Aluminum Surface Research Articles

Aluminum Micropillar Surfaces with Hierarchical Micro- and Nanoscale Features for Enhancement of Boiling Heat Transfer Coefficient and Critical Heat Flux.

The rapid progress of electronic devices has necessitated efficient heat dissipation within boiling cooling systems, underscoring the need for improvements in boiling heat transfer coefficient (HTC) and critical heat flux (CHF). While different approaches for micropillar fabrication on copper or silicon substrates have been developed and have shown significant boiling performance improvements, such enhancement approaches on aluminum surfaces are not broadly investigated, despite their industrial applicability. This study introduces a scalable approach to engineering hierarchical micro-nano structures on aluminum surfaces, aiming to simultaneously increase HTC and CHF. One set of samples was produced using a combination of nanosecond laser texturing and chemical etching in hydrochloric acid, while another set underwent an additional laser texturing step. Three distinct micropillar patterns were tested under saturated pool boiling conditions using water at atmospheric pressure. Our findings reveal that microcavities created atop pillars successfully facilitate nucleation and micropillars representing nucleation site areas on a microscale, leading to an enhanced HTC up to 242 kW m-2 K-1. At the same time, the combination of the surrounding hydrophilic porous area enables increased wicking and pillar patterning, defining the vapor-liquid pathways on a macroscale, which leads to an increase in CHF of up to 2609 kW m-2.

Innovative DIY drinking water disinfection for underserved communities

Waterborne pathogens threaten 2.2 billion people lacking access to safely managed drinking water services, causing over a million annual diarrheal deaths. Individuals without access to chlorine reagents or filtration devices often resort to do-it-yourself (DIY) methods, such as boiling or solar disinfection (SODIS). However, these methods are not simple to implement. In this study, we introduced an innovative and easily implemented disinfection approach. We discovered that immersing aluminum foil in various alkaline solutions produces alkali-treated aluminum foil (ATA foil) that effectively adsorbs Escherichia coli (E. coli), Salmonella, and Acinetobacter through the generated surface aluminum hydroxide. For example, a 25 cm2 ATA foil efficiently captures all 104E. coli DH5α strains in 100 mL water within 30 min. Using a saturated suspension of magnesium hydroxide, a type of fertilizer, as the alkaline solution, the properties of the saturated suspension eliminate the need for measuring reagents or changing solutions, making it easy for anyone to create ATA foil. ATA foils can be conveniently produced within mesh bags and placed in household water containers, reducing the risk of recontamination. Replacing the ATA foil with a foil improves the adsorption efficiency, and re-immersing the used foil in the production suspension restores its adsorption capacity. Consequently, ATA foil is an accessible and user-friendly alternative DIY method for underserved communities. Verification experiments covering variations in the water quality and climate are crucial for validating the efficacy of the foil. Fortunately, the ATA foil, with DIY characteristics similar to those of boiling and SODIS, is well-suited for testing under diverse global conditions, offering a promising solution for addressing waterborne pathogens worldwide.

Initiation mechanism of arcing generated in RF capacitively coupled plasma

In our previous study, we established an arcing generation and measurement system and we observed prior light emission before arcing current development. However, we briefly analyzed those light emissions with strong assumptions without detailed experiment evaluations and thus, the investigation of the formation mechanism in the initiation phase with detailed experiment evaluations has yet to be conducted. In this work, we investigated the initiation mechanism of arcing generated on an arcing inducing probe (AIP) in a radio frequency capacitively coupled plasma (CCP) environment. Here, the AIP is an aluminum rod covered by anodized film and its tip edge is partially stripped to localize arcing on this edge. We measured emission light, voltage, and current waveforms induced by arcing. The spatiotemporal image of the emission light revealed that the tip glow is the brightest intensity and has longest lifetime during arcing, meaning that it is the primary process in whole arcing process. The current waveform induced by arcing corresponds to the time evolution of the tip glow and estimations revealed that the electron emission is the predominant component of the current formation. Furthermore, snapshot images with AIPs having enlarged stripping area exhibited that arcing occurs at the boundary between the alnuminum and anodized film (dielectric), where charging of ions from the CCP on the film surface can induce high-electric field. In addition, we found that the energy relaxation length of emitted electrons for collisions with Ar atoms, which are the background gas, is much larger than the tip glow diameter, meaning that the electon-Ar collision cannot maintain tip glow. This result supports additional source of atoms to sustain the tip glow such as the surface evaporation from arcing spot, of which evidence was speculated our previous study. We estimated minimum aluminum vapor density and surface temperature, which is sufficiently high enough to induce surface vaporization. Combining those experiment results and estimations, that are electron emission, high surface temperature, and surface evaporation, we can speculate that the initiation mechanism of arcing near dielectric surface in radio-frequency CCP environment is the thermionic emission and surface evaporation from arcing spot.

