Electronic properties of electrolyte/anodic alumina junction during porous anodizing

The growth of porous oxide films on aluminum (99.99% purity), formed in 4% phosphoric acid was studied as a function of the anodizing voltage (23-53 V) using a re-anodizing technique and transmission electron microscopy (TEM) study. The chemical dissolution behavior of freshly anodized and annealed at 200 °C porous alumina films was studied. The obtained results indicate that porous alumina has n-type semiconductive behavior during anodizing in 4% phosphoric acid. During anodising, up to 39 V in the barrier layer of porous films, one obtains an accumulation layer (the thickness does not exceed 1 nm) where the excess electrons have been injected into the solid producing a downward bending of the conductive and valence band towards the interface. The charge on the surface of anodic oxide is negative and decreases with growing anodizing voltage. At the anodizing voltage of about 39 V, the charge on the surface of anodic oxide equals to zero. Above 39 V, anodic alumina/electrolyte junction injects protons from the electrolyte. These immobile positive charges in the surface layer of oxide together with an ionic layer of hydroxyl ions concentrated near the interface create a field, which produces an upward bending of the bands.     

Effect of the current density on the volume expansion of the deposited thin films of aluminum during porous oxide formation

The effect of the anodic current density, temperature and concentration of the oxalic acid on the volume expansion of porous alumina films formed from 1.8 μm thick aluminum films has been investigated. The volume expansion of the aluminum during oxidation was determined by the step height between the aluminum surface and the porous alumina surface at the edge of the anodized region, which was measured with a mechanical profiler with computer signal processing. Experiments showed, that the volume expansion factor as well as the cell dimensions is proportional to the anodizing voltage. The dependence of the volume expansion factor (k) on the anodizing voltage (U) has the linear nature. The volume expansion factor in the 4% solution of oxalic acid can be defined by the following equation: k=1.092+0.007U. It was established, that the dependence of the logarithm of the ion current density on the inverse volume expansion factor of porous alumina has the linear nature.     

Study the effect of striping in two-step anodizing process on pore arrangement of nano-porous alumina

Two-step anodic oxidation of aluminum is generally employed to produce the ordered porous anodized alumina (PAA). Dissolving away (striping) the oxide film after the first anodizing step plays a key role in the final arrangement of nano-pores. In this work, different striping durations between 1 and 6 h were applied to the sample that was initially anodized at a constant voltage of 40 V at 17 °C for 15 h. The striping duration of 3 h was realized as the optimum time for achieving the best ordering degree for the pores. Scanning electron microscopy (SEM) was used during and at the end of the process to examine the cross section and finishing surface of the specimens. Linear-angular fast Fourier transform (LA-FFT), an in-house technique based on MATLAB software, was employed to assess the ordering degree of the anodized samples.     

Improvement of corrosion resistance of NiTi sputtered thin films by anodization

Anodization of sputtered NiTi thin films has been studied in 1 M acetic acid at 23 °C for different voltages from 2 to 10 V. The morphology and cross-sectional structures of the untreated and anodized surfaces were investigated by field emission scanning electron microscopy (FE-SEM). The results show that increasing anodization voltage leads to film surface roughening and unevenness. It can be seen that the thickness of the anodized layer formed on the NiTi surface is in the nanometer range. The corrosion resistance of anodized thin films was studied by potentiodynamic scan (PDS) and impedance spectroscopy (EIS) techniques in Hank's solution at 310 K (37 °C). It was shown that the corrosion resistance of the anodized film surface improved with increasing voltage to 6 V. Anodization of austenitic sputtered NiTi thin films has also been studied, in the same anodizing conditions, at 4 V. Comparison of anodized sputtered NiTi thin films with anodized austenitic shape memory films illustrate that the former are more corrosion resistant than the latter after 1 h immersion in Hank's solution, which is attributed to the higher grain boundary density to quickly form a stable and protective passive ?lm.     

