Aluminum Surface Research Articles

Computational Investigations of the Water Structure at the α-Al2O3(0001)-Water Interface.

The α-Al2O3(0001)-water interface is investigated using ab initio molecular dynamics (AIMD) simulations. The spectral signatures of the vibrational sum frequency generation (vSFG) spectra of OH stretching mode for water molecules at the interface are related to the interfacial water orientation, hydrogen bond network, and water dissociation process at different water/alumina interfaces. Significant differences are found between alumina surfaces at different hydroxylation levels, namely, Al-terminated and O-terminated α-Al2O3(0001). By calculating the vibrational sum frequency generation spectrum and its imaginary component from AIMD results, the structure of interfacial waters as well as the termination of alumina slab are related to the spectral signatures of vSFG data.

Study on the tribological properties and corrosion resistance of the in-situ grown Zn–Al-LDHs film on anodic aluminum surface

In this study, the LDHs film was successfully prepared in-situ on the surface of AAO substrate. By using SEM, EDS, XRD, Vickers microhardness tester, pull-off tester, electrochemical workstation and tribometer, the morphology, composition, crystal structure, hardness, binding force, corrosion resistance and tribological performance of the LDHs film produced within a range of pH values (6.5/7.5/8.5/9.5) were researched. The results revealed that the pH of solution is important in the formation of Zn-Al-LDHs film and their characteristics: when the pH of 8.5, the LDHs film surface is the most smooth and flat, the crystal structure of LDHs nanosheets is the most complete and grows perpendicular to the substrate surface, the thickness of the film reaches to about 96.77 μm, and the interfacial bonding force achieves to about 8.50 MPa. The LDHs film could effectively enhance the corrosion resistance by sealed the anodic aluminum oxide film, and the dry friction coefficient of alumina substrate decreases to about 0.2 for 3600 s, which exhibits excellent tribological properties.

Controlling Microparticle Morphology in Melt-Jet Printing of Active Pharmaceutical Ingredients through Surface Phenomena.

Achieving homogeneity and reproducibility in the size, shape, and morphology of active pharmaceutical ingredient (API) particles is crucial for their successful manufacturing and performance. Herein, we describe a new method for API particle engineering using melt-jet printing technology as an alternative to the current solvent-based particle engineering methods. Paracetamol, a widely used API, was melted and jetted as droplets onto various surfaces to solidify and form microparticles. The influence of different surfaces (glass, aluminum, polytetrafluoroethylene, and polyethylene) on particle shape was investigated, revealing a correlation between substrate properties (heat conduction, surface energy, and roughness) and particle sphericity. Higher thermal conductivity, surface roughness, and decreased surface energy contributed to larger contact angles and increased sphericity, reaching a near-perfect micro-spherical shape on an aluminum substrate. The integrity and polymorphic form of the printed particles were confirmed through differential scanning calorimetry and X-ray diffraction. Additionally, high-performance liquid chromatography analysis revealed minimal degradation products. The applicability of the printing process to other APIs was demonstrated by printing carbamazepine and indomethacin on aluminum surfaces, resulting in spherical microparticles. This study emphasizes the potential of melt-jet printing as a promising approach for the precise engineering of pharmaceutical particles, enabling effective control over their physiochemical properties.

Antibacterial efficacy of surface aluminum oxide nanostructures produced by hot water treatment

