Current Issue : January - March Volume : 2014 Issue Number : 1 Articles : 6 Articles
In this work, CaWO4 nanoparticles have been synthesized by microwave-assisted method at a low temperature of 120�°C. The asprepared\r\npowders were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier\r\ntransforminfrared spectroscopy (FT-IR). It is found that the reaction time played an important role in the morphology controlling\r\nand crystallinity level of CaWO4 crystals. The effects of photoluminescent properties have a great relationship with crystallinity....
Microwave energy based chemical synthesis has several merits and is important from both scientific and\r\nengineering standpoints. Microwaves have been applied in numerous inorganic and organic chemical syntheses;\r\nperhaps, from the time their ability to work as heat source was discovered. Recent laboratory scale microwave\r\napplications in biodiesel production proved the potential of the technology to achieve superior results over\r\nconventional techniques. Short reaction time, cleaner reaction products, and reduced separation-purification times\r\nare the key observations reported by many researchers. Energy utilization and specific energy requirements for\r\nmicrowave based biodiesel synthesis are reportedly better than conventional techniques. Microwaves can be very\r\nwell utilized in feedstock preparation, extraction and transesterification stages of the biodiesel production process.\r\nAlthough microwave technology has advanced in other food, pharmaceutical and polymer chemistry related\r\nresearch and industry, it has yet to prove its potential in the biodiesel industry at large scale applications. This paper\r\nreviews principles and practices of microwave energy technology as applied in biodiesel feedstock preparation and\r\nprocessing. Analysis of laboratory scale studies, potential design and operation challenges for developing large scale\r\nbiodiesel production systems are discussed in detail....
Low-phase-noise microwave oscillators are important to a wide range of subjects, including communications, radar and metrology. Photonic-based microwave-wave sources now provide record, close-to-carrier phase-noise performance, and compact sources using microcavities are available commercially. Photonics-based solutions address a challenging scaling problem in electronics, increasing attenuation with frequency. A second scaling challenge, however, is to maintain low phase noise in reduced form factor and even integrated systems. On this second front, there has been remarkable progress in the area of microcavity devices with large storage time (high optical quality factor). Here we report generation of highly coherent microwaves using a chip-based device that derives stability from high optical quality factor. The device has a record low electronic white-phase-noise floor for a microcavity-based oscillator and is used as the optical, voltage-controlled oscillator in the first demonstration of a photonic-based, microwave frequency synthesizer. The synthesizer performance is comparable to mid-range commercial devices....
An efficient synthesis of arylidene acetophenones have been achieved by using the microwave heating in comparison to the conventional\r\nheating. In this work compound 1-phenyle-3-(4-droxyphenyle)-2-propen-1-one, 1-(4-chlorophenyle)-3-phenyle-2-propen-1-\r\none, and 1-(4-chlorophenyle)-3-(4-hydroxyphenyle)-2-propen-1-one have been synthesized by the condensation reaction between\r\naromatic aldehydes and substituted acetophenones under microwave irradiation.The compounds of aldehydes and acetophenones\r\nwere used as benzaldehyde, parahydroxybenzaldehyde, acetophenone, and parachloroacetophenone.Theresult shows that the time\r\ntaken for the reaction was reduced from the conventional 1-2 hours to 60ââ?¬â??120 seconds. The yield of the compounds in the conventional\r\nheating was moderate while the highest yield of 90ââ?¬â??98% was observed in MWI method. The structure of the compounds was\r\ncharacterized by their IR, 1H-NMR spectral data....
In a continuous-flow system equipped with a nonresonant microwave applicator we have investigated how to best assess the actual\r\ntemperature of microwave heated organic solvents with different characteristics. This is non-trivial as the electromagnetic field will\r\ninfluence most traditional methods of temperature measurement. Thus, we used a microwave transparent fiber optic probe, capable\r\nof measuring the temperature inside the reactor, and investigated two different IR sensors as non-contact alternatives to the internal\r\nprobe. IR sensor 1 measures the temperature on the outside of the reactor whilst IR sensor 2 is designed to measure the temperature\r\nof the fluid through the borosilicate glass that constitutes the reactor wall. We have also, in addition to the characterization of the\r\nbefore mentioned IR sensors, developed statistical models to correlate the IR sensor reading to a correct value of the inner temperature\r\n(as determined by the internal fiber optic probe), thereby providing a non-contact, indirect, temperature assessment of the\r\nheated solvent. The accuracy achieved with these models lie well within the range desired for most synthetic chemistry applications....
In order to control reaction temperature and reduce processing time, a new method of ultrasound irradiation with microwave\r\nheating was used to synthesize (Ca1-??, Ln??)MoO4:Eu3 (Ln = La, Gd; 0 < ?? < 0.5) phosphors at only 80�°C in 30 minutes.\r\nTheir crystal structures and morphologies which have been verified by X-ray diffraction (XRD) and scanning electron microscopy\r\n(SEM) exhibited gradual changes due to the insertion of lanthanide ions (La or Gd) in calcium molybdates. Codoping of\r\nlanthanum ions (?? = 0.2) would enhance the emission intensities that were supported by fluorescent spectrophotometry\r\n(FL)....
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