• R K MISHRA

      Articles written in Bulletin of Materials Science

    • Thermodynamic behaviour of undercooled melts

      R K Mishra K S Dubey

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      The Gibbs free energy difference (ΔG) between the undercooled liquid and the equilibrium solid phases has been studied for the various kinds of glass forming melts such as metallic, molecular and oxides melts using the hole theory of liquids and an excellent agreement is found between calculated and experimental values of ΔG. The study is made for non-glass forming melts also. The temperature dependence of enthalpy difference (ΔH) and entropy difference (ΔS) between the two phases, liquid and solid, has also been studied. The Kauzmann temperature (T0) has been estimated using the expression for ΔS and a linear relation is found between the reduced glass transition temperature (Tg/Tm) and (T0)/Tm). The residual entropy (ΔSR) has been estimated for glass forming melts and an attempt is made to correlate ΔSR,Tg,T0, andTm which play a very important role in the study of glass forming melts.

    • Viscous behaviour of glass-forming liquids: a thermodynamic approach

      R K Mishra K S Dubey

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      The temperature dependence of the viscosity of the undercooled melts exhibits an important role in the study of nucleation, crystal growth and the glass-forming ability of materials. Several attempts have been made to study the viscous behaviour of the glass-forming melts and these investigations are mainly based on free volume theory as well as on the configurational entropy model. In the present investigation, an attempt has been made to correlate the thermodynamic parameters with the viscosity of the glass-forming melts and to study the temperature dependence of the viscosity of undercooled liquids on the basis of the free volume theory as well as on the basis of the configurational entropy model of Adam and Gibbs. The entire study is confined on the expression for thermodynamic parameters reported by the authors recently. The expression obtained has been successfully applied to study the temperature dependence of the viscosity of the metallic, molecular and oxide glass-forming liquids.

    • Leaching studies on borosilicate glasses for the immobilization of high-level radioactive waste in the pellet form subjected to aggressive test conditions

      VIDYA S THORAT R K MISHRA V SUDARSAN AMAR KUMAR A K TYAGI C P KAUSHIK

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      Pellet leaching and associated thermal and structural changes of sodium borosilicate (NBS) glass, used for the immobilization of high-level radioactive liquid waste, subjected to aggressive test conditions have been compared with international simple glass (ISG) subjected to the same leaching conditions. The crystalline phase getting separated out from NBS glass is found to be different for pellets and powder leaching experiments and this has been explained based on the difference in the extent of leaching occurring with glass samples in the two experiments. Based on Fourier transform infrared studies, it is inferred that, unlike in the ISG sample, Si–O–Si/B structural units become more ordered with the leaching in the case of NBS glass, and this is attributed to the partial network destruction occurring with NBS glass and crystallization of the SiO₂ phase from the glass matrix. Both the NBS glass and ISG sample show L-centre emission and the emission intensity remained unaffected with leaching, confirming that the local environment around non-bridging oxygen atoms in the NBS glass and ISG sample are unaffected and leaching occurs through network dissolution.

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