Abstract This study utilizes a hot water treatment (HWT) method for introducing antibacterial properties to aluminum (Al) surfaces, which has relevance in several industries ranging from food packaging and ventilation systems to biomedical materials. The HWT process can produce a nanostructured oxide layer on a wide range of metallic materials by simply immersing the metal in water at temperatures ranging from 75 °C to 95 °C. In this work, Al foil was treated in deionized (DI) water for 5 min at various temperatures, including 75 °C, 85 °C, and 95 °C. Concentrations of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus epidermidis (S. epidermidis) were placed on Al foil for different times, ranging from 30 seconds to 60 min The survival time was measured, and the analysis of the results indicates a direct correlation between when the bacteria was exposed to HWT Al foil and the number of bacteria killed. As the temperature of the HWT increased, there was an increase in antibacterial activity. This finding is consistent with our expectations; at higher HWT temperatures, more prominent nanostructures are produced, causing increased inactivation of bacteria. Our results show the nanostructured HWT Al foil was superior at inactivating Gram-negative (E. coli) and Gram-positive (S. epidermidis) bacteria compared to the untreated control Al foil. HWT Al foil treated at 75 °C, 85 °C, and 95 °C was 58%, 64%, and 73% more effective in killing the Gram-negative bacteria, respectively, after only 30 seconds of contact time compared to untreated control Al foil, while the antibacterial efficacy was enhanced 88%, 92%, and 94% for the Gram-positive bacteria, respectively. The HWT nanostructures synthesized at 95 °C, after 60 min of contact time, were able to inactivate 97% of the gram-negative bacteria and 100% of the gram-positive bacteria, demonstrating the efficacy of its antibacterial properties. This research presents a novel, inexpensive, and environmentally friendly method of producing nanostructures that inhibit bacterial activity.

Studying Molecular Rearrangement of P1 Dye at a Passivating Alumina Surface Using Vibrational Sum-Frequency Generation Spectroscopy: Effect of Atomic-Level Roughness.

The effect of roughness and thickness of alumina layers, mimicking the passivation layer commonly used in dye-sensitized photoelectrodes, on the molecular adsorption of P1 dye, 4-(bi(4-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl]-aminobenzoic acid) has been studied using surface-sensitive vibrational sum frequency generation(VSFG) spectroscopy. The VSFG spectra reveal the formation of poorly ordered dye layers on relatively rough surfaces where XPS measures a higher dye loading. Furthermore, these poorly ordered dye molecules are responsible for the generation of trapped electronic states as probed by successive photoluminescence (PL) measurements. Surface sensitive VSFG spectroscopy in combination with XPS and PL measurements provide complementary spectral information on ordering of the adsorbed dyes, their density on the surface and electronic states of the adsorbed monolayer which are prerequisite for improving our understanding of molecularly functionalized photoelectrodes and their further development.

Investigation of Oxide Thickness on Technical Aluminium Alloys—A Comparison of Characterization Methods

In this study the oxide layer of technical 6xxx aluminium surfaces, pickled as well as passivated, were comparatively investigated by means of transmission electron microscopy (TEM), Auger electron and X-ray photoelectron spectroscopy (AES, XPS), the latter in two different operating modes, standard and angle resolved mode. In addition, confocal microscopy and focused ion beam cutting were used for structural studies of the surfaces and for specimen preparation. The results illustrate in detail the strengths and weaknesses of each measurement technique. TEM offers a direct way to reliably quantify the thickness of the oxide layer, which is in the range of 5 nm, however, on a laterally restricted area of the surface. In comparison, for AES, the destructiveness of the electron beam did not allow to achieve comparable results for the thickness determination. XPS was proven to be the most reliable method to reproducibly quantify the average oxide thickness. By evaluating the angle resolved XPS data, additional information on the average depth distribution of the individual elements on the surface could be obtained. The findings obtained in this study were then successfully used for the investigation of the increase in the aluminium oxide thickness on technical samples during an aging test of 12 months under standard storage conditions.

Effect of modified MgAl-LDH coating on corrosion resistance and friction properties of aluminum alloy

