Alumina Substrates Research Articles

Characterization of droplet freezing on superhydrophobic surfaces with different microstructures

Superhydrophobic surfaces with microstructures have garnered significant attention for anti-icing applications due to their lower cost and higher efficiency. In this paper, we designed and prepared surfaces with differently spaced groove microstructures on aluminum substrates using femtosecond laser technology combined with low-surface-energy coatings. In addition, droplet freezing times and freezing processes were investigated to study the anti-icing properties of different surfaces. The results demonstrated that the sample surfaces exhibit excellent superhydrophobicity. At the cold surface temperature of −15 °C, the freezing time of droplets on the surface with a spacing of 100 μm is 707.9 s, which is far more than that of other sample surfaces. Additionally, groove spacing has a more pronounced effect on the rate of change in height compared to the diameter before and after droplet freezing. During the freezing process, the freezing front initiates from the cold surface and grows upward in a convex shape. As the growth of the freezing front at the edge accelerates, it eventually becomes concave, and this phenomenon occurs earlier at lower temperatures. Freezing is considered complete when the freezing tip appears. As the temperature decreases, both the droplet supercooling time and phase change time shorten. This paper is anticipated to provide a reference for the design of efficient anti-icing materials.

Optimization of superconducting niobium nitride thin films via high-power impulse magnetron sputtering

Abstract We report a systematic comparison of niobium nitride thin films deposited on oxidized silicon substrates by reactive DC magnetron sputtering and reactive high-power impulse magnetron sputtering (HiPIMS). After determining the nitrogen gas concentration that produces the highest superconducting critical temperature for each process, we characterize the dependence of the critical temperature on film thickness. The optimal nitrogen concentration is higher for HiPIMS than for DC sputtering, and HiPIMS produces higher critical temperatures for all thicknesses studied. We attribute this to the HiPIMS process enabling the films to get closer to optimal stoichiometry before beginning to form a hexagonal crystal phase that reduces the critical temperature, along with the extra kinetic energy in the HiPIMS process improving crystallinity. We also study the ability to increase the critical temperature of the HiPIMS films through the use of an aluminum nitride buffer layer and substrate heating.

Remediation of crude oil contaminated oily wastewater using nanostructured ZnO-decorated ceramic membrane: Membrane fouling and their mitigation using photo-catalytic self-cleaning process

In membrane-based oil water separation, the fouling of oil on the membrane pores due to the adsorption of oily feed components (crude oil) is a major disadvantage. In order to address the problem of membrane fouling, in this work, the filtration membrane itself was coated with a photoactive semiconducting material to self-clean the fouled membrane by photo-catalytic degradation. In addition to the self-cleaning, the other major functionality of the coating is to render a favorable surface wettability, conducive for water passing oil water separation. The basic membrane is porous alumina (Al2O3) substrate, on which a layer of crystalline Zinc Oxide (ZnO) thin film was coated by single step RF magnetron sputtering. The fabricated membrane is super-hydrophilic in the air and super-oleophobic underwater, and this contrasting wettability is crucial for the water passing oil water separation. The advantage of preferentially water passing membrane is that the oil clogging on the membrane surface is less than that of the oil passing membrane. However, after prolonged use with crude oil-contaminated feed, the accumulation of organic pollutants on the membrane surface hinders the smooth permeation of water through the membrane. The oil water filtration system involves cross flow through the ZnO-deposited Al2O3 membrane with the application of trans-membrane pressure. The membrane achieved an excellent separation efficiency (99.66 %) of oil and water from the oil emulsified water, and high permeates flux (908.4 L/m2.h.bar) for 200 ppm crude oil contaminated oily feed (surfactant stabilized crude oil-in-water emulsion). After a prolonged use of 540 min, the permeate flux declined due to the accumulation of organic pollutants present in the oily water. The original flux was restored by initiating photocatalytic degradation of organic pollutants by the exposure of UV radiation on the used membrane surface. The ZnO-deposited Al2O3 membrane shows an excellent light induced photocatalytic self-cleaning and antifouling with flux recovery ratio of around 88 %. In addition to this application, this manuscript also presents the morphological, elemental, structural, and topological characterizations of coated membrane.

Fabrication and evaluation of the superhydrophobic RTV-NanoSiO2 composite coating on aluminum 1350 using plasma electrolytic oxidation (PEO)

Surface modification through coating has recently attracted significant attention as a practical approach to mitigating various types of damage, such as dust accumulation, pollution, and icing. Altering surface wettability to achieve superhydrophobicity, with contact angles exceeding 150°, has proven highly effective in such cases. This research aims to enhance the wettability of an aluminum substrate by employing plasma electrolytic oxidation techniques combined with a secondary nanocomposite polymer coating. The objective is to transform the surface from hydrophilic, or water-attracting, to superhydrophobic, or highly water-repellent. When ceramic-polymer nanocomposite coatings are applied, the contact angle of 167° confirms the superhydrophobic properties of the treated aluminum surface.

Stability of trivalent and hexavalent chromium oxide layers on aluminum substrates from electronic structure calculations

Stability of trivalent and hexavalent chromium oxide layers on aluminum substrates from electronic structure calculations

Stainless Steel Deposits on an Aluminum Support Used in the Construction of Packaging and Food Transport Containers

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the present paper, layers of food stainless steel were deposited using thermal arc spraying on an aluminum alloy substrate to stop the migration of aluminum ions inside liquid food products. The physical-chemical and mechanical properties of the protection system: stainless steel layer used in the food industry (suggestively called: food-grade stainless steel)—aluminum substrate were investigated, and then the organoleptic properties of the food liquids that came into contact with the deposit were evaluated. It was found that food-gradestainless steel deposits have low porosity (3.8%) and relatively high adhesion and hardness, which allows complete isolation of the substrate material. The investigations carried out on the properties of food liquids that come into contact with the stainless steel deposit revealed the fact that it perfectly seals the aluminum start. The food-grade stainless steel coating (80T) was much better and safer for preserving dairy products maintaining a constant acidity up to 17 degrees Thorner, wines (with an average acidity of 3.5–4 degrees), juices (with natural pigments), and oils (with a good absorbance level correlated with clarity). This aspect suggests that the created system can be successfully used to manufacture containers for the transport of liquid products.

Topography-Mediated Induction of Epithelial Mesenchymal Transition via Alumina Textiles for Potential Wound Healing Applications.

Substrate topography is vital in determining cell growth and fate of cellular behavior. Although current invitro studies of the underlying cellular signaling pathways mostly rely on their induction by specific growth factors or chemicals, the influence of substrate topography on specific changes in cells has been explored less often. This study explores the impact of substrate topography, specifically the tricot knit microfibrous structure of alumina textiles, on cell behavior, focusing on fibroblasts and keratinocytes for potential wound healing applications. The textiles, studied for the first time as invitro substrates, demonstrated support for keratinocyte adhesion, leading to alterations in cell morphology and the expression of E-cadherin and fibronectin. These topography-induced changes resembled the epithelial-to-mesenchymal transition (EMT), crucial for wound healing, and were specific to keratinocytes and absent in identically treated fibroblasts. Biochemically induced EMT in keratinocytes cultured on flat alumina substrates mirrored the changes seen with alumina textiles alone, suggesting the tricot knit microfibrous topography could serve as an invitro model system to induce EMT-like mechanisms. These results enhance our understanding of how substrate topography influences EMT-related processes in wound healing, paving the way for further evaluation of microfibrous alumina textiles as innovative wound dressings.

Electrochemical Degradation of Methylene Blue using Aluminum Doped Copper Oxide Electrode: Modeling and Optimization

An electrochemical oxidation process with an aluminum-doped copper oxide (Al@CuO) anode was modeled and optimized for the degradation of methylene blue (MB). The Al@CuO anode material was prepared by the thermal decomposition method. X-ray fluorescence (XRF) analysis confirmed the successful deposition of CuO on the aluminum substrate. The influence of current density, electrolysis time, and MB concentration on the performance of the electrochemical degradation of MB was modeled using Box-Behnken design (BBD). The accuracy of the proposed quadratic model by BBD was confirmed with a p-value < 0.0001 and adj-R2 > 0.9. The optimum MB degradation efficiency of 53.23 % was obtained at 80 mg MB concentration, 40 min electrolysis time, and 3.75 V applied current. The kinetics on the MB electrochemical degradation process using Al@CuO followed pseudo first-order kinetics model. These studies revealed that the Al@CuO anode electrode is not a promising anode for the electrochemical degradation of methylene blue.

