Global warming and the high energy demands of fossil fuel in industries have led governments to implement legislation aimed towards developing more energy efficient and sustainable processes. In the brickwork industry, the burning of coal and natural gas provides the energy to fire clay bricks in the 900-1200 oC range into high quality building materials. Microwaves powered by renewable energy sources have been suggested as a sustainable alternative to fossil fuels. Microwave heating has been considered a promising technique for the processing of clays due to the potential energy consumption and carbon footprint reductions, and for its volumetric heating nature, which enables the fast and uniform heating of a load. This could result in improving the mechanical properties of the fired products. The aims of this project were to develop an understanding of how microwaves interact with clays in order to show whether they could be used to fire clay-based building materials, and to understand how this could be achieved and the parameters that affect it. The composition of Danish clays was quantified, i.e. quartz, calcite, albite, orthoclase, kaolinite, montmorillonite and muscovite, and their thermal evolution was studied across the firing range. The dielectric properties of clays were measured at 912-2470 MHz and 20-950 oC in order to investigate the microwave/clay interaction, assess the effects of changing composition, temperature, frequency and material's density on their potential for microwave processing, and provide critical information on the design and scale up of this technology. Relating the mineralogy of a material and its evolution during heating to changes on the dielectric property trends, and thus microwave processability, was examined for the first time in this thesis. Insight into the influence of individual components on the potential for microwave heating was gained from an analogous study on clay constituents. While the dielectric constants of clays were found to be relatively stable during heating, their loss factors fluctuated with temperature. Free and physically bound water were the dominant dielectric species near room temperature, while their removal halved the loss factors until 350 oC. Beyond this temperature, a steady increase in the loss factors concurred with the mineral dehydroxylations. The loss factors sharply rose beyond 800 oC due to sintering effects, while calcite decomposition partially counteracted this growth. Montmorillonite and muscovite were the most microwave absorbing mineral species due to their water affinity and interlayer cation content, enabling the microwave treatment of the whole clay. On the other hand, a frequency shift from 2470 MHz to 912 MHz resulted in a loss factors increase. This is mainly due to the frequency shifting towards the dipolar dispersion area of physically bound water and the zone in which ionic conductivity heating effects dominate. Mixing rules were used to relate each single mineral to dielectric property variations, and thus rapidly gain knowledge of the microwave processability of any clay across the firing range based on its composition. Böttcher model provided accurate estimations when compared to experimental measurements, and with the same degree of uncertainties at the 912-2470 MHz frequencies and 0.56-0.37 void fraction ranges. The model was expanded for different compositions with clays from Spain, England and Netherlands. This was the first time that mixing rules were successful in estimating mixtures of more than three constituents. A microwave system was developed with the aim of firing clay products of comparable quality to conventional specimens. The basis of design focused on maximising the thermal uniformity of the clay load. The process design steps involved remodelling the clay load, building heat transfer models of the load, carrying out trials to study whether clays behave as expected from their dielectric properties, i.e. volumetric or selective heating, minimising thermal gradients, and assessing alternative methods for the control of the holding stage. Microwave firing cycles manufactured clays with a thermal uniformity at the height of firing of 1050±55 oC and reduced processing times to < 3 h. This is 92% faster than in brickworks, where conventional samples could not match the heating rates without cracking. High temperature (>800 oC) mineral reactions went unfinished due to the reduced holding time of the microwave treatment (30 min), which resulted in dimmer surface colorations. Enhanced thermal uniformity and reduced time for densification resulted in specimens with a 12% higher compressive strength, 38% larger water absorption and 7% higher void fraction. Clay samples three times as big were fired to gain an insight into the scale up of the technique. A tighter process control and higher reproducibility were reported, which is promising for potentially allowing longer holding times in scaled up processes, but the product quality improvement did not change. Looking into an industrial scale up, further work would be required to assess possible design concepts, and an optimal microwave firing process may require complete redesign of the furnace configuration, where several challenges need to be considered, such as brick arrangement, power availability and applicator size and shape. For the purposes of assessing the possible economic and environmental impact of implementing microwave clay firing at industrial scale, one of the most straightforward designs, i.e. retrofitting of an industrial tunnel kiln for microwave processing, was considered. Although energy expenditures would decrease from 11.6 GJ fuel/h to 6.1 GJ electricity/h when using a microwave system for the same throughput, the higher cost of electricity and microwave equipment over conventional burners made the conventional technique more economically feasible. The substitution of natural gas by electricity powered by green energy sources resulted in carbon footprint reductions of >95%, and agreed with the energy policies of numerous countries and supranational organisations worldwide.

