List of Titles

Rocking curve measurements revisited

- Masiello, Fabio, Cembali, Gianfranco, Chumakov, Alexander I., Connell, S. H., Ferrero, Claudio, Hartwig, Jurgen, Sergeev, Ilya, Van Vaerenbergh, Pierre

Authors: Masiello, Fabio , Cembali, Gianfranco , Chumakov, Alexander I. , Connell, S. H. , Ferrero, Claudio , Hartwig, Jurgen , Sergeev, Ilya , Van Vaerenbergh, Pierre
Date: 2014
Subjects: Crystallography , Diffraction , X-rays - Diffraction , Crystals - Optical properties , Curves
Type: Article
Identifier: uj:5515 , ISSN 1600-5767 , http://hdl.handle.net/10210/13755
Description: The study of materials by diffraction methods started about 100 years ago with the pioneering experiment of Laue, Friedrich and Knipping, when the first X-ray diffraction patterns of single crystals were obtained (Friedrich et al., 1912). This was the beginning of a rapid development fostering many diffraction-based methods and techniques, which is still continuing. The measurement of rocking curves and the associated derived quantitative parameters, such as the ‘full width at half-maximum’ (FWHM) of the curves, has been performed since at least 1921 (Davis & Stempel, 1921) by exploiting the X-ray diffraction (XRD) properties of crystals. Since then, this has become one of the most powerful methods for the diffraction-based characterization of crystalline materials. The experimentally closely related method of X-ray diffraction imaging or X-ray diffraction topography has been used since about 1931 (Berg, 1931). Soon after World War II, the requirements of the electronics industry for the nondestructive analysis of defects in semiconductor materials like silicon and germanium (and others) boosted the improvement of these methods to their modern high-resolution variants like high-resolution X-ray diffraction and in particular high-resolution and high strain sensitivity X-ray topography (Bond & Andrus, 1952; Lang, 1957). This evolution was additionally accelerated in the late 1970s by the use of synchrotrons as dedicated X-ray sources and later on, starting in the 1990s, by the use of third-generation synchrotron sources....
Full Text:

Quick View

The crystal chemistry of heptadecyl- and octadecyl- containing n-alkylammonium halides and esters

- Rademeyer, Melanie

Authors: Rademeyer, Melanie
Date: 2012-08-27
Subjects: Crystallography , Hydrocarbons , Halides , Esters
Type: Thesis
Identifier: uj:3249 , http://hdl.handle.net/10210/6658
Description: M.Sc. , Molecules containing a long saturated carbon chain are present in many natural and commercial products. Due to the conformational flexibility of the carbon chain, different molecular conformations of these molecules are possible resulting in polymorphism. The crystal structure of a material greatly influences its chemical and physical properties, leading to different properties for different polymorphs. Designing materials with specific properties requires the understanding of the underlying fundamental parameters and forces influencing the packing of molecules in the crystal. A thorough literature study was conducted to determine the crystallographic research that has been done long chain compounds. Not only did this literature study lead to the identification of possible research fields, but also provided a solid background concerning the crystallographic behavior of these systems. In this project we investigated the polymorphism of simple molecules containing a saturated carbon chain with seventeen or eighteen carbons. Two systems are investigated namely n-alkylammonium halides and esters of fatty acids. By varying crystallization conditions different polymorphs of each compound can be obtained. Various experimental techniques were employed to shed light on the structure and packing of the long chain molecules in the different polymorphs. The crystal structure of the low temperature polymorph of n-octadecylammonium bromide was determined, as well as the cell dimensions of the low temperature form of noctadecylammonium chloride. The unit cell dimensions of n-octadecylammonium iodide monohydrate was also determined. The structures of the methyl and ethyl esters of noctadecanoic acid and the symmetrical -ester heptadecyl-heptadecanoate was investigated. In this project a young, dynamic research field was investigated. This led to the identification of other possible fields of study. Because there are not many reports in the literature on the crystallographic characteristics of these compounds, the evolving of the project required a lot of creativity.
Full Text:

Quick View

Removal and recovery of heavy metal from multi-component metal effluent by reduction crystallization

- Phetla, Tebogo Pilgrene

Authors: Phetla, Tebogo Pilgrene
Date: 2012-06-06
Subjects: Wastewater treatment , Sewage purification , Heavy metals absorption and adsorption , Heavy metal recovery , Chemical reduction , Crystallography
Type: Thesis
Identifier: uj:2486 , http://hdl.handle.net/10210/4940
Description: M.Tech. , The removal and recovery of heavy metals from effluents has been a subject of significant importance due the negative impact these toxic metals have on human health and the environment as a result of water and soil pollution. Precipitation is the mostly widely used wastewater treatment method because it is the most economical and easier to implement and operate on a large scale. However, traditional precipitation methods using lime, sulfides or hydroxides recover metals in the form of a sludge which is not reusable and has to be disposed in landfills creating a potential environmental hazard and resulting in loss of valuable minerals. The current focus in effluent treatment is now on the recovery and re-use of these heavy metals rather than removal and disposal. This study investigated the use of hydrazine as a reducing agent to remove and recover Ni2+, Cu2+, Co2+ and Fe2+ from effluent by reduction crystallization. In this process chemically reduced aqueous metal ions were plated on to a base substrate (nickel powder) with no electrical current required for deposition. A feasibility study was carried out to test the efficiency and find the optimum operating conditions for this method and generate an understanding of the chemical and particulate process occurring. The results obtained indicate that hydrazine is an effective reducing agent for removal and crystallization of Ni2+, Cu2+, Co2+ and Fe2+/ Fe3+ into their elemental states with nickel powder as a seeding material. Over 99 % of metals were removed from the effluent in all the systems (Ni-only, Ni-Cu, Ni-Fe and Ni-Fe). Breakage, aggregation and molecular growth were identified as the predominant mechanisms occurring during the reduction crystallization process in Ni-only, Ni-Cu, Ni- Co systems and there was evidence of nucleation in Ni-Fe solution. These finding were confirmed by analysing the scanning electron micrographs of the powder obtained. A nearly spherical structure powder with wide distribution in particle size and evidence of fragmentation was obtained in all the experimental runs. vii The residual concentrations obtained were far below the required limit for effluent discharge into sewer where 20 mg/L Ni, 20 mg/L Cu and 20 mg/L Fe and the total metal concentration of 50 mg/L for Fe, Cr, Cu, Ni, Zn and Cd is stipulated. Reduction crystallization using hydrazine as a reducing agent can be utilized for controlling environmental pollution and eliminating hazardous metals from the environment.
Full Text:

Quick View

Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal.

- Guzei, Ilia, Herbst-Irmer, Regine, Munyaneza, Apollinaire, Darkwa, James

Authors: Guzei, Ilia , Herbst-Irmer, Regine , Munyaneza, Apollinaire , Darkwa, James
Date: 2012
Subjects: Crystallography , X-ray structural determination , Twinned crystals
Type: Article
Identifier: uj:5852 , ISSN 0108-7681 , http://hdl.handle.net/10210/7939
Description: A detailed description of the procedures utilized in the nonroutine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.
Full Text: