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1.
Tantalum(V) and niobium(V) oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Ta and Nb anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. At the initial stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the acetone solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. In this stage, anodic corrosion proceeds only in the presence of Br2, and not in acetone containing I2. Finally, Ta or Nb species are deposited directly on the cathode surface via the reactions with cathodically generated hydroxide ions, and the films need to be annealed at high temperature to effect crystallization. In these processes, the metal plate acts as a soluble anode with respect to Br and as a metal source for electrodeposition. The coating on a stainless steel substrate prepared by the present technique acts as an effective barrier against electrolytic corrosion.  相似文献   

2.
Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H2 permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H2/N2 permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H2/N2 permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H2 permeance and the H2/N2 permselectivity of the amorphous silica membrane on the block type were 1.1 × 10-7 mol/m2 · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.  相似文献   

3.
    
Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H2 permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H2/N2 permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H2/N2 permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H2 permeance and the H2/N2 permselectivity of the amorphous silica membrane on the block type were 1.1 × 10?7 mol/m2 · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.  相似文献   

4.
Self-organized porous titanium oxide prepared in Na2SO4/NaF electrolytes   总被引:1,自引:0,他引:1  
The anodic formation of nanoporous TiO2 on titanium was investigated in Na2SO4 electrolytes containing low concentrations of NaF (0.1-1 wt.%). It was found that under optimized electrolyte conditions and extended polarization, a self-organized nanostructure consisting of porous TiO2 is obtained. The porous structure is arranged in sections of arrays with single pore diameters of typically 100 nm and an average spacing of 150 nm. The pores are open at the top and covered by oxide at the bottom. Compared with earlier work, we show that using a neutral NaF electrolyte significantly thicker porous layers can be obtained than in acidic solutions.  相似文献   

5.
The interfacial adhesion of the carbon fiber (CF) reinforced polyurethane (PU) composite was improved by the means of anodic oxidation treatment. The mechanical and reciprocating sliding wear properties were studied and results showed that the anodic oxidation treatment have definitely improved the mechanical strength. And the wear and the friction coefficient of PU decreased with the addition of CF. The friction coefficients of anodic oxidation treated CF/PU composites are lower than those of PU and CF/PU composite. The interfacial adhesion between the CF and PU dominated the main wear mechanisms.  相似文献   

6.
The effect of the solvent on the anodic growth of titania nanotubes in HCl dissolved in water, ethylene glycol and 2-propanol was studied. These nanotubes grow with locally rapid breakdown of the passive TiO2 film forming a forest of nanotubes-bearing microtowers with the background of passive TiO2 Film. These bundles of assembled-groups of titania nanotubes look like Pillars corals. The low relative permittivity of the 2-propanol led to lowering of dissociation of HCl and hence lowering the activity of H+ and Cl ions which in turn led to suppress of dissolution of titania and increasing the growth rate of the titania nanotubes. The X-ray diffraction pattern showed that the titania nanotubes after annealing change to the crystalline anatase phase. The anodic films showed characteristic coloration with intensity and color that changes (qualitatively) with time of anodization.  相似文献   

7.
In this paper, basic electrochemical processes (such as oxide film growth, anodic dissolution and oxygen liberation) on an aluminium anode in a model alkaline solution are considered under conditions of galvanostatic DC plasma electrolytic oxidation (PEO). The experiments performed include: (i) recording and analysis of the main electrical characteristics of the process; (ii) determination of the oxide layer thickness; (iii) anodic gas collection and composition analysis and (iv) electrolyte analysis to determine dissolved aluminium. Four different stages of the PEO process have been identified, characterised by various rate proportions of the partial anodic processes. Overall current efficiency of the oxide film formation has been estimated to be in the 10-30% range. The film growth rate decreases significantly with increasing electrolyte concentration from 0.5 to 2 g l−1 KOH, since the rate of anodic dissolution increases. Oxygen evolution is shown to be the main electrochemical process at the potentials corresponding to the plasma stages of the electrolysis. The overall rate of oxygen liberation at the anode exceeds the Faraday yield, which is probably due to the radiolytic effect of the plasma discharge on the adjacent electrolyte volume.  相似文献   

8.
Anodic behaviour of amorphous Ni-P alloys containing 23 and 27 at.% P was compared to that of pure Ni. Measurements were performed in 0.1 M sulphate solutions of different pH by means of potentiodynamic polarization and impedance spectroscopy at selected anodic potentials. Significant discrepancies in the course of anodic polarisation curves and impedance spectra between amorphous Ni-P and pure Ni were seen. Amorphous Ni-P alloys exhibit a suppression of dissolution in the active range of Ni, whereas they show a faster dissolution in the passive domain of Ni. From the other side, there are minor modifications in impedance spectra taken for Ni-P over a wide range of anodic potentials, whereas Ni exhibit essential changes of impedance spectra within the same potential region, related to the active-passive transition of this metal. The charge transfer resistance of the anodic dissolution for amorphous Ni-P decreases gradually with increasing anodic potential in contrast to a sharp increase of this parameter for pure Ni in the region of its passivation. In contrast to Ni, the anodic dissolution of amorphous Ni-P exhibits a slight dependence on pH. These findings prove that the anodic dissolution suppression of amorphous Ni-P cannot be associated with the oxide passivity typical of pure Ni.  相似文献   