Study of The Inhibition Corrosion of Aluminum Metal Using Peppermint Oil in An Acidic Medium

This study included the study of the efficiency of peppermint oil inhibition of aluminum corrosion in acidic medium HCl at concentrations (0.5, 1, 1.5, 2 M) on the corrosion rate in the presence and absence of the inhibitor peppermint oil at different concentrations (1000, 2000, 3000, 4000 ppm).In order to study the effect of changing the temperature (303, 313, 323, 333 K) on the corrosion rate in the absence and presence of the inhibitor, different concentrations of the inhibitor were chosen in addition to the acid concentration (1M). The experiments were carried out using the weight loss method to calculate the erosion rate. The expected heat of adsorption enthalpy was (-29.913 KJ/mol), with a negative sign indicates that the process is exothermic. The value of the free energy of adsorption ranged from (11.086-15.067 KJ/mol. (The results showed that Freundlich adsorption isotherm equation is the best fit to examine the adsorption process, also a scanning electron microscope. Showed the surface of aluminum before and after corrosion according to the results of the study, it was found that the used inhibitor reduces corrosion in acidic media. Its anti-corrosion efficacy also improves with increasing inhibitor concentration and with decreasing temperature.

Sorption behavior of Molybdenum (IV) onto commercial acidic alumina surface

Sorption behavior of Molybdenum (IV) onto commercial acidic alumina surface

Ultrasonic welding of CF/PA6 composite to 6061Al alloy utilizing an interfacial coating as energy director

This study investigates ultrasonic plastic welding to join the carbon fiber-reinforced thermoplastics and 6061Al alloy in a lap-type joint configuration. An interfacial polymer coating through a fluidized bed on aluminum alloy was considered an energy director, as it was essential for concentrating heat at the interface during welding. The significant ultrasonic process setting (weld pressure: 0.5 MPa, weld time: 600 ms, hold time: 1000 ms) was statistically realized for a maximum lap shear strength of the joint that showed the interlaminar shear (first-layer ply) failure of the composite, while the welding interface morphology revealed interdiffusion of thermoplastics with the load-bearing carbon fibers attached to the composite-coating resin mixtures, whereas the coating interface offered a strong adhesion of polymer on the aluminum surface asperities through mechanical interlocking. An efficient multi-material joint was obtained within 1.6 s in comparison to the adhesive bonding technology that required at least 20 min. Additionally, the interfacial coating serves as an insulator, avoiding galvanic corrosion in joints as well as fretting damage. The encouraging findings of this research provide deeper insight into joining thermoplastic composites to metals by ultrasonic plastic welding without the use of a separate energy director, which simplifies the process of industrialization.

Studies of the mechanism of adhesion of polymer coatings on the oxidized surface of aluminum and magnesium alloys

Studies of the mechanism of adhesion of polymer coatings on the oxidized surface of aluminum and magnesium alloys

Chemical Activity of Nascent Surfaces for Tribochemical Reactions of Lubricant Components.

