Normalized increment of crystal mass as a possible universal parameter for dendritic growth

The unsteady growth of ammonium chloride dendrites during crystallization from an aqueous solution in a thin capillary is experimentally investigated. The dependence of the crystal area S on the time t for various sectors located along primary branches and side branches is measured. The hypothesis that the ratio between the area change and the area itself [S'(t)/S(t)] is one and the same for different but simultaneously growing parts of an unsteady dendrite is advanced and confirmed. This conclusion allows a curve to be proposed to describe the evolution of the dendrite area (or its part), with the form S(t)=const ta exp(-bt), where a and b are the parameters whose values are determined in the paper. The nondimensionalization of S(t) and S'(t)/S(t) (using the full dendrite growth time) produces simple one-parameter functions that depend on a single parameter a (which is presumably associated only with the physical and chemical characteristics of the crystallized system and, in our case, is equal to 1.7±0.2).