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1.
Al 2O 3/Cu-O composites were fabricated from the paper-derived alumina matrix infiltrated with a Cu-3.2?wt% O alloy. Paper-derived alumina preforms with an open porosity ranging from ~ 14 to ~ 25?vol% were prepared by sintering of alumina-loaded preceramic papers at 1600?°C for 4?h. Pressureless infiltration at 1320?°C for 4?h of the preforms with Cu–O alloy resulted in the nearly dense materials with good mechanical and electrical properties, e.g. fracture toughness up to 6?MPa?m 0.5, four-point-bending strength up to 342?MPa, Young's modulus up to 281?GPa and electrical conductivity up to 2?MS/m depending on the volume fraction of copper alloy in the composites. The technological capability of this approach was demonstrated using prototypes in various engineering fields fabricated by lamination, corrugating and Laminated Object Manufacturing (LOM) methods. 相似文献
2.
Core-shell structural composites are promising to quench the desire for low-cost, lightweight and multifunctional magnetic materials, but the fabrication of highly pure shell nanoparticles with a desired morphology on a heterogeneous nuclear is still a big challenge. This study gives a successful illustration by in-situ synthesizing BaFe 12O 19 nanoparticles as a shell on Al 2O 3 core powders using BaCl 2 and FeCl 3 as precursors, instead of commonly used Ba(NO 3) 2 and Fe(NO 3) 3, by a modified heterogeneous precipitation process followed by calcination for crystallization. After calcination of the precipitants from the raw precursor mixture of BaCl 2:FeCl 3 for 1:10 at 800?°C, and for 1:8.5 at 900?°C, respectively, pure BaFe 12O 19 formed on pristine Al 2O 3, mostly with a hexagonal plane, about 100–200?nm in basal diameter and 20–100?nm in thickness. The highest saturation magnetization and coercivity of the coated Al 2O 3 @?BaFe 12O 19 powders was 23.3?emu/g and 5149?Oe, quite higher than that of the direct-mixed Al 2O 3-BaFe 12O 19 composite powder, and BaFe 12O 19-containing composites reported in literature, which could be attributed to the hexagonal shape of BaFe 12O 19 and uniform shell dispersion on Al 2O 3 core. The formation mechanism for the Al 2O 3@BaFe 12O 19 powders was discussed in detail. 相似文献
3.
Cu-coated Al 2O 3 composite powders were synthesized by using the electroless plating method. The influence of the components proportion and the pH value of the plating solution on the Cu layer were analyzed with XRD and SEM. The results showed that the proportion of the plating solution components plays an important role for synthesizing the Al 2O 3/Cu composite powders. The content of copper in the composite powders could be effectively controlled by adjusting the content of copper sulfate and formaldehyde in the plating solution. Furthermore, the pretreatment of the Al 2O 3 powders is also a key factor to form a uniform Cu layer coating Al 2O 3 particles. The optimum technical parameters for producing Al 2O 3/Cu composite powders with uniform Cu coat were obtained. 相似文献
4.
Ceramic fibers and whiskers have been used for modification of toughness because they increase fracture energy due to their high elastic modulus and strength. The mechanism of this increase is well known to be pull-out, crack deflection and a bridging mechanism. This study focused on the increase in toughness, strength and thermal shock resistance when using ceramic fibers in a gas filter for high temperatures. The basic systems studied were clay bonded SiC-mullite and Al2O3-mullite with carbon black (to improve filtering efficiency). The Al2O3-mullite system showed lower porosity (2745%) and higher strength (131 kg/cm2) than the same system fired in air. The strength was higher than for the SiC-mullite system with the same treatment because of the high sintering rate. Also, the hot strength at 1000 °C was higher than for the SiC-mullite system. Strength degradation was only 14% and 5% after thermal shock tests. Resistance to thermal shock was better than the Al2O3-mullite system owing to better thermal shock resistant raw materials (like SiC) and the fibrous microstructure. Both systems fired in air showed broader pore size distributions than when fired in a coke bed. 相似文献
5.
