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

• Published in: Materials Vol. 15; no. 11; p. 3875
• Main Authors: Lee, Hyun, Jeon, Jong-Won, Koh, Young-Hag, Kim, Hyoun-Ee
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 29.05.2022; MDPI
• Subjects: Alumina; Aluminum oxide; Ceramics; Compressive strength; freeze casting; Freezing; Heat; Heat treatment; Honeycomb structures; Microspheres; Microstructure; multi-scale porous ceramic; Phase separation; Polymers; Polymethyl methacrylate; Pore size; porogen; Porosity; Raw materials; Room temperature; sacrificial templates; Scanning electron microscopy; Sintering; multi-scale porous ceramic; porogen; freeze casting; sacrificial templates
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15113875

This study demonstrates the utility of thermo-regulated phase separable alumina/camphene suspensions containing poly(methyl methacrylate) (PMMA) microspheres as porogens for the production of multi-scale porosity structures. The homogeneous suspension prepared at 60 °C could undergo phase separation during freezing at room temperature. This process resulted in the 3D networks of camphene crystals and alumina walls containing PMMA microspheres. As a consequence, relatively large dendritic pores with several tens of microns size could be created as the replica of frozen camphene crystals. In addition, after the removal of PMMA microspheres via heat-treatment, micron-sized small spherical pores could be generated in alumina walls. As the PMMA content with respect to the alumina content increased from 0 vol% to 40 vol%, while the camphene content in the suspensions was kept constant (70 vol%), the overall porosity increased from 45.7 ± 0.5 vol% to 71.4 ± 0.5 vol%. This increase in porosity is attributed to an increase in the fraction of spherical pores in the alumina walls. Thus, compressive strength decreased from 153 ± 18.3 MPa to 33 ± 7.2 MPa. In addition, multi-scale porosity alumina objects with a honeycomb structure comprising periodic hexagonal macrochannels surrounded by dual-scale porosity walls were constructed using a 3D plotting technique.