ZnO is a promising semiconducting material for manufacturing optoelectronic devices. Its most important properties are its wide and direct band gap and its high electron-hole binding energy. Synthesis of ZnO in bulk and thin film form has been investigated intensively over recent decades. Likewise, nanomaterials have been in the point of focus for their different properties compared to their bulk form. The vastly increased ratio of surface area to volume and change in electronic properties with great reduction in particle size enable improved performance in conventional applications where their bulk counterparts have been used for decades. As a result of this trend, research on synthesis of ZnO nanowires and their incorporation in prototype optoelectronic devices has been intensive in recent years. Therefore, synthesis of ZnO nanowires in a cost effective way and understanding the factors influencing the ZnO nanowire growth is essential for contribution to ongoing research. V In this thesis, hydrothermal synthesis of ZnO nanowires, which is a solution based method enabling vertically aligned ZnO nanowire array fabrication over large areas, is investigated. In the first part of this thesis, the effect of using various zinc salts as zinc sources on ZnO nanowires is investigated by monitoring pH, temperature and light transmittance of growth solutions. In the second part, a detailed parametric study on the use of zinc acetate dihydrate salt is provided with regard to the existence of its unique properties compared to other two zinc salts. The effect of growth time, temperature, ratio of concentration of precursor chemicals and precursor chemical concentrations is investigated. The results show that hydrothermal synthesis method could replace the conventional ZnO nanowire fabrication methods. It was shown that specific nanowire lengths for any application can be obtained simply by adjusting the parameters of hydrothermal growth system.

This study investigates the physical, mineralogical and chemical characteristics of a group of pottery sherds that are mostly Miletus-ware ceramics, belonging to the Early Ottoman period and excavated during 2003 season, from the The sherds examined are mostly characterized by cobalt-blue designs which are occasionally coupled with black, green and purple paintings. After grouping the sherds according to their stylistic and color differences / petrographic, X-ray diffraction, scanning electron microscope coupled with energy dispersive X-ray and Fourier Transform Infrared analyses were carried out for investigating the mineralogical and chemical properties. Most of the ceramic samples have slip and glaze on both sides. The glaze part is mostly fresh without any devitrification products. Bodies of the ceramics have tones of reddish yellow and/or red, indicating abundant amount of iron in their raw material. Grains consist mainly of metamorphic rock fragments (quartz-mica schist), quartz, feldspar, hornblende, hematite and biotite. Pyroxene, epidote, chert, muscovite, opaque minerals, chlorite are also encountered. Micritic calcite occurs in some of the pores. Ceramic bodies investigated are usually fine-grained and well-sorted. Clay raw material used for the production of the ceramics seems to be originated from a metamorphic source. Bodies usually show a low degree of vitrification with few exceptions, indicating a rather simple technology with non-uniform and low degree of firing, probably not exceeding 900&deg / C. Technological characteristics of the sherds examined do not seem to have changed much between 14th and 16th century.

MFI type zeolites, are the most widely studied zeolites for membrane separations. Conventionally, zeolite membranes are prepared in batch systems by hydrothermal synthesis in autoclaves. This method has several disadvantages for use in industrial scale for the synthesis of membranes with large areas and complex geometries that are commonly used in membrane modules. The objective of this study is to prepare MFI type zeolite membranes on tubular alumina supports in a continuous system where the synthesis solution is circulated through the tubular supports. Syntheses were carried out using clear solutions, at atmospheric pressure and at temperatures below 100&deg / C. The membranes were characterized by N2, SF6, n-butane and isobutane permeances, X-ray diffraction and scanning electron microscopy. A 2-&amp / #956 / m membrane was synthesized using the composition 80SiO2: 16TPAOH: 1536H2O at 95&deg / C in the continuous system. The membrane showed N2 permeance of 4.4 x 10-7 mol/m2.s.Pa and N2/SF6 selectivity of 11. The membrane synthesized in the batch system showed a N2 permeance of 3.4 x 10-7 mol/m2.s.Pa and a N2/SF6 selectivity of 27. Both membranes showed n-butane/isobutane mixture (50%-50%) selectivities of about 6 at temperatures of 150 and 200&deg / C. Among many zeolite membranes reported in literature, these membranes are one of the few zeolite membranes synthesized in a flow system and the first MFI type membranes synthesized in a continuous flow system with circulation of the synthesis solution. The permeances and selectivities of the membranes synthesized in the continuous system are comparable with the MFI type membranes synthesized in batch systems in literature.

Clinoptilolite is the most abundant zeolite mineral in nature. In this study a reproducible synthesis recipe for clinoptilolite was established and the limits of the crystallization field were developed by changing synthesis parameters such as temperature, composition and the nature of reactants. Clinoptilolite was reproducibly synthesized as a pure phase and in high yield at 140oC using a benchmark batch composition of 2.1 Na2O:Al2O3:10SiO2:110.1 H2O. Clinoptilolite was crystallized from 10wt% or 28wt% seeded systems while it was not formed if no seeds were present. Clinoptilolite was also crystallized as a pure phase when the cation in the benchmark batch composition was Na,K mixture, or when alkali salts such as carbonates or chlorides were used besides alkali hydroxides, or when the SiO2/Al2O3 ratio was in the range of 10-12. Clinoptilolite was still crystallized as a single phase when alkali hydroxides in the batch were reduced by 20%. With the benchmark batch composition, clinoptilolite was crystallized in pure phase form at 100oC, 120oC, 140oC and 160oC while synthesis at 175oC resulted in the formation of pure mordenite. At 140oC clinoptilolite was crystallized together with Linde L when cation in the benchmark composition is only potassium. Phillipsite crystallized together with clinoptilolite at SiO2/Al2O3 ratio of 8 to 9. At SiO2/Al2O3 ratios of 6 or 4, phillipsite or analcime was formed as pure phase respectively. When the alkali hydroxides in the batch was increased by 20%, sanidine was formed. Use of reactive aluminosilicate gels enhanced the formation of clinoptilolite while attempts to use mineral raw materials were unsuccessful. For both Na and (Na,K)-clinoptilolite, Si/Al ratio of products were greater than four. Thermal stability of synthetic clinoptilolites were comparable with natural clinoptilolite and potassium ion increased thermal stability of clinoptilolite.

The effect of seeding on the properties of alumina supported MFI membranes was investigated in this study. Membranes were synthesized from clear solutions with a molar batch composition of TPAOH:9.80SiO2:0.025NaOH:0.019Al2O3: 602.27H2O:39.16C2H5OH on bare and seeded alumina supports at 130oC in autoclaves. The amount of seed on the support surface was changed between 0.6 mg/cm2 and 6.9 mg/cm2 by vacuum seeding method, which provided uniform and closely packed seed layers. Membranes were characterized by XRD and SEM, and by measuring single gas permeances of N2, SF6, n-C4H10 and i-C4H10. The quality of membranes was evaluated on the basis of N2/SF6 ideal selectivity. Membranes, which showed N2/SF6 ideal selectivity higher than 40, were considered to be good quality, comprising few defects. Good quality membranes were also used to separate butane isomers. Membranes synthesized on seeded supports had compact and uniform MFI layer if the seed amount is less than 1.0 mg/cm2 on the support surface. Membranes that were synthesized on the supports coated with higher amount of seed crystals showed an asymmetric structure with a dense and uniform MFI layer at the top, the support at the bottom and a seed layer between. Half of the membranes synthesized on seeded supports had N2/SF6 ideal selectivity higher than 40. These membranes exhibited n-C4H10/i-C4H10 separation selectivities between 5 and 27 and 8 and 21 at room temperature and at 200oC, respectively. High ideal and separation selectivities showed that membranes did not include non-zeolitic pores. Membranes synthesized on bare support had non-uniform MFI layer. Those membranes showed N2/SF6 ideal selectivities below Knudsen selectivity, indicating the existence of large non-zeolitic pores in the MFI layer.

