Dual-Scale Porosity Alumina Structures Using Ceramic/Camphene Suspensions Containing Polymer Microspheres

Current research on porous ceramics often focuses on single-scale structures. While these materials have applications in filtration, biomedical scaffolds, and thermal insulation, they may lack the structural versatility needed for advanced applications. Prior studies have explored phase separation and sacrificial templates to create porosity. However, the ability to control both macro- and micro-scale pores within a single structure remains limited. This gap motivated the development of new fabrication methods that can generate dual-scale porosity. Existing methods have not fully addressed how to integrate two distinct pore sizes within a single ceramic body. The need for a controllable and scalable process has driven recent innovations in suspension-based fabrication. Understanding how phase separation and sacrificial materials interact is key to advancing this field. This study builds on these insights to propose a novel approach.

The aim of this study is to develop a method for fabricating alumina structures with dual-scale porosity using a suspension-based approach. The specific problem addressed is how to control both macro- and micro-scale pores simultaneously in a single ceramic object. The motivation stems from the need for materials with hierarchical porosity for advanced applications. The researchers propose using phase separation and sacrificial polymer microspheres as a dual porogen strategy. This approach allows for the creation of interconnected macro-pores and micro-pores within the same structure. The study seeks to demonstrate the feasibility of this method in a controlled and scalable way. By varying the composition of the suspension, the researchers aim to tune the overall porosity and mechanical properties. This work contributes to the broader goal of tailoring ceramic structures for specific functional needs.

The researchers prepared a suspension of alumina and camphene at 60 °C. This suspension also contained poly(methyl methacrylate) (PMMA) microspheres as sacrificial porogens. The suspension was then cooled to room temperature to induce phase separation. During freezing, camphene crystals formed a 3D network while alumina particles settled into walls. The PMMA microspheres remained suspended within the alumina matrix. After freezing, the camphene was removed, leaving behind large dendritic pores. The PMMA microspheres were then removed via heat treatment, creating smaller spherical pores. The researchers varied the PMMA content from 0 to 40 vol% while keeping camphene constant at 70 vol%. A 3D plotting technique was used to construct honeycomb structures with macrochannels surrounded by dual-scale porosity walls.

As PMMA content increased from 0 to 40 vol%, overall porosity rose from 45.7 ± 0.5 vol% to 71.4 ± 0.5 vol%. This increase was mainly due to the formation of spherical pores from PMMA removal. The compressive strength decreased from 153 ± 18.3 MPa to 33 ± 7.2 MPa as porosity increased. The macro-pores, derived from camphene crystals, were several tens of microns in size. The micro-pores, from PMMA removal, were spherical and smaller. The 3D plotting technique successfully produced honeycomb structures with periodic hexagonal macrochannels. These structures had walls with dual-scale porosity. The phase separation process was found to be critical in forming the macro-pore network.

The authors propose that the dual-scale porosity in alumina can be achieved through a combination of phase separation and sacrificial PMMA microspheres. They suggest that increasing PMMA content leads to higher porosity and lower compressive strength. The study demonstrates that this method allows for the controlled creation of both macro- and micro-scale pores. The honeycomb structures produced show the potential for advanced applications requiring hierarchical porosity. The phase separation process is essential for forming the macro-pore network. The PMMA microspheres are necessary for generating micro-pores in the alumina walls. The results suggest that this method is scalable and tunable for specific functional needs. The authors conclude that this approach offers a promising route for fabricating multi-scale porous ceramics.