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1.
To investigate the effects of air annealing on the microstructure, components, and mechanical properties of ceramic composite coatings, Al 2O 3–Cr 2O 3–ZrO 2 composite coatings were prepared on silicon substrate using radio frequency magnetron sputtering at room temperature, and then air-annealed in a temperature range of 450–850 °C for 30 min. The results indicated that the phase-structure and superficial characteristics, including morphology and surface roughness, were not visibly altered in the annealed coatings up to 600 °C; the elemental component distributions remained uniform. The improvement in the mechanical properties was attributed to the growth of oxide grains. There were no significant changes in the components of Al, Cr, Zr, and O in the annealed coatings. However, an increase in the Cr component and a decrease in the Zr component occurred on the coating surface; the overall structure of the composite coatings possessed a favorable heat resistance. Upon annealing at 750 °C, the thermally-driven formation of uniform and refined nanoparticles on the coating surface was responsible for the effective enhancement of the mechanical properties. Furthermore, annealing at 850 °C induced the enlargement of the precipitated Cr 2O 3 nanoparticles and the generation of micro-defects, resulting in a drastic morphological evolution, an evident increase in the surface roughness, and a significant decrease in the mechanical properties. This study provides new perspectives on designing novel thermal barrier coatings and understanding the role of high temperature air annealing on the microstructural transformation. 相似文献
2.
A series of ordered mesoporous Cr 2O 3–Al 2O 3 composite oxides synthesized via improved one-pot evaporation induced self-assembly strategy were investigated as the catalysts for catalytic dehydrogenation of isobutane. These mesoporous catalysts with good structural properties and thermal stability performed excellent catalytic properties. Besides, the effect of the ordered mesopore structure on improving catalytic properties was also studied. Compared with non-mesoporous catalyst, the current mesoporous catalyst could accommodate the gaseous reactant with more “accessible” active sites. Therefore, the present materials were considered as promising catalyst candidates for catalytic dehydrogenation of isobutane. 相似文献
3.
The synthesis of a composite material by thermal explosion in a reaction mixture of Ni + Al + Cr 2O 3 was studied. The thermodynamic parameters of combustion of the systems studied were estimated to predict the composition of the inorganic products (condensed or gaseous) of self-propagating high-temperature synthesis and calculate the adiabatic combustion temperature. It is shown that the synthesis process involves competing reactions in the sample volume which are responsible for the formation of a multiphase product. The influence of the content of Cr 2O 3 in the reaction system on the strength characteristics of the product synthesis was studied. The microstructure of the synthesized samples was examined, and their micro-hardness, toughness and residual porosity were determined. The possibility of obtaining a homogeneous material based on NiAl intermetallic compound containing dissolved chromium and chromium oxide nanoparticles is shown. 相似文献
4.
In this paper, a free radical polymerization system consisting of DPE was used to prepare magnetic composite microspheres. Fe 3O 4/P(AA-MMA-St) core-shell magnetic composite microspheres have been synthesized by copolymerization of acrylic acid, methyl methacrylate and styrene using DPE as radical control agent in the presence of Fe 3O 4 nanoparticles. The structure and properties of the magnetic composite microspheres were analyzed by FTIR, 1H NMR, SEC-MALLS, TEM, TGA, VSM and other instruments, and the formation mechanism of composite microspheres was supposed by those results. It was found that the Fe 3O 4/P(AA-MMA-St) microspheres were nano-size with relatively homogeneous particle size distribution, perfect sphere-shaped morphologies, superparamagnetism with a saturation magnetization of 18.430 emu/g, and high magnetic content with a value of 40%. 1H NMR and TEM analysis indicated that at the first stage of polymerization, a DPE-containing copolymer of acrylic acid, methyl methacrylate formed and was then absorbed on the surface of Fe 3O 4 nanoparticles. Contact angle analysis indicated that the DPE-containing copolymer improved hydrophobicity of Fe 3O 4 nanoparticles through chemical absorption. In the second step polymerization, certain amount of monomers of styrene and residue methacrylate were initiated by the DPE-containing copolymer on the Fe 3O 4 nanoparticles' surface and resulted in the formation of Fe 3O 4/P(AA-MMA-St) composite microspheres. 相似文献
5.