Boundary lubrication characteristics are strongly dependent on tribochemical reactions at the contact interface. There are multiple factors that contribute to the activity of tribochemical reactions and the complexity of this phenomenon. Here, we focused on nascent surfaces created by friction and aimed to clarify their chemical properties. To achieve this, we first developed a method based on a mass spectrometer that can sensitively detect molecular adsorption and reactions on a nascent surface. We used various organic compounds as adsorbates and friction materials such as steel, aluminum, gold, and ceramics and examined adsorption of the organic compounds on the nascent surfaces. The adsorption properties of the additives differed between steel metal oxide and nascent steel surfaces. For example, polar organic phosphates, which are extreme-pressure additives, were more easily adsorbed on oxide surfaces, whereas nonpolar organic sulfur compounds were more easily adsorbed on nascent steel surfaces. Alcohols and ethers also adsorbed on nascent aluminum surfaces, whereas olefins and benzene did not. Nascent gold surfaces showed high catalytic activity. Saturated hydrocarbons and fluorinated compounds, which are chemically inert, were also adsorbed on nascent ceramic surfaces, showing high activity. Hydrocarbon oils decomposed through the influence of frictional heat on a nascent steel surface to generate hydrogen and methane. We applied reactive molecular dynamics to simulate the adsorption phenomenon on iron surfaces. As a result, the adsorption energy obtained by simulation and the experimentally determined adsorption activity correlated well. Thus, adsorption and reaction behaviors on nascent surfaces inferred by our method were theoretically supported. On the basis of the chemical properties of the nascent surfaces obtained here, it is possible to explain boundary lubrication phenomena.

Acid-base properties and modeling by quantum chemistry of adhesion interactions at the interface of thermoplastic-aluminum systems

Thermoplastic-aluminum systems are used in the manufacture of corrosion-resistant lightweight constructions in aerospace and automotive industries. The adhesion strength of such systems is determined by the mechanism of adhesion interaction. In this article, adhesion interactions between the surfaces of polyethylene terephthalate, poly(propylene carbonate), poly(methyl methacrylate), polystyrene, polypropylene and aluminum were studied to identify a correlation between the acid-base properties of the studied surfaces, the mechanism of adhesion interaction and energy characteristics in thermoplastic-aluminum systems using experimental and theoretical approaches. The experimental approach consisted of finding the values of the free surface energy components, the acidity parameters of thermoplastics and aluminum by the E.J. Berger and van Oss-Chaudhuery-Good methods. The theoretical approach consisted of the study of adhesion interactions in thermoplastic-aluminum systems using the quantum chemistry method B3LYP-GD3/6-31G(d,p). It was theoretically established the functional groups to be the active sites on the thermoplastics surface. At the same time, the strongest adhesion interaction is manifested in systems formed by a carbonyl oxygen atom.The experimental values of the components of the free surface energy of thermoplastics and aluminum are in good agreement with the theoretical values of the energy and force of the adhesion interaction of the systems under consideration.

Liquid metal compatibility of pre-oxidized FeCrAl in flowing Sn

A flowing Sn thermal convection loop (TCL) experiment was conducted in FeCrAlMo (Kanthal alloy APMT) tubing for 1000 h with a peak temperature of 400 °C. Oxide dispersion strengthened (ODS) Fe-(10–12)Cr-6Al and APMT specimens were exposed and all were pre-oxidized to form an external alumina scale. Unlike static exposures at 400° and 500 °C where pre-oxidation prevented dissolution, large mass losses were observed in the TCL hot leg after the specimens were cleaned in Li. The observed pitting suggests that localized failure of the pre-formed alumina surface oxide caused significant metal loss. Specimen mass gains were not observed on the cold leg implying that mass transfer did not occur and the small levels of Fe and Cr in the Sn after the experiment implies that Sn-rich phases may have formed. Post exposure room temperature tensile testing showed limited impact of the Sn exposure on the 12Cr ODS FeCrAl alloy, comparable to a 1000 h anneal in Ar at 400 °C. These results suggest that pre-oxidation is not sufficient to protect FeCrAl alloys in contact with flowing liquid Sn at 350°-400 °C.

INVESTIGATION OF MICROSTRUCTURAL EVOLUTION AND MECHANICAL PROPERTIES OF SURFACE GRAPHITIZED AL-1100 ALLOY

This paper explains about the mechanical insertion of graphite particles into aluminum (Al-1100) surface for forming composites on the surface through an electrical resistance heat-supported pressing procedure. The surface of the aluminum is first graphite coated by solution casting. To achieve impregnation, the graphite–aluminum interface is locally heated with the assistance of electrical resistance heating followed by mechanical pushing. The degree to which aluminum surface softens can be regulated by process factors like current and heating time. Microstructural characterization of aluminum–graphite composite was carried out with SEM, TEM, Raman spectroscopy and XRD. It was revealed from the microstructural characterization that graphite particles were impregnated into the aluminum surface without agglomeration. Raman spectroscopy of graphite-impregnated surface shows a shift in major graphite peaks and an increased ratio of intensity ([Formula: see text]). The presence of carbide compound (Al4C3) was not detected from the XRD and TEM studies. The mechanical property examination of the surface was carried out by nanoindentation and the subsurface was characterized by microhardness tests. It was observed that surface mechanical property and reduced Young’s modulus were improved by more than 200% and 150%, respectively. The projected method can be utilized as a 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 an open producing environment.

