Most energy studies on the traditional ceramic manufacturing process focus on the firing stage because this is the process stage that consumes the greatest amount of thermal energy. At present in Europe, using typical technologies, about 50% of the energy input in the firing stage is still lost through the kiln stacks. A key issue in energy studies is the accurate determination of the energy efficiency of the process, an issue that may become crucial in coming years to enable the energy management of different facilities and products to be compared. To reliably determine energy efficiency, accurate determination is required of the energy needed for the necessary physico-chemical transformations to develop in the material in the firing stage. This energy is also the only strictly unrecoverable energy, as the energy contained in other streams could, potentially at least, be partly recoverable. The present study was undertaken to develop an analytical methodology for estimating the heat of reaction of seven different traditional ceramic products, involving a broad spectrum of compositions, with peak firing temperatures ranging from 850 ºC to 1200 ºC. The following industrial ceramic compositions were studied: four ceramic tile compositions (red-body stoneware tile, porcelain tile, red-body earthenware wall tile, and white-body earthenware wall tile); two structural ceramics compositions (white brick and roof tile), and a porcelain tableware composition. To estimate the energy involved in the physico-chemical reactions in the firing stage, an analytical methodology was developed, based on   the mineralogy data of the unfired body composition and on the enthalpy of formation of the minerals in the fired tiles. The methodology was validated by comparing the results with experimental data.

No abstract

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 CO 2 on both sides of the gas solid interface in the test pieces was conditioned by an equilibrium law of the form 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. I ntroduction Object of this researchCalcite is the calcium compound that is usually added, as a source of CaO, to the raw materials mixture used to form the tile body in the single-fire manufacturing process of whitebody wall tiles 1 . During firing, the calcite particles need to completely decompose before the Corresponding author. e-mail address: aescardino@itc.uji.es 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 glaze melts and seals the tile surface in order to keep the CO 2 released in the tile body by this reaction from being trapped as small bubbles in the molten glaze layer 2 . *Manuscript Click here to view linked ReferencesIn order to optimise the calcite decomposition stage in the industrial firing cycle used to manufacture this type of tile, it was deemed useful to have a mathematical expression that would relate the decomposition progress of the calcite contained in the tile body to the operating variables (time, temperature, tile shape and size, etc.).The thermal decomposition process of very small calcite particles contained in ceramic compacts, analogous to those used in the manufacturing process to form white-firing earthenware tile bodies, has been studied in two previous papers 3,4 . The experiments were conducted in air atmosphere, at different temperatures, using disks of different initial porosity, thickness, and calcite content. The results were interpreted using an equation derived on applying the Shrinking Unreacted Core Kinetic Model.These papers have been the first phase of a study which has yielded a kinetic model that takes into account the influence of the dimensional and structural characteristics of the test disk and of the chemical reaction of decomposition that is developed. This kinetic model satisfactorily describes the kinetics of the process when is conducted in air atmosphere.In industrial practice, however, the thermal decomposition process of the calcite contained initially in the body of this type of tiles occurs in presence of a mixture of air and carbon dioxide that contains between 5 1...

No abstract

The requirement of a ceramic product with high technical and aesthetic performance makes it necessary to select and control raw materials to avoid losses caused by low-quality products. Many defects have their origin in impurities present in clay minerals such as sulfides and sulfates. It is important to study the oxidation, decomposition, and pyrolysis reactions that affect these minerals and their dependence on environment conditions (humidity and temperature) during the extraction and beneficiation of clay minerals in an open pit mine. The development of hyphenated techniques coupling mass spectrometry with a thermal analysis instrument provides information that is not available from either technique alone, such as decomposition behavior and the determination of emissions with a lower limit of detection. The evolution of sulfur dioxide from the oxidation of different sulfides provides information on the in situ oxidation and decomposition reactions that happen when a thermal treatment is applied. The results obtained show important differences in the reactions that take place in sulfides when they are stored under different environmental conditions. Specifically, the general tendency is that the sulfurs stored under high relative humidity show a decrease in the intensity of the emission as well as changes in the onset of the peak emission.

Mineralogical characterization of clays used in manufacturing of traditional ceramic products is critical for guarantee the quality of the final product, but also for assessing the environmental impact of the industrial process in terms of atmospheric emissions. In fact, the presence of impurities even in low-level concentrations can have a big impact. So, it is very important to carry out an accurate mineral quantification of those minerals which are related to carbon dioxide and acid emissions (hydrogen fluoride, hydrogen chloride or sulfur dioxide). The development of hyphenated techniques coupling thermal analysis equipment with mass spectrometry and Fourier-transform infrared spectroscopy provides more valuable information and lower limit quantification than other primary techniques, such as X-ray diffraction or infrared spectroscopy. The main objective of this work is to develop an analytical procedure using evolved gas analysis to identify and quantify minerals such as chlorides, sulfides, carbonaceous materials and minor clay minerals. In addition to this, the study includes the analysis of acid emissions during the ceramic firing treatment even if they are present at low quantitative levels. This methodology was applied to reference materials so that it allows the identification of sulfur, chlorine, fluorine and carbonaceous compounds in concentrations lower than 1%.

The effect of a post-synthesis thermal treatment on CoCr 2-2Y Al 2Y O 4 (0.0≤Y≤1.0) ceramic pigments synthesized by Solution Combustion Synthesis (SCS) has been studied. Assynthesized SCS pigments were treated at two different calcination temperatures (800 ºC and 1000 ºC) to study changes in mineralogy, microstructure and thermal behaviour, as well as their effect over the colouring power. Spinel-type Fd-3m crystalline structure was developed in all cases. Nevertheless, crystallinity parameters were highly affected by both analysed processing parameters: composition (Y) and post-synthesis calcination temperature (T c). A Cr(III) enrichment along with T c increase favoured ion rearrangement to promote sample crystallization and crystallite growth. Fast kinetics of SCS makes Al-rich spinels with transition metals difficult to be synthesized. The application of a secondary thermal treatment resulted in a favourable evolution towards a well-crystallized structure. Lattice parameter did not seem to be affected by T c , although it evolved indeed with composition. From a microstructural point of view, as-synthesized pigments were foamy, with a very low bulk density and nanometric grain size. After the thermal treatment, larger grain sizes were obtained, especially for the samples richer in Al and treated at higher T c. All pigments developed intense colours in a transparent glaze without showing heterogeneities, indicating a stable behaviour against glazing process. Glaze colour evolved from green to perfectly blue shades, indicating an important dependence on composition. Nevertheless, colouring power seemed to be rather affected by calcination process.

The aesthetic characteristics and mechanical properties of a new raw glaze of the matt type, developed for porcelain tiles, referenced SG, were determined and compared with those of a commercial matt glaze for porcelain tiles, referenced RG. Glaze SG was formulated by introducing boron as calcined borate E4972 [1]. In contrast, glaze RG contained a frit (30%) that included boron among its constituents. Despite the different chemical and mineralogical characteristics of these glazes, their chemical and mechanical properties, as well as their aesthetic characteristics, were appropriate. The dissolution of crystalline particles and the crystallisation and sintering phenomena in glaze SG were studied. The effective viscositytemperature curve of this glaze was experimentally obtained by hot stage microscopy (HSM). A model describing the effective viscosity of a glaze, based on Kriegers equation for concentrated colloidal suspensions, was developed in this study. The agreement between the experimental data and the calculated values was quite good.