Characterization of the Ain Khemouda halloysite (western Tunisia) for ceramic industry

Pozzolanic activity of calcined halloysite-rich kaolinitic clays

“…An exothermic peak was also observed in the temperature range of 980-990 °C, and attributed to structural rearrangement of the clay minerals to form mullite (M'barek Jemaï et al, 2015). The largest area of the first endothermic peak and the highest loss of mass in the corresponding temperature range were determined on the NC1 clay, in agreement with the highest content of halloysite as determined by XRD.…”

Halloysite in Different Ceramic Products: A Review

“…This was attributed to their advanced amounts of cordierite formation and glass phase derived from the low melting impurities presented in their initial raw material. Then, halloysite-rich clay from Ain Khemouda (W. Tunisia) was investigated by Jemai et al [46] in order to be used in the ceramic industry. Raw material was characterized as aluminous zinciferous halloysite while in halloysite lattice iron participation was detected.…”

“…Among studies in which clay raw material's quantitative mineralogical results were provided, the halloysite amount varied over a wide range (7-90 wt%), with most of cases detected up to 40 wt% and only a few <20 wt%. Despite of these differentiations, the majority of these studies focused on the same direction of mullite-based ceramic production and less other refractories after firing in most cases up to~1350 • C. The increased halloysite content affected the final mullite content increase, starting to be formed at~950-1170 • C. Higher amounts of clay raw material with low percentages of halloysite could be used in the prepared initial mixtures compared to halloysite-rich clays with higher contents of halloysite, in order to produce acceptable ceramics (e.g., [46,54]). Moreover, among different clay raw materials, those with higher contents of halloysite exhibited higher plasticity as well drying shrinkage (e.g., [37]) due to predominant tubular morphology of halloysite with its small particle size and water content.…”

“…Disordered halloysite or impurities in its lattice, its low particle size (nanocrystals) and high surface area promoted its reactivity and consequent mullitization and refractoriness during the heating treatment [28,36,39,46]. Moreover, the interlocked tubular halloysite crystals of raw material suggested that it could increase the strength of final products: halloysite retained its primary morphology at high temperatures and produced elongated mullite crystals which also exhibited a similar interlocking texture [44].…”