Katya Brunelli

Cerium-based chemical conversion coating on AZ63 magnesium alloy

Abstract A CeCl 3 /H 2 O 2 aqueous solution treatment is assessed for the formation of conversion coatings on a AZ63 magnesium alloy. The coating composition and morphology are examined. The conversion coating appears to consist of a thin and cracked coating with ‘dry-mud’ morphology with large agglomerates over cathodic intermetallic particles. The corrosion resistance in NaCl solution has been investigated. The cerium-based conversion process improves the pitting potential of the alloy. Better corrosion resistant surfaces are obtained when the samples are submitted to repeated immersions in the conversion bath for 30 s up to 180 s of total immersion time. The thickness of the cerium conversion coating rapidly grows up in the first 30 s; afterwards it remains nearly constant. An increase of both hydrogen peroxide concentration and immersion time produces a worsening of the alloy to corrosion.

Self-assembling peptide-enriched electrospun polycaprolactone scaffolds promote the h-osteoblast adhesion and modulate differentiation-associated gene expression

Electrospun polycaprolactone (PCL) is able to support the adhesion and growth of h-osteoblasts and to delay their degradation rate to a greater extent with respect to other polyesters. The drawbacks linked to its employment in regenerative medicine arise from its hydrophobic nature and the lack of biochemical signals linked to it. This work reports on the attempt to add five different self-assembling (SA) peptides to PCL solutions before electrospinning. The hybrid scaffolds obtained had regular fibers (SEM analysis) whose diameters were similar to those of the extracellular matrix, more stable hydrophilic (contact angle measurement) surfaces, and an amorphous phase constrained by peptides (DSC analysis). They appeared to have a notable capacity to promote the h-osteoblast adhesion and differentiation process by increasing the gene expression of alkaline phosphatase, bone sialoprotein, and osteopontin. Adding an Arg-Gly-Asp (RGD) motif to a self-assembling sequence was found to enhance cell adhesion, while the same motif condensed with a scrambled sequence did not, indicating that there is a cooperative effect between RGD and 3D architecture created by the self-assembling peptides. The study demonstrates that self-assembling peptide scaffolds are still able to promote beneficial effects on h-osteoblasts even after they have been included in electrospun polycaprolactone. The possibility of linking biochemical messages to self-assembling peptides could lead the way to a 3D decoration of fibrous scaffolds.

Effect of process parameters of plasma electrolytic oxidation on microstructure and corrosion properties of magnesium alloys

Abstract In this work, a plasma electrolytic oxidation process was applied to AZ91 and AM50 magnesium alloys and commercially pure magnesium to produce a protective surface layer. The plasma electrolytic oxidation process was carried out in an alkaline phosphate solution with a DC power supply, using relatively high current densities and short treatment times. The influence of some important process parameters such as current density, treatment time and voltage was studied. The layers were characterised by scansion electron microscopy, X-ray diffraction and X-ray photoelectron spectrometry, in order to investigate the effect of the process parameters on the microstructure and chemical composition. The corrosion resistance properties of the obtained layers were investigated by potentiodynamic anodic polarization and electrochemical impedance spectroscopy tests. The current density, applied during the treatment, influenced the morphology and the thickness of the coatings, and, consequently, the corrosion resistance. The corrosion tests evidenced that the layers obtained with plasma electrolytic process provided a good corrosion protection to the magnesium and magnesium alloys.

Electric Arc Furnace Slag as Coarse Recycled Aggregate for Concrete Production

Electric arc furnace (EAF) slag is a by-product of steel production in electric arc furnaces. Several studies have tried to demonstrate its suitability in civil engineering application, such as in bituminous mixtures and cement-based materials, due to its good physical, chemical and mineralogical properties. Particularly the re-use as coarse aggregate for concrete production has been shown to be a promising valorisation, when physical and chemical stability is guaranteed. Additionally, EAF slags high mechanical strength makes it suitable for high-performance concrete production. In this work three EAF concretes, with various cement content and also with silica fume addition, were compared with a reference concrete, to identify a convenient mix design to reach a concrete strength class between C50/60 and C60/75. Mechanical strength was evaluated analysing compressive and tensile strength, and elastic modulus. A complementary microstructural analysis was performed after the failure of the specimens, with the aim of analysing the morphology of the interfacial transition zone. Results indicate that the use of EAF slag in concrete allows reaching higher compressive strength than with coarse natural aggregates. EAF slag application in structural concrete promotes also the reduction of cement content in the mix to reach the same strength class.

Electrochemical behaviour of Cu-Zr and Cu-Ti glassy alloys

Abstract Hydrogen evolution is a fundamental reaction for better understanding of electrochemical activity of electrode materials. Amorphous Cu–Zr and Cu–Ti ribbons were produced by melt spinning methods and were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from cathodic polarization curves carried out in both acid and basic medium at 25°C. The surfaces of amorphous materials were prepared, before electrochemical measurements, by immersion in HF solutions. The results were compared to those obtained on polycrystalline copper and on untreated ribbons. The HF treatment yielded a porous copper structure with a higher roughness factor which had improved electrocatalytic activity compared with that of polycrystalline copper electrode.