Mechanically robust and durable polyurethane-based superhydrophobic coating containing silica nanoparticles derived from hydrothermal assisted sol–gel method

In the current study, a suspension of hydrothermal assisted sol–gel synthesised superhydrophobic silica nanoparticles (h-SNPs) are sprayed over apartially cured polyurethane (PUR) surface on aluminium substrate. The surface exhibited superhydrophobic (SH) property with a water contact angle of 166 ± 2° and awater sliding angle of < 5°. X-ray diffraction study confirmed the formation of amorphous silica nanoparticles. The particle size determined by field emission scanning electron microscope is about 19–21 nm. The roughness of the coating is 3.5 µm as characterised using a surface profilometer. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy investigations indicated the presence of urethane linkages from PUR and siloxane stretching from h-SNPs. The adhesion of the coating tested with a cross-hatch cutter as per ASTM D3359 shows a rating of 5B. The coating qualified mandrel bend test conducted according to ASTM D255. No cracks are observed at the deformed areas and water drops roll off the surface, demonstrating the integrity of the coating and its superhydrophobicity. The coating exhibits high robustness as evident from sandpaper abrasion and tape peel tests. When compared to superhydrophobic polyurethane (SH PUR) coating developed using commercial silica as reported in our previous work, the developed h-SNPs coating is much more durable as confirmed by accelerated weathering test and anti-icing test. The SH coating also exhibits superhydrophobicity even after 200 h of accelerated weathering test and 16 de-icing cycles. The coating withstands 15 days of water immersion and also displays self-cleaning property.

Green synthesis of lignin-based non-isocyanate polyurethanes as reusable, self-healable and removable adhesives

Lignin-based non-isocyanate polyurethanes (LNIPUs) represent a class of polymers synthesized from lignin—an abundant, renewable polymer found in the cell walls of plants—without the use of toxic isocyanates. This makes LNIPUs an eco-friendly alternative to traditional petroleum-based polyurethanes. Despite their advantages, the synthesis of LNIPUs often entails complex processes, the use of additional catalysts, and highly polar solvents, which largely restrict their accessibility and practical applications. In this study, we present an higly efficient, catalyst-free, and solvent-free methodology for synthesizing LNIPUs. A series of novel LNIPUs were successfully prepared through a one-pot, catalyst-free and solvent-free polymerization reaction involving aminated fractionated lignin (ALFE) and bis(6-membered cyclic carbonate) (6CC). We systematically investigated the properties of the resulting LNIPUs, with a particular focus on the adhesion performance. The incorporation of ALFE significantly enhanced the adhesive properties of the resultant LNIPUs on aluminum, wood, and plastic substrates, achieving a maximum bonding strength of 3.09 MPa on aluminum. Furthermore, LNIPUs exhibit exceptional functionalities, including reusability, self-healing capabilities, and removability, along with improved thermal stability and photothermal properties.

Microwell-assembled aluminum substrates for enhanced single-cell analysis: A novel approach for cancer cell profiling by Raman spectroscopy

