This work supplements the adsorption model of 2D‐isomorphism proposed earlier for the NH4Cl‐CO(NH2)2 system and reveals the correspondence between the growth rates of the NH4Cl crystals in the presence of carbamide and the co‐crystallization of carbamide with ammonium chloride. It follows from the kinetic data that the NH4Cl · CO(NH2)2 impurity capture becomes significant when the carbamide concentration in solution is sufficient for almost monolayer adsorption of the impurity on the crystal surface and the onset of multilayer adsorption. The concentration of the guest phase intergrowths falls with the increase in the host crystal growth rate.
The nonequilibrium partition of components between a crystal and solution is mainly controlled by impurity adsorption on the surface of the growing crystal. The specificity of adsorption on the faces of various simple forms leads to the sectorial zoning of crystals. This effect was studied experimentally for several crystallizing systems with different impurities, including isomorphous, 2d-isomorphous, and nonisomorphous, readily adsorbed impurities. In all systems, the sectorial selectivity of impurity incorporation into host crystals has been detected with partition coefficients many times higher than in the case of equilibrium partition. Specific capture of impurities by certain faces is accompanied by inhibition of their growth and modification of habit. The decrease in nonequilibrium partition coefficients with degree of oversaturation provides entrapment of impurities in the growing crystals. Thereby, the adsorption mechanism works in much the same mode for impurities of quite different nature. The behavior of partition coefficient differs drastically from impurity capturing by diffusion mechanism.
The phase equilibrium and growth of mixed (Ba,Pb)(NO 3 ) 2 crystals in aqueous solutions were investigated. The microcrystallization method was adapted to systems with isomorphic components, where crystal composition deviates from the thermodynamic equilibrium even at a low supercooling. The solid phase is characterized by continuous miscibility of the components within the analyzed ranges of temperature and solution composition. The diagram is characterized by substantial nonlinearity of the solubility isotherms and nonuniformity of the solid isocomposite location. Quasiequilibrium paths change their slope depending on solution enrichment in Ba(NO 3 ) 2 and depletion in Pb(NO 3 ) 2 . The area of curvature of quasiequilibrium paths is coordinated with the area of the changing isotherm slope, i.e., the area of "remarkable" points, where the behavior of the system changes drastically. Examples of theoretical zoning of a crystal approximated to a sphere were calculated for paths at a temperature decreasing from 50 to 15 ° C. The content of the Ba component decreases toward the periphery with the consecutive overgrowing of zones. Each zone corresponds to one gram of (Ba,Pb)(NO 3 ) 2 . Crystals grown from different initial solutions consist of different numbers of zones owing to the nonlinearity of solubility isotherms. Specific features of mixed crystal formation should be taken into account in genetic interpretation of natural minerals of mixed composition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.