Papers by Keyword: Traditional Ceramics

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Authors: Patrick Henrique, Augusto Wanderlind, Agenor de Noni
Abstract: Planarity is one of indispensable attribute of a ceramic tile quality. During the firing changes on curvature may be permanent causing damage on quality and productivity. The objective was to evaluate curvature evolution on porcelain tile during heating stage of firing. Effects of engobe and glaze coating were evaluated. The performance of two compositions of porcelain tile was studied on industrial (1000 mm x 500 mm x 10 mm) and laboratorial (100 mm x 50 mm x 6 mm) scale. Industrial test pieces were fired at 950 and 1200 °C. Final curvature was measured by conventional dial indicator. Curvature evolution of laboratorial test pieces was evaluated by thermal fleximetry from 25 to 1200 °C. This characterization was capable to identify very significant positive curvature deflection on temperature range from 930 to 1200 °C, directly associated to permanent planarity defects. Differences on composition affect significantly the curvature evolution.
Authors: Y. Pontikes, I. Vangelatos, Dimitri Boufounos, Dimitris Fafoutis, G.N. Angelopoulus
Abstract: Bauxite Residue (BR) is the main waste generated during the alumina-producing Bayer process. With the aim to utilize BR in the production of traditional ceramics, the potential impact such a use might have on the leaching behaviour and radioactivity levels of the final products was investigated. Leaching behaviour of Cr, Ni and V on calcined BR was studied according to the maximal availability test, NEN 7341. Firing atmosphere, firing temperature and soaking time were the investigated parameters. Results demonstrate that the soluble fraction of Cr is higher for oxidizing atmosphere whereas the soluble fraction of V and Ni increases for inert and reducing atmosphere, respectively. For assessing radioactivity, the activity concentrations of 226Ra, 40K, and 232Th were determined by means of gamma ray spectroscopy. For an excess gamma dose less than 1mSv/a, the maximum quantity of BR that can be introduced replacing the raw materials ranges from 14wt.% up to 100wt.%, depending on the type of product and the extent of use in the dwelling.
Authors: Carlos Maurício Fontes Vieira, Sérgio Neves Monteiro
Abstract: The incorporation of a granite waste into a vitrified ceramic tile body was investigated. The granite waste came from an industry of stone sawing operations located in the municipal area of Santo Antônio de Pádua, State of Rio de Janeiro, Brazil. The investigated compositions were elaborated substituting partially and totally the feldspar by the granite waste. Cylindrical specimen were prepared by uniaxial pressure at 30 MPa and then fired at temperatures varying from 1050 to 1200oC. Fired properties such as bulk density, linear shrinkage, water absorption and diametrical compression were determined. The microstructure of fired samples was evaluated by scanning electron microscopy. The results showed that the replacement of feldspar by granite waste promoted a better vitrification, decreasing the open porosity and increasing the mechanical strength.
Authors: Y. Pontikes, G.N. Angelopoulus, Ungsoo Kim, H. Lee, William Carty
Abstract: “Bauxite Residue” (BR) is the main waste of alumina-producing Bayer process. With the aim to use BR in the heavy clay industry, the plasticity of clay mixtures with BR was studied by the “High Pressure Annular Shear Cell” (HPASC) technique. The information obtained is cohesion and pressure dependence values that enable the determination of optimal conditions for extrusion. The results for 30wt% BR addition, substituting the clay mixture, demonstrate that the maximum cohesion is increased. Nevertheless, the water demand is increased for achieving the appropriate cohesion and pressure dependence levels for extrusion, a factor that imposes increased demand for drying. By shifting the particle size distribution towards a higher mean particle size, redesigning the clay mixture or by polymer addition, the rheological behaviour of the paste can be adjusted.
Authors: C. Venturelli, Mariano Paganelli
Abstract: Residual stresses in traditional ceramics may have different origin and nature. In glazed tiles (both porous and sintered), they can be due to the thermal expansion mismatch of glaze and body. Another type of residual stresses in glazed and unglazed porcelain tiles is due to temperature gradients during cooling, which give rise to volume variations in different areas of the same ceramic ware. Thermal gradients may originate not only between the surface and the core of the tile, but also between the upper and the lower face of the tile. The common practice in the porcelain tile industry to use differential cooling to control the planarity of the finished product induces permanent changes of volume in different areas of the ceramic ware, which give rise to permanent states of stress. At room temperature there are two main stress relaxation mechanisms, depending on the nature of the tiles: cracks growth in porcelain tiles and post-expansion in porous tiles. Generally, residual stresses relaxation cause delayed curvature according to these different mechanisms. Optical dilatometry and optical fleximetry techniques allow to investigate the volume changes induced by the cooling rate and the glaze-body coupling, factors responsible for residual stresses.
Authors: S.R. Bragança, H.C.M Lengler, Carlos Pérez Bergmann
Abstract: Wollastonite is a calcium silicate mineral natural or synthetic. Commercial wollastonite starts to melt at about 1450°C and can not be considered a "flux" as alkali feldspar. For this function, it depends on the reaction with other raw materials. Faced with this, came the goal of this work which was to investigate the mechanism of action of wollastonite as a ceramic flux. The use of wollastonite in ceramic bodies was investigated by analysis of its reactivity with other materials such as quartz, kaolin, talc and feldspar. It was analyzed the technological properties of the final parts, especially in relation to the firing temperature, phase formation and technological properties (mechanical strength, porosity, etc.). The results of this characterization showed that the technical properties of the parts are developed according to commercial porcelain products.
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