In situ observation and numerical calculations of the evolution of metallic foams

During the past two decades the drainage behaviour and temporal evolution of aqueous foams has been subjected to intensive research activities. For the in situ monitoring of liquid metallic foams, it is not possible to use the established drainage observation methods employed for aqueous foams. The generally high melting point and conductivity as well as the opaque nature of these systems require the use of high temperature furnaces in combination with radiography techniques based on x-rays or neutrons. Due to these experimental difficulties, the data from a direct in situ observation of the material redistribution in liquid metallic foams has not been tested quantitatively with numerical solutions from any of the existing drainage models. In two recent studies the density profiles of solidified aluminium foam columns at different stages of the ageing process have been compared with corresponding numerical solutions of the Plateau channel-dominated drainage equation. However, due to the stochastic nature of the foam structure and its development, it was not possible to achieve a reliable quantitative comparison. In our paper we will show a direct quantitative comparison between experimental observations performed by means of x-ray radioscopy and numerical solutions of an adapted version of the channel-dominated drainage equation. Our results indicate that this theory can in principle be used to predict the temporal evolution during the ageing of metallic foams. By incorporating coalescence effects into the numerical description it can be shown that the material redistribution strongly depends upon the rate at which the pore structure evolves. This is in good agreement with our experimental observations.