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Precipitation Processes in Concentrated Electrolytic Solutions and Temperature Effects on Silver Halide Sols in statu nascendi

Đ. Težak ; Institute »Ruder Boskovic«, 41000 Zagreb, Croatia, Yugoslavia

Puni tekst: engleski pdf 19.191 Kb

str. 275-295

preuzimanja: 71



For the differentiation of physical, and chemical characteristics
of various interactions playing part in interboundary ! layer) of solid/liquid systems the kinetics of precipitation
under systematic variation of internal and external factors, and
especially of concentration and temperature, is used.
The discontinuities in the formation of the precipitate as well
as the differences iin the morphology and behavior enables the
definition of the formation of various substructures as a result
of at least five subsystems from which the precipitating system is
usually composed.
For illustration some ionic systems, mainly exemplified by silver
halides, where the complexation, embryonation, nucleation, crystal
growth, micellation (formation of primary particles), and aggregation
(two-step crystalLisation, coagulation, or flocculation) could be
distinguished, are presented.
The solubility effects (in very great excess of one of the
precipitating ion - the complex solubility, and the simple ionic
solubility) and the changing pattern of the precipitation maxima
between two extremes are correlated to the prevailing tendencies
either of agglomeration (concentration maxima) or of ordering
(crystallisation maxima). The concentration maximum, and especially
the boundary towards the complex solubility limit is characterized
by various approaches to equilibrium states by direct mixing
of precipitation components at 20 °c, or by cooling the homogeneous,
already mixed systems from 90 °c to 20 oc.
The chemistry and physics of the surface layer of the solid,
the structure and specific concentrational condition (e . g., the ,steady
state in the stagnant layer) of the constituents in methorical layer,
and the chemical and physical changes occurring owing to the
difference in concentrations and entropy either in the methorical
layer or in bulk solution, are taken as responsible for stability/instability
conditions of the emerging colloidal particles.

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