A New Direct Coagulation Casting Process Via Controlled Release Of High Valence Counter Ions

In the field of application of controlled release of high valence counter ions （HVCIs）in direct coagulation casting （DCC） of ceramics, the influence of HVCIs on theviscosity of ceramic suspensions, controlled release of HVCIs and its effect oncoagulating ceramic suspensions were studied systematically in Al₂O₃suspension.The ability of liposome to entrap and release HVCIs, the performance of liposomesand Ca₃（PO₄）₂to controlled release of HVCIs and coagulation property to Al₂O₃suspension were also investigated. The prospective of controlled release of HVCIs bythe use of liposome and insoluble salt of ions on DCC were also discussed.The results show that coagulation of HVCIs to Al₂O₃suspensions is effective. Thecritical coagulation concentration （CCC） of HVCIs in Al₂O₃suspensions variesbetween5mmol/L and30mmol/L. Because their viscosity are less than1Pas at100s-1of the shear rate when the concentrations of HVCIs is below CCC, all kind ofAl₂O₃suspensions can be cast. The sensitivity of the ions to suspensions depends onnot only valences of ions themselves, but also solids loading of suspensions, reactionconstant of ions with water and dispersants. For Al₂O₃suspensions dispersed byammonium citrate （TAC）, the CCC of Ca²⁺ has lower and better sensitivity tosuspensions by comparing with other high valence cations.The liposomes can entrap perfectly the ion solution. The entrapment efficiency canreach83.58%for high valence anions and55.3%for high valence cations. The phasetransition temperature stays at38℃with50wt%addition of cholesterol. It is theopposite charged surface of liposomes to the high valence ions ensured the usefulnessof liposomes in the processing of coagulation of suspensions. However, the release ofions by liposomes shows so slow that the possible demolding time is8h²4h afteradding liposomes into suspensions at38℃for3.5h.50vol%Al₂O₃suspension atpH=4.5can be coagulated slowly by adding Ca₃（PO₄）₂solutionl.The demolding timeof wet green body is135mins when the addition of Ca₃（PO₄）₂solution is0.2wt%at60℃. The compressive strength of wet green body can reach2.87MPa.