Dimensional changes during binder removal in a mouldable ceramic system

Abstract

Significant dimensional changes involving linear expansion and shrinkage of 6% occur during heating of a thermoplastic SiC/ethylene vinyl acetate (EVA) mixture. Thermal expansion occurs before weight loss begins, and can be quantitatively explained in terms of the thermal expansion behaviour of the constituents and the crystallization or melting of the semicrystalline polymer. Irreversible anisotropic displacements occur during the first heating cycle due to relaxation of moulding strains. These can be reduced by annealing for periods comparable to the viscoelastic relaxation of the ceramic/polymer system. Shrinkage occurs during the early stages of degradation of EVA. This shrinkage is quantitatively accounted for with volume losses resulting from removal of the EVA. Shrinkage continues as weight loss proceeds and stops only at the point the ceramic particles contact one another. Total displacement behaviour is the sum of the shrinkage from weight loss plus the expansion from thermal expansion of the individual components, and can be quantitatively predicted for simple or multi-step heating schedules.