Study on oxidation mechanism of aluminum surface under applied electric field

The oxidation behavior of aluminum alloy has a significant impact on its industrial application of aluminum alloy, and studying how aluminum alloy oxidizes in electrolyte solutions is crucial. However, current research predominantly focuses on aluminum anodization at higher voltages and the second-phase corrosion behaviors in halide ion-containing solutions. The research on the formation mechanism of the oxide film on the aluminum surface lacks in-depth analysis, and there is no unified opinion on the method of oxygen invasion into the oxide film. This study establishes an experiment on the corrosion of aluminum alloy in an oxygen-free water environment. By scrutinizing the oxidation behaviors of aluminum surface under conditions of no voltage and low voltage, we investigate the effect of applied electric field on the mode of oxygen invasion in alumina. The findings reveal that under the condition of no external voltage and an alkaline environment, self-passivation products of aluminum undergo a transformation from AlO(OH) to Al(OH)3 as the pH value increases. At a pH of 10, complete transformation into Al(OH)3 occurs. When external voltage is applied, Al(OH)3 is initially formed on the aluminum surface with an increase of potential. As the potential reaches a certain value, the potential energy barrier for the reaction of H and O in OH− is disrupted, leading to the reaction of Al3+ replacing H+ and generating an Al2O3 film, with the current on the membrane surface changes unevenly during this process, resulting in the emergence of a double-layer film structure on the aluminum surface. Therefore, under the electrochemical environment of applying a small current, the film formation process on the surface of aluminum alloy is carried out under the action of OH− heterocracking in water, and the O in the water molecule forms two distinct oxide films with the Al matrix in the form of O2− and OH−.

Multiscale Model for Hydrogen Chloride Uptake on Aluminum for Spacecraft Fire Safety

An electrical fire within spacecraft environments often produces poisonous gases, such as hydrogen chloride (HCl). These gases adsorb on the interior materials of the spacecraft, primarily treated aluminum surfaces. A safe design of the spacecraft can be facilitated by modeling the spacecraft compartment. In this study, a multiscale model is developed to predict HCl uptake by anodized aluminum, which has a thick oxide layer covering its surface compared to other treatments. X-ray photoelectron spectroscopy revealed that aluminum chloride is found deep in the oxide layer of anodized aluminum, implying that the pore-scale transport and reaction of HCl within the oxide layer covering the aluminum surface must be considered. Hence, a multiscale approach is warranted. A pore-scale model is first developed, wherein the HCl reacts with the aluminum oxide pore walls to create an aluminum chloride layer. The HCl then diffuses through that layer for further reaction, until the layer (diffusion resistance) grows too large and the uptake of HCl stops. This pore-scale model is coupled with a reactor-scale model to predict overall HCl uptake. Results show that this new multiscale approach predicts the uptake of HCl far more accurately when compared to experimental data than previously used single (reactor)-scale models.

Hyperhidrosis: problems and solutions

The functional role of sweating is not limited only to thermoregulation and excretion. There are other functions of it — the ability to enhance and maintain hydration and barrier function of the skin. Excessive sweating can lead to an exacerbation or cause many skin diseases, form psychological discomfort in a person due to wet clothes or an accompanying unpleasant odor. Primary hyperhidrosis may be an autosomal dominant genetic disease. Secondary, usually generalized hyperhidrosis is often associated with drug effects on the body or a systemic disease. The following approaches are used in the treatment of hyperhidrosis: 1) blocking the release of sweat to the skin surface (aluminum salts and formaldehyde); 2) physiotherapy (iontophoresis); 3) destruction of sweat glands and cessation of sweat production (excision of a skin flap with subcutaneous fat, curettage, microwave technology, etc.); 4) termination of the signal from the central nervous system to the sweat glands (transthoracic endoscopic sympathectomy, percutaneous radiofrequency sympathectomy, botulinum toxin injections, systemic anticholinergic drugs). External remedies for excessive sweating include the Russian drug Formagel®, containing 3.7% formaldehyde. This drug is a non-invasive, easily doable, effective, safe method of treating hyperhidrosis.

