Growth of AgBr microcrystals during double-jet crystallization
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Growth of AgBr Microcrystals during Double-Jet Crystallization T. A. Larichev, E. V. Prosvirkina, A. B. Abisheva, E. N. Kharchenko, and B. A. Sechkarev Kemerovo State University, Krasnaya ul. 6, Kemerovo, 650043 Russia e-mail: [email protected] Received October 31, 2005
Abstract—The problems arising in description of mass crystallization of silver halides with application of the existing theoretical models are considered. It is shown that the growth of silver halide microcrystals is primarily related to the collective recrystallization in the system accompanied with transfer of material through the solution. On the basis of the results of investigation of mass-exchange processes between AgBr microcrystals in a gel medium, an improved qualitative model is proposed to describe the microcrystal growth during mass crystallization of silver halides. PACS numbers: 81.10.Jt DOI: 10.1134/S1063774507040219
INTRODUCTION The method of mass crystallization, which is widely used in modern chemical technology, makes it possible to obtain a large variety of solid-phase products with required characteristics. An example of such application is the production of silver halide photomaterials [1]. It is known that the detecting elements of a photographic film are silver halide (AgHal) microcrystals of complex structure and composition, about 0.1 µm in size [2]. For direct fabrication of a photographic emulsion, double-jet crystallization is most often used [1].
tion occurs, there are at least two zones with different properties in the reactor (Fig. 1). Homogeneous nucleation of AgHal occurs in one of these zones and predominantly recrystallization processes occur in the other zone.
The difficulties in development of an efficient theoretical model for adequate description of mass crystallization of poorly soluble compounds are well known [3]. The main problem is the necessity of taking into account the interaction between an immense number of simultaneously forming and growing crystals. In scientific photography, the model proposed by Berry in 1976 [4] is generally used to describe double-jet crystallization. This model made it possible to systematically and consistently explain the experimentally observed regularities of AgHal mass crystallization. In particular, it was explained why, despite the extremely low solubility of AgHal, introduction of reagents in the late synthesis stages does not lead to growth of new AgHal particles in the system. In accordance with this model, the solid phase formation occurs during the entire period of reagent introduction. However, unstable ultradisperse particles (nuclei) with a diameter no larger than 20 nm, newly formed in the region of reagent introduction, then penetrate the bulk of the reaction mixture, where they serve as a material for growth of larger crystals via Ostwald ripening. Thus, when double-jet crystalliza721
AgNO3 solution
KBr solution
1 4
2
3 Fig. 1. Schematic diagram of controlled double-jet crystallization: (1) growth zone (water–gelatin solution, t = 40– 60°C,
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