Abstract
A systematic study of the kinetics of the interactions occurring between solid iron and liquid zinc in the temperature range 440°C - 560°C has been carried out. It has been found that both below and above the temperature range 495°C - 518°C, the rate of interaction is parabolic with time, whilst within this range it is linear with time. An attempt has been made to elucidate these changing kinetics of interaction with reference to the nature and growth rates of the individual intermetallic layers which constitute the interaction zone. It has been shown that in the parabolic regions, the rate of iron dissolution is controlled by the diffusion of zinc through the interaction zone. In the linear range, the rate of attack is probably controlled by chemical reactions. A new technique has been devised in order to assess the relative protective properties of the various intermetallic layers when exposed to the action of molten zinc. This method has shown that the absence of the zeta phase above 495°C and the anisotropic nature of the delta, phase is responsible for a change in the rate of attack from parabolic to linear. The inert marker technique which has been used extensively for disclosing the mechanism of reaction diffusion in solid-solid metal couples, has been shown to be equally applicable in the study of solid-liquid couples with intermetallic layer formation. This technique has conclusively shown that zinc is the diffusing constituent during the interaction of solid iron with liquid zinc. It has been discovered during this study that unusual cruciform patterns were formed, whether or not the overall reaction rate was parabolic or linear with time. Previously these patterns had only been observed in this and other systems when the rate of interaction was linear with time. The interaction layers have been studied using metalllographic, microhardness and X-ray diffraction techniques. These studies did not reveal the presence of capillaries or porosity in the delta, palisade layers as previously believed. Investigations on the temperature range of stability to the zeta phase indicate that its melting point is appreciably lower than the value given by the equilibrium phase diagram. The effect of added elements on the peritectic reaction : delta1 + L ↔ zetahas been carried out. A relationship has been established between the rate of the delta to zeta transformation and the attack on the iron by liquid zinc.