Application Of Microwave Irradiation Research Articles

Microstructural characterization and the influence of the chemical composition of the raw material mix on the physicochemical characteristics of waste-derived ceramic aggregates

This work presents the possibility of using a mixture of different mining and industrial wastes (fly ash, waste rock, glass cullet and waste solution as a binder) for ceramic aggregate production with the application of microwave radiation. The effect of the chemical composition of the raw material mix reflected by F/SA ratio (flux oxides/SiO2 + Al2O3) on the mechanical and microstructural properties of the aggregates was evaluated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and X-ray nanotomography (nCT). A higher proportion of fly ash relative to waste rock in the mixture composition led to an increase in the F/SA ratio. The greater the F/SA, the higher the values of particle density and compressive strength, ranging from 1.72 to 1.87 g/cm3 and 6.31–7.31 MPa, respectively. Moreover, higher F/SA led to lower water absorption and porosity, which oscillated between 2.12 - 3.44% and 3.22–5.00%, respectively. X-ray nanotomography studies revealed an increasing contribution of larger pores with a radius of and an overall increase in porosity as the F/SA ratio rose. This finding was further confirmed by SEM investigations. TG-QMS analysis showed that organic matter could act as a pore-forming agent. The basic physical and mechanical paramaters of the obtained ceramic aggregates indicate the suitability of the studied wastes for the production of valuable construction materials.

Study on lap joining and characterization of tin (Sn) powder on stainless steel SS304 using microwave heating

AbstractMetal bonding via joints of low melting point materials such as zinc and tin has been technically challenging. This paper presents a unique technique for bonding small dimensions and the low melting point of materials through the microwave hybrid heating (MHH) process. Joint of stainless steel SS304 was applied to the joint with the tin (Sn) powder with the application of microwave radiation by using domestic microwave oven at 2.45 GHz of constant frequency, 200–360 W of microwave power, 120–180 s of exposure time, and 10–20 % of the epoxy rate. A developed heat chamber was used as a susceptor and insulator in the microwave hybrid heating (MHH) process. The tin powder and parent metals were strongly bonded as lap position by the microwave hybrid heating (MHH) process at 360 W of microwave power, 180 s of constant exposure time, and 20 % of the constant epoxy rate. Characterization of the joint was evaluated through microhardness and x‐ray diffraction (XRD) analysis techniques. It was found that the intermetallic compounds (phase) of nickel tin (NiSn), iron tin (Fe1.84Sn), sulfur tin (SSn), chromium tin (Cr2Sn3), chromium tin (CrSn2), and tin phosphorus (SnP) at the joint surface with highest microhardness obtained at 498.4 HV 0.05 at 360 W of microwave power.

Green and Fast Strategies for Energy-Efficient Preparation of the Covalent Organic Framework TpPa-1.

Three synthesis procedures for the covalent-organic framework (COF) TpPa-1 are studied with the purpose of setting up the most promising one in a fast and green way, leading to a more environmentally friendly and sustainable process. With conventional heating, good crystallinity and a high BET specific surface area (SSA) of up to 1007 m2 ⋅ g-1 are achieved at 170 °C for 3 days using water as the quintessential green solvent. However, the application of microwave radiation in the synthesis for this crystalline porous polymer allows reaction times to be shortened to 30 min while maintaining structural and textural properties (BET SSA of 928 m2 ⋅ g-1 ) and obtaining yields close to 98 % (vs. 90 % in the hydrothermal synthesis). The water-assisted mechanochemical synthesis is also an environmentally friendly synthetic approach; with heating at 170 °C in a two-step process (10+10 min), high crystallinity is achieved, a BET SSA of 960 m2 ⋅ g-1 and a yield of 98 % for TpPa-1.

Reduction of amputations of frostbitten limbs by treatment using microwave rewarming

Drug treatment of limb frostbite injuries is complicated due to the poor delivery of medications to affected tissues. External rewarming of the frostbitten area is risky and does not always result in positive outcomes because the dilatation of superficial vessels with constricted deep vessels can lead to irreversible damage, necrosis, and amputation. One of the techniques to restore perfusion of deep vessels in an affected extremity is rewarming with low-power microwave radiation in a specially designed metal chamber. Below are findings following treatment of 14 volunteers with this technique in 2 Tomsk hospitals during winters of 2018–2021. It is demonstrated that timely, i.e. in the early reactive period, application of microwave radiation and appropriate supportive drug treatment results in positive amputation-free outcomes. The key requirement is prompt thermal insulation of the trauma and no prior exposure to external heat sources.

