Alexandre Velhinho

Regio‐ and Chemoselective Reduction of Nitroarenes and Carbonyl Compounds over Recyclable Magnetic FerriteNickel Nanoparticles (Fe3O4Ni) by Using Glycerol as a Hydrogen Source

Reduction by magnetic nano-Fe(3)O(4)-Ni: a facile, simple and environmentally friendly hydrogen-transfer reaction that takes place over recyclable ferrite-nickel magnetic nanoparticles (Fe(3)O(4)-Ni) by using glycerol as hydrogen source allows aromatic amines and alcohols to be synthesized from the precursor nitroarenes and carbonyl compounds.

A facile synthesis of cysteine–ferrite magnetic nanoparticles for application in multicomponent reactions—a sustainable protocol

A facile, simple and environmentally friendly Fe3O4–cysteine MNP was synthesized without any additive or additional source of linkers. Fe3O4–cysteine MNPs were successfully used for the synthesis of β-amino carbonyl and hydroquinoline compounds, which were obtained in excellent yields via multicomponent reactions. Magnetic organocatalysts can be easily recovered by simple magnetic decantation and their catalytic activity remains unaltered after 9 consecutive cycles, making them environmentally friendly and widely applicable due to their efficiency, ease of handling, and cost effectiveness.

Magnetically recyclable magnetite–palladium (Nanocat-Fe–Pd) nanocatalyst for the Buchwald–Hartwig reaction

The immobilization of Pd on the magnetite surface afforded Nanocat-Fe–Pd using inexpensive precursors and its catalytic role in the Buchwald–Hartwig reaction for arylation of amines and amides was investigated; C–N bond formation was achieved in moderate to excellent yields and the catalyst could be separated and recycled up to five cycles by magnetic decantation without a significant loss in yield.

X-ray tomographic imaging of Al/SiCp functionally graded composites fabricated by centrifugal casting

Abstract The present work refers to an X-ray microtomography experiment aiming at the elucidation of some aspects regarding particle distribution in SiC-particle-reinforced functionally graded aluminium composites. Precursor composites were produced by rheocasting. These were then molten and centrifugally cast to obtain the functionally graded composites. From these, cylindrical samples, around 1 mm in diameter, were extracted, which were then irradiated with a X-ray beam produced at the European Synchrotron Radiation Facility. The 3-D images were obtained in edge-detection mode. A segmentation procedure has been adapted in order to separate the pores and SiC particles from the Al matrix. Preliminary results on the particle and pore distributions are presented.

Nano-MgO–ZrO2 mixed metal oxides: characterization by SIMS and application in the reduction of carbonyl compounds and in multicomponent reactions

A nano-sized Magnesia–Zirconia (nano-MgO–ZrO2) catalyst was prepared by a simple ultradilution co-precipitation method and by using inexpensive precursors. The nano-MgO–ZrO2 was extensively characterized by SIMS together with other analytical techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nano-MgO–ZrO2 catalyst proved to be very efficient for the reduction of carbonyl compounds and multicomponent reactions under mild reaction conditions. The recyclability and reusability of the nano-MgO–ZrO2 catalyst has been tested.

Tribocorrosion Studies in Centrifugally Cast Al-Matrix SiCp-reinforced Functionally Graded Composites

The present work reports results obtained from a series of preliminary experiments aiming at complementing the current knowledge about the wear behaviour of centrifugally-cast FGM Al/SiCp composites, through concurrent corrosion processes. Precursor MMCs were prepared by rheocasting, using 118.8 µm SiC particles and an Al-10Si-2.2 Mg alloy. Those MMCs were then molten and centrifugally cast in order to produce cylindrical FGMMCs. Discs machined from the top surface of each sample were tested against nodular cast iron pins, using an inverted configuration pin-on-disc tribometer. Sliding tests took place at room temperature, over a 50000 m sliding distance, with a sliding speed of 0.3 m s -1 , under a 5 N normal load; both dry-sliding and water-lubricated tests were performed. In order to elucidate the mechanisms involved, the wear coefficients were calculated for each condition, and the samples were subjected to morphological characterization via SEM/EDS. Concurrently, in the case of the water-lubrication tests, the corrosion potential of the tribological pair was monitored. The results obtained show an increase in material loss for the water-lubricated cases, although variations are registered depending on reinforcing particle volume fraction. At the same time, the open circuit potential response of the tribological pair may be correlated with the events of formation/destruction of the tribolayers.

Al/SiCp Functionally Graded Metal-Matrix Composites Produced by Centrifugal Casting: Effect of Particle Grain Size on Reinforcement Distribution

Functionally graded materials (FGM’s), particularly in the form of Al-Si metal matrix composites (MMC’s) selectively reinforced at the surface with SiC particles, are advanced materials, combining high wear resistance with high bulk toughness or even a thermal barrier at the surface. Centrifugal casting is one of the most effective methods for processing this type of MMC, but accurate control of the ceramic particles distribution/gradient in the metallic matrix has not yet been completely attained. In this work, precursor Al/SiC composites were prepared by rheocasting, using SiC particles and an Al-10Si–2.2 Mg alloy. Morphology of the SiC particles was previously characterized by laser interpherometry and SEM. Differing grain sizes were selected as reinforcing elements. The MMC’s were then molten and centrifugally cast in order to produce the FGM composites, whose structure and properties were investigated by XRD, quantitative image analysis of optical micrographs and longitudinal hardness profiles. Therefore, it was possible to evaluate the influence of the particle grain size on the structure and properties of the FGM. Apart from the evaluation of the effects of particle grain size per se, its influence when combined with differing casting conditions are reported as well.

Corrosion behaviour of aluminium syntactic functionally graded composites

Syntactic Functionally Graded Metal Matrix Composites (SFGMMC) are a type of composites reinforced by microballoons exhibiting a graded reinforcement distribution. These materials constitute a promising new generation of lightweight structural materials for aerospace, marine and shielding/insulation applications. In this work, A356 alloy reinforced with silica-alumina microballoons (SiO2-Al2O3) was processed by casting techniques. The influence of the microballoon distribution gradient on the corrosion behaviour of the composite was investigated by potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS). Composite surfaces were analysed before and after testing by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) to determine the influence of microstructural changes.

Assessment of Particle Clustering in MMCs by Quantitative Image Analysis

In the present paper, work of a preliminary nature pertaining to the development of a simple tool for easy identification of reinforcement clustering in particle-reinforced MMCs is reported. The tool consists of an image processing and analysis routine performed with the aid of a public-domain software. Results obtained were in the form of distribution curves pertaining to the Euclidian distances between particle centroids within sample images. Analysis of that distribution allowed the identification of cluster occurrence. The technique was successfully applied to computer-generated images of virtual MMCs, as well as to micrographs of rheocast MMCs. Apart from particle clustering, the distribution curves were found useful to roughly assess the matrix cell size, for cases where this is significantly higher that the size of the reinforcing particles.

Elastic Behaviour of Spherical Particles Reinforced Metal-Matrix Composites

Current technology provides means of fabrication of spherical micro-particles, either hollow or compact, for all engineering materials. Such spherical particles can be further embedded into another material to build-up either random dispersions or close-packed arrays, according to the production route and the degree of anisotropy intended for the ultimate composite material. In this study, a simple analytical formula for the composite stiffness is derived from an early micromechanics model, to describe the actual reinforcement of ductile matrices by a random dispersion of uniform spherical ceramic particles. Predictions from this model are checked against some other relevant models, and specific features arising from its theoretical derivation are pointed out.