Gilsoo Han

High-Temperature Corrosion of Fe3Al in 1% Cl2/Ar

The high-temperature corrosion of iron aluminide (Fe3Al) in environments containing chlorine has been investigated using the thermogravimetric method. The corrosion experiments were performed in a 1%Cl2–Ar mixture in the temperature range of 750 to 900°C. Two distinct stages of weight change during corrosion were observed: slow linear weight loss and subsequent fast linear weight-loss stage. Considering corrosion kinetics and products, different corrosion mechanisms are proposed for each stage. The first stage is characterized by localized chlorine attack, repassivation or defect healing by alumina- forming active oxidation and diffusion of volatile aluminum chloride to the gas/scale interface through dense aluminum oxide. The depletion of aluminum in the alloy near the metal–oxide interface after the first stage and the subsequent evaporation of iron chlorides may result in rapid weight loss during the second stage. It was observed that a significant amount of porous nonprotective oxide scale was formed by active oxidation in the second stage. The segregation of sulfur at the metal–oxide interface during the second stage was also observed.

High-temperature corrosion of Y-doped Fe3Al in environments containing chlorine and oxygen

The high-temperature corrosion performance of Y-doped Fe3Al was studied in various environments containing chlorine, oxygen, and argon. Results were compared with Y-free Fe3Al in terms of corrosion rate and microstructure of corrosion products. The kinetic pattern shown in the two types of alloy features two consecutive stages: initial slow mass loss followed by fast linear mass loss. However, addition of Y decreased the rate but increased the duration of the first stage of the corrosion. Microstructure examination indicates that the beneficial effect of Y may be due to the formation of pegs and the development of dense oxide layers.

Interphase Mass Transfer with Bulk Flow Normal to the Phase Boundary

The effect of bulk flow normal to the interface on the interphase mass transfer rate is analyzed by using a convective mass transfer coefficient, and a method of deriving the correct choice of the reference mole fraction in the bulk flow term is developed. The effect of the bulk flow and the definition of the proper reference mole fraction have been derived based on diffusion in a binary gas mixture across the boundary layer and expanded to the system of an interfacial gas-solid reaction. The results show that the bulk flow effect together with the proper choice of the reference mole fraction in the bulk flow term is important in obtaining an accurate expression of interphase mass transfer rate. In an extreme situation, the bulk flow effect can cause mass transfer to occur in the direction of increasing concentration. The theoretical development is applied to the rate analysis of the hydrogen reduction of silica.

Effect of CaSO4 pelletisation conditions on pellet strength and reactivity for converting SO2 to elemental sulphur by reaction cycles involving CaSO4/CaS

Abstract A new process for converting sulphur dioxide to elemental sulphur by a cyclic process involving calcium sulphide and calcium sulphate without generating secondary pollutants was developed at the University of Utah. In this process, sulphur dioxide is reacted with calcium sulphide to produce elemental sulphur and calcium sulphate. The latter is reduced by hydrogen to regenerate calcium sulphide. In the present work, the effects of different pelletisation conditions for the initial reactant calcium sulphate on the strength and reactivity of CaSO4 pellets and on the reactivity of CaS pellets produced from CaSO4 pellets toward sulphur dioxide were determined. These pelletisation conditions included the type, amount and impregnation method of catalyst, the binder amount and sintering. The pellets with the best properties were then utilised for kinetics measurements over several cycles of the two step process in the temperature range of 973–1173 K. Nickel catalysed and fired pellets produced by the use of molasses or cement as a binder showed the highest compressive strength as well as good reactivity during the cyclic tests. The binder amount did not significantly affect the reaction rate.