Electrical properties of biomorphic SiC ceramics and SiC/Si composites fabricated from medium density fiberboard

A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature in the range 1.8-1300 K and on magnetic fields of up to 28 kOe for the biomorphic SiC/Si (MDF-SiC/Si) composite and biomorphic porous SiC (MDF-SiC) based upon artificial cellulosic precursor (MDF - medium density fiberboards). It has been shown that electric transport in MDF-SiC is effected by carriers of n-type with a high concentration of ∼10²⁰ cm⁻³ and a low mobility of ∼0.4 cm² V⁻¹ s⁻¹. The specific features in the conductivity of MDF-SiC are explained by quantum effects arising in disordered systems and requiring quantum corrections to conductivity. The TEM studies confirmed the presence of disordering structural features (nanocrystalline regions) in MDF-SiC. The conductivity of MDF-SiC/Si composite originates primarily from Si component in the temperature range 1.8-500 K and since ∼500 to 600 K the contribution of MDF-SiC matrix becomes dominant.     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Micellar polymerization,characterization, and viscoelasticity of combined thermally insensitive terpolyacrylamides

Polymer chains consisting of water‐soluble polyacrylamides and N‐isopropylacrylamide (NIPAM), hydrophobically modified with low amounts of N,N‐dialkylacrylamides (N,N‐dioctylacrylamide) have been prepared via free radical micellar polymerization, using a hydrophobic initiator derived from 4,4′‐azobis(4‐cyanopentanoic acid) containing a long linear chain of 16 (C16) carbon atoms. This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. These polymers are named “combined associative polymers” and include within their structure a water‐soluble monomer (acrylamide), a thermosensitive monomer (NIPAM) and a hydrophobic monomer. The polymers were characterized by different techniques, also studying the effect of adding a surfactant anion such as sodium dodecylsulfate. The viscoelastic properties as a function of temperature of these associative polymers were investigated using steady‐flow and oscillatory experiments considering the relaxation time (T_R) and the plateau modulus (G₀). The effect of concentration of acrylamide and NIPAM on the viscosity of the associative polymer solutions was investigated. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Parallel sphere detector algorithm providing optimal MIMO detection on massively parallel architectures

Multiple‐input multiple‐output (MIMO) systems have attracted considerable attention in wireless communications because they offer a significant increase in data throughput and link coverage without additional bandwidth requirement or increased transmit power. The price that has to be paid is the increased complexity of hardware components and algorithms. The sphere detector (SD) algorithm solves the problem of maximum likelihood (ML) detection for MIMO channels by significantly reducing the search space of possible solutions. The main drawback of the SD algorithm is in its sequential nature, consequently, running it on massively parallel architectures (MPAs) is very inefficient. In order to overcome the drawbacks of the SD algorithm, a new parallel sphere detector (PSD) algorithm is proposed. It implements a novel hybrid tree search method, where the algorithm parallelism is assured by the efficient combination of depth‐first search and breadth‐first search algorithms. A path metric‐based parallel sorting is employed at each intermediate stage. The PSD algorithm is able to adjust its memory requirements and extent of parallelism to fit a wide range of parallel architectures. Mapping details for MPAs are proposed by giving the details of thread dependent, highly parallel building blocks of the algorithm. Based on the building blocks proposed, a mapping to general‐purpose graphics processing unit is provided, and its performance is evaluated. In order to achieve high‐throughput, several levels of parallelism are introduced, and different scheduling strategies are considered. Copyright © 2015 John Wiley & Sons, Ltd.     

Deposition of thick and 50% porous YpSZ layer by spraying nitrate solution in a low pressure plasma reactor

The deposition of Yttria partially Stabilized Zirconia (YpSZ) for Thermal Barrier Coating application (TBC) is a current topic of interest. The TBC must exhibit high thickness (100–300 μm), vertical cracks in order to be a strain tolerant layer, and high porosity to decrease the thermal conductivity. In this paper, a solution of nitrate salt is introduced into a low pressure plasma discharge (600 Pa, 80–220 W) to obtain YpSZ layers.Several analytical techniques were used to study the characteristics and the stability of the YpSZ layers obtained in the low pressure plasma reactor. Optical emission spectroscopy indicated that the oxidant chemistry in the plasma is responsible for the formation of the oxide and the elimination of the nitrates at low temperature (T < 300 °C on the layer). SEM, water porosimetry, thermal diffusivity and XRD analyses were performed to study the effect of the parameters (power of the plasma discharge, post-treatment, heat treatment) on the structure, the morphology and the stability of YpSZ coatings. For example, it was observed that YpSZ is 50% porous in all cases and that the nanostructures of the coating resist against high temperature conditions (1200 °C/5 h).     

