Study of the Thermomechanical Behavior of a Mixture of Two Aluminosilicate Powders

This work focused on studying the thermomechanical behavior of a mixture of two aluminosilicate powders. The particle-size distribution of the mixture was determined by wet sieving. The mixture of aluminosilicate powders was characterized by its plasticity (Atterberg limits), as well as its chemical and mineralogical composition (XRD) and microstructure (SEM). Shrinkage before and after firing was measured. Water absorption rates and three-point flexural strength were also determined. Mixtures M1, M2, M3, M4, and M5 were formulated and showed moderate shrinkage, with plasticity indices (24, 27, 31, and 33%) below 35%, making them suitable for extrusion. The addition of sodium hexametaphosphate to the slips prepared from the mixtures decreased the pH (from 5.85 to 4.23) and promoted particle flocculation. The addition of sodium metasilicate increased the pH from 4 to 8.7, enhanced dispersion, and resulted in a stable slip. The diffractograms of the ceramic products were obtained at firing temperatures of 1100 and 1150°C. Mullite was clearly present after the thermal treatment of the mixtures, and the degree of crystallinity was significant. At 1150°C, mixture ND2 exhibited a flexural strength of 11.97 MPa, a water absorption rate of 6.82%, and a shrinkage of 4.53%, compared to ND1 at the same temperature, which showed a flexural strength of 9 MPa, a water absorption rate of 10.03%, and a shrinkage of 2.85%. Keywords: Clay mixture; determination; technological and mechanical properties; Ntokou; Dongou.