Microstructure control in functionally graded Al-Si castings

Al-Si functionally graded castings (FGCs) were prepared under centrifugal force. Three compositions were selected; 356, 413 and 390 representing hypoeutectic, eutectic and hypereutectic alloys, respectively. The microstructure and the mechanical properties of the FGCs at different positions were dependent on the centrifugal force. This was more pronounced in 390 FGCs, where the hardness and wear resistance increased towards the inner surface containing the highest volume fraction of primary Si. Grain refining of α-Al was observed in the inner section of 356-FGCs. In 413FGCs, Fe-intermetallics were refined gradually towards the outer surface. Heat treatment spherodized the eutectic Si in case of 356FGCs and increased the hardness from ~60 to 83 (HV). In 390FGCs, precipitation hardening raised the hardness by 20 % while no improvement was observed in 413FGCs. These results emphasize the role of centrifugal force and heat treatment in controlling the microstructure and the mechanical properties of Al-Si FGCs.     

Investigation into Reactions of Starch with Monochlorotriazinyl-β-Cyclodextrin and Application of their Products in Textile Sizing

This article presents a study on the chemical modification of starch and hydrolyzed starches through their reactions with reactive cyclodextrin (RCD). Monochlorotriazinyl-β-cyclodextrin was investigated under a variety of conditions. The results obtained signify that the reaction was favored in an alkaline media rather than an acidic media, and in shorter rather than larger liquor ratios. Maximization of the reaction could also be achieved at 40°C for 60 min. Of the several alkaline catalysts used, NaOH proved to be the best when used at a concentration of 10 g/l. The reaction of starch and hydrolyzed starches with RCD was determined using a concentration of the latter. The apparent viscosity of the resulting polymeric products depends upon both the extent of reaction, expressed as a nitrogen percentage, and the degree of acid hydrolysis prior to the modification. Evidence for involvement of starch and RCD via chemical bonding was obtained through FT-IR analysis. Furthermore, the newly synthesized starch-based polymeric products were applied to a light cotton fabric and further evaluation of the sized materials was conducted by monitoring the size add-on, size removal, and strength properties of the fabric was conducted.     

A method to calibrate a solar pyranometer for measuring reference diffuse irradiance

Accurate pyranometer calibrations, traceable to internationally recognized standards, are critical for solar irradiance measurements. One calibration method is the component summation, where the pyranometers are calibrated outdoors under clear sky conditions, and the reference global solar irradiance is calculated as the sum of two reference components, the diffuse and subtended beam solar irradiances. The beam component is measured with pyrheliometers traceable to the World Radiometric Reference, while there is no internationally recognized reference for the diffuse component. In the absence of such a reference, we present a method to consistently calibrate pyranometers for measuring the diffuse component with an estimated uncertainty of ±(3% of reading+1 W/m²). The method is based on using a modified shade/unshade method, and pyranometers with less than 1 W/m² thermal offset errors. We evaluated the consistency of our method by calibrating three pyranometers four times. Calibration results show that the responsivity change is within ±0.52% for the three pyranometers. We also evaluated the effect of calibrating pyranometers unshaded, then using them shaded to measure diffuse irradiance. We calibrated three unshaded pyranometers using the component summation method. Their outdoor measurements of clear sky diffuse irradiance, from sunrise to sundown, showed that the three calibrated pyranometers can be used to measure the diffuse irradiance to within ±1.4 W/m² variation from the reference irradiance.     

Rheological modeling and finite element simulation of epoxy adhesive creep in FRP-strengthened RC beams

We have shown that a significant creep occurs at the concrete–fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete–FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete–FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained.     

Investigation of improving wear performance of hypereutectic 15%Cr-2%Mo white irons

This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.     