Effect of processing temperature on the micro- and macro-interfacial properties of carbon fiber/epoxy composites

Three different temperature schemes were applied on carbon fiber/epoxy composite to elucidate the effect on interfacial shear strength (IFSS) and inter-laminar shear strength (ILSS). It showed that carbon fiber/epoxy IFSS was significantly influenced by the processing temperature, while ILSS was only slightly changed. Moreover, the mechanical properties revealed no necessary relationship between the micro- and macro-interfacial strengths with the properties of epoxy matrix. Among all the temperature schemes, Pro2 (the one-platform curing scheme with relatively rapid heating rate) produced highest IFSS and ILSS. Fourier transform infrared spectroscopy analysis demonstrated that the sizing agent can chemically react itself and also react with epoxy resin at temperature 180?°C. The resin rheological data showed that different temperature schemes can considerably impact diffusion behavior of the resin molecules. Hence, the highest interfacial strengths for Pro2 scheme were ascribed to large extent of chemical reactions and good inter-diffusion between components, at the interface region.     

Synthesis of Y-junction carbon nanotubes within porous anodic aluminum oxide template

Y-junction carbon nanotubes with the average diameter about 200 nm were successfully synthesized within porous anodic aluminum oxide template, which was prepared by anodic anodizing aluminum sheet in 1.0 mol/l H₃PO₄ solution at a constant anodization voltage 90 V.     

Compositional and structural characterization of nanoporous films produced by iron anodizing in ethylene glycol solution

We report on the composition and morphology of as-grown anodic oxide films onto the iron surface in an ethylene glycol solution containing some NH₄F and H₂O by anodizing under direct current bias. Decrease in the content of NH₄F and the temperature of electrolyte allow us to form either nanochannel or nanotubular films over a larger potential window, ca. from 30 to 100 V. By this way, the films in thickness of up to10 μm have been formed. Mössbauer spectra recorded at room to cryogenic temperatures under conversion electron and transmission modes revealed the formation of lepidocrocite (γ-FeOOH) film containing some Fe(OH)₂ and/or FeF₂·4H₂O. An increase in anodizing voltage results in fabrication of more porous and less Fe(II) compounds containing films.     

Improved electrical properties of silicon-incorporated anodic niobium oxide formed on porous Nb-Si substrate

In the present study, porous Nb-Si alloy films with isolated nano-column morphology have been successfully developed by oblique angle magnetron sputtering on to aluminum substrate with concave cell structure. The deposited films are amorphous with the 15 at% silicon supersaturated into niobium. The porous Nb-15 at% Si films, as well as niobium films with similar morphology, are anodized at several voltages up to 50 V in 0.1 mol dm⁻³ ammonium pentaborate electrolyte. Due to the presence of sufficient gaps between neighboring columns, the gaps are not filled with anodic oxide, despite the large Pilling-Bedworth ratio (for instance, 2.6 for Nb/Nb₂O₅) and hence, a linear correlation between the reciprocal of capacitance and formation voltage is obtained for the Nb-15 at% Si. From the comparison with the anodic films formed on porous niobium films, it has been found that silicon addition improves the thermal stability of anodic niobium oxide; the change in capacitance and increase in leakage current become small for the Nb-Si. The findings indicate the potential of oblique angle deposition to tailor porous non-equilibrium niobium alloy films for high performance niobium-base capacitor.     

Influence of carbon fiber’s surface state on interlaminar shear properties of CFRP laminate

In order to investigate the influence of carbon fiber’s surface state on the interlaminar shear properties of carbon fiber-reinforced plastic (CFRP) laminate, the carbon fiber’s surface state was modified by thermal treatment at elevated temperatures. The interlaminar shear strength (ILSS) of CFRP laminates reinforced with treated fibers was measured by means of short-beam shear test, and the surface state of fiber was characterized by Electron Spectroscopy for Chemical Analysis (ESCA) analysis to reveal the dominate factor for controlling the ILSS. Combining the ILSS measurement with the ESCA analysis, the results indicated that: (1) the ILSS is strongly dependent on the oxygen-containing functional groups on the surface of carbon fiber; (2) the fiber treated at 600?°C has the highest oxygen-containing functional groups that lead to the highest ILSS of CFRP; and (3) at temperatures beyond 600?°C, the oxygen-containing functional groups decrease with increasing the heat treatment temperature, resulting in a low ILSS of CFRP laminates. Furthermore, from the microstructure observation, it was found that the CFRP mainly failed in the mode of multi-interlaminar shear. The multi-interlaminar shear failure in the CFRP laminates with low ILSS is more severe due to a weak fiber-matrix interface.     

