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MM: Fachverband Metall- und Materialphysik
MM 2: Computational Materials Modelling I - Multiscale: Fundamentals
MM 2.3: Talk
Monday, March 26, 2012, 10:45–11:00, TC 006
A Two Scale Approach to Model the Freeze Casting Process — •Frank Wendler1,2, Marcel Huber2, and Britta Nestler1,2 — 1IMP, Karlsruhe University of Applied Sciences, Karlsruhe — 2IAM-ZBS, Karlsruhe Institute of Technology, Karlsruhe
In the last years the freeze casting process has been adapted to a broad variety of materials with open porosities between 10 and 90 % (ceramics, polymers, metals). The crystallization kinetics of ice into an aquaeous colloidal suspension leads to the rejection of dispersed ceramic particles from the growing ice front and results in complex lamellar patterns, commonly explained by a Mullins-Sekerka instability of the constitutionally supercooled ice-colloid interface.
For a quantitative prediction of macro- and microscopic process variables (freezing conditions, solid fraction, particle size, colloidal interaction) on the microstructure, we simulate the free boundary problem using a multi phase-field model based on a thermodynamic free energy formulation on two different length scales: At the particle scale (50 µm) the inert particles are resolved and interact with each other and the ice front. We briefly show how the model parameters (interface tensions + mobilities, higher order potential, interface width) represent capillary properties of the colloid. At a large scale (1000 µm) the osmotic pressure of the colloid as a function of the solid particle fraction is integrated into the free energy formulation, from which diffusion coefficients are derived. We determine the limiting velocities for particle pushing and the transition from lamellar to isotropic growth from simulations, and compare them to an experimental system (ZrO2/water).