Synthesis and characterization of MgO nanostructures: A comparative study on the effect of preparation route

In this study, MgO nanostructures were synthesized by five facile and diverse chemical synthesis routes, viz. precipitation (PT), sonication-precipitation (SPT), microwave combustion (MWC), conventional combustion (CC), and solvothermal (ST) processes. The influence of aforementioned synthesis routes on crystallinity, crystallite size, morphology, optical, and surface traits of MgO nanostructures was evaluated by XRD, BET, FESEM, FETEM, optical absorption, steady-state and time-resolved photoluminescence analyses. Furthermore, antioxidant and antibacterial properties of MgO nanostructures were examined. XRD analysis revealed that crystallite size and relative crystallinity (%) of MgO varied from 9 to 42 nm and 90.70–99.06%, respectively, depending on the synthesis route followed. The application of microwave irradiation (MWC) and sonication (ST) reduced particle size and increased specific surface area of MgO nanostructures compared to nanostructures obtained via CC and PT methods. This could be due to faster reaction kinetics in MWC and small-scale turbulence generated during sonication that restricts growth and agglomeration of nuclei during nanostructure synthesis. FESEM analysis revealed flake, sphere, natural rose, and marigold flower-like morphologies of MgO due to different methods followed, that can be attributed to the differences in nanostructure formation mechanism involved. The highest photoluminescence intensity observed with MgO synthesized via MWC is likely to produce a maximum number of reactive oxygen species. Consequently, MgO synthesized through MWC process showed highest bactericidal and antioxidant activities compared to MgO synthesized via other routes. Thus, present study demonstrated that properties of nanostructures required for a particular application could be customized by proper choice of the synthesis route.

Effects of microwave-assisted freezing on the quality attributes of lamb meat

The objective of this study was to investigate the effect of microwave-assisted freezing (MAF) on some quality attributes of lamb meat. The lamb meat was frozen under microwave irradiation with different power levels of 0%, 40%, 50%, and 60%. The microstructure of frozen lamb meat was investigated immediately after freezing by light microscopy technique. Also, the quality properties such as drip loss, texture, and color were assessed after thawing of frozen meat samples. Results showed that the average size of ice crystals at the highest level of microwave power was approximately 38% lower than the frozen sample without the application of microwave irradiation (control sample). drip loss and color change decreased by increasing the power level of microwave irradiation. Also, MAF at the power levels of 50% and 60% improved the hardness of thawed lamb meat.

The evolution of microwave assisted thermal processing of pre-transfusion human blood: A review

The application of microwave radiation in the biomedical field has gained its acclaim owing to its property of volumetric processing which enhances thermal uniformity in the procedure. This review is aimed to highlight the scope and efficiency of microwave assisted warming of whole human blood and its components in comparison to other existing procedures. The advantages of microwave assisted warming encompass a drastic enhancement of the sterility and also significant reduction in the occurrence of denaturation of the blood samples as opposed to contemporary procedures. Overall, microwave radiation has manifested tremendous potential in achieving the desired benefits for blood samples.

Microwave‐assisted Groebke‐Blackburn‐Bienaymé multicomponent reaction to synthesize imidazo fused heterocycles via in‐situ generated isocyanides from N‐formylamines: An undergraduate organic laboratory experiment

AbstractA one‐pot methodology is developed for the direct conversion of N‐formylamine, 2‐amino pyridine, and aldehyde into 2,3‐substituted imidazo[1,2‐a]pyridine heterocycles using I2‐PPh3‐Et3N reagent system under microwave irradiation. During the reaction, I2‐PPh3‐Et3N converts N‐formylamine into isocyanide, which in the presence of in‐situ generated hydrogen iodide (HI) undergoes Groebke‐Balckburn‐Bienaymé (GBB) multicomponent reaction with aldehyde and 2‐aminopyridine. The in‐situ generated HI eliminates the need for an external catalyst for the GBB reaction. The developed process incorporates the use of readily accessible and cheap reagents and also avoid a separate step for the synthesis of isocyanides having disagreeable odor. Fourteen different GBB based heterocycles have been synthesized to demonstrate the feasibility of the optimized protocol. The preparation of N‐formylamines utilized in the synthesis is also elaborated and the overall process was optimized to be suitable for a typical undergraduate organic laboratory experiment. One of the final products was characterized using FT‐IR, 1H NMR, 13C NMR, DEPT, COSY, HSQC, HRMS, and single‐crystal X‐ray diffraction. Overall, the experiment will be useful in the organic chemistry curriculum to teach about multicomponent reactions, the importance of isocyanides in organic synthesis, formylation of amines, application of microwave irradiation in organic synthesis, and structural elucidation of small organic molecules.

