Effects of nickel content on the microstructure, microhardness and corrosion behavior of high-entropy AlCoCrFeNix alloys.

In this study the effect of three different nickel concentration on the microstructure, hardness and corrosion properties of high entropy alloys (HEAs) from AlCrFeCoNi system as an alternative material for medical instruments fabrication was investigated. The analyzed HEAs were AlCrFeCoNix obtained by vacuum arc remelting from high purity raw materials and having nickel atomic ratio x = 1.0, 1.4 and 1.8. The microscopy examination revealed the dendritic morphology for the reference alloy (AlCrFeCoNi) and that the extent of the interdendritic areas increased with the concentration of nickel while Cr was more segregated in the interdendritic areas than in dendrites. Hardness values decreased as the percentage of nickel increased due to the dissolution of the precipitates in a nickel-rich matrix and consequently the formation of continuous solid solutions. The corrosion properties of the synthesized HEAs were evaluated using a potentiodynamic polarization method. The alloys were immersed in Simulated Body Fluid during one week and the corrosion parameters were recorded. The low corrosion rates, low corrosion currents and high polarization resistance attest the good stability of these HEAs in simulated biological environment indicating their possible use for surgical and dental instruments.

Optical properties of Ar ions irradiated nanocrystalline ZrC and ZrN thin films.

Thin nanocrystalline ZrC and ZrN films (<400 nm), grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique, were irradiated by 800 keV Ar ion irradiation with fluences from 1 × 1014 at/cm2 up to 2 × 1015 at/cm2. Optical reflectance data, acquired from as-deposited and irradiated films, in the range of 500 - 50000 cm-1 (0.06 - 6 eV), was used to assess the effect of irradiation on the optical and electronic properties. Both in ZrC and ZrN films we observed that irradiation affects the optical properties of the films mostly at low frequencies, which is dominated by the free carriers response. In both materials, we found a significant reduction in the free carriers scattering rate, i.e. possible increase in mobility, at higher irradiation flux. This is consistent with our previous findings that irradiation affects the crystallite size and the micro-strain, but it does not induce major structural changes.

Band offsets in YSZ/InGaZnO4 heterostructure system.

The energy discontinuity in the valence band (deltaE(v)) of Y2O3-stabilized ZrO2 (YSZ)/InGaZnO4 (IGZO) heterostructures was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The YSZ exhibited a bandgap of 4.4 eV from absorption measurements. A value of deltaE(v) = 0.57 +/- 0.12 eV was obtained by using Ga 2P3/2, Zn 2p3/2 and In 3d5/2 energy levels as references. This implies a conduction band offset (deltaE(c)) of 0.63 eV in YSZ/InGaZnO4 heterostructures and a nested interface band alignment.

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition.

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti-5Al-2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500-600 degrees C. The UV-assisted PLD films were grown in (10(-2)-10(-1) Pa) oxygen directly on Ti-5Al-2.5Fe substrates heated at 500-600 degrees C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6-7 and 150-170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca(2)P(2)O(7), Ca(2)P(2)O(9) and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.

Electron-microscopic studies on the effect of calcium pantothenate upon rat liver and locally irradiated epidermis.

Calcium pantothenate was administered to Wistar rats in a dose of 180 mg/day/rat for 42 days, in order to investigate its effect upon the ultrastructure of the epidermis locally irradiated with a dose of 600 rep and upon partly hepatectomized liver and locally irradiated epidermis, as compared to control. The resulting data have revealed that calcium pantothenate is metabolized without entailing ultrastructural changes. Both liver and epidermis appear to be protected by calcium pantothenate, which greatly diminishes or even cancels the display of irradiation-induced negative effects. The changes brought about by irradiation are throughly presented and the subcellular mechanisms providing the radioprotection of epidermis and liver are accurately defined.

Ultrastructural changes in the mouse fetal choroid plexuses following chronic maternal alcoholization.

Female mice (RAP strain) were alcoholized for 30-50 days before mating and during pregnancy until killing, with a 20% solution of ethanol administered instead of drinking water. From foetuses of 16, 18 and 20 days and from newborn puppies (day 1) choroid plexuses were excised and electronmicroscopically examined. Chronic maternal alcoholization induced the lowering of glycogen content in the choroid cells of 16 day old foetuses, the swelling and vacuolization of mitochondria with the disappearance of cristae and enlargement of the Golgi complex--in the choroid cells at all the developmental stages controlled, the enlargement of intercellular spaces within the choroid epithelium and between the capillaries and the epithelial layer. The changes detected are presumedly due to disturbances of intracerebral fluid homeostasis and may be responsible for at least some of the CNS pathology observed in alcohol embryo- and fetopathy.

Ultrastructural changes in the mouse fetal neocortex following chronic maternal alcoholization.

Female mice (RAP strain) were alcoholized for 30-50 days before mating and during pregnancy until killing, with a 20% solution of ethanol administered instead of drinking water. From foetuses of 16, 18, 20 days and from newborn puppies on day 1 parietal neocortex fragments were excised and examined electronmicroscopically. Chronic maternal alcoholization induces in the neocortex of mouse foetuses and newborn puppies various ultrastructural changes: swelling of mitochondria with the disappearance of cristae and vacuolation, both in the capillary endothelium and in the cells of the neural tissue; enlargement of intercellular spaces; in the neocortex zones rich in neuronal processes (marginal and intermediary zone) vacuolation and structural wastage of these processes are detected. Moderate chronic alcohol intake leads to persistent ultrastructural changes in the fetal and newborn neocortex which may contribute to the appearance of some neuro-psychical and behavioral symptoms in alcohol embryo- and fetopathy. The possible pathogenetic pathways leading to the pathological changes detected are discussed.

Comparative ultrastructural study of the neuro-intermediary lobe in fresh-water teleosts under natural conditions.

A comparative study of the hypophyseal neuro-intermediary lobe (NIL)j is 8 species of fresh-water teleosts (Cyprinidae) was performed by means of light and electron microscopy. NIL is well developed in all species and consists of two types of glandular cells, three types of peptidergic nerve fibres, pituitary cells and blood cappillaries. Type A glandular cells (lead-haematoxylin staining cells) are elongated and small (8...12 micrometer/ 3...6 micrometer). They contain a large number of secretory granules with an average diameter of 160 nm. Type B cells (PAS-positive) are larger (13...16 micrometer/ 7...9 micrometer), constituting the NIL major substance. They present two variants: cells with a clear cytoplasm (light cells) and cells with a dark cytoplasm (dark cells). All the B-type cells include numerous vesicles (300...350 nm in diameter) with a slight electrondens content. In some of them a small number of intense electrondens secretory granules also appear. Type I peptidergic nerve fibres (PNF) are the most frequent; they contain numerous granules with an average diameter of 170 nm. Type II PNF are less frequent and contain granules with an average diameter of 170 nm. Type II PNF are less frequent and contain granules with an average diameter of 220 nm. The least frequent are type III PNF. Their secretory granules have an average diameter of 200 nm. The fenestrated aspect of the endothelial wall of the capillaries and the local discontinuities of the perivascular space indicate the existence of an especially tight neuro-cascular relation. The cytological "picture" of NIL is very similar in all species and characteristic for the period of the autumnal sexual repose of these animals.