Zircon is the mostly widely occurring zirconium-containing mineral mined commercially. Thorium and uranium may substitute for zirconium in the zircon crystal lattice. The radioactivity levels in zircon lies typically within the ranges 500-1000 Bq kg −1 for 232 Th and 1000-5000 Bq kg −1 for 238 U [1]. One of the most important use of zircon is as opacifier for ceramic tiles. Body of ceramic tiles is a mixture of different raw materials, including: clays, quartz materials and feldspathic materials. The body may be glazed or left unglazed. Due to the presence of zircon in the glaze or in the body, ceramic tiles can show natural activity concentration significantly higher than the average values of Earth's crust. This study contains a summary of results obtained by a survey on Italian ceramic tiles collected over three years (2005-2007). About one hundred ceramic tiles were analysed. The survey consisted of measurement of 226 Ra, 232 Th and 40 K activity concentrations and of the gamma-index [2] and radium-equivalent [3, 4] calculation. The activity concentrations of 226 Ra, 232 Th and 40 K result in the order of 100, 50 and 500 Bq kg −1 , respectively. Gamma index and radium equivalent activity have been found well below the acceptable limit in most of the samples.
The rheological properties of porcelain stoneware tile slips were investigated using a rotational rheometer. The first step in the study was to evaluate the rheological behaviour of a reference slip at different particle size distributions to determine the optimum conditions at which to carry out the investigation of the influence of nepheline syenite in the mix. In the second step part of the K-feldspar in the reference mix was replaced with nepheline syenite such that the mix composition contained 10 % nepheline syenite. The flow curve, yield stress and thixotropy of the slips were evaluated at different milling times in order to study the effect of particle size on the rheological behaviour. The milling times for the reference mix and for the mix with nepheline syenite which resulted in the best rheological parameters were found.Keywords: Porcelain Stoneware Tile Slip; Rheology; Yield Stress; Thixotropy; Nepheline Syenite
Influencia de nefelina sienita y del tiempo de molienda en las propiedades reológicas de una barbotina de porcelana gresSe han investigado las propiedades reológicas de barbotinas de porcelana dura para pavimentos usando un reómetro rotacional. El primer paso del estudio fue evaluar el comportamiento reológico de una barbotina de referencia con diferentes distribuciones de tamaño de partícula con el fin de determinar las condiciones óptimas bajo las cuales estudiar la influencia de nefelina sienita en la mezcla. En la segunda etapa, parte del feldespato potásico de la mezcla de referencia se substituyó por nefelina sienita de forma que la composición de la mezcla tuviera un 10% de neflina sienita. Se evaluaron las curvas de flujo, los puntos de fluidez y la tixotropía de las barbotinas tras diferentes tiempos de molienda con el fin de estudiar el efecto del tamaño de partícula en el comportamiento reológico. Se determinaron los tiempos de molienda en los que se alcanzaban los mejores parámetros reológicos para la mezcla de referencia y la de nefelina sienita.Palabras clave: barbotinas de porcelana gres, reología, punto de fluidez, tixotropía, nefelina sienita.
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