Current Issue : April-June Volume : 2023 Issue Number : 2 Articles : 5 Articles
In this paper, we present a novel method for growing carbon nanotubes (CNTs) via microwave plasma chemical vapor deposition (MPCVD) on diamond and silicon substrates. Scanning electron microscopy (SEM) and Raman spectroscopy analyses revealed dense, multi-walled carbon nanotubes growing on the diamond substrate. Optical Emission Spectroscopy (OES) showed that in the process of growing carbon nanotubes with the MPCVD method, the CH4 introduced into the system is excited by microwaves and dissociated to form active radicals such as C2 and CH, which are considered the C source of the synthesized carbon nanotube. Observation with highresolution transmission electron microscopy (HRTEM) showed that most Ni catalyst nanoparticles that catalyze the growth of carbon nanotubes are located close to the diamond surface. In contrast, on the Si substrate, Ni catalyst nanoparticles were randomly distributed. A unique transition layer was observed between the diamond and carbon nanotubes, with the Ni particles being immersed into this transition layer and acting as anchors to fix the carbon nanotubes, resulting in a robust connection between the diamond and the CNT coating....
Enzymatic synthesis of ethyl hexanoate from hexanoic acid and ethanol in a solvent-free system, carried out at optimum conditions, has been modeled. The process follows a Ping-Pong Bi-Bi reaction rate and it is endothermic, so microwave heating is provided to prevent its shutdown. The mathematical model has been numerically solved with the FEM method. Results show that microwave heating can be successfully used to carry out this kind of reaction....
Fe–based metallic microwires possess unique microstructure and size effects, exhibiting favorable mechanical, electrical, and magnetic properties, thus distinguishing them as a possible agents for use as microwave absorbing materials. In this paper, the absorbing properties of Ni– doped Fe–based metallic microwires optimized by orthogonal experiments were investigated, and based on the optimal parameters, the influencing mechanism of the Ni doping amount on the absorbing properties was further analyzed. It was noted that at the frequency f = 8.36 GHz, the maximum reflection loss RL and electromagnetic wave absorption efficiency Aeff can reach −54.89 dB and 99.999%, respectively. Moreover, the Ni doping amount could result in the improved Waveabsorbing properties of composites, obtain the corresponding optimal parameters, and even change the position of the maximum absorption peak, which are all of great significance for practical engineering applications....
The application of recycled concrete can alleviate environmental pollution and has great practical value. In this study, microwave irradiation technology is used to treat recycled concrete in order to obtain reinforced recycled coarse aggregate. Then, the quasistatic and dynamic mechanical properties of concrete (C), recycled concrete (RC), and recycled concrete irradiated by microwave (MRC) were studied, and the effect of the replacement rate of coarse aggregates on its mechanical properties was also studied. The results showed that the quasi-static compressive strength ofMCRis higher than that of CR at all replacement rates. With the increase in the replacement rate, the quasi-static compressive strength of MCR decreases gradually, while the quasi-static compressive strength of CR decreases first and then increases, reaching the minimum value at 60%. The dynamic mechanical properties of CR and MCR all have an obvious strain rate effect. The dynamic increase factor (DIF) has an exponential relationship with the natural logarithm of the strain rate. The dynamic constitutive model of RC was established based on composite material mechanics and viscoelastic theory. The research content can provide guidance and basis for the study of mechanical properties and constitutive relationship of RC....
The precise calculation of atmospheric absorption in a microwave band is highly important for atmospheric remote-sensing with ground-based and satellite-borne radiometers, as it is a key element in procedures for temperature, humidity or trace gas concentration retrieval. The accuracy of the absorption model directly affects the accuracy of the retrieved information and reliability of the resulting forecasts. In this study, we analyze the difference between observed and simulated microwave spectra obtained from more than four years of microwave and radiosonde observations over Nizhny Novgorod (56.2◦N, 44◦E).We focus on zenith-measured microwave data in the 20–60 GHz frequency range in clear-sky conditions. The use of a conventional absorption model in simulations leads to a significant difference in frequency channels within the 51–54 GHz range, while calculations employing a more accurate model based on the Energy Corrected Sudden (ECS) formalism for molecular oxygen absorption reduces the difference several-fold....
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