Four sol-gel systems (alumina, aluminum hydroxide, zirconia, and magnesia) were investigated, primarily by laser spectroscopy, on several series of materials prepared by systematically varying the synthesis procedures. Key material phases analyzed were: (1) nanocrystalline boehmite [AlO(OH)]; (2) bayerite, nordstrandite, and gibbsite [Al(OH)₃ polymorphs]; (3) amorphous zirconia [a-ZrO₂]; and (4) magnesite [MgCO₃], hydromagnesite [4MgCO₃·Mg(OH)₂·5H₂0], and magnesia [MgO]. Crystal nucleation and crystal growth kinetics were studied in several cases, with x-ray experiments carried out to calibrate the Raman-scattering technique I developed for monitoring crystallite size. Nanocrystalline boehmite, γ-AlO(OH), was found to be the principal component in the sol-gel alumina system. Materials were prepared by the hot-water hydrolysis/condensation of Al(OC₄H₉)₃, the Yoldas process, as a function of process variables such as the time spent in the sol phase. Small but systematic changes, as a function of sol aging time, were discovered in the lineshape and position of the dominant boehmite Raman band observed in the alumina hydrogels. These spectral changes were interpreted in terms of nanocrystallinity-induced finite-size effects associated with the slow growth of AlO(OH) nanocrystals in the sol. X-ray diffraction experiments were used to determine nanocrystal sizes (as small as 3 nm for gels prepared from fresh sols) and to estimate growth kinetics from the Raman-lineshape results. These results appear to be among the first available for crystallite growth kinetics (ripening) in the near-atomic-scale nanocrystal regime. The Raman peak-position shift is proportional to L^-α, where L is the average nanocrystal size and α is a Raman-versus-size scaling exponent. For AlO(OH), I determined α to be 1.0, close to the scaling-exponent values reported for graphite and BN and different from the values (about 1.5) that describe the reported behavior of Si, Ge, and GaAs. The trihydroxide polymorph system is closely related to the sol-gel alumina system. The processing temperature and the method of hydrolysis were varied, in order to determine their effect on the trihydroxide phase mix. The trihydroxide phase mix does not change with time; it depends only on the initial hydrolysis conditions. Bayerite is the primary phase present for materials processed at 25 C, while nordstrandite is the primary phase present for materials processed at 60 C. It is shown that the trihydroxide crystal nucleation kinetics are responsible for the Al(OH)₃ phase mix. Hydroxide/oxyhydroxide phase-mix kinetics were also studied; this ratio increases with time. The associated rate constant decreases with increasing temperature. Sol-gel zirconia was prepared by using atmospheric water to hydrolyze a mixture of zirconium propoxide, acetic acid, and n-propanol. This produces a clear gel. Hydrogen peroxide was found to chemically react with the gels. Clean Raman spectra reveal a broad-band structure (the full width at half maximum is 150 cm⁻¹) centered at about 460 cm⁻¹. This band is interpreted as the signature of an amorphous phase of zirconia. Raman and luminescent spectra (both obtained on the Raman spectrometer) were used to monitor the conversion of magnesium-carbonate-based materials to magnesium oxide, as a function of temperature. This new phase-determination technique utilizes the krypton 674.1 nm laser line so that the carbonate symmetric-stretch band and the MgO:Cr⁺⁺⁺ luminescence band are readily observable on the same spectrum. / Ph. D.

