Recycling of aluminum beverage cans for metallic foams manufacturing

This paper proposes recycling beverage cans (aluminum cans) to reduce the manufacturing cost of metallic foams, while it is discussed the effects of the alloying elements that reinforce the metallic matrix in resistance to compression, due mainly in part to the formation of the phase β-Al₆(FeMn). The manufacturing process used for the metallic foams was the Alporas modified, using an excess of 10 wt% pure calcium. This allowed not only to modify viscosity of the molten alloy but also to obtain important quantities of the reinforcing phase Al₄Ca. Once obtained, the foams were characterized using techniques including differential thermal analysis, optical microscopy, scanning electron microscopy, chemical analysis and compression tests. Additionally, Image J software was used to determine the percentage of porosity and the average pore size of the metallic foams. Foam density was calculated by immersion in water using the Archimedes principle. The results showed that foams manufactured with beverage cans have a homogeneous porous structure with an average porosity of 80%, an average pore size of 3 mm, a specific gravity 0.4 and a compressive strength of 22 MPa. These results are superior to those obtained in foams manufactured with pure aluminum as well as alloying foams such as Al–12Si–0.6Mg (A413), and Al–1Mg–0.6Si (A356).     

Fabrication and characterization of hybrid coating on Mg–Zn–Ca Mg alloy for enhanced corrosion and degradation resistance as medical implant

Magnesium (Mg)-based alloys have appealing properties as promising implants for medical applications. However, their clinical applications are hindered due to the rapid corrosion and degradation rate in the physiological environment. In this investigation, we reported a novel interfacial engineering approach for the fabrication of polymer/ceramic hybrid coating on Mg–Zn–Ca Mg alloy. Firstly, hydroxyapatite (HA) coating was fabricated on the Mg–Zn–Ca sample followed by an alkali treatment that was performed in 1 M NaOH solution at 60 °C. Finally, polycaprolactone (PCL) coating was synthesized using a dip-coating approach on the top of the HA-coated Mg–Zn–Ca specimen. Microhardness test and adhesion test revealed that PCL/HA hybrid coating significantly improved mechanical properties and enhanced biointerface property between the substrate and coating. The immersion tests showed that the hybrid coating considerably slowed down the degradation in the simulated body fluid (SBF) solution. In addition, in vitro electrochemical investigations confirmed that PCL/HA coating significantly improved corrosion resistance and greatly reduced corrosion rate by about 10 times compared to HA coating and about 900 times to untreated Mg–Zn–Ca sample. Moreover, cytotoxicity assessment exhibited PCL/HA hybrid coating enhanced biocompatibility and bioactivity due to adopting a suitable interfacial engineering approach.     

Evaluation of the corrosion protection performance of epoxy coatings containing Mg nanoparticle on carbon steel in 0.1 M NaCl solution by SECM and EIS techniques

The effect of corrosion protection performance of epoxy coatings containing magnesium (Mg) nanoparticles on carbon steel was analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 0.1 M NaCl in the epoxy-coated sample. Line profile and topographic image analysis were measured by applying ?0.70 and +0.60 V vs the Ag/AgCl/saturated KCl reference electrode as the tip potential for the cathodic and anodic reactions, respectively. The tip current at ?0.70 V for the epoxy-coated sample with Mg nanoparticles decreased rapidly, which is due to cathodic reduction in dissolved oxygen. The EIS measurements were conducted in 0.1 M NaCl after wet and dry cyclic corrosion test. The increase in the film resistance (R _f) and charge transfer resistance (R _ct) values was confirmed by the addition of Mg nanoparticles in the epoxy coating. Scanning electron microscope/energy-dispersive X-ray spectroscope analysis showed that Mg was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. Focused ion beam–transmission electron microscope analysis confirmed the presence of the nanoscale oxide layer of Mg in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.     

Electrochemical and structural characterization of AZ63 alloy surface film in MgSO4 solution

The formation and growth of surface film on AZ63 (Mg–6Al–3Zn) magnesium alloys were studied in 2 M MgSO₄ aqueous solution using electrochemical methods. Surface examinations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and microscopic Fourier transform infrared spectroscopy. Experimental results show that the corrosion current decreases with prolonged immersion time, the three stages of hydrogen evolution rate correspond with the growth processes of the surface film on AZ63 magnesium alloys, and charge transfer resistance increases with the accumulation of corrosion products. A layer of MgO with sulfate salt grains underneath seems smooth at first. However, a few surface micro-cracks caused by inner stress appear on the smooth base film after 5 h of immersion, followed by the aggregation of spherical grains and the formation of cracks after 12 h. It is suggested that sulfate salt, carbonate salt, and hydroxide of magnesium should be the main composition of the surface film.     