In‐Situ Carbon Doping of TiO2 Nanotubes Via Anodization in Graphene Oxide Quantum Dot Containing Electrolyte and Carburization to TiOxCy Nanotubes

Anodic production of self‐organized titania nanotubes (TNTs) in an electrolyte enriched with graphene oxide quantum dots (GOQDs) is reported. The TNT‐GOQD composites grown under these conditions show in‐situ carbon doping, leading to the formation of anatase TiO₂ domains and to the reduction to substoichiometric oxide (TiO_x) and TiC. Surface science and electrochemical techniques are used in synergy to reveal that graphitic carbon is incorporated into TiO₂ upon anodic nanotube growth promoting the formation of oxygen vacancies and thus TiO₂ reduction. Upon annealing in ultrahigh vacuum, titanium oxycarbide (TiO_xC_y) is formed at temperatures ≥400 °C, where the material changes from a semiconductor to a semimetal. At the solid/liquid interface, the apparent electron donor density increases from as‐grown TNTs to as‐grown TNT‐GOQD composites due to the carbon doping, and the conductivity increases further with annealing temperature due to the increasing concentration of coordinatively unsaturated C atoms, crystallinity, and TiO₂ reduction. The materials synthesized and characterized in this study find application in different areas ranging from visible light photocatalysis and photo‐electrochemistry to use as Li‐ion battery anodes and electrocatalyst supports, because it is possible to gradually tune the density of states below the Fermi level, which can be referred to as band‐gap engineering.     

Synthesis of planar inductors in low temperature co-fired ceramic technology

A simple bisection algorithm for the synthesis of planar inductors using a fast electromagnetic analysis algorithm is presented in this work. Both bisection and electromagnetic analysis algorithms are based on a set of heuristic and physical rules obtained from the study of the electromagnetic behavior of these planar devices. With this procedure, the benefits are two fold: (i) the number of iterations is kept moderately low in the synthesis loop, and (ii) the analysis at each iteration step is speed up without compromising accuracy. The algorithm is applied to the development of an inductor library for a low temperature co-fired ceramic process technology.     

MaxPHOS Ligand: PH/NH Tautomerism and Rhodium‐ Catalyzed Asymmetric Hydrogenations

MaxPHOS is an active and robust P‐stereogenic ligand for asymmetric catalysis. The presence of an  NH bridge between the two phosphine moieties allows the NH/PH tautomerism to take place. The neutral ligand, in which the NH form predominates, is an air‐sensitive compound. However, protonation of MaxPHOS leads to the stable PH form of the ligand, in which the overall positive charge is distributed on both P centers. This protonation turns the MaxPHOS⋅HBF₄ salt 3 into an air‐stable compound both in the solid state and in solution. The salt 3 is also a convenient precursor for the preparation of rhodium(I) complexes by direct ligand exchange with the complex [Rh(acac)(cod)]. Finally, the corresponding rhodium(I)‐MaxPHOS complex was tested in the asymmetric hydrogenation of a wide range of substrates. The complex proved to be a highly selective and robust system in these reactions.

     

Selective suspension of single layer graphene mechanochemically exfoliated from carbon nanofibres

This paper presents the first report of the successful ball-milling exfoliation of graphitic filaments （GANF~ carbon nanofibres） into single layer graphene. The addition of small amounts of solvent during the milling process makes it possible to enhance the intercalation of the exfoliating agent （melamine） between the graphene layers, thus promoting exceptional exfoliation. Advantage has also been taken of the fact that the Hansen solubility parameters of graphene are different from those of carbon fibres, which allows single and few-layer graphene to be suspended in a particular solvent, thus discriminating them from poorly exfoliated carbon nanofibres.