117,885 research outputs found
Atomic layer deposition an innovative technology to improve corrosion and surface functionalities of alloys
No full textWith the fast-growing request for miniaturized electronic components, in the last few decades deposition of nanometric, conformal ceramic, and metallic coatings has been a challenging scientific topic. Atomic layer epitaxy, more recently also known as atomic layer deposition, has proved to be a powerful and flexible deposition technique capable of growing many different oxide and nitride layers onto a wide range of substrates, ranging from metals to polymers. Apart from their potential as semiconductors and electronic materials, chemically stable and defect-free nanometric coatings offer many additional properties of industrial interest, such as wear and corrosion protection. Papers on the potential application of atomic layer deposition outside of microelectronics and semiconductors have known an exponential growth in the last decade and atomic layer deposition has shown the potential to protect substrates from corrosion with a comparable if not superior efficiency when compared to thicker organic or ceramic conventional coatings
Mechanical and tribocorrosion properties of HVOF sprayed WC-Co coatings
No full textHVOF technology has been proposed in recent years for the production of engineered cermet coatings suitable for the replacement of hard chromium surface treatments of mechanical components, for aeronautical and automotive applications. The aim of this study has been to compare the mechanical and tribocorrosion properties of WC-Co cermet coatings fabricated with different processing parameters, to optimise the spraying process by evaluating the dependence of the macroscopic coating properties on the spraying procedure. Barrel length, oxygen:fuel ratio and torc-1 specimen spraying distance were selected as the main variables since their influence on cooling microstructure and macroscopic properties in the absence of corrosion is already well known. WC-Co samples were subjected to 'block on ring' wear testing, carried out in an electrochemical cell, to assess wear properties in combination with a range of corrosive conditions. The results were compared to those obtained by ordinary wear testing and electrochemical characterisation. Mechanical properties of the coatings, such as microhardness, fracture toughness and coating substrate adhesion, were also measured. Tribocorrosion testing proved better able to distinguish coating properties than conventional wear tests, due to the more severe damage induced by the corrosive attack
SPECTROSCOPIC INVESTIGATION OF ELECTROLUMINESCENT POROUS SILICON
No full textLight‐emitting porous silicon films have been obtained by anodic etching p‐type Si samples in a HF‐ethanol solution. Porous Si samples efficiently luminesce at room temperature in the visible region. A degradation of the luminescence intensity with time is observed. Micro‐Raman spectroscopy of free‐standing porous silicon layers indicates phonon confinements as well as a strong laser heating effects. The surface chemical composition and the effect of electron‐beam irradiation has been investigated through Auger spectroscopy. The Si LVV Auger transition dominates the spectrum, even in aged samples. The Si line shape gives evidence of a covalent bond between the porous Si surface atoms and some adsorbed species. A prolonged electron irradiation results in a strong variation of the surface chemical composition, with an anomalous carbon accumulation. Gold thin films have been deposited on the porous Si surface to form metal‐semiconductor junctions. Schottky diodes with large rectifying ratio, ideality factor, and series resistance are obtained. When the junction is forward biased, electroluminescence is observed. Electroluminescence degrades with time while the current does not. When the junction is reverse biased a significant photocurrent is obtained. The results are discussed in the framework of the surface state emission model for the luminescence
Porous metallic structures for orthopaedic applications: a short review of materials and technologies
No full text
Porous metallic structures for orthopaedic applications: a short review of materials and technologies
No full textPorous structures already have a wide range of applications in almost every modern sector of science, from catalysis to structural applications. Due to the possibility to easily tailor porosity and mechanical properties, porous structures also found application in the orthopaedic field, in particular to improve osteointegration properties of implants. Discussion: Different techniques were developed or adapted to obtain a good combination of mechanical strength, pore dimensions and Young's modulus, without neglecting biocompatibility and corrosion resistance. The aim of this work is to summarise and compare the most important characteristics of the technologies currently used for the production of commercial orthopaedic porous structure
Bioluminescent Ca2+ indicators
No full textIn the last two decades, the study of Ca2+ homeostasis in living cells received a great impulse by the explosive
development of genetically encoded Ca2+-indicators. The cloning of the Ca2+-sensitive photoprotein
aequorin and of the green fluorescent protein (GFP) from the jellyfish Aequorea victoria has been enormously
advantageous for the biologists.
As polypeptides, aequorin and GFP allow their endogenous production in cell system as diverse as
bacteria, yeast, slime moulds, plants and mammalian cells. Moreover, it is possible to specifically localize
them within the cell by including defined targeting signals in the amino acid sequence.
These two proteins have been extensively engineerized to obtain several recombinant probes for
different biological parameters, among which Ca2+ concentration reporters are probably the most relevant.
In this review, we will not treat the GFP-based Ca2+ probes, but we will present the applications
offered by aequorin in the study of intracellular Ca2+ homeostasis, discussing also the new generation of
bioluminescent probes that couple the Ca2+ sensitivity of aequorin to GFP fluorescence emission. In these
probes, aequorin Ca2+-dependent photon emission delivers energy to the GFP acceptor in a bioluminescence
resonance energy transfer (BRET): this process enhances the stability and the high signal-to noise
ratio of the probes and permits real-time measurements of subcellular Ca2+ changes in single cell imaging
experiments. Very recently, the development of transgenic animals expressing GFP–aequorin bi-functional
probes has also permitted the video-imaging of Ca2+ concentrations changes in live animals
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