• V Saraswati

      Articles written in Bulletin of Materials Science

    • Microcrystals of cooperative-behaviour materials

      M S Multani R Vijayaraghavan M R Srinivasan P Ayyub V R Palkar V Saraswati A V Gurjar

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      Properties of materials exhibiting cooperative phenomena are likely to be modified on restricting the lattice size. Several such microcrystalline materials have been studied to infer general underlying principles. Ferroelectricity, ferromagnetism, superconductivity, and superfluidity in limited lattice sometimes not only show modified behaviour but also new behaviour not present in bulk. Microcrystals are considered to be free, coupled, grain-boundary-separated, or domain-wall-separated.

    • Amorphous state ferroelectricity, magnon scattering and phase stability in microparticle materials

      M S Multani P Ayyub V R Palkar M R Srinivasan V Saraswati R Vijayaraghavan DO Shah

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      Microparticles and micrograin ceramics show features distinct from the usual-sized polycrystalline materials. Amorphous state material combined with microparticle size for Pb(Zr0.51 Ti0.49)O3 mimics the dielectric behaviour of crystalline ferroelectricity in ABO3 compounds. Fine-grained Y3Fe5O12 (yig) synthesized by pressure sintering ofyig microparticles exhibit spinwave relaxation due to transit time across grain diameter. Applying microemulsion techniques for microparticle synthesis,γ-Fe2O3 has been synthesized. The phase stability fractionγ-Fe2O3/α-Fe2O3 is found to be a function of particle size. At very small sizesγ-Fe2O3 becomes amorphous, leading to interesting Mössbauer studies.

    • Optical properties of coloured transparent alumina gel monolith glasses

      V Saraswati G V Ramarao

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      Optical properties of transparent alumina prepared through gel process at room temperature and coloured with dopants have been studied. The absorption bands, molar absorptivity, effect of concentration and the dependence of oxidation state of copper on the copper content and water content are similar to the random network glasses. The ultraviolet absorption edge at lower energies confirm the disordered nature of the transition phase aluminasγ andδ. The absorption bands in the visible suggest the octahedral symmetry of oxygen around aluminum.

    • Microhardness measurement in nonmetallic materials

      V Saraswati

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      The load dependence of Vicker’s indentation hardness has been measured in some non-metallic materials and thin foils. A load of 100 g appears to be appropriate for comparing materials. Foil thickness, especially for soft metals like copper, must be at least twenty times the impression diagonal to get a correct value of hardness. The Meyer index varies for materials and can be used for comparison because it seems to pertain to the nature of chemical bonds. The index for boron carbide is similar to glass as was expected by Rice.

    • Special features of transparent, porous alumina xerogels

      V Saraswati

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      The process of gelation through chemical polymerization is described for the preparation of transparent alumina. The nature of disorder in the transition phases of alumina is discussed using the results of XRD, IR, optical absorption and NMR. The microstructures in the monolithic porous xerogels are observed to be fractals arising due to instabilities while drying. Phase separation noticed in copper and chromium-doped xerogels is attributed to fluctuations in polymer density.

    • Optical properties of chromium-doped transparent alumina xerogels

      V Saraswati

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      Optical properties of chromium-doped transparent alumina xerogels have been studied in the ultraviolet, visible and near infra-red regions. The coordination, valence state and symmetry of crystal field around the transition metal ion is found to change in different transition phases of the xerogel in accordance with the earlier conclusion that the metal ion penetrates into the alumina matrix and occupies aluminium sites. In boehmite and α-Al2O3 chromium is essentially in trivalent state, octahedrally coordinated, whereas in the transitionγ andδ phases tetrahedrally coordinated hexavalent state appears to be dominant. This agrees with the spinel structure expected for the transition phases.

    • Sintering and oxidation in gel-coated SiCw/Al2O3 composites

      V Saraswati

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      Boehmite gel-coated SiC whiskers have been studied as discs and as dispersed in gel and commercial alumina. The coated whiskers oxidize and react to some extent in alumina-rich composite compacts when heated in vacuum. In the absence of alumina as matrix, discs of coated whiskers turned brittle on heating above 1600°C. A density of 3.7g/cc was obtained for compacts of SiC whiskers in submicron alumina when sintered pressureless for 2 h at 1600°C. A smooth interface, compatible with the matrix, has resulted in good mechanical properties.

    • Crystallization of mica in the K2O-SiO2-MgO-MgF2 glass system

      V Saraswati K V S R Anjaneyulu

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      The growth of crystalline mica in K2O-SiO2-MgO-MgF2 glass has been studied and characterised through various techniques, viz. differential thermal analysis (DTA), X-ray diffraction (XRD), microscopy (SEM), and microhardness tests. It is observed that the addition of titania has a stronger influence on the growth of mica crystallites as compared to variation in heat treatment schedules.

    • In vivo andin vitro evaluation of a biomachinable glassceramic

      K Rathinam R Sivakumar V Saraswati

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      In this paper we describe the toxicological tests done on a machinable glassceramic, prepared at the Defence Metallurgical Research Laboratory. Tests show no toxicity and biocompatibility is inferred.

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