Silver bromide dispersions

While examining time-dependent phenomena of silver bromide particles, we made many repeat measurements. With care, standard deviations could be kept below 1%. Figure 6, for instance, contains the diameters calculated from the peak maxima for 44 injections of a silver bromide dispersion. Four consecutive injections were made into the same dodecane-protected spin fluid, so that experiments in 10 different spin fluid gradients are represented here. Monitoring of the spin fluid temperature was required, since this variable affects both density and viscosity. Corrections were also made for the volume change of the spin fluid caused by successive injections Cl, 3). 

Figure 7. Apparent particle size distributions of a silver bromide dispersion (a) in 0.001 N NaNO with the gelatin layer...

Colloids are classified according to the phases of the substances involved (Table 15.10). A colloid that is a suspension of solids in a liquid is called a sol, and a suspension of one liquid in another is called an emulsion. For example, muddy water is a sol in which tiny flakes of clay are dispersed in water mayonnaise is an emulsion in which small droplets of water are suspended in vegetable oil. Photographic emulsions also contain solid colloidal particles of light-sensitive materials such as silver bromide. Foams are suspensions of a gas in a liquid or solid. Foam rubber, Styrofoam, soapsuds, and aerogels are foams. Zeolites (Box 13.4) are a type of solid foam in which the openings in the solid are comparable in size to molecules. 

Although S-sensitization decreases low intensity reciprocity failure it usually does not eliminate it. In our experiments with monodisperse fine-grain silver bromide emulsion, vacuum outgassing of the S-sensitized emulsion eliminated the LIRF, just as it did for the unsensitized emulsion. Moreover, the sensitivities of the two emulsions under vacuum were nearly the same. Whatever may be the role of S-sensitization in this emulsion, it became inconsequential for exposures made under vacuum. However, the degree of increase in sensitivity caused by S-sensitization of the fine grain emulsions for exposures in air is much smaller than can be achieved with coarse-grain poly-disperse emulsions. 

Production of the film or plate. A thin layer of gelatin containing a colloidal dispersion of silver bromide is placed on a film (made of cellulose nitrate or cellulose acetate) or a glass plate. After drying, the film (or plate) is ready for use. 

Other aging effects Aging due to cementing of primary particles is difiScult to observe directly because of other simultaneous changes. Nevertheless, it may be inferred that such processes going on in the flocculated state render impossible the subsequent peptization, or dispersal, of an aged product. Kolthofif and others have discussed the cementing process for barium sulfate, lead chromate, and silver bromide. ... 

Colloidal dispersions owe their stability to a surface charge and the resultant electrical repulsion of charged particles. This charge is acquired by adsorption of cations or anions on the surface. For example, an ionic precipitate placed in pure water will reach solubility equilibrium as determined by its solubility product, but the solid may not have the same attraction for both its ions. Solid silver iodide has greater attraction for iodide than for silver ions, so that the zero point of charge (the isoelectric point) corresponds to a silver ion concentration much greater than iodide, rather than to equal concentrations of the two ions. The isoelectric points of the three silver halides are ° silver chloride, pAg = 4, pCl = 5.7 silver bromide, pAg = 5.4, pBr = 6.9 silver iodide, pAg = 5.5, pi = 10.6. For barium sulfate the isoelectric point seems to be dependent on the source of the product and its de ee of perfection. ... 

A compound of iodine that deserves mention is silver iodide, Agl. It is a pale-yellow solid that darkens when exposed to light. In this respect it is similar to silver bromide. Silver iodide is sometimes used in cloud seeding, a process for inducing rainfall on a small scale (Figure 21.21). The advantage of using silver iodide is that enormous numbers of nuclei (that is, small particles of silver iodide on which ice crystals can form) become available. About 10 nuclei are produced from 1 g of Agl by vaporizing an acetone solution of silver iodide in a hot flame. The nuclei are then dispersed into the clouds from an airplane. 

Even without atomic resolution, AFM has proved its worth as a technique for the local surface structural determination of a number of bio-inorganic materials, such as natural calcium carbonate in clam and sea-urchin shells [123]. minerals such as mica [124] and molybdenite [125] as well as the surfaces of inorganic crystals, such as silver bromide [126] and sodium decatungstocerate [127]. This kind of information can prove invaluable in the understanding of phenomena such as biomineralization, the photographic process or catalysis, where the surface crystallography, especially the presence of defects and superstructures, can play an important role, but is difficult to determine by other methods. AFM has the considerable advantage that it can be used to examine powdered samples, either pressed into a pellet, if the contact mode is employed, or loosely dispersed on a surface, if intermittent or non-contact AFM is available. 

Mix equal amounts of 0.020 mol din sodium bromide solution and 0.018 mol dm silver nitrate solution. A colloidal dispersion of silver bromide is formed immediately. A silver iodide sol maybe prepared in a similar manner. 

The dispersed filter paper assists in the filtration of the silver halide, f Equivalent amounts of sodium or potassium bromide may be substituted for ammonium bromide. 

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