Effects of the polymeric binder system in slurry-based three dimensional printing of ceramics

Abstract

The factors dictating the minimum feature size in Slurry-based Three Dimensional Printing (S-3DPTM) of ceramics have been examined, focusing on effects related to the polymeric binder system polyacrylic acid (PAA, MW 60000) and its interaction with the ceramic powder bed. Methods for retrieving structures characteristic of the minimum feature, referred to as the "binder primitive," and for characterizing the size and shape of the binder primitive have been developed. Impact-related spreading of the printed binder droplets has been found to play little or no role on the primitive structure. Two dominant factors controlling primitive width were however identified. The first is wetting-induced spreading of the printed binder solution on the surface of the powder bed. The spreading process is halted prior to completion by infiltration of the printed liquid into the pore space. The role this factor plays thus depends on wetting properties and the relative rates of spreading and infiltration. The spreading and infiltration rates were modeled, and a means of predicting the maximum extent of spreading was developed. The second factor controlling minimum feature size is adsorption of the polymeric binder molecules from solution onto the surface of the ceramic particles during infiltration of the printed binder solution. This effectively filters the polymer from solution, resulting in a progressive decrease in concentration as the binder solution penetrates deeper into the pore space of the powder bed, which serves to limit the primitive size.

(cont.) This was confirmed via the generation of adsorption isotherms for PAA on A1203, SiO2, and TiO2 surfaces and correlating adsorption to measured primitive size in each of these systems, and by correlating the trend of primitive size with specific surface area of the powder in the high affinity A1203 - PAA system. A general model for predicting the combined effects of spreading and adsorption in the PAA-A1203 system was developed, and suggestions for future directions based on this research have been made.