Use Of Microwave Energy Research Articles

Effect of Microwave Energy on Disperse Dyeability of Polypropylene Fibers

Because of the savings in energy consumption and the shortened process time, the use of microwave energy in textile wet processes has become an important research topic in the eco-friendly studies. In this experimental work, 100 % isotactic polypropylene (iPP) which is widely used in technical textiles, 80/19/1 and 60/30/10 % iPP/ LLDPE (linear low-density polyethleylene polymer fibers) / EVA (elastomer of ethylene-vinyl acetate) ternary polymer blend fibers were dyed by conventional and microwave heating methods under atmospheric condition with C.I. Disperse Yellow 114, Red 60 and Blue79. The colour yields of conventionally dyed samples were compared to those of the dyed samples using the microwave heating. Finally, the high proportion of EVA in triple fiber mixes can be improved the coloristic properties of ternary polymer blend fiber. The colour fastness to light was quite good for dyed samples by microwave heating with C.I. Disperse Blue 79, to washing and rubbing were adequate for all dyed samples. The process time was reduced almost 90% by microwave heating.

Magnetic and magnetization properties of iron oxide thin films by microwave assisted sol–gel route

Iron oxide thin films have attracted worldwide attraction due to their technological importance in magnetic tunnel junctions, recording media, as a catalyst etc. However, the use of microwave energy for obtaining crystallinity and phase transition in the form of thin films has long being neglected. We here report preparation of iron oxide thin films using microwave energy instead of conventional heating methods during sol–gel synthesis. The solution was subjected to microwave radiations, for sol synthesis, with variation in microwave power. The maximum power used in this study is 800 W with variation in power as 136, 264, 440, 616 and 800 W. These are among the lowest powers applied for synthesis of iron oxide sol. XRD, FTIR and VSM results indicate that use of microwaves can lead to enhanced crystallinity and phase stability, thus enhancing the magnetic properties with variation in power of the incident microwaves. At low power of microwaves mixed phases of iron oxide exist whereas with increased power up to 616 W pure maghemite phase was obtained. Further increasing the microwave power to 800 W, results in formation of pure magnetite phase. FTIR bands at 477 and 550 cm−1 indicate formation of pure magnetite phase. The films exhibit ferromagnetic behaviour with saturation magnetization of 453 emu/cm3. Verwey transition, determined using low temperature electrical properties, reveals sharp reduction in resistivity at a temperature of 125 K.

ChemInform Abstract: Microwave‐Assisted Synthesis of Benzo‐Fused Seven‐Membered Azaheterocycles

AbstractReview: such as benzodiazepines, benzothiazepines and benzoxazepines; 102 refs.

Microwave-assisted metallurgy

Microwave heating has been extensively explored in various fields of materials processing. This technology exhibits unique characteristics including volumetric and selective heating, which eventually lead to many exceptional advantages over conventional processing methods including both energy and cost savings, improved product quality, faster processing and greater eco-friendliness, making microwave heating appropriate for applications in metallurgy. This paper presents a critical review on the use of microwave energy in metallurgy, with emphasis on both fundamentals of microwave heating and recent experimental efforts on extractive metallurgy via pyrometallurgical and/or hydrometallurgical routes. Applications to metallurgical processes for extraction of various metals, including heavy metals (Fe, Ni, Co, Cu, Pb and Zn), light metals (Al and Mg), rare metals (Ti, Mo, W and Re) and precious metals (Au, Ag and Pt), are reviewed and discussed.