The wear resistance of chromium oxide (Cr 2O 3) coatings could be improved by doping modification and changing the structural scale, etc. In this study, micrometric Cr 2O 3 coatings were doped with different additives, CeO 2 and Nb 2O 5. Moreover, Cr 2O 3 coatings were deposited from nanostructured feedstock by the combination process of plasma spraying and dry-ice blasting. The correlation between the microstructure, chemical components and tribological properties of plasma-sprayed Cr 2O 3-based coatings was discussed based on the investigation of their porosity, hardness and friction behaviors. The results showed that the composite coatings doped with additives exhibited a higher microhardness, corresponding to a lower porosity than pure Cr 2O 3 coating under the identical plasma-spray condition. CeO 2 constituent was found to improve the wear resistance of Cr 2O 3 coating while Nb 2O 5 incorporation corresponds to a steep rise in the friction coefficient. The mismatch of coefficient of thermal expansion (CTE) between Cr 2O 3 and Nb 2O 5 lamellae facilitated the origin of fatigue cracks and the formation of microfracture pits. Although the combination process promotes a porosity reduction, the nanostructured Cr 2O 3 (n-Cr 2O 3) coatings present a lower microhardness than micrometric coatings, due to their loosen microstructure from insufficient plasma power compared to microscaled coatings. The wear mechanisms of both the micro- and nanometric Cr 2O 3 coatings are fatigue cracks and material transfer. 相似文献
6.
Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer‐sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr 2O 3) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles ( Φ≈50 nm) with Cr 2O 3 micro‐ and nanoparticles ( Φ≈20 nm), respectively, in hexane solution. The dried Cr 2O 3/Al composite powders were ignited by using a CO 2 laser beam. The use of nanosized Cr 2O 3 particles incontestably improves the energetic performances of the Al/Cr 2O 3 thermite since the ignition delay time was shortened by a factor 3.5 (16±2 vs 54±4 ms) and the combustion rate (340±10 mm s −1) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al‐based thermites formulated from Cr 2O 3 is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO 2, WO 3). Finally, our study shows that the decrease of Cr 2O 3 particle size has an interesting and beneficial effect on the energetic properties of Cr 2O 3/Al thermites and appears as an alternative to tune the properties of these energetic materials. 相似文献
7.
This study was aimed to assess the effects of reinforcement nanoparticles content, on the microstructural features, mechanical properties, and corrosion-related properties of Ni-Co-Cr 2O 3 nanocomposite coatings. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analysis were employed in order to evaluate the microstructural features and chemical composition of the nanocomposites. Moreover, the microhardness tester and electrochemical impedance spectra (EIS) tests coupled with potentiodynamic polarization measurements were used to investigate the mechanical and corrosion-related properties, respectively. Results demonstrate that albeit the volume fraction of cobalt in coating, average particle size, Cr 2O 3 nanoparticle content in coating, and microstructural features are of prime significance in determining the mentioned properties of the nanocomposite coatings, Co content is more important. Actually, Cr 2O 3 nanoparticles serve as suitable nucleation sites for Co particles deposition throughout the microstructure. Thus, combined actions of Cr 2O 3 nanoparticles incorporation and their optimal content ensures the nucleation of high population of Co particles, which significantly contributes to the improvement in the properties. The Ni-Co-8.9 wt%Cr 2O 3 nanocomposite coating exhibits the superior mechanical and corrosion-related properties. 相似文献
8.
