Reliability of ferrocement slabs under cyclic thermal-shock loading

The reliability of ferrocement slabs subjected to cyclic thermal-shock loading induced by raindrops during service is investigated. The data are obtained experimentally by subjecting specimens to heating and wetting cycles and monitoring the residual first-crack strength at different periods. The imposed thermal-shock loads simulate actual service conditions and are estimated by monitoring the temperature of typical roofing slabs just before the commencement of rain over a period of time. The mean deterioration in strength obtained after correcting for curing effects due to ageing and temperature, as well as the uncertainty present, are used to assess the reliability of slabs having residual first-crack strengths above some prescribed values at different periods. The results indicate that ferrocement slabs posses good flexural resistance with respect to the cyclic loadings studied and are suitable for use as roofing elements.     

A Review of Photocatalysis using Self‐organized TiO2 Nanotubes and Other Ordered Oxide Nanostructures

Photocatalytic approaches, that is the reaction of light‐produced charge carriers at a semiconductor surface with their environment, currently attract an extremely wide scientific interest. This is to a large extent due to the high expectations: i) to convert sunlight directly into an energy carrier (H₂), ii) to stimulate chemical synthetic reactions, or iii) to degrade unwanted environmental pollutants. Since the early reports in 1972, TiO₂ has been the most investigated photocatalytic material by far; this originates from its outstanding electronic properties that allow for a wide range of applications. Not only the material, but also its structure and morphology, can have a considerable influence on the photocatalytic performance of TiO₂. In recent years, particularly 1D (or pseudo 1D) structures such as nanowires and nanotubes have received great attention. The present Review focuses on TiO₂ nanotube arrays (and similar structures) that grow by self‐organizing electrochemistry (highly aligned) from a Ti metal substrate. Herein, the growth, properties, and applications of these tubes are discussed, as well as ways and means to modify critical tube properties. Common strategies are addressed to improve the performance of photocatalysts such as doping or band‐gap engineering, co‐catalyst decoration, junction formation, or applying external bias. Finally, some unique applications of the ordered tube structures in various photocatalytic approaches are outlined.     

Electrical conduction in evaporated terbium fluoride thin films

The current-voltage characteristics of thin-film capacitors with evaporated terbium fluoride dielectric have been studied as a function of temperature (in the range 300 to 418 K). For sufficiently high electric fields (> 10⁴ V cm^–1, the leakage current is found to increase exponentially with the square root of the applied electric field. Analysis of the data suggests an electrode-limited mechanism such as that suggested by Schottky. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field. Dielectric break-down and its dependence on film thickness have also been investigated. Break-down field strength follows the Forlani-Minnaja relation.     

Visualization of internal energy flows in optical fields carrying a pair of fractional vortices

The internal energy flows resulting from the azimuthal component of optical currents in beams carrying a pair of fractional vortices during propagation have been experimentally detected in a knife edge test. Two optical vortices of fractional charge in a beam pair up by means of a connecting dark intensity line between intensity zeros of the vortices. Independent of the polarity of the fractional vortices, this pairing up process occurs. This is in contrast to the isolated intensity null points of vortices of integer charges and thus calls for a study on the internal energy flows in such beams.     

Effect of Fiber Bridging Stress on the Fracture Resistance of Silicon-Carbide-Fiber/Zircon Composites

The room-temperature fracture-resistance behavior ( R -curve) of unidirectional silicon-carbide-fiber-reinforced zircon-matrix composites has been studied experimentally and numerically. The composites showed strong rising R -curve behavior from experimental results that used in situ crack-length measurements taken via optical microscopy as well as the compliance method. A numerical calculation, based on the available models, then was performed to determine the bridging-stress function from the experimental R -curve. In addition, the effect of the residual stress and constituent properties on the bridging-stress function also has been considered in the numerical calculations. These results have indicated that the bridging-stress function, which controls the fracture resistance of ceramic composites, can be obtained from the carefully measured R -curve.     

