Semiconducting properties and related defect disorder for well defined TiO2 single crystal were studies. Semiconducting properties have been determined using simultaneous measurements of two independent electrical properties, including electrical conductivity, ??, and thermoelectric power, S, at elevated temperatures (1073-1323 K) in the gas phase of controlled oxygen activity (10-10 Pa &lt p(O2) &lt 75 kPa). Measurements of s and S were conducted (i) in the gas/solid equilibrium and (ii) during equilibration. Oxygen vacancies have been identified as the predominant defects in TiO2 over a wide range of p(O2). Individual conductivity components related to electrons, electron holes and ions, were determined from the obtained ?? data. The effect of p(O2) on these individual components was considered in the form of a diagram. This work led to the discovery of the formation and diffusion of Ti vacancies. However, the obtained diffusion data indicate that, in the temperature ranges commonly used in studies of semiconducting properties (1000-1400K), the Ti vacancies concentration is quenched and may thus be assumed constant. In addition it was shown that Ti vacancies in appreciable concentrations form only during prolonged oxidation. It was determined that the discrepancies in the reported n-p transition point are related to the concentration and spectrum of impurities as well as the concentration of Ti vacancies. It has been shown that the n-p transition point in high-purity TiO2 is determined by the Ti vacancy concentration. A well defined chemical diffusion coefficient, Dchem, was determined using kinetic data obtained during equilibration. A complex relationship between p(O2) and Dchem was observed. These data showed a good agreement between the obtained diffusion data and defect disorder. Examination of the determined equilibration kinetics, led to the discovery of two kinetic regimes, the result of the transport of defects at different mobilities. The determined data are considered well defined due to the following reasons: 1. The studied specimen was of exceptionally high purity and free of grain boundaries (single crystal) 2. The specimen was studied in the gas phase of controlled and well defined oxygen activity which was continuously monitored. 3. Whenever the experimental data were measured in equilibrium, the gas/solid equilibrium has been verified experimentally. 4. A good agreement between the two, self-confirmatory, electrical properties, including ?? and S has been determined simultaneously and independently. The defect disorder model derived in the present work may be used for tailoring controlled semiconducting properties through the selection of annealing conditions involving the temperature and oxygen activity.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 145-153). Also available on the World Wide Web.

Thesis (Ph.D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Huang, Ching-Hua; Committee Member: Kim, Jaehong; Committee Member: Pavlostathis, Spyros; Committee Member: Stack, Andrew; Committee Member: Yiacoumi, Sotira

Thesis (Ph. D.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2005. Directed by Ching-Hua Huang. / Wine, Paul, Committee Member ; Pavlostathis, Spyros, Committee Member ; Mulholland, James, Committee Member ; Yiacoumi, Sotira, Committee Member ; Huang, Ching-Hua, Committee Chair. Includes bibliographical references.

Thesis (M.S.)--Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 67-72). Also available on the World Wide Web.

Submitted in the fulfillment of the requirement for the Master's Degree in Chemistry,Durban University of Technology, 2017. / Knoevenagel condensation reaction is a useful protocol for the formation of C=C bond in organic synthesis. This protocol is extensively utilized by synthetic chemist to generate dynamic intermediates or end-products such as perfumes, polymers, pharmaceuticals and calcium antagonists. The reaction is catalyzed by bases such as ammonia, primary and secondary amines, quaternary ammonium salts, Lewis acids, catalysts containing acid-base sites, which are carried out under homogeneous conditions. This necessitates the use of organic solvent which generate the large volumes of solvent waste. From green chemistry perspective, solvent free heterogeneous catalysts have received considerable attention. Since, these heterogeneous catalysts not only avoid the use of organic solvents but also suppress side reactions such as self-condensation and oligomerisation leading in better selectivity and product yield. In recent years, therefore, the use of heterogeneous catalyst, their recovery and reusability are in demand in industry. The use of cobalt, iridium and platinum hydroxyapatites, MgO/ZrO2, MgO/HMCM- earlier been reported in the literature, and used as heterogeneous catalysts for the Knoevenagel condensation of aldehydes and esters. Based on these evidences, we envisioned that MgO and VMgO could also be used as heterogeneous catalysts for this reaction. Magnesium oxide was synthesized from three precursors, viz. magnesium nitrate, magnesium carbonate and magnesium acetate. Magnesium oxide prepared from magnesium nitrate precursor was found to be the optimum giving an 81 % product yield. Vanadium-magnesium oxide catalysts with different vanadium loadings; 1.5, 3.5 and 5.5 wt. %, were synthesized by wet impregnation of magnesium oxide with aqueous ammonium metavanadate solution. The synthesized catalysts were characterized by ICP-AES, FTIR, Powder XRD, SEM-EDX and TEM. The Knoevenagel condensation reactions between benzaldehyde and ethyl cyanoacetate were carried out in a 100 mL two-necked round bottom flask equipped with a reflux condenser, magnetic stirrer and a CaCl2 guard tube. An equimolar quantity (10 mmol) of substrates and 0.05g of catalyst were added to the flask and heated at 60 °C, stirred vigorously for the required time. The yields were determined using GC-FID equipped with a capillary column. Elemental composition of the catalysts (vanadium and MgO) was determined by ICP-AES. IR spectra of MgO showed that magnesium oxide was the only phase present in the catalysts prepared from different precursors. The 1.5 and 5.5 wt. % VMgO showed weak bands attributed to pyrovanadate and orthovanadate phases present in small quantities. The phases manifested more with the increase in the vanadium concentration (3.5 and 5.5 wt. % VMgO). The diffraction patterns of all the catalysts showed the existence of MgO and magnesium orthovanadate. The morphology of the catalysts with increasing vanadium was more affected by precursor treatment rather than chemical differences. Electron microscopy showed that the VMgO surface is only sparingly covered with vanadium and MgO showed stacked with large rounded particles. Good to excellent yields were obtained for the MgO catalysts: MgO(1) 68 %, MgO(2) 65 %, MgO(3) 72 %, MgO(P) 73 % and MgO(DP) 82 %. Excellent yields were obtained for the VMgO catalysts: 1.5VMgO 83 %, 3.5VMgO 91 % and 5.5VMgO 97 %. The 5.5VMgO catalyst was found to be the optimum catalyst and was further tested for it activity using different aldehyde substrates. Excellent yields of the products were obtained for benzaldehyde 97 %, nitrobenzaldehyde 94 %, bromobenzaldehyde 96 %, chlorobenzaldehyde 93 % and methoxybenzaldehyde 95%. / M