Preparation of mechanically durable superhydrophobic aluminum surfaces by LST/MAO and chemical modification

In this paper, a superhydrophobic surface with mechanical durability was prepared on 6061 aluminum (Al) alloy by combining laser surface texturing (LST) and micro-arc oxidation (MAO) techniques followed by chemical immersion treatment. The effects of processing on Al alloys with different texturing spacings on the surface morphology, roughness, surface wettability, and corrosion resistance of the subsequently formed composite coatings were analyzed. The results show that a superhydrophobic surface was obtained with the water contract angle (WCA) of 158.3 ° and the roll-off angle of 9.5 ° at a texture spacing of 300 μm. This was due to the fact that the surface microroughness texturization process created by LST on the surface increased the generation of surface nanostructures, and combined with the natural nanostructure possessed by MAO, unique " double " nanostructure was formed on the surface. This surface structure increased the area of fluoride attachment, reduced the solid-liquid contact area, and decreased the adhesion of droplets to the surface, resulting in higher hydrophobicity. Electrochemical corrosion experiment showed that the corrosion current density of LM-300 was 2 orders of magnitude lower than that of the LM-0 sample, clearly demonstrating better corrosion resistance. In addition, the prepared superhydrophobic surface presented excellent mechanical durability, and in the ceramic zirconia cyclic abrasion experiment, the superhydrophobic surface was able to withstand 61 cycles of abrasion at a pressure of about 2.5 kPa.

Capacitive sensing of frost growth dynamics on aluminum surfaces with different wettabilities

Frost formation is a critical issue in many industries including air conditioning and refrigeration, aviation, transportation, and cryogenics. Frost buildup on heat exchanger surfaces reduces their efficiency by acting as a thermal resistance and by reducing or blocking the airflow. Defrosting is therefore necessary to maintain system efficiency. However, defrost initiation and cycle duration are critical parameters that govern system performance. Excessively early or late defrosting can result in energy loss. Frost detection is thus essential to carry out defrosting efficiently. To know when to initiate defrost, both the density and thickness of the frost must be known as both affect the frost thermal resistance. However, state of the art approaches are not sensitive to both frost density and thickness. Here, a capacitive sensing method is proposed that is sensitive to both the density and thickness of the frost. The method can achieve precise frost detection, offering insights into the ideal time to initiate defrosting by being sensitive to factors that affect frost specific thermal resistance. Experiments are carried out on plain (hydrophilic), superhydrophobic, and superhydrophilic aluminum surfaces at three different surface temperatures (−6 °C, −10 °C, −16 °C) to investigate the sensing performance. The capacitance measured increases with time as frost forms and grows. This change in capacitance, along with mass and thickness data, was used as a tool to characterize frost growth. The results indicate that decreasing wettability (superhydrophilic to plain (hydrophilic) to superhydrophobic) results in a decreasing trend in mass accumulation, frost density, and change in capacitance and an increasing trend in frost thicknesses and thermal resistance. It was also demonstrated that increasing surface temperature results in decreasing changes in capacitance (measurement sensitivity), mass accumulation, frost thicknesses, and thermal resistance, with an increasing trend in frost density. A strong correlation between frost mass and change in capacitance was observed regardless of surface temperature or wettability. This rendered implications for the best time of defrosting initiation. The proposed approach offers high accuracy, sensitivity, and convenience as a non-invasive method to study dynamic frost growth with insights into more optimal defrosting cycles, contributing to the development of more efficient energy systems.

