Anodic Aluminum Research Articles

Tenfold Enhancement of Wear Resistance by Electrosynthesis of a Nanostructured Self‐Lubricating Al2O3/Sn(S)MoS2 Composite Film on AlSiCu Casting Alloys

Enhancing tribological performance through nanostructure control is crucial for saving energy and improving wear resistance for diverse applications. We introduce a new electrochemical approach that integrates aluminum (Al) anodization, tin alternating current (AC) electrodeposition, and anodic MoS2 electrosynthesis for fabricating nanostructured Al2O3/Sn(S)MoS2 composite films on AlSiCu casting alloys. Our unique process uses Sn‐modified MoS2 deposition to form robust solid lubricant MoS2–SnS electrodeposits within the nanochannels and microsized voids/defects of anodic alumina matrix films on the base materials, resulting in a bilayered Al2O3/SnSMoS2 and MoS2–SnS–Sn composite film. The AC‐deposited Sn enhances conductivity in the anodic alumina matrix film, acts as catalytic nuclei for Sn@SnS@MoS2 core‐shell nanoparticles and a dense top layer, and serves as a reductant for the direct synthesis of hybrid solid lubricant MoS2–SnS from MoS3 by anodic electrolysis of MoS42− ions. The resulting nanocomposite film provides a two‐fold increase in lubricity (friction coefficient (COF) μ = 0.14 ⇒ 0.07) and a ten‐fold improvement in wear resistance (COF μ < 0.2) compared to conventional Al2O3/MoS2 film formed by anodizing and reanodizing. The effectiveness of the Al2O3/Sn(S)MoS2 composite is further validated through real automotive engine piston tests.

High Density 3D Carbon Tube Nanoarray Electrode Boosting the Capacitance of Filter Capacitor

HighlightsA novel method is developed for precise control over the structure of 3D anodic aluminum oxide templates, enabling fine-tuning of both the vertical pore diameter and interspace within the templates.3D carbon tube nanoarrays featuring significantly thinner and denser tubes are constructed as high-quality electrodes for miniaturized filter capacitors.The 3D compactly arranged carbon tube-based capacitor achieves a remarkable specific areal capacitance of 3.23 mF cm−2 with a phase angle of − 80.2° at 120 Hz.

Effect of substrate temperature and electrolyte composition on the fabrication of through-hole porous AAO membrane with SF-MDC

Fabrication of novel nanostructure materials on various metal substrates receives large attensions for numerous industrial applications. In this research, the influence of substrate temperature and electrolyte composition on pore parameters and oxide film thickness of anodic porous alumina (AAO) were studied. A 3D-printed solution-flow type microdroplet cell (SF-MDC) was used for the fabrication of AAO membranes in aluminum substrate. Alumina lines were formed at a constant applied voltage. The temperature of the substrate was controlled with a thermoelectric Peltier device system in the range of 10 °C to 60 °C. The surface and cross-section morphology of the anodic oxide lines were observed using a scanning electron microscope (SEM). The result showed that the pore diameter and interpore distance of the anodized lines increased as the substrate temperature increased. A highly ordered with hexagonal pore arrangement and lowest film thickness were obtained at the highest substrate temperature of 60 °C. The porous AAO membrane film thickness formed in the oxalic acid electrolyte increased from 32.2 μm to 52.5 μm as the anodizing substrate temperature reached 30 °C and then declined to 12.8 μm with increasing temperature to 60 °C. A through-hole porous AAO membranes were successfully fabricated at constant applied voltage and room temperature in oxalic and phosphoric acid without chemical etching.

Submerged nanoporous anodized alumina structure for solar-powered desalination.