The in-situ growing approach was utilized in this article to construct the magnesium–aluminum layered double hydroxide (MgAl-LDH) film on the surface of a 1060 aluminum anodized film. To improve the corrosion resistance and friction qualities of aluminum alloy, the MgAl-LDH coating was treated using stearic acid (SA) and thiourea (TU). The aluminum substrate and anodized aluminum film layer corroded to varying degrees after 24 h of immersion in 3.5% (mass) NaCl solution, while the modified hydrotalcite film layer continued to exhibit the same microscopic morphology even after being immersed for 7 d. The results show that the synergistic action of thiourea and stearic acid can effectively improve the corrosion resistance of the MgAl-LDH substrate. The tribological testing reveals that the hydrotalcite film layer and the modified film layer lowered the friction coefficient of the anodized aluminum surface substantially. The results of the simulations and experiments demonstrate that SA forms the dense LDH-TU interlayer film layer by exchanging NO3– ions between TU layers on the one hand and the LDH-SA film layer by adsorption on the surface of LDH on the other. Together, these two processes create LDH-TU-SA, which can significantly increase the substrate's corrosion resistance. This synergistically modified superhydrophobic and retardant hydrotalcite film layer offers a novel approach to the investigation of wear reduction and corrosion protection on the surface of aluminum and its alloys.

Study on ultrasound-assisted preparation of sphere-like high-purity alumina

Spherical alumina with a purity greater than 99.999% is calcined by the precursor obtained from the reaction of high-purity aluminum with ultrapure water, which is of great interest for grinding in semiconductor processing and other fields. In this study, tetramethylammonium hydroxide is introduced to the aluminum-water (Al-H2O) reaction, and the crystal growth of the HPA precursor is adjusted by ultrasonication. The ultrasound can break the gas barrier film at the early stage of the reaction, then increase the reaction potential energy on the aluminum surface, accelerate the reaction rate, and inhibit the preferential growth of Al(OH)3 crystals along (110), (111), (131), and (202) faces. It increases the dissociation rate of crystals in the corresponding crystal faces and promotes the formation of the Al-O bond in Al(OH)3 and Al2O3 to obtain fine HPA precursors with uniform size distribution. Then, the ultrafine and sphere-like α-Al2O3 powders with a particle size D50 of 370 nm are prepared after calcination at 1250 °C.

Effect of ball milling and subsequent size reduction of graphite flakes on the surface mechanical properties of graphitized Al-1100 alloy

Current study explains about ball milling and subsequent mechanical insertion of graphite particles into aluminium (Al-1100) surface for forming composites on surface through an electrical resistance heat supported pressing procedure. Ball milling of as-received 60 mesh graphite particles was carried out which successfully reduced the particle size. After that surface of the aluminium is coated with ball-milled graphite by solution casting. For impregnation, the interface of graphite/aluminium is locally heated by the assistance of an electrical resistance heating followed by mechanical pushing. Heat generation and thus level of aluminium surface softening can be structured by process factors like current and heating time. SEM, TEM, Raman spectroscopy and XRD were employed for microstructural characterization. Successful impregnation and agglomeration of graphite particles inside aluminium matrix is revealed from microstructural characterization. Impregnated graphite particles when characterized with Raman spectroscopy shows band shifting and increased intensity ratio (ID/IG). Presence of intermetallic compound (Al4C3) was not detected from the XRD and TEM study. Surface and subsurface mechanical characterization was carried out nanoindentation and microhardness respectively. The modified surface while shows an improvement of more than 120 % in mechanical properties, 130 % improvement is also observed in Young’s modulus. The projected method can be utilized as surface modification technique in solid-state by fabricating surface composites fabricated through mechanical insertion of particulate reinforcement at sub-melting temperatures of substrate and under open producing environment.

Capillary performance of vertically grooved wicks on laser-processed aluminum surfaces with different wettability

Ultra-thin heat pipes have been employed extensively for the thermal management of electronic devices. Their capacity for heat transfer is significantly influenced by the capillary performance of the wicking structure in the pipes. In this study, superhydrophilic (SHPi) and superhydrophobic (SHPo) background surfaces were prepared on aluminum sheets using a nanosecond fiber laser. SHPi grooves with widths ranging from 0.1 to 0.4 mm were then produced on the surfaces with the same laser. The effects of the background wettability on the capillary performance of the grooves were investigated. The fastest ascent of the water in the grooves on the SHPo background surface occurred when the groove widths were between 0.1 and 0.2 mm. As the groove width increased to 0.3–0.4 mm, the water level rose most quickly in the groove on the SHPi surface. Furthermore, water absorption was always larger on the SHPi background surface for grooves of the same width as on the other two surfaces. As a result, a wettable background surface that matches the application requirements should be selected. The SHPo background surface should be used when a rapid water rise in the groove is desired. The SHPi background surface, on the other hand, increases water absorption capacity. Water absorption achieved a maximum of 6.8 mg with a groove width of 0.4 mm, and capillary performance parameters reached 4.62 × 10–7 N, which was 117.9% higher than the pristine background surface. This study presents fresh suggestions for increasing the capillary performance of vertically grooved wicks.

