EVOLUTION OF MECHANO-CHEMISTRY AND MICROSTRUCTURE OF A CALCIUM ALUMINATE-POLYMER COMPOSITE .1. MIXING TIME EFFECTS

Paste development and evolution of microstructure, microchemistry, and mechanical properties of macro-defect-free composites were investigat ed, Mixing torque plots from a Banbury mixer showed a ''window of proc essibility'' within which an optimum polymer-particle network structur e formed, This processing window can be controlled by mixing rate and temperature. Network development during paste formation governed the f lexural strength and microstructure of the cured material, Electron mi croscopy studies of the composites corresponding to various points alo ng the mixing torque curve revealed a matrix formation-destruction pro cess that was linked to the mixing activity and the mechano-chemistry of the system. Microchemical evolution in the composite was studied by EDS. These studies suggested that a combined convection and diffusion mechanism was responsible for the migration of Al3+ and Ca2+ ions int o the different regions of the microstructure. Increasing concentratio ns of these elements in the polymer regions stiffened the matrix, lead ing to complete degradation on further mixing.