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The Precipitation of Sparingly‐Soluble Alkaline‐Earth Metal and Lead Salts with Slow Development of Supersaturation (Slow Anion and Hydroxyl Ion Addition): Kinetics of Nucleation and Induction Periods
Author(s) -
Packter A.,
Sahay S.
Publication year - 1974
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.19740090505
Subject(s) - supersaturation , nucleation , precipitation , chemistry , salt (chemistry) , induction period , solubility equilibrium , inorganic chemistry , aqueous solution , solubility , reaction rate constant , alkali metal , metal , ion , kinetics , organic chemistry , physics , quantum mechanics , meteorology , catalysis
Barium and lead sulphate and chromate precipitations were studied at 20° to 95°C at precipitation rates varying from 10 −3 to 10 −7 ion l −1 sec −1 : the supersaturation was developed by slow direct addition of anion to metal nitrate solution and by neutralisation of equivalent metal salt in excess acid solution. Slow heterogeneous nucleation occurred onto particles dispersed within the aqueous solution. The nucleation rate at any time wasWhere k n is the rate constant for heterogeneous nucleation, N ∞ is the maximum number of potential nuclei, n t is the number of nuclei after time t , I . P t is the ionic product ( C mt )( C mt ) and 2π is the number of metal salt ions in the critical nucleus, generally eight. Crystal growth started after induction periods (t̄) at times just after the times for maximum rate of formation of nuclei. The induction periods (t̄) for precipitations from solutions of initial cation concentration c M 0 varied with precipitation rate ( R ) according to the relation, where γ = π/(π + 1) and k 1 (the unit reciprocal induction period) = . Nucleation rate constants for different precipitations were estimated from the k 1 values and are tabulated. For slow precipitations by direct anion addition, the rate constants were lower for precipitation from solution of the salt of greater solubility. The rate constants for slow precipitation of metal chromates from acid solution were far lower than those for slow precipitation by direct chromate addition. Rate constants decreased somewhat with rise in precipitation temperature.