Ultrasonic investigation of the mechanical behaviour at high temperature of alumina-spinel castables

Two different ways can be used to formulate spinel low cement castables : one way is to add some aggregates of preformed Al2O3-MgO spinel in an alumina castable, the second one is to add some magnesia in order to form spinel in situ within the castable during use. This paper deals with the characterisation up to high temperature of the elastic properties of different alumina-spinel castables : preformed spinet or spinel forming. To determine the elastic properties at high temperature, measurements have been made by the way of a specific ultrasonic technique. Different changes in the curve E=f(T) during thermal cycle up to 1550 degreesC attest of the formation of new calcium aluminates phases by reaction of the cement with the reactive alumina. In the same manner, the in-situ formation of spinel by reaction of the magnesia with the reactive alumina can also be identified in the case of spinel forming castables.