Single-cell analysis is critical for advancing personalized medicine, as it reveals cell population heterogeneity that influences disease outcomes. We present a microwell-assembled aluminum substrate platform that enhances single-cell Raman spectroscopy in liquid suspension by isolating individual cells and preventing stacking and movement, which significantly improves signal stability and the signal-to-noise ratio (SNR).We applied this novel platform to analyze PC-9 lung cancer cells and BEAS-2B normal bronchial epithelial cells, identifying distinct biochemical differences. Notably, cancer cells showed higher levels of adenine, cytochromes, DNA/RNA, and unsaturated lipids, along with an increased unsaturation ratio and protein content. These findings were further validated using machine learning models. An eXtreme Gradient Boosting (XGBoost) model achieved perfect classification accuracy of 100 %, underscoring the robustness of the spectral features identified by our platform.Our platform not only enhances single-cell Raman signal detection but also holds promise for biomedical applications, including early cancer detection, treatment monitoring, and drug development. The high-throughput capacity of this platform featuring over 120,000 wells, along with its compatibility with techniques such as Raman-activated cell sorting (RACS) further extends its potential for clinical diagnostics and personalized medicine.

An approach to breaking the 100-milli-Kelvin barrier in electron temperature with a dilution-refrigerator ultrahigh vacuum scanning tunneling microscope.

This study presents a newly constructed dilution-refrigerator ultrahigh vacuum (UHV) scanning tunneling microscope (STM) with a 9/2/2T superconducting vector magnet capable of achieving electron temperatures as low as 76 mK. Our design emphasizes robust thermal contacts, particularly with the sample holder through a thin insulating layer. Additionally, we focus on effective shielding and grounding against radio-frequency electromagnetic interference by integrating the critical electronics as a physically and electrically integral component of the STM setup. Scanning tunneling spectroscopy results obtained from a superconducting aluminum substrate and a gold tip indicate superior energy resolution, with a higher aspect ratio of the superconducting coherence peak in the dI/dV spectra compared to other dilution-refrigerator UHV STMs. Given that only a handful of UHV STMs with dilution refrigerators have reached electron temperatures below 100 mK, these results demonstrate the effectiveness of our design and methodology in achieving low electron temperatures.

A high-performance boron nitride nanocomposite coating with enhanced anticorrosion and flame retardant properties for aerospace applications

The efficiency of impermeable, two-dimensional material-infused nanocomposites in preventing metal corrosion is becoming more widely acknowledged. The remarkable chemical and thermal durability of 3-(2-aminomethylamino)butyltrimethoxysilane (AMBMS)-functionalized hexagonal boron nitride (BN) sets it apart from others. This study looks into adding more graphitic carbon nitride (GCN) and functionalized BN to the polymer to make it more resistant to corrosion and fire. Electrochemical methods were used on aluminum substrates to evaluate the performance of the proposed polyurethane (PU)/functionalized BN/GCN coating in a 3.5 wt% NaCl solution. After 800 h of exposure, Electrochemical Impedance Spectroscopy (EIS) indicated a coating resistance of 1.15 × 109 Ω.cm2, indicating significant increases in corrosion resistance. The protection efficiency of the composite coating was calculated to be 99.9 %. Furthermore, the coating exhibited an angle of contact with water of 163°, indicating its exceptional water repellency. The PU/functionalized BN/GCN composite had a much lower peak heat release rate than pure PU, which means it is better at keeping flames from spreading. These enhancements contribute to improved safety in potential applications. This durability is particularly important for aerospace applications, where long-term performance is critical. In short, the addition of functionalized BN/GCN to PU coatings significantly enhances the material’s mechanical, flame retardant, and corrosion resistance qualities, making it ideal for use in harsh environments such as aerospace.

High-performance surface defect detection of aluminum substrate based on event camera

Abstract Traditional industrial surface defect detection often employs CCD/CMOS cameras, but they are difficult to detect the minute defects on aluminum substrates in highly dynamic industrial scenes due to their nature. Event camera is a novel high-resolution vision sensor which measures per-pixel brightness changes in an asynchronous manner and outputs as event information flow (EIF). Small and weak defects on aluminum substrate can be captured by event camera effectively, but the EIF contain a large amount of noise, making it difficult to perform accurate and high-precision defect detection. To address this problem, we propose a frame aggregation method to realize good event information flow processing (EIFP), and then use an improved circle detection method to locate the aluminum substrate in each frame, removing abundant event information outside the aluminum substrate. Subsequently, we enhance the event signals under different frames based on optical flow tracking using multiple features, and construct a semi-supervised detector based on pseudo-labels to achieve high-precision defect localization. Finally, considering the small inter-class differences in defects on the surface of aluminum substrates, we construct a defect class corrector based on ensemble learning to enhance the ability to determine defect classes, achieving high-precision automatic quality inspection of aluminum substrate surfaces. The performance of our method is compared with other advanced methods based on event camera data of aluminum substrates in real industrial scenarios. The experimental results show that our method has improved the detection accuracy by about 10% and the classification accuracy by about 25% compared to the original state-of-the-art methods.

