Regensburg 2010 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 56: Topical Session Growth Kinetics VI

MM 56.2: Vortrag

Donnerstag, 25. März 2010, 15:45–16:00, H4

Zeolite thin film growth studied with a phase-field model — •Frank Wendler, Christian Mennerich, and Britta Nestler — Institute of Materials and Processes, Karlsruhe University of Applied Sciences, Moltkestr 30, 76133 Karlsruhe, Germany

Hydrothermally grown zeolite films are exeptionally interesting as molecular sieves, where the transport through the nanosized pores is strongly modulated by the grain orientation and boundary morphology. The objective of the simulation study is an understanding of the competitive growth behaviour and the formation of undesired mesoscale porosity during polycystalline growth to optimize process conditions. We adopt a multi-phase field model of Allen-Cahn type to describe the process, where each solid grain and the aquaeous solution are represented by individual order parameters. First, single coffin- or leaflet-shaped MFI zeolite crystals are modeled choosing appropriate anisotropies of surface tension and kinetic coefficient. Different aspect ratios and a transition between both crystal growth shapes emerge. Then, the selection dynamics is studied in simulations with several hundreds of grains in 2D and 3D, showing a gradual extinction according to misorientation and the influence of non-isotropic orientation distributions (seeded growth). The occurence and influence of growth twinning on the morphological evolution is discussed, which - similar to nucleation - produces new growth orientations during the process. Parts of the complex silicate chemistry are represented by taking into account the initially present gel phase (solution + amorphous solid), acting as a buffer layer in the transport of the silicate building blocks.