Simple and low-cost synthetic route for SiBCN ceramic powder from a boron-modified cyclotrisilazane

This study reports a simple and low-cost synthetic route for preparing SiBCN ceramic powder via pyrolysis of boron-modified cyclotrisilazane (BCTS). BCTS resins were synthesized by reacting boric acid with 1, 3, 5-trimethyl-1′, 3′, 5′-trivinylcyclotrisilazane (CTS) in the molar ratio of 1:1, 1:3, and 1:5. The boron modification in CTS resin resulted in optimum properties for preceramic polymers such as solubility in common solvents, processable viscosity (<20 cps) and high ceramic yield (>80 wt. %). The polymer to ceramic conversion was carried out at 1450 and 1650°C under a nitrogen atmosphere. The study demonstrated that the changes in CTS concentration and pyrolysis temperature significantly affected the evolution of ceramic phases, morphology, and elemental composition which were thoroughly investigated through XRD, SEM, and HRTEM techniques. The results revealed the formation of β-SiC, β-Si₃N₄, and oxide ceramic phases with BCTS in the molar ratio of 1:1 and 1:3; whereas, β-SiC, β-Si₃N₄, and turbostratic BN(C) ceramic phases were obtained with BCTS in the molar ratio of 1:5.     

An Aqueous Gelcasting Process for Sintered Silicon Carbide Ceramics

An aqueous gelcasting process for the preparation of dense as well as porous-sintered SiC ceramics has been described in this paper. A commercial silicon carbide powder coated with phenolic resin was used in this investigation. For the purpose of comparison, a pure SiC powder was also studied. ς potential and viscosity studies revealed that the pure SiC powder requires an electro-steric stabilization, whereas the phenolic resin-coated powder requires an electrostatic stabilization in order to produce their corresponding aqueous slurries with high solids content. Thermogravimetry and differential thermal analysis techniques have been used to study the decomposition behavior of phenolic resin. Aqueous slurries containing 25–50 vol% SiC powder were gelcast and sintered at 2150°C for 1 h. The sinterability of gelcast SiC samples was found to be highly influenced by the SiO₂ formed on the surface of SiC during aqueous processing, as confirmed by the Fourier transform infrared spectroscopy study. The results obtained from various characterization techniques suggest that in order to make dense SiC parts with >3.13 g/mL bulk density (a theoretical density of 97.5%) by an aqueous gelcasting process, the starting phenolic resin (∼5%)-coated SiC powder should possess a median particle size of <11.0 μm, surface area of >3.2 m²/g, a compact (green) density of >1.67 g/mL, and a B content of >0.5%. Further, by using polyethylene granules and organic foaming agents, sintered SiC foam with a porosity of >80%, a compressive strength of >16 MPa and a coefficient of thermal expansion of 4.574 × 10⁻⁶/°C between 30° and 700°C can be prepared by an aqueous gelcasting process, followed by sintering at 2150°C for 1 h.     

High-speed response of optically-pumped InGaAs/InGaAsP microdisklasers

Transient step-response and small-signal response of intensity-modulated InGaAs/InGaAsP microdisk lasers have been measured for the first time at room temperature. Microdisk lasers operating at room temperature have a measured turn-on delay of 100 ps and a -3 dB small-signal bandwidth in excess of 1.4 GHz     

Numerical and experimental studies on DC plasma spray torch

One of the challenging problems in the plasma spray technique is reproducibility of the coating quality. This problem is mainly associated with arc fluctuations, which affect the plasma jet temperature and velocity, inside the plasma torch. In this study, 3D numerical models are developed to study the arc behavior inside the torch and effect of arc fluctuations on plasma jet temperature and velocity. Plasma arc is simulated for different operating parameters. Different arc sizes are predicted by using thermo-dynamical principle of minimum entropy production for given torch power. The influence of arc current and gas flow rate on the Ar-N₂ plasma arc characteristics, plasma jet and torch efficiency is presented. Predicted torch efficiencies and arc voltages are comparable with measurements. At the nozzle exit, velocity shows stronger three-dimensional effect than temperature. Plasma jets are simulated using different nozzle exit profiles obtained from the plasma arc model and their temperature and velocity distributions are clarified.     

