Electrically conductor black zirconia ceramic by SPS using graphene oxide

The use of graphene as a component for developing electroconductive ceramic composites is being profusely studied. It is a very promising additive as it has excellent mechanical properties, high electrical and thermal conductivities, it is lightweight and its aspect ratio allows reaching percolation with low contents.In the particular case of zirconia, preparation of black coloured materials remains a challenge while many high added value applications are waiting for a solution. Graphene appears as a candidate for fulfilling all these requirements. In this work, 3Y–TZP/rGO composites were prepared by Spark Plasma Sintering Zirconia-rGO mixtures. Simultaneous sintering and in-situ reduction of graphene oxide opens a very interesting technological route for preparing this type of materials. The influence of graphene content on the electrical, mechanical and optical properties was studied. An rGO content as low as 0,29 vol% allows nanostructured black zirconia to be obtained but it has to be increased up to 1 vol% in order to reach electrical resistivity values <100Ωcm, required for electrodischarge machining.     

Ion-induced desorption of surface contaminants

We report measurements of mean desorption areas per incident ion for hydrocarbon contaminated surfaces of different solids bombarded with 30 keV H₂⁺, O⁺₂, and Ar⁺ and 15 keV O⁺ ions. The results for heavy ions are consistent with a momentum transfer mechanism for desorption. A molecular effect is observed for O₂⁺ ions which desorb significantly more than two separate O⁺ of the same velocity. Our results for hydrogen ions; together with results of other workers for low-energy light ions, lead us to the conclusion that desorption occurs efficiently in inelastic collisions.     

Towards the development of technical specifications for the production of lithium–lead alloys for the ITER HCLL TMB

The ITER and DEMO projects are developing new Test Blanket Modules (TBM), where the Pb–Li alloy plays a key role in the new commercial fusion reactors functionality. The Breeding Blanket (BB) has to perform several functions which are essential for the reactor operation. The HCLL TBM is one of the Breeding Blanket concepts to be tested in ITER. It is cooled by He and uses the eutectic liquid metal LLE (Lithium–Lead Eutectic) as breeder material (enriched at 90% in ⁶Li).Pb–Li eutectic alloy has no known uses outside of fusion technology, so the available databases of this material are currently incomplete. It is very important, within the material specifications, to have a complete characterization in order to define their chemical and physical properties, because any variation in the alloy composition has significant consequences in their behaviour, and therefore in their regenerative function inside the blanket.The chemical characterization methodology developed and presented in this paper (useful for both Pb–Li alloys as any Pb alloy) is a key tool that allows performing standard quality control procedures for base material and/or monitoring the alloy during the reactor operation. This report provides a procedure to perform a wide material chemical characterization, assessing the concentrations of major elements, as well as a review of trace level elements that can be found both in the eutectic alloy and in starting materials. In this determination plays an important role the ICP-MS technique because, as a highly sensitive technique, allows very low detection limits.     

Empirical approach to the description of spectral performance degradation of silicon photodiodes used as particle detectors

The spectral deterioration of Hamamatsu S5821 silicon photodiodes for ion types and energies frequently used in Ion Beam Analysis was investigated. Focused proton beams with energies 430 keV and 2 MeV were applied to generate radiation damage via an area selective ion implantation in unbiased diodes at room temperature. The variations of spectroscopic features were measured “in situ” by Ion Beam Induced Current (IBIC) method as a function of fluence, within the 10⁹–5 × 10¹² ion/cm² range and diode bias voltages, between 0 and 100 V.An empirical model has been developed to describe the radiation damage. Equations are derived for the variations of the normalized peak position and peak width. The derived empirical equations are physically correct, as far as they account for the superposition of the influence of charge carrier trapping by native and radiation-induced defects and for the effect of charge carrier velocity saturation with electric field strength, as well.     

Improved interfacial adhesion with the help of functional polyhedral oligomeric silsesquioxanes in silicone rubber/rayon fiber composites: Physical,mechanical, thermal,and morphological properties

The aim of this article is to improve the interfacial adhesion between silicone rubber (SR) and Rayon fiber by the help of functional hybrid POSS nanoparticles. Two POSS types were compared, octavinyl-POSS (O-POSS) and methacryl-POSS (M-POSS), having reactive  CC double bonds that can impart in peroxide crosslinking. O-POSS is nonpolar, whereas M-POSS is polar and is able to make H-bond with Rayon fibers. POSS type and their concentrations were examined as the experimental parameters. H-adhesion tests indicated that both POSS types enhanced the adhesion of SR composites to Rayon fibers compared with control recipe. Specifically, slightly higher values were obtained with the use of M-POSS. It was observed that both O-POSS and M-POSS slowed down the curing rate but increased the degree of crosslinking. The cure extent of O-POSS containing composites was found to be higher than that of M-POSS containing ones. Thermal gravimetric analyses revealed that thermal stability of SR composites was significantly improved by the addition of POSS particles. Higher char yield and degradation temperatures were obtained with O-POSS at higher loadings with respect to M-POSS. The POSS distribution at lower loading levels was found to be homogenous for both POSS types as observed from scanning electron microscope and transmission electron microscope.     