Nature-Inspired Surface Engineering for Efficient Atmospheric Water Harvesting.

Atmospheric water harvesting is a sustainable solution to global water shortage, which requires high efficiency, high durability, low cost, and environmentally friendly water collectors. In this paper, we report a novel water collector design based on a nature-inspired hybrid superhydrophilic/superhydrophobic aluminum surface. The surface is fabricated by combining laser and chemical treatments. We achieve a 163° contrast in contact angles between the superhydrophilic pattern and the superhydrophobic background. Such a unique superhydrophilic/superhydrophobic combination presents a self-pumped mechanism, providing the hybrid collector with highly efficient water harvesting performance. Based on simulations and experimental measurements, the water harvesting rate of the repeating units of the pattern was optimized, and the corresponding hybrid collector achieves a water harvesting rate of 0.85 kg m-2 h-1. Additionally, our hybrid collector also exhibits good stability, flexibility, as well as thermal conductivity and hence shows great potential for practical application.

Catalytic hydrogenation of Cl-oxyanion pollutants in water

Pt and Pd catalysts supported on alumina have been tested and characterised for the catalytic hydrogenation of chlorates at room temperature and atmospheric pressure. Metallic nanoparticles are the catalytic active species, obtaining better results with the Pt than with the Pd catalysts. It is observed that the activity of the Pt catalysts depends on the metal precursor used for their preparation and the calcination temperature as these factors lead to different platinum dispersion on the alumina surface. The best results were obtained with the catalysts prepared from metal precursors containing Cl atoms and calcined at lower temperatures, as smaller metallic crystallites are formed. The chlorate reduction profiles displayed a pseudo-first order kinetic towards chlorate. The optimised catalyst was tested for the reduction of the different Cl-oxyanions, proving that the reaction rate depends on the chlorine valence of the ion following this order: ClO4- < ClO3- < ClO2-. This is due to the different molecular geometry of the anions that results in different stability of the ClOx-. The optimised catalyst was fully stable in successive uses, being active for the simultaneous reduction of chlorate, chlorite and bromate in water.

Comparative Evaluation of the Repair Bond Strength of Dental Resin Composite after Sodium Bicarbonate or Aluminum Oxide Air-Abrasion.

The dental prophylactic cleaning of a damaged resin-based composite (RBC) restoration with sodium bicarbonate can change the surface characteristics and influence the repair bond strength. The purpose of this study was to compare the effect of sodium bicarbonate (SB) and aluminum oxide (AO) surface treatments on the microtensile bond strength (µTBS) of repaired, aged RBC. Bar specimens were prepared from microhybrid RBC and aged in deionized water for 8 weeks. Different surface treatments (AO air-abrasion; SB air-polishing), as well as cleaning (phosphoric acid, PA; ethylene-diamine-tetraacetic-acid, EDTA) and adhesive applications (single bottle etch-and-rinse, ER; universal adhesive, UA), were used prior to the application of the repair RBC. Not aged and aged but not surface treated RBCs were used as positive and negative controls, respectively. The repaired blocks were cut into sticks using a precision grinding machine. The specimens were tested for tensile fracture and the µTBS values were calculated. Surface characteristics were assessed using scanning electron microscopy. AO-PA-UA (62.6 MPa) showed a 20% increase in µTBS compared to the NC (50.2 MPa), which proved to be the most significant. This was followed by SB-EDTA-UA (58.9 MPa) with an increase of 15%. In addition to AO-PA-UA, SB-EDTA-UA could also be a viable alternative in the RBC repair protocol.

