Pattern Formation and Dendritic Crystal Growth of Ammonium Nitrate*

Dendritic crystal growth is often observed when a non-faceted material crystalizes from a supercooled or supersaturated solution. Many metal alloys solidify in a dendritic pattern, as do some transparent inorganic and organic compounds, and the materials properties of those alloys are influenced by the underlying dendritic microsctructure.  In this work, we will present results for the dendritic solidification of ammonium nitrate from supersaturated aqueous solution.  This system has previously been studied by van Driel et al.[1], who identified several different phases of growth, depending on the saturation temperature.  In the highest-temperature phase (phase I), the dendrites have an approximately hemispherical cap followed almost immediately be a large set of sidebranches.  In the lower-temperature phase II growth, the main dendrite stem is approximately parabolic, but the sidebranches display a distinctive tip-splitting morphology.  We compare these results with those seen for other, similar systems.

[1] Van Driel, C.A., Van der Heijden, A.E.D.M, Van Rosmalen, G.M., "Growth of Ammonium-Nitrate Phase-I and Phase-II Dendrites." J. Cryst. Growth 128 (1993) 229–233.  https://doi.org/10.1016/0022-0248(93)90324-P