Silver bromide particles

In brief, the fixing process is the removal, after exposure and development, of unused silver halides, such as silver bromide, from the paper or film. This is necessary because unused silver bromide particles will eventually ruin the image. For this reason proper fixation is as important to the print-making process as proper development. Fixing can make the difference between an image of lasting value and an image that doesn t last. 

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). 

The ability to make very precise measurements has allowed us to use the disk centrifuge to determine the thickness of adsorbed gelatin layers on silver bromide particles (4). When particles are coated with an adsorbed polymer layer, the sedimentation time reflects the size and density of the particle core as well as the thickness and density of the adsorbed layer. An apparent (incor-... 

Rapid mixing of silver nitrate and sodium bromide may produce a hydrophobic colloidal suspension rather than a precipitate of silver bromide. The tiny silver bromide particles are kept from further aggregation by Brownian motion, the motion of small particles resulting from constant collisions with solvent molecules. The sol is further stabilized by adsorption of ions on the surfaces of the particles. The adsorbed ions are hydrated by surrounding water molecules and help prevent further aggregation. 

Figure 11.5 Change with electrolyte concentration of the potential energy (a) and stability ratio (b) curves for silver bromide particles with a zeta potential equal to -50 mV and a particle radius of 50 nm. The electrolyte is symmetrical and of 1 1 type. In (a), the top curve corresponds to 5 mM, then follows 20 mM, and finally 50 mM. Reprinted from Goodwin (2009), with permission from John Wiley Sons, Ltd...

In order to distinguish between the two models of AgBr stabilization (see earlier), the NMR experiments mentioned have also been carried out in presence of silver bromide nanoparticles. As the only difference between the two experiments is the presence of silver bromide particles, all observed differences must be due to the particles. In the presence of these particles, the quantity of trapped water is larger, as shown by a comparison of spectra in the presence and in the absence of nanoparticles (Fig. 17). It could be hypothesized that the particles repel the boimd water into the interface and, as a consequence, the amount of trapped water increases. The total intensity is also higher in presence of silver bromide particles, also stemming from the greater importance of the trapped water. In fact, this water freezes at a lower temperature. Fmthermore, not all the water cores of the microemulsion... 

Synthesis of Silver Bromide Particles in the AOT/p-Xylene/Water Microemulsion... 

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

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. 

When a photographic film is developed, silver bromide is reduced by hydroquinone (the developer) in a basic aqueous solution to give quinone and tiny black particles of silver metal ... 

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

Consider Wiener s interference experiment shown in Fig. 11 on the particle theory. On this theory we have photons moving towards the mirror, which bounce off from it and come back. These photons pass through the photographic film as they move towards the mirror, and as they come back. If a photon hits a grain of silver bromide in the film, it is absorbed by the grain and so disappears. It is clear that the plate should be uniformly affected all over and not show the bands which are actually observed. In the bands, however, only some of the grains are affected, which cannot be explained on the wave theory. It is clear that what is required is some sort of combination of the two theories. This will be considered in the next chapter. 

The chance of the particle appearing anywhere is proportional to the intensity of the waves, and so we can say that there is an even chance that it will appear at A or B. The intensity of the waves will be uniform over the area on each plate on which the beam falls, so that the particle will be equally likely to appear at any point on these areas. A grain of silver bromide somewhere on one of these areas will be affected by the particle and will show up when the plates are developed. We cannot predict which plate the particle will appear at, or at what point it will appear. 

Lorenz and Hiege 3 state that exposure of silver chloride or bromide to light causes the separation of colloidal, metallic silver, the particles increasing in size as the action continues. They regard this phenomenon as constituting important e " hat the... 

Further work [86] showed that the specific surface free energy of silver particles was the same whether they were evaporated on carbon or silver bromide, but was lowered by coating with gelatin. The latter is given as the reason for the stabilizing effect of gelatin on latent image specks. 

They concluded that exchange exceeding the equilibrium value is due to phase transition. During aging the total number of precipitate particles decreases strongly. Meehan and Chiu found that for colloidal silver bromide the number of particles decreased 80-fold during the aging that occurred after 2 min and up to 1 day. 

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. ... 

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