Thermodynamic modelling of aqueous solutions and applications in some functional materials synthesis

Abstract: Modern advances in science and technology require thedevelopment of functional materials with improved performance.Such engineered materials often have a very complex compositionand specific microstructures. These factors impose a seriouschallenge for the synthesis and processing of advancedfunctional materials.With the developments in computational modelling techniquesand the available computer power, it is now possible to design,synthesise and fabricate advanced materials with fine tunedcharacteristics suitable for the required applications. Theavailable databases ofcondensed systems provide a powerfulmodelling tool for the design of materials with the desiredmicrostructure, phase, compositions and properties. Where as,the application of thermodynamic modelling of reactions insolution offers a rational approach for optimisation of thesynthesis route for advanced functional materials.Thus, the scope of this thesis covers several aspects ofmaterials chemistry. The first part deals with the criticalevaluation of thermodynamic data and modelling of condensedphase and aqueous solutions. The second part is an experimentalstudy on the synthesis and characterisation of some functionalmaterials.Several models for the correlation of the reaction constantsto ion-hydration and ion-interaction were reviewed and thespecific interaction theory(SIT) model was selected formodelling aquatic reactions. Thermodynamic evaluation ofCu(I,II)-OH--Cl--e-system has been performed. A series ofthermodynamic properties of stability constants log K°298, and enthalpy changes ?H°298, at infinite dilution as well as the values of?fG°298, ?fH°298, S°298for complex species were critically evaluated.The interaction coefficients of the SIT, ??, for theconcentration dependence of log K and ?H on the ionicmedia, were also obtained. A summary of the thermodynamicassessment of the Mn-O system is performed.In the second part, a brief review of the experimentaldetails of the synthesis, based on the modelling of aqueoussolution, is presented. Different functional materials havebeen prepared by the solution chemical method. This includesaluminium-based ceramic materials: Al13cluster based materials, Al2O3based intergranular TiN nanopowder composite, andMgAl2O4spinel and thermoelectric materials, CoSb3.Several techniques have been used for thecharacterisation of these materials.The synthesis of Al13cluster based sulphate or oxalate powders wasundertaken. It was found that the Al13sulphate powders formed 3 different crystalmorphologies. The pure tetrahedral-shaped crystals of Al13sulphate was obtained with cubic structure andthe unit cell parameter a= 17.9 Å. The Al13-oxalate precipitate had spherical particles withabout 200 nm in diameter and with a narrow particle sizedistribution. A study of the decomposition and phasetransformation of both precipitated salts showed that bothpowders were converted to ?-Al2O3at 1000 °C. The synthesis technique ofalumina based intergranular TiN nanopowder composite have beeninvestigated. MgAl2O4spinel ceramic powder was prepared and pure spinelphase fine powder was obtained after calcination at 1000°C. The synthesis and fabrication technique ofthermoelectric materials CoSb3with the Skutterudite structure have beeninvestigated and pure Skutterudites structure and nano sizedCoSb3has been obtained.Keywords:thermodynamics, modelling, nano-structure,Keggin, Skutterudites, spinel Al13-cluster, ?-Al2O3, MgAl2O4, CoSb3, thermoelectric, TiN composite, ceramic precursor,chemical synthesis, aqueous solution, coprecipitatation.