Nanostructured FeAl 2O 4-based ceramic matrix composite coatings were prepared in-situ by reactive plasma spraying micro-sized Al–Fe 2O 3 and Al–Fe 2O 3–Cr 2O 3 powders. The microstructure, toughness, Vickers hardness, and adhesive strength of these coatings were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and mechanical tests. The results indicated that both the coatings exhibited a nanostructured microstructure. The grains of coating AFC sprayed with Al–Fe 2O 3–Cr 2O 3 powders are finer than those of the coating AF sprayed with Al–Fe 2O 3 powders. The composite nano-coating sprayed with Al–Fe 2O 3–Cr 2O 3 powders exhibited higher hardness and better wear resistance compared with those of the composite nano-coating sprayed with Al–Fe 2O 3 powders. The adhesive strength, toughness, and wear resistance of the composite coating sprayed with Al–Fe 2O 3–Cr 2O 3 powders were significantly enhanced compared with those of the composite coating sprayed with Al–Fe 2O 3 powders, which were attributed to the Cr 2O 3 addition. 相似文献
9.
The current study is focused on the microstructure, phase transition, and mechanical properties of the aluminum yttrium oxide (Al–Y2O3) composite material. Microwave hybrid sintering using Y2O3 nanoparticles as reinforcement at various (i.e., 0.5, 2, 3.5 and 5) wt% was used. Simultaneous thermal analysis (STA) and X-ray photoelectric spectroscopy (XPS) were used to investigate the chemical interaction between Al and Y2O3. This research will aid in gaining a better knowledge of the changes in thermal characteristics and compositional changes that occur throughout the microwave hybrid sintering process. The insight into material properties reveals that intermetallic Al3Y and Al2O3 are generated during the synthesis process, which was substantiated by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDX) analysis. The Al–Y2O3 composite material has a well-consolidated microstructure and improved mechanical characteristics. To further understand material behaviour, a robust and non-destructive depth sensing nano-indentation technology was being used. With the addition of 5 wt% Y2O3, the microhardness of composite material is enhanced by 1.62 times. Furthermore, with 5 wt% Y2O3, the produced composite's nano hardness and elastic modulus augmented by 2.43 and 1.8 times, respectively. It is caused by the presence of intermetallic in the composite material, as well as the prevalence of uniform reinforcement distribution. 相似文献
10.
Chromium sesquioxide (Cr 2O 3) films were deposited on Ni-based high-temperature alloy substrates by an arc ion plating technique and then annealed at different temperatures and heating rates. The influence of annealing conditions on the toughness of Cr 2O 3 films was calculated according to spherical indentation tests. The increase in grain size and compressive stress, variety of microstructure and surface morphology, and atom diffusion that resulted from annealing caused toughness variations. The increase in grain size closed micro-cracks along the direction of film growth. Compressive stress and a multi-crystal plane led to cracks caused by indentation that required more energy to break through the film. In the process of indentation, turning, bifurcating, and bridging of cracks on film surface was also able to dissipate energy. Atom diffusion in the process of 1000 °C annealing also played a role in grain boundary toughening. The toughness improvement of Cr 2O 3 film significantly improved friction life. 相似文献
11.
The development of self‐assembled ZnO nanoparticles within a diblock copolymer matrix using wet chemical processing specific to ZnO is reported. Diblock copolymers consisting of polynorbornene and poly(norbornene–dicarboxcylic acid) (NOR/NORCOOH) were synthesized with a block repeat unit ratio of 400 for the first block and 50 for the second block, to obtain spherical microphase separation. The block copolymer self‐assembly was used to template the growth of ZnO nanoparticles by introducing a ZnCl 2 precursor into the second polymer (NORCOOH) block at room temperature and processing the copolymer by wet chemical methods to substitute the chlorine atoms with oxygen. X‐ray photoemission spectroscopy (XPS) verified the conversion of ZnCl 2 to ZnO by monitoring the disappearance of the Cl 1 s peak and the shift in the binding energy of the Zn 2 p3 peak in the high‐resolution spectra. The substitution of Cl by O was found to be a highly preferential process, whereby only one approach using a weak base (NH 4OH) succeeded in effectively replacing Cl with O to result in spherical ZnO nanoparticles having a size ranging from 7 to 15 nm, as determined by transmission electron microscopy. The development of such block copolymer‐templated ZnO nanoparticles% is important in enabling the functionalization of large‐area nanodevice technologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1058–1061, 2003 相似文献
12.
