EVALUATION OF THE USE OF HYDRAULIC ALUMINA FOR THE PRODUCTION OF CALCIUM HEXALUMINATE

Reference	Presenter	Authors (Institution)	Abstract
14-080	Vitoria Marques Cesar Leite	Leite, V.M.(Universidade do Vale do Paraíba); Gonçalves, E.P.(Universidade do Vale do Paraíba); Salomão, R.(Universidade de São Paulo); Oliveira, I.R.(Universidade do Vale do Paraíba);	Hydraulic alumina (HA) was developed as a direct alternative to the use of refractory cements, since the calcium oxide from the cement leads to a deterioration of the mechanical properties of the concretes at high temperatures in systems containing silica. Such binder is generally produced by the rapid calcination of gibsite, resulting mainly in alumina-rho (?), which presents low crystallinity and high surface area. The binding capacity of this material comes from its easy rehydration when it is in contact with the water at room temperature. In this work, calcium hexaluminate (CA6) was produced using HA and different sources of calcium (CaCO3, CaO or Ca(OH)2) by direct molding. The obtained materials were characterized by the percentage of retraction after firing, the flexural modulus of rupture and the Young's modulus before and after thermal shock treatment. Higher shrinkage after firing, lower flexural strength and lower elastic modulus were found for compositions prepared with HA when compared to the use of calcined alumina. This is due to the fact that CA6 prepared with HA presents high content (65%) of microporous (1 ?m) what should hamper heat transfer by radiation at temperatures exceeding 1000 oC resulting in a low thermal conductivity. Besides that, the advantage of using HA is that it is not necessary to add organic binders to consolidate the mixture, which releases large volumes of gases such as carbon dioxide from the green body during heating.
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