Critical heat flux enhancement of pool boiling using a porous nanostructured coating

Surface coating techniques are commonly used to increase heat transfer and control critical heat flux. In this research, we used anodizing—an electrochemical coating process—to coat an aluminum oxide layer on the aluminum plain surface. This porous nanostructured coating has uniform, cylindrical, parallel nanochannels, and closed end pores. Next, we conducted saturated pool boiling tests on the anodized samples, using deionized water and the CHFs were measured. We found that porous nanostructured coatings, due to their improved surface characteristics, particularly wettability, increased CHF values and also critical heat flux increased linearly with decreasing the contact angle.     

激光辐照下预加载CFRC层合板断裂行为实验研究

针对激光与机械载荷联合作用下碳纤维/环氧树脂增强复合材料（CFRC）层合板失效时间的预测需求,实验研究了不同激光功率密度（70～210 W/cm2）、不同预应力水平（拉伸强度的50%和70%）、不同光斑尺寸（拉伸试件宽度的70%和100%）下2 mm厚层合板的失效机理,获取了不同影响因素对断裂时间的影响规律。结果表明:预加载层合板失效机制为迎光面环氧树脂基底材料热解、纤维氧化断裂,背光面剩余结构偏脆性断裂;在预应力一定条件下,试件断裂时间与辐照激光功率密度成指数规律;预应力水平对断裂时间影响显著。     

The anodization of ZK60 magnesium alloy in alkaline solution containing silicate and the corrosion properties of the anodized films

The anodization of ZK60 magnesium alloy in an alkaline electrolyte of 100 g/l NaOH + 20 g/l Na₂B₄O₇·10H₂O + 50 g/l C₆H₅Na₃O₇·2H₂O + 60g/l Na₂SiO₃·9H₂O was studied in this paper. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques and the microstructure and composition of films were examined by SEM and XRD. The influence of anodizing time was studied and the results show that the anodizing time of 60 min is suitable for acquiring films with good corrosion resistance. The influence of current density on the corrosion resistance of anodizing films was also studied and the results show that the film anodized at 20 mA/cm² has the optimum corrosion resistance. The film formed by anodizing in the alkaline solution with optimized parameters show superior corrosion resistance than that formed by the traditional HAE process. The XRD pattern shows that the components of the anodized film consist of MgO and Mg₂SiO₄.     

Dielectric properties of anodic films on sputter-deposited Ti-Si porous columnar films

For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti-7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti-7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100-200 nm. When the porous Ti-7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti-7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti-7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.     

Surface Modification of Para-Aramid Fiber by Direct Fluorination and its Effect on the Interface of Aramid/Epoxy Composites

Surface modification of a para-aramid fiber (DAFIII) was performed by direct fluorination. The properties of treated and untreated fibers were characterized and compared in detail by mechanical testing, Fourier transform infrared (FTIR) spectroscopy characterization, X-ray photoelectron spectroscopy (XPS) analysis and static contact angle measurements. The results showed that little damage of the fiber occurred after direct fluorine treatment, and the content of polar groups on the fibers surfaces were increased significantly, which resulted in a lower value of contact angle. The interlaminar shear strength (ILSS) of DAFIII fiber/epoxy composites and the tensile strength of NOL-ring specimens increased by 33% and 12%, increasing to 56.2 MPa and 2340 MPa, respectively, which indicated that the interfacial adhesion between the matrix and the aramid fiber was improved significantly by the fluorination treatment. Further tests showed that the durability of the direct fluorination treatment on the aramid fiber was also satisfactory.     

Two-dimensional spatially ordered Al2O3 systems: Small-angle neutron scattering investigation

The structure of anodized aluminum oxide films has been investigated by the small-angle neutron scattering method. A theoretical solution is obtained for describing neutron scattering from the Al₂O₃ ordered porous structure. Analysis of the neutron-experiment data shows the possibility of obtaining porous membranes with ideally periodic hexagonal packed pores on a large area (～0.5 cm²).     