Different additives (metals, ceramics, and metal/ceramic assembles) were incorporated into chromium oxide (Cr 2O 3) coatings to improve its wear resistance. The doping or co-doping effects were compared in terms of the microstructure, phase composition, microhardness and sliding wear properties of plasma-sprayed Cr 2O 3-7wt.% Mo, Cr 2O 3-7wt.% Nb 2O 5, Cr 2O 3-4wt.% MoO 3-3wt.% Mo, and Cr 2O 3-4wt.% Nb 2O 5-3wt.% Mo coatings. Under the low sliding loads, the composite coatings mated with WC-Co counterparts have lower friction coefficients than those against Si 3N 4, which are inverse with their microhardnesses, but more obvious fatigue wear characteristics. Under the high sliding loads, Mo/Nb 2O 5 co-doped Cr 2O 3 coating (CNM) has the best wear resistance than other coatings, due to the delaying co-effects of crack formation and propagation on basis of the crack deflection and the toughening effects of Mo additives and the high hardness of Nb 2O 5 additives. As the reciprocating sliding loads exceed the critical stress of brittle Cr 2O 3-based coatings, the coating detachments occur, displaying obvious fatigue wear characteristics. 相似文献
13.
Cr 2O 3Mo and (CrAl) 2O 3 eutectics were investigated. Directional solidification was observed in these eutectics. By changing the solidification rate, the dependence of the microstructure on this parameter has been defined. The possibility of forming composites with a random metal fibre orientation has been demonstrated when the solidification rate is very high. A composite microstructure containing 30–60 μm grains can be obtained when these eutectics are cooled naturally after melting. After mechanical grinding these materials can be hot-pressed, resulting in a high strength, high work of fracture material. 相似文献
14.
In this study, individual Al 2O 3 and Cr 2O 3 coatings and Cr 2O 3-25, 50, 75 wt% Al 2O 3 composite coatings were applied on carbon steel by atmospheric plasma spraying method. Corrosion experiments were performed on as-sprayed and epoxy resin sealed coatings including potentiodynamic polarization, electrochemical impedance spectroscopy and long-term immersion in 3.5 wt% NaCl solution. Phase composition and microstructure of the coatings were investigated by x-ray diffraction, optical microscopy and scanning electron microscopy, before and after the corrosion experiment. The results showed that the Cr 2O 3 coating exhibited the best corrosion resistance, due to the densest microstructure and highest adhesion strength. The Cr 2O 3-25 wt% Al 2O 3 coating had the highest interconnected porosities and thus had the least corrosion resistance compared to other coatings. In general, the as-sprayed coatings induced a maximum increase of 3.93 times the polarization resistance (R p) in the polarization experiment and a 3.5 times increase in the charge transfer resistance (R ct) in the EIS experiment, which was not significant. Stresses caused by increased volume of corrosion products in the coating-substrate interface resulted in the spallation of Cr 2O 3-25, 50 wt% Al 2O 3 coatings from the substrate over long-term of immersion. The adhesion strength of the coatings was a determining criterion for the long-term durability of the coatings. The sealing treatment resulted in a significant increase in R p and R ct. 相似文献
15.
Graft copolymer nanocomposites based on cashew gum and poly(acrylamide) with different concentrations of nano‐iron‐oxide particles (Fe 3O 4) have been prepared by an in situ polymerization method. The characterization of graft copolymer composite was carried out by FTIR, UV, XRD, SEM, DSC, and TGA, electrical conductivity, and magnetic property [vibrational sample magnetometer (VSM)] measurements. The shift in the spectrum of UV and FTIR peaks shows the intermolecular interaction between metal oxide nanoparticles and the graft copolymer system. The spherically shaped particles observed from the SEM images clearly indicating the uniform dispersion of nanoparticles within the graft copolymer chain. The XRD studies revealed that the amorphous nature of the graft copolymer decreases by the addition of Fe 3O 4 nanoparticles. The glass transition temperature studied from DSC increases with increase in concentration of metal oxide nanoparticles. Thermal stability of composite was higher than the pure graft copolymer and thermal stability increases with increase in content of nanoparticles. Electrical properties such as AC conductivity and dielectric properties of the composites increased with increase in concentration of metal oxide nanoparticles. The magnetic property of graft copolymer nanocomposites shows ferromagnetic and supermagnetism and the saturation of magnetism linearly increased with increasing the Fe 3O 4 content in the polymer composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43496. 相似文献
16.