In the light of previous investigations of the cyclodehydration of o-benzylbenzophenones and analogous compounds to polycyclic aromatic hydrocarbons a study of 2'-substituted-2-benzylbenzophenones was undertaken. The previous work had been concerned with the rates of cyclization or 3'-substituted and 4'-substituted ketones in which no ortho effects were operating. The results of these investigations could be adequately interpreted according to the electronic theory of the English school. In the 2'-series ortho effects are superimposed upon the usual electronic effects. When the 2'-substituents were halogens a decrease in rate was observed with an increase in the size of the halogen atom. This indicates that one aspect of these ortho effects is steric. These reactions were carried out in a sealed tube in hydrobromic and acetic acids at 150°C rather than at 117.5°C which was the temperature used previously. This increase was necessary to get a reaction with all the ketones concerned. Even under these conditions the 2'-hydroxy-2- benzylbenzophenone cyclized very poorly. This was attributed to a second ortho effect due to intramolecular hydrogen-bonding between the hydroxy group and the keto group. Infrared spectroscopy demonstrated that this type of hydrogen-bonding is present. The 3'-hydroxy-2-benzylbenzophenone apparently cyclizes very readily since the 3'-methoxy compound is cyclized to 9-(3-hydroxyphenyl)anthracene quite readily. Thus, the two reactions in the 3'-series, ether cleavage and the cyclization reaction both proceed more rapidly than the cyclization of the 21-hydroxyketone. The 9-(2- methoxyphenyl)anthracene can be prepared in good yield by the use of phenyl acid phosphate or polyphosphoric acid as a cyclizing agent. This compound can be easily converted to 9-(2-hydroxyphenyl)anthracene by heating under reflux with a mixture of hydrobromic and acetic acids. The halogen substituted ketones are very viscous oils. In order to have solid derivatives for identification purposes these ketones and the methyl derivative were oxidized to the corresponding o-dibenzoylbenzenes which are all solids. Chromium trioxide in acetic acid was usually found to be the best reagent for this purpose. Two of the 9-phenylanthracenes were oxidized to the corresponding 9-phenyl-9-hydroxy-10-anthrones using sodium dichromate in acetic acid. This reaction is carried out very readily and in excellent yield. It may prove to be valuable in the identification of other aromatic polycyclic hydrocarbons. The reduction of 2'-fluoro-2-benzylbenzophenone to 2'-fluoro-2-benzylbenzhydrol was carried out using sodium borohydride in pyridine. The infrared spectrum showed no evidence of intramolecular hydrogen-bonding between the fluorine atom and the hydroxy group. A study of the use of solid surfaces in aromatic cyclodehydration was made using 4'-chloro-2-benzylbenzophenone as a model compound. Experiments with a large number of solids brought to light two factors which seem to contribute to the ability of a surface to catalyze the reaction. One is the acidity of the surface and the other is the ability of a surface to bind the ketone irreversibly. Surface acidity was measured in terms of the H₀ function by the use of Hammett indicators adsorbed on the surface. The color of the adsorbed indicators was used to obtain the H₀ values. The activity of each surface was measured in terms of the percent yield of the product. The solid of highest activity and highest acidity was a silica-alumina cracking catalyst containing 13% alumina. This catalyst gave a 94% yield with 4'-chloro-2-benzylbenzophenone compared to only about 25% on the commonly used Fisher activated alumina. 2'-Methyl-2-benzylbenzophenone was cyclized in 60% yield. This ketone gave a yield of only 20% when cyclized in the hydrobromic-acetic acid mixture at 180° for 9 hr. 2’,6’-Dimethyl-2-benzylbenzophenone has resisted all attempts to cyclize it including an attempt with the most active solid surface available, the silica-alumina cracking catalyst. / Ph. D.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / The synthesis of mixed metal oxides, specifically the need and ability to successfully and accurately control the particle size, their stability and the reactivity of these nanoparticles is required, so as to allow the attachment of catalyst nanoparticle to the surface of a substrate or to other particles without leading to coalescence of the catalyst particle and hence to loss of their size induced properties. However, the synthesis of mixed metal oxides is a complex problem. Though various methods of preparing these types of oxides have been reported and applied, such methods they rarely produced pure forms and have often been recorded as having been contaminated with other phases. Often the particle sizes are too large in the micrometer range, and the size distribution is overly wide. Moreover, even if particles of nanometer size are formed, they tend to aggregate or agglomerate. In the current research, microemulsions were used to synthesize the nanoparticles. Such microemulsion consists of water droplets encapsulated by surfactant molecules in a pool of oil, comprising: water in oil (w/o) or reverse micelles. Reverse micelles in the nanometer size range are thermodynamically stable and optically transparent in the solution. They are believed to be highly dynamic structures whose components rearrange themselves over time and space through interaction or collision, coalescing and redispersing. However, the advantage of this method over using the standard method is that the particle size can largely be controlled, and a narrow size distribution obtained. The aim of the research was to investigate the feasibility of using the reverse micelle technique for the synthesis of mixed metal oxides - specifically α-bismuth molybdate (α- Bi2Mo3O12) with a controlled and desirable particle size and a narrow size distribution...

Mesoporous monocrystalline metal oxides (e.g. Co₃O₄, Cr₂O₃, NiO, CeO₂, In₂O₃ and WO₃) templated by SBA-15 or KIT-6 were synthesised successfully by using a simple solvent-free approach, the so-called solid-liquid method, which was the principal development of methodology in this project. A metal-containing precursor, whose melting point is lower than its decomposition temperature, was directly ground with a mesoporous silica and impregnated into the pores of the silica template after melting when the temperature was increased above its melting point. The liquid precursor then decomposed to form metal oxide inside the silica pores when the temperature was further increased to its decomposition temperature and crystallization temperature of the oxide. The structural characterisations of these porous metal oxides were performed by using TEM, XRD and N₂ adsorption/desorption techniques. The solid-liquid method is convenient and solvent-free. On the other hand, its limitation is that the precursor must have a melting point lower than its decomposition temperature. A novel porous single crystal of rutile TiO₂ as well as anatase nanocrystal-silica composite was also synthesised successfully for the first time using SBA-15 and KIT-6 as templates. These materials have interesting properties of proton conductivity, Li insertion and photoactivity. Likewise, the characterisation of porous TiO₂ was achieved by using XRD, TEM, SAED and N₂ adsorption/desorption. The residual SiO₂ component in porous TiO₂ was detected by using the EDX technique. Porous cubic metal oxides of Co₃O₄, NiO, CeO₂ and In₂O₃ were prepared using novel mesoporous silicas FDU-12 and SBA-16, which contain spherical nanocavities linked together by smaller windows. These porous materials have larger surface areas than those templated by SBA-15 and KIT-6. Unlike the cubic metal oxides, syntheses of porous crystals of non-cubic metal oxides such as rhombohedral Cr₂O₃, Fe₂O₃ and hexagonal TiO₂, WO₃ were not successful when using cage-containing mesoporous silicas as templates. The three-dimensional arrangements of nanospheres in porous crystals of cubic oxides mentioned above were observed by TEM and the corresponding larger surface areas were confirmed by N₂ adsorption/desorption technique. Additionally, fabrication of porous crystals of other metal oxides such as MgO, ZnO and ZrO₂ were unsuccessful by using either mesoporous silicas or mesoporous carbons as templates. Possible drawbacks of using mesoporous silica and carbon as templates were discussed.

This dissertation reports the application of nonlinear optical effects for the investigation of vibrational and electronic spectroscopy of molecules adsorbed on thin film metal oxide surfaces and metal oxide surfaces. The main emphasis of the experiments cited here is to introduce the recently developed multi-photon technique, Waveguide Surface Coherent anti-Stokes Raman Scattering Spectroscopy (WSCARS), to the scientific community. Planar optical waveguides have been utilized to generate large optical field enhancements on metal oxide surfaces. Guided waves have been employed to obtain the surface coherent anti-Stokes Raman scattering spectra of pyridine, phenol, benzene, methanol, CD₃OD, 2,4-pentadione, oxygen, ammonia and ND₃ adsorbed onto a ZnO (0001) surface. Vibrational spectra of transient species (O₂⁻) adsorbed on ZnO (0001) surface are also presented. Furthermore, the WSCARS has been used to monitor catalytic hydrogenation of ethylene adsorbed on ZnO (0001) surface. The WSCARS technique is compared with the other vibrational surface probes. Future directions and limitations of the technique are also discussed. Electronic spectra of surface bound species have been examined by resonantly enhanced surface second harmonic generation (SSHG). SHG spectra of trans-cinnamic acid adsorbed on optically cleaned fused silica have been obtained at room temperature and at 4 K. Surface second harmonic generation has been applied to study the adsorption of water and acetone onto thermally grown silicon dioxide/silicon surface. SSHG has been successfully applied to monitor photo-oxidation and photo-reduction of a rutile (110) surface. Experiments are described, data are presented, and surface-adsorbate binding modes are discussed.

Nanocrystalline praseodymium oxide films have been successfully generated on stainless steel substrates. The electrochemical deposition was performed in the cathode compartment of a divided electrochemical cell with a regular three-electrode configuration. The green films obtained by electrodeposition were then annealed at high temperatures for 1-3 hours. X-ray diffraction revealed the fluorite structure of Pr6O11 and the crystallite size was calculated. X-ray photoelectron spectroscopy was employed to study the composition of the oxide films and also the oxidation state of Pr. Scanning electron microscopy was utilized to study the surface texture and microstructure of deposits. Fourier transform infrared spectrometery was used to investigate the composition of the films. The effects of different conditions on the green films were also studied such as different pH values of the electrolyte solution, different deposition modes, different supporting electrolytes and different applied current densities. Sintering experiments were conducted to investigate the properties of the green films. Praseodymium oxide powders were also successfully prepared by combining electrochemical methods with sintering processes. The praseodymium oxide powders were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The crystallite sizes of the powders were evaluated.

The research into materials for use as cathode materials for solid oxide fuel cells (SOFC) is ongoing, with many different avenues being investigated. Copper based delafossites were studied for cathode side applications in SOFCs, as a novel and comparatively cheap material. The aim was to identify suitable materials with appropriate electrical conductivity, thermal, chemical and mechanical stability in air. Furthermore, understanding the behaviour of the delafossites during the thermal oxidation to spinel and copper oxide would be beneficial to further development of the materials. The structure and properties of the copper based delafossites CuFeO₂, CuAlO₂ and CuCrO₂ were studied, alongside several doped compositions for each parent composition. The electronic conductivity of the CuFeO₂ family was improved by doping fluorine into the structure, with 1 atomic % doping producing ~3.8 S cm⁻¹ at 800 °C. However, as reported in literature the structure is vulnerable to oxidation at higher temperatures. In contrast, CuAlO₂ was stable over the SOFC temperature range, and therefore had appropriate thermal expansion coefficients (TEC) of ~11 x 10⁻⁶ K⁻¹, but relatively low electronic conductivity. CuCrO₂ compositions had good overall TECs, but aliovalent doping of Mg²⁺ improved the conductivity to ~17.1 S cm⁻¹ at 800°C for 2.5 atomic % doped CuCrO₂. Neutron diffraction was utilised to study members of the solid solution CuFe₁₋ₓCrₓO₂ (x = 0, 0.25 and 0.5) during in-situ oxidation at high temperature. Points of positive scattering density were identified within the CuFeO₂ structure, which were attributed to the location of the intercalated oxygen ions before the transformation proceeded. Additionally, the cation distribution between the tetrahedral and octahedral sites within the developing spinel were characterised for x = 0, and partially for the x = 0.25 and 0.5 compositions using complimentary XRD patterns. Finally, magnesium doped CuCrO₂ delafossites were used in several different preliminary symmetrical cells for study using electrochemical impedance spectroscopy (EIS). Pure delafossite inks gave relatively large area specific resistance (ASR) values, 1.29 - 2.69 Ω cm² at 800 °C. It was attempted to improve upon these values through infiltration of CeO₂ and through change in microstructure using composite type inks, without much success. Inks using CuCr₀.₈Fe₀.₂O₂ were also tested as both a single phase electrode and as a composite type electrode. The pure delafossite electrode still had a large ASR value, (~33.4 Ω cm² at 800 °C) while composite electrodes obtained much more respectable ASR values ~0.75 Ω cm² at 800 °C.

Made available in DSpace on 2015-04-22T22:02:03Z (GMT). No. of bitstreams: 1 Dissertacao - Erclila Monteiro.pdf: 1813187 bytes, checksum: 850ab77574accbe9e4596200a21359ae (MD5) Previous issue date: 2007-04-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Today, several countries adopted rigorous environmental laws for regulating the industrial wastes, mainly because they have high heavy metal contents. Therefore, environmental clean procedures low cost provide a great field of study. The retention capacity of lead ions battery solution through the use of kaolinite modified with metallic oxides (MnO2, Fe(OH)3 and Al(OH)3) at 600, 700 and 900 °C was corried out to validate a waste industrial treatment. Twenty seven adsorbents were synthesized and submitted to Xray diffraction and infrared spectroscopy with Fourier transformation for adsorbent synthesized lattice characterization. Lead ion adsorption tests were assayed by kinetic experiments using the flame atomic absorption spectrometry (FAAS) for determination of lead contents through the Lagergren model. Finding showed that only seven adsorbents were efficient for removing lead from battery solution, in which the adsorption rate was 99%. As kaolinite is an abundant mineral this result represents a great tool for the development of a cost-effective environmental clean procedure. / Diante da legislação cada vez mais rígida para o descarte de efluentes contendo metais pesados sobre o ambiente, o desenvolvimento de procedimentos eficientes e de baixo custo para o tratamento desses resíduos, torna-se de grande interesse. Um estudo sobre a capacidade de retenção de íons chumbo, presentes em solução de bateria, pelo uso de caulinita modificada com óxidos metálicos (MnO2, Fe(OH)3 e Al(OH)3) e calcinada em diferentes temperaturas (600, 700 e 900 °C), foi realizado para a avaliar seu uso potencial no tratamento desse resíduo. No total, foram sintetizados 27 adsorventes, que passaram pela técnica de difração de raios-X e de infravermelho com transformada de Fourier para caracterização físico-química. Os testes de adsorção de íons chumbo foram realizados com auxílio da técnica de absorção atômica e pelo uso do modelo de Langergren. Dos 27 adsorventes, 7 removem 99% dos íons chumbo presente em solução de bateria, demonstrando resistência e seletividade em meio ácido e possibilidade de reutilização. Aliado aos fatos de a caulinita ocorrer em abundância e de não ser impactante ao meio ambiente, sua seletividade e elevada capacidade de adsorção, quando modificada, torna o seu uso na retenção de íons chumbo presentes em solução de bateria potencialmente útil econômica e ecologicamente.

Yuan, Wenxiang = CCTO陶瓷材料的制备和性质研究 / 苑文香. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 63-67). / Text in English; abstracts in English and Chinese. / Yuan, Wenxiang = CCTO tao ci cai liao de zhi bei he xing zhi yan jiu / Yuan Wenxiang. / Acknowledgement --- p.ii / Abstract --- p.iii / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Structure --- p.1 / Chapter 1.3 --- Models --- p.3 / Chapter 1.3.1 --- Parallel RC --- p.3 / Chapter 1.3.2 --- Two parallel RCs in series --- p.5 / Chapter 1.4 --- Motivation --- p.7 / Chapter 1.5 --- Our work --- p.7 / Chapter Chapter 2 --- Experiment --- p.8 / Chapter 2.1 --- Sources and substrate --- p.8 / Chapter 2.2 --- Preparation of the CCTO samples --- p.8 / Chapter Chapter 3 --- Experimental equipment --- p.13 / Chapter 3.1 --- Furnace --- p.13 / Chapter 3.2 --- X-ray diffraction (XRD) --- p.13 / Chapter 3.3 --- Scanning electron microscopy (SEM) --- p.16 / Chapter 3.4 --- Impedance analyzers --- p.17 / Chapter Chapter 4 --- Selections of the experimental conditions --- p.18 / Chapter 4.1 --- Selection of calcining-process conditions --- p.18 / Chapter 4.1.1 --- Experimental results --- p.18 / Chapter 4.1.2 --- Comparison with the results of other research groups --- p.21 / Chapter 4.2 --- Selection of sintering-process conditions --- p.22 / Chapter 4.2.1 --- CuO volatilization --- p.22 / Chapter 4.2.2 --- CCTO decomposition --- p.24 / Chapter 4.3 --- Optimizing of the Cu/Ca ratio --- p.29 / Chapter Chapter 5 --- Results and discussion --- p.31 / Chapter 5.1 --- Properties of CCTO ceramics sintered at different temperatures for 10 h --- p.32 / Chapter 5.2 --- Properties of CCTO ceramics sintered for different durations at 1000°C --- p.43 / Chapter 5.3 --- Properties of CC3+ΧTO ceramics --- p.52 / Chapter 5.4 --- Discussion --- p.58 / Chapter Chapter 6 --- Conclusions --- p.61 / References --- p.63

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.