Silver-black film

Fig. 2.10 (a) The cross-section of a black-silver film (b) the cross-section of a black-yellow-silver film where fluid has accumulated in the yellow region. 

Silver is attacked by most compounds of sulphur, becoming covered with a yellow, brown or black sulphide film. 

Silica-gel-precoated preparative TLC plates impregnated with AgNOj are widely applied in this technique [60,90]. To impregnate a silica-precoated plate with silver nitrate, the plate is dipped for 3 min in a 1% AgNOj solution in a methanol-water mixture (4 1, v v). The plate is then dried, first in air with exclusion of light, and next, it is activated at 80°C in a drying oven. If impregnated plates are not used immediately, they should be stored wrapped in black plastic film in a desiccator [90-92]. 

Figure 19.2 Self-similarity analysis for nanotextured silver surfaces prepared in different ways. The root mean square roughness inferred from atomic force microscopy is plotted versus measurement area. The various surfaces are 100 nm thick evaporated silver films (solid squares, red line)-, 5.2 nm thick evaporated silver films (open circles, green line) nanoparticle films assembled from colloid attachment to self-assembled monolayers (solid circles, blue line) films from deliberate precipitation of silver colloid (solid up-triangles, black line) Tollens reaction films (open down-triangles, orange line). Lines with slopes H = 1.0 and H = l.S representing two-dimensional and 1.5 dimensional surfaces respectively are...

Black Film Fluid films yield interference colors in reflected white light that are characteristic of their thickness. At a thickness of about 0.1 /xm, the films appear white and are termed silver films. At reduced thicknesses, they first become grey and then black (black films). Among thin equilibrium (black) films, one may distinguish those that correspond to a primary minimum in interaction energy, typically at about 5-nm thickness (Newton black films) from those that correspond to a secondary minimum, typically at about 30-nm thickness (common black films). 

Formulations similar to those used in Dry Silver but without the AgX component are light stable but can be imaged thermally. The silver behenate develops to form a black silver image where (and only where) heat is applied. Materials of this type were originally intended for reflex exposure. Here the film is sandwiched with a document and exposed to a source of infrared radiation. The ink on the document absorbs the infrared and converts it to heat, which initiates development of the film, where it is in contact with the ink image on the paper. Overhead projector transparencies, sometimes called view graphs, ... 

Photographic and diazo-type papers are coated with colloidal silica (720-723). In Polaroid photographic Film colloidal silica plays an essential role in the receiving layer to which the image is transferred and in which the black silver positive image is... 

When silver halide emulsions are used as photographic films, development of the parts exposed to light to give black silver is followed by fixing, which is simply metal complexing. The unchanged (nonimaged) silver halide (usually chloride and bromide) must be removed before... 

Typical fillers filmed silica, calcium carbonate, carbon black, silver, glass beads, metal powders, precipitated silica, aluminum oxide, montmorillonite, mica, zinc oxide... 

The boundary between the black and silver region is horizontal except near the vertical border. This sudden change in colour from black to silver at a horizontal level indicates that the thickness of the film has altered rapidly. This region is indicated in Fig. 2.8 by the horizontal level at which the thin black film meets the draining film. This is an important characteristic that distinguishes the simple mobile film from the irregular mobile film. The rapid variation in the thickness of the film at the black-silver border occurs when the thickness of the film becomes comparable to the range of the van der Waals interaction between the water molecules in the film. 

Fig. 2.11 The stages in the production of critical fall (a) the isolation of a region of silver film by the black film (b) the resulting thickening of the silver film causes it to sink into the coloured film (c) this causes the growth of a river of black film (d) tributaries of black film form and rise to form lakes .

The fixed plate is now a negative , for those patches on which most light fell are black. The process is reversed in printing to make the positive —the printing paper having a covering of silver chloride or bromide or a mixture of the two. This, in turn, is developed and fixed as was the plate or film. 

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

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