3. Electronic Theses and Dissertations (ETDs) - All submissions
Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/45
Browse
3 results
Search Results
Item X-ray crystallographic studies of the amino acid serine(1998) Vlachakis, Natalie Georgia MargaretItem Structure and thermoresponsive behaviour of porous and non-porous borophosphates(2016) Mogodi, Mashikoane WilsonIn this PhD thesis, the synthesis, crystal chemistry and thermoresponsive behaviour of non-porous borophosphates [ABPO5 (A= Ca, Sr, Ba) and BPO4] and porous borophosphates [NH4Fe(III)[BP2O8(OH)] and MIxMIIz(H2O)2[BP2O8].zH2O (MI = Na, NH4 and MII = Mn, Co)] phases were investigated. Understanding the crystal structure dynamics as a function of temperature of the selected porous and non-porous borophosphates revealed the thermal stability of the studied compounds, while serving as a predictive measure of the effects of temperature on other materials properties and subsequent applications. The non-porous borophosphates were synthesized using the solid state method, whereas the porous borophosphates were synthesized using the hydrothermal method. The powder X-ray diffraction (PXRD) technique, along with the application of the Rietveld refinement method, was the principle characterisation technique employed for the non-destructive and non-invasive thermoresponsive characterisation of the studied borophosphate phases. This thesis consists of seven chapters, four of which are independent papers corresponding to four chapters. Chapter 1 reviews the relevant scientific literature, while chapter 2 describes the methods of characterisation used in this thesis. Concerning the highly thermally stable non-porous borophosphates, chapter 3 presents the thermal expansion behaviour of ABPO5 compounds, which have been determined from the sequential application of the Rietveld refinement method of variable temperature powder X-ray diffraction (VT-PXRD) data. For trigonal ABPO5 compounds, a near linear expansion of the unit cell axes was found for all structures as a function of temperature. The variation of the crystal structure with temperature of ABPO5 compounds was also established. With the general understanding that borophosphates display intriguing crystal structure architectures, chapter 4 describes the synthesis and characterisation of four metal borophosphate hydrates: NaMII(H2O)2[BP2O8](H2O); MII = Co (I), Mn (II) and (NH4)0.5MII1.25(H2O)2[BP2O8](H2O)0.5; MII = Co (III), Mn (IV). The structures refined at room temperature from PXRD data revealed that isostructural phases I and II have an ordered arrangement of water molecules in the voids, whereas isostructural phases III and IV have fractional and disordered distribution of water molecules in the voids. Scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR), variable temperature powder X-ray diffraction (VT-PXRD) and thermogravimetric analysis (TGA) for all compounds are also presented. Chapter 5 was an investigation into the synthesis, crystal structure and thermal properties of the porous iron borophosphate NH4Fe(III)[BP2O8(OH)]. Variable temperature PXRD and thermogravimetric analysis were used to investigate the compounds thermal stability and expansion behaviour. Thermal investigations indicated that the compound is stable up to 470 °C. Of great importance to the accurate and/or precise measurement of the crystal structures and lattice parameters of the phases investigated using powder diffraction was the correct application of the Rietveld refinement method to the measured diffraction data. Therefore, chapter 6 is an investigation into a number of different Rietveld refinement approaches, which were aimed at modelling the changes in the atomic coordinates of BPO4 as a function of temperature. Parametric Rietveld refinements and rigid body Rietveld refinements were among the refinement strategies employed.Item Crystallographic investigation of n-Aminopyridinium perhalometallates(2012-02-06) Lawrence, EsteeThis dissertation presents the results of a crystallographic investigation into nineteen novel n-aminopyridinium perhalometallates of the general formula (C5H7N2 +)2MX4 2- where n = 2, 3 or 4, M = Zn, Cd or Hg and X = Cl, Br or I. The aim was to identify positional effects of the cation hydrogen bonding donor groups on the structures and to possibly identify robust synthons. Overall structural trends were also studied. The hybrid crystals were synthesized using temperature controlled crystallization methods and were characterized using X- ray diffraction techniques. Eighteen of the nineteen hybrid crystals displayed isolated tetrahedral perhalometallate anions. The results were classified into six different classes of isostructural compounds. Eight of the nineteen hybrid structures (42%) contained water. The 42% include two 3-ammoniopyridinium structures and all cadmium and mercury containing 4-aminopyridinium structures. The effect of a change in metal and/ or halide on the structure was investigated, and the overall structural trends in each n-aminopyridinium family were identified. Four different synthons were observed in the 2-aminopyridinium series while one synthon was observed throughout the 4-aminopyridinium series. A common synthon was observed in both the 3-aminopyridinium and 3-ammoniopyridinium series.