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Ultra-Rapid Crystallization of L-Alanine Using Monomode Microwaves, Indium Tin Oxide and Metal-Assisted and Microwave-Accelerated Evaporative Crystallization
摘要： The use of indium tin oxide (ITO) and focused monomode microwave heating for the ultra-rapid crystallization of L-alanine (a model amino acid) is reported. Commercially available ITO dots (< 5 mm) attached to blank poly(methyl)methacrylate (PMMA, 5 cm in diameter with 21-well silicon isolators: referred to as the iCrystal plates) were found to withstand prolonged microwave heating during crystallization experiments. Crystallization of L-alanine was performed at room temperature (a control experiment), with the use of two microwave sources: a 2.45 GHz conventional microwave (900 W, power level 1, a control experiment) and 8 GHz (20 W) solid state, monomode microwave source with an applicator tip that focuses the microwave field to a 5-mm cavity. Initial appearance of L-alanine crystals and on iCrystal plates with ITO dots took 47 ± 2.9 min, 12 ± 7.6 min and 1.5 ± 0.5 min at room temperature, using a conventional microwave and focused monomode microwave heating, respectively. Complete evaporation of the solvent using the focused microwaves was achieved in 3.2 ± 0.5 min, which is ~52-fold and ~172-fold faster than that observed at room temperature and using conventional microwave heating, respectively. The size and number of L-alanine crystals was dependent on the type of the 21-well iCrystal plates and the microwave heating method: 33 crystals of 585 ± 137 μm in size at room temperature > 37 crystals of 542 ± 100 μm in size with conventional microwave heating > 331 crystals of 311 ± 190 μm in size with focused monomode microwave. FTIR, optical microscopy and powder X-ray diffraction analysis showed that the chemical composition and crystallinity of the L-alanine crystals did not change when exposed to microwave heating and ITO surfaces. In addition, theoretical simulations for the binding of L-alanine molecules to ITO and other metals showed the predicted nature of hydrogen bonds formed between L-alanine and these surfaces.
关键词： ITO,Microwave heating,Silver island films,Evaporative crystallization
更新于2025-09-23 15:22:29
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Microwave transmission performance of fused silica ceramics in microwave high-temperature heating
摘要： Compared with traditional heating methods, microwave heating is widely used in many industrial heating fields because of its advantages, such as material-selective heating, volumetric heating and high-efficiency heating. However, previous studies have shown that the heating mode depends on the transmission performance of refractory insulation materials. In this study, a commonly used refractory material (fused silica ceramics) for microwave heating was studied, according to the law of electromagnetic wave propagation in a single-layer plate, the power transmission coefficient (PTC) of the material at different thickness, temperature and frequency (915 MHz and 2360 MHz) was calculated and analysed, in order to design the refractory structure which has good microwave transmission performance in the whole microwave heating process. The results show that the transmission performance of fused silica ceramics fluctuates regularly with increasing thickness, and there are several microwave transmission peaks in the PTC patterns, the thicknesses corresponding to the transmission peaks at frequency 2360 MHz are in order 0.033 m, 0.065 m and 0.098 m; as the temperature increases, the position of the transmission peaks will shift to a smaller thickness, the transmission performance of fused silica ceramics decreases slightly with increasing temperature. Comparing the transmission performance of mullite, alumina (Al2O3) and fused silica ceramics, it was found that the fused silica ceramics have excellent transmission properties; especially it is at high temperature. The results of this study can provide guidance for the selection of refractory structure materials and sizes as well as the optimization of heating process parameters in high-temperature microwave heating.
关键词： A. Microwave heating,D. Transmission performance,B. Fused silica ceramic,C. High temperature wave transmitting material
更新于2025-09-23 15:22:29
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Importance of carbon-monoxide-induced reaction in microwave heating synthesis of β-SiC from silicon powder in air
摘要： Microwave heating is known to provide extremely rapid synthesis of silicon carbide (SiC) from mixtures of silicon and carbon powders. The formation mechanism has long been considered to be a solid-state reaction among the powders in the mixture. Here, we present a new reaction mechanism via a gas-phase route. We have confirmed successful synthesis of ￠-SiC powder by microwave-heating of a small amount of Si powder that was entered into a quartz tube and then embedded in graphite powder, although no direct contact between the Si and graphite powders was allowed. Scanning electron microscopy observations revealed that the ￠-SiC powder was formed by direct carbonization of the Si powder. Since the atmosphere during the reaction comprises a vast majority of carbon monoxide (CO) gas according to the Boudouard equilibrium, the carbonization appears to have taken place via the CO gas. The contribution of such a gas-phase reaction could account in part for the rapidity of the microwave-heating reactions reported so far, which can hardly be explained solely by solid-state reactions among the mixed powders.
