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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.
The present paper deals with optimizing different mix variables that affect the rheology of a clay sewer pipe paste. Investigated variables consist of percent water, percent grog and average particle size of clay. Shear stress and strain rates were calculated using an extrusion process through an orifice by means of compressed air. All pastes exhibited Bingham flow behaviour. The effect of percent water, percent grog and clay particle size on the following properties of paste were investigated: Plasticity of extruded paste, dry strength and drying shrinkage. It was found that the optimum parameters to be used are: 27% water (on dry basis), 30% grog mixed with clay of average particle size of 0.2 mm.
The effects of addition of a fly ash-marble waste mixture (2:1), in gradual replacement of sandstone and limestone, on the thermo-mechanical properties of traditional earthenware wall tile composition have been studied. Improvement in mechanical strength of the body was observed by addition of more than 22.5 wt% of the mixture as a substitute for sandstone and limestone at temperature of 1050 °C and above. In this temperature range, water absorption values of the body mixes exhibited a marginal variation (~1%). The improved results encourages the utilization of hazardous waste materials like fly ash and marble waste in the production of value added traditional ceramic product like glazed wall tile.
MgO-CaZrO3 based composite aggregates have been prepared by reaction sintering of dolomite and ZrO2. The sintered MgO-CaZrO3 aggregates were characterized in terms of bulk density, microstructure, thermal expansion, hot modulus of rupture and thermal shock resistance. It was found that the lime phase of dolomite was converted to high melting CaZrO3 whose high thermal expansion mismatch with MgO makes the aggregate thermal shock resistant due to the effect of micro cracking at the grain boundaries. The product may be useful as hydration and thermal shock resistant basic refractory aggregate.
A prototype superheated steam generator was developed and simple activation tests were conducted. High-temperature superheated steam at 1000 °C could be generated by sending low temperature (100 °C) saturated steam from the bottom of a silica tube filled with silicon carbide heater elements heated by microwave irradiation. The temperature of the superheated steam could be precisely controlled by adjusting the microwave output power for heating the SiC heater elements. Activation of cotton by microwave-assisted superheated steam treatment at 650 °C for 10 min was found to be effective to achieve a specific surface area of ca. 670 m2/g, which is higher than that obtained by the conventional method.
The preparation of new monotubular macroporous supports prepared from natural moroccan phosphates by extrusion process is reported. The characterization of the supports was performed by MEB to evaluate surface quality and mercury porosimetry for pore diameter. The surface morphology of supports fired at 1000 °C for 3 h does not show any macro defects and the supports show good final characteristics. The average pore diameter is near 10μ m and the porosity is about 43%. Filtration tests of a yeast suspension suggest suitability of these supports for microfiltration or ultrafiltration applications.
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