A Time-Course Study on a Food Contact Material (FCM)-Certified Coating Based on Titanium Oxide Deposited onto Aluminum

Aluminum is the second most widely used metal worldwide. It is present as an additive in cosmetics, pharmaceuticals, food, and food contact materials (FCM). In this study, we confirm the bactericidal effect of a special anodizing method, based on TiO2 nanoparticles (DURALTI®) deposited on aluminum disks with different roughness and subjected to two sanitizing treatments: UV and alcohol 70%. Consequently, we perform a time-course evaluation against both Gram-negative and Gram-positive bacteria to better frame the time required to achieve the best result. Approximately 106 CFU/mL of Escherichia coli ATCC 25922; Salmonella Typhimurium ATCC 1402; Yersinia enterocolitica ATCC 9610; Pseudomonas aeruginosa ATCC 27588; Staphylococcus aureus ATCC 6538; Enterococcus faecalis ATCC 29212; Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888 were inoculated onto each aluminum surface and challenged with UV and alcohol 70% at 0, 15”, 30”, 1′, 5′, 15′, 30′, 1, 2, 4 and 6 h. DURALTI® coating already confirmed its ability to induce a 4-logarithmic decrease (from 106 to 102 CFU/mL) after 6 h. Once each sanitizing treatment was applied, an overall bacterial inhibition occurred in a time ranging from 15′′ to 1′. The results are innovative in terms of preventing microbial adhesion and growth in the food industry.

The Effect of Sugar Content for the Wettability of Superhydrophobic Aluminum Substrate

A chemical etching technique is used to prepare a superhydrophobic surface with a honeycomb rough structure on the aluminum surface. Use SEM, Optical contact angle meter and Surface tension detector to characterize the etched aluminum substrate. After the 8th etching, the surface of the sample showed the morphology of micro/nano-scale honeycomb pores and protrusions, and the water contact angle (WCA) is 135°. After being modified with octadecanethiol methanol solution, WCA is 153.1°. After modification, the contact angle of the sample surface decreases with the increase of the glucose solution concentration. When the glucose solution concentration reaches 1000 mg/L, the superhydrophobicity is lost.

Aluminum surface nitriding by an atmospheric-pressure non-thermal plasma technique

The application of aluminum is often limited by low hardness, and plasma nitriding can make it have excellent mechanical property. The purpose of this study is to nitride the aluminum surface by non-thermal transferred arc plasma technology. During the plasma nitriding process, the maximum effective value of output current is about 390 mA and the overall temperature of the samples is much lower than the solidus temperature. It is found that the microstructure and mechanical properties of the aluminum surface are improved by adding hydrogen into the nitrogen plasma. Compared with the surface treated by pure N2 plasma, the particle size of aluminum surface treated by N2/H2 plasma is smaller. The surface hardness of aluminum is nearly doubled after being treated in 6.0 vol%H2 + 94.0 vol%N2 atmosphere.

Fabrication of superhydrophobic surface with corrosion resistance via cyclic chemical etching process on aluminum substrate

Aluminum (Al) is a metal material commonly used in industry, but its surface is easily corroded. The superhydrophobic surface has great self-cleaning and anti-corrosion properties, and it is an ideal method to construct a functional aluminum surface. Here, a simple method based on cyclic chemical etching was proposed to achieve the superhydrophobic Al surface with honeycomb structures. The surface of the sample etched eight times comprised micro/nano-scale honeycomb cavities, while exhibiting a water contact angle (WCA) of 135°. After being treated with an octadecanethiol (C18H38S) methanol solution, this sample demonstrated a WCA of 153.1°. A self-cleaning test was performed on the superhydrophobic Al surface, showing the excellent self-cleaning property. Finally, the electrochemical anti-corrosion test demonstrated that the above-mentioned superhydrophobic Al surface had great corrosion resistance property. Overall, this work has enriched the theory and technology for fabricating aluminum to achieve superhydrophobic.

Surface Pretreatments of AA5083 Aluminum Alloy with Enhanced Corrosion Protection for Cerium-Based Conversion Coatings Application: Combined Experimental and Computational Analysis

The effects of surface pretreatments on the cerium-based conversion coating applied on an AA5083 aluminum alloy were investigated using a combination of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), polarization testing, and electrochemical impedance spectroscopy. Two steps of pretreatments containing acidic or alkaline solutions were applied to the surface to study the effects of surface pretreatments. Among the pretreated samples, the sample prepared by the pretreatment of the alkaline solution then acid washing presented higher corrosion protection (~3 orders of magnitude higher than the sample without pretreatment). This pretreatment provided a more active surface for the deposition of the cerium layer and provided a more suitable substrate for film formation, and made a more uniform film. The surface morphology of samples confirmed that the best surface coverage was presented by alkaline solution then acid washing pretreatment. The presence of cerium in the (EDS) analysis demonstrated that pretreatment with the alkaline solution then acid washing resulted in a higher deposition of the cerium layer on the aluminum surface. After selecting the best surface pretreatment, various deposition times of cerium baths were investigated. The best deposition time was achieved at 10 min, and after this critical time, a cracked film formed on the surface that could not be protective. The corrosion resistance of cerium-based conversion coatings obtained by electrochemical tests were used for training three computational techniques (artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and support vector machine regression (SVMR)) based on Pretreatment-1 (acidic or alkaline cleaning: pH (1)), Pretreatment-2 (acidic or alkaline cleaning: pH (2)), and deposition time in the cerium bath as an input. Various statistical criteria showed that the ANFIS model (R2 = 0.99, MSE = 48.83, and MAE = 3.49) could forecast the corrosion behavior of a cerium-based conversion coating more accurately than other models. Finally, due to the robust performance of ANFIS in modeling, the effect of each parameter was studied.