Development of nanoporous structures utilizing a single step of anodization technique is well recognized as a cost-effective and straightforward approach for several applications. In the current work, anodized alumina was developed with nanoporous structure by utilizing oxalic acid as an electrolyte with a continuous voltage of 40 V. The formed nanoporous structure was subjected to desalination application because of its high absorbance of broadband solar spectrum energy. The desalination setup consists of two solar stills namely conventional and modified. The developed structure is placed in the modified still to examine its performance. It was observed that the structure distributing heat to surrounding water by absorbing photon energy from the sun through the nanopores and giving an efficient pathway to the water vapours for developing effective desalination. The nanoporous structure having ~ 45 nm average diameter. Furthermore, the band gap energy of nanoporous structure was found to be ~ 2.5 eV (absorption spectrum fitting) and ~ 2.8 eV (Tauc plot). The nanoporous structure possess the visible light spectra in solar region which helps the band gaps of nanoporous structure to provide an additional supply of energy for generating more water to evaporate. Moreover, the Urbach energy of the structure is 0.5 eV which reveals less defects in the modified still. The overall distillate yield of modified still was increased to 21% in contrast to conventional. Water quality analysis was also carried out before and after the desalination experiments, and the results were within acceptable limits set by World Health Organization (WHO).

Surface Engineering on Palladium and Zinc Nanowires for Hydrogen Sensing Working at ≈190–388 K Temperature Range

AbstractReliable detection of hydrogen (H2) leakage at low temperatures (e.g., < 273 K) is highly desired in those critical environments that may cause failure in detection, which needs further development. Herein, H2 sensing that can work at ≈190–388 K temperature range has been developed by integrating palladium and zinc nanowires enwrapped with nanosheets (PdZn NWs) as the sensing materials, which have been prepared via combined anodic aluminum oxide (AAO) template‐confined electrodeposition and surface engineering. Typically, as‐synthesized PdZn NWs with a diameter of ≈50 nm present rough surfaces, along which abundant pores and fractures have been observed. Beneficially, the PdZn NWs show a lower critical temperature (≈190 K) of the “reverse sensing behavior” than that of pure Pd NWs (287 K), indicating the PdZn NWs are able to work at ≈190–388 K temperature range. Theoretically, such stable H2 sensing can be attributed to the rough surfaces and chemical composition of PdZn NWs, which facilitates H atoms diffusion and accommodates the expansion of PdHx intermediates. The surface engineering of PdZn NWs may contribute to stable H2 sensing at low temperatures, which can be applied to other gas‐sensing materials working at low temperatures.

Incorporation of Anions into Anodic Alumina-A New Track in Cr(VI) Anodizing Substitution?

Aluminum technical alloys are well known for their outstanding mechanical properties, especially after heat treatment. However, quenching and aging, which improve the mechanical properties, by the formation of Cu-rich zones and phases that are coherent with the matrix and block the dislocation motion, cause uneven distribution of the elements in the alloy and consequently make it prone to corrosion. One method providing satisfactory corrosion protection of aluminum alloys is anodizing. On an industrial scale, it is usually carried out in electrolytes containing chromates that were found to be cancerogenic and toxic. Therefore, much effort has been undertaken to find substitutions. Currently, there are many Cr(VI)-free substitutes like tartaric-sulfuric acid anodizing or citric-sulfuric acid anodizing. Despite using such approaches even on the industrial scale, Cr(VI)-based anodizing still seems to be superior; therefore, there is an urge to find more complex but more effective approaches in anodizing. The incorporation of anions into anodic alumina from the electrolytes is a commonly known effect. Researchers used this phenomenon to entrap various other anions and organic compounds into anodic alumina to change their properties. In this review paper, the impact of the incorporation of various corrosion inhibitors into anodic alumina on the corrosion performance of the alloys is discussed. It is shown that Mo compounds are promising, especially when combined with organic acids.

Plasmonic Bound States in the Continuum Metasurface-Semiconductor-Metal Architecture Enables Efficient Hot-Electron-Based Photodetector.