Enhanced Activity via Surface Modification of Fe-Based Fischer–Tropsch Catalyst Precursor with Titanium Butoxide

The surface of a model iron catalyst precursor was modified with titanium butoxide to introduce Fe–O–Ti interactions in a controlled manner and to investigate the role of these interactions in the catalyst. The reduction of the model catalyst precursors in hydrogen at 350 °C for 16 h leads to the formation of α-Fe and an iron–titanium mixed oxide, due to the incorporation of Ti into the iron oxide structure. The α-Fe phase is transformed into χ-Fe₅C₂ during the Fischer–Tropsch synthesis at 250 °C, whilst the Fe–Ti mixed oxide phase is preserved. A higher reaction temperature of 300 °C is required to transform some the oxide phase into a carbide phase under Fischer–Tropsch conditions. The intrinsic activity of the iron carbide phase in samples also containing the Fe–Ti mixed oxide phase is at a reaction temperature of 250 °C ca. 20 % more active than in the sample, which does not contain the mixed oxide.     

Poly(vinyl alcohol) foams reinforced with carbon nanotubes for stapedial annular ligament applications

This study aims to develop carbon nanotubes (CNTs) reinforced poly(vinyl alcohol) (PVA) foams as a possible material for stapedial annular ligament (SAL) application. As-grown (AG) and purified CNTs are used as reinforcing fillers for PVA foams. Uniaxial and cyclic compression tests reveal that specific modulus and energy dissipation behavior improve after reinforcing foam with CNTs. A relatively higher improvement in specific modulus is recorded for purified CNTs as they tend to produce stiffer cell walls. Thermogravimetric analysis shows thermal stability improves after addition of CNTs in PVA foams. The 50 wt % degradation temperature is higher for PVA_AG foam in comparison to neat PVA foam. Under dynamic loading storage, modulus is found to be higher for CNT doped foams with higher relative improvement with purified CNTs than AG CNTs. It is shown that reinforcing PVA foams with purified CNTs is a feasible strategy to improve their average mechanical properties and microstructure for SAL application. While the specific elastic modulus of neat PVA foam found to be in range of 0.05–0.06 MPa gcc⁻¹ with almost zero porosity. The addition of CNTs provides a wide range of specific elastic modulus 0.1–1.3 MPa gcc⁻¹ with an average pores size of about 300 μm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48736.     

Polycaprolactone coating with varying thicknesses for controlled corrosion of magnesium

Controlled corrosion of magnesium is critical for its clinical application to orthopedic devices. For this purpose, we coated the surface of Mg with a biodegradable polymer, polycaprolactone (PCL) and attempted to control the Mg corrosion with varied coating thicknesses in a reproducible manner. As we increased the coating thickness from 0 to 13.31 ± 0.36 μm, the volume of hydrogen gas and amount of Mg ions, the indicators of Mg corrosion, decreased by almost half from 0.57 mL/cm²/day and 0.55 mg/day to 0.20 mL/cm²/day and 0.26 mg/day, respectively. However, the elemental compositions on the surface revealed possible detachment of polymer coating and rapid water absorption at the early stage of corrosion for all coating thicknesses. Therefore, the lessons learned from this study suggest pre-treatment of the Mg surface for better polymer–metal adhesion, as well as preparation of the coating with lowered porosity as a stronger water-permeation barrier, to eventually allow precise control on Mg corrosion.     

Electrochemical properties of electrodeposited nanocrystalline cobalt and cobalt–iron alloys in acidic and alkaline solutions

Nanocrystalline Co and CoFe with varied iron contents ranging from 5 to 25 wt% Fe were electrodeposited from a sulfate bath. The average grain sizes of the coatings obtained were measured using Scherrer equation and calculated to be in between 16 and 65 nm. Electrochemical corrosion behavior of electrodeposited nanocrystalline cobalt (Co) and cobalt–iron (CoFe) alloys was investigated in both acidic (0.1 M H₂SO₄) and alkaline solution (0.1 M NaOH). This study investigates the corrosion behavior of electrodeposited CoFe alloy coatings using polarization tests, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy techniques. The nanocrystalline Co and CoFe showed active behavior for all alloy coatings in acidic condition, while an active–passive–transpassive behavior was seen for all coatings in alkaline condition.     