Applications of microwave energy in cement and concrete – A review

Microwave heating is a highly efficient technique for various thermal processes. Advantages of microwave heating compared to conventional processing methods include energy-saving rapid heating rates and short processing times, deep penetration of the microwave energy (which allows heat to be generated efficiently without directly contacting the work-piece), instantaneous and precise electronic control, clean heating processes, and no generation of secondary waste. Microwave energy processes for heating, drying, and curing have been developed for numerous laboratory-scale investigations and, in some cases, have been commercialized. Microwave energy use should theoretically be advantageous in the processing of cement and concrete materials (e.g., hydraulic Portland cement, aggregate, and water). These materials exhibit excellent dielectric properties and, therefore, should be able to absorb microwave energy very efficiently and instantaneously convert it into heat. This paper provides a comprehensive review of the use of microwave energy to process cement and concrete materials, as well as a critical evaluation of currently utilized microwave heating mechanisms and high-performance microwave systems. The current status of microwave applications and future research and development trends are also discussed, including such thermal processing methods as the high-temperature sintering of cement materials, the accelerated curing of precast concrete products, as well as the drilling and cleaning of decontaminated concrete surfaces by the built-up internal pressure. The results of this review indicate that microwave heating is directly associated with dielectric loss by the cement and concrete. Microwave processing can be used to improve clinkering and to reduce the clinkering temperature by about 100 °C. Considerations when constructing mathematical models of microwave heating for cement and concrete should include the influences of heat and mass transfer during microwave curing on the temperature difference in the concrete, the degree of uniformity of the internal structure, and the ultimate performance of the product. Future studies of microwave energy in cement and concrete applications might include investigations of adaptive (time-dependent) dielectric properties, coupling chemical reactions in the presence of microwave energy, the design and construction of suitable microwave systems, and the prediction of related phenomena (e.g., thermal runaway, as a highly regulated safety issue).

Microwave Synthesis and Characterization of the Series Co1−x Fe x Sb3 High Temperature Thermoelectric Materials

The use of microwave energy for materials processing has a major potential and real advantages over conventional heating such as (1) time and energy savings, (2) rapid heating rates (volumetric heating vs. conduction), (3) considerably reduced processing time and temperature, (4) fine microstructures and hence improved mechanical properties and better product performance, and (5) finally lower environmental impact. In this study, we investigated the use of microwave-assisted synthesis to synthesize a series of Co1−x Fe x Sb3 using this novel approach, which gave high quality materials with little or no impurities in a fraction of the time needed for conventional synthesis. X-ray diffraction analysis was used to examine the structure and the lattice parameters of the samples, while scanning electron microscopy with energy dispersive x-ray spectroscopy was used to study the morphology of the compounds. The samples were sintered by spark plasma sintering, and the highest ZT of 0.33 was obtained for x = 0.2 at 700 K.

Integrated microwave drying, pyrolysis and gasification for valorisation of organic wastes to syngas

The development of integrated platforms is desirable in order to improve the efficiency of biorefineries. This study deals with an innovative all-in-one thermochemical process (drying, pyrolysis and gasification) based on the use of microwave energy, which could eliminate the need to pre-dry municipal solid waste in order to produce a high quantity of synthesis gas. Depending on the initial moisture content and pyrolysis time, it is possible to obtain different syngas compositions but only during the first 20min. Beyond this time the syngas composition remains almost constant. In addition, the moisture content was found to improve the volumetric gas production by almost 50%. The energy consumption of this all-in-one process is discussed by comparing it with the scarce information available in the literature concerning the scaling-up of microwave-assisted processes, which may be more cost-effective at a higher scale.

Microwave-Assisted Synthesis of Benzo-fused Seven-membered Azaheterocycles

The use of microwave energy in chemical reactions has revolutionized the field of heterocyclic chemistry in the past two decades. Synergy of microwave methodology with reactions performed on support media and/or in the absence of solvent constitutes an environmentally clean technique, which offers tremendous advantages such as clean chemistry, reduction in reaction times, improved yields, and applicability to wide range of reactions, safety and tremendous scope for automation over the traditional heating. The benzoannulated azaheterocycles display an impressive repertoire of biological activities. The present review will provide an in-depth view of microwave-assisted preparation of benzo-fused seven- membered azaheterocycles such as benzodiazepines, benzothiazepines and benzoxazepines.

