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Microwave Drilling in Sub-Wavelength Diameters
Published in Amit Bansal, Hitesh Vasudev, Advances in Microwave Processing for Engineering Materials, 2023
Microwaves are widely used in communication and radar systems, and they also have great potential (although not fully utilized yet) in industrial, scientific, and medical (ISM) applications [11, 12]. Current industrial applications of microwaves include heating, drying, material processing and manufacturing, ceramic sintering, and microwave chemistry [13, 14]. Applications of microwave energy for destructive purposes, such crushing rocks for mining operations, tunneling, and so on [7, 15], as well as demolition of concrete structures, have also been proposed and developed but typically for larger size scales compared to the microwave wavelength λ (~0.12 m at 2.45 GHz, or ~0.33 m at 915 MHz). The heat-affected zone (HAZ) size in microwave heating is typically in the order of the microwave wavelength, which is approximately 104 longer than that of a CO2 laser, for instance. Hence, a remote, far-field focusing of microwaves for fine drilling operations, such as performed by laser-based drills [16], is limited to the minimal order of the microwave wavelength, due to the diffraction limit.
Microwave-Assisted Synthesis: A New Tool in Green Technology
Published in Shrikaant Kulkarni, Ann Rose Abraham, A. K. Haghi, Renewable Materials and Green Technology Products, 2021
C. R. Sreerenjini, Bhagyalakshmi Balan, Gladiya Mani, Suresh Mathew
A revolutionary milestone in the history of microwave synthesis happened in 1990s, the first high pressure microwave vessel “HPV 80” was established by Milestone Srl Italy, for complete digestion of materials like oxides, oils, and pharmaceutical compounds. Later in 1992–1996, CEM Corporation developed a more efficient batch system reactor (MDS 200) and a single-mode cavity system (Star 2) for chemical synthesis. During 1997, Prof. H. M. Kingston of Duquesne University, USA culminated an innovative book titled “Microwave-Enhanced Chemistry-Fundamentals, Sample Preparation and Applications,” edited by H. M. Kingston and S. J. Haswell. Since 2000 microwave chemistry emerged as a promising field of study in chemical synthesis. Companies like CEM, Biotage, Anton parr, and Milestone marketed a number of microwave reactors of varying capacities and temperature control that enlarges the applicability and prosperity of microwave-assisted synthesis.
Microwave Heating and Interaction with Materials
Published in Veera Gnaneswar Gude, Microwave-Mediated Biofuel Production, 2017
Microwave chemistry generally relies on the ability of the reaction mixture to efficiently absorb microwave energy, taking advantage of “microwave dielectric heating” phenomena involving dipolar polarization or ionic conduction mechanisms (Dallinger and Kappe 2007). In most cases this means that the material used for a particular transformation must be microwave absorbing. The ability of a specific solvent to convert microwave energy into heat at a given frequency and temperature is determined by the so called loss tangent (tan δ), expressed as the quotient, tan δ = ε”/ε’, where ε” is the dielectric loss, indicative of
In-situ Immobilization of Cd in Acidic Paddy Soil of Hunan Province, China by Layered Double Hydroxides
Published in Soil and Sediment Contamination: An International Journal, 2022
Peng Yu, Biao Li, Shun Li, Hui Liu, Zhiguo Wang, Chun Zhang, Wei Huang
Two kinds of LDHs (102A and 112A) were purchased from Shandong Vansivena Material Technology Co., Ltd. The pH values of amendments were measured by the pH meter (PHS-3C, Shanghai Precision Instrument Co., Ltd), 5.0 g of the amendment’s samples were initially sieved to < 1 mm, then adding to 250 mL of deionized water and shaking for 3 min. After that, the suspension stood for 15 min for pH determination. The BET surface area of amendments was carried out in Surface Area system (Quantachrome SI, Quantachrome, USA). Firstly, the sample was loaded into the sample tube and degassed at 120 °C in a vacuum for 6 h. After degassing, the sample was cooled to room temperature and then backfilled with helium. Finally, the weighed sample tube was loaded into the analysis station, and the liquid nitrogen was added to the dewar to start the adsorption and desorption test. The crystalline structure of samples was recorded by X-ray diffractometer (XRD-6000, Shimadzu, Japan). For total Cd of amendments determination, the amendments (0.2 g) were digested with HNO3 (6 mL), HCl (3 mL), and HF (2 mL) in a microwave digestion system (MDS-6G, Shanghai Sineo Microwave Chemistry Technology Co., Ltd., China) for 1 h. The concentration of Cd was determined by GF-AAS (Graphite Furnace Atomic Absorption Spectrometry) (Z-2700, Hitachi, Japan).
Distribution, pollution, and ecological risks of rare earth elements in soil of the northeastern Qinghai–Tibet Plateau
Published in Human and Ecological Risk Assessment: An International Journal, 2019
Jun Wu, Jian Lu, Leiming Li, Xiuyun Min, Zhenhua Zhang, Yongming Luo
Before instrumental analysis, 50 mg of soil sample was first put into a microwave digestion PTFE (poly tetra fluoroethylene) vessel, and followed by adding 2 mL of 37% HCl, 3 mL of 65% HNO3, and 2 mL of 65% HF. The PTFE vessel was placed into the microwave digestion system (MDS-6G, SINEO Microwave Chemistry Technology Co., Shanghai, China) and soil sample was digested for 1 h. After the digestion solution naturally cooled down, 2 mL of 65% HClO4 and 15 mL of 65% HNO3 were added into the solution, which was then evaporated at 180ºC to dry. The digestion samples were re-dissolved by 2.0 mL of 65% HNO3 and added with 2% HNO3 to a final volume of exactly 100 mL for analysis. Total 16 REEs including Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu were analyzed using an Agilent7900 inductively coupled plasma mass spectrometry (ICP-MS, Agilent Inc, USA). Standard solutions of individual REEs were purchased from Alfa Aesar (Thermo Fisher Scientific, USA). Method detection limits of REEs in soil are listed in Table 1. Two quality control samples spiked by standard REE solution were analyzed for every 10 real soil samples to assure the data quality. The recoveries of REEs in spiked quality control samples ranged from 96.1% to 107.3%.
Microwave assisted scolecite as heterogeneous catalyst for multicomponent one-pot synthesis of novel chromene scaffolds with quantitative yields
Published in Journal of the Chinese Advanced Materials Society, 2018
4H-chromenes, which are tetrahydrobenzo[b]pyrans [1–3] are heterocyclic compounds known for their diverse important biological characteristics like anticancer, anticoagulant, anti-anaphylactic, diuretic, and spasmolytic for a long time.[4–5] These 4H-chromenes have wide usability in cosmetics and agrochemicals.[6] Earlier, microwave chemistry [7] was used only when all other options to perform a particular reaction remained unsuccessful like long reaction times or high temperatures to complete the synthetic reactions.[8] These days, the practice has changed a lot due to the growing availability of microwave reactors in laboratories, and routine synthetic transformations are now being carried out by using microwave heating.[9] Microwave heating has capability to convert electromagnetic radiations into heat to initiate the chemical reactions.[10]