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The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. In addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.
An alumino-silicate based fireclay used in the production of refractory materials contains iron impurity which is not in the desired limits. The magnetic conversion conditions have been experimented in the reduction of iron content in the fireclay by magnetic separation. Effects of heating temperature, heating time and grain size and coal addition were investigated in the magnetization of fireclay samples. An artificial neural network was developed for modeling the dependency of magnetization on temperature, time and grain size as well as on coal addition during heating and an optimization problem was formulated in order to achieve the optimum conditions of magnetization. The results indicate that heating clay particles of 5/7 mesh (average 3.36 mm) grain size at 458 °C for 15 min without any coal addition will give the optimum magnetization.
Starting from an industrial body mix for porcelain stoneware tiles, part of its fluxing agent, sodium feldspar was replaced by a fine-grained microgranite. Sintering behaviour of the studied porcelain stoneware bodies with and without microgranite was investigated using a double beam optical non-contact dilatometer according to the corresponding industrial firing profiles. The degree of vitrification of the densified samples and the other samples separately heated at different temperatures were determined by measuring the shrinkage, bulk density, water absorption and flexural strength. Furthermore, the colour measurements were carried out on the fired samples. X-ray diffraction (XRD) was used in order to analyze the phases formed after firing. In addition, scanning electron microscopy (SEM) was undertaken to observe the microstructural characteristics of fired bodies with respect to peak firing temperature. The results indicate that possible use of fine-grained microgranite as an effective fluxing agent in porcelain tile bodies.
The mineralogical composition and technological characteristics of an industrial porcelain type body mixed with 3 wt.%, 6 wt.%, 9 wt.%, 12 wt.% and 15 wt.% of carbonates respectively have been studied. The added components were two samples from limestones and dolomites from carbonate formations of Kozani area, northwestern Macedonia, Greece and one magnesite from Gerakini formation of Chalkidiki peninsula, northern Greece. After firing the prepared ceramic specimens at 1200 °C for half an hour, the addition up to 9 wt.% of magnesite, up to 6 wt.% of dolomite and 3 wt.% of limestone gave better values of shrinkage, porosity and water absorption compared to the reference porcelain type body. The addition of carbonates lowers in general the compressive strength of the fired specimens. No correlation of the amorphous phase and the technological properties was found. Limestone addition favoured the formation of feldspars, dolomite the formation of feldspars, cordierite and forsterite and magnesite the formation of cordierite and forsterite.
Thermite welding of rails is now a standard operating practice to successfully join rails conjunctions in the field. Alumina crucible, an essential component of this operation, will be damaged and unusable after not more than 30 operations. This is due to direct contact of crucible with molten iron. Factors influencing this damage, including chemical reactions, penetration and infiltration of molten iron into the body, were studied using a scanning electron microscope equipped with X-ray spectroscopy (SEM/EDS) and X-ray diffraction. The results of this study supported by the kinetics of reaction between iron melt and alumina crucible in thermite welding showed that the thermite process does not significantly affect the crucible body component chemically; i.e. corrosion was not a major factor in crucible deterioration. The penetration and infiltration of melts into the crucible body via the grain boundaries and porosities were the major factor. A higher rate of the melt penetration into the parts containing impurities especially the silica was more harmful.
Ceramics are characterized by their special wear and temperature resistance. Thus, they are especially suited for the cutting of high-temperature alloys and difficult-to-cut materials. Due to their low ductility, they show brittle-hard properties during the process, which lead to a sudden failure of the tool. But it is possible to create composite materials that counteract the brittle-hard behavior of the substrate material by PVD-coating. The objective of the investigations is to increase the process stability of coated ceramic indexable inserts made of aluminum oxide and silicon nitride through the optimisation of the mechanical pre-treatment of the substrate materials. To this end, the ceramic substrates are pre-treated by different abrasive machining processes. Comprehensive measurement evaluations show the influence of the machining process and strategy on the formation of surface and subsurface. The workpieces ground and lapped in different ways are subsequently coated by an especially developed PVD process. Measurements show the influence of the pre-treatment on the surface structure and on the mechanical properties of the composite material. The application of the developed and manufactured tools in cutting tests verifies the results of the measurements.
Since more than twenty five years, composite materials have been with continuously increasing spatial and aeronautical applications requirements. The thermostructural composites materials are of utmost importance for satisfying the needs of mechanical and thermal characteristics at very high temperature and in severe environments. This paper deals with a large variety of applications concerning the aerospace and nuclear applications like nozzles and hot gas valves for Solid Rocket Motor (SRM), brake disks for planes, aerospace turbine engine exhaust nozzles, thermal protection system for reentry vehicles, but also Divert and Attitude Control System (DACS) for interceptors, heat exchangers for hypersonic propulsion systems, plasma facing components for nuclear fusion applications and special components for nuclear fission applications. We will see that Carbon/Carbon and Ceramic Matrix Composites are leading candidate materials for these high-temperature structural applications. This lecture will identify the current state-of-the-art and new technological developments. A description of the main steps of the manufacturing processes will be made.
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