New route to form micro-pores on 316L stainless steel surface

In order to seek an effective way for preventing restenosis after coronary stent implantation, a proposal of increasing the amount of loaded drug without changing the size of struts was given. Thereafter, a process of fabricating in-situ formed sub-micro-pores on 316L stainless steel (316L SS) was demonstrated. An aluminum thin film was deposited by magnetron sputtering on a 316L substrate. The aluminum film was then anodized in different acids (0.3 M oxalic and 10 vol.% sulfuric) by regulating direct current power supply. Through an appropriate chemical dissolution, the anodic alumina film was removed and the underlying porous 316L was obtained. The morphology of the porous 316L surface was examined by scanning electron microscope and the composition of the pores was investigated by energy dispersive X-ray analysis. The corrosion behavior of the porous 316L was evaluated by the polarization measurement. The results indicate that the shape and size of pores could be affected evidently by the acids used in anodization. The pores density is found to change with variation of the applied voltage in anodization. The corrosion current of the anodized specimens decrease and the corrosion voltage increase, compared with the untreated specimens.     

Improvement in thermo mechanical and optical properties of in situ synthesized PMMA/TiO2 nanocomposite

In this paper, transparent thin films of nano titania filled Poly(methyl methacrylate) (PMMA) composites were synthesized by solvent casting method using tetra hydro furan as a solvent, with in situ nonaqueous ‘sol-gel’ transformation involving the mixing of titanium isopropoxide (as sol-gel precursor) and methanol. The present research work is focused at studying the effect of titania loading on optical and mechanical behavior of transparent nano hybrid thin films. The effect of nano Titanium dioxide (TiO₂) loading on PMMA morphology was studied by using a scanning electron microscope (SEM). Bowl shaped structures were obtained in pure PMMA thin film, which were deformed on incorporation of TiO₂ nanoparticles. This nanocomposite exhibits enhanced optical and mechanical properties. The peak of UV absorption is blue shifted to 261 and 266?nm with the incorporation of TiO₂. At this wavelength, the absorption is increased up to approximately 397%. The nanocomposites exhibit increased tensile strength up to 40% and modulus up to 16%. Tg of PMMA increased from 84.8 to 86.7?°C on adding 1.25% TiO₂ nanoparticles.     

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Effects of half-wave and full-wave power source on the anodic oxidation process on AZ91D magnesium alloy

Anodic films have been prepared on the AZ91D magnesium alloys in 1 mol/L Na₂SiO₃ with 10 vol.% silica sol addition under the constant voltage of 60 V at room temperature by half-wave and full-wave power sources. The weight of the anodic films has been scaled by analytical balance, and the thickness has been measured by eddy current instrument. The surface morphologies, chemical composition and structure of the anodic films have been characterized by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the thickness and weight of the anodic films formed by the two power sources both increase with the anodizing time, and the films anodized by full-wave power source grow faster than that by half-wave one. Furthermore, we have fitted polynomial to the scattered data of the weight and thickness in a least-squares sense with MATLAB, which could express the growth process of the anodic films sufficiently. The full-wave power source is inclined to accelerate the growth of the anodic films, and the half-wave one is mainly contributed to the uniformity and fineness of the films. The anodic film consists of crystalline Mg₂SiO₄ and amorphous SiO₂.     

Novel structure formation at the bottom surface of porous anodic alumina fabricated by single step anodization process

A simple approach for the growth of long-range highly ordered nanoporous anodic alumina film in H₂SO₄ electrolyte through a single step anodization without any additional pre-anodizing procedure is reported. Free-standing porous anodic alumina film of 180 μm thickness with through hole morphology was obtained. A simple and single step process was used for the detachment of alumina from aluminum substrate. The effect of anodizing conditions, such as anodizing voltage and time on the pore diameter and pore ordering is discussed. The metal/oxide and oxide/electrolyte interfaces were examined by high resolution scanning transmission electron microscope. The arrangement of pores on metal/oxide interface was well ordered with smaller diameters than that of the oxide/electrolyte interface. The inter-pore distance was larger in metal/oxide interface as compared to the oxide/electrolyte interface. The size of the ordered domain was found to depend strongly upon anodizing voltage and time.