Plasmonic hot-electron-based photodetectors (HEB-PDs) have received widespread attention for their ability to realize effective carrier collection under sub-bandgap illumination. However, due to the low hot electron emission probability, most of the existing HEB-PDs exhibit poor responsivity, which significantly restricts their practical applications. Here, by employing the binary-pore anodic alumina oxide template technique, we proposed a compact plasmonic bound state in continuum metasurface-semiconductor-metal-based (BIC M-S-M) HEB-PD. The symmetry-protected BIC can manipulate a strong gap surface plasmon in the stacked M-S-M structure, which effectively enhances light-matter interactions and improves the photoresponse of the integrated device. Notably, the optimal M-S-M HEB-PD with near-unit absorption (∼90%) around 800 nm delivers a responsivity of 5.18 A/W and an IPCE of 824.23% under 780 nm normal incidence (1 V external bias). Moreover, the ultrathin feature of BIC M-S-M (∼150 nm) on the flexible substrate demonstrates excellent stability under a wide range of illumination angles from -40° to 40° and at the curvature surface from 0.05 to 0.13 mm-1. The proposed plasmonic BIC strategy is very promising for many other hot-electron-related fields, such as photocatalysis, biosensing, imaging, and so on.

Dispersion and stability of gold nanorods prepared by anodized aluminum oxide (AAO) templates in alkaline solution

Dispersion and stability of gold nanorods prepared by anodized aluminum oxide (AAO) templates in alkaline solution

Ultra‐high bonding strength of carbon fiber–doped polyamide–aluminum alloy composite structure achieved by changing crystallinity

AbstractLightweight and high‐strength polymer–metal hybrid structures are favored for reducing material and energy consumption. In this study, carbon fiber‐reinforced polyamide 6 (CFPA) composite materials were prepared through melt blending, and 30 wt% CFPA exhibited the highest shear strength and lowest shrinkage rate among other carbon fiber contents. With pretreatments of anodizing and etching treatment, injection molded direct joining was employed to create polyamide 6 (PA)/CFPA–Aluminum alloy (Al) composites. The impacts of the injection temperature and speed on the bonding strength of the PA/CFPA–Al composite materials were investigated. The characterization results confirmed that carbon fiber doping reduces the coefficient of linear thermal expansion (CLTE) and enhances crystallization ability of PA. The higher injection temperatures and lower injection speed significantly increase the crystallinity of PA and the infiltration of the molten polymer into the nanoporous anodic aluminum oxide films. When the injection temperature was 270°C and the speed was 6 mm/s, the bonding strength of the PA–Al hybrid structure reached a maximum of 36.6 MPa. When the injection temperature was 300°C, the bonding strength of the CFPA–Al hybrid structure reached a maximum of 40.8 MPa. Adhesive parts with high shear bonding strength are critical to satisfying engineering requirements and have significant potential, particularly in polymer–metal composite structures. The polymer‐metal hybrid structure can meet the high interfacial bonding strength required in most engineering applications.Highlights Injection temperature and speed in IMDJ affect PA crystallinity. Carbon fiber doping reduces the CLTE of PA and increases the shear strength. High temperatures and low injection speeds are beneficial to adhesives. The bonding strength of PA–Al reached a maximum of 36.6 MPa. The bonding strength of CFPA–Al reached a maximum of 40.8 MPa.

Advancing Nanopore Technology: Anodic Aluminum Oxide Membranes with Anisotropic Pores through Controlled Stretching for Applications in Nanopatterning

Advancing Nanopore Technology: Anodic Aluminum Oxide Membranes with Anisotropic Pores through Controlled Stretching for Applications in Nanopatterning

Research on variation in nanopore parameters and surface characteristics of anodic aluminum oxide (AAO) films with time-controlled anodization processes

Research on variation in nanopore parameters and surface characteristics of anodic aluminum oxide (AAO) films with time-controlled anodization processes

3D Nanostructured Electrodes Based on Anodic Alumina Templates for Stable Pseudocapacitors