M.S.

This thesis consists of an investigation of a deposit of Hudson River clay from the Terry Brick Corp. of Kingston, N.Y., to determine the best possible uses for the clay in the ceramic industry. The effect of blending the Goldrick clay with shale, and the addition of sodium carbonate and chestnut extract as electrolytes in the stiff mud process were investigated. The uses of Goldrick clay as a slip clay to produce a glaze was investigated. Particle size determinations of samples taken from points over the entire clay deposit were made to measure the variability of the particle size distribution. Recommendations were made for improvements in difficulties encountered at the plant. / M.S.

Thermal mismatch between different components of a system could cause of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with customized thermal expansion coefficient is a counter-measure to resolve such problems. Zirconium tungstate (ZrW2O8) with negative thermal expansion coefficient is capable of being used in synthesis of composites with tailored coefficient of thermal expansion (CTE). In this work, the sol-gel method which had been already set up in our group was characterized and the sources of the factors imposing impurities in the product were distinguished in all the steps of precursor preparation and heat treatment. In the second part of study, zirconium tungstate particles synthesized by the sol-gel method were utilized as core in synthesis of ZrW2O8&ndash / ZrO2 core&ndash / shell composite particles. Shell layer was composed of ZrO2 nanocrystallites and precipitated from an aqueous solution by urea hydrolysis. Volume of the shell was effectively controlled by concentration of the initial zirconium ion in the solutions. The rate of precipitation was a function of the ratio of initial urea concentration to zirconium ion. It is hypothesized that isolation of the ZrW2O8 within a layer of ZrO2, will be a key element in solving problems associated with reactivity of ZrW2O8 towards other components in sintering of ceramic&ndash / ceramic composites with tuned or zero thermal expansion coefficient.

Alumina (Al2O3) is one of the most widely used engineering ceramic. It can be used in a wide range of applications like electrical/thermal insulation, wear resistance, structural refractories, cutting tools, abrasives, catalyst carriers and coatings. A traditional ceramic process has several steps (i.e. powder synthesis and processing, shape forming, drying, organic burnout and densification). Accessing powders with sizes in the range of a couple of micrometers down to several tens of nanometers is considered critical in attaining higher densities in the final ceramic bodies. Besides since significant shrinkage can be observed in the thermal treatment steps due to the excessive use of additives (e.g. binders, solvents and plasticizers) in the powder processing and forming steps, it is important to take remedies that would increase the solids loading in the initial mixtures. In addition, most of the conventional additives and solvents used in these steps are toxic and it is necessary to replace them with the environmentally benign aqueous-based alternatives. Alumoxanes could be used as a benign aqueous-based alternative to be used as a ceramic precursor or an agent. They are a group of compounds that have nano sized boehmite cores encapsulated with the organic groups used in its production steps. In this research work, alumoxane nano particles which can be used as precursors for nano-alumina were developed starting from aluminum trihydroxide. As a preconditioning step, grinding was applied to decrease the aluminum hydroxide particle size (&amp / #8804 / 60 &amp / #956 / m) to submicron sizes. This process was followed by the glycothermal ageing step, and organic derivative of boehmite was obtained. The amorphous particles thus obtained were further treated mechanochemically in a high energy ball mill with organic chemicals like acetic acid, methoxy acetic acid, stearic acid and L-lysine. After this step the observed sizes of the particles were as low as 10-100 nm. The effects of organic molecules used in each step were studied by FTIR spectroscopy and their effectiveness in exfoliation of hydroxide layers were identified with dynamic light scattering from processing solutions dispersed in aqueous medium. Moreover, in each step, structural analyses were carried out by XRD.