Alberto Fabrizi

Morphology evolution of gold nanoparticles as function of time, temperature, and Au(III)/sodium ascorbate molar ratio

In this work the morphology evolution of Au nanoparticles (AuNPs), obtained by direct reduction, was studied as a function of time, temperature, and Au(III)/sodium ascorbate molar ratio. The NPs morphology was examined by transmission electron microscope with image analysis, while time evolution was investigated by visible and near-infrared absorption spectroscopy and dynamic light scattering. It is found that initially formed star-like NPs transform in more spheroidal particles and the evolution appears more rapid by increasing the temperature while a large amount of reducing agent prevents the remodeling of AuNPs. An explication of morphology evolution is proposed.Graphical Abstract

Microstructure, texture evolution, mechanical properties and corrosion behavior of ECAP processed ZK60 magnesium alloy for biodegradable applications

Ultra-fine grained ZK60 Mg alloy was obtained by multi-pass equal-channel angular pressing at different temperatures of 250°C, 200°C and 150°C. Microstructural observations showed a significant grain refinement after ECAP, leading to an equiaxed and ultrafine grain (UFG) structure with average size of 600nm. The original extrusion fiber texture with planes oriented parallel to extrusion direction was gradually undermined during ECAP process and eventually it was substituted by a newly stronger texture component with considerably higher intensity, coinciding with ECAP shear plane. A combination of texture modification and grain refinement in UFG samples led to a marked reduction in mechanical asymmetric behavior compared to the as-received alloy, as well as adequate mechanical properties with about 100% improvement in elongation to failure while keeping relatively high tensile strength. Open circuit potential, potentiodynamic and weight loss measurements in a phosphate buffer solution electrolyte revealed an improved corrosion resistance of UFG alloy compared to the extruded one, stemming from a shift of corrosion regime from localized pitting in the as-received sample to a more uniform corrosion mode with reduced localized attack in ECAP processed alloy. Compression tests on immersed samples showed that the rate of loss of mechanical integrity in the UFG sample was lower than that in the as-received sample.

The Effects of Microstructure Heterogeneities and Casting Defects on the Mechanical Properties of High-Pressure Die-Cast AlSi9Cu3(Fe) Alloys

Detailed investigations of the salient microstructural features and casting defects of the high-pressure die-cast (HPDC) AlSi9Cu3(Fe) alloy are reported. These characteristics are addressed to the mechanical properties and reliability of separate HPDC tensile bars. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes throughout the tensile specimen. The results indicate that the die-cast microstructure consists of several microstructural heterogeneities such as positive eutectic segregation bands, externally solidified crystals (ESCs), cold flakes, primary Fe-rich intermetallics (sludge), and porosities. In addition, it results that sludge particles, gas porosity, as well as ESCs, and cold flakes are concentrated toward the casting center while low porosity and fine-grained structure is observed on the surface layer of the castings bars. The local variation of the hardness along the cross section as well as the change of tensile test results as a function of gage diameter of the tensile bars seem to be ascribed to the change of porosity content, eutectic fraction, and amount of sludge. Further, this behavior reflects upon the reliability of the die-cast alloy, as evidenced by the Weibull statistics.

Testing nano-silver food packaging to evaluate silver migration and food spoilage bacteria on chicken meat

ABSTRACT Migration of nanomaterials from food containers into food is a matter of concern because of the potential risk for exposed consumers. The aims of this study were to evaluate silver migration from a commercially available food packaging containing silver nanoparticles into a real food matrix (chicken meat) under plausible domestic storage conditions and to test the contribution of such packaging to limit food spoilage bacteria proliferation. Chemical analysis revealed the absence of silver in chicken meatballs under the experimental conditions in compliance with current European Union legislation, which establishes a maximum level of 0.010 mg kg–1 for the migration of non-authorised substances through a functional barrier (Commission Regulation (EU) No. 10/2011). On the other hand, microbiological tests (total microbial count, Pseudomonas spp. and Enterobacteriaceae) showed no relevant difference in the tested bacteria levels between meatballs stored in silver-nanoparticle plastic bags or control bags. This study shows the importance of testing food packaging not only to verify potential silver migration as an indicator of potential nanoparticle migration, but also to evaluate the benefits in terms of food preservation so as to avoid unjustified usage of silver nanoparticles and possible negative impacts on the environment.

