This study is focused on understanding the effects of kaolinite content and freezing rate on the microstructure, surface area, and flexural strength of freeze-cast kaolinite–silica nanoparticle composites. Scanning electron microscopy reveals that the bulk of the composites contain interconnected pores and that the size of the pores increases with kaolinite concentration. Lowering the freezing rate from 2.0 to 0.05 K/min produces much larger pores on the outer surface of the sample and only minor effects on the bulk morphology. BET measurements indicate that the specific surface area (area/mass) of the composites is controlled primarily by the relative amounts of kaolinite and silica in the sample and not by the freezing rate. Equibiaxial flexural strength tests show that the strength of the composites is substantially higher than freeze-cast samples produced using either kaolinite only or silica only, indicating that the two components work cooperatively. The strength is slightly higher for composites produced at the lower freezing rate. Adsorption tests indicate that during gel formation, the silica nanoparticles strongly adsorb to the much larger kaolinite platelets, which could be the primary cause for the increased strength of the composites.
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Document Type: Research Article
Materials Science and Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Chemical Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Publication date: 2011-04-01