Mineralogical characterization of ceramic tiles prepared by a mixture of Cretaceous and Mio-Pliocene clays from Tunisia: factory and laboratory products

Abstract

Thermal transformations in ceramic products at high temperatures were studied for admixture of Cretaceous and Mio-Pliocene clays, either carbonatic or with plastic behaviour, used for Lab-tiles and factory biscuits with amounts (25%) of quartz-sand added as temper. Clay admixtures contained illites, smectites series, interstratified I/S species and kaolinite. Firing steps of pastes in the factory took place in a tunneled gas kiln at 1080°C; whereas, tiles used for laboratory experiments were fired in an electric kiln (6001050°C). SEM and XRD patterns help identify minerals disseminated in a glassy matrix as well as idiomorphic crystals formed in pored ceramic tiles, including feldspars (anorthite, sanidine), wollastonite, diopside and melilite (gehlenite). In the fired products, minerals form preferably in pores and crystal genesis is mainly controlled by melt flow. Wollastonite, diopside and gehlenite appear at 800°C. Gehlenite amounts remain nearly constant or may diminish slightly above 1000°C. Enough calcite amounts favor formation of anorthite, gehlenite and wollastonite; whereas gehlenite doesn't appear necessarily as a precursor for anorthite. It is worthy of noting that gehlenite persists at 1100°C and coexists with anorthite. The later crystallizes above 850°C and its amounts increase abruptly above 1000°C. Following mineral crystallization at elevated temperature, the melt precursor can be either completely consumed or remains as relicts in biscuits.

Composition, firing behavior and ceramic properties of the Sejnène clays (Northwest Tunisia)

“…The gehlenite as unstable intermediate phases in formed from metakaolinite and calcium oxide recorded in the ClaySej2 sample clays which are rich in calcite when processed at 1000°C (Azzouz et al, 2011). In contrary to El-Mahhlawy (2008) and Manoharan et al (2011), indicating that the presence of anorthite of the fired specimens demonstrated that the firing process reached the equilibrium state; suggesting that the reaction was completed.…”

“…The mineralogical structure and other physico-chemical properties of various types of clay samples have been extensively studied and discussed in the literature (Moore and Reynolds, 1997;Aras, 2004;Azzouz et al, 2011).…”

Characterisation and ceramic application of clays from North Africa

“…Above 800°C its mineralogy converts gehlenite, haematite and calcic plagioclase (anorthite) (Figure 9). The anorthite CaAl 2 Si 2 O 8 and gehlenite Ca 2 Al 2 SiO 7 are considered the result of multistage solid-state reactions between the clay matrix and carbonates (González-García et al, 1990; Sedmale et al, 2006; Trindade et al, 2010; Azzouz et al, 2011). Gehlenite starts to form at 1000°C, when manganese is near zero (∼0.01%), by reaction between lime, alumina and silica, the first deriving from carbonates and the latter two from already dehydroxylated phyllosilicates (Trindade et al, 2010).…”

“…In Africa, during the last two decades, most study was directed to the characterisation of clay sediments (e.g. Baccour et al, 2008; Mahmoudi et al, 2008; Daoudi et al, 2014; El Ouahabi et al, 2014; Hammami-Ben Zaied et al, 2015; Mahmoudi et al, 2014; Bennour et al 2015a; Mahmoudi et al, 2016), firing transformations of raw materials (Sahnoune et al, 2008; Baccour et al, 2009; Khalfaoui and Hajjaji, 2009; Mahmoudi et al, 2010; Azzouz et al, 2011; Hajjaji and Mezouari, 2011; Bennour et al 2015b; El Ouahabi et al, 2015) and their application in tile and brick products. Despite the antiquity of the pottery industries, few studies have been carried out on the clays and raw materials used in North Africa.…”

Physico-chemical characterization of clay mineral mixtures from Boyacá-Colombia

“…Natural clay minerals contain impurities and are not homogenous, which cause their use to be difficult for technological applications [2]. Therefore, in order to improve their properties, it is necessary to prepare mixtures [7][8][9][10] or to enhance them with the use of additives [11]. Some of the relevant properties for brick masonry have to do with color and brightness [12,13], which ultimately depend on the clay's mineral content and the firing temperature it is subjected to [12].…”