JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS – SYMPOSIA Vol. 3, No. 3, 2011, p. 134 - 136 Physicochemical characterization of Algerian kaolin to be used in the production of refractories M. KOLLI * , M. HAMIDOUCHE, N. BOUAOUADJA, G. FANTOZZI a Laboratoire des matériaux non métalliques, Dépt OMP, Faculté des sciences de l’ingenieur, Université de Setif, 19000 Algérie. a Laboratoire MATEIS (UMR CNRS 5510), Bat Blaise PASCAL, INSA, 20 Avenue Albert Einstein, Villeurbanne 69621, France In this work, an Algerian kaolin noted DD3 (Djebel Debbagh, site N° 3) was characterized. The measured specific surface (BET) is found approximately 93 m 2 /g. This strong specific surface is justified by the kaolinite grains morphology (elongated tablets) observed by SEM. Then, we studied the dry pressing behavior of this kaolin. We noted that it obeys to Heckel’s model: until about 125 MPa the model parameters are (k = 0.00362, A = 0.78882) whereas beyond this pressure the parameters becomes (k = 0.0021, A = 0.98071). The rheological behavior of slurries without and with addition of dispersing agent (Darvan 821A), were studied. Results show that the behavior follows Cassen’s model. With the addition of dispersing agent, the stress threshold decreases and becomes less important. For a percentage of 0.44% the behavior appears nearly linear (Newtonian). The optimal amount of dispersant agent is included between 0.44 and 0.53%. During firing, DD3 kaolin undergoes several transformations leading to the formation of mullite (3Al 2O3 2SiO2), cristobalite and rich-silica amorphous phase. The mullite grains developed at T= 1250°C are irregular whereas those observed from 1350°C are acicular. (Received May 05, 2011; accepted October 15, 2011) Keywords: Kaolin, mullite, Amorphous phase, Dry pressing, Rheological behavior 1. Introduction Clays are the most important industrially exploited minerals [1, 2]. They are used extensively in different domains: agriculture, construction, engineering, medicine… etc. The most important classic applications are in the preparation of ceramics, cosmetic products, paper, paintings, plastics, pharmaceutical products… etc. [2, 3]. The kaolinitic clays, characterized by their abundance and their very weak extraction costs, are extensively used for the production of refractories [4]. In our country (Algeria), several kaolin mines were exploited (Djebel Debbagh, Tamazert,…). Facing this availability of the raw materials, the local needs on refractories are entirely assured by importation. In this optics, we judged useful to conduct the development of refractory materials from local kaolin. In a previous work [5], we noted that the DD3 kaolin extracts from Djebel Debbagh (site N°3) presents a particular interest for the development of these materials. In addition to the easiness of its extraction, this kaolin contains some relatively elevated amounts of alumina against an acceptable percentage of impurities. The rational use of this kaolin in the manufacture of refractories requires the knowledge of its physicochemical properties and its ability to be shaped. 2. Experimental procedure 2.1 Pressing behavior In order to determine its behavior during pressing, the used kaolin was uniaxially pressed (7 MPa) and then isostatically pressed up to 300 MPa. The density was measured and normalized to the absolute kaolin density (2.6). 2.2 Rheological behavior The rheological behavior of the DD3 kaolin was studied on slurries containing 10% of dry matter (Ф ≤ 75 µm), without and with addition of dispersing agent (Darvan 821A). Before measuring the viscosity, the mixture was agitated in a magnetic agitator during 10 min. and then subjected to ultrasound action to avoid any possible particles agglomeration. The viscosity measuring system is composed of a rotating cylinder in the shape of bell and a pot including an internal cylinder (NV installation type of Haake type VT 501 viscosimeter). 2.3 Transformations during firing The kaolin transformations during firing were followed by TDA and TGA, meaning a Setaram 85 measuring system type. These analyses were completed by