Piezoelectric properties of zinc oxide/iron oxide filled polyvinylidene fluoride nanocomposite fibers

Piezoelectric nanogenerators (PENG) with flexible and simple design have pronounced significance in fabricating sustainable devices for self-powering electronics. This study demonstrates the fabrication of electrospun nanocomposite fibers from polyvinylidene fluoride (PVDF) filled zinc oxide (ZnO)/iron oxide (FeO) nanomaterials. The nanocomposite fiber based flexible PENG shows piezoelectric output voltage of 5.9 V when 3 wt% of ZnO/FeO hybrid nanomaterial is introduced, which is 29.5 times higher than the neat PVDF. No apparent decline in output voltage is observed for almost 2000 s attributed to the outstanding durability. This higher piezoelectric output performance is correlated with the β-phase transformation studies from the Fourier transformation infrared spectroscopy and the crystallinity studies from the differential scanning calorimetry. Both these studies show respective enhancement of 3.79 and 2.16% in the β-phase crystallinity values of PVDF-ZnO/FeO 3 wt% composite. Higher dielectric constant value obtained for the same composite (three times higher than the neat PVDF) confirms the increased energy storage efficiency as well. Thus the proposed soft and flexible PENG is a promising mechanical energy harvester, and its good dielectric properties reveals the ability to use this material as good power sources for wearable and flexible electronic devices.

     

Electrochemical Synthesis of Ammonium Persulfate (NH4)2S2O8 Using Oxygen-Depolarized Porous Silver Cathodes Produced by Powder Metallurgy Methods

Powder Metallurgy and Metal Ceramics - The stage-by-stage mechanism of the reduction process proceeding in an acidic environment in the cathodic depolarization of ammonium sulfate (NH4)2SO4...     

Analysis of a Passive Power Converter as a Nonlinear Feedback System

An orthogonal-flux passive power converter operating under conditions of sinusoidal excitation is analyzed, using a non-linear feedback approach based on the principle of harmonic balance. The stability of possible states of oscillation is discussed via a frequency domain approach. Analytical bounds on system parameters and an expression for the secondary flux oscillation amplitude are derived.     

Optimization of the polymer concrete used for manufacturing bases for precision tool machines

Due to its superior damping ratio, high adhesion and fast curing, polymer concrete is used in manufacturing bases for a wide range of precision machines. The coefficient of thermal expansion for polymer concrete is one of the main parameters that can affect the level of accuracy in precision tool machines. Flexural strength is a fundamental strength of the base. In this study six aggregates (basalt, spodumene, fly ash, river gravel, sand and chalk) were investigated. Polymer concrete samples were prepared with different compositions of aggregates containing the same resin volume fraction (aggregates 83% and risen 17%). A four points flexural test was employed to measure the flexural strength of the polymer concrete samples. The coefficient of thermal expansion for polymer concrete was measured using a custom built device. The preliminary optimum composition, with the highest flexural strength and lowest thermal expansion coefficient, was found to be basalt, spodumene and fly ash. Basalt, sand and fly ash composition was the second in the rank. The second composition was nominated for further optimization in terms of resin volume fraction in consideration of its ability to adapt a smaller amount of resin. Different samples of polymer concrete were prepared with a variety of resin volume fractions as follows; 17%, 15% and 13%. The resin volume fraction has been demonstrated to have a significant effect on the coefficient of thermal expansion and flexural strength for polymer concrete. The final optimized composition was basalt, sand and fly ash (filler 87% and resin 13%). ANSYS 13 software was employed in visualizing the influence of polymer concrete compositions on the thermal expansion of the base and how it affected the level of precision of the tool machine.     

Enhanced frontier-based exploration for indoor environment with multiple robots

In this paper, the exploration and map-building of unknown environment by a team of mobile robots is intensively investigated. A new exploration technique is proposed to increase the exploration efficiency. In particular, the new technique has two main objectives: firstly, it aims at reducing the exploration time and the traveled distance by reducing the overlap which takes place when a certain area in the environment is explored by more than one robot. To achieve this, a new procedure to assign the next target location for each individual robot is proposed. And secondly, it aims at reducing computations complexity required by target selection and path planning tasks. More importantly, the proposed technique obviates the need for environment segmentation complex procedures which is adopted in some previous important research works. The new technique is intensively tested with different environments. The results showed the effectiveness of the proposed technique.     

A combined device for the joint study of the surface tensions and electron work functions of liquid-metal melts at low temperatures

The design and test data of the combined device, which is intended to simultaneously measure the surface tensions and electron work functions of metals and alloys in static high-vacuum conditions in a temperature range of 60–400 K, are given. The measurements of the electron work function of pure Na, K, Rb, and Cs and near-eutectic alloys of the ternary Na-K-Cs system showed high reliability and accuracy of the obtained data.     

Hydrogenation of p‐Nitrophenol to p‐Aminophenol as a Test Reaction for the Catalytic Activity of Supported Pt Catalysts

Hydrogenation of p‐nitrophenol (PNP) to p‐aminophenol (PAP) using NaBH₄ as a reducing agent was studied as a test reaction for determining the catalytic activity of supported Pt catalysts. The initial reaction rate, which is accessible within less than 10 min via online UV‐vis spectroscopy at room temperature, ambient pressure, and in water as solvent, was applied as measure for catalytic activity. For three Pt catalysts supported on porous SiO₂, porous glass, and Al₂O₃, respectively, significant differences in the catalytic activity by almost one order of magnitude were observed. However, especially in the case of very active catalysts, limitations of the reaction by internal or external mass transfer have to be considered.     

Charge transport mechanism of graphite‐nanosheet‐loaded rubber nanocomposites

Nitrile butadiene rubber loaded with different concentrations of thin graphite nanosheets have been successfully prepared by using a two‐roll mill. The percolation concentration of the nanocomposites was 0.5 phr. The I–V characteristic curves showed that the nanocomposites exhibited ohmic behaviour at a certain voltage and then non‐linear behaviour. The Richardson–Schottky and Poole–Frenkel models were used to investigate the reason for the space charge. The experimental data fit the Schottky model well. The conductivity as a function of temperature was also studied and the data were fitted by using the Mott relation. The Mott relation showed that as the concentration of graphite nanosheets in the rubber composite increases, the hopping distance between the graphite nanosheet layers decreases, which enhances the conductivity of the nanocomposite at low concentrations. Copyright © 2011 Society of Chemical Industry     

Physicochemical properties of nanopowdered eggshell

This study was carried out to investigate the physicochemical properties of nanopowdered eggshell (NPES). These characteristics were determined based on the particle size, particle morphology, zeta potential, moisture sorption behaviour, purity and crystallinity. Homogeneous, aggregated and spherical crystals of NPES particles were observed through scanning electron microscope and transmission electron microscope. The average particle sizes of NPES and powdered eggshell (PES) were 202.3 ± 28.9 nm and 113.89 ± 79.37 μm, respectively. Zeta potentials of NPES (?15.41 mV) suggested an incipient instability of the colloidal system. Moisture sorption analysis indicated a higher water adsorption capacity of NPES than that of PES. X‐ray diffractometer (XRD) analysis confirmed the presence of calcite in both NPES and PES. The chemical compositions of the NPES and PES particles were strongly associated with the presence of calcium carbonate, as determined by the Fourier transform infrared (FTIR) spectra. Therefore, eggshell nanopowder has a great potential to be utilised as a component for biomedical applications.