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Zircon is the most used opacifier for ceramic glazes. Zircon sands of different beach placers have been investigated for their mineralogical, morphological and chemical characteristics. Mineralogical investigations have been carried out by SEM, polarizing microscope and XRD. In particular the refractive index has been determined by immersion in liquids at the polarizing microscope. While the morphometric characteristics have been established using both grain size distribution and automatic image analysis, the morphotropic ones have been elaborated directly from their image analyses. The chemical composition has been detected using XRF, ICP-AES, NAA (for the rare earths) and EPR. The zircon sands resulted to be very good or excellent opacifiers: the values of refractive indices are high, the content of Ti02 is low (XRF), Nd and Co are less than the detection limits (ICP-AES and NAA) and Mn is absent (EPR). The distribution of the U-content is strictly correlated with the grain size distribution and with the refractive index.
Because of its outstanding physical and technological properties, asbestos has been widely used in the past for several industrial applications in all the industrialized countries such as Italy. Asbestos in Italy was one of the main raw materials for cements (the well known cement-asbestos or eternit). Nowadays it is generally accepted that asbestos is a priority substance for health hazard and one of the main concerns is the recover of the areas which contain asbestos and the buildings built with cement-asbestos. In this work we will define the conditions for the thermal inertization of the raw cement-asbestos slabs, define the main characteristics of an industrial plant for the thermal treatment of asbestos, estimate its production capacity. In addition, we will indicate a possible use of the treated product (recycle) as raw material for traditional bulk ceramic pigments.
Through the analysis of the production data of Italian ceramic tiles, written by Assopiastrelle, is evident that 2001 has been the worst year of the last quinquennium. In this setting, the production of porcelain stoneware goes to the apposite direction; in fact, it has increased its production and since 1999 has passed the one of fast firing (monocottura). Porcelain stoneware success is related to the technological evolution of the processing, that has allowed aesthetical improvement and better mechanical properties of the final fired product. At present, in Italy, the research is engaging in the design of customized tile of high quality, that is difficult to be reproduced and that presents a new aesthetical aspect. The aim of the following article is to summarize the most important innovations in terms of processing and product in the field of porcelain stoneware in the last year.
The ceramic properties of test pieces fabricated from the rock-type porcelanite, with the aid of bitumen and a small amount of a low-plasticity clay and high-plasticity clay as binders, have been investigated after sintering in the temperature range 1200-1350 "C. On firing at and above 1225 °C the porcelanite fused, resulting in microstructures characterized by dispersed silica particles embedded in a continuous matrix, predominantly of potassium silicate and mullite composition. Within the firing temperature range, the porcelanite/high-plasticity clay samples exhibited optimum strength (modulus of rupture) of 18 MPa while for the porcelanite/low-plasticity clay and the porcelanite/bitumen samples optimum was of the order of 12 MPa. In addition, for the samples involving the clays optimum strength was combined with both low bulk density and low apparent porosity.
Temperature difference and fracture resistance parameters have been used to predict the thermal shock behavior of alumina based commercial refractories with different content of Alz03 from 28% to 78%. Thermal and mechanical properties were measured. Thermal shock stability of the samples was measured using the water quench test. Values of temperature difference were calculated using heat transfer conditions and material properties. Calculated values of temperature difference and fracture resistance parameters were compared to results of quench experiments. Linear regression analysis was used to determine the correlation between calculated values for the critical temperature difference and the damage resistance parameter with the results of water quench test. Excellent correlation with the experimental results was observed for all used equations for prediction of thermal shock behavior of the samples. Correlation between damage resistance parameters, temperature difference and results from the water quench test also are presented.
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