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1.
《Journal of the European Ceramic Society》2002,22(2):183-189
We have developed a novel combination of electrophoretic deposition (EPD), reaction bonding and low temperature sintering techniques for the fabrication of yttria stablised zirconia (YSZ)/alumina composite coatings on Fecralloys. A mixture of ethanol and acetylacetone solvent was found to be an effective medium for YSZ and aluminium particle suspension. With the particle size of YSZ and aluminium being significantly reduced during ball milling. By using the EPD process, uniform green form coatings containing YSZ and aluminium particles were produced on Fecralloys. After oxidation of aluminium at 500°C and sintering at 1200°C, a dense and adherent YSZ/Al2O3 coating was produced. The presence of aluminium in the green form coatings not only contribute to the bonding between the coating and the metal substrate, but also compensate for the volume shrinkage of the coatings during sintering by the volume expansion arising from oxidation of aluminium to alumina. 相似文献
2.
We report a simple fabrication method for large-scale free-standing graphene–gold nanoparticle and graphene-single wall carbon nanotube composite films by using a centrifugal vacuum evaporation followed by a thermal reduction process. The homogeneous mixture of a graphene oxide (GO) suspension with gold nanoparticle (Au NP) or single wall carbon nanotube (SWCNT) is self-assembled at the air/liquid interface, resulting in the multilayered GO–Au NP and GO–SWCNT composite films. The cross-sectional image reveals that the graphene layers are orderly stacked in the reduced GO–Au NP film, while the reduced GO–SWCNT film shows a randomly packed morphology due to the dominant π–π interaction between the side wall of SWCNTs and the GO surfaces. In particular, the reduced GO–Au NP film shows an increased electrode kinetics and cyclic voltammetric response in proportion to the amount of Au NPs, and 3-fold enhancement of anodic peak current was observed compared with that of the reduced GO films. We employed the reduced GO–Au NP film as a matrix to immobilize tyrosinase enzyme for phenol detection, and the phenol-induced electrochemical catalytic reaction can be monitored with 3-fold higher sensitivity than the reduced GO film, demonstrating great potential of graphene composite as an electrochemical enzyme biosensor for environmental pollutant screening. 相似文献
3.
《Ceramics International》2015,41(7):8630-8636
Mullite-based cellular ceramics were prepared via the polymer precursor route using poly(silsesquioxane) in combination with particulate alumina or alumina/aluminum mixtures. The multi-functional preceramic polymer was used as pore-forming agent by employing a self-foaming process during the polymer cross-linking step, as well as a precursor for reactive silica, one of the reagents in mullite formation. The size of filler particulates was found to strongly affect foaming of the polymer/filler mixtures, with coarser particles facilitating an improved foaming performance. Thermal conversion in air at 1600 °C resulted in the formation of cellular ceramics with high mullite contents. The partial substitution of alumina with aluminum in the initial mixtures resulted in improved mechanical properties at comparable porosities, resulting in compressive strengths of 0.3 MPa at total porosities of 93%. A correlation between thermal analysis data and crystalline phase development during the thermal treatment allowed for the clarification of processes taking place during heat treatment, yielding information for a future process optimization approaches. 相似文献
4.
Fabrication and characterization of composite sol-gel coatings on porous ceramic substrate 总被引:2,自引:0,他引:2
Highly porous ceramic materials were coated using a composite sol-gel method. Alumina powder is dispersed in a silica sol-gel solution and then dip-coated on the substrate. The resulting coatings present a composite microstructure in which crystalline alumina grains are linked to each other by an amorphous silica phase. In this work, we show that, by accurately controlling the sol-gel parameters (water, solvent and silica precursor (TEOS) ratio, pH and ageing time of the sol) and also the powder grain size distribution it is possible to obtain crack-free thick films (more than 20 μm in one step). These coatings present good adherence to the substrate, decrease the roughness and also close the surface porosity of the substrate. Coating mechanical properties have been evaluated thanks to micro-indentation measurements and linked to coating structural evolution with the thermal treatment temperature. 相似文献
5.
Electrochemical noise measurements (the study of the spontaneous fluctuations in electrode voltage and current which occur with respect to time) have been used to study the degradation of coated metal substrates. The technique has been found capable of distinguishing between paints in terms of both the extent and the mechanisms of corrosion occurring below the paint film and should prove to be an effective means of generating comparative performance data rapidly. Nominally identical coupled pairs of electrodes immersed in 0.6 M NaCl were studied at intervals over 2300 h. Two computer-controlled digital voltmeters simultaneously monitored each coupled electrode pair potential and also the current flow between the electrode pair, via a low noise zero resistance ammeter. Simple statistics were used to analyse the data. Standard deviations of voltage noise (σV) and current noise (σi) values were found to be indicative of the quality of corrosion protection. Good coatings gave relatively large σV values, whereas poor coatings gave relatively large σi values. An estimate of the extent of delamination can be obtained from the total charge passed. 相似文献
6.
