Advanced ceramics and ceramic composites have a variety of advantageous properties, such as high hardness, strength, and wear resistance. This makes them good candidates for materials in the aerospace, automotive and defense industries, among others. A major disadvantage of advanced ceramics and ceramic composites is their requirement for specialized processing which often makes manufacturing complex shaped ceramic objects challenging and costly. Additionally, these materials are susceptible to flaw incorporation during production. These flaws are initiation points for failure and thus lead to a drastic reduction in strength. Repeatable manufacturing methods and optimized processes are compulsory for cost saving and production of high quality parts. In recent years, new processing technologies, such as gelcasting, have been developed to accommodate the formation of complex shaped ceramics and also the manufacture of ceramic composites. The use of wet forming technologies, like slip casting or gelcasting, necessitates the careful drying of ceramic objects. Complex shaped objects are particularly difficult to properly dry without introducing internal stresses which may result in warping and cracking, thus rendering the object unusable. Additionally, traditional drying processes are often energy intensive and lengthy, neither of which are favorable in a production setting. To improve manufacturability, the processing-structure-property relationships developed during the drying process must be investigated further. This work addresses the need to define optimized process conditions for the drying of alumina objects gelcast using gelatin. The osmotic drying process was employed to remove solvent from the objects through the use of an aqueous liquid desiccant solution of poly(ethylene glycol) (PEG). The process settings for the solution’s osmotic pressure and molecular weight were investigated, in addition to the total immersion time. The mass transfer processes that occurred between the ceramic object and the liquid desiccant solution were quantified in several case studies. For one sample, 40 weight% of the initial water content was removed in 75 minutes demonstrating the potential drying efficiency of this method. Depending on the initial solution conditions, the PEG solute was found to diffuse into the ceramic object to varying degrees. The effect of the drying condition on the object’s density and hardness was also measured. Through the development of regression equations, the process settings were optimized based on the goals to maximize water loss, minimize solids gain, and maximize the object’s density. The optimum drying settings for the objects studied in this work were an osmotic pressure of 2.50 MPa, a molecular weight of at least 100,000 g/mol, and an immersion time of 60 minutes. When objects of similar geometry, composition, and solution-to-object volume ratio are immersed in this type of solution, they are expected to lose 28 weight% of the object’s initial water content, gain solids of 0.82 weight% of the object’s initial mass, and have a density of 3.54 g/cm3. Furthermore, the regression models were validated using an independent experimental study. A model based on mass balance was used to define the kinetics of the mass transfer, along with the equilibrium values. Lastly, a demonstration of the feasibility of combining gelcasting, osmotic drying, and sacrificial templating is presented. Overall, these results may be used as the basis for further investigation into the scale up of the osmotic drying of gelcast alumina with the eventual implementation of the process in an industrial setting.