Preparation and characterization of hydroxyapatite coating by magnetron sputtering on Mg–Zn–Ag alloys for orthopaedic trauma implants

The aim of the present paper was to evaluate the effect of hydroxyapatite coatings on the two types of Mg–Zn–Ag alloys as a possible solution to control magnesium alloy degradation. The coatings were prepared by the radio frequency magnetron sputtering method at a deposition temperature of 300 °C. To perform this evaluation, the coated alloys were immersed in a simulated body fluid solution at body temperature (37 ± 0.5 °C) to determine the corrosion resistance through electrochemical and immersion tests. Moreover, the investigation also consisted of the evaluation of microchemical, mechanical, and morphological properties. The deposition temperature of 300 °C was enough to obtain a crystalline hydroxyapatite structure with a Ca/P ratio close to the stochiometric one. The adhesion of coatings was not influenced by the nature of Mg–Zn–Ag alloys, so similar values for both coated alloys were found. The results showed that the coating was homogonous deposited on the Mg–Zn–Ag alloys and the corrosion resistance of uncoated magnesium alloys was improved.     

Low-Temperature Growth of Carbon Nanotubes on Bi- and Tri-metallic Catalyst Templates

Low temperature growth process of carbon nanotubes (CNTs) over bi-metallic (Co–Fe) and tri-metallic (Ni–Co–Fe) catalysts on Si/Al/Al₂O₃ substrates is carried out from acetylene precursor using hydrogen, ammonia or nitrogen as a carrier in a low pressure chemical vapor deposition system. Using the tri-metallic Ni–Co–Fe catalyst template, vertically aligned CNTs of ~700 nm length could be grown already at 450 °C within 10 min using ammonia as a carrier. Within the same period of time, on bi-metallic Co–Fe catalyst templates, ~250 nm long aligned nanotubes emerged already at 400 °C in nitrogen carrier. At low temperatures most of the catalyst materials were elevated from the support by the grown nanotubes indicating tip growth mechanism. The structure of catalyst layers and nanotube films was studied using scanning and transmission electron microscopy and atomic force microscopy.     

Electrochemical behavior of hydrophobic silane–zeolite coatings for corrosion protection of aluminum substrate

The anticorrosive properties of a silane–zeolite composite coating applied on a 6061 aluminum substrate was investigated. The composite film, deposited by dip-coating technique, was prepared with different contents of SAPO34 powder (60–90 wt%) with the purpose of evaluating the protective action offered by the zeolite-filled silane matrix. Corrosion protection performance, during immersion in 3.5% NaCl solution, was evaluated by means of a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). The coating evidenced good barrier properties and high hydrophobicity. The addition of zeolite in the silane matrix induced, as expected, a reduction of cathodic and anodic current. The zeolite improved the barrier properties of the hybrid sol–gel films, enhancing the resistance to localized corrosion attacks. Better results were observed for the sample with 80 wt% of zeolite filler that evidenced still acceptable protective action after 3 days of immersion in the sodium chloride solution.     

Self-healing hybrid coating of phytic acid/silane for improving the corrosion resistance of magnesium alloy

In order to improve the corrosion resistance of a biodegradable magnesium alloy, a series of phytic acid/3-aminopropyltrimethoxysilane (γ-APS) hybrid coatings was prepared on AZ31 magnesium alloys by dipping the magnesium alloy into the mixing solution of phytic acid and γ-APS. During the preparation of hybrid coatings, the pH values of the mixing solutions greatly affected the uniformity of the coatings and subsequently influenced their corrosion resistance. Electrochemical tests indicated that the hybrid coating prepared in the solution of pH = 8.0 could highly improve corrosion resistance of AZ31 magnesium alloys. Meanwhile, corrosion current density of the hybrid coating coated sample was significantly decreased from the uncoated sample of 138.1 ± 11.9 to 8.5 ± 0.8 μA cm^?2. Immersion test in simulated body fluid revealed that the cracks on the surface of the hybrid coating gradually healed up during the lengthy immersion.     

