Investigation of metastable zone width of ammonium oxalate aqueous solutions

Abstract

The metastable zone width of pure ammonium oxalate aqueous solutions, as represented by maximum supercooling ΔT max , is investigated as functions of cooling rate R and saturation temperature T 0 by the polythermal method. The experimental results are discussed by using two recently advanced approaches: (1) self-consistent Nývlt-like approach based on a power-law relationship between nucleation rate J and maximum supersaturation lnS max , and (2) a novel approach based on the relationship between J and lnS max described by the classical three-dimensional nucleation theory. Analysis of the experimental data revealed that both approaches describe the experimental data on metastable zone width by the polythermal method reliably and provide useful information about the physical processes and parameters involved in nucleation kinetics. The values of various physical quantities predicted by both of these approaches are reasonable for a fairly-soluble compound. A careful examination of the data on ΔT max as a function of T 0 obtained by polythermal method and from density measurements showed that ΔT max has a slight tendency to decrease with increasing saturation temperature T 0 . The values of lnS max at saturation temperature 303 K suggest that the metastable zone width of ammonium oxalate aqueous solutions is determined by primary nucleation in the polythermal method and by secondary nucleation during density measurements.

The influence of concentration and supersaturation ratio of CuI·HI on CuI crystal growth by decomplexation method

“…The schematic drawing for CuI crystals growth by decomplexation method in silica gel was shown in figure 1 and detailed experimental parameters were summarized in table 1. Mass-transfer testing was carried out when the feed solution diffused at the stated periods (6,11,16,21, 26 and 30 days). After the diffusion period, the silica gel column was sliced as 10 mm length segments, and the silica www.crt-journal.org…”

“…In all methods of crystal growth, decomplexation has been proved to be useful to grow regular and high purity CuI single crystals in silica gel [6][7][8][9]. Obviously, the parameters of solubility, supersaturation and metastable zone width are very important for crystal growth from solution because they directly affect nucleation, growth rate, size and morphology of growing crystals [10][11][12][13]. The parameters can provide a guide to control the crystal growth process and to optimize the experimental scheme.…”

Effect of cooling rate on the critical undercooling for crystallization

“…(15) and (18) in the definition equalities a(u c )=a det and N(u c )=N det , which correspond to the crossing points of the dotted line with the curves in Fig. 1, it is a simple matter to find an expression for the experimentally obtainable u c (q) dependence in terms of q as a function of u c .…”

“…(15) in the d =0 case when it describes the undercooling dependence of the total number N of crystallites and takes the form (upon replacing a by N).…”

“…In the years that followed, this equation was found to be successful in describing many experimental DT c (q) data on cooling crystallization [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Its use, however, has not contributed to a deeper understanding of crystal nucleation and growth mechanisms, because it contains two semi-empirical parameters to which, in Nyvlt's own words, ''a concrete physical meaning should not be ascribed'' [1].…”