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Five sample mixtures of Ugandan kaolin, ball clay, feldspar and flint were formulated and porcelain samples fabricated by extrusion through a vacuum pugmill. Samples were evaluated for formability. The degree of densification of sintered specimens fired at 1200 to 1350 °C was evaluated by measuring the firing shrinkage, bulk density, water absorption and bending strength. Crystalline phases and mullite morphology were studied using XRD and SEM respectively. Dielectric strength measurements were carried out on disc specimens. Dielectric and bending strength properties deteriorated at high temperatures because of pore formation and decreasing amount of undissolved quartz in the crystalline phase. An optimum composition of 30% kaolin, 15% ball clay, 30% feldspar and 25% quartz yielded an unglazed body with highest bending strength of 72MPa and dielectric strength of 19MVm-1 after firing at 1250 °C. The body consisted of small, closely packed mullite needles and undissolved quartz crystals embedded in a glass matrix.
Objective of this study is to investigate and optimize an industrial batch ball mill by using the population-balance modeling. Experimental work involved taking samples after different grinding times from an industrial batch ball mill. The parameters of specific rate of breakage and breakage function were calculated from the population-balance modeling equation using the back-calculation method. As the time of grinding increases, the specific rate of breakage increases to a peak value at 6 h grinding, and then decreases. One of the main reasons for the above is that the particle size decreases continuously in a batch grinding process; however the ball size remains constant. Therefore, allowing an excessively long grinding time without changing the media size is an inefficient method of production of fines. The specific rate of breakage values indicated maximum selection at the end of 6 h. Any further grinding after this time is considered inefficient. In order to obtain finer particles, the samples were taken from the industrial ball at after 6 h milling and fed to a laboratory stirred media mill obtaining the desired product within 15 min of grinding.
This article relates to a presentation given at the 11th International Ceramics Congress of CIMTEC 2006, Acireale, Sicily, Italy, June 4-9, 2006, and discusses early work carried out on a 3-year European framework VI Collective Research Project entitled “Studies aimed at assisting legislation and encouraging continual improvement in the field of Respirable Crystalline Silica”. This project was ultimately completed in September 2007. The article provides an overview of the project before discussing the development of novel equipment for sampling airborne factory dusts. The envisaged role for the equipment in achieving the project objectives and so assisting SMEs is emphasized.
This paper reports an investigation carried out on the deskulling problem of tundishes at the Mobarakeh Steel Plant in Iran. Bad deskulling of tundishes is a major problem in continuous casting of steel, and can occur due to the chemical reactions between the refractory lining and the slag carry over from ladle to tundish. Post-mortem analysis of the slag/commercial magnesia-olivine mix refractory interface by XRF, XRD, OM, TEM, SEM and EDS techniques showed that the volume of slag carry over from ladle to tundish has a direct effect on refractory wear in the tundish. The percentage of tundishes where the skull was locked into the safety lining was dependent on the slag basicity and amount of Al2O3 in the slag inside the tundish. It has been shown that a direct corrosion mechanism occurs in basic slag and also in acidic slag containing low alumina, but an indirect corrosion mechanism occurs in acidic slag containing high alumina.
Spinel formation was studied by phase analysis and dilatomeric experiment using commercially available caustic magnesia and technical alumina in the temperature range of 1000 °C to 1400 °C. AlF3 as mineralizer was added up to 3 wt%. AlF3 was found to reduce the spinel formation temperature significantly, but also reduces the reactivity of the calcined products, measured by specific surface area.
SiC/(W,Ti)C functionally graded ceramic composites were produced by hot pressing for use as sand-blasting nozzles, and their microstructure and wear behaviours were examined. The wear resistance of the graded nozzles and of a stress-free nozzle with the same composition, was assessed by sand blasting surface treatments. Results showed that the surface hardness (nozzle entry zone) of the functionally graded nozzle is greatly improved compared to the homologous stress-free nozzle. The functionally graded nozzle shows higher wear resistance than the homologous stress-free nozzle, and the ceramic nozzle graded both at the entry and at the exit area exhibited higher wear resistance over the one graded only at the entry area.
A rapid manufacturing method for fabrication of 3D ceramic parts will be presented. The structural information is printed by ink jet in powder layers of 80 μm thickness. Different granulated powders can be used, such as zirconia and alumina if they show a good flow ability. After printing the structures a heating process takes place. After these the parts can picked out from the powder bed. The manufactured parts can be impregnated with epoxy. Another option is the infiltration with ceramic slurries and glass with sintering to higher density. The sintering process has been studied and the shrinkage and material properties evaluated. The interrelationship between the raw material qualities, infiltration media and the sinter parameters as well as the material-specific properties such as density and stability will be presented. The manufacturing method is used for fabrication of moulds and cores for casting processes. Otherwise the process can be used for fast fabrication of models and prototypes. The possibilities to use these methods for implant manufacturing will be shown. A cost analysis has been performed comparing direct manufacturing of small batches of components to mould injection processes.
A solid oxide fuel cell (SOFC) electrochemically converts chemical energy of a fuel into electricity at temperatures from about 650 to 1000 °C. SOFCs offer certain advantages over lower temperature fuel cells, notably ability to use CO as a fuel rather than being poisoned by it, and high grade exhaust heat for combined heat and power, or combined cycle gas turbine applications. This paper reviews the operating principle, materials for different cell and stack components, cell designs, and applications of SOFCs. Among different designs of solid oxide fuel cells (SOFCs), the electrical resistance of tubular SOFCs is high, and areal power density (W/cm2) and volumetric power density (W/cm3) low. Planar SOFCs, in contrast, are capable of achieving very high power densities.
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