About the thermal transformations and sintering of a Ghassoul clay from Morocco Effect of the particle grinding and selection G. L. Lecomte-Nana 1 • Y. El Hafiane 2 • A. Badaz 1 • N. Tessier-Doyen 1 • Y. Abouliatim 2 • A. Smith 1 • L. Nibou 2 • B. Tanouti 3 Received: 28 December 2014 / Accepted: 13 September 2015 / Published online: 29 September 2015 Ó Akade ´miai Kiado ´, Budapest, Hungary 2015 Abstract A Ghassoul clay from Morocco was studied regarding the effect of (1) grinding and (2) selection of the particle size distribution (classification) on the thermal transformations during sintering. Ghassoul clay contains stevensite, dolomite and quartz as major minerals. Prior to the classification, the starting coarse aggregates of the raw clay were first dry-ground below 500 lm and the obtained particles of powder were then granulated in order to pro- duce adequate pellets for shaping by uniaxial pressing. Classification was performed to obtain three grain size distributions, namely greater than 500 lm, between 500 and 315 lm and lower than 315 lm. As the grain size distribution became finer, the proportion of carbonate phases was increased. DTA–TG analyses were in agree- ment with this trend, and in addition, dilatometry analyses showed that the densification was shifted to lower tem- peratures when decreasing the size of granules. The major phases occurring after sintering at 1200 °C were diopside, enstatite and forsterite as expected from the equilibrium phase diagram. Moreover, the smaller clay fraction (typi- cally lower than 40 lm) enhanced the formation of melilite and monticellite. Nevertheless, a swelling occurred during sintering that balanced the densification shrinkage. According to these results, the sintering of Ghassoul clay proceeds through several stages regardless of the particle size selection. With a mean size of granules lower than 315 lm, the densification can be achieved at 1100 °C, while for greater sizes, a similar densification state of the raw material requires a significantly higher temperature of sintering of 1200 °C. In addition, some dedensification drawbacks may occur when using granules whose size is greater than 315 lm and therefore could induce unex- pectedly a significant damage to materials. The observed trends may be useful for further applications of such Ghassoul clay in the silicate ceramics field. Keywords Ghassoul clay Á Stevensite Á Grain size selection Á Thermal transformations Á Sintering Introduction Clays are readily available raw materials that allow the manufacture of most wide diffusion ceramics (low-added- value products). They are characterized by the layered structure of their main minerals (clay minerals) which belong to the phyllosilicates. Among clay minerals, kaolinites and montmorillonites, thermal transformations have been widely studied [1–15]. On the contrary, Ghas- soul clay which mainly contains stevensite (clay mineral) has been studied for adsorption capacities [16–22]. It is related to the cation exchange capacity similar to that of montmorillonites. Very few investigations have been per- formed regarding the manufacture of ceramics using & G. L. Lecomte-Nana gisele.lecomte@unilim.fr 1 Laboratoire Science des Proce ´de ´s Ce ´ramiques et de Traitements de Surface (SPCTS, UMR CNRS 7315), Centre Europe ´en de la Ce ´ramique - Ecole Nationale Supe ´rieure de Ce ´ramique Industrielle, 12 rue Atlantis, 87068 Limoges Cedex, France 2 Laboratoire Mate ´riaux Proce ´de ´s Environnement Qualite ´, LMPEQ, Universite ´ Cadi Ayyad - Ecole Nationale des Sciences Applique ´es de Safi, Route Sidi Bouzid, BP 63, 46000 Safi, Maroc 3 Laboratoire de la Matie `re Condense ´e et de l’Environnement, LMCE, Universite ´ Cadi Ayyad - Faculte ´ des Sciences Semlalia, Avenue My Abdellah, BP 2390, 40000 Marrakech, Maroc 123 J Therm Anal Calorim (2015) 122:1245–1255 DOI 10.1007/s10973-015-5042-x