Mass transfer, kinetics, and thermodynamics studies during the extraction of polyphenols from Feijoa sellowiana peels

Mass transfer mechanism, kinetic behavior, and thermodynamics analysis during the microwave-assisted extraction of total polyphenols from Feijoa sellowiana peels have been investigated with aqueous ethanol (60%, v/v) under several temperature values (295, 298, 301, and 304 K). Diffusion coefficient (1.446 10–10, 2.576 10–10, 2.320 10–10, and 5.653 10–10 m2 s−1), mass transfer coefficient (0.2335, 0.3520, 0.3555, and 0.9724), and Biot number (690.23 103, 584.16 103, 655.00 103, and 735.36 103) increased by temperature. Pseudo-wfirst-order kinetic model described the kinetic data better over the pseudo-second-order kinetic model. Activation energy (106.30 kJ mol−1) calculated for the current system denotes an extraction process controlled by the reaction, rather than diffusion. Thermodynamics terms such as enthalpy (12.87 kJ mol−1), entropy (0.068 kJ mol−1K−1), and Gibbs free energy changes (−7.187, −7.390, −7.595, and −7.799 kJ mol−1) have been also evaluated to comprehend the nature (an endothermic and spontaneous process leading to more irregularity) of the extraction system. Practical applications Comprehension of mass transfer mechanism and kinetic behavior during the solid–liquid extraction by application of microwave irradiation would let the estimation of process conditions for industrial fulfillments. Additionally, evaluation of the thermodynamic parameters would provide information on the nature of the microwave-assisted extraction of polyphenols from Feijoa sellowiana peels.

Application of microwave radiation in the grafting of acidic sites on SBA-15 type material

Mesoporous silica of SBA-15 type was modified for the first time with 3-(trihydroxysiyl)-1-propanesulfonic acid (TPS) by post-synthesis modification involving microwave or conventional heating in order to generate the Brønsted acidic centers on the material surface. The samples structure and composition were examined by low temperature N2 adsorption/desorption, XRD, HRTEM, elemental and thermal analyses. The surface properties were evaluated by esterification of acetic acid with n-hexanol used as the test reaction. A much higher efficiency of TPS species incorporation was reached with the application of microwave radiation for 1 h than conventional modification for 24 h. It was found that the structure of mesoporous support was preserved after modification using both methods applied in this study. Materials obtained with the use of microwave radiation showed a superior catalytic activity and high stability.

Application of Microwave Radiation to Produce Uranium Dioxide Powder from Its Trioxide

The possibility of producing UO2 powder from UO3 using microwave radiation (power 300 W) in the presence of organic compounds with amino groups: carbohydrazide (CH), acetohydroxamic (AHA), and aminoacetic (glycine) acids has been investigated. It was found that in these processes in an oxygen-free atmosphere, UO2 is produced from UO3, and in an air, U3O8. It was shown that under the action of microwave radiation in the presence of CH and AHA, powdered UO2 are synthesized from UO3. The physical properties of the powders obtained (bulk density with tapping 2.6–2.7 g/cm3, specific surface area up to 3.2 m2/g, moisture content less than 0.1 wt %) meet the requirements for ceramic-quality powders in the production of fuel pellets.

