COLLOIDAL PROCESSING OF CALCIUM-CARBONATE

Two natural calcium carbonate (CaCO3) powders were dispersed in aqueou s media and their colloidal processing ability was studied. In absence of dispersant, electrophoretic measurement showed a very low surface charge density on calcium carbonate particles that do not allow the pr eparation of stable suspensions suitable for the casting process. Howe ver, the addition of an appropriate dispersant caused a significant in crease of the surface charge density of CaCO3 powders, enabling the pr eparation of relatively dense suspensions. Calcium carbonate suspensio ns with very high solid loading (60 vol%) and viscosities low enough f or casting operations could be prepared. Rheological measurements and casting experiments were performed in order to correlate the flow char acteristics of the slips with the particle ability towards packing. Ve ry high green and sintered densities were obtained, reaching more than 74 and 95% of the theoretical density, respectively. Considering the availability, low price and the processing ability of calcium carbonat e by colloidal techniques, as revealed in this work, this material can represent a useful option for ceramic manufacture. (C) 1998 Elsevier Science Limited and Techna S.r.l.