This study investigates the preparation of nickel nanostructured electrodes for the enhancement of supercapacitor performance. The nanostructured electrodes are synthesized using nanoporous anodic alumina (NAA) as a template via the pulsed electrodeposition method. Structural properties are examined using field‐emission scanning electron microscopy, while electrochemical characterization is conducted through cyclic voltammetry (CV) and electrochemical impedance spectroscopy. The results reveal that Ni nanorod arrays can be obtained embedded in the NAA matrix and with electrical contact with the aluminum substrate. On average, the rods are spaced 90 nm apart, with a diameter of 70 nm and a length of 2 μm. The Ni@NAA electrode exhibits an enlarged active area and exceptional electrochemical performance, demonstrating remarkable stability over 5000 cycles of CV at a scan rate of 50 mV s−1. Specific capacitance values exceeding 100 mF cm−2 and maximum charging times of less than 10 min are reported, highlighting its suitability for high‐power energy devices requiring pseudo‐supercapacitance. The study underscores the significance of nanostructured electrodes in advancing energy storage technologies and presents promising prospects for practical applications.

Temperature dependent structural and magnetic properties of permalloy (Ni80Fe20) nanotubes

One dimensional Permalloy (Ni80Fe20) nanotubes (NTs) were successfully fabricated using Anodic Aluminum Oxide (AAO) templates with 100 nm diameter by employing a low-cost electrodeposition route at room temperature. As prepared Ni80Fe20 NTs morphology, elemental analysis and structural details have been investigated by using field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and X-Ray diffraction (XRD) respectively. The structure of prepared Permalloy nanostructures has face centered cubic (FCC) phase with polycrystalline in nature. The Ni80Fe20 NTs were annealed at 200 °C, 400 °C and 600 °C. The vibrating sample magnetometer (VSM) measurements showed that all the samples exhibit ferromagnetic nature. Furthermore, VSM has been employed to study the saturation magnetization (MS), Squareness (SQ) and Coercivity (HC) as the function of annealing temperature. A comparative study of magnetization reversal mechanism has also been conducted. The easy axis lies in the direction perpendicular to the NTS axis due to the dominance in shape anisotropy. Annealing temperature improved the magnetic properties of Permalloy (PA) NTs. This work will provide significant applications in the field of spintronics and high-density data storage devices.

The Influence of the Structural Parameters of Nanoporous Alumina Matrices on Optical Properties

In this work, two types of nanoporous alumina membranes were prepared and tested. Structural features of the samples obtained by using different acids were investigated by scanning electron microscopy (SEM). And further SEM-images were analyzed by different types of fractal dimension estimation methods. The transmission and scattering of accelerated He+ ions were studied in experiments on the ion irradiation of dielectric channels based on porous alumina. An ion accelerator was used as a source of the He+ beam with an energy of 1.7 MeV. Ion scattering was studied by Rutherford backscattering spectrometry. Helium transition through nanoporous alumina at various angles between the normal to the sample and the beam direction were observed. It is shown that the porous structure of anodic aluminum oxide is excellent as a dielectric matrix of nanocapillaries. Owing to the small angle scattering, it allows for the transportation of the accelerated charged particles through the dielectric capillaries, and, as a result, the localization of high energy ion irradiation effects. Additionally, according to the transmission of UV–V is spectra, the energy gaps of samples obtained were calculated.

Influence of Normal-to-High Anodizing Voltage on AAO Surface Hardness from 1050 Aluminum Alloy in Oxalic Acid.