Drop-on-demand metal jetting of pure copper: On the interaction of molten metal with ceramic and metallic substrates

Copper, renowned for its exceptional electrical and thermal conductivity at a low cost, holds great promise in electronic applications. While additive manufacturing of copper has attracted interest, the exploration of applying Drop-on-demand Metal Jetting (DoD-MJ) to 3D print pure copper remains uncharted. To fill this research gap, we employed an in-house DoD-MJ platform, MetalJet, to generate Cu microdroplets and deposit them onto ceramic and metallic substrates, a first-time achievement in this research context. Our study demonstrates the successful generation of uniform Cu microdroplets, emphasising the pivotal role of oxygen content control in preventing nozzle-level reactions, a factor that can disrupt droplet formation. Both alumina and aluminium nitride substrates exhibited poor wettability with molten Cu droplets, and no interface formed between these surfaces due to thermodynamically unfavourable reactions. Nevertheless, the irregular surface of alumina displayed an interesting capability to enable the adhesion of Cu droplets to the substrate through an interlocking mechanism. Lastly, the electrical resistivity of MetalJet printed pillars was measured as low as 6.75×10-8Ωm without any post-treatment, offering exciting possibilities for applications in 3D electronics.

Thermal pre-treatment of reactive aluminium alloy waste powders

AbstractThis study focussed on assessing the efficiency of thermal pre-treatment of Al alloy waste powders to facilitate their subsequent treatment and disposal. Five samples originating from aluminium surface finishing industries underwent thermogravimetric analyses and were subjected to a laboratory tub furnace. Four set temperatures (450, 475, 500, 525 °C) for the tubular furnace were selected based on the TG results. Using sequential images of the sample inside the tubular furnace, the ignition delay time was calculated. In addition, the efficiencies of medium-temperature thermal pre-treatment were determined using the gas volume method. The shot blasting samples (S1 and S2) exhibited shorter ignition delay times compared to the sandblasting (S3) and one of the polishing samples (S4). The influence of ZnO alloy content on the ignition delay time was investigated, revealing that the ignition delay time decreased with an increase in ZnO alloy content. The raw and pre-treated materials were analysed for morphology, composition and reactivity. The pre-treatment efficiency of the samples improved, especially with a retention time longer than the ignition delay of the samples. Recommendations for the storage and handling of pre-treated products were provided.

Impact of gas bubbles on bacterial adhesion on super-hydrophobic aluminum surfaces

Super-hydrophobic surface (SHS), which traps micro/nano-scale gas bubbles on solid walls, has been reported to greatly reduce bacterial adhesion and biofouling. However, it is unclear whether and how the trapped gas bubbles reduce the bacterial adhesion. Here, we examine the role of the trapped gas on the bacterial adhesion by measuring the spatial distributions of attached bacteria on SHS using scanning electron microscopy (SEM). Two SHSs, one with regular micro-grooves, and the other with randomly roughed textures at micro/nano-scales, both created on aluminum substrates, were tested. We found that for a SHS where gas bubbles are trapped between roughness elements, bacteria only attach to the surface areas that are not covered by gas (e.g., top of roughness elements), while the areas covered by gas bubbles - gaps between roughness elements - are free of bacteria. In contrast, for a rough surface with the same texture geometry as that of SHS but no hydrophobic chemistry, bacteria are distributed evenly to the top and gap of roughness elements. Our results suggest that the SHS may reduce biofouling by providing a physical barrier of gas-liquid interface which separates bacteria from the solid walls. Furthermore, we showed that nano-scale roughness on SHS is insufficient to prevent bacterial adhesion. Our results should provide useful guidance for the future engineering design of efficient anti-biofouling materials.

Transformation of ZnS microspheres to non-centrosymmetric nanoplates for the fabrication of flexible piezoelectric nanogenerators: Electrode surface area modification for boosting the output performance

We report the transformation of ZnS particles from microsphere to 2D nanoplate having a non-centrosymmetric phase by optimizing growth parameters of hydrothermal method, and fabrication of flexible piezoelectric nanogenerators (PENGs). ZnS nanoplates-based PENG showed maximum open circuit voltage and short circuit current of ∼ 3.8 V and 1.8 μA, respectively. Thereafter, surface of aluminium (Al) electrode was modified by making parallel and cross-parallel lines using a cost-effective technique. Surface-modified Al-electrode-based PENG device generated ∼ 6.6 and 2.5 times higher open circuit voltage and short circuit current, respectively, with a power density of ∼ 41.5 μWcm−2. This device was successfully used as portable electronics by flashing 15 red LEDs after charging a 1 μF capacitor up to 7.1 V in 75 s. Furthermore, the device exhibited noticeable electric output signals under various kinds of human body motions, which makes it a promising candidate for self-powered wearable sensor applications.