Cu-based amorphous alloy electrodes for fuel cells

The present work describes the characteristics of Cu–Zr and Cu–Ti amorphous alloys as catalysts for oxidation of methanol and formaldehyde in alkaline solutions. Two Cu-based amorphous alloys, Cu60Zr40 and Cu60Ti40 both prepared by melt spinning were investigated. Two types of electrode were used: as-quenched amorphous alloys and surface-activated amorphous alloys. The surface-activation treatment consisted in the immersion of the ribbons in 1 M HF solution for 30 s. The determination of the oxidation activity of methanol and formaldehyde was carried out by galvanostatic and by steady-state polarization measurements and cyclic voltammetry experiments in 1 M NaOH solutions containing CH3OH or CH2O, deoxygenated by nitrogen bubbling for 30 min at 30 °C. The HF-treated amorphous alloys exhibit catalytic activity only for formaldehyde oxidation; Zr-based alloys show higher current densities than pure crystalline copper and Ti-based alloys.

Characterization of a Cold-Rolled 2101 Lean Duplex Stainless Steel

Duplex stainless steels (DSS) may be defined as a category of steels with a two-phase ferritic-austenitic microstructure, which combines good mechanical and corrosion properties. However, these steels can undergo significant microstructural modification as a consequence of either thermo-mechanical treatments (ferrite decomposition, which causes σ- and χ-phase formation and nitride precipitation) or plastic deformation at room temperature [austenite transformation into strain-induced martensite (SIM)]. These secondary phases noticeably affect the properties of DSS, and therefore are of huge industrial interest. In the present work, SIM formation was investigated in a 2101 lean DSS. The material was subjected to cold rolling at various degrees of deformation (from 10 to 80% thickness reduction) and the microstructure developed after plastic deformation was investigated by electron backscattered diffraction, X-ray diffraction measurements, and hardness and magnetic tests. It was observed that SIM formed as a consequence of deformations higher than ~20% and residual austenite was still observed at 80% of thickness reduction. Furthermore, a direct relationship was found between microstructure and magnetic properties.

Ultrasound effects on zinc recovery from EAF dust by sulfuric acid leaching

In this work, an ultrasound-assisted leaching process was studied for the recovery of zinc from electric arc furnace (EAF) dust, in which zinc was mainly present in the form of franklinite (60%). Hydrometallurgy is emerging as a preferred process for the recovery of a variety of metals, and the use of ultrasound could offer advantages over the conventional leaching process, especially for the dissolution of franklinite. Franklinite is a refractory phase that is difficult to leach and represents the main obstacle in conventional hydrometallurgy processing. Atmospheric leaching with different sulfuric acid concentrations (0.2–2.0 M) at two temperatures (323 and 353 K) was performed. The tests were conducted using both conventional and ultrasound-assisted leaching. After the leaching tests, the solid residues were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, whereas the leach liquor was analyzed by inductively coupled plasma spectroscopy (ICP). The use of ultrasound facilitated the dissolution of franklinite at low acid concentrations and resulted in a greater zinc recovery under all of the investigated operating conditions.

Method to improve corrosion resistance of AA 5083 by cerium based conversion coating and anodic polarisation in molybdate solution

Abstract The corrosion resistance of aluminium alloys can be improved by the formation of chemical conversion coatings. Usually, chromate pretreatment processes are used. However, because of their high toxicity, alternative methods have been studied in the last years. In the present paper, a process to improve the corrosion resistance of AA 5083 was investigated. The main process consisted of serial immersion in two solutions containing two different cerium salts, followed by a further step involving anodisation in Na2MoO4. The corrosion resistance was investigated by potentiodynamic anodic polarisation tests and electrochemical impedance spectroscopy. The morphology and composition of the oxide layers were characterised by scanning electronic microscopy equipped with an energy dispersive X-ray detector. Serial treatment in the two solutions with different cerium salts and H2O2 produced a more uniform and thicker layer with a larger amount of deposits above the alloy cathodic areas than the single two treatments. In this way, the alloy corrosion resistance in chloride environments was improved and decreased the anodic reaction rate. When anodisation in molybdate salts was added, even better results were found. The corrosion resistance was higher due to a thicker and less conductive passive layer.

Structural characterization and electrocatalytic properties of Au30Zr70 amorphous alloy obtained by rapid quenching

The present work describes the characteristics of Au30Zr70 amorphous alloy as a precursor of a catalyst for hydrogen evolution both in acid and in basic environments and for oxidation of methanol and formaldehyde in alkaline solutions. Amorphous Au–Zr ribbons were prepared by melt spinning methods and were characterized by X-ray diffraction, optical and scanning electron microscopy. In order to obtain an active electrocatalyst, the surface of the amorphous ribbons was treated by immersion in 1 M HF solution. The results of electrocatalytic tests were compared to those obtained with untreated ribbons and also with electrodes made in polycrystalline pure gold. Moreover, some untreated samples were aged in air for 30 days before the electrochemical measurements, in order to investigate the effect of surface oxidation on the electrochemical behaviour of the alloys. The HF treatment yielded a porous structure rich in nanocrystalline gold particles which had better electrocatalytic activity than untreated ribbons or polycrystalline gold electrodes. Ageing in air produced a duplex phase structure, comprising of ZrO2 scales and nanocrystalline gold which had also improved electrocatalytic activity.