9.
《Ceramics International》2022,48(18):26028-26041
Multilayered C–Si–Al coatings with various morphologies were deposited on carbon fibers (CFs) using magnetron sputtering. The thickness of the coatings was increased from 0.5 to 1.5 μm by magnetron sputtering between 90 and 120 min. C–Si–Al coatings of suitable thickness were heat-treated at 600 °C and transformed into C–Si–Al2O3 coatings by one-step anodic oxidation (AO). The oxidation time for the one/two-step anodic oxidation and the ratio of oxidation time for the two-step anodic oxidation significantly influenced the morphologies of the C–Si–Al2O3(AO) coatings. Al2O3 coatings with satisfactory morphologies and structures were prepared by two-step anodic oxidation with a total time of 30 min and a ratio of 1:1 between the initial and secondary oxidation times. The multilayered C–Si–Al2O3(AO) coatings were modified to C–Si–Al2O3 coatings by secondary heat treatment at 1050 °C. Subsequently, hot-press sintering was used to prepare CFs with multilayered C–Si–Al2O3 coating-reinforced hydroxyapatite (CF/C–Si–Al2O3/HA) composites. The multilayered C–Si–Al2O3-coated CFs demonstrated good resistance to oxidation and thermal shock. This could effectively protect CFs from oxidative damage and maintain its strengthening effect during sintering. The multilayered C, Si, and Al2O3 coatings effectively reduced the difference between the coefficient of thermal expansion of the CFs and HA matrixes. The interfacial gaps between the multilayered coatings and HA were reduced. This could enhance the mechanical performance of the composites. The CF/C–Si–Al2O3/HA composites exhibited improved mechanical properties with a bending strength of 83.94 ± 12.29 MPa, and fracture toughness of 2.45 ± 0.08 MPa m1/2. This study can broaden the application of CF/C–Si–Al2O3/HA biocomposites as bone-repair materials and help obtain CF-reinforced composites with excellent mechanical properties that are fabricated or serviced at high temperatures.  相似文献   

10.
Porous anodic alumina (PAA) has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure.  相似文献   

11.
稳定多晶氧化铝纤维质量之研究   总被引:1,自引:0,他引:1  
通过改变胶体添加剂和热处理参数,提高纤维化器的转速,达到了稳定胶体粘度、改善成纤性能、降低纤维直径、稳定并提高氧化铝纤维质量、降低生产成本之目的。  相似文献   

12.
The generation of oxygen gas within an amorphous anodic alumina film is reported. The film was formed by anodizing aluminum, which was first electropolished and then chemically polished in CrO3-H3PO4 solution, in sodium tungstate electrolyte. The procedure results in incorporation of mobile Cr3+ species, from the chemical polishing film, and mobile W6+ species, from the electrolyte, into the amorphous structure. The tungsten species are present in the outer 27% of the film thickness, while Cr6+ species occupy a thin layer within the tungsten-containing region. Above the Cr3+ containing layer, a band develops that contains oxygen bubbles of a few nanometres size. The oxygen is generated by oxidation of O2− ions of the alumina. A mechanism of oxygen generation within the alumina is proposed based on the electronic band structure of the oxide, modified by the Cr3+ and W6+ species, and on the ionic transport processes during oxide growth.  相似文献   

13.
The growth of barrier-type anodic films at high efficiency on a range of sputtering-deposited Al-Hf alloys, containing from 1 to 95 at.% Hf, has been investigated in ammonium pentaborate electrolyte. The alloys encompassed nanocrystalline and amorphous structures, the latter being produced for alloys containing from 26 to 61 at.% Hf. Except at the highest hafnium content, the films were amorphous and contained units of HfO2 and Al2O3 distributed relatively uniformly through the film thickness. Boron species were confined to outer regions of the films. The boron distributions suggest that the cation transport number decreases progressively with increasing hafnium concentration in the films, from ∼0.4 in anodic alumina to ∼0.2 for a film on an Al-61 at.% Hf alloy. The distributions of Al3+ and Hf4+ ions in the films indicate their similar migration rates, which correlates with the similarity of the energies of Al3+-O2− and Hf4+-O2− bonds. For an alloy containing ∼95 at.% Hf, the film was largely nanocrystalline, with a thin layer of amorphous oxide, of non-uniform thickness, at the film surface. The formation ratios for the films on the alloys changed approximately in proportion to the hafnium content of the films between the values for anodic alumina and anodic hafnia, ∼1.2 and 1.8 nm V−1 respectively.  相似文献   

