Phase formation in Al2O3-C refractories with Al addition

Depending on the recipe and the firing conditions, several non-oxides can be formed in Al₂O₃-C refractories. In this paper, the effect of the purity of the recipe components on the phase formation in Al₂O₃-C refractories with Al addition was investigated. Two test series were sintered from 800 °C to 1600 °C under air embedded in coke breeze. One test series was with brown fused alumina, and the other was with tabular alumina. At temperatures of up to 1200 °C the phase formation was the same for both recipes. For temperatures greater than 1400 °C, the impurities of brown fused alumina enhanced the formation of a polytype, while Al₄O₄C and Al₂₈O₂₁C₆N₆ were formed in the other series. The findings explain the occurrence of several non-oxides in disequilibrium at the chosen temperatures. The occurrence of Al₄C₃ was of particular interest due to its low hydration resistance. It was formed at 1200 °C.     

Effect of MQL and nanofluid on the machinability aspects of hardened alloy steel

Abstract

The current research comprises of various machinability aspects of 4340 hardened alloy steel which are scrutinized with in context of improvements in main cutting force, tool flank wear, crater wear, surface roughness, micro-hardness, machined surface morphology, chip morphology, chip reduction coefficient and apparent coefficient of friction under three different cutting fluid applications i.e. compressed air, water soluble coolant and nanofluid (using eco-friendly radiator coolant as the base fluid and Al₂O₃ as the nanoparticle) using uncoated cermet cutting inserts and a comparative assessment was performed to select which fluid performed better in terms of various machining attributes among three cutting fluids. The minimum quantity lubrication technique (MQL) was used in which a smaller volume of coolant sprinkled at high pressure. This method is found as the most effective alternative to minimize health risks and machining costs, which is quite high in other setups. The test specimen was machined at three different cutting speeds i.e. 100, 120 and 140?m/min along with two machining parameters i.e. feed and depth of cut were kept constant respectively at 0.2?mm/rev and 0.4?mm. Outcomes made a conclusion that Al₂O₃ enriched ecofriendly nanocoolant outperformed both compressed air and water soluble coolant in terms of every machinability aspects.     

A delay and energy aware coordination mechanism for WSAN

In this paper, a delay and energy aware coordination mechanism (DEACM) has been devised for wireless sensor–actor networks. In DEACM, a two‐level hierarchical K‐hop clustering mechanism is used to organize the sensors and actors for communication. In the first level, sensors form a K‐hop cluster using actors as cluster heads, and sink is made as the cluster head in the second level to form a cluster among actors. Sensor nodes, which are 1‐hop away from the actors, also called as relay nodes are elected as backup cluster head (BCH) based on the residual energy and node degree. BCH collects the data from sensors when an actor is away to perform actions in the affected area. The scheme is evaluated through exhaustive simulation in NS2 along with other existing schemes. Different parameters like average event waiting time, event reliability, and average energy dissipation are compared, varying the number of sensors, actors, and data transfer rate. In general, it is observed that the proposed DEACM outperforms other existing schemes. Copyright © 2016 John Wiley & Sons, Ltd.     

Si/SiC-based DD hetero-structure IMPATTs as MM-wave power-source: a generalized large-signal analysis

A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (～ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 10⁶S/m²), susceptance (10.4 × 10⁷ S/m^2}), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (> 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.     

Design and development of a machine vision system using artificial neural network-based algorithm for automated coal characterization

Coal is heterogeneous in nature,and thus the characterization of coal is essential before its use for a specific purpose.Thus,the current study aims to develop ...     

Development of electronic materials from industrial waste red mud

The current research work presents the preparation and characterization of some new electronic materials using bismuth oxide (Bi₂O₃) and industrial waste red mud in different proportion by weight using a cost-effective mixed-oxide technique. Preliminary X-ray structural analysis exhibits the formation of compounds with structure analogous to that of BiFeO₃ compound along with some impurity phases. Studies of dielectric parameters (ε_r and tanδ) of these compounds as a function of temperature and frequency exhibit that they are almost temperature independent in the low temperature range and possess high relative permittivity with low loss in the high temperature range. Detailed studies of impedance and related parameters exhibit that the electrical properties of these materials are strongly dependent on temperature, and bear a good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR)—type behavior similar to that of semiconductors. Studies of electric modulus indicate the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The low leakage current and NTCR behavior of the sample have been verified from I–V characteristics. The nature of variation of dc conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The ac conductivity spectra show a typical-signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

Effect of MgO in the microstructure formation of zirconia mullite composites from sillimanite and zircon

The effect of MgO additive on the structural, microstructural and hardness properties of zirconia mullite (MUZ) has been discussed. The MgO additive in MUZ not only stabilizes the cubic zirconia phase but also acts as a sintering aid for the formation of cross-linked mullite grains. The electron micrographs of plasma fused MgO–MUZ shows a uniform arrangement of platelet structure of mullite and dendrite structure of zirconia on mullite surface. The micrograph of plasma sintered composites shows a ladder like structure and a complete cross-linked mullite grains whereas the surface morphology of conventionally sintered composites clearly indicates the presence of small and big grains close packed to each other. Appreciable hardness and higher optical band gap have been observed for plasma fused MgO–MUZ composites. A complete dissociation of sillimanite and zircon has been occurred in plasma fused composites for the complete conversion of MUZ whereas the complete dissociation of sillimanite and zircon has not observed in plasma sintered and conventionally sintered composites. These observations have been realized from the X-ray diffraction and Fourier transform infrared studies.     

Integration of nisin into nanoparticles for application in foods

Nisin and other similar food preservatives of natural origins have seen a substantial upsurge in global interest in recent years. The use of nanotechnology to regulate and manipulate nisin for enhanced capacities in the food and nutrition sector is expanding dramatically. Nanotechnology has significant food science applications in nanoparticle delivery systems, packaging, food security, and safety. However, there have been considerable issues regarding the use of nisin in the food sector, including its uncontrolled interactions with various food components, its degradation and electrostatic repulsion. These issues potentially limit its use. Alternate strategies, including a variety of nanoparticle systems such as nanoemulsions, polymeric nanoparticles, nanofibers, and combinations of nisin with other technologies, are employed to enhance the utility of nisin in the food industry. This review highlights the recent developments and new perspectives related to the uses of nisin in the food industry.Industrial relevanceThis review highlights the current status of nanotechnology in the food industry. The issues concerning use of nisin by the food industry are addressed. Nisin shows enhanced efficacy in combination with other current technologies for improved food safety.     

Prediction of acceleration length in turbulent gas–solid flows

CFD investigation for gas–solid flows in a horizontal pipe was performed using Euler–Euler approach or two-fluid model and accounting for four-way coupling. Calibration of the numerical model is obtained by confirming the numerical predictions with published experimental data. Based upon the axial profiles of the pressure gradient, the authors investigated the acceleration length for different particle properties and loadings. It is found that acceleration length increases generally with increasing particulate loading and/or decreasing gas phase mean flow velocity. However, the variations of acceleration length with particle diameter are quite different under different operating conditions. Finally, an empirical correlation for acceleration length (L_a) is proposed, which contains two terms: the first-term matches with the entrance length for gas only flow; whereas the second term is regarded as the enhancement due to addition of solids to gas flow. The accuracy of the correlation is approximately ±11%.