Aluminum surface defect detection method based on a lightweight YOLOv4 network

Deep learning is currently being used to automate surface defect detection in aluminum. The common target detection models based on neural networks often have a large number of parameters and a slow detection speed, which is not conducive to real-time detection. Therefore, this paper proposes a lightweight aluminum surface defect detection model, M2-BL-YOLOv4, based on the YOLOv4 algorithm. First, in the YOLOv4 model, the complex CSPDarkNet53 backbone network was modified into an inverted residual structure, which greatly reduced the number of parameters in the model and increased the detection speed. Second, a new feature fusion network, BiFPN-Lite, is designed to improve the fusion ability of the network and further improve its detection accuracy. The final results show that the mean average precision of the improved lightweight YOLOv4 algorithm in the aluminum surface defect test set reaches 93.5%, the number of model parameters is reduced to 60% of the original, and the number of frames per second (FPS) detected is 52.99, which increases the detection speed by 30%. The efficient detection of aluminum surface defects is realized.

Experimental and theoretical assessments of the chamomile flower extract as a green corrosion inhibitor for aluminum in artificial seawater

The anticorrosive qualities of a number of natural items have been researched because of the growing concern regarding the environmental contamination produced by conventional corrosion inhibitors. Through electrochemical measurements, the current study evaluated the effectiveness of chamomile flower extract (CFE) in preventing the corrosion of aluminum in an artificial seawater solution. Atomic force microscopy (AFM) and scanning electronic microscopy (SEM) were used for surface examination. Utilizing FTIR, the chemical composition of CFE extract was investigated. Density functional theory (DFT) computations were used to conduct theoretical analyses of its main constituents. According to the electrochemical tests, corrosion inhibition increased as inhibitor concentration increased and reached a moderate inhibition efficiency of 75.66% at 20 mL/L. Polarization curves showed that CFE molecules behaved as mixed-type inhibitors and that their adsorption process primarily followed the Freundlich isotherm. Examination of the corroded aluminum surface by SEM and AFM confirmed the adsorption of compounds present in the extract. The main constituents of the natural extract's electronic characteristics were determined using chemical quantum calculations, which also clarified interactions between inhibitors and metal surfaces as well as adsorption modalities.

Design of interface dynamic cross-linked hybrid network with highly improved mechanical, recycling and adhesive performance

Engineering interface dynamic crosslinking is particularly favorable for nanocomposite to acquire intriguing properties such as energy dissipation, recyclability and adhesion, yet it still remains a formidable task. Herein, we report a robust and recyclable nanocomposite hot melt adhesives (HMAs) enabled by employing noncovalent interactions at the interface between core–shell structured silica nanoparticles (T-SiO2 NPs) and carboxylated ethylene vinyl acetate copolymer (EVA-COOH). Through elaborate architecture by hydrogen bonds and Fe-based coordination bonds assembly of interface crosslinking network, the resultant hybrid network exhibits excellent mechanical properties, with tensile strength of 11.34 MPa, modulus of 2.64 MPa and toughness of 104.4 MJ m−3, which are 2.89 times, 1.77 times and 1.80 times that of the neat EVA, respectively. Furthermore, due to the dynamic nature of the network, its mechanical properties could be well maintained (∼100 %) even after multiple generations of recycling. More strikingly, the as-prepared HMAs displayed an outstanding ability to bond diverse substrates tightly. In addition, stable adhesion performance is realized on the aluminum (Al) surface under air and harsh conditions. This inorganic–organic interface crosslinking strategy shows great significance for fabricating low-cost and environmentally adaptive functional materials.

