Drying mechanisms and stress development in aqueous alumina tape casting

Mass loss, shrinkage, Young's modulus evolution and stress development of aqueous (alumina + latex) tape cast suspensions were observed during drying. Mass loss showed a constant drying rate period, followed by a falling rate period. Concurrently a linear shrinkage rate has been observed in the thickness direction, up to a drying point after which shrinkage abruptly stops. End of constant drying rate and end of shrinkage were not necessarily concomitant and depend on the latex/alumina ratio in the tape. A Young's modulus value appears in the tape cast suspensions at the transition from liquid to solid like state. Then an increase of Young's modulus is observed corresponding to latex film formation. The stresses generated by drying in the tape exhibited a first period of increase due to capillary pressure in the pores, a small relaxation immediately followed by a second stress increase due to latex film formation, and a stress plateau at the end of latex coalescence. Alumina powder granulometry and surface tension of the liquid had a preponderant influence on the first stress maximum whereas the properties of the latex and the drying conditions dominated the second stress maximum. By increasing latex proportion up to 25 wt.% on alumina basis, it was possible to make the first and the second stress rise concomitant.