Design and investigation of a fractional crystallization-based method using an immersed rotational crystallizer for the production of high purity aluminum

The advances in high technology and semiconductor industries push the limits of materials science, requiring more efficient and economical purification processes. Fractional crystallization is among the few methodologies that can fulfill such requirements, and the immersed rotational crystallizer technique (cooled finger) presents itself as a very promising way of achieving such conditions. Its main characteristic is related to the intense forced convection generated by a high-speed rotation, promoting the decrease in the thickness of the diffusion layer ahead of the crystallization interface, hence a better impurity segregation. This dissertation focuses on the design of an efficient fractional crystallization cooled finger equipment, and to develop an in-depth investigation and understanding of the process mechanisms. To accomplish that, the influencing process parameters were defined and investigated within the framework of this research. Additionally, a series of trials aimed to investigate the effect of the type and concentration of impurities in the purification ratio of aluminum. Furthermore, to better understand the effect of convection on the solute segregation, the results obtained by purifying aluminum via the cooled finger process were applied to the model based on the static layer thickness theory as well as the convection coefficient model. The results and knowledge obtained within this investigation were later applied for the development of a second cooled finger equipment, designed for and installed in a vacuum resistance furnace for the purification of Germanium.