Influence of casting-warm pressing process on the thermal conductivity of micro–nano-Al2O3 substrate

Alumina substrates are increasingly used for high-power integrated circuits due to their high thermal conductivity, low thermal expansion coefficient, and excellent insulation properties. However, pores in the green tape from the tape casting process reduce the thermal conductivity and permittivity of the sintered ceramic substrate. Researchers have attempted to minimize ceramic porosity with chemical additives or by sintering pure alumina at temperatures above 1650 °C, but these methods often degrade thermal conductivity or quality of substrate evenness. This study proposes a low-cost casting-warm pressing process to densify pure alumina ceramic substrates using micro–nano-mixed alumina powders and sintering at relatively low temperatures. The results indicate that the relative density of the pure alumina ceramic substrate prepared at 1500 °C is 93%, a 4.4% improvement over the tape casting process. Additionally, the thermal conductivity of the alumina substrate from the casting-warm pressing process reaches 15.89 W/(m K), which is 1.4 times higher than that of the tape casting process. Microstructure analysis shows that the casting-warm pressing process with micro- and nano-multi-scale mixed alumina powders forms a novel thermal conduction enhancement mechanism. Large particles in the green tape overlap, while small particles fill the spaces between the large particles. The connected micrometer-sized particle skeletons form high thermal conduction net channels in the substrate, improving the thermal conductivity for heat transfer.

Formation of Multiscale Porous Surfaces via Evaporation-Induced Aggregation of Imprinted Nanowires with Highly Viscous Photocurable Materials

AbstractNumerous structures at the nano and microscale manifest distinctive properties with far-reaching implications across diverse fields, including electronics, electricity, medicine, and surface engineering. Established methods such as nanoimprint lithography, photolithography, and self-assembly play crucial roles in the fabrication of nano- and microstructures; however, they exhibit limitations in generating high-aspect-ratio structures when utilizing high-viscosity photocurable resins. In response to this inherent challenge, we propose a highly cost-effective approach facilitating the direct replication of high-aspect-ratio structures, specifically nanowires, through the utilization of anodized aluminum substrates. This study elucidates the streamlined fabrication process for multiscale porous surfaces achieved through the evaporation-induced integration of solid nanowires printed with high-viscosity photocurable resin.

Pt-Ta microhotplate with low resistance temperature coefficient and low resistance drift

Micro thermal plates are widely used in various sensors in the aerospace and automotive fields. With the reduction of chip size and the development of MEMS, micro thermal plates are also moving towards integration. The device failure caused by the Pt film at high temperatures seriously affects the stability of the sensor, and degradation determines the sensor's operating temperature and service life. In this paper, Pt, Pt-Ta, and Pt-Pd microcalorimetric plates were prepared and analyzed for their sintering behavior, microstructure, electrical properties, and high-temperature stability using co-firing of resistors and alumina substrates. The film layers prepared by co-firing were better matched to the alumina substrate, and the sintered network of the film layers was better. The Pt-10 %Ta microthermal plate has a 46 % lower resistance temperature coefficient TCR compared to the Pt microthermal plate, and the resistance drift at 800°C is reduced to 2.11 %/Day. And even at 1100°C, the Pt-Ta system also has a very low resistance drift −12 %/Day (Pt26.6 % /Day and Pt-Pd35.18 %/Day) with improved high temperature stability. The addition of Ta allows the membrane layer to have fewer voids at high temperatures, reinforcing the high temperature characteristics of the resistance thermometer. It improves the stability and accuracy of the heating plate in high temperature gas sensor applications.