Eco-friendly microextraction method for the quantitative speciation of 13 haloacetic acids in water

This paper describes the first micro liquid–liquid extraction (MLLE) gas chromatography–mass spectrometry (GC–MS) method for the speciation of emerging iodinated acetic acids, along with conventional chlorinated and brominated acids in water. The haloacetic acids (HAAs) were derivatised using 3 reagents for their methylation, both in aqueous and organic media. The acidic methanol derivatisation in aqueous medium provided the best efficiency, requiring minimal sample manipulation. The derivatisation yield was improved through the use of microwave energy that drastically reduced reaction time (2min). The HAA methyl esters were finally extracted using 250μL of methyl tert-butyl ether. This MLLE combined with the use of a large-volume sample injection coupled to a programmed temperature vaporiser–GC–MS improved the sensitivity of the method and minimised the generation of hazardous residues in accordance with the principles of “Green Chemistry”. Detection and quantification limits (excepting tribromoacetic acid) within the range of 0.01–0.15μg/L and 0.03–0.5μg/L, respectively, were obtained and the relative standard deviation was lower than 10%. The eco-friendly method was applied to the speciation of the 13 HAAs in treated (chlorinated and chloraminated water) and untreated water. Up to 8 HAAs were found at detectable levels in treated water. The highly toxic monoiodoacetic acid was detected in almost all the chloraminated water.

Dissociation and excitation coefficients of nitrogen molecules and radical generation in nitrogen plasma

The dissociation and excitation coefficients of nitrogen molecules are investigated by making use of the Boltzmann distribution of the electrons in atmospheric plasma. The excitation and electron-impact dissociation coefficients are analytically expressed in terms of the electron temperature Te in units of eV. As an application example of these coefficients, hydroxyl generation through nitrogen plasma jet is investigated, showing that the hydroxyl concentration nOH increases, reaches its peak value and then deceases, as the mole fraction χ of water molecules increases from zero to a few percents. The experimental data of the hydroxyl generation agree qualitatively with analytical results obtained from a theoretical model, confirming that a nitrogen plasma jet is one of the best means of hydroxyl production. The other example of the coefficient application is the nitrogen monoxide generation by making use of microwave energy at 2.45 GHz. The nitrogen monoxide concentration can easily be controlled by the nitrogen flow rate, the mole fraction of the oxygen gas, and the microwave power. An experiment involving nitrogen monoxide production was conducted, and the experimental data were found to agree remarkably well with the theoretical results from the analytical expression.

Bauxite Enrichment by Microwave-Magnetising Roasting Using Sawdust as Reducing Agent

As high grade bauxite is getting depleted in several parts of the world, bauxite with high iron content is becoming increasingly important, and this trend has called for studies into the reduction of iron in bauxite. This study investigated the use of microwave energy in the magnetising roasting of high-iron bauxite using sawdust as reducing agent. Mineralogical studies revealed gibbsite and goethite as the main constituents of bauxite. The sawdust utilised had a fixed carbon content of 7.2% and ash, 1.7%. Microwave heating responses of bauxite and sawdust were determined as a function of mass and time, and both materials proved to be active microwave absorbers as they heated rapidly. Magnetising roasting of the bauxite sample was conducted with 20-40% sawdust at temperatures between 870oC and 880oC. After magnetic separation, the major phase in the magnetic fraction was magnetite, while gibbsite and boehmite were the major phases in the non-magnetic fraction. The alumina content of the non-magnetic fraction increased to 87.5% from an as-received sample grade of 53.6%. The use of sawdust in this manner satisfies a dual role of environmental clean-up and bauxite enrichment.

Microwave Assisted Peptide Synthesis as a New Gold Standard in Solid Phase Peptide Synthesis: Phospholamban as an Example

In this study, we report the microwave assisted synthesis of Phospholamban protein (WT-PLB) as a new gold standard in solid phase peptide synthesis. Microwave energy offers benefits for both the coupling and deprotection reactions during peptide synthesis. The use of microwave energy for both the coupling and deprotection steps makes the microwave peptide synthesizers the most versatile and powerful systems available. It produces high yield and fast synthesis when compared to conventional peptide synthesizers.

Monoqueima de porcelanas esmaltadas em forno de micro-ondas

A utilização da energia de micro-ondas no processamento de materiais cerâmicos apresenta vantagens quanto ao tempo de processo e homogeneidade microestrutural. Este trabalho tem como objetivo estudar a monoqueima de porcelanas de decoração esmaltada em um substrato de geometria complexa utilizando o aquecimento ultrarrápido híbrido por micro-ondas. As peças foram conformadas por colagem de barbotina e, ainda a verde, esmaltadas por imersão e queimadas pelo processo de monoqueima em forno convencional e em forno de micro-ondas. As peças queimadas por micro-ondas apresentaram características físicas, como aparência da superfície, adesão do esmalte, densidade aparente e resistência mecânica igual ou superior ao processo convencional de queima em apenas 24 min, equivalente a menos de 10% do tempo utilizado na sinterização convencional.

