Microwave Assisted Synthesis of Nanostructured Titanium Dioxide with High Photocatalytic Activity

TiO2 (anatase) was synthesized using a microwave-irradiation-assisted chemical method. The reaction conditions were varied to obtain unique nanostructures of TiO2 comprising nanometric spheres giving the materials a very porous morphology. The oxide was characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The specific surface area and porosity were quantified by the BET method, and the degradation of dyes was carried out using these materials. The photocatalytic activity of the nanometric TiO2 was significantly higher than that of commercially available TiO2 (Degussa P25) for the degradation of the dyes.

Thin film amorphous semiconductor microwave switches

Microwave switches operating in the X band were designed and fabricated using amorphous chalcogenide semiconductors of composition GexTeyAsz. Threshold devices were shown to operate as microwave modulators at modulation frequencies of up to 100 MHz. No delay time was observed at the highest frequency although the modulation efficiency decreased above 10 MHz owing to the finite recovery time which was approximately 0.3 × 10−8s. The devices can also be used as variolossers, the insertion loss being 0.5 dB in the OFF state and increasing on switching from 5 dB at 1 mA device current to 18 dB at 100 mA.The behaviour of the threshold switches can be explained in terms of the formation of a conducting filament in the ON state with a constant current density of 2 × 104Acm−2 that is shunted by the device capacitance. The OFF state conductivity σ varies as ωn (0.5 < n < 1) which is characteristic of hopping in localized states. However, there was evidence of a decrease in n or a saturation of the conductivity at high frequencies.As a result of phase separation memory switches require no holding current in the ON state and may be used as novel latching semiconductor phase-shifters.

Acceleration of ortho ester Claisen rearrangement by a commercial microwave oven

Microwave irradiation, using a commercial microwave oven accelerates (in 10–15 min) the three-step ortho ester Claisen rearrangement of allyl and propynyl alcohols in dry DMF in open Erlenmeyer flasks.

Comparison of the effect of processing parameters and degradation on the DC and microwave properties of thin films and polycrystalline bulk high-Tc superconducting materials

The sharp increase in microwave power loss (the reverse of what has previously been reported) at the transition temperature in high-Tc superconducting systems such as YBaCu oxide (polycrystalline bulk and thin films obtained by the laser ablation technique) and BiPbSrCaCu oxide is reported. The differences between DC resistivity ( rho ) and the microwave power loss (related to microwave surface resistance) are analysed from the data obtained by a simultaneous measurement set-up. The influence of various parameters, such as preparation conditions, thickness and aging of the sample and the probing frequency (6-18 GHz), on the variation of microwave power loss with temperature is outlined.

