.85 × 10−6/K. In the range 0-900 °C, their CTE is also very low, and the CTE vs. T curves have almost the same slope. In the same temperature range composites prepared using chopped fibers show the smallest CTE values and those using the felts show the highest. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture. Their expansion is mainly caused by atomic vibration, pore shrinkage and volatilization of water. However, the PyC structure has a large effect on thermal conductivity (TC) with rough laminar PyC giving the highest value and isotropic PyC giving the lowest. All five composites have a high TC, and values in the X-Y direction (25.6-174 W/m K) are much larger than in the Z direction (3.5-50 W/m K). Heat transmission in these composites is by phonon interaction and is related to the preform and PyC structures. 相似文献
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G. Moskal L. Swadźba M. Hetmańczyk B. Witala B. Mendala J. Mendala P. Sosnowy 《Journal of the European Ceramic Society》2012,32(9):2025-2034
We present herein a characterization of the microstructure and thermal properties of thermal barrier coatings (TBCs), which we obtained via plasma spraying of powder Gd2Zr2O7. By using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), we evaluated the phase composition of a ceramic layer and estimated the ceramic-layer stress state by the sin2ψ method. The tests revealed that the TBC layer consisted of a single-phase structure of Gd2Zr2O7, namely, an Fd3m lattice. The thermal diffusivity of the outer ceramic layer was determined based on a bilayer model and corrected with a factor to account for the presence of pores. The results reveal that the use of the standard parameters in a standard spraying process gives good-quality Gd2Zr2O7 TBCs with a thermal conductivity considerably lower than 8YSZ-type TBCs. 相似文献
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La2Zr2O7 is a promising thermal barrier coating (TBC) material. In this work, La2Zr2O7 and 8YSZ-layered TBC systems were fabricated. Thermal properties such as thermal conductivity and coefficient of thermal expansion were investigated. Furnace heat treatment and jet engine thermal shock (JETS) tests were also conducted. The thermal conductivities of porous La2Zr2O7 single-layer coatings are 0.50–0.66?W?m?1?°C?1 at the temperature range from 100 to 900°C, which are 30–40% lower than the 8YSZ coatings. The coefficients of thermal expansion of La2Zr2O7 coatings are about 9–10?×?10?6?°C?1 at the temperature range from 200 to 1200°C, which are close to those of 8YSZ at low temperature range and about 10% lower than 8YSZ at high temperature range. Double-layer porous 8YSZ plus La2Zr2O7 coatings show a better performance in thermal cycling experiments. It is likely because porous 8YSZ serves as a buffer layer to release stress. 相似文献
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《Ceramics International》2015,41(8):9488-9495
The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO2-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles. 相似文献
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《Ceramics International》2016,42(11):12922-12927
The single-ceramic-layer (SCL) Sm2Zr2O7 (SZO) and double-ceramic-layer (DCL) Sm2Zr2O7 (SZO)/8YSZ thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying on nickel-based superalloy substrates with NiCoCrAlY as the bond coat. The mechanical properties of the coatings were evaluated using bonding strength and thermal cycling lifetime tests. The microstructures and phase compositions of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that both coatings demonstrate a well compact state. The DCL SZO/8YSZ TBCs exhibits an average bonding strength approximately 1.5 times higher when compared to the SCL SZO TBCs. The thermal cycling lifetime of DCL SZO/8YSZ TBCs is 660 cycles, which is much longer than that of SCL 8YSZ TBCs (150 cycles). After 660 thermal cycling, only a little spot spallation appears on the surface of the DCL SZO/8YSZ coating. The excellent mechanical properties of the DCL LZ/8YSZ TBCs can be attributed to the underlying 8YSZ coating with the combinational structures, which contributes to improve the toughness and relieve the thermal mismatch between the ceramic layer and the metallic bond coat at high temperature. 相似文献