Supplementary Material On the brittle fracture characteristics of lamella walls of ice-templated sintered alumina scaffolds and effects of platelets โ
Dipankar Ghosh, Mahesh Banda, Sashanka Akurati, Hyungsuk Kang, Vivian O. Fakharizadeh
Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, VA 23529, USA *Corresponding author. Tel.: +1-757-683-3738; fax: +1-757-683-5344. E-mail address:
[email protected] (D. Ghosh).
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Preparation of aqueous alumina (Al2O3) suspensions, freeze casting and characterization In this work, commercially available Al2O3 powders were utilized (0.3 ยตm and equiaxed morphology, APA-0.5, Sasol, Tuscan, AZ; platelets, AlusionTM, Antaria Ltd., Bentley, Western Australia). For each suspension, required amount of the Al2O3 powder(s) and small amount (0.5 wt.% of the powder) of ammonium polymethacrylate anionic dispersant (Darvan C, R.T. Vanderbilt Co., Norwalk, CT) were first mixed in deionized water, and milled for 24 hours. Next, an organic binder poly(2-ethyl-2-oxazoline) was added to the slurry (5 wt.% of the powder) and mixed for another hour. Afterwards, the ZrO2 spheres were separated from the slurry and de-aired for 30 min. Freeze casting was conducted using a custom-made set up. In this set up, a Teflon tube is placed on the top of a thin (0.5 mm) steel plate, partially filled with Al2O3 slurry, and the whole assembly is inserted inside a liquid nitrogen (N2) Dewar. By adjusting the distance between the steel plate and liquid N2, freezing front velocity (FFV) was controlled. In this study, all the scaffolds were processed at a fixed gap between the liquid N2 and steel plate. Average FFV was estimated by dividing the frozen sample height with the total time required for freezing of the sample. Sintered density (๐โ ) of each extracted specimen was estimated from the measurements of mass and dimensions, and relative density (๐! ) was determined using ๐! = ๐โ ๐! , where ๐! is the bulk density of ฮฑ-Al2O3 (3.96 g/cm3). Top surface (also referred to as top plane, Fig. S1) of each specimen was utilized for microstructural characterization. Each specimen was compressed uniaxially along the ice-growth direction at a displacement rate of 0.5 mm/min (Tinius Olsen, 10ST), 6 mm ร 6 mm being the loading surface.
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Ice growth direction
Bottom plane
Top plane
5 mm
8 mm
Fig. S1: A schematic of the sintered ice-templated scaffold sample illustrating location of the specimen extracted for density measurement, microstructural characterization, and compression test. Locations of the top and bottom of the specimen are also shown. (Not to scale)
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