Multistep soluble polymer-supported, microwave-assisted synthesis of quinoxalines

A multistep liquid-phase, polymer-supported, microwave-assisted synthesis of quinoxalines on polyethylene glycol, PEG-4500, is demonstrated. The usage of microwave energy to accelerate organic reactions reduces reaction time from hours (under reflux) to only minutes. The solution-phase chemistry on soluble polyethylene glycol, PEG, support facilitates the use of microwave energy (since PEG easily absorbs microwaves) and avoids the silica gel chromatography purifications of intermediate compounds, supporting parallel, combinatorial, and ultimately automated syntheses.

Microwave Treatment of Mung Bean (Vigna radiata) for Reducing the Cooking Time

<abstract><title><italic>Abstract. </italic></title> Use of microwave energy for reduction of cooking time of dehulled mung beans was investigated. Mung beans having initial moisture contents (m.c.) of 10%, 12%, 14%, 16%, and 18% (wet basis) were exposed to 400, 600, and 800 W power level for 14, 28, and 56 s exposure time in a pilot-scale industrial microwave drier operating at 2450 MHz frequency. Exposure to microwave energy significantly reduced the cooking time of mung beans with untreated 10% m.c. mung beans having the highest (11.8 min) and 12% m.c. mung bean treated at 600 W for 56 s having the lowest (4.8 min). Due to exposure to microwave energy, dhal yield increased and dehulling time decreased. A decrease in particle density of microwave-treated mung beans demonstrated structural changes in mung bean due to exposure to microwave energy. Crude protein content and color of dehulled mung bean were not affected by microwave treatment.

New Microwave Antenna Structures for Treating Gastro-Oesophageal Reflux Disease (GERD)

The design and initial pre-clinical evaluation of microwave traveling-wave antenna structures to deliver high-frequency microwave energy with controlled depth of penetration of the electric field to produce controlled ablation around the inner wall of the oesophagus (confined to the mucosal layer) at the junction between the stomach and the oesophagus is described in this paper. The structures were fabricated using flexible microwave substrates to enable them to be attached to the outer wall of oesophageal balloons for introduction into the oesophagus. It is shown that the uniform electromagnetic field produced along the length of the structure produces controlled circumferential tissue ablation, which could be used to tighten the muscles in the lower oesophageal sphincter, where the stomach connects to the oesophagus, to reduce or eliminate regurgitation and acid exposure to the oesophagus, a condition known as gastro-oesophageal reflux disease. This paper also presents the results obtained from in-vitro tissue studies and initial in-vivo work carried out using the porcine model. This is the first study to assess the use of microwave energy to treat medical conditions associated with the oesophagus.

Preliminary investigations into the use of microwave energy for reversible stunning of sheep

AbstractStunning prior to slaughter is commonly used to render the animal insensible to pain. However, for certain markets, stunning is disallowed, unless the animal can fully recover if not slaughtered. There are very few available methods of inducing a fully recoverable stun. This preliminary study investigates the potential for microwave energy application to be used to induce a recoverable stun in sheep. Cadaver heads were used to demonstrate that brain temperature could be raised to a point at which insensibility would be expected to occur (44°C). Trials on four anaesthetised sheep confirmed this finding in a live animal model where brain temperatures between 43 and 48°C were achieved with 20 s of microwave energy application. Although the applicator and process variables require some further development, this technology seems eminently suitable for use as an alternative method of inducing a recoverable stun.

