Microstructure,wear and corrosion characteristics of multiple-reinforced (SiC–B4C–Al2O3) Al matrix composites produced by liquid metal infiltration

In this study, AA7075 aluminum matrix composites reinforced with the combination of SiC, Al₂O₃, and B₄C particles were fabricated by the liquid metal infiltration method. The effects of the relative ratio of B₄C and Al₂O₃ particles on the microstructural, wear, and corrosion features of the composite samples were analyzed using XRD, light metal microscopy, SEM, EDS, Brinell hardness, ball-on-disc type tribometer, and potentiodynamic polarization devices. It was determined that infiltration occurred more successfully, and homogenously distributed particles with reduced porosity were obtained as the amount of Al₂O₃ increased. Worn surface studies revealed that the specimens were predominantly worn by abrasion and adhesion. The increase in B₄C/Al₂O₃ ratio caused a decrease in the hardness and wear strength, whereas it increased the corrosion resistance.     

Flexible poly(styrene-ethylene-butadiene-styrene) hybrid nanofibers for bioengineering and water filtration applications

Among the thermoplastic elastomers that play important roles in the polymer industry due to their superior properties, styrene-based species and polyurethane block copolymers are of great interest. Poly(styrene-ethylene-butadiene-styrene) (SEBS) as a triblock copolymer seems to have the potential to meet many demands in different applications due to various industrial requirements where durability, biocompatibility, breaking elongation, and interfacial adhesion are important. In this study, the SEBS triblock copolymer was functionalized with natural (Satureja hortensis, SH) and synthetic (nanopowder, TiO₂) agents to obtain composite nanofibers by electrospinning and electrospraying methods for use in biomedical and water filtration applications. The results were compared with thermoplastic polyurethane (TPU) composite nanofibers, which are commonly used in these fields. Here, functionalized SEBS nanofibers exhibited antibacterial effect while at the same time improving cell viability. In addition, because of successful water filtration by using the SEBS composite nanofibers, the material may have a good potential to be used comparably to TPU for the application.     

Inhibition of atmospheric corrosion of mild steel by sodium benzoate treatment

The objective of this study was to evaluate the effectiveness of sodium benzoate as an inhibitor to slow down or prevent atmospheric corrosion/discoloration of the local mild steel during storage in the Arabian Gulf region. Test specimens were prepared from locally produced reinforcing steel products. The inhibitor solution was applied on steel specimens at a concentration of 100 mM for 1 day at room temperature. Wooden exposure racks were used to hold as-received and inhibitor-treated specimens during atmospheric exposure for different periods. Corrosion was evaluated through weight loss determination and electrochemical technique. As expected, the Arabian Gulf atmosphere was corrosive on the as-received local mild steel. On the other hand, treatment of steel with sodium benzoate lowered its corrosion rate during initial days of its exposure to atmosphere. However, atmospheric corrosion inhibition performance of sodium benzoate deteriorated with exposure time after 30 or more days of atmospheric exposure, and the corrosion rates of sodium benzoate-treated specimens reached that of the unprotected specimens at the end of 90 days of atmospheric exposure.     

Production of hydrogen over bimetallic Pt–Ni/δ-Al2O3: I. Indirect partial oxidation of propane

Indirect partial oxidation (IPOX) of propane was studied over bimetallic 0.2 wt.% Pt–15 wt.% Ni/δ-Al₂O₃ catalyst in the 623–743 K temperature range. The unreduced and reduced forms of the catalyst were characterized by ESEM–EDAX and X-ray diffraction (XRD). In the IPOX tests, the effects of steam to carbon ratio (S/C), carbon to oxygen ratio (C/O₂) and residence time (W/F (g_cat h/mol HC)) on the hydrogen production activity, selectivity and product distribution were studied in detail. The effect of temperature program applied (increasing from 623 to 743 K, ITP; decreasing from 743 to 623 K, DTP) during reaction was also tested. The results showed that the Pt–Ni bimetallic system has superior performance characteristics compared to the monometallic catalysts reported in literature. The reason is thought to be the utilization of the catalyst particles as micro heat exchangers during IPOX; the heat generated by Pt sites during exothermic total oxidation (TOX) being readily transferred through the catalyst particles acting as micro heat exchangers to the Ni sites, which promote endothermic steam reforming (SR). The optimal conditions were found as S/C = 3, C/O₂ = 2.70 and W/F = 0.51 g_cat h/mol HC for IPOX of propane on the basis of high hydrogen productivity and selectivity between 623 and 748 K for the experimental conditions tested. The thermo-neutral points obtained showed the sustainability of reaction in terms of energy.     

Electrical and optical properties of fluorine-doped CdO films deposited by ultrasonic spray pyrolysis

The CdO:F samples have been deposited onto microscope glass substrates at 250 °C by ultrasonic spray pyrolysis method. With the incorporation of fluorine into CdO, the direct optical transition has shifted towards the shorter wavelengths, and the transparency of the material has increased at a given wavelength above the fundamental absorption edge. The shift in the absorption edge is explained by means of the Moss–Burstein effect, which is also supported with the results of the current–voltage characteristics. Here, a correlation has been established between the band broadening and the increase in conductivity due to the increase in carrier density.     

Soluble and conductive polypyrrole copolymers containing silicone tegomers

Soluble and processable conductive copolymers of silicone tegomers and pyrrole were developed. This was easily accomplished by the oxidative polymerization of pyrrole monomer by Ce(IV) salt in the presence of silicone tegomers with hydroxyl chain ends. The resulting copolymers were soluble in dimethylformamide. The products were characterized by Fourier transform infrared, ¹H‐NMR, and four‐point probe conductivity, and their surface properties were investigated with contact‐angle measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2896–2901, 2003     

Thermodynamic analysis of solar photovoltaic cell systems

The thermodynamic characteristics of solar photovoltaic (PV) cells are investigated from a perspective based on exergy. A new efficiency is developed that is useful in studying PV performance and possible improvements. Exergy analysis is applied to a PV system and its components, and exergy flows, losses and efficiencies are evaluated. Energy efficiency is seen to vary between 7% and 12% during the day. In contrast, exergy efficiencies, which incorporate the second law of thermodynamics and account for solar irradiation exergy values, are lower for electricity generation using the considered PV system, ranging from 2% to 8%. Values of “fill factors” are determined for the system and observed to be similar to values of exergy efficiency.