http://nopr.niscair.res.in/handle/123456789/2554 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/2592 Title: A self-sustaining reaction for titanium aluminides production via alumino-calciothermic reduction of TiO₂ <br/> <br/>Authors: Kamali, Ali Reza <br/> <br/>Abstract: Titanium aluminides can be produced via an alumino-calciothermic reduction of TiO₂ in presence of KClO₄. This reaction, named KRH process, has been studied in this paper. The results show that after heating of starting materials with rate of 20°C/min, a self-sustaining reaction is ignited at about 550C which led to the rapid increasing of system temperature to 1950°C during a short time of 192 s with a mean internal heating rate of around 437°C/min. <br/> <br/>Page(s): 429-432 http://nopr.niscair.res.in/handle/123456789/2591 Title: Effect of variation of PVP/PVA weight ratio on the behaviour of nanocrystalline silver <br/> <br/>Authors: Mallik, Manab; Mandal, R K <br/> <br/>Abstract: The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting size and shape of nanocrystalline (NC) silver is presented. It is shown that all the NC silver samples investigated, in this study, have displayed face centered cubic structure. The average coherently scattering domain size is estimated with the help of Scherrer equation. Having computed this, an attempt has been made to understand the UV-Vis spectra of the NC sols in terms of localized surface plasmon resonance (LSPR) behaviour. The change in the nature of LSPR in visible range of spectrum of the sols has been attributed to the complex interplay of shape, size and distribution of NC silver. <br/> <br/>Page(s): 425-428 http://nopr.niscair.res.in/handle/123456789/2590 Title: Synthesis and characterization of boron nitride nanotubes using a simple chemical method <br/> <br/>Authors: Singhal, S K; Srivastava, A K; Singh, B P; Gupta, Anil K <br/> <br/>Abstract: A simple two-step process is used for the growth of high purity multiwalled boron nitride (BN) nanotubes. In the first step, disordered nanostructured BN powder (aBN) is prepared chemically by heating a powdered mixture of KBH₄ and NH₄Cl (1:1) at 850ºC in N₂ followed by quenching the reaction product. In the second step, BN nanotubes are grown from the as-prepared aBN powder by annealing it at about 1200-1300ºC for 5-10 h in N₂. No catalyst material (Fe, Ni, Co, etc.) is intentionally added to aBN powder. This method of synthesis resulted in high purity multiwalled BN nanotubes of almost uniform diameter (10-30 nm) and length up to 5 µm, and, thus has a high aspect ratio with inherent characteristics of BN nanotubes, which may be useful for different applications. The BN nanotubes have been characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results obtained by this process are also compared with the similar type of BN nanotubes produced employing ball-milling and annealing technique. <br/> <br/>Page(s): 419-424 http://nopr.niscair.res.in/handle/123456789/2589 Title: On the calculation of derivatives of stress intensity factors using fractal finite element method <br/> <br/>Authors: Reddy, R M; Rao, B N <br/> <br/>Abstract: This paper presents a new fractal finite element based method for continuum-based shape sensitivity analysis for a crack in a homogeneous, isotropic, and two dimensional linear-elastic body subject to mixed-mode (modes I and II) loading conditions. The method is based on the material derivative concept of continuum mechanics, and direct differentiation. Unlike virtual crack extension techniques, no mesh perturbation is needed in the proposed method to calculate the sensitivity of stress-intensity factors. Since the governing variational equation is differentiated prior to the process of discretization, the resulting sensitivity equations predict the first-order sensitivity of the stress-intensity factors, K╻ and K╻╻, more efficiently and accurately than the finite-difference method. Unlike the integral based methods such as J-integral or M-integral no special finite elements and post-processing are needed to determine the first-order sensitivity of the stress-intensity factors, K╻ and K╻╻. Also a parametric study is carried out to examine the effects of the similarity ratio, the number of transformation terms, and the integration order on the quality of the numerical solutions. One mixed mode numerical example is presented to calculate the first-order derivative of the stress-intensity factors. The results show that the first-order sensitivities of the stress intensity factors obtained using the proposed method are in excellent agreement with the reference solutions obtained using the finite-difference method. <br/> <br/>Page(s): 391-418