Preparation of a functional nanofibrous polymer membrane incorporated with poly(2-aminothio phenol) stabilized gold nanoparticles

Functional nanofibrous polymer membranes were prepared by incorporating poly(2-aminothio phenol) (P2AT) stabilized Au NPs onto electrospun polyvinylidene fluoride (PVdF) nanofibers (designated as P2AT-Au NPs@PVdF-NFM). The preparation of P2AT-Au NPs@PVdF-NFM involves two steps: loading of 2AT (monomer) into electrospun PVdF nanofibrous membrane and polymerization of 2AT by gold chloride. P2AT and Au NPs were simultaneously formed into the electrospun PVdF-NFM. Transmission electron microscope image of P2AT-Au NPs@PVdF-NFM informs the presence of Au NPs (with sizes ~10 nm) onto PVdF-NFM.     

Thermal stress and probability of failure analyses of functionally graded solid oxide fuel cells

Thermal stresses and probability of failure of a functionally graded solid oxide fuel cell (SOFC) are investigated using graded finite elements. Two types of anode-supported SOFCs with different cathode materials are considered: NiO-YSZ/YSZ/LSM and NiO-YSZ/YSZ/GDC-LSCF. Thermal stresses are significantly reduced in a functionally graded SOFC as compared with a conventional layered SOFC when they are subject to spatially uniform and non-uniform temperature loads. Stress discontinuities are observed across the interfaces between the electrodes and the electrolyte for the layered SOFC due to material discontinuity. The total probability of failure is also computed using the Weibull analysis. For the regions of graded electrodes, we considered the gradation of mechanical properties (such as Young’s modulus, the Poisson’s ratio, the thermal expansion coefficient) and Weibull parameters (such as the characteristic strength and the Weibull modulus). A functionally graded SOFC showed the least probability of failure based on the continuum mechanics approach used herein.     

Low Pressure DC Glow Discharge Air Plasma Surface Treatment of Polyethylene (PE) Film for Improvement of Adhesive Properties

The present work deals with the change in surface properties of polyethylene (PE) film using DC low pressure glow discharge air plasma and makes it useful for technical applications. The change in hydrophilicity of the modified PE film surface was investigated by measuring contact angle and surface energy as a function of exposure time. Changes in the morphological and chemical composition of PE films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap-shear strength. The results show that the wettability and surface energy of the PE film has been improved due to the introduction of oxygen-containing polar groups and an increase in surface roughness. The XPS result clearly shows the increase in concentration of oxygen content and the formation of polar groups on the polymer surface. The AFM observation on PE film shows that the roughness of the surface increased due to plasma treatment. The above morphological and chemical changes enhanced the adhesive properties of the PE film surfaces, which was confirmed by T-peel and lap-shear tests.     

In-vitro digestibility,textural and quality characteristics of ditalini pasta fortified with green banana flour and its type -IV modified starch

Resistant starch in unripe banana offers a possibility to alter the glycemic properties in convenience foods, such as pasta. In this study, pasta formulations were tried by replacing 30% semolina with varying proportions of green banana flour (GBF) and banana-modified starch (MS). The effect of substitution on physicochemical and functional properties, including in-vitro starch digestibility, antioxidant property and consumer acceptability, was evaluated. Among the composite flours, MS recorded higher swelling power and water holding capacity. The replacement of semolina with GBF resulted in higher resistant starch, 4–5 times enhanced indigestible fraction, phenols, flavonoids and antioxidant activity in pasta. Pronounced increment was also observed in potassium, calcium and magnesium content in blended pasta. Optimal cooking time was reduced with the addition of GBF, whereas it was enhanced with MS. GBF and MS in the blends, decreased the hydrolysis rate (up to 24%) and glycemic index (up to 17%) of pasta. However, the addition of MS beyond 10% negatively influenced springiness and chewiness. Microstructural studies explained the positive structural changes with the addition of GBF and MS. Sensory attributes disclosed that the addition of 25% GBF and 5% MS is a desirable proportion for pasta with a functional characteristics.