Novel tubular alumina substrates produced by the freeze-casting method

Reference	Presenter	Authors (Institution)	Abstract
17-087	Daniel Dornellas Athayde	Athayde, D.D.(Universidade Federal de Minas Gerais); Sousa, B.M.(Universidade Federal de Minas Gerais); Vasconcelos, W.L.(Universidade Federal de Minas Gerais);	Ceramic membranes are potential candidates for a variety of industrial applications, due to the superior thermal and mechanical stability. They usually consist of a macroporous substrate and a top layer. The substrate must not show resistance to the diffusion of particles. However, conventional methods produce substrates with a random pore structure, leading to constrictions and dead-end pores that increase the resistance to mass transport. An alternative is the freeze-casting method, since it is capable of producing substrates with unidirectional pore structure. It consists of a controlled freezing of a liquid ceramic suspension, followed by solvent sublimation and sintering of the green body. In this work, novel tubular alumina substrates were produced by the freeze-casting. Liquid nitrogen was used to freeze an aqueous suspension for 30 s. Solvent sublimation was carried out in a freeze dryer and, finally, the green body was sintered at 1500 °C for 1 h, with heating and cooling rate of 2 °C/min. Suspensions with solid concentration of 10-30 vol% were used to evaluate the influence on pore morphology. SEM images confirmed that the substrates showed radially aligned pores. The pores displayed thicknesses of 1-30 µm and lamellae structure. Microphotographies were treated on the IMAGEJ software for evaluation of the pore directionality and the preferential pore orientation. Finally, the relative porosity and the open and closed porosity were estimated by the Archimedes method.
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