Metal dopant infused superhydrophobic aluminum surface through sustainable processing

The present work proposes a simple, scalable, and economical route for producing superhydrophobic surfaces using thermomechanical and microwave-assisted hydrothermal treatments. Infusing dopants (Mg, Fe) during thermomechanical processing resulted in a distinct and denser nanostructures on aluminum surface. The silanization of these surfaces resulted in superhydrophobicity (θa > 160°) with low hysteresis (≈ 2°) and adhesion (≈ 25 µN) compared to un-doped surface. The reduction in pitch between nanostructures enhanced capillary pressure (> 900 kPa), stabilizing Cassie state and restricting three-phase line sagging. The present work highlights the importance of doping in enhancing the durability of nanostructures for improving de-wettability.

The role of acid–base interactions in the pitting corrosion of aluminum: a review

Abstract The review describes an electrode kinetic model of aluminum pitting nucleation taking into account the charge of the metal surface, the adsorption of chloride ions on the oxide surface, their penetration through the oxide film with the help of oxygen vacancies, and the dissolution of the underlying substrate with the initiation of pitting corrosion at the metal/oxide interface. It is shown that the critical pitting potential is a function of the potential of a thin layer of aluminum surface covered by oxide and the value of the pitting potential of a binary surface alloying is related to the isoelectric point of the alloying element oxide in the binary alloy. An electrode kinetic model of pitting initiation is described, which was used to explain the effect of surface alloying on the pitting initiation on binary alloys. A method for changing the surface charge by forming foreign surface organosilicon nanolayers bearing both negatively and positively charged groups was proposed. It has been established that four characteristics (q, Ψ 1-potential, E pit and the tendency of aluminum to depassivate) depend on the nature of ion-exchange groups, the degree of their acid dissociation, and the ion-chemical interaction with activator ions.

A Novel Polishing Process for Ultra-Smooth Aluminum Surfaces via Anodizing in Sodium Metaborate

A novel ultra-smoothing process for aluminum surfaces was developed using porous alumina formation and subsequent oxide dissolution. A submicron-scale periodic dimpled aluminum surface with an arithmetic mean roughness of 31.5 nm was prepared by anodizing in an etidronic acid solution. This dimpled aluminum specimen was then anodized in a sodium metaborate (NaBO2) solution to form a unique porous alumina film with an extremely flat barrier layer, which differs from the typical hemispherical barrier layer. The outer porous layer became thicker with time during anodizing, whereas the thickness and smoothness of the inner barrier layer were maintained without oxide breakdown. As the porous alumina film was chemically removed in a CrO3/H3PO4 solution, a smooth aluminum surface was exposed. The mean roughness of the aluminum surface drastically decreased to 0.5 nm by short-term anodizing for 15 min and slightly decreased with further anodizing. As a result, an ultra-smooth aluminum surface measuring 0.4 nm in roughness, which is much smaller than that of an electropolished aluminum surface (1.3 nm), was successfully obtained via anodizing in NaBO2 and subsequent oxide dissolution. Our smoothing process was compared with conventional smoothing processes such as electropolishing and barrier oxide formation.

Electrochemical Separation of Porous Anodic Aluminum Oxide with Thick Barrier Layers

We investigated an electrochemical separation method for anodic aluminum oxide (AAO) films possessing thicker barrier layers by electrolysis in sodium chloride (NaCl) and ethylene glycol (EG) solution and subsequent fabrication of through-hole AAO membranes by immersion in phosphoric acid (H3PO4) solution. The AAO films with different barrier layer thicknesses were formed on the aluminum surface by anodizing in sulfuric, oxalic, and H3PO4 solutions at up to 130 V. The AAO-covered aluminum specimens were immersed in NaCl/EG solution, and then constant voltage electrolysis at 10 V higher than the anodizing voltage was performed for the separation of AAO from the aluminum surface. Many nanoscale paths were formed throughout the barrier alumina layer in the initial stage of electrolysis, and then the aluminum substrate electrochemically dissolved through these narrow paths during electrolysis. Although the AAO film formed by anodizing at 130 V was partially fractured by electrolysis, the AAO films formed at up to 80 V were uniformly separated from the aluminum surface. As the separated AAO membrane was immersed in H3PO4 aqueous solution after electrolysis, the barrier layer with narrow paths preferentially dissolved into the solution, and a through-hole AAO membrane could be successfully obtained.