The effect of annealing on the structure,magnetic properties and AC heating of CoFe2O4 for biomedical applications

Single and nanosized spinel CoFe₂O₄ phase has been prepared successfully by a simple combination of mechanical milling from a mixture of Fe₂O₃ and Co₃O₄ powder precursors followed by a subsequent annealing. X-ray diffraction analysis reveals that the estimated crystallite size of CoFe₂O₄ increases with increasing temperature but remains at the nanoscale, i.e. 85 nm at 900 °C. Moreover, magnetic measurements show that a great enhancement in the saturation magnetization was achieved whereas a large hysteresis loop was observed (i.e.72 emu/g at 900 °C). Evaluation and applicability of CoFe₂O₄ nanoparticles under high frequency AC magnetic field for heating in biomedical applications were examined. It was found that under fixed amplitude (516 Oe) and frequency (229 kHz), the prepared nanoparticles generate significant heat: after 5 s the temperature was around 97 °C for the as-milled powder and reached almost 178 °C for the powder annealed at 900 °C.     

A preliminary study on the development of an easy method for beef freshness using a cyclic voltammetric system

This study was carried out to develop an easy method for beef freshness using a cyclic voltammetric system. Prime graded (USDA) beef loin at 48 h postmortem was cut into pieces 3 cm thick, packaged into commercial plastic zipper bag, and then stored at 4 °C for 0, 3, 6 and 9 days. A commercial cyclic voltammetry and data processing software were used for this study and the interdigitated electrode was fabricated according to semiconductor manufacturing. The homogenated beef was filtered through Whatman No. 1 filter paper and 250 μL of the filtrate was applied on the interdigitated electrode sensor chip for electrochemical detection. Electrochemical signals changed as storage periods increased. The shape of the cyclic voltammogram changed from a roundish curve to a shapely curve. Redox values (V) also increased during storage. Electrochemical signals matched well with lipid oxidation values (Thiobarbituric acid reactive substances: TBARS). A linear relationship between redox value and TBARS was obtained with a correlation factor of 0.957. Thus, the electrochemical signal of a cyclic voltammetric system can be used as an indicator of beef freshness.     

The effect of recycled plastic aggregate on chemico-physical and functional properties of composite mortars

In this paper the interaction mechanism between recycled plastic aggregates and lime matrix in composite mortars was investigated by means of thermal, morphological and Fourier Transform Infrared Spectroscopy (FTIR) analyses. In order to assess the fire behavior of the composite mortars, a cone calorimeter method was adopted. The plastic aggregate, mainly made of polyolefin and polyethylene terephthalate, is obtained from an industrial waste, through a process that provides a plasticization and densification by extrusion of plastic waste. Several composite mortars were prepared by replacing silica powder with 10%, 15% and 20% of recycled aggregate. Experimental results attest that, even if the filler was not chemically modified, there is a good chemical interaction between the plastic aggregate and mortar, involving a reduction of the negative effects on physical and functional properties of the mortar composites, such as thermal degradation and fire resistance. In fact all the specimens showed a scarce sensitivity to flashover, and can be classified as low risk materials.     

Porous graphene networks as high performance anode materials for lithium ion batteries

Porous graphene obtained by chemical vapor deposition (CVD) using porous MgO sheets as template is demonstrated to exhibit a high reversible capacity (1723 mAh g^-1), excellent high-rate capability and cycling stability for Li-ion batteries. The simple CVD approach offers a new way for large-scale production of porous graphene materials for energy storage.     

Doping effect on secondary phases,microstructure and electrical conductivities of LaGaO3 based perovskites

The intermediate temperature electrolytes La_1?xSr_xGa_1?yMg_yO_3?δ (LSGM, where δ = (x + y)/2) with perovskite structure were prepared using a poly(vinyl alcohol) (PVA) solution polymerization method. Three secondary phases were identified by X-ray diffraction, LaSrGaO₄, LaSrGa₃O₇ and La₄Ga₂O₉. The relative amount of these secondary phases depended on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. LaSrGaO₄ could not be detected by SEM for the sintered pellets. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased conductivity activation energy. La_0.8Sr_0.2Ga_0.9Mg_0.1O_2.85 had the highest ionic conductivity σ = 0.128 S/cm at 800 °C in this work.     

