Current Issue : October-December Volume : 2021 Issue Number : 4 Articles : 5 Articles
A novel microwave annealing system and a specific processing condition are proposed for the pre-oxidation of carbon fiber. The microwave annealing system consists of a TM-mode resonant cavity and a silicon carbide (SiC) susceptor. The TM-mode cavity enhances the electric field at the center. The SiC susceptor absorbs part of the microwave energy and converts it to heat. The enhanced fields and the SiC susceptor provide both nonthermal and thermal treatments for fibrous materials with various dielectric properties. Furthermore, a two-step microwave annealing process is used to oxidize polyacrylonitrile (PAN) fiber. The scanning electron microscopy (SEM) images, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) results support the theory that the microwave annealing can achieve a high aromatic index of 66.39% in just 13 min, 9 times faster than the traditional processing time. The results of the Raman spectra also illustrate that the sheath-core factor of the microwave-heated specimen is closer to one than that of the conventional furnace-heated type, which agree with the images of the cross-section area....
'e oil and gas industry requires accurate sensors to control fluid flow in pipelines during the production process from horizontal and near horizontal wells. 'e extracted crude oil is usually a multiphase mixture of oil, water, and gas, and the accurate measurement of the ratio of each multiphase within the pipeline is an important parameter to manage wells efficiently by maximizing the hydrocarbons that can be extracted. Various methods have been developed for determining the phase ratio including mechanical, optical, X-ray or gamma ray, ultrasound, nuclear magnetic resonance (NMR), and rarely microwave techniques. However, these methods do not permit the knowledge of the real-time evolution of the phase ratio and are less precise. Here, we propose and develop by simulation two microwave systems, in horizontal and vertical polarizations, to choose the optimal configuration for crude pipeline imaging applications. First, the pipeline containing crude oil was modeled and its thermal and dielectric properties are proposed. 'en, the antennas array performances were optimized and assembled to the pipeline. Different numbers of antenna elements were successfully investigated using CST simulation in both vertical and horizontal polarizations to find the optimal number of antenna elements for the pipeline applications....
A diamond’s color grading is a dominant property that determines its market value. Its color quality is dependent on the light transmittance through the diamond and is largely influenced by nitrogen contamination, which induces a yellow/brown tint within the diamond, as well as by structural defects in the crystal (in rare cases boron contamination results in a blue tint). Generally, spectroscopic instrumentation (in the infrared or UV–visible spectral range) is used in industry to measure polished and rough diamonds, but the results are not accurate enough for precise determination of color grade. Thus, new methods should be developed to determine the color grade of diamonds at longer wavelengths, such as microwave (MV). No difference exists between rough and polished diamonds regarding stray light when the MW frequency is used. Thus, several waveguides that cover a frequency range of 3.95–26.5 GHz, as well as suitable resonator mirrors, have been developed using transmission/reflection and resonator methods. A good correlation between the S12 parameter and the nitrogen contamination content was found using the transmission/reflection method. It was concluded that electromagnetic property measurements of diamonds in the MW frequency range can be used to determine their nitrogen content and color grading. The MW technique results were in good agreement with those obtained from the infrared spectra of diamonds....
The synthesis of partially substituted silicon hydroxyapatite (Si-HAp) nanopowders was systematically investigated via the microwave-assisted hydrothermal process. The experiments were conducted at 150 C for 1 h using TMAS (C4H13NO5Si2) as a Si4+ precursor. To improve the Si4+ uptake in the hexagonal structure, the Si precursor was supplied above the stoichiometric molar ratio (0.2 M). The concentration of the TMAS aqueous solutions used varied between 0.3 and 1.8 M, corresponding to saturation levels of 1.5–9.0-fold. Rietveld refinement analyses indicated that Si incorporation occurred in the HAp lattice by replacing phosphate groups (PO4 3) with the silicate (SiO4 ) group. FT-IR and XPS analyses also confirmed the gradual uptake of SiO4 units in the HAp, as the saturation of Si4+ reached 1.8 M. TEM observations confirmed that Si-HAp agglomerates had a high crystallinity and are constituted by tiny rod-shaped particles with single-crystal habit. Furthermore, a reduction in the particle growth process took place by increasing the Si4+ excess content up to 1.8 M, and the excess of Si4+ triggered the fine rod-shaped particles self-assembly to form agglomerates. The agglomerate size that occurred with intermediate (0.99 mol%) and large (12.16 mol%) Si contents varied between 233.1 and 315.1 nm, respectively. The excess of Si in the hydrothermal medium might trigger the formation of the Si-HAp agglomerates prepared under fast kinetic reaction conditions assisted by the microwave heating. Consequently, the use of microwave heating-assisted hydrothermal conditions has delivered high processing efficiency to crystallize Si-HAp with a broad content of Si4+....
Intense ion beam production is of high importance for various versatile applications from accelerator injectors to secondary ion mass spectrometry (SIMS). For these purposes, different types of ion beams are needed and, accordingly, the optimum plasma to produce the desired ion beams. RFtype plasma features a simple structure, high plasma density and low plasma temperature, which is essential for negative ion beam production. A very compact RF-type ion source using a planar coil antenna has been developed at IMP for negative molecular oxygen ion beam production. In terms of high-intensity positive ion beam production, 2.45 GHz microwave power-excited plasma has been widely used. At IMP, we developed a 2.45 GHz plasma source with both ridged waveguide and coaxial antenna coupling schemes, tested successfully with intense beam production. Thanks to the plasma built with an external planar coil antenna, high O 2 production efficiency has been achieved, i.e., up to 43%. With 2.45 GHz microwave plasma, the ridged waveguide can support a higher power coupling of high efficiency that leads to the production of intense hydrogen beams up to 90 emA, whereas the coaxial antenna is less efficient in power coupling to plasma but can lead to attractive ion source compactness, with a reasonable beam extraction of several emA....
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