The effect of Al additions on the properties and microstructures of carbon refractories for blast furnaces was evaluated in terms of phase and microstructure evolutions as a function of the coking temperature. The formation and evolution of Al 4 C 3 , AlN and SiC crystalline phases in the matrix contribute to the excellent properties of such materials, namely high thermal conductivity and low mean pore diameter of open pores. The experimental results indicate that about 2-4 wt-%Al plus about 4-6 wt-%Si additions at y1300uC were optimum for the manufacture of carbon refractories.
This study was carried out to determine the minimum Al content needed to form an Al2O3scale on creep resistant ferritic steels at 650 °C. Two steels differing mainly in Al content were oxidized in air at 650 °C for 3000 h. One of the steels contained 2.3 wt% Al and the other 1.9 wt% Al. Oxidation resistance of the two steels was also compared with that of the commercial P92 steel at the same temperature. The oxidation was monitored by weight gain measurement. XRD, SEM and EDS techniques were used to analyze the scale formed on the surface of the steels. For the steel containing 2.3 wt% Al, a continuous Al2O3scale was observed after 3000 h of oxidation and growth of the scale was parabolic with an extremely low rate constant of 0.00058 mg cm-2h-1/2. For the steel containing 1.9 wt% Al, however, only a non-protective scale was formed, which exhibited a layer structure that consisted of an outermost porous Fe2O3layer, followed by a relatively dense intermixed Fe2O3and FeCr2O4inner layer and then by an internal oxidation layer containing voids, Al2O3and un-reacted metal particles in addition to Fe and Cr oxides; growth of this type of non-protective scale followed the logarithmic kinetics Δmt=klln(αt+ 1) for oxidation times up to 3000 h.
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