No description available.

No description available.

No description available.

This work describes the preparation and the determination of some properties of two magnesium SiAlON ceramics, one with a low substitution level and one with a high substitution level ' phase. Each had a specific amount of spinel as second phase which would form on sintering or after a post-sintering heat-treatment. The work was undertaken because (a) the improvement in the properties of pressureless-sintered yttrium SiAlON ceramics was not as high as anticipated and (b) by applying the knowledge gained with the widely researched yttrium system to the MgSiAlON ceramic system, the properties of the magnesium system may be further improved. Under consideration in this thesis were the sintering of these ceramics and some sintering reactions are proposed. Also discussed is the effect on the microstructure of heating the ceramic in both oxidising and inert atmospheres. Some mechanical properties were determined, including fracture toughness and hardness testing at ambient temperature, and creep testing at upto 1300^oC. It was expected that MgSiAlONs would be easier to sinter due to the lower ternary oxide eutectic temperature and from a sintering view-point the high z materials do offer an alternative system to the yttrium system by being easier to sinter, but the low z material was as difficult to sinter as the yttrium system. Whilst the MgSiAlONs that were produced in this project were generally out-performed, encouraging results were obtained for the high z material in oxidation resistance. Low z material had the highest fracture toughness and hardness - both of which increased by heat-treatment. It is proposed that alterations to this heat-treatment would improve matters and would form a useful area for future work.

Chalcogenide glasses have several potential uses for new photonic devices for two reasons: i) their infrared (IR) transparency and ii) viscous flow at the glass transition temperature (Tg). Because of the latter, these glasses can be drawn to optical fibre and polished glass discs can be patterned above Tg for instance as planar waveguides. The fibre or waveguide shaped chalcogenide glasses have several potential uses as chemical sensors, biosensors, laser power delivery etc. and hence efforts have been made to synthesise high optical quality chalcogenide glasses. The well-established melt-quenching method was used as a comparative to prepare chalcogenide glass-melts in this project. Conventionally, the chalcogenide glass-melts are prepared using a rocking resistance furnace but this process is very long and cumbersome. To make the glass-melting process fast, simple and cost effective microwave heating was investigated instead in this project, and this was the main aim of the project. As2S3,Ge33As12Se55, Te20As30Se50 glasses were made with partial success and As2S3, Gel7As18Se65 glasses successfully, for the first time to the author's knowledge, through microwave heating in a domestic microwave oven (DMO) working at a frequency 2.45 GHz in less than an hour while the resistance heating method took about 1.5 days. The DMO output power was 800 W or 1000 W, and co-heating using both the microwaves and convection current heating to 220°C enabled some glass preparations to be carried out in ca. 10 minutes. The reactants were crushed manually for the DMO preparation of chalcogenide products keeping in mind that electric current tends to flow at the surface of the material which is known as 'skin effect'. The size of the silica glass melt-ampoule was kept as small as possible (normally - 10 cm) so that the DMO chalcogenide-melt could collect at the bottom of the ampoule and form a DMO chalcogenide rod product. The increased rate of reaction in the DMO compared to the rate of reaction in the rocking resistance furnace was attributed to the formation of plasma which caused a very high temperature (> 1000°C) of the reaction system leading to the almost instant melting of the some reactants. The boiling DMO chalcogenide-melt was seen in several cases but As/S = 2:3 (at%) did not boil when exposed to microwaves. Visually homogenous DMO chalcogenide-products were formed in each of the above stated compositions except in the case of DMO As-S product when four distinct layers could be seen. The red transparent portion of the DMO As-S sample was X-ray amorphous and showed no crystal feature in SAED (Selected area electron diffraction) using TEM (Transmission electron microscopy) whereas the non-glassy portion showed some crystalline peaks in XRD (X-ray diffraction) but showed no crystalline features in SAED. The DMO Ge/As/Se=33/12/55 (at%) rod product showed a single crystalline peak in the XRD pattern but it was completely amorphous according to SAED. On the other hand, the DMO Te/As/Se = 20/30/50 (at %) rod product showed slight evidence of crystallinity from SAED but was completely amorphous in XRD. DMO As/Se = 40/60 (at %) rod product and DMO Ge/As/Se= 17/18/65 (at %) rod did not show any crystalline structure from XRD and from SAED. The inhomogeneity of the DMO As-S glass was further reflected in the multiple Tgs observed using DTA (Differential thermal analysis) viz.:166°C, -194°C (broad) and 300°C in the first DTA run. Though, the sample showed a single Tg value of 202°C during the second DTA run after quenching in-situ the sample from the first DTA run. The stoichiometry of this glass wasAs43.9Se56.1 when observed through EDX (Energy dispersive X-ray analysis) which was performed using ESEM (Environmental scanning electron microscopy) showing that the glass was inhomogeneous. The DMO As/Se = 2:3 (at %) rod product showed a single Tg value of 180°C ± 5°C and the stoichiometry was found to be As40.1Se59.9 from EDX analysis which was very close to the desired value. The DMO rod product obtained from the composition Ge/As/Se = 17/18/65 showed a single Tg value of 246°C ± 5°C and the observed stoichiometry of the DMO chalcogenide product was Gel7.6As19.2Se63.5. Whereas the Ge32.8As11.0Se56.4 DMO rod product could be made from the batch composition Ge/As/Se=33/12/55 with a Tg value of 368°C ± 5°C but the conventionally prepared glass exhibited a stoichiometry Ge33.8As12.5Se50.6 with Tg value 371 DC± 5°C showing that a slight increase in percentage of germanium in the glass composition increases the Tg value. The Te19.6As30.4Se50.0 DMO rod product was obtained from Te/As/Se = 30/20/50 batch composition having a Tg value of 371°C ± 5°C showing that the experimental values for the stoichiometry and Tg of the product were very close to the desired value. A sample of Te/As/Se = 20/30/50 was heated in the DMO only for 5 minutes when stoichiometry of the product was found to be Te19.6As32.6Se47.8 showing that prolonged exposure of microwaves, which facilitated boiling, was important for homogenisation of the product (note that DMO As-S product never boiled) since the ampoule was not rocked inside the DMO. It was observed that optical absorption at 2.9 urn wavelengths due to hydroxide contamination for the DMO As-S product was reduced to - 3% of that of the AS2S3 glass made through conventional heating. The absorption bands for -OH group at 2.9 urn and H20 at 6.3 mum were very low in almost all the DMO products. Some carbon and silica contamination was found to be slightly larger in DMO products than that present in the conventionally prepared products and the reasons for this are not known at present. The DMO chalcogenide products were obtained reproducibly except in the cases of the DMO As-S product.