Integrated climatic impacts of forestry and fibre-based packaging

The purpose of this study was to examine the integrated climatic impacts of forestry and the use fibre-based packaging materials. The responsible use of forest resources plays an integral role in mitigating climate change. Forests offer three generic mitigation strategies; conservation, sequestration and substitution. By conserving carbon reservoirs, increasing the carbon sequestration in the forest or substituting fossil fuel intensive materials and energy, it is possible to lower the amount of carbon in the atmosphere through the use of forest resources. The Finnish forest industry consumed some 78 million m3 of wood in 2009, while total of 2.4 million tons of different packaging materials were consumed that same year in Finland. Nearly half of the domestically consumed packaging materials were wood-based. Globally the world packaging material market is valued worth annually some €400 billion, of which the fibre-based packaging materials account for 40 %. The methodology and the theoretical framework of this study are based on a stand-level, steady-state analysis of forestry and wood yields. The forest stand data used for this study were obtained from Metla, and consisted of 14 forest stands located in Southern and Central Finland. The forest growth and wood yields were first optimized with the help of Stand Management Assistant software, and then simulated in Motti for forest carbon pools. The basic idea was to examine the climatic impacts of fibre-based packaging material production and consumption through different forest management and end-use scenarios. Economically optimal forest management practices were chosen as the baseline (1) for the study. In the alternative scenarios, the amount of fibre-based packaging material on the market decreased from the baseline. The reduced pulpwood demand (RPD) scenario (2) follows economically optimal management practices under reduced pulpwood price conditions, while the sawlog scenario (3) also changed the product mix from packaging to sawnwood products. The energy scenario (4) examines the impacts of pulpwood demand shift from packaging to energy use. The final scenario follows the silvicultural guidelines developed by the Forestry Development Centre Tapio (5). The baseline forest and forest product carbon pools and the avoided emissions from wood use were compared to those under alternative forest management regimes and end-use scenarios. The comparison of the climatic impacts between scenarios gave an insight into the sustainability of fibre-based packaging materials, and the impacts of decreased material supply and substitution. The results show that the use of wood for fibre-based packaging purposes is favorable, when considering climate change mitigation aspects of forestry and wood use. Fibre-based packaging materials efficiently displace fossil carbon emissions by substituting more energy intensive materials, and they delay biogenic carbon re-emissions to the atmosphere for several months up to years. The RPD and the sawlog scenarios both fared well in the scenario comparison. These scenarios produced relatively more sawnwood, which can displace high amounts of emissions and has high carbon storing potential due to the long lifecycle. The results indicate the possibility that win-win scenarios exist by shifting production from pulpwood to sawlogs; on some of the stands in the RPD and sawlog scenarios, both carbon pools and avoided emissions increased from the baseline simultaneously. On the opposite, the shift from packaging material to energy use caused the carbon pools and the avoided emissions to diminish from the baseline. Hence the use of virgin fibres for energy purposes, rather than forest industry feedstock biomass, should be critically judged if optional to each other. Managing the stands according to the silvicultural guidelines developed by the Forestry Development Centre Tapio provided the least climatic benefits, showing considerably lower carbon pools and avoided emissions. This seems interesting and worth noting, as the guidelines are the current basis for the forest management practices in Finland.

Microwave Irradiation Assisted Method for the Rapid Synthesis of fine Particles of alpha Al2O3 And alpha (Al1-XCrx)(2)O-3 And Their Coatings on Si(100)

Chromium substituted beta diketonate complexes of aluminium have been synthesized and employed as precursors for a novel soft chemistry process wherein microwave irradiation of a solution of the complex yields within minutes well crystallized needles of alpha (Al1 XCrx)(2)O-3 measuring 20 30 nm in diameter and 50 nm long By varying the microwave irradiation parameters and using a surfactant such as polyvinyl pyrrolidone the crystallite size and shape can be controlled and their agglomeration prevented These microstructural parameters as well as the polymorph of the Cr substituted Al2O3 formed may also be controlled by employing a different complex Samples of alpha (Al1 XCrx)(2)O-3 have been characterized by XRD FTIR and TEM The technique results in material of homogeneous metal composition, as shown by EDAX and can be adjusted as desired The technique has been extended to obtain coatings of alpha (Al1 XCrx)(2)O-3 on Si(100)

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO2/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 degrees C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications. (C) 2010 Elsevier B.V. All rights reserved.

Electro-magnetically Actuated Minute Polymer Pump Fabricated using Packaging Technology

Design, fabrication and preliminary testing of a flat pump with millimetre thickness are described in this paper. The pump is entirely made of polymer materials barring the magnet and copper coils used for electromagnetic actuation. The fabrication is carried out using widely available microelectronic packaging machinery and techniques. Therefore, the fabrication of the pump is straightforward and inexpensive. Two types of prototypes are designed and built. One consists of copper coils that are etched on an epoxy plate and the other has wound insulated wire of 90 mu m diameter to serve as a coil. The overall size of the first pump is 25 mm x 25 mm x 3.6 mm including the 3.1 mm-thick NdFeB magnet of diameter 12 mm. It consists of a pump chamber of 20 mm x 20 mm x 0.8 mm with copper coils etched from a copper-clad epoxy plate using dry-film lithography and milled using a CNC milling machine, two passive valves and the pump-diaphragm made of Kapton film of 0.089 mm thickness. The second pump has an overall size of 35 mm x 35 mm x 4.4 mm including the magnet and the windings. A breadboard circuit and DC power supply are used to test the pump by applying an alternating square-wave voltage pulse. A water slug in a tube attached to the inlet is used to observe and measure the air-flow induced by the pump against atmospheric pressure. The maximum flow rate was found to be 15 ml/min for a voltage of 2.5 V and a current of 19 mA at 68 Hz.

