科研之友
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摘要
Our understanding of the fundamental mechanisms controlling the rate of crystal growth is largely based on the groundbreaking works done in the first half of the 20th century. There are however still aspects of crystal growth that are not satisfactorily explained with the present state-of-the-art models. One is the effect of solution stoichiometry on the crystal growth rate of ionic compounds, with rates peaking at or close to stoichiometric solutions. The most updated models are all based on the mechanistic model proposed by Zhang and Nancollas in 1998 (ZN98) ( J. Colloid Interface Sci. 1998, 200, 131-145). We have done a review of experimental growth rate data and evaluated ZN98 and the more recent Wolthers et al. model (W12) ( Geochim. Cosmochim. Acta 2012, 77, 121-134). In order to quantify the variation in the experimental data, we constructed an empirical model, and it was found that two adjustable parameters (alpha and beta reflecting the width and position of a Gaussian respectively) were sufficient to satisfactorily reproduce all data. On the basis of the data analysis, it was found that the ZN98 and W12 models cannot generally reproduce the experimental data and that critical assumptions of the models must be reevaluated. Potential relations between beta and saturation state and a and ionic strength and saturation state were found, and a possible relation between a and the aqueous ionic charge density z(2)/r may be indicated in the data. One possible explanation for the large variation in a is statistical in nature, where the number of possible incorporation sites for the A and B units determines the width of the Gaussian. If there are few incorporation possibilities, growth will be strongly limited by the deficient growth unit, whereas if the number of incorporation possibilities at steady-state is large, both for the deficient and surplus growth units, the Gaussian will be less pronounced.
- 出版日期2014-12