This work investigates the behaviour of clay in a commercial screw driven extruder used to manufacture clay drainage pipes.  Based on a striping effect observed within the clay during extrusion, experiments and models have been constructed to determine if these stripes can be removed.  The aim is to improve product yield and reduce waste. During the course of this work, it will be described how it is believed that the stripes are the result of localisation and shear banding which allows water to evaporate quicker from some areas than others, causing stripes.  Some preliminary work is discussed regarding a hopper, used as a step towards generating models for the extruder.  Latter sections detail the models created using various mathematical techniques which are used to simulate the material as it flows through the system.  Of particular relevance is optimisation theory which allows various parameters to be determined based on a pre-determined function and a set of initial guesses.  Building upon this work leads to the conclusion that modifying the design of both the auger and extension can reduce the chances of localisation, thereby reducing the chances of stripes forming. Finally, a set of recommendations are made regarding potential design changes, and a complete redesigned system is proposed as an example of what would be required.

No description available.

The flow characteristics of neutral sodium silicate glass in an open hearth regenerative furnace have been studied using a one tenth scale physical model. The constraints of similarity have been investigated and discussed, and the use of sodium liquor as a cold modelling solution has been developed. Methylene Blue and Sulphacid Brill Pink are used as delineators, and a technique for analysing the concentration of each even in a mixture has been developed. The residence/time distributions from the model have been simulated using a mixed model computer program which identifies the nature and size of the most significant flow streams within the furnace. The results clearly show that the model gives a true representation of the furnace and illustrates a number of alternatives for operating or design changes which will lead to improved production efficiency.

