Enrichment of schist mined in Morocco resulted in an extract essentially made of andalusite, quartz and muscovite, which was investigated with the aim to synthesize mullite refractory materials. X-ray diffraction analysis was used to assess phase transformations upon heating at different temperatures. Mullite formation starts as early as 1200℃ and seems almost total at 1450℃. This process correlates with a weak shrinkage (3.5% at 1450℃) and the formation of an important glass phase. Green compacts obtained by unidirectional pressing the extract powder were heated under air in the temperature range 1200℃ - 1600℃. Chemical and mechanical properties of these materials were investigated and correlated with their microstructure

Re ´sumeDeux sources de feldspath exploite ´es au Maroc sont e ´value ´es pour leur aptitude au broyage, puis sont analyse ´es et compare ´es a ùn feldspath commercial utilise ´dans l'industrie, en termes de leurs compositions chimique quantitative et mine ´ralogique, ainsi que de leur comportement thermique. Des produits ont alors e ´te ´e ´labore ´s en associant ces feldspaths a `diffe ´rentes pa ˆtes ce ´ramiques. L'e ´tude des courbes de gre ´sification (e ´volution du retrait, de la densite ´et de l'absorption d'eau en fonction de la tempe ´rature de cuisson) et des proprie ´te ´s me ´caniques (contrainte de rupture et te ´nacite ´) indique qu'en sus de la bonne aptitude au broyage, la composition mine ´ralogique de la source feldspathique est de ´terminante pour les proprie ´te ´s technologiques et me ´caniques des produits fritte ´s.

Mullite is the only stable phase of the Al 2 O 3 -SiO 2 system. It is credited with a high technological interest in the ceramic refractories domain due to its excellent thermal properties, chemical inertia and mechanical behaviour at high temperature. Mullite can be synthesized by different ways, and also by the thermal transformation of natural aluminosilicates, namely the andalusite. A physico-chemical characterization of scattered andalusite crystals has been achieved The thermal behaviour and the different phase transformations have been investigated for temperatures up to 1450 °C.

Chiastolite-type andalusite, whose genesis occurred in the currently unexploited deposit of Sidi Bou Othman (Morocco), has been extensively characterized. The phase composition, microstructure, thermal behavior, sinterability, and evolution of the crystallographic structure associated with the transformation of andalusite to mullite were accurately analyzed. Parallelepiped-shaped crystal grains exhibited off-white X crosses, typical of the chiastolite group. The chemical composition is closely dependent on the crystal size and proportion of alumina. The crystal structure was successfully refined using XRD, and chemical analysis was performed for different crystal sizes up to 30 mm. Powder compacts were prepared from these chiastolites for further characterization after various thermal treatments. According to the Rietveld refinement analysis, the mullization ranges from 1200 to about 1500 °C, and crystallographic parameters have been compared with other andalusites reported in literature. In agreement with this phase transformation, variations related to different material properties such as thermal expansion, pore volume fraction, and mechanical strength were evaluated. These results highlight the potential for further exploitation of the Sidi Bou Othman deposit to produce ceramic materials.