Capillary Flow Behaviour of Microcrystalline Wax and Silicon Carbide Suspension

Suspensions of ceramic particles in low or high molecular weight polymers are shaped into various three-dimensional parts using various moulding and extrusion technologies. Such bodies are subsequently fired-up and sintered to remove the binder. The utilities of such three-dimensional ceramic bodies depend on the restrictions related to the shapeability of the ceramic suspension, hence to the flow and deformation behaviour of the suspension. In this study, factors affecting the flow and deformation behaviour of a 50% by volume of silicon carbide in a wax binder was investigated. Consistent with the previously observed behaviour of other highly filled materials, the ceramic suspension exhibited viscoplasticity, plug flow and wall slip. Furthermore, flow instabilities associated with the axial migration of the low viscosity binder under the imposed pressure gradient were observed. These results pinpoint to the various difficulties associated with the collection of rheological data and emphasize the relevance of various flow mechanisms, including wall slip and mat formation and filtration based flow instabilities, which would also occur in processing/shaping flows of such ceramic suspensions including extrusion and moulding.     

Statistical pattern analysis of partial discharge measurements for quality assessment of insulation systems in high-voltage electrical machinery

In this paper, we present a new statistical analysis method of phase-resolved partial discharge (PD) measurements for the quality assessment of electrical insulation in high-voltage machinery. The method is based on a supervised classification approach which utilizes histogram similarity analysis. The motivation for choosing histogram similarity analysis is twofold. First, the phase-resolved PD measurement itself is, in fact, a two-dimensional histogram. Therefore, a histogram-matching-based approach suits the very nature of the data. Second, histogram similarity analysis combines the typical statistical parameters, used in PD analysis, in a statistically powerful and rigorous way. In our study, we utilize various histogram types and similarity analysis, including correlation, chi-square, and Kolmogorov-Smirnov tests. Further, we propose a postprocessing method to quantify the accuracy of classification results which enables the user to make soft decisions. Our experimental study on laboratory samples demonstrates that the method shows strong potential in detection and classification of insulation defects. The results from our study suggest that the proposed method provides a powerful, general, and mathematically simple approach to the analysis of phase-resolved PD measurements.     

Mass transfer layer for liquid fuel cells

Performance of a new type of mass transfer layer (MTL) compared to a commercial material has been shown in single fuel cell testing. GRAFCELL^® natural graphite MTL is used as a cathode diffusion media along with carbon cloth. Its chemically modified permeable structure is diffusion limited at high current densities, independent of temperature, while perforated structure provides temperature dependent performance increases. The impact of open area variation in perforated mass transfer layer (PMTL) is demonstrated at high current densities and shows advantages over commercial material at room temperature operation. Performance reaches about 25 mW cm⁻² at room temperature testing with maximum current density around 250 mA cm⁻². Better performance is attributed to large openings for liquid transfer with PMTL compare to ELAT. Being able to design perforations on expanded graphite material may also play role in developing passive fuel supply systems for future liquid fuel power sources.     

Extractives of Turkish and Pakistani Tree Species

The composition and amount of hydrophilic and lipophilic extractives in knots and stemwood of eight Turkish and one Pakistani tree species were analysed. Lignans were the main polyphenols in most studied species and pinosylvins in the pines. The two studied juniper species contained no or only little lignans. Most species also contained juvabiones or phenolic diterpenoids. Both polyphenols and lipophilic extractives were more abundant in the knots than in the stemwood.     

Anodizing and corrosion behaviour of aluminium

In this study, aluminum was anodized in 0.4 M H₂SO₄ + 0.145 M H₃BO₃ solution by means of potentiostatic method. In first step, the most appropriate conditions (anodizing voltage and period) were determined. The voltage-current behavior was investigated between 0 to 30 V and oxide formation potential (15 V) was determined. Then chorono-amperometric measurement was obtained at this potential during 2 hours. Therefore, anodizing process was applied at 15 V between aluminium anode and mild steel cathode. In the second step, the corrosion performance of non-anodized (Al) and anodized samples (Al₂O₃) have been investigated in 3.5% NaCl solution by using electrochemical impedance spectroscopy and polarization techniques. The interface between metal and solution was modeled with the equivalent circuit successfully. The circuit’s elements were calculated with Ivium Soft fitting program. The polarization curves were obtained between −1.8 V and 0.5 V potential ranges. The experimental results proved that the thickness and quality of oxide film was improved with help of anodizing process. Thus the corrosion resistance of anodized aluminum is significantly increased.     