In the current research, the effects of TiO 2 additive on mechanical and physical properties of SiC bodies, sintered by liquid phase methods were investigated. Al 2O 3 and Y 2O 3 were used as sintering-aids (10?wt% in total) with an Al 2O 3/Y 2O 3 ratio of 43/57 to provide liquid phase during Sintering. TiO 2 was also used as the oxide additive with an amount ranging from 0 to 10?wt%. After scaling and mixing the starting materials by a planetary mill, the obtained slurry was dried at 100?℃ for four hours. The derived powders were finally pressed under a pressure of 90?MPa. The samples were then pyrolyzed and sintered at 600?℃ and 1900?℃, respectively under argon atmosphere for 1.5?h. Phase analysis showed no trace of TiO 2 after the sintering process, demonstrating the complete TiO 2 to TiC transformation. The results showed that an increase in TiO 2 content up to 5?wt%, led an improvement in all the measured properties including the relative density, hardness, Young's modulus, bending strength, indentation fracture resistance and the brittleness factor, reaching to 96.2%, 24.4?GPa, 395.8?GPa, 521?MPa, 5.8?MPa?m 1/2 and 286.5?×?10 ?6 m ?1, respectively. However more than 5?wt% additive resulted in a decrease in all the above-mentioned properties. Microstructural studies demonstrated that crack deflection and crack bridging were the major mechanisms responsible for an increase in the indentation fracture resistance. 相似文献
6.
Nanocrystalline Al 2O 3 powders containing different amounts of MgO (0.1–5.0 mol%) or added boehmite (AlOOH) have been synthesized by combustion synthesis from aluminium nitrate and magnesium nitrate, using urea or sucrose as fuels. The as synthesized alumina powders were deagglomerated, compacted by dry pressing and sintered at 1625 °C for 2 h. For comparison purposes, a commercial high purity α-Al 2O 3 powder (ACC) was also processed following the same route. The sintered materials were characterized for bulk density (BD), apparent porosity (AP), and water absorption (WA) capacity, microstructure using SEM, and XRD phase composition. In comparison to boehmite, the MgO had a considerable effect on the densification behaviour of combustion-synthesized powder. 相似文献
7.
Fine particles of anatase were suspended in solutions of ammonium alum with Al 2O 3/TiO 2 molar ratios from 0.1:1 to 7:1. By spray drying the suspensions and calcining the spray-dried powders, Al 2O 3-TiO 2 composite particles were obtained. The results show that after the spray drying, coatings of ammomium alum are formed on the surface of the anatase particles, leading to composite precursor powders (CCPs) with larger particle sizes. Upon calcining the CCPs, ammomium alum pyrolyzes to amorphous Al 2O 3 and anatase transforms into rutile. Both are mainly responsible for the observed particle size reductions as well as the densification of each composite particle. The in-situ formed α-Al 2O 3 and rutile may have higher reactivities, forming aluminum titanate at 1150 °C, about 130 °C lower than the theoretical temperature for the formation of Al 2TiO 5 by solid reaction. The reaction between α-Al 2O 3 and rutile starts from the interface between the anatase and the alum coating and mainly takes place in the single particles formed by spray drying. The molar ratio of Al 2O 3 to TiO 2 influences the final crystalline phases in the composite powders, but not stoichiometrically. 相似文献
8.
Porous Si 3N 4-bonded SiC ceramics with high porosity were prepared by the reaction-sintering method. In this process, Si 3N 4 was synthesized by the nitridation of silicon powder. The X-ray diffraction (XRD) indicated that the main phases of the porous Si 3N 4-bonded SiC ceramics were SiC, α-Si 3N 4, and β-Si 3N 4, respectively. The contents of β-Si 3N 4 were increased following the sintering temperature. The morphology of Si 3N 4 whiskers was investigated by scanning electron microscope (SEM), which was shown that the needle-like (low sintering-temperature) and rod-like (higher sintering-temperature) whiskers were formed, respectively. From low to high synthesized temperature, the highest porosity of the porous Si 3N 4 bonded SiC ceramic was up to 46.7%, and the bending strength was ~11.6?MPa. The α-Si 3N 4 whiskers were derived from the reaction between N 2 and Si powders, the growth mechanism was proved by Vapor–Solid (VS). Meanwhile, the growth mechanism of β-Si 3N 4 was in accordance with Vapor–Solid–Liquid (VSL) growth mechanism. With the increase of sintering temperature, Si powders were melted to liquid silicon and the α-Si 3N 4 was dissolved into the liquid then the β-Si 3N 4 was precipitated successfully. 相似文献
9.
This paper describes the development and fabrication of pastes suitable for screen printing process using Ti 3SiC 2 as the ceramic filler and ethyl cellulose as the binder. With the aim of obtaining high quality screen printed films, the influence of different amounts of Ti 3SiC 2 filler (20–40?vol%) and binder (0–5?vol%) on the rheological properties of the pastes was investigated. Samples with higher viscosity, such as pastes containing 30?vol% and 40?vol% Ti 3SiC 2 filler, regardless of the amount of ethyl cellulose, showed a higher printing quality compared to the samples with other compositions. The different paste compositions were screen printed onto paper-derived Al 2O 3 substrates containing 28.6 ± 4.8% open porosity and sintered for 1?h under an argon atmosphere at 1600?°C. X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) analysis showed that the sintered films contained TiC as a primary phase and Ti 3SiC 2 as a secondary phase. The partial decomposition of Ti 3SiC 2 after sintering can be attributed to residual carbon from the organic additives, which decreases the thermal stability of this material. 相似文献
10.