A comprehensive review on application of microwave irradiation for preparation of inclusion complexes with cyclodextrins

A comprehensive review on application of microwave irradiation for preparation of inclusion complexes with cyclodextrins

Comparative evaluation of physicochemical properties of Lingzhi (Ganoderma lucidum) as affected by drying conditions and extraction methods

SummaryLingzhi (Ganoderma lucidum) is a high‐potential mushroom which is used as a dietary supplement or a source of nutrients and antioxidant agents. The aims were to investigate the effect of drying conditions (hot air and vacuum dry) and to compare the extraction methods of microwave‐assisted extraction (MAE) and pulsed electric field extraction (PEF) for obtaining triterpenes, flavonoid and polysaccharides. The favourable drying condition was 80 °C for 1 h and 37 min, which achieved 1.17 ± 0.05 mg quercetin/g of flavonoids and 11.49 ± 0.87 mg ursolic acid/g of triterpenes. The MAE condition was 800 W, 1 min 30 s extraction time and 65.35% ethanol, achieving polysaccharides of 13.08 mg glucose/g and triterpenes of 9.15 mg ursolic acid/g. Additionally, MAE was significantly more efficient than reflux and PEF methods. The application of microwave radiation is beneficial in saving time and solvent and also provides high extraction efficiency for dried Lingzhi.

Novel Microwave-Assisted Method of Y2Ti2O7Powder Synthesis.

In the paper, a novel technique for highly dispersed pyrochlore Y2Ti2O7 is proposed. The experimental results proved that the application of microwave irradiation at a certain stage of calcination allowed synthesizing of Y2Ti2O7 in much shorter time, which ensured substantial energy savings. An increase up to 98 wt.% in the content of the preferred phase with a pyrochlore-type structure Y2Ti2O7 was obtained after 25 h of yttrium and titanium oxides calcination at a relatively low temperature of 1150 °C, while the microwave-supported process took only 9 h and provided 99 wt.% of pyrochlore. The proposed technology is suitable for industrial applications, enabling the fabrication of large industrial amounts of pyrochlore without solvent chemistry and high-energy mills. It reduced the cost of both equipment and energy and made the process more environmentally friendly. The particle size and morphology did not change significantly; therefore, the microwave-assisted method can fully replace the traditional one.

Enhanced electro-adsorption desalination performance of graphene by TiC

Capacitive deionization (CDI) process is aiming to desalinate water samples by electrosorption of salty ions on the surfaces of electrodes with opposite charges. Therefore, the choice of the electrode material has its main role in controlling the overall efficiency of synthesized CDI cell. In this work, graphene nanoflakes (GNFs) were examined as an interesting carbon-based material in CDI technology. Their electrochemical and desalination characteristics were significantly enhanced by introducing TiC nanoparticles in different wt.% values [5, 10 and 20] through the application of microwave irradiation followed by hydrothermal treatment. The morphology, crystal structure, porosity, composition and hydrophilic nature of fabricated nanomaterials were investigated using scanning and transmission electron microscopes (SEM, TEM), X-ray diffractometer (XRD), N2 adsorption – desorption isotherms, energy dispersive X-ray analyzer (EDX) and water contact angle measurements, respectively. Electrochemical studies revealed outperformed specific capacitance values of TiC incorporated graphene nanoflakes by 5.53, 14.47 and 7.64 folds for those containing 5, 10 and 20 wt% TiC, respectively when compared to the estimated one using GNFs at 5 mV s−1. An excellent salt removal efficiency value of 91% was calculated when 10 wt% TiC was added to GNFs with electrosorption capacity of 22.8 mg g−1 at conductivity value of 1 mS cm−1. Galvanostatic charge–discharge experiments revealed good reversible performance of this nanomaterial with high stability over 30 cycles. These obtained results could elect TiC incorporated GNFs as suitable candidates for water desalination using CDI technology.

Microwave-assisted Carbon-carbon and Carbon-heteroatom Cross-coupling Reactions in Organic Synthesis

Conventionally, the organic reactions are accomplished by conductive heating with an external heat source like an oil bath. On the contrary, since its inception, the application of microwave irradiation is growing as a suitable alternate heating method in organic synthesis. Microwave heating considerably reduces the reaction time without promoting any side reactions. The fundamental synthetic organic chemistry majorly deals with transition-metal-catalyzed C–C and C–heteroatom bond formation reactions. It is one of the most important methods in contemporary chemistry resulting in a tremendous increment in the applications of these reactions during the last few years. This field has been acknowledged with a number of Nobel Prizes during the last decade (2001, 2005 and 2010). A considerable effort has been done on the continuous development of new ligands and catalysts as well as an increased understanding of the mechanisms for the improvement of the reaction condition. This review focuses on some of the latest developments in the area of cross-coupling reactions aided by microwave irradiation.