Characterization and fuel cell performance analysis of polyvinylalcohol–mordenite mixed-matrix membranes for direct methanol fuel cell use

Polyvinylalcohol–mordenite (PVA–MOR) mixed matrix membranes were synthesized for direct methanol fuel cell (DMFC) use. For the structural and the morphological characterization, Scanning Electron Microscopy and Thermal Gravimetric Analysis methods were used. Zeolite distribution within the polymer matrix was found to be homogeneous. An impedance spectroscope was used to measure the proton conductivity. In order to obtain information about methanol permeation characteristics, swelling tests and a series of pervaporation experiments were carried out. 60–40 wt% PVA–MOR membranes were found to give the optimum transport properties. Proton conductivity of these membranes was found to be slightly lower than that of Nafion117™ whereas their methanol permeability was at least two orders of magnitude lower than Nafion117™. DMFC performance of the PVA–MOR membranes was also measured. The inferior DMFC performance of PVA–MOR membranes was linked to drying in the fuel cell medium and the consequent proton conductivity loss. Their performance was improved by adding a dilute solution of sulfuric acid into the feed methanol solution. Future studies on the improvement of the proton conductivity of PVA–MOR membranes, especially via sulfonation of the polymer matrix, can overcome the low-performance problem associated with insufficient proton conductivity.     

Exploring the power of social hub services

World Wide Web - Given the diverse focuses of emerging online social networks (OSNs), it is common that a user has signed up on multiple OSNs. Social hub services, a.k.a., social directory...     

A noniterative method for robustly computing the intersections between a line and a curve or surface

The need to compute the intersections between a line and a high-order curve or surface arises in a large number of finite element applications. Such intersection problems are easy to formulate but hard to solve robustly. We introduce a noniterative method for computing intersections by solving a matrix singular value decomposition and an eigenvalue problem. That is, all intersection points and their parametric coordinates are determined in one-shot using only standard linear algebra techniques available in most software libraries. As a result, the introduced technique is far more robust than the widely used Newton-Raphson iteration or its variants. The maximum size of the considered matrices depends on the polynomial degree q of the shape functions and is 2q × 3q for curves and 6q² × 8q² for surfaces. The method has its origin in algebraic geometry and has here been considerably simplified with a view to widely used high-order finite elements. In addition, the method is derived from a purely linear algebra perspective without resorting to algebraic geometry terminology. A complete implementation is available from http://bitbucket.org/nitro-project/ .     

Determination of crystallinity ratio and some physicochemical properties of poly(4‐methyl‐1‐pentene)

It was determined that the thermal stability of poly(4‐methyl‐1‐pentene) (P4MP) was maintained up to 424°C in an inert atmosphere by thermogravimetric analysis. The retention diagrams of ethyl acetate, tert‐butyl acetate, and benzene on P4MP were plotted at temperatures between 30 and 280°C by inverse gas chromatography (IGC) technique. Melting temperature of the polymer was determined as 230 and 239.5°C by IGC and differential scanning calorimetry (DSC), respectively. The percent crystallinity of P4MP was obtained from the retention diagrams at temperatures below melting point. The percent crystallinity obtained by IGC is in good agreement with the ones obtained by DSC. Then, specific retention volume, V, weight fraction activity coefficient, Ω, Flory‐Huggins polymer‐solvent interaction parameter, χ, equation‐of‐state polymer‐solvent interaction parameter, χ, and effective exchange energy parameter, X_eff of octane, nonane, decane, undecane, dodecane, tridecane, n‐butyl acetate, isobutyl acetate, isoamyl acetate with P4MP, were determined between 240 and 280°C by IGC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009