In this paper, the Al 2O 3-20 wt.%ZrO 2 (8 wt.%Y 2O 3) feedstocks were fabricated and treated by spray drying, calcination, and plasma treatment technology. The morphology of feedstocks was characterized by scanning electron microscope (SEM). The phase structure and grain size were analyzed by X-Ray diffraction (XRD). The flowability and density were measured by Hall Flowmeter and density instrument, respectively. The sphericity and flowability of feedstocks treated by plasma flame increased greatly compared with that of the feedstocks without plasma treatment, and the particle surfaces were very smooth. The optimum flowability was obtained when the critical plasma spray parameter (CPSP) was 363. The compactness also increased greatly with the increment of CPSP, and the maximum value of compactness was got with CPSP of 325. Calcination can make the grain grow and plasma treatment can lead to the decrement of grain size. The phase structure of Al 2O 3 did not change, which was α-Al 2O 3 in the composites. The phase structure of ZrO 2 (8 wt.%Y 2O 3) changed from t-phase to c-phase which was affected greatly by plasma treatment. 相似文献
11.
The oxidation-resistance of thin film sensors, particularly at high temperatures, is critical for the lifetime and performance of the sensor. The preparation and oxidation-resistance of an Al 2O 3/ZrBN-SiCN/Al 2O 3 composite film with a sandwich-structure was performed using reactive magnetron sputtering. The microstructure evolution of the composite film is examined herein using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. Oxygen diffusion was significantly inhibited by the formation of crystalline Al 2SiO 5 and Zr-B-C amorphous phase inside the composite film. The Pt-13%Rh/Pt thin film thermocouple (TFTC) with the Al 2O 3/ZrBN-SiCN/Al 2O 3 composite film as a protective layer was fabricated and calibrated. Both the stability and lifetime of the TFTC was significantly enhanced for temperatures up to 1000?℃. The test error of the TFTC was reduced by half, compared with that of the TFTC with the Al 2O 3 protective layer, indicating an excellent oxidation-resistant performance of the composite film. 相似文献
12.
A novel layered microstructure in the Al 2O 3/ZrO 2 composites system was fabricated by the multipass extrusion method. The microstructure consisted with very fine alternate lamina of Al 2O 3-(m-ZrO 2) and t-ZrO 2. The composites were designed in such a way that a small group of 7 cylindrical alternate layers of Al 2O 3-(m-ZrO 2) and t-ZrO 2 made a concentric microgroup around 40 μm in diameter, with a common boundary layer between the adjacent groups. The thickness of both layers was around 2-3 μm. The microstructure was unidirectionally aligned throughout the composites. The composite microstructure was fibrous due to the unidirectional orientation of these microgroups. Detailed microstructure of the fabricated composites was characterized by SEM. The effect of the concentric layered microstructure on mechanical behavior was discussed. Material properties such as density, bending strength, Vickers hardness and fracture toughness were measured and evaluated depending on different sintering temperatures. 相似文献
13.
The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi 2(Zn 1/3Nb 2/3) 2O 7 (BZN) and Bi 2(Zn 1/3Nb 2/3−xV x) 2O 7 (BZNV, x = 0.001) sintered under air and N 2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V 2O 5 and N 2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N 2 atmosphere with r = 76.1, Q = 850 and Qf = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with r = 76.7, Q = 890 and Qf = 3580 GHz. The temperature coefficient of resonant frequency τf was not obviously influenced by the different atmospheres. For BZN ceramics the τf was −79.8 ppm/°C while τf is −87.5 ppm/°C for BZNV ceramics. 相似文献
14.
The impact of MnO 2 as an additive on the properties of NiFe 2O 4-based cermets prepared by the two-steps sintering method has been investigated. The new material was characterized in terms of the crystal structure, microstructure, linear shrinkage, relative density and porosity. Moreover, the bending strength of NiFe 2O 4-based cermets was measured. Differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD) shows that the addition of MnO 2 has no obvious influence on the crystal structure of the cermets. Scanning electron microscope (SEM) studies reveals that the grain sizes of cermets decreases slightly with doped MnO 2. The results show that the linear shrinkage, relative density and bending strength increase at first and then decrease slightly. A high-density (99.56%) and high-strength (84.28 MPa) NiFe 2O 4-based cermets has been obtained by adding 0.50 wt% MnO 2 into the matrix. 相似文献
15.