Waste Aluminum Application as Energy Valorization for Hydrogen Fuel Cells for Mobile Low Power Machines Applications

This article proposes a new model of power supply for mobile low power machines applications, between 10 W and 30 W, such as radio-controlled (RC) electric cars. This power supply is based on general hydrogen from residual aluminum and water with NaOH, so it is proposed energy valorization of aluminum waste. In the present research, a theoretical model allows us to predict the requested aluminum surface and the required flow of hydrogen has been developed, also considering, in addition to the geometry and purity of the material, two key variables as the temperature and the molarity of the alkaline solution used in the hydrogen production process. Focusing on hydrogen production, isopropyl alcohol plays a key role in the reactor’s fuel cell vehicle as it filters out NaOH particles and maintains a constant flow of hydrogen for the operation of the machine, keeping the reactor temperature controlled. Finally, a comparison of the theoretical and experimental data has been used to validate the developed model using aluminum sheets from ring cans to generate hydrogen, which will be used as a source of hydrogen in a power fuel cell of an RC car. Finally, the manuscript shows the parts of the vehicle’s powertrain, its behavior, and mode of operation.

Silver Flowerlike Structures for Surface-Enhanced Raman Spectroscopy

Micro- and nanoflowers are a class of materials composed of particles with high surface-to-volume ratio. They have been extensively studied in the last decade due to simple preparation protocols and promising applications in biosensing, as drug delivery agents, for water purification, and so on. Flowerlike objects, due to their highly irregular surface, may act also as plasmonic materials, providing resonant coupling between optical waves and surface plasmon excitations. This fact allows us to infer the possibility to use micro- and nanoflowers as effective surface-enhanced Raman scattering (SERS) substrate materials. Here, we report on the design and Raman enhancement properties of silver flowerlike structures, deposited on aluminum surface. A simple and cost-effective fabrication method is described, which leads to SERS substrates of high developed surface area. The morphology of the silver flowers on a nanoscale is characterized by self-organized quasiperiodic stacks of nanosheets, which act as plasmonic cavity resonators. The substrates were tested against rhodamine-6G (R6G) water solutions of concentration varying between 10−3 M and 10−7 M. Optimal SERS enhancement factors of up to 105 were established at R6G concentrations in the 10−6–10−7 M range.

Nanoscale Schottky diodes for studying the activity of aluminum nanoparticles in reaction with water

Hydrogen is a promising fuel for energy storage, transportation, production and consumption. At the same time, hydrogen in its pure form is not found on Earth in large quantities and therefore it is necessary to develop a technology for its production. One of the promising technologies for hydrogen production is the reaction of aluminum nanoparticles with water. At the same time, experimental studies of the elementary mechanisms of this reaction are difficult due to the aggressive properties of a concentrated alkaline solution, which is used to activate the aluminum surface. Here we show that the kinetics of the aluminum-water reaction can be monitored in real time using a Schottky nanodiode sensor, provided that the characteristic size of the nanodiode electrodes does not exceed 10 nm. The investigated nanoparticles are applied to the sensor surface by means of nanofabrication. The charge generated in the aluminum nanoparticles as a result of the reaction creates an electrical signal that is proportional to the rate of the chemical process. This makes it possible to use this technology to study the activity even of small groups of nanoparticles, when the volume of released hydrogen is insufficient to measure the reaction rate.

Droplet sweeping to enhance heat transfer during dropwise condensation

It is well known that dropwise condensation (DWC) can achieve heat transfer coefficients (HTCs) up to 5-8 times higher as compared to filmwise condensation (FWC). The interaction between the condensing fluid and the surface defines the condensation mode. Coatings that present low surface energy and high droplet mobility are a solution to promote DWC instead of FWC on metallic substrates. In the present paper, the effect of vapor velocity during DWC has been investigated over a sol-gel coated aluminum surface and a graphene oxide coated copper surface. Heat transfer coefficients and droplets departing radii have been measured at constant saturation temperature and heat flux, with average vapor velocity ranging between 3 m s−1 and 11 m s−1. A recent method developed by the present authors to account for the effect of vapor velocity on the droplet departing radius is here presented. The results of the proposed method, when coupled with the Miljkovic et al. [1] heat transfer model, are compared against experimental data.