Strength of green ceramics with low binder content

Acrylic-based polymers are common binders that impart high, green strength (>2 MPa) at low concentrations (<5.0 vol%). Strength at low binder concentrations may be determined by chemical bonding at the ceramic-polymer interface. We have studied the binding mechanisms as a function, of ceramic surface chemistry using a cross-linkable binder, which is based, on a soluble poly(acrylic acid) (PAA, MW = 60 000) and glycerol. The cross-linked PAA binder system has been integrated into a solid freeform fabrication process, which provides a means of fabricating very reproducible green bodies, including SiO2, TiO2, Al2O3, multicomponent oxides, and non-oxides, with uniform density and composition. The ceramic parts contain only 2.5 vol% binder (solids basis), which increases the strength of the ceramic systems by at least a factor of 8 while the strength of Al2O3 components increases by a factor of similar to 24 (0.3 to 7.6 MPa). Addition of the binder improves the toughness of the ceramic bodies by an order of magnitude with SiO2 representing the largest relative increase: (2.8 x 10(-3) to 4.4 x 10(-2) MPa.m(1/2)). The mechanical properties are dictated by two binding mechanisms: binder adsorption and mechanical interlocking. High green strengths result from adsorption of the binder onto the ceramic surface whereas toughness is enhanced by poor adhesion of the binder to the ceramic surface.