Novel In-situ Coagulation Casting Of Ceramic Suspensions Via Dispersant Removal

Advanced ceramic colloidal processing is the important processing for preparing high performance ceramics which plays a key and pivotal role.Based on the stabilization mechanism of ceramic suspension,we systemically investigate a new ceramic colloidal forming method,namely,in-situ coagulation casting of ceramic suspensions via dispersant removal.Dispersant reaction,hydrolysis,crosslink and separation have been used to control the dispersant removed processing.(1)The influence of types and addition content of dispersant,pH value and solid loading on zeta potential and rheological properties of ceramic suspensions have been systematically investigated.Electrostatic,steric,electrosteric and semisteric stability ceramic suspensions have been prepared and Krieger-Dougherty model is applied to optimize the highest solid loading for each ceramic suspension.(2)Five new methods for controlled removal of dispersants have been proposed.In-situ coagulation of electrostatic stability ceramic suspensions by dispersant reaction or hydrolysis.In-situ coagulation of steric stability ceramic suspensions by dispersant crosslink.In-situ coagulation of electrosteric stability ceramic suspensions by dispersant reaction and crosslink.In-situ coagulation of semisteric stability ceramic suspensions by dispersant separation via temperature induced.(3)A novel direct coagulation casting menthod is proposed firstly.The ceramic suspensions are in-situ coagulated by directly shift the isoelectric point of the suspension via dispersant reaction or hydrolysis without adjusting pH and increasing the ions strength.The coagulation mechanism of electrostatic stability ceramic suspensions via dispersant removal have been expounded.The coagulation time is shortened and the green compressive strength is increased significantly.The technology of direct coagulation casting is enriched and perfected.(4)In-situ coagulation of steric and electrosteric stability ceramic suspensions via dispersant removal have been achieved by dispersant cross linking reaction.The green compressive strength has been significantly increased by the three-dimensional net structure which produced via the dispersant cross linking.(5)In-situ coagulation of semisteric stability ceramic suspensions via dispersant removal have been achieved by dispersant separating out from solvent.The coagulation processing is simplified without degassing and coagulation agent.The homogeneity of green body is increased and the line shrinkage is decreased significantly.It provides the basis for the preparation of high reliability ceramic parts.In this paper,the coagulation mechanism of different ceramic suspensions system with different stabilization mechanism are systematically investigated and the idea of the dispersant removal has been proposed.The different kinds of oxide and non-oxide ceramics and green bodies with excellent performance have been successfully prepared by dispersant removal mothed.The results of this thesis are the basis for the deep research and applications of ceramic colloidal forming.It provides a new idea and new method for the further study of the advanced ceramics colloidal processing,also provides a new way for the industrialization of advanced ceramics with complex shapes.