In this work we successfully obtained freeze-cast alumina (Al 2O 3) and magnesium aluminate spinel (MgAl 2O 4) samples. Camphene was used as the freezing vehicle in this study. The specimens prepared herein were examined by Archimedes tests, scanning electron microscopy, and X-ray powder diffraction. Cold crushing tests were also carried out at room temperature. It was observed that the pore structure of Al 2O 3 samples can be tailored by changing the solid loading and freezing rate; the higher the solid loading and freezing rate, the finer the pore structure of the freeze-cast sample. MgAl 2O 4-based specimens were fabricated by keeping the solid loading in the starting slurry at 30 vol% and using liquid nitrogen as the cooling agent. The material obtained from a 60 Al 2O 3?40 MgO slurry showed a spinel amount of about 90%, an expressive total porosity (63 ± 3%), and a significant cold crushing strength (58 ± 6 MPa). In addition, this material exhibited the finest pore structure among the composition studied herein, showing a mean pore size of about 4 µm. 相似文献
16.
ZrO 2@Al 2O 3 composite ceramic powders were prepared by solution combustion method with aluminum nitrate (Al (NO 3) 3) and 3?mol% yttria-stabilized tetragonal zirconia polycrystal (3Y- TZP) as the main raw materials, ammonium polyacrylate (PAA-NH 4) as a dispersant, urea (CO (NH 2) 2) as a reducing agent. The effects of PAA-NH 4 concentration and drying method on the microstructure and morphology of the ZrO 2@Al 2O 3 powders were investigated. The results showed that when the concentration of PAA-NH4 was 1.5?wt%, and the molar ratio of Al (NO 3) 3 to CO (NH 2) 2 was 1:2, the ZrO 2@Al 2O 3 powders with uniform grain size and high crystallinity could be synthesized by solution combustion drying method. Additionally, the abnormal growth of 3Y- TZP grain in ZrO 2@Al 2O 3 was suppressed and the crystalline phase transformation trend (t-ZrO 2 to m-ZrO 2) was obviously decreased after sintering at 1600?°C. 相似文献
17.
Functionally pore-gradient Al 2O 3–ZrO 2 composites where the porosity is dependent on the extrusion ratio and number of shell layer were fabricated by a fibrous monolithic process. The size and volume fraction of the pores were controlled by different numbers of shell layers, which contained various sizes and a different volume percentage of the pore-forming agent. In the pore-gradient, Al 2O 3–ZrO 2 bodies having a dense core part, some defects such as cracks, swelling and delamination occurred during the sintering process due to the low extrusion ratio. However, these defects were completely removed as the extrusion ratio increased, and the shell layers as well as the core part had a continuously porous structure. In the shell part, various sizes of pores from 70 to 250 μm in diameter were observed. 相似文献
19.
Fe 2O 3 catalysts supported on Al 2O 3 were used to remove nitrous oxide from the nitric acid plant simulated process stream (containing O 2, NO and H 2O). Catalysts were prepared by the coprecipitation method and were characterized for their physico-chemical properties by BET, XRD, AFM and TPR analysis. A strong influence of the post-preparation heating conditions on the structural and catalytic properties of the catalysts has been evidenced. Laboratory tests revealed 95% conversion of N 2O at temperature 750 °C and a slight decrease in activity in the presence of H 2O and NO. The catalysts were inert towards decomposition of NO. The pilot-plant reactor and real plant studies (up to 3300 h time-on-stream) confirmed high activity and very good mechanical stability of the catalysts as well as no decomposition of nitric oxide. 相似文献
20.
Al 2O 3 nanopowders were synthesized by a simple chitosan-polymer complex solution route. The precursors were calcined at 800–1200 °C for 2 h in air. The prepared samples were characterized by XRD, FTIR and TEM. The results showed that for the precursors prepared with pH 3–9 γ-Al 2O 3 and δ-Al 2O 3 are the two main phases formed after calcination at 800–1000 °C. Interestingly, when the precursor prepared with pH 2 was used, α-Al 2O 3 was formed after calcination at 1000 °C, and pure α-Al 2O 3 was obtained after calcination at 1200 °C. The crystallite sizes of the prepared powders were found to be in the range of 4–49 nm, as evaluated by the XRD line broadening method. TEM investigation revealed that the Al 2O 3 nanopowders consisted of rod-like shaped particles and nanospheres with particle sizes in the range of 10–300 nm. The corresponding selected-area electron diffraction (SAED) analysis confirmed the formation of γ- and α-Al 2O 3 phases in the samples. 相似文献
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