Cerâmicas porosas obtidas por Freeze-casting utilizando gelatina como modificador de poros.

Abstract

Porous ceramics obtained by freeze-casting have been extensively studied because they make it possible to obtain materials with high porosity. However, most of the materials obtained have anisometric / oriented pores (lamellar and / or dendritic), which is harmful for several potential applications involving porous materials.

Therefore, this work aims to obtain ceramics with high porosity through the freeze- casting process, using gelatin as a pore morphology modifier, aiming to eliminate the

development of anisometric / oriented pores. Alumina (Al2O3) and quartz (SiO2) were used to produce porous ceramics. These materials were characterized and used in the preparation of aqueous dispersions. Dispersions with 30% and 40% by volume of solids were prepared. Ammonium polyacrylate, oleic acid and ammonium hydroxide were used as additives and gelatin as a pore modifying agent. 2.5% by weight of gelatin was added for dispersions containing 30% solids and 1.5% by weight for dispersions containing 40% solids. The dispersions remained for 2 hours in a ball mill and were poured into molds and frozen for 24 hours. After freezing, the samples were lyophilized and sintered at 1450 °C. The ceramics produced were characterized by X-ray diffraction, thermal analysis and computed microtomography and determination of apparent density, apparent porosity and resistance to compression. The formulations showed a loss in fire of less than 5%, evidencing the low amount of organics used in the formulations and it was observed that the final ceramic consisted of alumina, quartz and cristobalite. From the microtomographs, it was observed that the addition of gelatin changed the morphology of the lamellar pores to spherical and that the addition of oleic acid promoted the formation of a ceramic with high porosity, up to 90%. A large pore size distribution was observed, varying between 20 - 2600 μm, in which greater porosity was obtained for samples with less solid load and higher proportions of oleic acid and ammonium hydroxide. Thus, the freeze-casting process was effective in obtaining ceramics with high porosity, in addition, the inclusion of gelatin in the process successfully modified the pore morphology.