12/27/2023 0 Comments Dendrites in crystalsA model to explain the symmetry of dendritic crystals-e.g., snow crystals-is developed, based on the interaction of crystal shape and heat flow in the crystal. On the other hand, when the growing crystal contained parallel twin boundaries (Figure 6b), dendrite growth appeared at a portion of the parallel twin. The main effect of convection under Earth’s gravity is the compression of the diffusive temperature field around the downward-growing tip. Finite-element calculations of the heat flow and the convective flow in the growth vessel show that the idea of a single axisymmetric toroidal convection roll across the whole growth vessel has to be dropped. The occurrence of three- and four-tip configurations is explained with this mechanism. The latter then surpass the main tip and develop into new tips. The tip splitting for dendritic free growth is found not to be a splitting of the tip in two rather, the respective growth velocities of the main tip and the fins change. Together the two perturbation mechanisms allow a “dendrite engineering”-i.e., a reproducible controlling of the crystal shape during its growth. The existence of a limit cycle is supported by the findings. A deterministic behavior is found besides the random-noise-driven growth. ![]() The translational velocity of the equiaxed crystals in motion is calculated using the classical mechanical law. The solidliquid boundary of the solute field in the movement process is assessed using the solute extrapolation method. ![]() On the other hand, heating leads to controlled sidebranching and characteristic transitions of the tip shape. The interactions between dendrites and the melt are assessed using the Ladd method. Spontaneous and metastable multitip configurations are stabilized, coarsening is reduced, leading to a denser sidebranch growth, and a periodic tip splitting is found during perturbation by shaking. Dendritic free growth is perturbed by two different mechanisms: Shaking and heating up to the melting temperature. The experimental work presented focuses on transient growth, morphological transitions, and control of xenon dendrites.
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