Kinetic study of the thermal decomposition process of calcite particles in air and CO2 atmosphere

The thermal decomposition process of calcite particles (0.45–3.60 mm average diameter), made up of porous agglomerates of very small CaCO3 microcrystals, was studied in the 975–1216 K temperature range. The experiments were carried out under isothermal conditions in air atmosphere, in CO2 atmosphere, as well as in a gas stream comprising different concentrations of air and CO2. An equation is proposed that relates the calcite conversion degree to both reaction time and operating conditions. The equation satisfactorily fits to the experimental results obtained in the entire tested range of particle sizes and temperatures in all the studied carbon dioxide concentrations

Calcium carbonate decomposition in white-body tiles during firing in the presence of carbon dioxide

This study examines the thermal decomposition process of the calcium carbonate (calcite powder) contained in test pieces of porous ceramics, of the same composition as that used in manufacturing ceramic wall tile bodies, in the presence of carbon dioxide, in the temperature range 1123–1223 K. The experiments were carried out in a tubular reactor, under isothermal conditions, in a gas stream comprising different concentrations of air and carbon dioxide. Assuming that the relationship between the molar concentrations of CO2 on both sides of the gas–solid interface in the test pieces was conditioned by an equilibrium law of the form , the equation proposed in a previous paper was modified to correlate the results obtained when the experiments were conducted in the presence of carbon dioxide. The modified equation fitted well to the experimental data obtained in the temperature and carbon dioxide concentration ranges studied. The knowledge derived from this research has enabled the firing cycle used in the single-fire manufacture of this type of wall tile to be optimised

O Processo de coloração a seco de porcelanato. Parte 1: Variáveis envolvidas e influência sobre as propriedades das peças

Dentre as tipologias de revestimentos cerâmicos atualmente produzidos o porcelanato tem se destacado pela grande expansão em sua produção, observada nos últimos anos. O sucesso do produto se deve pelas propriedades técnicas e estéticas oferecidas. Dentro deste contexto a técnica de coloração a seco surge como alternativa a ser adotada no processamento da massa do material, pois confere ao produto características estéticas que podem ser obtidas através de uma simples mistura de pigmentos e grânulos atomizados. Entretanto, pouco se conhece sobre as variáveis envolvidas neste processo de mistura e a real interferência de cada uma delas nas propriedades apresentadas pelo produto queimado. Este trabalho apresenta o resultado de um estudo que revela o efeito das principais variáveis relacionadas à mistura do pigmento com os grânulos atomizados sobre as propriedades apresentadas pelo produto fina

Development of lightweight porcelain stoneware tiles using foaming agents

Recent market trends for porcelain stoneware tiles indicate that there is a growing interest for lightweight products, to be used vertically, in internal walls or ventilated facades. The decorative and structural functions have now been coupled with additional features, such as thermal insulation. The optimization of all functionalities depends on a careful control of porosity, in terms of overall amount, size and morphology. In this paper, we propose fundamental correlations between mechanical properties, water absorption, porosity and technological aspects, and particle size and the amount of foaming agent (SiC). The data indicate that the addition of SiC powder with a size < 10 μm enables the fabrication of tiles possessing a suitable strength, negligible water absorption and a weight reduced by 26%. The loss of mechanical strength of the tiles and their pyroplastic deformation controls the maximum attainable decrease in weigh

Thermal conductivity of traditional ceramics. Part I: Influence of bulk density and firing temperature

The thermal conductivity of traditional ceramics is known to be a function of their porosity or bulk density. However, the scatter in the thermal conductivity-bulk density data in certain studies, particularly when data from industrially processed brick are involved, suggests that thermal conductivity depends, apart from porosity, on other characteristics such as phase composition, microstructure, humidity or the presence of soluble salts. A red-firing clay used in brick manufacture has been used in this study with a view to systematising the impact of the different variables that could influence thermal conductivity and mechanical strength. This first paper presents the results obtained when the dry bulk density of the pieces and their firing temperature were modified. It was confirmed that thermal conductivity did not solely depend on the total porosity of the fired pieces, but that pore size distribution and pore interconnectivity need to be considered, which depend on the degree of firing attained, and may also be influenced by the phases present in the pieces, whose content and/or composition could vary with firing temperature. © 2010 Elsevier Ltd and Techna Group S.r.l

Lightweight Porcelain Stoneware by Engineered CeO2 Addition

none5The use of porcelain stoneware in innovative applications such as the covering of internal walls or the manufacturing of ventilated facades may be limited by its relatively high density. In this paper, we discuss the achievement of a reduction in density of about 30%, coupled to a limited water absorption (about 2%), by the addition of CeO2 to the raw materials. This additive provides some porosity due to the evolution of oxygen, in turn caused by the high temperature reduction to Ce2O3. This gas formation depends both on sintering temperature, holding time, and is obviously affected by the concentration of additive. Two different processing strategies were found to match the density and water absorption requirements for the application of stoneware tiles. One involved the the control of the CeO2 content together with processing at high temperature for a limited holding time; the other one corresponded to the fabrication of a graded material, comprising a highly porous core (produced using a high content of CeO2) sandwiched between two external compact surface layers.noneBERNARDO E; DE LAZZARI M; COLOMBO P.; LLAUDIS AS; GARCIA-TEN FJBernardo, Enrico; DE LAZZARI, M; Colombo, Paolo; Llaudis, As; GARCIA TEN, F

O Processo de coloração a seco de porcelanato. Parte 2: Variáveis envolvidas e influência sobre as propriedades das peças

Dentre as tipologias de revestimentos cerâmicos atualmente produzidos o porcelanato tem se destacado pela grande expansão em sua produção, observada nos últimos anos. O sucesso do produto se deve pelas propriedades técnicas e estéticas oferecidas. Dentro deste contexto a técnica de coloração a seco surge como alternativa a ser adotada no processamento da massa do material, pois confere ao produto características estéticas que podem ser obtidas através de uma simples mistura de pigmentos e grânulos atomizados. Entretanto, pouco se conhece sobre as variáveis envolvidas neste processo de mistura e a real interferência de cada uma delas nas propriedades apresentadas pelo produto queimado. Este trabalho apresenta o resultado de um estudo que revela o efeito das principais variáveis relacionadas à mistura do pigmento com os grânulos atomizados sobre as propriedades apresentadas pelo produto fina

The porcelain tile dry colouring proces

The influence of the variables involved in the dry coloring process on the behavior of porcelain tile bodies and the properties of the fired product during different manufacturing stages was examined. The dry-colored spray-dried powders were prepared in which the spray-dried powder characteristics and pigment characteristic were modified. A polished cross-section of a tile obtained from dry-colored granules is found to consist of a light-colored matrix, corresponding to the cross-section of the spray-dried powder granules. The results also show that pigments are classified as those producing loss of tile mechanical strength below 10% and a second group of pigments with losses of 20%. Small changes are detected in the maximum densification temperature for the compositions with 2.0% pigment, though linear shrinkage and bulk density of tile pieces varied between the different colored composition