Analysis of the kinetics of polymerization in gelcast ceramic emulsion for the production of porous ceramics

Reference Presenter Authors
17-084 Mariana Cepeda Salama Salama, M.C.(Centro Universitário da FEI); Ortega, F.S.(Centro Universitário da FEI); Porous bioinert (alumina) and bioactive ceramics (hydroxyapatite) were produced by gelcasting with pores obtained from an apolar porogenic agent emulsified in aqueous ceramic suspension. Pure mineral oil of topical use and kerosene were used as porogenic agents (sacrificial phase). A deflocculant was added to disperse the ceramic powder and a surfactant to emulsify the oily sacrificial phase in the aqueous ceramic suspension. The gelcasting was based on the polymerization of vinyl monomer (methacrylamide) and divinyl oligomer (polyethylene glycol dimethacrylate), with the aid of the redox pair (initiator and catalyst) ammonium persulfate and N, N, N ', N' tetramethyl-ethylenediamine, respectively. Several tests were done to evaluate the polymerization rate and the effects of varying the concentration of initiator and catalyst, monomer and oligomer, besides the effect of the initial polymerization temperature. From the record of temperature variation over time, it was possible to understand the effect of such variables on the polymerization kinetics and to calculate the values of activation energy and propagation energy of the polymerization through the Arrhenius equation for energy. It was found that the energy for the propagation of the reaction in emulsions containing mineral oil is about half the value measured in kerosene emulsions. Additionally, emulsions containing hydroxyapatite have lower propagation energy than those of alumina. Porous ceramic pieces were produced by gradually increasing the fraction of emulsified porogenic agent, for a volume of emulsion fixed in 20 ml. It was possible to obtain pieces of hydroxyapatite with up to 75% emulsified porogenic agent. Sintered parts presented highly interconnected porosity, in micrometric scale.
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