No abstract

Slip/starch casting consolidation (SSCC) is a technique for obtaining porous ceramics, which joins the forming process by starch consolidation with the slip casting method. In this work, a slip which contains ceramic powders, starch and dispersant, is poured into a porous mold and is taken to an oven so that the gelling process occurs. After sintering, it is noticed that the ceramics show different characteristics from the ones obtained exclusively by slip casting or by starch consolidation. Alumina ceramics were produced by using the three methods presented in this work. The ceramics were characterized by apparent porosity, mechanical resistance and scanning electron microscopy. The ceramics produced by SSCC presented the highest mechanical resistance value (289 MPa), while the ones produced by starch consolidation and slip casting presented values of 126 MPa and 191 MPa, respectively.

For a Soderberg Technology, paste production process consists of four basic steps: raw material handling; dry aggregate preparation; mixing; and briquettes loading at electrolytic cells for aluminum production. Dry aggregate is prepared from calcined petroleum coke, where the grains are crushed and separated between 3 different fractions of pre-determined sizing and a dust component. Petroleum pitch blended with the finest particles from dry aggregate forms the binder used for wetting, lubricating and filling open pores of larger coke grains, resulting into a higher anode paste quality with adequate mechanical properties, higher density, oxidation resistance and lower electrical resistivity. Raw materials recent trends showed significant quality degradation and cost raise, pushing up industry to look forward for untraditional suppliers, in addition to process optimization. This paper describes enablers chosen to improve paste properties, through dry aggregate particle size distribution using two of the most traditional particle packing models: Andreasen and Alfred. The formulations developed in this work were compared to the formulation originally used by an industry through measures flowability and apparent baked density. The results have shown that both the equations of Alfred and Andreasen, for distribution coefficient 0.30 and 0.52 respectively, can be applied to the Aluminum Industry, resulting into products significantly different from the point of view of quality.

Several researches have been developed in order to verify the porosity effect over the ceramic material properties. The starch consolidation casting (SCC) allows to obtain porous ceramics by using starch as a binder and pore forming element. This work is intended to describe the porous mathematical behavior and the mechanical resistance at different commercial starch concentration. Ceramic samples were made with alumina and potato and corn starches. The slips were prepared with 10 to 50 wt% of starch. The specimens were characterized by apparent density measurements and three-point flexural test associated to Weibull statistics. Results indicated that the porosity showed a first-order exponential equation e-x/c increasing in both kinds of starches, so it was confirmed that the alumina ceramic porosity is related to the kind of starch used.