The Influence of Temperature on the Spatial Distribution of AuNPs on a Ceramic Substrate for Biosensing Applications

In this study, we investigated the spatial distribution and homogeneity of gold nanoparticles (AuNPs) on an alumina (Al2O3; AAO) substrate for potential application as surface-enhanced Raman scattering (SERS) sensors. The AuNPs were synthesized through thermal treatment at 450 °C at varying times (5, 15, 30, and 60 min), and their distribution was characterized using field-emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM). The FE-SEM and STEM analyses revealed that the size and interparticle distance of the AuNPs were significantly influenced by the duration of thermal treatment, with shorter times promoting smaller and more closely spaced nanoparticles, and longer times resulting in larger and more dispersed particles. Raman spectroscopy, using Rhodamine 6G (R6G) as a probe molecule, was employed to evaluate the SERS enhancement provided by the AuNPs on the AAO substrate. Raman mapping (5 µm × 5 µm) was conducted on five sections of each sample, demonstrating improved homogeneity in the SERS effect across the substrate. The topological features of the AuNPs before and after R6G incubation were analyzed using atomic force microscopy (AFM), confirming the correlation between a decrease in surface roughness and an increase in R6G adsorption. The reproducibility of the SERS effect was quantified using the maximum intensity deviation (D), which was found to be below 20% for all samples, indicating good reproducibility. Among the tested conditions, the sample synthesized for 15 min exhibited the most favorable characteristics, with the smallest average nanoparticle size and interparticle distance, as well as the most consistent SERS enhancement. These findings suggest that AuNPs on AAO substrates, particularly those synthesized under the optimized condition of 15 min at 450 °C, are promising candidates for use in SERS-based sensors for detecting cancer biomarkers. This could be attributed to temperature propagation promoted at the time of synthesis. The results also provide insights into the influence of thermal treatment on the spatial distribution of AuNPs and their subsequent impact on SERS performance.

Nature-Friendly Water-Based Resin Paints with SiO2 Nanoparticles for Electrostatic Spraying

ABSTRACT This study presents an environment-friendly and less toxic approach to electrostatic spraying using novel water-based resin paints enhanced with SiO2 nanoparticles. Addressing the environmental and health concerns of traditional toxic solvent-based coatings, our research emphasizes the development and application of these paints on anodized aluminum substrates. Our experimental procedure involves formulating water-based paints; applying them via electrostatic spraying; and analyzing their stability, coverage, and adhesion properties. The findings demonstrated that the paints maintained stability and showed improved adhesion and uniformity without using a toxic solvent-based resin, particularly on substrates with extended anodizing treatment. This study highlights the potential of using water-based resin paints in industrial applications, offering a sustainable, efficient, and high-performance alternative to conventional coatings, paving the way for future research into their broader application and environmental impact.

Mussel-inspired thermo-switchable underwater adhesive based on a Janus hydrogel

On-demand underwater adhesives with excellent adhesive and gentle detachment properties enable stable connections to various biomedical devices and biointerfaces and avoid the risk of harmful tissue damage upon detachment. Herein, we present a Janus hydrogel adhesive that can reversibly switch its adhesion strength, which is controlled by temperature, using a thermoresponsive polymer and mussel-inspired molecules. This thermoswitchable adhesive (TSA) hydrogel displays both strong adhesion and gentle detachment with an over 1000-fold gap in underwater adhesion strength onto glass, titanium, aluminum, and Teflon substrates when exposed to temperatures above and below the lower critical solution temperature (LCST). The adhesion switch is possibly caused by the change in toughness of the TSA hydrogels with temperature because the Janus hydrogel possesses gradient crosslinked structures. Moreover, the lowermost surface is sufficiently soft to gently detach from the substrate below the LCST. The electrode-integrated hydrogel remains on human skin, and electrical signals are continuous over 10 min above the LCST. In contrast, commercially available hydrogel electrodes quickly swell and detach from the skin. The thermoswitchability of the TSA hydrogel, with its robust adhesion and gentle detachment, offers significant potential for biomedical applications characterized by minimally invasive procedures.