Controlled double-jet precipitation

Another very useful technique that alleviates some of the aforementioned difficulties is the controlled double-jet precipitation (CDJP) process, which can be extended to a triple jet design. The technique was originally developed to produce uniform large particles (23-25), particularly of silver halides for photographic applications. Recently, it was demonstrated that the procedure may be used for the synthesis of a variety of uniform dispersions, including those of metal oxides of different modal sizes, ranging from several nanometers to several micrometers (26-29). 

Cu(I) oxide particles of different shapes were obtained by reductive hydrolysis of Cu(II) tartrate solutions in the presence of glucose (107,109) using a process originally described by Andreasen (106). More recently, an extensive study dealt with the precipitation of different copper (hydrous) oxide and oxide particles using controlled double-jet precipitation (CDJP). Thus, depending on experimental conditions, hexagonal platelets or rods of Cu2(0H)3N03 and ellipsoids or needles of CuO... 

The emulsions used in this work were composed of the suspension of AgBr grains in aqueous gelatin solution, and were prepared by the controlled double-jet precipitation method. The edge lengths... 

Using the same technique, it is also possible to precipitate composite particulates. The latter can be homogeneous of exact stoichiometry, as exemplified by pure or doped barium titanates [9]. To achieve these conditions rapid mixing is required, such as by using the controlled double jet precipitation process. In contrast, slow precipitation results, as a rule, in internal inhomogeneity, that is, the composition changes from the center to the periphery, although the particles may still be perfectly spherical, as observed with mixed alumina/silica [10] or copper/ lanthanum and copper/yttrium oxides [11]. 

Y.-S. Her, E. Matijevic, and M.C. Chon Preparation of Well Defined Colloidal Barium Titanate Crystals by the Controlled Double Jet Precipitation. J. Mater. Res., 10, 3106-3114 (1995). Controlled Double-Jet Precipitation of Uniform Colloidal CiystalUne Sr-and Zr-Doped Barium Titanates. J. Mater. Res., 11, 3121-3127 (1996). 

Stavek, J., Sipek, M., Hirasawa, I. and Toyokura, K. (1992) Controlled double-jet precipitation of sparingly soluble salts. Chemical Materials, 4, 545 -555. 

Its importance will become apparent during the discussion of experimental results. The validity of eq (1) was experimentally tested by double-jet precipitation of AgBr where reactant addition rate R, pAg and solubility, and temperature were closely controlled. In these experiments, initial reactor volume and gelatin concentration (2-8% grange) did not significantly affect the number of stable nuclei. 

In any batch precipitation scheme, a selection must be made between a high-yield, high-supersaturation (without exceeding the critical supersaturation), short operation, and a longer batch time, low-supersaturation one. Such a decision must weigh both the product properties desired and the cost factor associated with the implementation of either scheme. Often, additional considerations may need to be taken into account. For example, as reported by Yokoyama and Toyokura (1993), different polymorphic forms of precipitate can be obtained by controlling the supersaturation level in a double jet-precipitation. 

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