Papers by Keyword: Micro-Wave

Abstract: In this study, microwave (MW) heating of Fe powder in the separated electric (E-) and magnetic (H-) fields was performed first, and the heating behaviors on the field dependence were investigated. It was shown that they are heated better in H- field than in E- field. The MW heating mechanism of metals were briefly discussed. MW heating of soda-lime glass alone was not easy, however addition of iron powder enhanced the heating, depending on the volume fraction of the powder. Occurrence of deformation and melting of the glass spheres was observed. This technique is applicable to fabrication of glass-metal composites and vitrification of waste matters. MW heating of Ni-based metal glass was attempted with no external pressure and in an inert atmosphere, it was also shown that heating was better accomplished in H- field. Weakly sintered body was possibly obtained with retention of the amorphous phase.

Abstract: The possibility for preparation of biodegradable film from cellulose-enrich waste was studied. This work dealt with the synthesis of cellulose film in LiCl/DMAc solvent system by microwave-induced esterification of cellulose from waste cotton fabric using DMAP and lauroyl chloride as a catalyst and esterifying agent, respectively. The cellulose laurate film was prepared by casting method. The structure of cellulose laurate was confirmed by FTIR and 1H-NMR analyses. The thermal stability was characterized by TGA. The optimum condition for esterification in terms of microwave power and time was investigated. The films obtained were tested for their tensile properties and potentiality of biodegradation.

Abstract: Using nitrate precursors, a novel microwave-assisted progress for the preparation of nanocrystalline pure YFeO3 phase has been developed. Synthesis of perovskite YFeO3 has been achieved with carbon to enhance microwave absorption, polyvinyl alcohol as inhibitor and urea as homogeneous precipitator. The precursor led to formation of phase pure YFeO3 nanocrystalline (52-64 nm) after calcination. The obtained YFeO3 samples were characterized by XRD analysis, N2 adsorption, FT-IR, SEM, TEM, UV-vis/DRS. The synthesis is a fast, simple and inexpensive process and such nanosized YFeO3 has a potential application in photocatalysis under visible light irradiation due to its structure of perovskite-type and photo-absorption property.

Abstract: Recent work on the thermal and electrical challenges in realizing AlGaN/GaN microwave heterojunction field effect transistors grown on SiC substrates is discussed. Raman thermography has been used to directly measure the self-heating induced lattice temperature rise with dramatically improved resolution and accuracy compared to traditional infrared techniques. It is demonstrated that defects in the SiC substrate can influence the temperature distribution within the active device with potential consequences for reliability. Microwave devices require an insulating GaN substrate material for device isolation. It is shown that the net deep level acceptor concentration has to be accurately controlled to suppress short-channel effects and to achieve radio frequency power efficient operation.

Abstract: Quantitative evaluation of small cracks in stainless steel under water, which simulated the environment of unclear reactor, by using microwave, was demonstrated. The crack depth was evaluated by means of the microwave dual frequency technique, and the crack closure stress was estimated based on the compliance technique.

Abstract: The β-tricalcium phosphate (β-TCP)/ poly(lactide-co-glycolide) (PLGA) composites for biodegradable scaffolds in bone tissue engineering were synthesized by in situ polymerization with microwave energy. The degradation behavior of β-TCP/PLGA composite was investigated by soaking in simulated body fluid (SBF) for 4 weeks. The molecular weight of the β-TCP/PLGA composites decreased with soaking time until week 2, whereas the loss rate of molecular weight reduced after week 2. The incubation time was needed for the degradation of the β-TCP, indicating that the β-TCP should be detached from the PLGA matrix and then degraded into SBF solution. The studies of mass loss of the composites with the soaking time revealed that the degradation behavior of PLGA would be processed with the transformation from the polymer to the oligomer followed by the degradation. Morphological changes, whisker-like, due to transformation and degradation of polymer in the composites were observed after week 2. On the basis of the results, it found that the degradation behavior of β-TCP/PLGA composites was influenced by the β-TCP content in the composite and the degradation rate of the composite could be controlled by the initial molecular weight of PLGA in the composite.

Abstract: Structural and microwave properties of Fe-based nanoalloy powders, mechanochemically synthesized with a composition corresponding to Finemet (Fe73.5Si13.5B9Nb3Cu1), were investigated. The nanopowders, dominated by bcc-Fe (Si), consist of nanocrystallites and display high magnetization with low-coercivity. The microwave measurements show that the nanocomposites comprising the nanopowders possess high, broadband magnetic permeability.

Abstract: The microwave-assisted combustion synthesis as a route to obtain ultrafine α-alumina and magnesium aluminate composite powders starting from the ammonium aluminum carbonate hydroxide precursor was investigated. The synthetic temperature and the crystallite size of the α- alumina nanocomposite powder were significantly affected by the environmental atmosphere in the microwave assisted combustion. The α-alumina and spinel composite powder was obtained by the microwave-assisted combustion at temperature of 1000°C under H2/N2, but at 1150°C by the normal heat process under air. The rapid transformation from γ- to α-phase was achieved by microwave assisted nucleation at low temperature of 900°C under H2/N2 atmosphere. The least crystallite size of 26.2 nm was obtained under H2/N2 atmosphere at 1000°C for 10 min.

Abstract: The dielectric properties of alumina ceramics have been measured using a free-space time-domain technique from room temperature to 1400 oC in the frequency range 8.2 – 12.4 GHz. The effects of thickness and lateral size of specimen were investigated with comparing the measured values to the calculated ones based on the half-wavelength and the Gaussian beam focusing. From these results the optimum specimen dimension for the high temperature dielectric measurement was suggested with experimental verification.

Abstract: A first and efficient procedure has been developed for microwave-assisted transfer hydrogenation of ketones. Silica gel-supported ligand 2 has been prepared for the transfer hydrogenation. This immobilized ligand-Ru complex acted as an efficient catalyst for the hydrogen transfer reaction of ketones. The MW-assisted reactions using the supported ligand 2 could reach completion within 20~40 min.