Formation of tungsten carbide nanoparticles by wire explosion process

Tungsten carbide nanoparticles (NPs) were synthesized by wire explosion process (WEP) in gas ambient as carbon source. Formation of tungsten carbide (WC_1−X) in a single step by WEP using methane and argon-acetylene mixture as carburizing medium, is detailed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to observe the phase and morphology of the produced NPs. In WEP, morphology and phase of NPs are controlled using different levels of energy ratio, K (ratio of energy supplied to wire and sublimation energy of wire), type and pressure, P of ambience. High purity WC_1−X NPs was synthesized in methane ambience with a high K (=19) and a high P (270 kPa). A thorough study has been made to understand the impact of type of carburizing medium. Methane-acetylene mixture gave two phases of carbides. Argon-acetylene ambience provided complete carburization in specific cases. In general, the formed NPs are spherical in shape. Formation mechanism of tungsten carbide NPs is detailed in the work.     

Rapid synthesis of nanocrystalline YAG via microwave‐assisted solvothermal process

A rapid synthesis procedure for the preparation of nanocrystalline yttrium aluminium garnet (nYAG) particles has been developed, for the first time, using the combination of subcritical conditions and microwave irradiation. It is believed that the use of butanediol delayed the onset of pressure rise due to its low partial pressure, while the microwaves facilitated a selective crystallization of nanocrystalline YAG particles in the solvent medium. This methodology was found to encourage rapid bulk nucleation with minimal particle growth or agglomeration of nYAG particles. The resultant powder characteristics, examined using XRD and TEM analyses, revealed that a narrow window of pressure and temperature conditions needed to be maintained to achieve spherical particles in the size range 60‐80 nm without any intermediate phases being formed. The STEM/EDX and FTIR results obtained suggested that the nucleated YAG particles were masked by carbon clouds until they were completely crystallized into single phase YAG particles; this allowed them to be dispersed in water with little agglomeration.     

Understanding the water droplet initiated discharges on gamma irradiated silicone rubber insulation

Corona inception voltage (CIV) due to water droplet on gamma‐irradiated silicone rubber indicates that its value reduces with increase of conductivity and with number of droplet in the electrode gap along the axis of the electrode. Increase in dosage of gamma irradiation to silicone rubber reduces the CIV. The UHF signal generated during corona inception due to water droplet has frequency bandwidth in the range of 0.3–1.2 GHz. The discharges occur in the phase range of 30°–130° in the positive half cycle and about 210°–270° in the negative half cycle. The water droplet shape gets altered on application of voltage. Surface charge accumulation studies indicate characteristic change with gamma irradiated specimen. In the presence of water droplet, the charge decay occurs rapidly with a single droplet and with three droplets. Thermal analysis of gamma radiation dosed samples reveals the destabilization of silicone material and the formation of higher order cyclic siloxane oligomers and oxygenated organics, which are expected to act as potential charge trapping sites. POLYM. ENG. SCI., 59:182–191, 2019. © 2018 Society of Plastics Engineers     

Gas holdup and overall volumetric mass transfer coefficient in a modified reversed flow jet loop reactor

Experiments were conducted in a modified reversed flow jet loop reactor having the liquid outlet at the top of the reactor to determine the gas holdup and overall volumetric mass transfer coefficient in the air-water system. The influence of gas and liquid flow rates, and the draft tube to reactor diameter ratio were studied. It was observed that both gas holdup and volumetric mass transfer coefficient increased with increased gas and liquid flow rates and were found to be significantly higher in the modified reactor compared to the conventional one. The optimum draft tube to reactor diameter ratio was found to be in the range of 0.4 to 0.5. Empirical correlations are presented to predict gas holdup and overall volumetric mass transfer coefficient in terms of operational and geometrical variables.     

