• K S Dubey

      Articles written in Bulletin of Materials Science

    • Viscous and thermodynamic behaviour of glass-forming organic liquids

      K S Dubey P Ramachandrarao

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      The free energy difference (ΔG) between an undercooled liquid and its corresponding equilibrium solid has been evaluated on the basis of a method involving Taylor series expansion of ΔG around its value at the equilibrium melting temperature. The resultant expression is shown to be capable of correctly estimating ΔG at temperatures as low as the glass transition temperature. The method is then enlarged to obtain the configurational entropy and used in conjunction with the Adam and Gibbs model to derive a novel expression for the viscosity of undercooled liquids. Most commonly used expressions for the temperature dependence of viscosity are shown to be approximations of the equation obtained in this study.

    • 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.

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