Chemical ordering as a precursor to formation of orderedδ-UZr2phase: a theoretical and experimental study.

A combination of special quasi-random structure (SQS) analysis, density functional theory (DFT) based simulations and experimental techniques are employed in determining the transformation pathway for the disorderedγ-(U, Zr) phase (bcc structure) to transform into the chemically orderedδ-UZr2phase (C32, AlB2type structure). A novel Monte-Carlo based strategy is developed to generate SQS structures to study theß→ωdisplacive phase transformation in A1-xBxbinary random alloy. Structures generated with this strategy and using DFT calculations, it is determined that (222)bccplane collapse mechanism is energetically unfavorable in chemically disordered environment at UZr2composition. A mechanically and dynamically stable 24 atom SQS structure is derived which serves as a structural model of chemically orderedδ-UZr2structure. Finally, a thermodynamic basis for the mechanism of theγtoδtransformation has been established which ensures chemical ordering is a precursor to the subsequent displacive transformation to form chemically orderedδ-UZr2structure.

Organic-Inorganic Composite Films Based on Gd3Ga3Al2O12:Ce Scintillator Nanoparticles for X-ray Imaging Applications.

Organic-inorganic nanocomposite self-standing films of Gd3Ga3Al2O12 (GGAG) uniformly dispersed in poly(methyl methacrylate) (PMMA) and polystyrene polymer are prepared for radiography application. GGAG:Ce nanoscintillator has been chosen because of its high light output and fast decay time. The nanopowder of GGAG is synthesized by coprecipitation method and dispersed in the polymer matrix by a simple blending technique. The nanocomposite films of thickness in the range of 150-450 µm with a very high inorganic content is achieved by this technique. These films are characterized by their uniformity, optical absorption, photoluminescence, and radioluminescence. These films are further tested for their application in radiography by recording X-ray images using a commercially available charge-coupled device camera. A resolution of 10 lp/mm is obtained using GGAG:PMMA composite film with 50% loading, confirming their application in imaging devices.

Influence of Cu on modifying the beta phase and enhancing the mechanical properties of recycled Al-Si-Fe cast alloys.

High iron impurity affects the castability and the tensile properties of the recycled Al-Si alloys due to the presence of the Fe containing intermetallic ß-Al9Fe2Si2 phase. To date only Mn addition is known to transform the ß-Al9Fe2Si2 phase in the Al-Si-Fe system. However, for the first time, as reported here, it is shown that ß-phase transforms to the ω-Al7Cu2Fe phase in the presence of Cu, after solutionization at 793 K. The ω-phase decomposes below 673 K resulting into the formation of θ-Al2Cu phase. However, the present thermodynamic description of the Al-Si-Fe-Cu system needs finer tuning to accurately predict the stability of the ω-phase in these alloys. In the present study, an attempt was made to enhance the strength of Al-6wt%Si-2wt%Fe model recycled cast alloy with different amount of Cu addition. Microstructural and XRD analysis were carried out in detail to show the influence of Cu and the stability range of the ω-phase. Tensile properties and micro-hardness values are also reported for both as-cast and solutionized alloys with different amount of Cu without and with ageing treatment at 473 K. The increase in strength due to addition of Cu, in Fe-rich Al-Si alloys is promising from the alloy recyclability point of view.

Porous nano-structured micro-granules from silica-milk bi-colloidal suspension: Synthesis and characterization.

Synthesis and characterization of nano-structured porous granules, with fairly defined morphology and porosity, is crucial because such granules are widely utilized for various technological applications. However, an easy, one-step, economic synthesis protocol for large scale production is extremely desirable. In the present work, we have reported the synthesis and characterization of the nano-structured micro-granules using aerosol drying of bi-colloidal suspension of nano-silica and milk. Removal of soft organic component from the granules results in formation of meso and macro pores with moderate specific surface area. Granule morphology and porosity depends strongly on the concentration ratio of the individual components in the drying aerosol as well as the interaction between them.

Temperature Mediated Morphological Transition during Drying of Spray Colloidal Droplets.

Understanding how a tiny dilute evaporative colloidal spray droplet gets transformed into a microgranule with a characteristic morphology is crucial from scientific as well as technological points of view. In the present work, it is demonstrated that the morphology and the size distribution of the microcapsules can be tuned simply by adjusting the drying temperature. Shape and size of the capsules are quantified at four different drying temperatures. It is shown that the morphology transits gradually from sphere to toroid with increasing temperature keeping the average volume-fraction of the correlated nanoparticles nearly unaffected for the synthesized granules. A plausible mechanism for the chronological pathway of such morphological transformation is illustrated. Computer simulation corroborates the experimentally observed morphological transition. The variation in hollowness and buckling tendency of the capsules are elucidated by scattering and imaging techniques.

Optimization of parameters by Taguchi method for controlling purity of carbon nanotubes in chemical vapour deposition technique.

The process parameters (viz. temperature of synthesis, type of catalyst, concentration of catalyst and type of catalyst-support material) for controlling purity of carbon nanotubes synthesized by catalytic chemical vapour deposition of acetylene have been optimized by analyzing the experimental results using Taguchi method. It has been observed that the catalyst-support material has the maximum (59.4%) and the temperature of synthesis has the minimum effect (2.1%) on purity of the nanotubes. At optimum condition (15% ferrocene supported on carbon black at the synthesis temperature of 700 degrees C) the purity of nanotubes was found out to be 96.2% with yield of 1900%. Thermogravimetry has been used to assess purity of nanotubes. These nantubes have been further characterized by scanning electron microscopy, transmission electron microscopy and Raman Spectroscopy. Small angle neutron scattering has been used to find out their average inner and outer diameter using an appropriate model. The nanotubes are well crystallized but with wide range of diameter varying between 20-150 nm.