Application of lipase in shaping Al2O3-mullite composites
Mikołaj Szafran, Paulina Bednarek, Paweł Piwowarski
Quarterly No. 1, 2011 pages 90-94
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abstract The paper presents the method of Direct Coagulation Casting (DCC) which is a recently developed method of near-net-shaping of ceramic components at low costs. The process relies on electrostatic stabilized ceramic su-spensions and their destabilization owing to time delayed in situ reactions. In the method, the enzyme-catalized reaction is used to shift the pH of the ceramic suspension to the isoelectric point, which causes coagulation of the slurry. The aim of this work is the research on shaping alumina-mullite composites with the application of a lipase-catalyzed decomposition of glycerin triacetate. Zeta potential measurements in relation to pH were performed and the appropriate substrate and enzyme was chosen to conduct controlled coagulation of ceramic slurry. In the DCC method, the optimal composition of ceramic suspension was experimentally chosen. The slip gaining a high concentration of ceramic powders, small amount of organic additives, good flow properties and the shortest time after which the intensive increase of viscosity, was considered as optimal. The paper also presents the results of the viscosity of slurries with different concentrations of dispersant and lipase. The sintering temperature leading to the best density and mechanical strength parameters was found to be 1600°C. The relative densities of DCC sintered samples were higher than 95%. The Vickers hardness and fracture toughness KIC for DCC sintered samples were measured. The main conclusion is that the DCC method, using the lipaze-catalyzed decomposition of glycerin triacetate, can be successfully applied to the formation of complex-shaped alumina-mullite composites. Very good mechanical properties can be achieved due to the low content of binders and other additives. Keywords:Al2O3-mullite composites, direct coagulation casting, enzymatic reaction, lipase, Vicker’s hard-ness, fracture toughness