Microstructure evolution in densification of SiC ceramics by aluminium vapour infiltration and investigation of mechanical properties

The densification and phase formation of 6?wt% Y₂O₃ containing SiC compacts infiltrated by aluminium vapour were investigated. The densification occurred through infiltration of aluminium vapour that formed through a reaction between alumina and carbon powders at 2000?°C. Infiltrated specimens were evaluated concerning the density, phase, microstructure and mechanical properties including hardness and fracture toughness. X-ray diffraction studies showed the presence of yttrium aluminium garnet (YAG) and Al₂O₃ as the secondary phases along with other minor phases. Sectioning of the infiltrated specimen showed two regions: a dense layer starting from the surface of about 1?mm thickness followed by a relatively porous structure at the core. The effect of infiltration depth on densification and evolution of microstructure are studied. Also, the changes in Vickers’ hardness and fracture toughness with the increase in specimen depth are discussed.     

Effect of particle size on the mechanical properties of reaction bonded boron carbide ceramics

In the present communication, effect of boron carbide particle size on the mechanical properties such as hardness, fracture toughness and flexural strength of reaction bonded boron carbide (RBBC) ceramics were investigated. RBBC composites were produced by the reactive infiltration of molten silicon into porous preform containing boron carbide and free carbon. Boron carbide powders with mean particle size of 18.65 μm, 33.70 μm and 63.35 μm were chosen for the RBBC composites. The experimental results show that hardness increases from 1261.70±64.74 kg/mm² to 1674.90±100.00 kg/mm² and fracture toughness drops from 5.76±0.26 MPa m^1/2 to 3.4±0.37 MPa m^1/2. However, flexural strength decreases from 403.41±5.70 MPa to 256.15±25.05 MPa with the increase in particle size. Indentation induced cracks in RBBC are mainly median type and number of cracks increase with the increase of starting particle size.     

Predictions of High Strain Rate Failure Modes in Layered Aluminum Composites

A dislocation density-based crystalline plasticity formulation, specialized finite-element techniques, and rational crystallographic orientation relations were used to predict and characterize the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary distributions. Different layer arrangements were investigated for high strain rate applications and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-bonded interface and the potential delamination of the layers. Shear strain localization, dynamic cracking, and delamination are the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be used to optimize behavior for high strain rate applications.     

Development of a meta-model for the determination of technological value of cotton fiber using design of experiments and the TOPSIS method

To meet the requirements of the cotton spinning industry and achieve the best quality of ring-spun yarn, it becomes an imperative task to determine the technological values of cotton fibers. The availability of High Volume Instrument (HIV) data now makes it possible to evaluate the quality of cotton fiber with respect to some of its major physical properties. The fiber quality index (FQI), the spinning consistency index (SCI), and the multiplicative analytic hierarchy process (MAHP) are some of the popular approaches adopted by the spinning industry personnel to determine the quality values of cotton fibers. In this paper, while integrating the design of experiments (DoE) and the technique for order preference by similarity to ideal solution (TOPSIS), a regression meta-model is developed for determining the technological value of cotton fiber with respect to the TOPSIS score. This model identifies the statistically significant fiber properties and their interactions affecting the estimated TOPSIS score while fitting a polynomial to the experimental data in multiple linear regression analysis. It is observed that the uniformity index has no importance in quality value evaluation of the cotton fiber, although its interactions with other properties are statistically significant. A validation analysis shows an excellent degree of congruence of this meta-model with the existing models for cotton fiber quality determination.     

A literature review on integration of distributed energy resources in the perspective of control,protection and stability of microgrid

The concept of integration of distributed energy resources for formation of microgrid will be most significant in near future. The latest research and development in the field of microgrid as a promising power system through a comprehensive literature review is presented in this paper. It shows a broad overview on the worldwide research trend on microgrid which is most significant topic at present. This literature survey reveals that integration of distributed energy resources, operation, control, power quality issues and stability of microgrid system should be explored to implement microgrid successfully in real power scenario.     

Cadmium(II)‐Catalyzed C?N Cross‐Coupling of Amines with Aryl Iodides

Cadmium diacetate dihydrate [Cd(OAc)₂⋅2 H₂O] in combination with ethylene glycol catalyzes efficiently the C N cross‐coupling of amines with aryl iodides by a benzyne mechanism. Alkyl, aryl and heterocyclic amines are compatible with this system affording the aminated products in high to excellent yield.     

Geometry of quantum state space and quantum correlations

Quantum state space is endowed with a metric structure, and Riemannian monotone metric is an important geometric entity defined on such a metric space. Riemannian monotone metrics are very useful for information-theoretic and statistical considerations on the quantum state space. In this article, considering the quantum state space being spanned by \(2\times 2\) density matrices, we determine a particular Riemannian metric for a state \(\rho \) and show that if \(\rho \) gets entangled with another quantum state, the negativity of the generated entangled state is, upto a constant factor, equal to square root of that particular Riemannian metric . Our result clearly relates a geometric quantity to a measure of entanglement. Moreover, the result establishes the possibility of understanding quantum correlations through geometric approach.     

Influence of a few important parameters on the rheological behaviour of silicon carbide nanoparticles dispersed aqueous suspension

In this study, investigations have been carried out on the effect of a few important parameters such as molecular weight and concentration of dispersant (polyethyleneimine) as well as that of pH on the rheological behaviour of aqueous suspension comprising silicon carbide (SiC) nanoparticles. In addition to this, the effect of particle size and addition of finer SiC particles on the rheological behaviour of SiC suspension have been examined. It is observed that viscosity of suspension increases with the increase in molecular weight of dispersant and decreases as the concentration of dispersant increases. Further, it is noticed that viscosity of the suspension progressively increases below the pH ≈?7.6 and above the pH ≈?9.3, indicating that minimum viscosity i.e. maximum stabilization of suspension is obtained within the pH range of ≈ 7.6–9.3. It has been observed that variation of SiC particle size from submicrometer to nanometer range and addition of nanometric SiC powder in SiC suspension containing coarser particles increase the viscosity significantly.