Anodic aluminum oxide (AAO) has been widely applied for the surface protection of electronic component packaging through a pore-sealing process, with the enhanced hardness value reaching around 400 Vickers hardness (HV). However, the traditional AAO fabrication at 0~10 °C for surface protection takes at least 3-6 h for the reaction or other complicated methods used for the pore-sealing process, including boiling-water sealing, oil sealing, or salt-compound sealing. With the increasing development of nanostructured AAO, there is a growing interest in improving hardness without pore sealing, in order to leverage the characteristics of porous AAO and surface protection properties simultaneously. Here, we investigate the effect of voltage on hardness under the same AAO thickness conditions in oxalic acid at room temperature from a normal level of 40 V to a high level of 100 V and found a positive correlation between surface hardness and voltage. The surface hardness values of AAO formed at 100 V reach about 423 HV without pore sealing in 30 min. By employing a hybrid pulse anodization (HPA) method, we are able to prevent the high-voltage burning effect and complete the anodization process at room temperature. The mechanism behind this can be explained by the porosity and photoluminescence (PL) intensity of AAO. For the same thickness of AAO from 40~100 V, increasing the anodizing voltage decreases both the porosity and PL intensity, indicating a reduction in pores, as well as anion and oxygen vacancy defects, due to rapid AAO growth. This reduction in defects in the AAO film leads to an increase in hardness, allowing us to significantly enhance AAO hardness without a pore-sealing process. This offers an effective hardness enhancement in AAO under economically feasible conditions for the application of hard coatings and protective films.

Gas Permeation through V2O5 Nanoribbons‐Based Membrane

AbstractMembrane separation processes play a crucial role in gas separation applications, with the need for ongoing development to fulfill new needs for today's challenges. For this purpose, novel 2D nanomaterials are progressively showing promise over conventional polymer‐based membrane material, exhibiting excellent molecular transport properties. Beyond the 2D materials already studied in this field, this article presents the first gas separation performances of vanadium pentoxide membrane. Brand new in gas separation topic, 2D van der Waals nanoribbons of V2O5 are successfully synthesized and layered on an anodic aluminum oxide substrate. Gas permeation analysis of He, N2, and CO2 are performed on various membranes made from different quantities of the nanomaterial. Gas permeance results suggest a deviation from an expected Knudsen diffusion mechanism of the V2O5‐based membrane for He separation. The ideal selectivities of He/N2 and He/CO2 are compared to Robeson's upper bound for polymeric membranes. V2O5 membranes, prepared with the highest V2O5 quantity, exceeded the upper bound from 2008 for He/N2 and 2019 (the most recent) for He/CO2, demonstrating the interesting potential of V2O5 2D materials for gas separation.

Self-Assembly of Ionic Superdiscs in Nanopores.

Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs of cations and anions that spontaneously stack in linear columns with high one-dimensional ionic and electronic charge mobility, making them prominent model systems for functional soft matter. Compared to classical nonionic discotic liquid crystals, many liquid crystalline structures with a combination of electronic and ionic conductivity have been reported, which are of interest for separation membranes, artificial ion/proton conducting membranes, and optoelectronics. Unfortunately, a homogeneous alignment of the DILCs on the macroscale is often not achievable, which significantly limits the applicability of DILCs. Infiltration into nanoporous solid scaffolds can, in principle, overcome this drawback. However, due to the experimental challenges to scrutinize liquid crystalline order in extreme spatial confinement, little is known about the structures of DILCs in nanopores. Here, we present temperature-dependent high-resolution optical birefringence measurement and 3D reciprocal space mapping based on synchrotron X-ray scattering to investigate the thermotropic phase behavior of dopamine-based ionic liquid crystals confined in cylindrical channels of 180 nm diameter in macroscopic anodic aluminum oxide membranes. As a function of the membranes' hydrophilicity and thus the molecular anchoring to the pore walls (edge-on or face-on) and the variation of the hydrophilic-hydrophobic balance between the aromatic cores and the alkyl side chain motifs of the superdiscs by tailored chemical synthesis, we find a particularly rich phase behavior, which is not present in the bulk state. It is governed by a complex interplay of liquid crystalline elastic energies (bending and splay deformations), polar interactions, and pure geometric confinement and includes textural transitions between radial and axial alignment of the columns with respect to the long nanochannel axis. Furthermore, confinement-induced continuous order formation is observed in contrast to discontinuous first-order phase transitions, which can be quantitatively described by Landau-de Gennes free energy models for liquid crystalline order transitions in confinement. Our observations suggest that the infiltration of DILCs into nanoporous solids allows tailoring their nanoscale texture and ion channel formation and thus their electrical and optical functionalities over an even wider range than in the bulk state in a homogeneous manner on the centimeter scale as controlled by the monolithic nanoporous scaffolds.