Boris Lakard Jean-Claude Jeannot Guillaume Herlem Pascal Blind Bernard Fahys 《Electrochimica acta》2005,50(9):1863-1869
A new type of electrochemical cell has been developed for use in electrochemical, chemical and biological applications. Using a platinum microelectrode as working electrode, this cell incorporates a silver microelectrode as reference electrode. These microelectrodes, whose area is equal to 1 μm2, were fabricated using photolithography, sputtering, and focused ion beam (FIB) technologies since these micro-fabrication techniques allow us to develop miniaturized electrochemical cells useful either for nanoelectrochemistry or biosensors applications. In this study, we show it is possible to coat a surface by chemical or biological compounds by immersing the microelectrodes in a solution, then setting a difference of potential between the two microelectrodes of the cell. For example, we used this miniaturized cell to realize the electrochemical polymerization of aniline into polyaniline to show that this electrochemical cell is efficient to coat a surface with a thin film of polymer. 相似文献
7.
Ramakrishnan RajagopalanJude O. Iroh 《Electrochimica acta》2002,47(12):1847-1855
Polyaniline-polypyrrole composite coatings were formed on carbon fibers by potentiostatic electrochemical polymerization. Electropolymerization was done by varying the applied potential and molar feed ratio of monomers. The dual nature of the composite coatings was deduced from the current-time (I-t) curves traced during polymerization. I-t curves were also used to predict the mechanism of the formation of composite coatings. UV-vis absorption spectroscopy was used to study the electronic structure of the composite coatings. 相似文献
8.
《Ceramics International》2020,46(13):20871-20877
Cost-effective electrodes with high activity for hydrogen evolution reaction (HER) and durability are required to develop clean and renewable hydrogen energy. In this work, a porous Cu supported Ni-P/CeO2 composite coating was fabricated by a facile electrodeposition technique. Owing to the contribution from the 3D porous Cu support and the incorporating agglomeration-free and uniformly distributed CeO2 particles into the Ni-P matrix, the optimal composite coating (porous Cu supported Ni-P/CeO2 (20 g L-1)) exhibits outstanding electrocatalytic performance with small overpotentials (η) of 118 and 320 mV at a cathodic current density of 10 and 100 mA cm2. Moreover, the composite electrode also presents excellent electrochemical stability in the alkaline solution. This work provides a feasible option to fabricate composite electrodes that may have desirable electrochemical properties for HER. 相似文献
9.
镍-磷微米金刚石化学复合镀工艺及镀层性能 总被引:2,自引:0,他引:2
采用化学复合镀法在低碳钢表面镀覆Ni–P–金刚石复合镀层。化学镀基础镀液含硫酸镍25g/L、次磷酸钠25g/L、结晶乙酸钠15g/L和柠檬酸钠10g/L,pH为4~5,温度80~85°C。金刚石颗粒的平均粒径为5μm。比较了直接复合镀及两步复合镀工艺分别所得镀层的微观形貌。借助材料表面微纳米力学测试仪及磨损试验机研究了复合镀层的性能。先化学镀Ni–P合金30min,然后在机械间歇搅拌下加入金刚石0.4g/L,再复合镀10min,可使金刚石颗粒均匀地镶嵌在镍基镀层中,并有一部分凸出镀层表面,从而增大了镀层的摩擦因数及与GCr15相对面的咬合力。金刚石复合镀层的干摩擦因数可达0.518。动载条件下未出现脱落现象。 相似文献
10.
Water permeation, water absorption, d.c. resistance, and electrochemical impedance spectroscopy (EIS) measurements were performed
on films of epoxy-polyamide used as binder in paint formulations. Barrier properties were found to be highly dependent upon
the thickness of films. In thick films, water permeation measurements revealed the presence of pathways attributed to frozen
holes, through which the flow is not governed by diffusion. In thin films, the presence of pinholes was detected by d.c. resistance
and EIS measurements.
LACTEC, área de Materiais — AMAT, Caxia Postal 19067, CEP 81531 - 990, Curitiba, Paraná, Brazil.
Departamento de Química, Grupo de Processamento e Propriedades em Polímeros, Caixa Postal 675, CEP 13565-905, S?o Carlos,
S?o Paulo, Brazil. 相似文献
11.
