Preparation of high crystalline nanoparticles of rare-earth based complex pervoskites and comparison of their structural and magnetic properties with bulk counterparts

A simple route to prepare Gd$_{0.7}$Sr$_{0.3}$MnO$_3$ nanoparticles by ultrasonication of their bulk powder materials is presented in this article. For comparison, Gd$_{0.7}$Sr$_{0.3}$MnO$_3$ nanoparticles are also prepared by ball milling. The prepared samples are characterized by X-ray diffraction (XRD),field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscope (XPS), and Superconducting Quantum Interference Device (SQUID) magnetometer. XRD Rietveld analysis is carried out extensively for the determination of crystallographic parameters and the amount of crystalline and amorphous phases. FESEM images demonstrate the formation of nanoparticles with average particle size in the range of 50-100 nm for both ultrasonication and 4 hours (h) of ball milling. The bulk materials and nanoparticles synthesized by both ultrasonication and 4 h ball milling exhibit a paramagnetic to spin-glass transition. However, nanoparticles synthesized by 8 h and 12 h ball milling do not reveal any phase transition, rather show an upturn of magnetization at low temperature. The degradation of the magnetic properties in ball milled nanoparticles may be associated with amorphization of the nanoparticles due to ball milling particularly for milling time exceeding 8 h. This investigation demonstrates the potential of ultrasonication as a simple route to prepare high crystalline rare-earth based manganite nanoparticles with improved control compared to the traditional ball milling technique.Comment: 9 pages, 6 figure

Experimental investigation on synthesis, characterization, stability, thermo-physical properties and rheological behavior of MWCNTs-kapok seed oil based nanofluid

Several researchers devoted their efforts for the thermal conductivity enhancement of Carbon Nanotubes (CNTs) based nanofluids as CNTs have excellent thermal properties. However, limited research is reported on the detailed thermo-physical properties of CNTs and oil based nanofluids. In this work, the one-step method synthesis of a new MWCNTs-Kapok seed oil based nanofluid at constant nanoparticle concentration (0.1 wt./wt.) is reported. The nanofluid is characterized by FESEM, FTIR, visual stability analysis and thermophysical properties are experimentally measured. The viscosity found in the range of (0.049–10.101¿Pa·s), the thermal conductivity of (0.165–0.207¿W/m·K) and enhancement of thermal conductivity (6.1538%) were observed. Moreover, the viscosity decreases, and thermal conductivity increases with an increase in temperature. The experimentally obtained data are found in agreement with existing models and modified correlations. The rheological behavior showed that nanofluid is non-Newtonian in nature and exhibiting shear thinning or pseudo plastic behavior.Preprin

Polyetherimide foams filled with low content of graphene nanoplatelets prepared by scCO2 dissolution

Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shieldingPostprint (published version

Grain refinement efficiency of a new oxide-containing master alloy for aluminium casting alloys

In this study, grain refinement efficiency of a new oxide master alloy based on MgAl2O4 was demonstrated on an A357 alloy. The grain size of the reference alloy was reduced by 50-60% with the addition of the master alloy and introduction of ultrasonic cavitation. A higher addition of master alloy was found to be not benificial in further reducing the grain size.The ExoMet Project, which is co-funded by the European Commission in the 7th Framework Programme (contract FP7-NMP3-LA-2012-280421), by the European Space Agency and by the individual partner organisations

Microstructural modification of recycled aluminium alloys by high-intensity ultrasonication: Observations from custom Al–2Si–2Mg–1.2Fe–(0.5,1.0)Mn alloys

The effect of ultrasonication on the solidification microstructure of recycled Al-alloys is investigated using custom Al–2Si–2Mg-1.2Fe-xMn alloys (x = 0.5 and 1%, in wt.%) through cooling curve measurement, optical and electron microscopy, X-ray diffraction, differential scanning calorimetry and computational thermodynamic calculations. Applying ultrasonication throughout the primary-Al nucleation stage resulted in refined non-dendritic grain structure. Cooling curves indicate a noticeable reduction in primary-Al nucleation undercooling and reduction of the recalescence peak under ultrasonication. However, terminating ultrasonication prior to the nucleation of primary-Al led to dendritic grains with marginal refinement. Without ultrasonication, coarse Chinese-script α−Al15(Fe,Mn)3Si2 intermetallics developed from initially polygonal particles due to interface growth instability under thermo-solutal undercooling. In contrast, ultrasonication produced refined and polygonal α−Al15(Fe,Mn)3Si2 particles by promoting nucleation and growth stabilisation under strong fluid flow. The enhanced nucleation from ultrasonication is presumably due to the pressure-induced shift of freezing point along with improved wetting of insoluble inclusions under cavitation. The present results show that ultrasonication can effectively modify the Fe-intermetallics and refine the grain structure in recycled Al-alloys

Simple one-pot fabrication of ultra-stable core-shell superparamagnetic nanoparticles for potential application in drug delivery

Ultrastable superparamagnetic core-shell nanoparticles of average diameter 80 nm have been fabricated via a simple one-pot method involving superparamagnetic iron oxide nanoparticles (SPIONs) core ([similar]50 nm in diameter) and lipid bilayer shell by high energy ultrasonication. The surface charges (zeta potentials) were measured to be between −15 mV and + 16 mV depending on the batch composition. Anticancer drug mitomycin C (MMC) was loaded into four different samples of variable surface charges in aqueous solution (pH = 6.8) and released in PBS buffer (pH = 7.2) at room temperature. The kinetics of drug loading and releasing data indicated that the stable lipid bilayer coated SPIONs (LBCSPIONs) of nearly neutral surface exhibited the highest loading (10.9 μg of MMC/mg of materials), whereas uncoated or partially coated SPIONs of positive zeta potential exhibited the lowest loading (2.8 and 3.5 μg MMC/mg of materials, respectively). The release behavior of MMC was observed to be highest (5.8 μg MMC/mg of materials) from materials of negative zeta potential compared to materials of near neutral surfaces (3.68 μg MMC/mg of materials). The plausible mechanism of MMC loading and releasing behavior has been explained based on the electrostatic interaction and diffusion through the lipid bilayers. To ensure biocompatibility, the interaction of the prepared SPIONs with human cervical cancer cell line (HeLa) was also investigated using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and ROS (reactive oxygen species) production assay and the results confirmed the super-compatibility of LBCSPIONs

Optimization of cell disruption in Raphidocelis subcapitata and Chlorella vulgaris for biomarker evaluation

Raphidocelis subcapitata and Chlorella vulgaris are bioassay microalgae with rigid cellulosic cell wall which can hinder the release of intracellular proteins often studied as toxicity biomarkers. Since cell disruption is necessary for recovering intracellular biomolecules in these organisms, this study investigated the efficiency of ultrasonication bath; ultrasonication probe; vortexer; and bead mill in disintegrating the microalgae for anti-oxidative enzyme extraction. The extent of cell disruption was evaluated and quantified using bright field microscopy. Disrupted algae appeared as ghosts. The greatest disintegration of the microalgae (83-99.6 %) was achieved using bead mill with 0.42-0.6 mm glass beads while the other methods induced little or no disruption. The degree of cell disruption using bead mill increased with exposure time, beads-solution ratio and agitation speed while larger beads caused less disruption. Findings revealed that bead milling, with specific parameters optimized, is one of the most effective methods of disintegrating the robust algal cells

The effect of different frequencies of ultrasound on the activity of horseradish peroxidase

Ultrasound technology has been studied by food researchers as an alternative method for thermal processing. The use of ultrasound as a way to inactivate and/or activate enzymes has been widely studied at low frequencies (20–40 kHz), however, little research on the effect of high frequencies has been reported. Thus, the effect of high and low frequency ultrasound on commercial horseradish peroxidase with a concentration of 0.005 mg mL−1 is described. Experiments were performed for 60 min using 20, 378, 583, 862, 995, 1144 and 1175 kHz ultrasound at power levels (acoustic energy) between 2.1 and 64 W. Residual activity was monitored using a spectrophotometric method and data analysis was performed using ANOVA. A significant enhancement of enzyme inactivation (p < 0.05) was observed at each frequency with an increase of sonication time and power. Inactivation of peroxidase by ultrasound followed first order kinetics and an increase of the rate constant with the power applied was observed for all the frequencies studied. Overall, low frequency (20 kHz) and low power are not effective on the enzyme inactivation and the level of residual activity remained high. The use of 378 and 583 kHz (48 W) is particularly effective for complete enzyme inactivation

Ultrasonication improves the structures and physicochemical properties of Cassava starch films containing acetic acid

Cassava starch films are fabricated with acetic acid treatment and ultrasonication. Different ultrasound power levels from 200 to 750 W are used and the effects of ultrasonication on the morphology, microstructures, and properties of the starch–acetic acid films are investigated. Scanning electron microscopy shows a cohesive and compact structure of the films resulting from ultrasonication. X‐ray diffraction analysis reveals that the crystalline index is decreased by acid treatment and increased by ultrasonication. The tensile strength and elongation at break of the films first increase and then decrease with increasing ultrasound power level. Ultrasonication also results in higher opacity, higher water barrier performance, and lower water adsorption of the films. Thus, the results show that ultrasonication can be used as a simple and efficient way to modify the morphology, microstructure, and performance of starch–acetic acid films to better meet the application needs