Chemical Reactivity of Calcium Aluminate Cement Bond Phases in a Steam-CO Atmosphere at 199 Degree C

The properties of a dense, approx. = 94% alumina castable were investigated after exposure to a 47.5 steam--52.5 CO (vol %) atmosphere at 3.21 MPa (465 psia) and 199/sup 0/C for 6, 12 and 18 days. Within 6 days, the calcium--aluminate cement-bond phases in both as-dried and fired specimens decomposed to calcium formate, Ca(HCO/sub 2/)/sub 2/, and boehmite, ..cap alpha..-AlO(OH). The flexural strength increased considerably after 6 days and either became constant or decreased slightly at 18 days. During exposure, the apparent porosity decreased from approx. = 20% to approx. = 6%. The flexural strength and porosity after 18 days' exposure were essentially independent of the temperature to which the specimens were fired before exposure.