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Technological behaviour of some Tunisian clays prepared by dry ceramic processing

¹ Laboratoire de Géoressources, CERTE BP 273, 8020 Soliman, Tunisia, ² Faculté des Sciences de Sfax, 3018, Sfax, Tunisia, ³ Instituto Andaluz de Ciencias de la Tierra. CSIC - Univ. Granada. Avda. Fuentenueva, s/n. 18002-Granada, Spain, ⁴ ICES, 1 Pesek Road, Jurong Island 62 7833, Singapore, ⁵ Département de Géologie, Faculté des Sciences de Tunis, Université de Tunis El Manar, Tunisia, and ⁶ Ceramics and Glass Engineering Dept & CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

^* E-mail: alberto{at}ugr.es

(Received 19 September 2007; revised 21 January 2008)

Lower Cretaceous (AJO and AJR) and Oligocene clays (AS) from northern Tunisia were analysed to evaluate their possible use in the production of earthenware tiles by dry processing and fast double-firing. The Cretaceous clays are carbonate-rich (AJO = 20%, AJR = 12%) while the Oligocene ones are carbonate-free. This led to noticeable differences in firing behaviour (shrinkage, sintering rate and loss on ignition) and consequently in functional properties (water absorption, mechanical strength, porosity). The AJO firing shrinkage is very small, which makes this clay suitable for rapid firing. The clays are illite-kaolinite-rich but the AS sample is mostly smectitic (44%) and so is used (10 wt.% maximum) only to adjust the consistency of the powder during pressing. The average agglomerate size ranges from 100 to 350 µm and the distribution is suitable for easy pressing of powders without any special need for further adjustments. Characterization of fired products confirms the high potential of these clays since all properties fall within the ceramic International Standards (ISO). For both technical and economic reasons dry processing is recommended for production of earthenware tiles, in particular for countries in sunnier climates, where solar energy can be exploited for clay drying.

KEYWORDS: clays, Lower Cretaceous, Oligocene, dry process, ceramic tiles, Tunisia