Scytodecamide from the Cultured Scytonema sp. UIC 10036 Expands the Chemical and Genetic Diversity of Cyanobactins

Cyanobactins are a large family of cyanobacterial ribosomally synthesized and post-translationally modified peptides (RiPPs) often associated with biological activities, such as cytotoxicity, antiviral, and antimalarial activities. They are traditionally described as cyclic molecules containing heterocyclized amino acids. However, this definition has been recently challenged by the discovery of short, linear cyanobactins containing three to five amino acids as well as cyanobactins containing no heterocyclized residues. Herein we report the discovery of scytodecamide ( 1 ) from the freshwater cyanobacterium Scytonema sp. UIC 10036. Structural elucidation based on mass spectrometry, 1D and 2D NMR spectroscopy, and Marfey's method revealed 1 to be a linear decapeptide with an N-terminal N-methylation and a C-terminal amidation. The genome of Scytonema sp. UIC 10036 was sequenced, and bioinformatic analysis revealed a cyanobactin-like biosynthetic gene cluster consistent with the structure of 1 . The discovery of 1 as a novel linear peptide containing an N-terminal N-methylation and a C-terminal amidation expands the chemical and genetic diversity of the cyanobactin family of compounds.     

Prebiotic Origin of Pre-RNA Building Blocks in a Urea “Warm Little Pond” Scenario

Urea appears to be a key intermediate of important prebiotic synthetic pathways. Concentrated pools of urea likely existed on the surface of the early Earth, as urea is synthesized in significant quantities from hydrogen cyanide or cyanamide (widely accepted prebiotic molecules), it has extremely high water solubility, and it can concentrate to form eutectics from aqueous solutions. We propose a model for the origin of a variety of canonical and non-canonical nucleobases, including some known to form supramolecular assemblies that contain Watson-Crick-like base pairs.The dual nucleophilic-electrophilic character of urea makes it an ideal precursor for the formation of nitrogenous heterocycles. We propose a model for the origin of a variety of canonical and noncanonical nucleobases, including some known to form supramolecular assemblies that contain Watson-Crick-like base pairs. These reactions involve urea condensation with other prebiotic molecules (e. g., malonic acid) that could be driven by environmental cycles (e. g., freezing/thawing, drying/wetting). The resulting heterocycle assemblies are compatible with the formation of nucleosides and, possibly, the chemical evolution of molecular precursors to RNA. We show that urea eutectics at moderate temperature represent a robust prebiotic source of nitrogenous heterocycles. The simplicity of these pathways, and their independence from specific or rare geological events, support the idea of urea being of fundamental importance to the prebiotic chemistry that gave rise to life on Earth.     

Effect of height on the corrosion of steel and galvanized steel in nontropical coastal marine environments

In this study, the behavior of carbon steel and galvanized steel in nontropical coastal marine environments was evaluated. Evaluation was carried out with specimens with dimensions of 10 cm × 10 cm × 0.3 cm. These specimens were exposed to four testing stations (Iquique, Mejillones, Los Vilos, and San Vicente), where racks were installed both at ground level (ground), as well as in the upper zone of electrical transmission towers (tower). In each station, 24 specimens of A36 carbon steel and galvanized steel were placed (12 each). The corrosivity of the environment was measured using the ISO 9223, 9225, and 9226 standards. The specimens were evaluated on-site, monthly, through visual inspection and photographic record. Once withdrawn, the corrosion rate was determined and the corrosion products were analyzed through Raman and Fourier-transform infrared. The results show that, in all cases, the corrosion rate is greater in the tower than on the ground. However, even though the Los Vilos station is located farther from the sea (3,500 vs. ≈500 m), the corrosion rate of steel in the tower is the highest. This is caused by the generation of HCl from the transformation of lepidocrocite into goethite, in the presence of low chloride content, which acidifies the steel/corrosion product interface. In the case of galvanized steel, the corrosion rate is a function of the chloride content in the atmosphere, obtaining an excellent correlation between both parameters.