Enhanced production of reducing sugars from paragrass using microwave-assisted alkaline pretreatment

The main aims of this study were to examine the effectiveness of pretreatment methods for enhancing the conversion of Brachiara mutica (paragrass) lignocellulose into valuable reducing sugars by enzymatic hydrolysis. The pretreatments studied included alkali alone, microwave-assisted alkali, acid alone, and microwave-assisted acid. It was found that the application of microwave irradiation during alkaline pretreatment with an alkali-to-biomass ratio of 5% (w w−1) for 30 min at 120 °C markedly increased the total reducing sugar (TRS) yield after enzymatic hydrolysis from 316 mg g−1 dry pretreated paragrass without microwave irradiation to 750 mg g−1 dry pretreated paragrass with microwave irradiation. In particular, the microwave-assisted alkaline pretreatment markedly increased xylose production and enhanced the enzymatic digestibility of cellulose. The concentrations of 5-hydroxymethylfurfural (HMF) and furfural after the microwave-assisted pretreatment were well below 1.0 kg m−3, the suggested threshold concentration of furfurals where yeast inhibition may begin.

Heating and Drying of Autoclaved Aerated Concrete Blocks for Defects of Buildings by Application of Microwave Radiation

Experiments of heating and drying of autoclaved aerated concrete blocks were divided into several areas, in which the depth of heating in relation to irradiation time intervals was checked. The impact of individual heating phases on the distribution of the irradiated field and comparison of drying rate at different lengths of the cycle “heating-cooling”. Theoretical potential of construction materials rehabilitation with the use of microwave radiation has been known for many years. This technique has been used by a number of companies in the construction practice. However, obtaining accurate information on suitable devices, procedures of their use, remedial action technique, positives and negatives and potential risks when using microwave radiation is very demanding since the findings obtained from practice are protected by individual companies for their own needs. It is understood that it is part of their “know-how”. The long-term research based on close cooperation between Civil Engineering Faculty, BUT Brno, and S. P. UNI company, tries to make accessible enough information on potential and suitable use of the microwave technology in practice, based on laboratory and in-situ experiments.

A Green Approach for Organic Transformations Using Microwave Reactor.

Microwave-assisted organic transformation (MAOR) is presently gaining wide popularity in the field of organic synthesis. The conventional heating technique is gradually being removed from the laboratory and a novel microwave heating technique established to be used in both academia and industry. As compared to the classical organic methodology, the green technology tools have several advantages like dramatically reduced reaction times, improved yields, site selectivity, and the increased product purities with simplification of work-up procedures. In the current study, we have briefly described the overview of recent developments and applications of microwave irradiation in organic transformation with schematic compiling of the organic reactions, bioactive heterocyclic compounds, and so on. This review also presents a critical analysis of the various advantages of microwave irradiation in organic synthesis/transformation compared to the classical or conventional heating. So, we believe that our current study of the green microwave heating technique will be highly beneficial for the researchers from both academia and industry in their near future.

Synthesis and physicochemical properties of hierarchical zeolites containing ruthenium oxide nanoparticles and their application in the reaction of dihydroxyacetone isomerization

Abstract Hierarchical zeolites containing ruthenium oxide nanoparticles were applied in the reaction of dihydroxyacetone isomerization to alkyl lactates and lactic acid. The synthesis of these materials was performed by dispersing the specified amount of two microporous zeolites (HFAU and NaBEA) withan ultrasound bath for 30 min, in a mixture containing cetyltrimethylammonium bromide, water, ethanol and ammonia. Then, tetraethyl orthosilicate and a source of ruthenium, were added and subjected to mixing for 4 h at 65 °C. The synthesized zeolites displaying secondary porosity in the range of mesopores were characterized by using a series of measurement techniques: XRD, SEM/EDX, TEM, low temperature adsorption/desorption of nitrogen. The reaction of triose isomerization, in this case dihydroxyacetone, was conducted by means of two methods, i.e., with the use of conventional heating and microwave radiation. The application of microwave radiation allowed for reduction of the reaction time to 1 h and accomplishing high dihydroxyacetone conversion (>90%) and high yields of the desired reaction products (>80%). Methanol, ethanol and water were used as reaction media.