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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.
In the welding process large amounts of waste are discarded. This waste is usually deposited in landfills. This paper reports on the incorporation of the welding flux slag waste into clay bricks for civil construction. The waste was characterized with respect to crystalline phases present, chemical composition, morphology, and particle size. Claywaste powder mixtures containing up to 10-wt. % of welding flux slag waste were prepared, pressed and fired at temperatures between 850 °C and 1050 °C. The effects of the waste incorporation and firing temperature on properties such as linear shrinkage, water absorption, apparent density, and flexural strength have been determined. The microstructure of the fired pieces was evaluated by SEM. The results showed that the waste incorporated pieces fulfill the specifications required for use in clay bricks at all firing temperatures.
The effects of addition of a fly ash-marble waste mixture (2:1), in gradual replacement of sandstone and limestone, on the thermomechanical 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 MgOCaZrO3 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.
This paper reviews a new, low-temperature process for soldering and brazing ceramics to metals that is based on the use of reactive multilayer foils as a local heat source. The reactive foils range in thickness from 40μ m to 100μ m and contain many nanoscale layers that alternate between materials with large heats of mixing, such as Al and Ni. By inserting a free-standing foil between two solder (or braze) layers and two components, heat generated by the reaction of the foil melts the solder (or braze) and consequently bonds the components. The use of reactive foils eliminates the need for a furnace, and dramatically reduces the heating of the components being bonded. Thus ceramics and metals can be joined over large areas without the damaging thermal stresses that are typically encountered when cooling in furnace soldering or brazing operations. This paper draws on earlier work to review the bonding process and its application to a variety of ceramic-metal systems. Predictions of thermal profiles during bonding and the resulting residual stresses are described and compared with results for conventional soldering or brazing processes. The microstructure, uniformity, and physical properties of the reactive foil bonds are reviewed as well, using several different ceramic-metal systems as examples.
This paper deals mainly with the materials and processes associated with structuration of LTCC (Low Temperature Cofired Ceramics) in fabrication of micro/meso scale devices, including sensors, actuators and micro fluidic structures. LTCC, which is traditionally seen as a packaging material or substrate for Multi Chip Packaging Modules, is projected as an advantageous alternative to many of the technologies and processes used for various sensor and micro/meso device fabrication, which is a technology yet to be mastered in terms of processes. A roadmap for the fabrication process is drawn in detail, while the description of the devices is limited to the extent of providing the reader with sufficient information of the final structural details that have to be met. Issues in structuration like sagging, delamination, swelling, etc. are discussed. Graphite based sacrificial pastes (GB) are taken as the main structuration material, where the selection of the sacrificial material is the key to good structuration.
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 10μm 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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