Ag surface diffusion and out-of-bulk segregation in CrN-Ag nano-composite coatings

CrN-Ag nanocomposite coatings are deposited on Si(100) wafers and 20MnCr5 steel disks in a mixed Ar+N2 atmosphere by reactive magnetron sputtering. Structure, composition and morphology were investigated by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), X-ray Photoemission Spectroscopy (XPS), X-ray Diffraction (XRD) and Focused Ion Beam (FIB) cross sectional analysis. The as deposited film matrix is mainly composed by CrN phase (78%), but a relevant part (28%) is composed by Cr2N. Ag agglomerates in the CrN matrix forming elongated grains 200-400 nm wide and 50-100 nm high, which extends on the top of CrN columns. At the surface Ag aggregates into two different structures: large tetrahedral crystalline clusters, with typical dimension ranging from 200 to 500 nm, and smaller Ag nanoparticles with diameter of 15-25 nm. The annealing in N2 atmosphere up to 500 degrees C does not affect size and distribution of the Ag grains in the sub-surface region, while it induces a size increase of the bigger Ag clusters on the surface, mainly related to Ag surface diffusion and clusters coalescence. Annealing at higher temperature leads to an evident Ag out-of-bulk segregation, generating Ag depleted voids in the near-surface region, and further increasing of the Ag clusters size at the surface. Tribological tests on as deposited CrN-Ag film reveal a coefficient of friction against a steel ball reduced with respect to CrN film, probably related to the presence of Ag which acts as solid lubricant, but the coating is removed after a very short sliding distance. The poor mechanical properties of the realized Ag-based coatings are confirmed by lower hardness and Young modulus values with respect to pure CrN.     

Seeded growth of TPA-MFI films using the fluoride route

The fluoride route in combination with surface seeding was used for the preparation of TPA-MFI films on dense amorphous silica glass supports. The use of F⁻ as mineralizing agent allowed the crystallization of TPA-MFI at near-neutral pH (6.7 ± 0.1). The supports were seeded with colloidal TPA-MFI crystals and hydrothermally treated in a synthesis gel at 100 °C for various durations (24–192 h). The synthesis products were characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). A film growth rate of about 9 nm/h was found. The crystals in these films exhibit a preferred orientation, with the (1 0 1) planes of the crystals parallel or near parallel to the support surface. Film growth in the near-neutral synthesis gel was also attempted on seeded porous -alumina supports. However, epitaxial growth of the seed crystals was inhibited by the formation of a uniform layer of colloidal silica particle which covered the seed crystals even in an early stage of hydrothermal treatment. Continuous films could only be prepared by increasing the pH of the initial synthesis mixture from 6.7 to 9.6, thus using both OH⁻ and F⁻ as mineralizing agents. These films are composed of a columnar layer on top of a layer built up of small grains. Such microstructure has previously been reported in the literature for TPA-MFI films grown in conventional synthesis mixtures.     

Regional selectivity to ochratoxin A, distribution and cytotoxicity in rat brain

Ochratoxin A (OTA) a chlorodihydro-isocoumarin linked through an amide bond to phenylalanine, is a mycotoxin found as a contaminant in foodstuffs and shown to be nephrotoxic, teratogenic, immunosuppressive, genotoxic, mutagenic and carcinogenic in rodents. Ochratoxin A is known to induce teratogenic effects in neonates (rats and mice) exposed in utero, characterised by microcephaly and modification of the brain levels of free amino acids. Since OTA has been found to accumulate in the brain according to the duration of exposure to doses in the range of natural contamination of feedstuffs, experiments were designed to determine more precisely the structural target of OTA in the brain. After intracerebral injection, OTA (403 ng/10 microl) was not found in the following parts of the brain: the frontal cortex (FC), striatum (ST), ventral mesencephalon (VM) and the cerebellum (CB) in contrast to the rest of the brain, probably due to the detection limit of 0.1 ng/g of tissue. However lactate dehydrogenase (LDH) was increased in extracellular space in the VM to a greater extent than in the rest of the brain, indicating that this structure could be one of the targets of OTA in the brain. Contents of free amino acids were morever similarly modified in the VM and in the rest of the brain. Male rats were given OTA (289 microg/kg per 24 h) by gastric intubation for 8 days and the main brain structures analysed for OTA content and cytotoxicity. OTA was found in the following structures in decreasing order: rest of the brain (50.3%), cerebellum (34.4%), VM (5.1%), striatum (3.3%) and hippocampus (2.9%) of the total OTA amount found in the brain, which represents 0.022% to 0.028% of the given dose. Interestingly cytotoxicity as measured by lactate dehydrogenase (LDH) release in the extracellular space was much more pronounced in the VM, hippocampus, and striatum than in the cerebellum, whereas no cytotoxicity was observed in the rest of the brain. Similarly deoxyribonuclease (DNase) activity in relation to possible necrotic cells was increased in the VM and cerebellum. Altogether these results designated the ventral mesencephalon, hippocampus, striatum and cerebellum as the main OTA-targets in the brain of adult rats and excluded the rest of the brain.     

High-Throughput Nanoindentation Mapping of a Microsegregated CoCrFeNi Multi-Principal Element Alloy (MPEA): Challenges and Limitations

Equimolar CoCrFeNi is a popular multi-principal element alloy, generally obtained by melt-aided routes. The dendritic microstructure of as-cast alloys is cooling-rate dependent and thus may show different macromechanical behaviors. Knowledge about the nanomechanics of chemically/structurally distinct zones is important for explaining these differences and facilitating material's design through processing conditions. To this aim, high-throughput nanoindentation mapping is a potentially powerful tool. However, results are possibly biased by the indentation size effect (ISE) and plastically deformed surfaces induced by inadequate sample preparation. This work is aimed at giving some guidelines for map acquisition and sample preparation based on data from various nanoindentation techniques (i.e., high-throughput nanoindentation, continuous stiffness, and quasi-static measurements) collected on differently polished surfaces. It is shown that conventional metallographic preparation leads to a plastically deformed layer that penetrates deep into the surface (11–17 μm). Electropolishing is efficient in removing this layer. However, difficulties may arise due to preferential corrosion in a multiphase system wherefore polishing conditions needs optimization. Nanoindentations of adequately prepared surfaces of CoCrFeNi result in an important ISE, which affects measurements at depths lower than ca 2000 nm. This must be taken into account when performing high-throughput nanoindentation mapping of this material.