Physico-chemical properties of illite suspensions after cycles of freezingand thawing

The effect of freezing and thawing on the rheological behavior of illite su spensions was studied by examining viscosity and plasticity. Stability of s uspensions was characterized by a hysteresis loop of thixotropy. Thermal gr avimetric and differential scanning calorimetry analysis were also used. Af ter initial freezing and thawing, the flow curves of the suspensions show a n increased viscosity, an "irregular up line", and a greater hysteresis loo p of thixotropy. The ratios of mean viscosity of previously frozen (F) and control (O) samples (eta(F)/eta(O)) for non-expandable 2:1 phyllosilicates ranges from 1.3 to 2.1. Addition of monovalent (0.1% Na2SiO3) and divalent cations (0.3% CaCl2 or BaCl2) increase and decrease the shear-stress differ ence between F and O samples, respectively. Prior freezing of clay samples results in an increase of plasticity by similar to 20-30%. The thermal anal ysis data of F samples show an increase in weight loss, and a decrease in e nthalpy of dehydration. The changes of physico-chemical properties from cyc les of freezing and thawing are long lasting. The freezing memory effect of illite-type clays is expected to play an important role in ceramic process ing, i.e., casting processes, plastic formation, and sintering.