Non-resonant RF and microwave response: A novel technique for the characterization of superconducting materials

When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the high T-c superconductors give rise to intense, low field, 'non-resonant' absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such as J(c) and H-c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed

Surface barrier effects in non-resonant microwave absorption by superconducting thin films of YBa2Cu3O7??

We present an unusual temperature dependence of hysteresis in the Lion resonant microwave absorption (NRMA) signals from superconducting thin films of YBa2Cu3O7-delta. We observe that the hysteresis increases with increase in temperature till T-c which we interpret as evidence for the presence of Bean-Livingston surface barriers (BLSB) in the single crystalline films.

Application of microwave heating technique for rapid synthesis of ?,?-unsaturated esters

The use of microwave heating technique for the acceleration of ortho ester Claisen rearrangement (a three step transformation) is described. Irradiation of a DMF solution of the allyl alcohol 5, triethyl orthoacetate and propionic acid (catalytic) in an Erlenmeyer flask for 10 minutes in a microwave oven generated the ester 8 in 83% yield. Analogously, ortho ester Claisen rearrangement of a variety of allyl and propargyl alcohols (9, 12-22) were achieved. The formation of the diester 10 from 2-butyne-1,4-diol (9) via the ortho ester Claisen rearrangement of two allyl alcohol moieties (involving sh steps) in 15 minutes, demonstrates the versatility of the microwave heating technique.

Microwave assisted synthesis and UV-Vis spectroscopic studies of silver nanoparticles synthesized using vanillin as a reducing agent

The present investigation explores the adaptability of a microwave assisted route to obtain silver nanoparticles by the reduction of AgNO3 with vanillin, an environmentally benign material. Anionic surfactants such as AOT and SDS were used separately for encapsulating AgNPs and their role was compared. The UV-Visible absorption spectra present a broad SPR band consisting of two peaks suggesting the formation of silver nanoparticle with bimodal size distribution. The TEM image shows particles with spherical and hexagonal morphologies which confirms the results of UV-Vis studies. The anisotropy in the particle morphology can be attributed to the surface oxidation which in turn produces Ag@Ag2O core-shell nanostructures. Thus an intriguing feature of this system is that the obtained colloid is a mixture of AgNPs with and without Ag2O layers. Studies on the influence of pH on the stability of the synthesized nanoparticles revealed that the presence of excess Ag2O layers has a profound influence on it. Ag2O layers can be removed from AgNPs' surface by changing the solution pH to the acidic regime. The present study attests the enhanced ability of AOT in stabilizing the AgNPs in aqueous media. (C) 2011 Elsevier B.V. All rights reserved.

Microwave-assisted selective deoxygenation of layer- and chain-containing oxides

Very rapid (within 5 min), selective, single-step deoxygenation of layer- and chain-containing oxides, MoO3, CrO3, V2O5, alpha-VOPO4 . 2H(2)O and Ag6Mo10O33 has been accomplished using graphitic carbon in a microwave-assisted reaction. The products were found to be MoO2, Cr2O3, VO2, VPO4 and a mixture of (Ag + MoO2), respectively. Products were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), IR and electron paramagnetic resonance (EPR) spectroscopies. Although conventional methods of preparing these materials are tedious, the present method is simple, fast and yields very homogeneous products of good crystallinity. Our results reveal that while layer- and chain-containing oxides undergo rapid microwave-assisted carbothermal reduction, the non-layered materials do not. The high structural selectivity of these reactions is suggestive of the topochemical nature of the fast reduction process.

Rapid microwave assisted synthesis of hydroxyapatite

A fast, efficient and novel method of preparation of hydroxyapatite using microwaves has been described.

''Phase reversal'' of non-resonant microwave absorption in superconducting YBaCuO/CuO powder mixtures

Non-resonant microwave absorption is studied as a function of temperature and composition in superconducting YBa2Cu3O7/CuO ceramic composite samples. In pure YBa2Cu3O7 only normal field dependence of the absorption is observed, where as in composites an anomalous non-monotonic field dependence is seen. The results are explained using an extended resistively shunted junction model and invoking the occurrence of junctions with phase difference psi(0) such that pi/2 < psi(0) < 3 pi/2. Copyright (C) 1996 Elsevier Science Ltd