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One of the major environmental issues within the ceramic industry is the fluorine emission in the flue gases exhausted during the firing process. European and National regulations limit these emissions, and there is a trend towards the harmonization and restrictions of these limits among the EU countries.The present study reports the investigation of the fluorine emissions process, from the raw materials (chemical composition and fluorine content, crystal nature, effect of selected body additives) to the thermal process control (heating rate, peak temperature, oxygen and water vapour pressure and overall flow of gases in kiln atmosphere).A laboratory scale apparatus was developed to study the effect of several parameters on the emissions during firing.The experiments results show that some primary measures can be adopted in industrial operation to reduce fluorine emissions of clay based ceramic materials by means of adjustments in body composition and the control of the atmosphere and firing cycle.
The objective of this work is to evaluate the feasibility of using alum sludge, a by-product from potable water plants, as raw material for ceramic production.Thus, 10, 20 and 30 wt% of alum sludge were added to a clay used for the production of building materials. In order to increase the densification of the ceramic bodies, a silicate-based fluxing agent was also added.The clay and alum sludge were characterised by chemical and mineralogical composition and particle size distribution. Porosity, linear shrinkage, mechanical strength and leaching tests according to Brazilian standards were determined on the fired bodies which showed properties comparable to similar commercial products.The results indicated that the ceramic products are inert to leaching according to Brazilian environmental regulations, and present an interesting potential for recycling alum sludge as raw material for ceramic products.
The addition of 9, 14, 15 wt. % Afyon Volcanic Tuff (AVT) into a standard wall tile body has been studied. Dry pressed samples were produced by adding volcanic tuff into the standard wall tile batch composed of Istanbul Etiler clay (IEc), Istanbul clay (Ic), kaolin(a), pegmatite, calcite, kaolin(b) and clay and fired at 1090°C for 40 min.The possible use of AVT has been investigated through a number of tests including viscosity, compressive strength, water absorption and firing shrinkage.Tests were performed on the fired specimens and compared with specifications.As a result, it was found that experienced AVT addition into the standard body can be used for the production of wall tiles. Alkaline properties and viscosity of recipes and water absorption and compressive strength of specimens are slightly affected by AVT addition.
The introduction of metallic fibres in a ceramic refractory matrix can limit its intrinsic brittle behaviour. Microstructural investigations, micromechanical and macromechanical tests have been performed for a better understanding of the thermomechanical behaviour of such composites. Results of pullout tests are presented and discussed. For non-inclined fibres, results allow to quantify the effect of a first heating on the microstructure and on the pullout performances. During the second heating the development of a fretting pressure at fibre/matrix interfaces has a beneficial effect on the pullout performances.When introducing a fibre inclination angle, supplementary pullout micromechanisms are observed and described.They can have a beneficial effect on the pullout performances. Results of macroscopic tensile tests are shown and discussed too. Analytical models have been developed to predict and to quantify the effect of variations in material parameters and/or in testing conditions. Links are established between the results of the micromechanical and macromechanical approaches both from an experimental and from a modelling point of view.
The thermo mechanical behavior of magnesia refractory with CaO/SiO2<1 containing 0-12 wt% CaZrO3 clinker was investigated after sintering at 1700°C for 6 hr. Results show that CaZrO3 additions improve sintering behavior of magnesia with formation of monticellite. Samples containing CaZrO3 have a higher strength at room temperature while their hot strength substantially decreases.Thermal shock is improved by the addition of CaZrO3 due to the decrease of the thermal expansion coefficient.
Mullite formation by reaction at high temperature of kaolinite with two types of alumina (aluminium hydroxide gel and reactive alumina) was investigated in the presence of three types of additives containing monovalent, divalent and trivalent cations i.e, MgO, Cr2O3 and TiO2. Role of these additives on product development was studied by bulk density, apparent porosity, true density, compressive strength measurements and XRD analysis of the sintered compacts. It was observed aluminium hydroxide gel containing samples to densify better and to contain more mullite after firing. Among the additives, MgO was found to influence the densification process to the maximum extent.
The role of magnesia and iron oxide additives on the synthesis and properties of aluminum titanate formed from reactive alumina and rutile powders was investigated. For this purpose the precursor powder mixtures containing MgO and Fe2O3 additives were compacted and sintered at 1300°C, 1400°C and 1500°C. Different properties of the sintered samples e.g. firing shrinkage, bulk density, apparent porosity, specific gravity, phase composition and microstructure were studied. It was observed that the simultaneous use of MgO and Fe2O3 additives facilitates the formation of aluminium titanate and its densification.
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