Dendritic crystal growth of ammonium nitrate and ammonium chloride

Dendritic crystal growth is an important example of nonequilibrium pattern formation that involves both nonlinear and noise-driven effects. The resulting large-scale structures are sensitively dependent on relatively small effects, such as surface tension, and on small anisotropies in those quantities. In this work, we present results for ammonium chloride dendrites, and compare them with new results for ammonium nitrate dendrites grown from supersaturated aqueous solution. This new system has been studied previously by van Driel et al.[1] and shown to exhibit several different morphologies, including both steady state dendritic growth and a state with persistent tip-splitting behavior. Specifically, we present new measurements of the tip radius ρ, growth speed v, and sidebranch spacing λ, along with initial estimates of the product Dd₀, where D is the chemical diffusion constant and d₀ is the capillary length, as well as the stability constant σ*=2d₀D/vρ². We discuss important similarities and differences between the two materials.

[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