Using the Mass Method to Produce PVC/Clay Nanocomposite Foams: The Effect of Nano-clay and Foaming Conditions on Density and Cell size

Nanocomposite foams contain very fine cells because of the fillers in nano scale. Due to the limited size of the cells, the mechanical and physical properties of nanocomposite foams are improved compared to polymer foams. In this study PVC/clay nanocomposite foams containing various concentrations of nano-clay (1, 3 and 5 phr) were successfully prepared. The samples were placed under CO₂ gas pressure at 5 MPa, by immersing in glycerin bath at 60, 70, 80 °C and 20, 30, 40 s, respectively, to form foams. The density and the cell size as a factor of nano-clay content, foaming time and temperature were investigated using Archimedes method and scanning electron microscopy, respectively. The minimum density was obtained in the sample containing 1 phr nanoclay prepared at 80 °C and 40 s. The minimum cell size was related to the sample containing 5 phr nanoclay at 60 °C and 20 s.     

Development of HA-CNTs composite coating on AZ31 Magnesium alloy by cathodic electrodeposition. Part 2: Electrochemical and in-vitro behavior

The carbon nano-tubes (CNTs) reinforced hydroxyapatite (HA), with various functionalized CNTs concentration ranging from 0 to 1.5?wt%, were deposited on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The corrosion resistance of the coatings was tested in simulated body fluid (SBF) using different electrochemical methods such as open circuit potential, polarization and electrochemical impedance spectroscopy. The in-vitro behavior, changes in solution pH as well as the amount of evolved hydrogen of these coatings were also evaluated during five days immersion in SBF. The results indicated that the pulse deposited HA having 1% CNTs coating was the optimum condition which decreased the corrosion current density of AZ31 magnesium alloy from 44.25?µA/cm² to 0.72?µA/cm². Moreover, it stabilized the alkalization behavior of AZ31 alloy and caused a tenfold decrease in the amount of hydrogen generation in SBF. Additionally, the formation of new hydroxyapatite layer on the surface of the pre-exist coatings after five days immersion in SBF was confirmed by SEM characterization.     

Low-temperature preparation of novel stabilized aluminum titanate ceramic fibers via nonhydrolytic sol-gel method through linear self-assembly of precursors

Stabilized aluminum titanate fibers were prepared via nonhydrolytic sol-gel (NHSG) method through linear self-assembly of precursors. The results show that NHSG method generates the heterogeneous condensation with the formation of Al–O–Ti, Mg–O–Ti, Fe–O–Ti, Mg–O–Al, Fe–O–Ti bonds, which ensures that magnesium ions and iron ions can enter aluminium titanate lattice and stabilize it at 750 °C. Bimolecular associated structure of chlorotitanium ethoxide titanium precursor promotes the self-linear-assemble of all precursors, which enables the excellent spinnability of sol. Stabilized aluminum titanate fibers have excellent corrosion resistance. The thermal expansion coefficient of stabilized aluminum titanate ceramic is −0.142 × 10⁻⁶°C⁻¹.     

Evaluation of the effects of surface treatments on the cathodic delamination and anticorrosion performance of an epoxy-nanocomposite on steel substrate

The St-37 type steel substrates were pretreated with Cr(VI) and Cr(III) conversion coatings where the latter was then post-treated with Co(II) and Ni(II) chemical treatments. The epoxy coatings containing 3.5 wt% nano-sized ZnO particles were applied over the chemically treated steel samples. The corrosion resistance of the samples was studied by a DC polarization technique. A scanning electron microscope (SEM) was utilized to investigate the morphology of the pretreated and post-treated samples. Electrochemical impedance spectroscopy (EIS) was utilized to investigate the corrosion resistance of the epoxy nanocomposites for different immersion times in 3.5 wt% NaCl solution. The adhesion strengths of the coatings were measured before and after 120 days of immersion in the corrosive electrolyte using a pull-off test. The cathodic delamination (CD) of the painted samples was also investigated. Results showed that conversion coatings can significantly increase the corrosion resistance and adhesion strength of the epoxy coating on the steel, and also reduce the rate of CD in comparison with an untreated sample. The adhesion strength and corrosion resistance of the epoxy coating on the Cr(III) pretreated samples were significantly greater than on the Cr(VI) sample. The increase in adhesion strength and corrosion resistance was more pronounced on the samples that were post-treated with Co(II) and Ni(II) chemical treatments. The cathodic disbonded areas of the Cr(III)–Co(II) and Cr(III)–Ni(II) post-treated samples were significantly lower than the Cr(III) and Cr(VI) pretreated samples. Results showed that Cr(III)-based conversion coatings can improve the anticorrosion performance and reduce CD compared with those with Cr(VI).     