SiC whisker reinforced reaction bonded SiC composites have been developed for fabricating large scale, complex shaped structural components. Here the composites were prepared with the method of slip casting and liquid silicon infiltration at 1650 °C. The distribution, morphology and reinforcing behaviors of the SiC whisker in the composite were investigated. It is revealed that the introduction of SiC whisker increases the porosity of the green body, and accordingly the bulk density of the composite. Whisker pullout can be clearly observed on the fracture surface, implying a moderate bonding strength between the whisker and matrix. After liquid silicon infiltration, the SiC whisker keeps its initial diameter and morphology in the case of 15 wt% whisker. The fracture toughness is enhanced by SiC whisker, reaching the peak value of 4.2 MPa m1/2 at the whisker fraction of 20 wt%. Whisker pullout, whisker bridging and crack deflection are considered as the main toughening mechanisms. 相似文献
12.
《Journal of the European Ceramic Society》2007,27(4):2095-2102
An in situ reaction bonding technique was developed to fabricate mullite-bonded porous silicon carbide (SiC) ceramics in air from SiC and α-Al2O3, using graphite as the pore-former. Graphite is burned out to produce pores and the surface of SiC is oxidized to SiO2 at high temperature. With further increasing the temperature, the amorphous SiO2 converts into cristobalite and reacts with α-Al2O3 to form mullite (3Al2O3·2SiO2). SiC particles are bonded by the mullite and oxidation-derived SiO2 to obtain porous SiC ceramics. The reaction bonding behavior, open porosity, pore size distribution and mechanical strength of porous SiC ceramics were investigated as a function of the sintering temperature, forming pressure and graphite content. In addition, the phase composition and microstructure were also studied. 相似文献
13.
通过恒电流和脉冲电流技术在钛基表面制备磷酸钙,然后经热碱处理得到羟基磷灰石(HAP)涂层。利用X射线衍射(XRD)、红外光谱(FT-IR)和扫描电镜(SEM)等手段对涂层的结构及形貌进行了表征,并对涂层的耐腐蚀性进行了研究。结果表明,恒电流与脉冲电流技术均可在钛基表面电沉积羟基磷灰石涂层,所得的2种涂层均具有良好的生物相容性;与恒电流方法制得的涂层相比,脉冲电流技术制得的涂层更均匀、致密,与基体结合强度较高,在模拟体液中表现出较好的耐腐蚀性。 相似文献
14.
Yttria-stabilized-zirconia (YSZ) coatings with thicknesses up to 420 μm have been prepared using a novel slurry process with pressure infiltration. Binary-sized particle slurries (binary-slurries), composed of nano-particle slurry (nano-slurry) and micro-sized preformed particles, were cast on metal substrates to form coatings. After sintering at 1150 °C for 1 h, preformed particles were cemented with nano-particles to form a porous YSZ coating. Subsequently, the nano-slurry was infiltrated into the porous coatings under pressure. The infiltrated nano-slurry filled the pores, and was sintered together with the porous coating, resulting in an increase in both density and mechanical properties of the coating. After 5–6 infiltration cycles, the coating reached 82% theoretic density and micro-hardness of 3.7 GPa. Such coatings could be used as thermal barrier coatings for high temperature applications. 相似文献
15.
Takanari Ouchi 《Electrochimica acta》2010,55(27):8081-9580
We investigated fabrication processes of magnetic nanodot arrays for the ultra-high density magnetic recording media by using an electrodeposition. A CoZrNb underlayer was sputter-deposited on a glass disk substrate as a soft magnetic underlayer (SUL). Nano-patterns were formed on the substrate by UV-nanoimprint lithography (UV-NIL) and CoPt was electrodeposited into the nano-patterns. For obtaining uniform CoPt nanodot arrays with high perpendicular coercivities, we applied thin Cu intermediate layer on CoZrNb SUL and minimized its thickness. As a result, we obtained CoPt nanodot arrays with 150-nm diameter, 300-nm pitches, and 20-nm heights, which have uniform structures, on the substrates with the construction of Cu (1-2 nm)/CoZrNb (100 nm)/Cr (5 nm)/glass disk. The perpendicular coercivity of the CoPt nanodot arrays was as high as 5.4 kOe. From these results, we showed that the Cu intermediate layer with even 1-2 nm thick considerably improved the deposition condition on the substrates with CoZrNb SUL to successfully fabricate CoPt nanodot arrays with the diameter and pitches of 80 nm and 160 nm with sufficient uniformity. 相似文献
16.
Thin polypyrrole coatings (∼ 10 μm thick) were formed on low carbon steel by an aqueous constant current electrochemical polymerization using oxalic acid as the electrolyte. The amount of polypyrrole coatings formed on steel increased with the applied current and monomer concentration. No significant change in the electropolymerization of pyrrole occurred as a result of increased electrolyte concentration. The induction time for electropolymerization decreased significantly with current density but was unaffected by the initial monomer and electrolyte concentration. The electropolymerization potential of pyrrole increased with increased current density (Cd), i.e., Ep = 0.62 + 0.41 [Cd], and decreased exponentially with increased monomer and electrolyte concentration, Ep = E0 exp-[M]. Scanning electron microscopy (SEM) showed that the microstructure of the polypyrrole coatings formed on steel was dependent on the current density to the extent that smoother and more uniform coatings are formed at low current density. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:417–424, 1997 相似文献
17.