Unraveling the Mysteries of Microwave Chemistry Using Silicon Carbide Reactor Technology

In the past few years, the use of microwave energy to heat chemical reactions has become an increasingly popular theme in the scientific community. This nonclassical heating technique has slowly progressed from a laboratory curiosity to an established method commonly used both in academia and in industry. Because of its efficiency, microwave heating dramatically reduces reaction times (from days and hours to minutes and seconds) and improves product purities or material properties among other advantages. Since the early days of microwave chemistry, researchers have observed rate-accelerations and, in some cases, altered product distributions as compared with reactions carried out using classical oil-bath heating. As a result, researchers have speculated that so-called specific or nonthermal microwave effects could be responsible for these differences. Much of the debate has centered on the question of whether the electromagnetic field can exert a direct influence on a chemical transformation outside of the simple macroscopic change in bulk reaction temperature. In 2009, our group developed a relatively simple "trick" that allows us to rapidly evaluate whether an observed effect seen in a microwave-assisted reaction results from a purely thermal phenomenon, or involves specific or nonthermal microwave effects. We use a microwave reaction vessel made from silicon carbide (SiC) ceramic. Because of its high microwave absorptivity, the vessel shields its contents from the electromagnetic field. As a result, we can easily mimic a conventionally heated autoclave experiment inside a microwave reactor under carefully controlled reaction conditions. The switch from an almost microwave transparent glass (Pyrex) to a strongly microwave absorbing SiC reaction vial under otherwise identical reaction conditions (temperature profiles, pressure, stirring speed) then allows us to carefully evaluate the influence of the electromagnetic field on the particular chemical transformation. Over the past five years we have subjected a wide variety of chemical transformations, including organic reactions, preparations of inorganic nanoparticles, and the hydrolysis of proteins, to the "SiC test." In nearly all of the studied examples, we obtained identical results from reactions carried out in Pyrex vials and those carried out in SiC vials. The data obtained from these investigations confirm that in the overwhelming majority of cases a bulk temperature phenomenon drives the enhancements in microwave chemistry and that the electromagnetic field has no direct influence on the reaction pathway.

Investigation on microwave heating for direct leaching of chalcopyrite ores and concentrates

The use of microwave energy in materials processing is a relatively new development presenting numerous advantages because of the rapid heating feature. Microwave technology has great potential to improve the extraction efficiency of metals in terms of both a reduction in required leaching time and an increase in the recovery of valuable metals. This method is especially pertinent in view of the increased demand for environment-friendly processes. In the present study, the influence of microwave heating on the direct leaching of chalcopyrite ores and concentrates were investigated. The results of microwave leaching experiments were compared with those obtained under conventional conditions. During these processes, parameters such as leaching media, temperature, and time have been worked to determine the optimum conditions for proper copper dissolution. Experimental results show that microwave leaching is more efficient than conventional leaching. The optimum leaching conditions for microwave leaching are the solid-to-liquid ratio of 1:100 g/mL, the temperature of 140°C, the solution of 0.5 M H2SO4 + 0.05 M Fe2(SO4)3, and the time of 1 h.

A facile microwave synthesis of 3-cinnamoylflavones and their antioxidant and antibacterial activities

BackgroundThe flavonoids are members of a class of natural compounds that have been the subject of considerable scientific and therapeutic interest. The interest in biological properties of the flavonoids has resulted intense synthetic efforts towards the synthesis of various flavonoids. ObjectiveIn the present study, novel α- cinnamoylchalcones 3(a-h) were synthesised from 1-(2- hydroxyphenyl)-5-phenyl-4-pentene 1,3-diones 1(a, b) and substituted aromatic aldehydes 2(a˗d) via Knoevenagel reaction. Further, new 3-cinnamoylflavones 4(a-h) were also synthesised by the cyclisation of α -cinnamoylchalcones 3(a-h) using microwave as well as conventional method. The use of microwave energy in the synthesis of flavones reduced the time of the reaction and also improved the yield. Materials and MethodsThe structures of synthesized compounds were established on the basis of their physical and spectral data. The synthesised compounds were screened for their antibacterial activity against four bacteria viz. S. sciuri, S. aureus, S. typhi and E. coli and their antioxidant potential was evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay. ResultsAll the compounds were found to possess antibacterial and antioxidant activities. ConclusionFrom the results it can also be concluded that the 3-cinnamoylflavones were more potent as antioxidants as compared to the corresponding α -cinnamoylchalcones.