Physico-mechanical and photoluminescence properties of EuxMg2−xSiO4 system sintered under different conditions

This work focuses on sintering of Eu_xMg_2?xSiO₄ (x = 0.0, 0.01, 0.03, 0.05) forsterite ceramics under different conditions and study their microstructures, physico-mechanical and photoluminescence characteristics. The starting materials were waste silica fume, pure MgO and europium oxide (Eu₂O₃). The prepared batches were sintered up to 1500 °C in the presence or absence of carbon in ambient atmosphere. The presence of carbon helped in reduction of Eu³⁺ into Eu²⁺. The effect of sintering conditions and formed phases on the properties of final product were investigated. The results indicated that the specimens sintered without carbon exhibited improved physico-mechanical properties with formation of forsterite and Eu_4.67 (SiO₄)₃O precipitated from the formed liquid phase. While the samples sintered in carbon exhibited lower physic-mechanical properties with formation of forsterite and clinoenstatite. Photoluminescence properties were improved with increasing the amount of added Eu₂O₃ for all sintered samples. The specimens sintered without carbon exhibited life time higher than those sintered in the presence of carbon.     

Non‐steroidal anti‐inflammatory pharmaceutical wastewater treatment using a two‐chambered microbial fuel cell

The two‐chambered microbial fuel cell (MFC) was designed and used for studying the efficiency of the real wastewater treatment from a non‐steroidal anti‐inflammatory pharmaceutical plant as well as from synthetic wastewater containing diclofenac sodium (DS). The removal of the contaminants was expressed regarding chemical oxygen demand (COD) removal, as measured by spectrophotometry experiments. Moreover, the effect of two different types of the cathode on current characteristics and COD removal was investigated. This research showed that the Pt‐coated Ti cathode could lead to higher efficiency of both power density and COD removal. In this case, the results indicated that the maximum power density (P_max) was 20.5 and 6.5 W/m³ and the maximum COD removal was 93 and 78% for MFCs using real and synthetic wastewater, respectively.     

On the self-similarity of 1/f sequences synthesized by recursive filtering

This paper describes an approximate method for synthesizing sequences of statistically self-similar processes and analyses its performance to generate sample sequences with this statistical property. The method is based upon approximating the infinite dimensional difference equation which describes the FARIMA(0, α, 0) model by a finite dimensional difference equation. The parameters estimation for parameterizing the binomial coefficients is performed by using deterministic signal modeling techniques. The three techniques considered are: Prony, Steiglitz MacBride, and Shaw methods. In addition to allow considerable savings in memory requirements and great reduction in computation time, the performance analysis results show that the generated sequences are statistically self-similar in the sense that the estimated Hurst parameter is very close to that imposed in the sequence generator.     

Electrochemically Induced Conformational Change of Di-Boronic Acid-Functionalized Ferrocene for Direct Solid-State Monitoring of Aqueous Fluoride Ions

While fluoride ions (F⁻) are abundant across environmental and biological systems, common procedures and potentiometric sensors for quantifying aqueous F⁻ are inefficient, time-consuming, and suffer from poor pH resiliency and high detection limits. Herein, this work reports a new di-boronic acid-functionalized ferrocene (FDBA) molecular receptor for noncovalent F⁻ recognition, toward the development of a solid-state miniaturized voltammetric fluoride sensor capable of direct and reversible F⁻ detection in drinking water (DW) (pH 6) and community water (pH 7.6–9.1) over the µg L⁻¹–mg L⁻¹ range. The associated sensing mechanism is enabled by the conformational change of FDBA from the open (charge-repelled) to closed (π-dimerized) conformation, which is facilitated by the unique linkage of two electron-accepting phenylboronic acid moieties with the electron-donating ferrocene moiety using rigid conjugated amide linkers. The square wave voltammetric (SWV) oxidation current response of the FDBA-based fluoride sensor is spectroscopically investigated, suggesting a combination of electrooxidation-triggered conformational change of FDBA on a nanocarbon-modified electrode, F⁻ anion–π interactions, and resulting electron transfer between F⁻ and FDBA. The performance of the voltammetric fluoride sensor is compared to that of a commercial liquid junction-based fluoride ion-selective electrode (F-ISE), and of a solid-contact (SC) F-ISE sensor chip, demonstrating significant advantages versus traditional potentiometric F-ISEs.