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The precipitation of alkaline‐earth metal and transition metal oxalates from aqueous solution. Induction periods and nucleation rates
Author(s) -
Packer A.,
Chauhan P.
Publication year - 1975
Publication title -
kristall und technik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0023-4753
DOI - 10.1002/crat.19750100606
Subject(s) - nucleation , supersaturation , oxalate , saturation (graph theory) , aqueous solution , inorganic chemistry , chemistry , precipitation , metal , physics , mathematics , organic chemistry , combinatorics , meteorology
Abstract The precipitation of magnesium, calcium, strontium and barium oxalates and of manganous, ferrous, cobalt, nickel and copper oxalates was studied from equivalent aqueous solutions at 22°C: the initial overall concentrations (C) generally varied from 0.001 to 0.2 M and the saturation ratios ( S mox ) varied from <10 to >3000. The induction periods before the main growth surge were measured and nucleation rates were determined from final crystal numbers and induction periods. Precipitation occurred through homogenous nucleation: the critical nuclei in supersaturated alkaline‐earth metal oxalate solutions were formed by aggregation of 6–8 M ++ Ox − ion‐pairs while the critical nuclei in supersaturated transition metal oxalate solutions were formed by aggregation of 6–8 MOx complexes (to units of 3–4 M ++ MOx 2 − ion‐pairs). Over the range studied, the nucleation rates then varied with saturation ratios according to the relation,Nucleation rates at any saturation ratio decreased in the order Mg > Sr, Ba > Ca and Fe > Mn > Co, Cu > Ni; that is, generally in the order of increasing M ++ –Ox − and M ++ –MOx 2 − bond strengths and increasing surface energies of the metal oxalate crystals. Induction periods decreased with increasing‐concentration and saturation ratio; overThe factors t C 1 and t S 1 depended in turn on the ‘rate constants’ for nucleation and growth during the induction periods and on metal oxalate solubilities.