The regulations for water fluoridation of South African municipal waters up to the optimum fluoride (F-) concentration of 0.7 mg/L, (Government Gazette, 2001) have been legislated. Fluoridation processes need accurate analytical methodology for the determination of F- , because F- has a narrow margin of safety between beneficial and toxic levels. In this work the analytical chemistry of F- was investigated comprehensively and guidelines compiled for the accurate determination of low level F- (between 0.05 to 1 mg/L) in aqueous systems. The first part of this study focused on method validation and the evaluation of the ISE and IC methods. The analytical methodologies were applied to the analysis of natural waters such as river water (Vaal and Crocodile Rivers), dam water (Hartbeespoort Dam), and drinking water (Johannesburg municipal tap water) to evaluate the performance of the chosen methods in the analysis of real samples and to assess the effect of the sample matrix on the accuracy of F- determinations. An inter-laboratory study in collaboration with the South African Bureau of Standard (SABS) was carried out to evaluate the proficiency of South African analytical laboratories and to check the proficiency of the procedures developed in this study. In the second part of this study, the development of an IC-ICP-OES and IC-ICP-MS method was investigated for the speciation of fluoro-aluminium complexes. This work was motivated by the fact that the water fluoridation could lead to remobilisation of scale from municipal pipes. Scale may contain aluminium hydroxide or oxide precipitates that can dissolve as fluoroaluminates or hydroxofluoro aluminates. The speciation of cationic fluoro-aluminates, free Al3+, AlF2+ and, AlF2 + together with the neutral AlF3 0, was based on cation exchange Ion chromatography (IC) coupled with Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass spectroscopy (ICP-MS). / Prof. P.P. Coetzee

Indiana University-Purdue University Indianapolis (IUPUI) / Two of the three fluoride varnishes sold on the American market today are sold in 10-ml tubes of 5.0-percent NaF varnish (Duraphat and Duraflor). Pilot studies have shown that a separation of contents within these tubes exists. The purpose of the current study was four-fold: 1) to measure the fluoride concentration gradient in 10-ml tubes of fluoride varnish, based on the resting position of the tube prior to use; 2 ) to compare a varnish 's concentration gradient to its ability to inhibit caries in an artificial caries environment; 3) to compare and contrast fluoride concentration gradients of Duraphat and Duraflor; and finally, 4) to determine if Quantitative Light Fluorescence(QLF) can detect differences in lesions developed when exposed to an artificial caries environment and fluoride varnish. Human teeth specimens were subjected to a caries challenge and treated with a sample of fluoride varnish from one of five categories: Duraphat stored horizontally and vertically for one week; Duraflor stored horizontally and vertically for one week; or a CavityShield 0.4 ml unit-dose. Results show that no significant fluoride/ppm differences exist between groups (p = 0.29). It was shown that the order in which Duraflor varnish was dispensed from the tubes significantly affected the fluoride concentration (p < 0.05). The order effect was not significant for Duraphat (p = 0.99). QLF data analysis shows there is no significant difference (p > 0.05) in the amount of remineralization obtained by using any varnish stored in any position. This was confirmed using confocal microscopy. These results indicate that all three brands of fluoride varnish are able to remineralize incipient in vitro carious lesions, regardless of from which part of the 10-ml tube the varnish is taken. However, a fluoride concentration gradient exists in tubes of Duraflor. Also, QLF is able to detect denmineralized and remineralized incipient lesions.

Indiana University-Purdue University Indianapolis (IUPUI) / This study was designed to determine if additional fluoride, ingested as a sodium fluoride - vitamin supplement would provide added protection against dental caries without causing any significant fluorosis. A total of 456 children, one to 14 months of age, residing in cities having 0.6 - 0. 8 ppm F in the water supply were randomly assigned according to age, sex and community to the following groups : Group A, 0. 5 mg F to age 3 then 1. 0 mg thereafter; Group B (control), vitamins throughout the study; and Group C, 0.5 mg F throughout the study. Dental examinations were started at approximately 2 1/2 to 3 years of age and were repeated every six months. A fluorosis examination ended the study after about seven years. When compared according to length of time on product, Group A had a significant reduction in deft and defs of 42.2 and 47.1 percent at 60 months. Group C had a 32.1 and 37.4 percent reduction. When compared by age, Group A had a 37.5 and 44.8 percent reduction in deft and defs at 66 months. Group C had a 34.3 and 40.1 percent reduction for the same period. No significant reductions were observed in permanent teeth. Based on the fluorosis index (Group A - 0.250; Group B - 0.033; and Group C - 0.188) none of the groups had any unacceptable amounts of fluorosis. The results indicate that up to 1.0 mg per day of additional fluoride does not cause objectionable fluorosis and may be ingested safely by children residing in areas containing 0. 6 - 0. 8 ppm F in the water supply. A 0.5 mg F supplement was almost as effective as a 1.0 mg level in providing added protection against dental caries in primary teeth.