An investigation on shape memory behaviours of hydro-epoxy/glass fibre composites

Shape-memory polymers (SMPs) have the capacity to return large strains by external stimuli. Among various SMPs, shape-memory epoxy has received considerable attention because of its superior mechanical and thermal properties as well as excellent shape-memory performance. In this study, short glass fibre-reinforced shape-memory hydro-epoxy composites are developed to improve further the mechanical property of shape-memory epoxy resin. The thermomechanical and shape-memory properties of the developed composite materials are investigated by dynamic mechanical analysis, bend test and shape recovery test. The results indicate that the glass modulus and bend strength of the developed composite materials initially increase and then slightly decrease with increasing short glass fibre content. The glass transition temperature of the developed composite materials does not change with increasing short glass fibre. When the short glass fibre content is less than 4.5 wt.%, full recovery can be observed after only several minutes at different temperatures. The shape-memory property of the composite materials is not affected greatly. However, when the short glass fibre content is more than 4.5 wt.%, the material would be destroyed after deformation.     

Thermal stability of nanostructured 13 wt% Al2O3–8 wt% Y2O3–ZrO2 thermal barrier coatings

Nanostructured 13 wt% Al₂O₃–8 wt% Y₂O₃–ZrO₂ (13AlYSZ) coatings were developed by atmospheric plasma spraying (APS). The phase structure and the morphology of the 13AlYSZ coatings were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). It was found that the as-sprayed coatings mainly consisted of tetragonal zirconia, with the Al element solid solution in ZrO₂. Heat treatment at 1100 °C increased the average grain size of the ZrO₂ phase from 61 to 120 nm and decreased the porosity from 23.8 to 18%. The addition of the nano-Al₂O₃ can effectively inhibit the grain growth of the zirconia phase. The mechanism on inhibiting the grain growth of nanostructured 8 wt% Y₂O₃–ZrO₂ thermal barrier coatings has been discussed in detail.     

Reverse saturable absorption of fullerodendrimers in porous SiO2 sol–gel matrices

The non-linear absorption properties and the dynamics of porous sol–gel SiO₂ glasses, doped with fullerodendrimers, i.e., fullerene derivatives functionalized with dendritic branches have been investigated using a double-pump–probe technique. A frequency doubled mode locked Nd:YAG laser (25 ps (FHWM), 532 nm) was applied as irradiation source. A reverse saturable absorption (induced absorption) in the samples containing the fullerodendrimers has been observed. A similar induced absorption was also obtained in the pure C₆₀ samples. In addition, the dendritic branches, which prevent aggregation of the molecules, lead also to an increase of the triplet quantum yield due to a faster singlet–triplet relaxation.     

Investigation of oxygen annealing effects on RF sputter deposited SiC thin films

Amorphous silicon carbide films were deposited by RF sputtering technique using a SiC target. These films were annealed in dry oxygen ambient in the temperature range of 400–700 °C. Subsequently the films were characterized using X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition at each annealing temperature. XPS indicated that increasing the anneal temperature results in a decrease in SiC phase, and an increase in SiO_x. Surface morphology of the oxidized films was characterized using atomic force microscope. Optical absorption studies indicated blue shifting effects as the annealing temperature was increased.     

Properties and application of lead–calcium–tin–aluminium–bismuth alloys for positive grids

The effects of bismuth addition less than 0.05 wt% on the electrochemical properties of lead–calcium–tin–aluminum alloys were investigated in detail. Passivation and corrosion phenomena were investigated by cyclic voltammetry, electrochemical impedance spectra, linear sweep voltammetry. The effect of bismuth on oxygen evolution and hydrogen evolution were also discussed. The experimental results show that the addition of bismuth leads to the decreases of the hydrogen overpotential and increase of the hydrogen evolution rate. Oxygen evolution rate increases with the increase of content of bismuth. The measurements of cyclic voltammetry suggested that bismuth may promote the formation of lead dioxide. A key result was that the presence of bismuth might have beneficial effect on the formation of Pb(II).