14.
The microporous alumina membrane with asymmetrical structure, having upper layer with pore diameter of 10 nm under and lower layer with pore diameter of 36 nm, was prepared by anodic oxidation using DC power supply of constant current mode in an aqueous H2SO4 solution as a electrolyte. The aluminum plate was pretreated with thermal oxidation, chemical polishing and electrochemical polishing before anodic oxidation. The membranes were prepared by controlling the current density such as a very low current density for upper layer and a high current density for lower layer of membrane. By controlling the cumulative charge density, the thickness of upper layer of membranes was about 6 Μm and the total thickness of membranes was about 80–90 Μm. We found from gas permeation experiments with the membranes prepared by above method that the mechanism of gas permeation of the all membranes prepared under each condition complied with model of the Knudsen diffusion.  相似文献   

15.
氧化铝基连续陶瓷纤维的发展现状   总被引:1,自引:0,他引:1  
李泉  宋慎泰 《耐火材料》2006,40(1):50-52
介绍了国内外氧化铝基连续陶瓷纤维的研究现状,并阐述了它在航天领域、机械制造领域和过滤材料方面的应用现状和发展前景。  相似文献   

16.
Gold nanoparticles supported on alumina have been produced using the anionic exchange method and ammonia washing procedure. The catalysts are tested in the reaction of total oxidation of a mixture of light hydrocarbons and carbon monoxide in order to study the possibility of application in the reduction of cold start emissions. The obtained results are promising according to the temperature range observed for the oxidation of unsaturated hydrocarbons. The results obtained for acetylene confirms the difference of oxidation of this hydrocarbon over gold catalysts. An ageing procedure has been employed. This procedure does not affect the comportment of the catalysts versus hydrocarbon oxidation.  相似文献   

17.
The non-Faradaic material loss is the difference between the material loss measured by the weight loss method and the one determined by Faraday's secondary law. Being observable in flowing corrosive electrolytes, it is promoted by increasing wall shear stress and anodic dissolution, is reduced by the increasing strength of electrode, and disappears in quiescent electrolytes or under cathodic protection. Therefore, the non-Faradaic material loss is likely a result of certain corrosion-aided mechanical damage mechanisms. A phenomenological model is proposed for the quantitative evaluation of the non-Faradaic material loss. The applicability of this model has been verified by the test data measured in both aqueous and non-aqueous electrolytes.  相似文献   

18.
The polarization behaviour of zinc in alkaline solution has been investigated using atomic emission spectroelectrochemistry. By independently measuring the oxidation rate of zinc (electrical current) and the rate of Zn2+ dissolution (partial elemental current) it is possible to calculate the amount of insoluble zinc cations produced at any instant. Assuming the insoluble cations are present as a zinc oxide film, the growth of this film as a function of potential and time was determined. On the basis of kinetic evidence, it was found that at least three forms of zinc based oxide/hydroxide films form during polarization experiments. Type I oxide formation occurs when the metal/electrolyte interface becomes locally saturated with Zn2+ ions. Type II oxide forms on the metal surface underneath the film of Type I oxide but has little inhibiting effect on zinc dissolution. Type III oxide is produced in much smaller quantity and results in a transition to the passive state. This may be due to a potential induced transition of Type II → Type III oxide.  相似文献   

19.
Influence of substrate microstructure on the growth of anodic oxide layers   总被引:2,自引:0,他引:2  
The effects of permanent mold cast microstructure on the growth of anodic oxide layers on three different aluminum substrates (i.e. Al99.8, AlSi10, and AlSi10Cu3, wt.%) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and laser scanning confocal microscopy (LSCM). The anodic oxidation was performed galvanostatically in 2.25 M H2SO4, at 0 °C. The oxide layers developed a microscale topography mainly determined by the morphology of aluminum grains and cells. A low amount of insoluble impurities, uniformly distributed, would contribute to the growth of oxide layers with minimum defects and uniform thickness on the pure aluminum substrate whereas for the binary and ternary systems, a fine cell structure and a modified morphology of Si particles would be favorable. The Al-Fe and Al-Fe-Si particles were occluded in the oxide layers next to Si particles, blocking locally the oxide growth whereas Al2Cu particles were preferentially oxidized. In addition, the presence of Si particles in the layer influenced pore morphology by development of deflected pores around the particles.  相似文献   

20.
The interface state densities of wet anodic oxide layers on Si are normally very high and, therefore, there is need for special post-treatments. Repetitive oxidation/hydrogenation cycles in the current oscillating regime lead to improved passivation of the SiO2/Si interface. The atomic force microscopy (AFM) images reveal the formation of macroscopically rough surfaces (holes with a diameter of at least 100 nm and a depth of up to 10 nm). This kind of surface structure is more favourable to decrease the strain induced by the Si---O---Si bond angle mismatch. This peculiarity of Si surfaces conditioning in acidic NH4F solutions leads to a reduction of the defect concentration at the SiO2/Si interface without further processing.  相似文献   

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