Corrosion of the zinc negative electrode of zinc–cerium hybrid redox flow batteries in methanesulfonic acid

Corrosion of zinc in aqueous methanesulfonic acid has been evaluated over a wide range of concentrations of acid (0.5–5 mol dm^?3), dissolved zinc (0.5–2 mol dm^?3), and electrolyte temperature (22–50 °C). The corrosion rate of zinc, in terms of weight loss and the volume of hydrogen evolved, varied with time and it was found to be highly dependent on the surface state and electrolyte conditions. With an initial active layer of zinc present, the corrosion rate rapidly increased following a decline when the proton concentration in the solution decreased to ca. 0.56 mol dm^?3. Organic and inorganic inhibitors were added to the electrolyte to suppress the zinc corrosion in 1 mol dm^?3 methanesulfonic acid. The strong adsorption and blocking effects of cationic organic adsorption inhibitors, such as cetyltrimethyl ammonium bromide and butyltriphenyl phosphonium chloride, led to a significant decrease in zinc corrosion over a 10 h immersion period. With the addition of indium and lead ions inhibitors, the zinc surface showed less activity. Zinc corrosion continued to a smaller extent in the presence of these metallic inhibitors during the first few hours, but the metallic layer of the inhibitors did not cover the surface completely resulting in continued hydrogen evolution and making the inhibitors less effective at longer times.     

High strength,low modulus and biocompatible porous Ti–Mo–Fe alloys

Porous Ti–10Mo–xFe (x = 2–5) alloys were prepared by powder metallurgy using ammonium hydrocarbonate (NH₄HCO₃) as the space-holder. When 7 wt% NH₄HCO₃ is added, the porosity of the Ti–Fe and Ti–Mo–Fe alloys is about 20 %. It was found that Fe has a significant strengthening effect on the Ti-based alloys, while Mo is effective in stabilizing the Ti–10Mo–xFe alloys into β-phase. The inherent better ductility of β-phase than that of the α-phase and the efficient strengthening effect Fe provide a good combination of strength and ductility to the Ti–10Mo–xFe alloys. The compressive yield strength of the porous Ti–10Mo–xFe alloys is from 500 to 800 MPa, much higher than that of the Fe–10Mo alloy (about 260 MPa) and human bone (about 130–180 MPa). Elastic modulus of the alloys is <10 GPa. The alloys also have corrosion resistance similar to that of pure Ti. Cytotoxic tests show that the L929 cell RGR values of the Ti–10Mo–xFe alloys are over 80 % at day 1, day 4 and day 7. The cells grew in good condition on the seventh day. The results indicate that the porous Ti–10Mo–xFe alloys have superior mechanical properties, good corrosion resistance, and excellent biocompatibility, and are promising candidates for bone substitute materials.     

低温等离子体技术对金属表面的改性与保护

概述低温等离子体技术在金属材料表面改性与保护方面的研究进展 ,以及低温等离子体技术的特点和应用。     

Electrochemical and morphological properties of zirconium conversion coating in the presence of nickel ions on galvanized steel

A hexafluorozirconic acid-based conversion coating was applied on a galvanized steel substrate and the influence of nickel ion from nickel sulfate solution (in zirconium solution and in a separate solution) on the corrosion resistance behavior and morphology of zirconium conversion coating was investigated. Electrochemical impedance spectroscopy and DC polarization were conducted in 3.5 wt% NaCl solution in order to optimize practical conditions of zirconium conversion coating and NiSO₄ solution on the galvanized steel substrate. Field emission scanning electron microscopy and X-ray photoelectron spectroscopy were employed to study the morphology and composition of the coated surfaces. Results revealed that the conversion coating obtained from solution containing zirconium and nickel ions (Zr + Ni) did not improve corrosion resistance and uniformity of the coating in comparison with Zr conversion coating in optimized condition. However, a positive effect was obtained from samples coated with separate solutions of zirconium and nickel (Zr–Ni). Improved corrosion resistance and morphology of Zr-based conversion coating were observed in Ni²⁺ concentration, pH, and immersion time of 10 g/L, 6 and 300 s, respectively. Morphology and surface composition analysis proved that two separate layers of conversion coating containing zirconium, zinc, and nickel oxide/hydroxide compounds were formed in the case samples that were treated by separate solutions. This led to better uniformity and higher thickness of the coating. Finally, adhesion strength of epoxy organic coating on galvanized steel with and without conversion coating was investigated by pull-off measurement. Zr–Ni conversion coating in optimum conditions had a positive effect on adhesion of organic coating in comparison with blank sample and samples pretreated with Zr and Zr + Ni conversion coatings through increased surface roughness and physical interlocking.