A thermodynamic and structural study of atomistic, nano and bulk systems

Atomistic and nanocrystalline materials exhibit significantly different properties than bulk materials. This work aims to compare thermodynamic and structural properties of atomistic, nanocrystalline and bulk materials using high temperature oxide melt drop solution calorimetry, high energy synchrotron X-ray diffraction and computational techniques using molecular mechanics modelling.; Oxidative drop solution calorimetry is being developed as a general method for sulfide thermochemistry. Enthalpies of formation (kJ/mol) from the elements (DeltaH°f) are determined for sphalerite (ZnS) (-206.53 +/- 4.03 kJ/mol), galena (PbS) (-98.12 +/- 4.37 kJ/mol), greenockite (hexagonal CdS) (-148.79 +/- 4.13 kJ/mol) and hawleyite (cubic CdS) (-147.65 +/- 4.28 kJ/mol). The enthalpy of formation of hawleyite was determined for the first time.; Oxide melt drop solution calorimetry was also developed for selenides. Enthalpies of formation (kJ/mol) from the elements (DeltaH°f) are determined for zinc selenide (ZnSe) (-160.13 +/- 2.91 kJ/mol), lead selenide (PbSe) (-100.83 +/- 4.39 kJ/mol), and cadmium selenide (CdSe) (-138.99 +/- 8.70 kJ/mol). The values for CdSe and PbSe match published data, the DeltaH°f value for CdSe from direct calorimetry is reported for the first time, and a more reliable value for ZnSe is proposed as available data for ZnSe are quite scattered.; High-temperature oxide melt solution calorimetry was used to determine the dehydration enthalpy and the formation enthalpy of cationic variants of zeolite beta (Li-BEA, Na-BEA, K-BEA, Rb-BEA and Cs-BEA) from the constituent oxides. The dehydration enthalpy per mole of water decreases in the order Li-BEA > Na-BEA >Cs-BEA > K-BEA >Rb-BEA. Molecular mechanics was used to investigate location of the alkali cations and bonding of water molecules in BEA zeolites. The somewhat smaller dehydration enthalpy of K-BEA can be attributed to weaker cation-water interaction, weaker cation-framework interaction, and absence of framework-water interaction.; The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25°C are 25.6 +/- 1.7 kJ/mol TO2 for the dehydrated zeolite and -8.45 +/- 0.94 kJ/mol TO2 for the fully hydrated zeolite; for Na-BEA they are -2.4 +/- 0.6 kJ/mol TO2 for the dehydrated and -17.8 +/- 1.0 kJ/mol TO2 for the fully hydrated zeolite. The integral dehydration enthalpy at 25°C is 33.2 +/- 1.8 kJ/mol H2O for Li-BEA and 16.5 +/- 1.1 kJ/mol H2O for Na-BEA. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents.; This study presents an analysis of the role of structural water in stabilization of bulk synthetic akaganeite (beta-FeOOH) and compare the structural behavior of bulk and nano akaganeite. Rietveld refinements using synchrotron X-ray powder diffraction data are presented. Akaganeite is, indeed, monoclinic with the Cl atoms located at the center of the tunnels and filling only ∼2.8% of the tunnel sites (0,0,0) in this sample. Structural water and vacancies occupy the remaining tunnel sites. There is no evidence of ordering of water molecules in the tunnels. In nanophase akaganeite, the diffraction pattern shows a mixture of akaganeite and a goethite-like phase. The destruction of the tunnel structure, because of the large fraction of tunnels exposed at the surface of the small particles, leads to the formation of this goethite-like phase, possibly a surface reconstruction on the akaganeite particles. As the particle size increases, the formation of the tunnel structure is complete and the goethite-like phase disappears. The closely balanced energetics of akaganeite and goethite permit this complex crossover in stability, with goethite or goethite-like phases present at small and large, but not intermediate, particle size.; The...