Study of the Behavior of Three Tunisian Clays ...

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tion are varied: tableware (earthenware, porcelain, etc.); the pharmaceutical, medical, and cosmetic industries; housing (tiles, bricks, etc.); and the refrac-.
ISSN 1068-3755, Surface Engineering and Applied Electrochemistry, 2017, Vol. 53, No. 2, pp. 202–211. © Allerton Press, Inc., 2017. Original Russian Text © A. Bennour, E. Srasra, N. Hatira, S. Harabi, 2017, published in Elektronnaya Obrabotka Materialov, 2017, No. 2, pp. 91–99.

Study of the Behavior of Three Tunisian Clays Suitable for the Manufacture of Ceramics1 A. Bennoura, c, *, E. Srasrab, N. Hatirac, and S. Harabia aDepartment

of Geology, Faculty of Sciences of Bizerte, Zarzouna, 7021, Tunisia Physical Chemistry Laboratory of Mineral Materials and its Applications National Centre of Research in Materials Sciences BP95, Hammam Lif, 2050, Tunisia cIndustrial Rocks and Useful Substances Direction, National Office of Mines, Charguia I, 3023, Tunisia *e-mail: [email protected] b

Received October 26, 2015

Abstract⎯The behavior of three clays collected from different locations in Tunisia has been studied through their chemical and mineralogical composition, plasticity, specific surface area, cation exchange capacity, via dilatometry and infrared spectroscopy. The mineralogical composition is an indication of the presence of kaolinite, illite and smectite associated with quartz, calcite and hematite. The study of the chemical composition showed that the main oxides in the ClayTeb sample are SiO2 and Al2O3, which were also found in the ClayHorb and ClayMed samples along with Fe2O3, CaO and K2O. The mineralogical metamorphoses during the firing process were recorded via the X-ray diffraction of the raw clays and subsequent firing at 300, 600, 800, 1000 and 1200°C for 3 hours. Kaolinite transformed to metakaolinite was not observed at 600°C. Illite underwent total deshydroxylation at 1000°C. This latter temperature characterizes the main evolution of all samples and the start of the crystallization of mullite, which is dependent on the presence of impurities (Fe2O3) and K2O (lent fondant). For the ClayMed clays, which have the maximum content of illite, only the spinel phase was defined at 1200°C. The samples were dry pressed and fired at temperatures of 950, 1050, and 1100°C and the characteristics of the ceramic were determined by firing shrinkage, water absorption, loss on ignition and flexural strength. Keywords: Tunisia, ceramic tests, chemical analysis, mineralogical metamorphoses DOI: 10.3103/S106837551702003X

INTRODUCTION The evolution of the construction sector, which has experienced a significant growth in most Mediterranean countries, is one of the main factors influencing the manufacture of the construction ceramics industry. In recent years, this phenomenon has made the construction ceramics sector one of the most important in terms of production. Clays are natural and abundant raw materials used since ancient times. Nowadays, their fields of application are varied: tableware (earthenware, porcelain, etc.); the pharmaceutical, medical, and cosmetic industries; housing (tiles, bricks, etc.); and the refractory industry. Clay raw materials are essential for the manufacture of many ceramic products for which they are shaped (pressing, casting, etc.), dried and thermally treated to strengthen them. When raw, clay is a crystalline material with a sheet–like structure. When thermally treated, clay undergoes a transformation 1 The article is published in the original.

and, after cooling, is composed of only an amorphous phase or a mixture of an amorphous phase and crystallized phases. Numerous studies have been carried out in recent decades on Tunisian clays and their applications, particularly in the field of the manufacture of ceramics [8, 5, 24, 36]. The present study was conducted with three clay deposits with important reserves and are easy to access. The aim of this work is to contribute to the knowledge of the different characteristics and technological properties of these clay deposits and to suggest their most suitable uses. To carry out the work, three deposits located in the eastern sector of Tunisia were chosen (Fig. 1) each containing clays of different qualities. ClayMed (Permo–Triassic), ClayHorb (Jurassic) and ClayTeb (Oligocene) were selected because they represent two of the main mines which still produce clays.

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