One-dimensional photonic crystals based on porous anodic alumina: Optical and morphology changes under thermal and chemical treatments

One-dimensional photonic crystals (1D PCs) based on porous anodic aluminium oxide (AAO) are promising for light manipulation and sensing. As-prepared AAO, being amorphous material, suffers degradation in acidic and alkaline media. It is commonly known that the chemical stability of AAO increases drastically after thermal treatment. Here, the effect of annealing up to 1200 °C on the morphology and the optical properties of AAO PCs is studied. The two-step crystallization of as-prepared AAO at 860 and 1190 °C leads to a two-step blue shift of the central wavelength of photonic band gap (PBG) and the decrease in PBG depth, whereas the Q-factor of the PBG enhances. The observed changes in optical transmittance spectra of PCs are mainly attributed to the increase in pore diameter, the formation of crystalline particles of alumina polymorphs, and the removal of impurities. Annealed AAO PCs demonstrate much higher stability of optical parameters during exposure in acidic media compared to the as-prepared ones. Thermal treatment at 600 °C results in 30% decrease in the rate of the PBG shift during chemical etching. Furthermore, AAO crystallization into a mixture of low-temperature alumina polymorphs at 860 °C leads in a negligible change in transmittance spectra even after chemical etching in 1 M HCl for 75 h. The excellent stability achieved for the annealed AAO PCs in aggressive media proves the perspectives of their application as the optical sensors with long-term stability.

Three-dimensional anodic aluminum templates via a single-step pulsed potential method

Recent advances in the fabrication of three-dimensional Anodic Aluminum Oxide templates have opened novel opportunities in the generation of photonic structures and material nanostructuration. So far these structures have been produced from the standard two-step pulsed potential anodization and modulated current density anodization approaches. However, their fabrication is slow, with the two-step approach relying on intermediate oxide removal steps that often use toxic etchants. In this work, we report the fabrication of 3D Anodic Aluminum Oxide templates from a single-step pulsed potential method, completely removing the need for intermediate etching steps, and decreasing total fabrication times to less than 24 hours. Structural coloration was also successfully demonstrated and analyzed in these templates, for 99.999% and 99.5% Al precursors, presenting the same morphology and optical functionality as templates produced from two-step processes.

High-performance separation for ultra-low concentration nanoparticles with mesoporous silica thin membrane

Mesoporous silica thin film membrane (MSTF) emerges as an ideal ultrafiltration membrane for the removal of nanoparticles, ensuring the production of particle-free water. This is mainly ascribed to its uniform and narrow pore size distribution, having vertical nanochannels with low tortuosity, and being ultrathin, which helps enhance its selectivity and permeability. In this study, we demonstrated the potential of MSTF overlayed on macroporous anodic aluminum oxide (AAO) support for separating gold nanoparticles even at a very low concentration. Moreover, with the addition of pore-expanding agents, E-MSTF⊥AAO (pore size 3.12 nm) and D-MSTF⊥AAO (pore size 5.26 nm) membranes are formed, and both membranes indeed showed high rejection efficiency towards 150 ppb gold nanoparticles of sizes 10 nm and 5 nm, ∼99 %, and ∼96 %, respectively. It is also worth noting that as compared to the state-of-the-art conventional UF membranes, the E-MSTF⊥AAO membrane showed significantly high permeance of 114.1 ± 12.76 L m−2 h−1 bar−1 and 104.1 ± 50.6 L m−2 h−1 bar−1 while efficiently separating 150 ppb and 50 ppb 5 nm gold nanoparticles, respectively. Moreover, the promising long-term stability and chemical stability of the MSTF⊥AAO membrane paved a promising path for applying mesoporous silica membranes for effective nanoparticle separation in wastewater treatment and particle-free water production in industries.