Dendritic ice crystal

Reid et al. [ 1.12] described the effect of 1 % addition certain polymers on the heterogeneous nucleation rate at-18 °C the rate was 30 times greater than in distilled, microfiltered water and at -15 °C, the factor was still 10 fold hogher. All added polymers (1 %) influenced the nucleation rate in a more or less temperature-dependent manner. However, the authors could not identify a connection between the polymer structure and nucleation rate. None the less it became clear that the growth of dendritic ice crystals depended on to factors (i) the concentration of the solution (5 % to 30 % sucrose) and (ii) the rate at which the phase boundary water - ice crystals moved. However, the growth was found to be independent of the freezing rate. (Note of the author the freezing rate influences the boundary rate). 

Snow crystals [4] Their macroscopic structure is different from a bulk three-dimensional ice crystal, but they are formed by homologous pair-pair interaction between water molecules and are static and in thermodynamic equilibrium. It should be noted, however, that dendritic crystal growth is a common phenomenon for metals [5-7] and polymers. The crystals grow under non-equilibrium conditions, but the final crystal is static. 

Nunner [ 1.104] photographed with a special cryomicroscope the change of the planar front of a 0.9 ck NaCl solution during directional freezing in 360 s to a stable dendritic ice structure (Fig. 1.37). The concentrated NaCl (dark border) ean be seen on the surface of the ice crystals. 

Hydrothermal, low temperature precipitation, and vapor deposition produce different crystal habits and sizes due to differences in growth rates, diffusion rates, and surface energy. Most Fe-Mn oxide-hydroxide phases are formed at low temperatures (below 100° C), but several are known to form unde hydrothermal conditions (above 100° C and up to several kbars pressure). Larger crystals are produced from hydrothermal processes as transport is much more rapid, and solubility of the growing phase in the growth medium (solution) is high. The latter growth process can produce crystals up to 10 cm in size. Ice crystals (snowflakes) are the most commonly observed vapor deposition-produced natural phases. These usually show complex dendritic patterns caused by rapid... 

Dendrite - A tree-like crystalline pattern often observed, for example, in ice crystals and alloys in which the crystal growth branches repeatedly. 

Stellar dendrites or dendrite sheets and, when a small ice crystal is introduced into a volume of supercooled water at temperature below — 2-5 °C, the growth pattern of the dendrites is such as to give twelve primary growth directions, resulting in a double... 

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