In this study, the microstructure and mechanical properties of the atmospheric plasma-sprayed Cr 2O 3 (C), Cr 2O 3-20YSZ (CZ), and Cr 2O 3-20YSZ-10SiC (CZS) coatings were evaluated and also compared with each other, so as to explain the coatings wear behavior. Microstructural evaluations included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and porosity measurements. Mechanical tests including bonding strength, fracture toughness, and micro-hardness tests were used to advance our understanding of the correlation between the coatings properties and their wear behavior. The sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of multimodal YSZ and subsequent SiC reinforcements to the Cr 2O 3 matrix resulted in an increase in the fracture toughness and Vickers micro-hardness, respectively. It was found that the composite coatings had comparable coefficients of friction with pure Cr 2O 3 coatings. When compared with the C coating, the CZ and CZS composite coatings with higher fracture toughness exhibited superior wear resistance. Observation of the wear tracks of the coatings indicated that the lower wear rates of the CZ and CZS coatings were due to the higher plastic deformation of the detached materials. In fact, improvement in the wear resistance of the composite coatings was attributed to a phase transformation toughening mechanism associated with tetragonal zirconia which created more ductile tribofilms during the wear test participated in filling the pores of coatings. 相似文献
17.
Nano-sized Nb 2O 5/carbon cluster/Cr 2O 3 composite material was prepared by the calcination of NbCl 5/chromium acetylacetonate/epoxy resin complex under an argon atmosphere. The Pt-loaded Nb 2O 5/carbon cluster/Cr 2O 3 composite material shows the photocatalytic activity under visible light irradiation. The composite material successfully decomposed the water into H 2 and O 2 in the [H 2]/[O 2] ratio of 2. Electron spin resonance spectral examination suggests a two-step electron transfer in the process of Nb 2O 5 → carbon cluster → Cr 2O 3 → Pt. 相似文献
18.
Alumina‐chrome (Al 2O 3–Cr 2O 3) refractories with Al 2O 3:Cr 2O 3 molar ratio 1:1 were synthesized in the temperature range of 1400–1700°C by conventional solid–oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al 2O 3–Cr 2O 3 refractories was investigated without changing the Cr 2O 3 source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al 2O 3–Cr 2O 3 refractories prepared with hydrated alumina as Al 2O 3 source show better densification and hot mechanical strength than corresponding calcined variety. 相似文献
19.
We report the encapsulation of the antiferromagnetic and magnetoelectric oxide Cr 2O 3 inside both multi - and single-walled carbon nanotubes. This is achieved by a two step post-synthesis filling process which involves the filling of nanotubes with CrO 3 either from aqueous solution or from the molten phase, followed by appropriate annealing sequences. TEM imaging confirms significant filling rates for both multi- and single-walled carbon nanotubes. Analytical transmission electron microscopy implies that after secondary annealing Cr 2O 3 is formed inside the nanotubes. 相似文献
20.
In this article, we present new samples of lamellar magnetic nanocomposites based on the self-assembly of a polystyrene- b-poly( n-butyl methacrylate) diblock copolymer synthesized by atom transfer radical polymerization. The polymer films were loaded with magnetic iron oxide nanoparticles covered with polystyrene chains grown by surface initiated-ATRP. The nanostructuration of the pure and magnetically loaded copolymer films on silicon was studied by atomic force microscopy, ellipsometry, neutron reflectivity and contact angle measurement. The present study highlights the strong influence of the copolymer extremity - driven itself by the choice of the ATRP chemical route - on the order of the repetition sequences of the blocks in the multi-lamellar films. In addition, a narrower distribution of the nanoparticles’ sizes was examined as a control parameter of the SI-ATRP reaction. 相似文献
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