Fatigue and electrical degradation including low voltage breakdown of ferroelectric lead zirconate titanate Pb(Zr_xTi_{1 - x})O₃ (i.e. PZT) thin films are the major limitations for commercial memory applications of these films. It is noted that the presence of oxygen vacancies and their entrapment at the electrode-ferroelectric interfaces are the sources of the degradation phenomena. Attempts were made in this study to solve these problems: 1) by minimizing oxygen vacancy entrapment at the interfaces by employing RuO₂ electrodes; 2) by lowering the oxygen vacancy concentration in PZT films using donor doping (e.g. La³⁺ at Pb²⁺ site and Nb⁵⁺ at Ti/Zr⁴⁺ site). For this study, PZT thin films were prepared by a sol-gel method and deposited on both Pt/Ti/SiO₂/Si and RuO₂/SiO₂/Si substrates. The microstructure and electrical properties, such as hysteresis properties, fatigue, leakage current, time dependent dielectric breakdown (TDDB) and retention, were studied with regard to the Zr/Ti ratio, the excess lead, the annealing temperature, the electrode material and the doping amount. Furthermore, the pyrochlore to perovskite phase transformation of PZT on RuO₂ electrodes was also investigated. It was shown that PZT films (Zr/Ti=50/50) with 10 at.% excess lead annealed at 650°C for 30 min possessed the best electrical properties for ferroelectric memory application. In confirmation with earlier theoretical and experimental results, no polarization loss was observed up to 10¹¹ switching cycles for the PZT films deposited on RuO₂ electrodes. However, the low Schottky barrier at the interfaces between RuO₂ and PZT films resulted in a higher leakage current at a high electric fields. Donor doping of PZT films decreased carrier concentrations in PZT films, and thus, decreased the leakage current to acceptable limits. In addition, it was also noted that the pyrochlore to perovskite phase transformation of PZT on RuO₂ was similar to that of PZT on Pt electrodes. It can be concluded that the combination of RuO₂ electrodes and donor doping produced PZT films with high fatigue endurance and low leakage currents which are suitable for memory applications. / Master of Science

This thesis is a study of the near infra-red absorption spectrum of ethylidene fluoride.

An exploration of some organic-inorganic hybrid metal fluorides and lanthanide containing metal organic frameworks (Ln-MOFs) has been carried out under ionothermal conditions. In this synthesis technique an ionic liquid (IL) or deep eutectic mixture (DES) is used as the solvent and in many cases as the provider of the organic structure directing agent. A wide range of ILs and DESs have been investigated as the reaction solvent for the synthesis of organically templated vanadium fluorides and oxyfluorides (VOFs), and initially this has proved to be successful with the isolation of 13 phases, including eight new materials. In the VOFs synthesis the IL acts as a solvent, however the DES acts as a solvent and also as a template delivery agent, where the expected template is provided by the partial breakdown of the urea derivative component. Interestingly, it has been shown that the same structure can be accessible via two different ways; either by using IL with an added templating source, or simply through the use of a DES without any other additive; since the template is provided by the in situ breakdown of the DES. The synthesis of VOFs with extended structures was achieved by the use of the hydrophobic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM Tf₂N) as the solvent. [HNC₅H₅][V₂O₂F₅] represents the first VOF with a 2D network that contains exclusively V⁴⁺. This material may be considered as arising via condensation of the previously known ladder-like chains. Furthermore, using imidazole as an added template has produced another layer material that has significant similarities to the [HNC₅H₅][V₂O₂F₅] structure, but with some key differences. Within the same system three other phases were also isolated, including two novel materials displaying the known ladder-type building units. Further investigations in the ionothermal synthesis of VOF using EMIM Tf₂N resulted in a successful synthesis of [NH₄]₂[HNC₇H₁₃][V₇O₆F₁₈], a novel material displaying a unique double layered topology featuring a S = ½ kagome type lattice of V⁴⁺ ions (d¹). Two of the V⁴⁺ based kagome sheets are pillared by V³⁺ ions to form a double layered structure templated by both ammonium and quinuclidinium cations. This compound exhibits a high degree of magnetic frustration, with significant antiferromagnetic interactions but no long range ordering was observed above 2 K. This material presents an interesting comparison to the famous Herbertsmithite, ZnCu₃(OH)₆Cl₂, and may provide an excellent candidate for realising a quantum spin liquid (QSL) ground state. Interestingly, in this system the use of EMIM Tf₂2N as a solvent produces mainly V⁴⁺-containing materials, despite the high reaction temperature (170 °C). This characteristic is unprecedented in VOFs synthesis, as rising the reaction temperature above 150 °C in other techniques (i.e. hydrothermal synthesis) would often result in further reduction of V⁴⁺ to V³⁺. Using the ionothermal technique in the synthesis of hybrid iron fluorides resulted in the isolation of three chain-type materials. Again, the IL acts as the solvent and the DES acts as the solvent and also as the template provider where the expected template is released by the partial breakdown of the urea derivative component of the DES. The synthesis of Ln-MOF using a choline chloride/ 1,3-dimethylurea deep eutectic mixture has produced three novel isostructural materials. Usually, in ionothermally prepared materials (i.e. zeolites) the urea portion of the DES is unstable and breaks down in situ to form ammonium or alkylammonium cations. In the ionothermal synthesis of Ln-MOF, 1,3-dimethyurea (DMU) remains intact and is occluded in the final structure. Using a choline chloride/ethylene glycol deep eutectic solvent led to the isolation of a Ln-MOF with interesting structural properties, however none of the DES components appeared in the final structure. These results demonstrate once more the usefulness and applicability of the ionothermal synthesis method and emphasise how this synthesis technique can be further extended and applied in the preparation of important structures with unique properties and functionalities.

No description available.

Made available in DSpace on 2014-10-09T12:38:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:07Z (GMT). No. of bitstreams: 1 05678.pdf: 6012797 bytes, checksum: fe9d7fe0fee771d558f91a7bffb7cfa3 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:55:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:04Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:38:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:07Z (GMT). No. of bitstreams: 1 05678.pdf: 6012797 bytes, checksum: fe9d7fe0fee771d558f91a7bffb7cfa3 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP