The replacement of chromate conversion coatings for zinc coated components has been necessitated by the materials finishing industries due to the inherent toxicity issues with Cr(VI) and the legislative enforcement of WEEE and ELV Directives by the European Union. Current replacements are based on non-chromate , Cr(III) systems, these may be perceived by some to be problematic as they still contain chromium . Molybdate based conversion coatings have long been viewed by many researchers to be a viable non-chromium alternative due to their low toxicity. An extensive literature review of the research carried out in the last 20 years was carried out, highlighting areas of interest for improving the corrosion resistance of the coatings studied. These were, primarily, the synergesis that exists with molybdate and phosphate compounds for corrosion resistance and the incorporation of nanoparticle silica into treatment solution. Also discovered was the importance of the acid used to adjust treatment solution pH, immersion time, oxidising agent additions and the incorporation of rare earth metal species. Silicate sealant layers were also highlighted as a post treatment. Molybdate-based coatings were formed on commercial electrodeposited acid zinc surfaces. Many treatment conditions were investigated, and initially performance analysed using DC Linear Polarisation Resistance (LPR) trials. Subsequently, the highest performing coatings were subjected to the more aggressive, industry standard, ASTM B 117 Neutral Salt Spray (NSS) corrosion test. The highest performing molybdate coatings were found to have an average LPR of ~ 9 000 Ω. cm2, in contrast to ~ 12 000 Ω. cm2 for the Cr(VI) based reference. NSS results were amongst the highest performing for molybdate based coatings documented, at 24 h until 5% white rust, however remained inferior to Cr(VI) coatings, which lasted 120 h. The highest performing coatings were characterised using FEG-SEM, Cryofracture EDXA and site specific AES. These techniques revealed that the enhanced molybdate coatings had a columnar structure that was around 300 nm thick, with pores that appeared to expose the substrate. AES showed this type of coating to have a mixed Mo, P and Zn oxide surface. Corrosion initiation was also studied; this can be thought of as an investigation to determine the point(s) of weakness or the mechanism that causes coating failure. Coatings were immersed in 5 % wt/ vol NaCl(aq) until they showed any surface change. Initial signs of corrosion were deemed to be any appearance of pitting or discolouration of the film, not a voluminous corrosion product. Untreated Zn, Cr(VI) and simple molybdate coatings were studied as well as enhanced molybdate coatings. There were clear differences in the way the coatings behaved at the onset of corrosion. Cr(VI) coatings delaminated, leaving an area of decreased Cr concentration. The enhanced molybdate coatings failed by the appearance of localised pores of ~ 70 µm in diameter. Substrate exposure was indisputably the reason for coating failure in chloride environments. In light of the work carried out in the present thesis the outlook for the use of molybdate as a potential replacement for chromate for the conversion coating of electrodeposited zinc surfaces is a positive one.

Diamond cuboid-, rhombohedron- and hexagon-shaped nanocrystals as well as branched rods of the solid solution Co1-xMnxO have been synthesized via a solvothermal synthetic route from manganese formate and cobalt acetate at elevated temperature. Rhombohedra and hexagons have dimensions no larger than 50 nm on the longest axis, rods have branches up to 150 nm long and cuboids grow up to 250 nm on a side. X-ray and electron diffraction and transmission electron microscopy analyses show that these nanoparticles are single crystals of wurtzite-type and rock salt-type Co1-xMnxO. Varying the surfactant, water and precursor ratios allows control of particle size, morphology and stoichiometry. Extending growth time at high temperatures (>370°C) leads to the disappearance of the wurtzite phase due to Ostwald ripening. Longer reaction times at temperatures between 345-365°C lead to more crystalline wurtzite-lattice particles. These results show that nanoparticle morphologies and crystal lattices arise from crystal growth and Ostwald ripening at different rates selecting for either small, smooth-surfaced wurtzite lattice particles or large, dendritically-grown rock salt lattice particles.

No description available.

The goal of this thesis is the development of scalable, low cost synthesis of metal oxide nanostructures based electrodes and to correlate the chemical modifications with their energy conversion performance. Methods in energy conversion in this thesis have focused on two aspects; a potentiometric chemical sensor was used to determine the analytical concentration of some components of the analyte solution such as dopamine, glucose and glutamate molecules. The second aspect is to fabricate a photo-electrochemical (PEC) cell. The biocompatibility, excellent electro-catalytic activities and fast electron transfer kinetics accompanied with a high surface area to volume ratio; are properties of some metal oxide nanostructures that of a potential for their use in energy conversion. Furthermore, metal oxide nanostructures based electrode can effectively be improved by the physical or a chemical modification of electrode surface. Among these metal oxide nanostructures are cobalt oxide (Co3O4), zinc oxide (ZnO), and bismuth-zincvanadate (BiZn2VO6) have all been studied in this thesis. Metal oxide nanostructures based electrodes are fabricated on gold-coated glass substrate by low temperature (< 100 0C) wet chemicalapproach. X-ray diffraction, x-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the electrodes while ultraviolet-visible absorption and photoluminescence were used to investigate the optical properties of the nanostructures. The resultant modified electrodes were tested for their performance as chemical sensors and for their efficiency in PEC activities. Efficient chemically modified electrodes were demonstrated through doping with organic additives like anionic, nonionic or cationic surfactants. The organic additives are showing a crucial role in the growth process of metal oxide nanocrystals and hence can beused to control the morphology. These organic additives act also as impurities that would significantly change the conductivity of the electrodes. However, no organic compounds dependence was observed to modify the crystallographic structure. The findings in this thesis indicate the importance of the use of controlled nanostructures morphology for developing efficient functional materials.

The purpose of this study is to develop catalysts for conversion of synthesis gas (H₂ and CO) to higher alcohols, primarily ethanol and propanol. Crude oil is consumed at a rate of more than 20 million barrels a day in the United States, mainly for producing fuels and chemical feedstocks. However, the total amount of crude oil is limited, and alternative ways of producing alcohols as precursors for chemical feedstocks are desirable. In this study, using a known K/MoS₂/metal oxide catalyst as the starting point, two different approaches were explored to improve catalytic properties: 1) Co promotion on K/MoS₂/mixed metal oxide (MMO) catalysts, and 2) Preparation of K/MoS₂/metal oxide catalysts with molybdenum carbide as a precursor, instead of molybdenum oxide. With respect to Co promotion on K/MoS₂/MMO catalysts, the effect of varying the Co content in the K/Mo-Co/MMO catalysts prepared by a co-impregnation method did not produce significant changes in catalytic acitivities or selectivities. It was due to the premature precipitation of cobalt molybdate during synthesis. Cobalt molybdate precipitation can generally be prevented by using water as a solvent, but this approach is not appropriate for this study because of the use of hydrotalcite-derived mixed metal oxide as the support. Co loadings on K/Mo/MMO-Co catalysts did not change selectivities significantly, either. However, they changed catalytic activities, represented by gas hourly space velocity (GHSV) required to obtain 8% conversion while maintaining high selectivities for higher alcohols. As a result, C ₂₊ alcohol productivities reached 0.01g(alcohol)/g(catalyst)/hr with Co loadings higher than 8%. With respect to using Mo2C as the precursor of Mo species instead of MoO3, comparisons between catalysts with different precursors for Mo species and different pretreatments were investigated. In this study, both K/Mo catalysts supported on MgO and α-Al₂O₃ showed similar tendencies of catalytic activities and selectivities. The highest C₂₊ alcohol selectivities and productivities were obtained on presulfided MoO₃ catalysts on both supports. In comparison of K/Mo ₂C catalysts with different pretreatments, higher C₂₊ alcohol selectivities and lower MeOH selectivities were obtained on presulfided catalysts compared to non-pretreated catalysts.

The role of sensor technology is obvious in improvement and optimization of many industrial processes. The sensor films, which are considered the core of chemical sensors, have the capability to detect the presence and concentration of a specific chemical substance. Such sensor films achieve selectivity by detecting the interaction of the specific chemical substance with the sensor material through selective binding, adsorption and permeation of analyte. This research focuses on development and verification of a comprehensive mathematical model of mixed metal oxide thin film growth using spray pyrolysis technique (SPT). An experimental setup is used to synthesize mixed metal oxide films on a heated substrate. The films are analyzed using a variety of characterization tools. The results are used to validate the mathematical model. There are three main stages to achieve this goal: 1) A Lagrangian-Eulerian method is applied to develop a CFD model of atomizing multi-component solution. The model predicts droplet characteristics in flight, such as spatial distribution of droplet size and concentration. 2) Upon reaching the droplets on the substrate, a mathematical model of multi-phase transport and chemical reaction phenomena in a single droplet is developed and used to predict the deposition of thin film. The various stages of droplet morphology associated with surface energy and evaporation are predicted. 3) The processed films are characterized for morphology and chemical composition (SEM, XPS) and the data are used to validate the models as well as investigate the influence of process parameters on the structural characteristics of mixed metal oxide films. The structural characteristics are investigated of nano structured thin films comprising of ZnO, SnO2, ZnO+In2O3 and SnO2+In2O3 composites. The model adequately predicts the size distribution and film thickness when the nanocrystals are well-structured at the controlled temperature and concentration.

No description available.

No description available.

L'òxid de zinc és un compost àmpliament utilitzat en la indústria del cautxú a causa de les excel•lents propietats que mostra com activador per a la vulcanització amb sofre. Malgrat les seves característiques superiors, hi ha una creixent preocupació sobre els seus efectes mediambientals i nombrosos estudis s’han portat a terme per tal de reduir els nivells de ZnO als compostos de cautxú o per a substituir-lo. Entre totes les alternatives propostes per reduir la quantitat d'òxid de zinc, l'ús de nanopartícules de ZnO amb una alta superfície específica sembla prometedor. Una altra proposta per reduir els nivells de ZnO que ha estat estudiada per nombrosos autors és l'ús d'altres òxids metàl•lics, com el CaO, MgO, CdO, CuO, PbO i NiO. En aquest treball, nous activadors amb un reduït contingut de zinc han estat desenvolupats per tal de reduir l'impacte ambiental de la indústria del cautxú. Nanopartícules d'òxids metàl•lics mixtes de zinc i altres metalls s’han sintetitzat per tal de beneficiar-se de la seva grandària i aprofitar-se del comportament tant del ZnO com del MgO a la vulcanització amb sofre. Un altre gran problema mediambiental relacionat amb la indústria del cautxú és la gestió dels compostos de cautxú que han arribat al final de la seva vida útil, especialment de pneumàtics. L'impacte mediambiental dels pneumàtics, juntament amb els problemes econòmics relacionats amb la seva gestió i eliminació, ha donat lloc a una gran varietat d'estudis per desenvolupar tecnologies per a reutilitzar i reciclar els pneumàtics fora d'ús. L'ús de cautxú recuperat o regenerat en mescles amb cautxú verge s’ha investigat per diferents autors. No obstant això, la migració de les substàncies químiques entre el cautxú triturat i la matriu verge no ha estat considerada com un avantatge per tal d'utilitzar el cautxú de pneumàtics fora d'ús com un activador i, per tant, reduir els nivells de zinc emprats en els compostos de cautxú i introduir noves aplicacions per als pneumàtics fora d'ús. Aquest enfocament ha estat investigat en aquesta tesi. / El óxido de zinc es un compuesto ampliamente utilizado en la industria del caucho debido a las excelentes propiedades que muestra como activador para la vulcanización con azufre. A pesar de sus características superiores, existe una creciente preocupación acerca de sus efectos medioambientales y numerosos estudios han sido realizados con el fin de reducir los niveles de ZnO en los compuestos de caucho o para sustituirlo. Entre todas las alternativas propuestas para reducir la cantidad de óxido de zinc, el empleo de nanopartículas de ZnO con una alta superficie específica parece ser prometedor. Otro propuesta para reducir los niveles de ZnO que ha sido estudiado por numerosos autores es el uso de otros óxidos metálicos, como el CaO, MgO, CdO, CuO, PbO y NiO. En este trabajo, nuevos activadores con un reducido contenido de zinc han sido desarrollados con el fin de reducir el impacto ambiental de la industria del caucho. Nanopartículas de óxidos metálicos mixtos de zinc y otros metales han sido sintetizados con el fin de beneficiarse de su tamaño y aprovecharse del comportamiento tanto del ZnO como del MgO en la vulcanización con azufre. Otro gran problema medioambiental relacionado con la industria del caucho es la gestión de los compuestos de caucho que han alcanzado el final de su vida útil, especialmente de neumáticos. El impacto medioambiental de los neumáticos, junto con los problemas económicos relacionados con su gestión y eliminación, ha dado lugar a una gran variedad de estudios para desarrollar tecnologías para reutilizar y reciclar los neumáticos fuera de uso. El uso de caucho recuperado o regenerado en mezclas con caucho virgen ha sido investigado por diferentes autores. Sin embargo, la migración de las sustancias químicas entre el caucho triturado y la matriz virgen no ha sido considerada como una ventaja con el fin de utilizar el caucho de neumáticos fuera de uso como un activador y, por lo tanto, reducir los niveles de zinc empleadas en los compuestos de caucho e introducir nuevas aplicaciones para los neumáticos fuera de uso. Este enfoque ha sido investigado en esta tesis. / Zinc oxide is a widely used compound in rubber industry due to the excellent properties that shows as activator for sulphur vulcanisation. Despite its superior characteristics, there is an increased concern about its environmental effects and several research studies have been carried out in order to reduce the ZnO levels in rubber compounds or substitute it. Between all the alternatives proposed to reduce the ZnO levels, the use of nano-sized ZnO particles with high surface area seems to be promising. Another approach to reduce the ZnO levels that has been studied by many authors is the use of alternative metal oxides, such us CaO, MgO, CdO, CuO, PbO and NiO. In this work, novel activators with reduced zinc content have been developed in order to reduce the environmental impact of the rubber industry. Mixed metal oxides nanoparticles of zinc and other metal have been synthesised with the aim of profiting from its size and to take advantage of the behaviour of both ZnO and MgO in sulphur vulcanisation. Another environmental problem related to the rubber industry is the management of end of life and waste rubber, especially tyres. The environmental impact of waste tyres, together with the economic problems related with the management and disposal, has led to a great variety of studies to develop technologies to re-use and recycle waste tyres. The use of reclaimed or regenerated rubber in blends with virgin rubber has been investigated by different authors. However, the migration of chemicals between the crumb and the matrix has not been considered as an advantage in order to use tyre crumb as an activator and, therefore, reduce the zinc levels employed in rubber compounds and introducing new applications for the waste rubber from end of life tyres. This approach has been investigated in this thesis.