Fabrication of SiC/diamond composite coatings by electrophoretic deposition and chemical vapor deposition 下载免费PDF全文
Shengjie Yu Zhaofeng Chen Yang Wang Ruiying Luo Tengzhou Xu Ying Pan Jiahao Liao 《International Journal of Applied Ceramic Technology》2017,14(4):644-651
In this research, SiC/diamond composite coatings were fabricated by a novel procedure that consisted of the electrophoretic deposition (EPD) of diamond particles onto graphite substrates followed by chemical vapor deposition (CVD) of SiC. Various concentrations of MgCl2 were employed to increase the deposition rate and uniformity of the deposits during the EPD process by giving a positive charge to diamond particles. The CVD of SiC was found to have a tightly connected diamond‐graphite interface and spherical texture. With higher weight fraction of diamond particles deposits, the wear of steel ball increased, while the wear of SiC coating decreased. 相似文献
18.
The performance of acrylic polyurethane composite coating and aliphatic urethane composite coating in 3.5% NaCl solution under ultra-violet radiation was studied with methods of EIS, SEM and FTIR. For aliphatic polyurethane coating, the coating resistance decreased and the coating capacitance and porosity increased more quickly than acrylic polyurethane coating. The acrylic polyurethane composite coatings showed better performance than aliphatic polyurethane composite coatings. IR spectra showed that under UV irradiation conditions, the failure mechanism of the two polyurethane coatings was the transformation of sec-amide to primary amides. The fractured bonds in acrylic polyurethane were mainly C–O bonds, while in aliphatic polyurethane they were mainly C–N bonds. The lower protection property of aliphatic polyurethane coating may be mainly attributed to the C–N bonds which are more liable to be broken. 相似文献
19.
For preparation of steel surfaces before applying an organic coating, waterjetting is a modern, effective and environmentally friendly method. However there is a lack of data on its performance in terms of the subsequent protection afforded by the paint compared with more conventional methods. Hence previously exposed steel panels had their surfaces prepared in a variety of ways (abrasion, blasting with garnet entrained in water (10 K psi) and waterjetting without garnet at two velocities (20 K psi and 40 K psi)) prior to coating with two typical maintenance coatings. These were then exposed under immersion condition in the laboratory and monitored using the DC resistance method. Another set of samples were exposed in a salt spray test in accordance with ASTM B 117 for 500 h. At the end of both tests DC measurements were carried out and the samples were inspected visually in terms of blistering and rust. Results showed that both the immersion test and the salt spray test differentiated the surface preparations methods in the same order. Thus control panels performed the best. Nearly as good though were the two (20 K psi and 40 K psi) sets of waterjetted samples. The abraded samples were variable but overall provided less protection. The panels blasted with garnet entrained in water (10 K psi) samples proved to be the worst. Characterisation of the surfaces prior to coatings using the scanning electron microscope was also conducted. A tentative explanation for the differing protection afforded involving the integrity of the oxide film was suggested. Further work is needed to substantiate this. Overall, with samples in the immersion test, results using electrochemical methods proved themselves to be very effective in assessing and even predicting performance in a relatively short period of time. The results also correlated with the salt spray test. Also the work showed that waterjetting is a very effective way of preparing the surface prior to maintenance painting. 相似文献
20.
Preliminary evaluation of the anticorrosive properties of aircraft coatings by electrochemical methods 总被引:5,自引:0,他引:5
L. B. Reynolds R. Twite M. Khobaib M. S. Donley G. P. Bierwagen 《Progress in Organic Coatings》1997,32(1-4):31-34
Strict regulations concerning the content of volatile organic compounds (VOCs) and heavy metals (Cr6+) in aircraft coating systems have increased the economic burden of the United States Air Force (USAF) in the area of coating maintenance. To this end, it is critical to have methods to characterize new coating systems in such a manner that the data can be used to predict accurately and reliably the expected lifetime of the coatings in service. Electrochemical noise method (ENM) and electrochemical impedance spectroscopy (EIS) are two techniques used to monitor extent and rate of corrosion. The USAF is currently employing these methods in order to supplement data acquired from traditional salt-spray methods. ENM and EIS are used to evaluate each component of the coating system and its contribution to corrosion prevention. Preliminary evaluations of an aircraft coating system on aluminum substrate (Al 2024-T3) produces resistance noise values of 106 to 107 Ω/cm2. It is hoped that these results will form the basis of coatings that give increased USAF fleet service life and reduction in maintenance manpower and materials costs. 相似文献