| This dissertation consists of two parts representing thermochemical study of two independent material systems. The first and major part presents calorimetric study on the thermodynamics of mixing, surface energies and water adsorption energies of SnO2, TiO2 and their solid solutions; the second part is a short side project, which describes an exploratory study of the heat of formation of GeSe2 phase change materials.;SnO2, TiO2 and their mixtures and solid solutions have attracted considerable attention. They are of interest in the fields of gas sensing and photocatalysis, There have been several theoretical calculations of energies of variously oriented surfaces of SnO2, but the surface energy and water adsorption energy of the rutile SnO2 and Ti xSn1-xO2 nanoparticles surface have not yet been experimentally investigated. The thermodynamics of mixing in oxide solid solutions is important in determining solid solubility, physical properties, diffusion coefficients, and the distribution of components among coexisting solid and liquid phases. No prior calorimetric data for mixing properties in SnO2 - TiO2 have been reported.;Surfaces and interfaces play a major role in chemical reactivity, catalysis, sintering and other processes involving solids. The surface energies of anhydrous and hydrated SnO2 nanoparticles were measured by combining high-temperature oxide melt solution calorimetry and water adsorption calorimetry. The average surface energies (enthalpies) of hydrated and anhydrous SnO2 nanoparticles were experimentally determined to be 1.49 +/- 0.01 J·m -2 and 1.72 +/- 0.01 J·m-2, respectively. The integral heat of water adsorption is -75 kJ·mol-1, with a chemisorbed maximum coverage of ∼ 5 H2O·nm -2. SnO2 has a smaller surface energy and less exothermic enthalpy of water adsorption than the isostructural TiO2 (rutile). This comparison suggests that the excellent sensing properties of SnO 2 may be a consequence of its relatively low affinity for surface H 2O molecules that compete with other gases for adsorption.;Using the same methodology, the surface energies of hydrated and anhydrous rutile SnO2-TiO2 solid solutions nanoparticles were also measured. The enthalpy of the anhydrous surface of Sn0.586Ti 0.414O2 is 2.02 +/- 0.03 J·m-2, and that of the hydrated surface is 1.68 +/- 0.03 J·m-2 . The integral heat of water adsorption is -80 kJ·mol -1, with a chemisorbed maximum coverage of ∼ 6 H2O·nm -2. These values are between those of TiO2 (rutile) and SnO2 (rutile).;We measured the average grain boundary energy of nanograined tin dioxide prepared by calcination, conventional sintering, and by spark plasma sintering (SPS). While the interface energy for calcined samples was 0.8 +/- 0.2 J.m-2, that for conventional sintered SnO2 (cold pressed and rapidly sintered isothermically) was 1.1 +/- 0.2 J.m -2, and 1.4 +/- 0.3 J.m-2 for the SPS one. Both sintered samples showed somewhat higher energies than the calcined one.;Germanium selenide systems, amorphous and crystalline, have remarkable electronic and optical properties, and hence they have many potential applications in electronic and optoelectronic devices. GeSe2 has been studied extensively. However, very few studies looked into their thermodynamic properties. We have determined the enthalpies of formation for GeSe2 (crystal) and GeSe2 (glass) using oxidative high temperature oxide melt solution calorimetry. The heat of formation value in this work for crystalline GeSe 2 agreed well with Kleppa and Boone's value by direct combination calorimetry [1], but the value for class GeSe2 is much less exothermic compare to the reference data [1, 2], which might because the glass samples are partially oxidized. An important conclusion is that the calorimetric methodology is relatively straightforward and can be applied to other chalcogenide glasses in the future. (Abstract shortened by UMI.). |
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