GTD analysis of a hyperboloidal subreflector with conical flange attachment

A geometrical theory of diffraction (GTD) analysis of the principal plane far-field radiation patterns of a hyperboloidal subreflector with a conical flange attachment (HWF) fed by a primary feed located at its focus is presented. While using the uniform geometrical theory of diffraction (UGTD) for evaluating the nonaxial fields, the method of equivalent currents is used in the axial region. In this paper, both the diffraction by the wedge formed between the hyperboloid and the conical flange and the diffraction by the edge of the flange are considered. While considering the diffraction by the edge due to the diffracted ray from the wedge in theH-plane, the slope diffraction technique has been used. The computed diffracted farfields of a typical HWF illuminated by a high performance primary feed shows good agreement with the available measured data and with the results based on the method of physical optics (PO). The sharp cutoff and the low spillover characteristics of the HWF are highlighted by comparing its radiation pattern with that of a hyperboloid without a flange. Further, the effects of the different parameters of the HWF on its radiation pattern are also studied and plotted, so that these results can be utilized in the design of the HWF for a specific requirement.     

Ensembles of radial basis function networks for spectroscopicdetection of cervical precancer

The mortality related to cervical cancer can be substantially reduced through early detection and treatment. However, current detection techniques, such as Pap smear and colposcopy, fail to achieve a concurrently high sensitivity and specificity. In vivo fluorescence spectroscopy is a technique which quickly, noninvasively and quantitatively probes the biochemical and morphological changes that occur in precancerous tissue. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired from 361 cervical sites from 95 patients at 337-, 380-, and 460-nm excitation wavelengths. The multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs required to discriminate healthy tissue samples from precancerous tissue samples. The use of connectionist methods such as multilayered perceptrons, radial basis function (RBF) networks, and ensembles of such networks was investigated. RBF ensemble algorithms based on fluorescence spectra potentially provide automated and near real-time implementation of precancer detection in the hands of nonexperts. The results are more reliable, direct, and accurate than those achieved by either human experts or multivariate statistical algorithms     

Polarimetric investigation of materials with both linear and circular anisotropy

Abstract

We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four characteristics of anisotropic samples by measuring the output intensity and polarization corresponding to different input polarization azimuths and fitting the theoretical and experimental results. In our experiments we have used films of side-chain azobenzene polyesters in which optical anisotropy had been previously induced on illumination with elliptically polarized light.     

Suppression of Red Luminescence in Wire Explosion Derived Eu:ZnO

Europium oxide (Eu₂O₃) is coated on zinc (Zn) wire using the electrophoretic deposition process. The coated Zn wire is subjected to the wire explosion process (WEP) which is rapid (< 15 min), and chimie douce (soft chemical, low temperature), in nature; this results in the formation of Eu doped ZnO. The explosion chamber contains oxygen (99.9%) at atmospheric pressure. Electron micrographs indicate that the particle sizes are ～ 80 nm. Diffractogram-based analysis suggests that the crystallite size is ~ 18–20 nm in the as-prepared doped ZnO nanoparticles. Electron paramagnetic resonance shows the presence of Zn vacancies and the cryo-photoluminescence spectrum indicates that Eu exists in the + 3 state. A combined Williamson–Hall plot and Kisielowski’s model based analysis indicates that Eu is a substitutional dopant in WEP derived Eu:ZnO particles. It is estimated that this material has ～ 0.24 at.% doping. This analysis also shows that, unlike another popular material GaN, in the case of ZnO, Eu³⁺ strictly substitutes for Zn²⁺ (i.e., dopant replacing a cation–anion pair does not seem possible). It may be noted that Eu³⁺ in a suitable host is oftentimes reported to be an efficient luminophore. The IR spectra show a band shift from 486 cm^?1 to 493 cm^?1; with peak shifts from 436 cm^?1 to 430 cm^?1 in Raman spectra. These too indicate the presence of Eu in the samples. However, at room temperature, only green luminescence (centered at 534 nm) is observed from the sample indicating (1) high concentrations of O_Zn anti-site defects and Zn vacancies, and (2) concomitant quenching of the luminescence at room temperature. Our results suggest that WEP is viable for synthesizing rare earth doped ceramic materials. However, obtaining efficient phosphors using this approach will likely require, (1) reduction of defect densities, and (2) appropriate passivation using post-processing.     

S,N co-doped graphene quantum dots decorated TiO2 and supported with carbon for oxygen reduction reaction catalysis

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO₂/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO₂. This composite is supported on carbon on heating at 800 °C under N₂ atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO₂/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec^?1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO₂/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO₂, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO₂ interface and subsequently from the carbon surface to the S,N-GQD/TiO_2.