The electrical and optical characteristics of a cylindrical alumina insulator (94% Al203) have been measured under ultra-high vacuum (P < 10-8 mBar) conditions. A high-resolution CCD camera was used to make real-time optical recordings of DC prebreakdown luminescence from the ceramic, under conditions where DC current magnitudes were limited to less than 50μA. Two concentric metallized rings formed a pair of co-axial electrodes, on the end-face of the alumina tube; a third 'transparent' electrode was employed to study the effect of an orthogonal electric field upon the radial conduction processes within the metallized alumina specimen. The wavelength-spectra of the emitted light was quantified using a high-speed scanning monochromator and photo-multiplier tube detector. Concurrent electrical measurements were made alongside the recording of optical-emission images. An observed time-dependence of the photon-emission is correlated with a time-variation observed in the DC current-voltage characteristics of the alumina. Optical images were also recorded of pulsed-field surface-flashover events on the alumina ceramic. An intensified high-speed video technique provided 1ms frames of surface-flashover events, whilst 100ns frames were achieved using an ultra high-speed fast-framing camera. By coupling this fast-frame camera to a digital storage oscilloscope, it was possible to establish a temporal correlation between the application of a voltage-pulse to the ceramic and the evolution of photonic emissions from the subsequent surface-flashover event. The electro-optical DC prebreakdown characteristics of the alumina are discussed in terms of solid-state photon-emission processes, that are believed to arise from radiative electron-recombination at vacancy-defects and substitutional impurity centres within the surface-layers of the ceramic. The physical nature of vacancy-defects within an alumina dielectric is extensively explored, with a particular focus placed upon the trapped electron energy-levels that may be present at these defect centres. Finally, consideration is given to the practical application of alumina in the trigger-ceramic of a sealed triggered vacuum gap (TVG) switch. For this purpose, a physical model describing the initiation of electrical breakdown within the TVG regime is proposed, and is based upon the explosive destabilisation of trapped charge within the alumina ceramic, triggering the onset of surface-flashover along the insulator. In the main-gap prebreakdown phase, it is suggested that the electrical-breakdown of the TVG is initiated by the low-field 'stripping' of prebreakdown electrons from vacancy-defects in the ceramic under the influence of an orthogonal main-gap electric field.

This thesis describes the synthesis and application of complex metal oxide nanoparticles. The work is focussed on three core areas; the synthesis of CoFe2O4 nanoparticles and their application as CO oxidation catalysts, the controlled assembly of functionalised CoFe2O4 and BaTiO3 nanoparticles and the preparation and characterisation of magnetoelectric composites from chemically-bonded nanoparticle assemblies. Chapter 1 gives an introduction to the history of nanotechnology, recent developments in the synthesis of nanoparticles and other areas key to the work described herein. In Chapter 2 details the synthetic and analytical techniques employed. Chapter 3 describes the synthesis and characterisation of CoFe2O4 nanoparticles, and their application as catalysts in the CO oxidation reaction. Nanoparticles were prepared with a range of controlled sizes and were found to be active CO oxidation catalysts. Analysis of their size-dependent activity and stability is performed. Chapter 4 describes the assembly of CoFe2O4 and BaTiO3 nanoparticles by direct functionalisation of the nanoparticle surfaces using complementary organic functional molecules. Characterisation of the functionalised nanoparticles and assemblies is performed, and the extensibility of the developed functionalisation and assembly protocol is tested using particles with different sizes and morphologies. In Chapter 5 the assembled nanoparticles discussed in Chapter 4 are processed into dense ceramics with a view to preparing magnetoelectric composites. The magnetoelectric properties are tested, and optimisation of the ceramics is performed by modification of the starting nanoparticle sizes, composite composition and processing conditions. The composites are tested against control samples prepared by traditional grinding and firing, and characterisation of the ceramics using XRD and electron microscopy provides and insight as to why their magnetoelectric properties differ to those prepared by the traditional technique. The work contained in this thesis has been published in the following papers: - G. Evans, I. V. Kozhevnikov, E. F. Kozhevnikova, J. B. Claridge, R. Vaidhyanathan, C. Dickinson, C. D. Wood, A. I. Cooper, M. J. Rosseinsky, “Particle-size Activity Relationship for CoFe2O4 Nanoparticle CO Oxidation Catalysts,” J. Mater. Chem. 2008, 18, 5518. G. Evans, G. V. Duong, M. J. Ingleson, Z. Xu, J. T. A. Jones, Y. Z. Khimyak, J. B. Claridge, M. J. Rosseinsky, “Chemical Bonding Assembly of Multifunctional Oxide Nanocomposites,” Adv. Funct. Mater. 2010, 20, 231.