Unsupervised learning-based clustering approach for smart identification of pathologies and segmentation of tissues in brain magnetic resonance imaging

Human-made/developed algorithms provide automatic identification and segmentation of the tissues, lesions and tumor regions available in brain magnetic resonance scan images, which invocates predicaments such as high computational cost and low accuracy rate. Such hassles are reconciled with the utilization of an unsupervised approach in combination with clustering techniques. Initially, static features are chosen from the input image, which is fed to the self-organizing map (SOM), where the algorithm employs the dimensionality reduction of input images. Consecutively, the reduced SOM prototype of data is clustered by the modified fuzzy K-means (MFKM) algorithm. The MFKM algorithm can be modified in terms of membership variables because it operates with spatial information and converges quickly, and this would be of greater benefit to radiologists as they reduce the wrong predictions and voluminous time that normally occur owing to human involvement. The proposed algorithm provides 98.77% sensitivity and 97.5% specificity, which are better than any other traditional algorithms mentioned in this article.     

Formation and Densification Behavior of Magnesium Aluminate Spinel: The Influence of CaO and Moisture in the Precursors

Different grades of stoichiometric and non-stoichiometric dense magnesium aluminate spinel (MgAl₂O₄) grains were prepared by a conventional double-stage firing process using two types of alumina and four types of magnesia raw materials. The MgAl₂O₄ spinel formation was found to be highly influenced by CaO and moisture present in the precursor oxides as confirmed by thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (XRD) techniques. The Fourier transform-infrared spectroscopy (FTIR) study of the precursor oxides revealed the presence of moisture. Influence of alumina and magnesia composition on the densification behavior of MgAl₂O₄ spinels was assessed by characterizing bulk density (BD), apparent porosity (AP), water absorption (WA) capacity, and the microstructures of the stoichiometric, the magnesia-rich, and the alumina-rich spinels sintered at 1650°C for 1 h. Sintering studies indicate that to obtain dense stoichiometric spinel grains with >3.35 g/mL BD, <2.0% AP, and <0.5% WA, the spinel powder should possess a median particle size of <2 μm, CaO content of >0.9%, compact (green) density of >1.95 g/mL, and spinel content of >90%. Among various spinels synthesized, the magnesia-rich spinels exhibited superior properties in terms of high BD, low percentage of AP, and low WA capacity, whereas alumina-rich spinels showed inferior properties. Stoichiometric spinels exhibited an average grain size of 10 μm whereas alumina-rich spinels with 90% alumina had an average grain size of 20 μm. The increase in holding time at higher temperatures enhanced the sintering properties of the spinels, particularly the magnesia-rich spinels. Further, raw mixtures having >0.9% CaO exhibited better sintered properties as compared with others.     

A review on three‐dimensional graphene: Synthesis,electronic and biotechnology applications‐The Unknown Riddles

In the last decade, carbon‐based nanostructures such as buckyball (C₆₀), carbon nanotube (CNT), graphene and three‐dimensional (3D) graphene have been identified as promising materials for electronic, electrochemical energy storage (batteries and supercapacitors), optical and sensing applications. Since the discovery of graphene in 2004, scientists have devised mass production techniques and explored graphene as a promising material for a wide range of applications. Most of the electronic and solar cell applications require materials with good electronic conductivity, mobility and finite bandgap. Graphene is a zero bandgap material which prevents it from the mainstream applications. On the other hand, 3D graphene has good electronic conductivity, mobility, bandgap and electrochemical properties. This review article will focus on the synthesis of the 3D graphene, its structure‐property relationships, biotechnology and electronic applications and the hidden properties that are yet to be explored fully.     

ANFIS‐EM approach for PET brain image reconstruction

In this article, for the reconstruction of the positron emission tomography (PET) images, an iterative MAP algorithm was instigated with its adaptive neurofuzzy inference system based image segmentation techniques which we call adaptive neurofuzzy inference system based expectation maximization algorithm (ANFIS‐EM). This expectation maximization (EM) algorithm provides better image quality when compared with other traditional methodologies. The efficient result can be obtained using ANFIS‐EM algorithm. Unlike any usual EM algorithm, the predicted method that we call ANFIS‐EM minimizes the EM objective function using maximum a posteriori (MAP) method. In proposed method, the ANFIS‐EM algorithm was instigated by neural network based segmentation process in the image reconstruction. By the image quality parameter of PSNR value, the adaptive neurofuzzy based MAP algorithm and de‐noising algorithm compared and the PET input image is reconstructed and simulated in MATLAB/simulink package. Thus ANFIS‐EM algorithm provides 40% better peak signal to noise ratio (PSNR) when compared with MAP algorithm. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 1–6, 2015