关键词： Carbon monoxide,Gas-phase reaction,Microwave heating,Silicon carbide,Air atmosphere,Silicon
更新于2025-09-23 15:21:21
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Deposition of Cu2ZnSnS4 films by doctor blade printing using a one-step microwave heated ink as an absorber layer for solar cells
摘要： Kesterite (Cu2ZnSnS4, CZTS) semiconductors are known as the most suitable compounds for the synthesis of absorber layers. These compounds are used in solar cells due to their high solar energy absorption coe?cient and ideal band gap. In the present work, the microwave-assisted process and doctor blade printing were used to prepare Cu2ZnSnS4 ?lms. To this aim, ink solution was used, which consisted of copper, zinc acetate, tin chloride and thiourea as copper, zinc, tin and sulfur precursors, respectively. Ethylene glycol was used as a non-toxic solvent. The CZTS ink was prepared using microwave heating for 10 min. The CZTS layers were printed on soda lime silica glass substrates and heat treated at 150, 200, 250, 300, and 350°C. The microstructure, phase analysis, morphology, optical properties, and absorption ratio of the samples were evaluated using X-ray di?raction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, transmittance spectroscopy, ?eld emission scanning electron microscopy (FESEM), energy dispersive X-ray, and UV–Vis spectrophotometry. The formation of the Kesterite structure was con?rmed using X-ray di?raction and Raman spectroscopy. The FESEM micrographs and DLS (dynamic light scattering) revealed that the ?lms contained equated grains with the diameter range of 350–650 nm. According to the X-ray analysis and Raman spectrum, the highest crystallization and purity of the Kesterite phase as well as the best microstructure property and morphology (smooth spherical particles with good adhesion) of the CZTS ?lms were found in the synthesized specimen at 300°C. The band gap of the samples was measured to be about 1.5 eV using UV–Vis spectrophotometry.
关键词： Microwave heating process,UV–Vis spectrophotometry,Solar cell,CZTS ?lm
更新于2025-09-16 10:30:52
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Optimization of melting parameters and minimizing OH content in SiO <sub/>2</sub> -B <sub/>2</sub> O <sub/>3</sub> -Na <sub/>2</sub> O-BaO glass system in microwave heating
摘要： This study investigates the optimization of melting process for the glass comprising SiO2‐B2O3‐Na2O‐BaO under microwave (MW) heating. Batches were melted at different temperatures in the range of 900‐1250°C to optimize melting condition. X‐ray diffraction suggests amorphous nature of samples melted above 1150°C. Optimization of melting time was carried out by varying soaking time (8‐60 minutes) at 1250°C. UV‐Vis‐NIR spectra reveal ~90% transmission over 300‐2000 nm wavelength range for glass melted at 1250°C. Optical microscopic images suggest that the bubble‐free glass can be produced at 1250°C for 1 hour melting in MW heating. MW heating also helps in reducing OH content in glass. However, OH concentration is found to increase with melting time. OH content could be minimized to 68.56 ppm in glass employing oxygen atmosphere melting, which prevents OH diffusion from atmosphere into the melt. Residual stresses are estimated to be less in MW heating than conventional heating. Maximum MW power was observed to be 1 kW with a total electrical power consumption of around 5 kWh. Also, total time needed to prepare the glass is around 2 hours. Thus, MW heating could be an alternate efficient tool in producing low OH content glass.
关键词： boro silicate glass,dehydration method,OH reduction process,microwave heating,optimization of glass melting process
更新于2025-09-10 09:29:36
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Manufacture of glass and mirrors from lunar regolith simulant
摘要： Future planetary surface missions to the Moon or Mars, for example, can be augmented by the use of local materials, in order to reduce launch mass and expand mission capability. Using lunar regolith simulant and heating it within a susceptor-assisted microwave oven, it was possible to manufacture a variety of basaltic glasses. Furthermore, it was possible to shape these glasses by grinding and polishing the surface flat and smooth. Glasses manufactured from different lunar regolith simulants were coated with aluminium or silver, and the reflective properties of the resulting mirrors and uncoated surfaces were measured. It was shown that with a porous and/or smooth surface finish, mirrors could be made that reflect the incident solar light (400 nm–1250 nm) in-between 30% for the worst and 85% for the best samples. The same samples with uncoated surfaces showed to reflect less than 7% of incident solar light in the same wavelength range.
关键词： microwave heating,mirror manufacturing,ISRU,basaltic glass,lunar regolith
更新于2025-09-04 15:30:14
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Rapid fabrication of KTa0.75Nb0.25/g-C3N4 composite via microwave heating for efficient photocatalytic H2 evolution
摘要： A novel KTa0.75Nb0.25O3 (KTN)/g-C3N4 composite photocatalyst was fabricated through microwave heating for realizing the e?cient photocatalytic H2 evolution. The energy-e?cient preparation method allowed g-C3N4 to be formed in-situ on KTN surface in thirty ?ve minutes. The binary constitution of the KTN/g-C3N4 composite was veri?ed by X-ray di?raction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. UV–visible di?use re?ection spectroscopy (DRS) experiments suggested that the photoabsorption performance was increased after the introduction of KTN. N2-adsorption analysis indicated that the addition of KTN slightly increased the surface area of g-C3N4. Photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS) and transient photocurrent response (PC) analyses con?rmed that the KTN/g-C3N4 composite displayed longer lifetime of photoexcited charge carriers than g-C3N4, owing to the suitable band potentials and the close contact of KTN and g-C3N4. This property was believed to the key characteristic of the composite, which led to its excellent photocatalytic performance. Under simulated sunlight irradiation, the optimal KTN/g-C3N4 catalyst presented a photocatalytic H2-generation rate of 1673 μmol·g?1·h?1, 2.5 and 2.4 times higher than that of KTN and pure g-C3N4, respectively. Under visible light irradiation, the value was determined to be 86.2 μmol·g?1·h?1, which achieved 9.3 times that of g-C3N4.
关键词： Microwave heating method,KTa0.75Nb0.25O3,Photocatalytic H2 evolution,g-C3N4
更新于2025-09-04 15:30:14