Effects of chromium and bismuth on secondary aluminium foundry alloys

Abstract The effects of impurities such as chromium and bismuth on the microstructure and mechanical properties of an AlSi9Cu3(Fe) secondary die casting alloy are investigated. Metallographic and image analysis techniques have been used to examine the microstructural changes. The results indicate that the area fraction and the size of brittle α-Alx(Fe,Mn,Cr)ySiz intermetallic compounds increase by increasing the Cr content, and this affects the ultimate tensile strength and the ductility of the alloy at higher Cr level. On the other hand, the Bi addition seems to not produce significant changes in the microstructure and in the average mechanical properties of the secondary AlSi9Cu3(Fe) alloy. However, the Weibull statistics show that the addition of Bi leads to less reliable castings, which may be associated with an increase in oxide film defects.

Non-isothermal Dissolution Modelling of Sigma Phase in Duplex Stainless Steels

In this work, the non-isothermal dissolution kinetics of the sigma phase in duplex stainless steels has been studied and modelled. A semi-empirical model is proposed to describe the kinetics of sigma phase precipitation/dissolution during continuous heating starting from the isothermal transformation kinetics. The proposed model, which presumes validity of the additivity rule, is validated by means of experimental investigations. A good agreement is found between experimental and analytical results.

Evolution of Fe-rich compounds in a secondary Al–Si–Cu alloy: influence of cooling rate

Abstract The influence of cooling rate on the chemical composition and morphological structure of Fe-rich intermetallics in a secondary Al–Si–Cu alloy has been investigated by using several analysis techniques such as optical microscopy, scanning electron microscopy, energy dispersive spec-troscopy and backscattered electron diffraction. Mor-phological, chemical composition and size evolution of α-Al(Fe, Mn, Cr)Si have been observed and characterized under different solidification conditions. By varying the cooling rate, α-Al(Fe, Mn, Cr)Si blocky crystals, as well as chinese-script, branched structures and dendrites form, while coarse β-Al(Fe, Mn)Si needles appear at lower cooling rates.

The Influence of Fe, Mn and Cr Additions on the Formation of Iron-Rich Intermetallic Phases in an Al-Si Die-Casting Alloy

The microstructure evolution of a high-pressure die-cast AlSi9Cu3(Fe) alloy is studied over different Fe, Mn and Cr content. Fe-rich intermetallic phases were characterized by using optical microscope, image analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). The results revealed that the amount of Fe-rich phases as well their size increase by increasing the elemental content. Needle-like particles appear in the alloy with higher Fe:Mn ratio, while coarse α-phases assume polygonal, stark-like or Chinese script morphology according to the Fe:Mn:Cr balance as revealed by EDS analysis. The 3D-SEM investigation suggests that both the polygonal and stark-like morphology can be associated to a rhombic dodecahedron structure. The morphology evolution of the Fe-bearing particles as a function of the chemical composition and casting process is proposed and discussed.

Effects of Bismuth on the Microstructure and Mechanical Properties of AlSi9Cu3(Fe) Die Casting Alloys

In secondary die cast Al alloys, Bismuth is generally considered an impurity element and present as a trace element in commercial foundry alloys. In the present work, the influence of different Bi content on the microstructure and mechanical properties of a commercial die cast AlSi9Cu3(Fe) alloy is investigated. The Bi level ranges between 0.015 and 0.3 wt.%. The results show that the presence of Bi seems to not produce significant changes in the microstructure and mechanical properties. Fine Bi-rich compounds are observed in the die cast alloys and they are mainly distributed in the interdendritic regions and along grain boundaries. TEM investigations revealed a complex Bi-Bi2Mg3 eutectic structure, which presents mainly rod-type and blocky morphology.

Assessment of the microstructure evolution of an austempered ductile iron during austempering process through strain hardening analysis

The aim of this investigation was to determine a procedure based on tensile testing to assess the critical range of austempering times for having the best ausferrite produced through austempering. The austempered ductile iron (ADI) 1050 was quenched at different times during austempering and the quenched samples were tested in tension. The dislocation-density-related constitutive equation proposed by Estrin for materials having high density of geometrical obstacles to dislocation motion, was used to model the flow curves of the tensile tested samples. On the basis of strain hardening theory, the equation parameters were related to the microstructure of the quenched samples and were used to assess the ADI microstructure evolution during austempering. The microstructure evolution was also analysed through conventional optical microscopy, electron back-scattered diffraction technique and transmission electron microscopy. The microstructure observations resulted to be consistent with the assessment based on tensile testing, so the dislocation-density-related constitutive equation was found to be a powerful tool to characterise the evolution of the solid state transformations of austempering.