Material silver halides

Principle. A known weight of the substance is heated with fuming nitric acid and silver nitrate in a sealed tube. The organic material is thus oxidised to carbon dioxide and water, whilst the halogen is converted quantitatively into the corresponding silver halide. The latter js subsequently washed out of the tube, filtered and weighed. 

A derivative of 163, 3-(2-morpholinoethylthio)[l,2,4]triazino[5,6-fo]indole dihydrochloride, is used as a thrombolytic (91URP1672373). Derivatives of the pyrazolo[5,l-c][l, 2,4]tria-zines were used as a constituent of silver halide color photographic supported material, which showed good color reproducibility [91JAP(K)03/291649]. The protective action of [l,2,4]triazino[4,3-a]benzimidazoles as corrosion inhibitors was studied (91MI8). 

At a given ideal composition, two or more types of defects are always present in every compound. The dominant combinations of defects depend on the type of material. The most prominent examples are named after Frenkel and Schottky. Ions or atoms leave their regular lattice sites and are displaced to an interstitial site or move to the surface simultaneously with other ions or atoms, respectively, in order to balance the charge and local composition. Silver halides show dominant Frenkel disorder, whereas alkali halides show mostly Schottky defects. 

Dye release developers are themselves colored molecules, the presence of which in silver halide photographic materials could interfere with light capture by the light-sensitive silver halide. Less light would be available to the sensitizing dyes. Another approach has been reported in which the leuco dye is linked to the coupling-off position of conventional photographic color... 

Silver halide electrodes (with properties similar to electrodes of the second kind) are made of AgCl, AgBr and Agl. These electrodes, containing also Ag2S, are used for the determination of Cl-, Br, I and CN ions in various inorganic and biological materials. 

Silver halide fibres (AgClxBri x) have the widest spectral range in the mid-IR, well into the fingerprint range. Due to their crystalline nature, they have a superior flexibility. Problematic is their tendency to decompose upon contact with UV radiation or base metals. Also sulphides will chemically destroy the fibre material. Other points against are the high intrinsic attenuation due to absorption by impurities or scattering at inclusions or micro-crystals and the non-availability of (applicable) core-clad fibres. 

These incorporate membranes fabricated from insoluble crystalline materials. They can be in the form of a single crystal, a compressed disc of micro-crystalline material or an agglomerate of micro-crystals embedded in a silicone rubber or paraffin matrix which is moulded in the form of a thin disc. The materials used are highly insoluble salts such as lanthanum fluoride, barium sulphate, silver halides and metal sulphides. These types of membrane show a selective and Nemstian response to solutions containing either the cation or the anion of the salt used. Factors to be considered in the fabrication of a suitable membrane include solubility, mechanical strength, conductivity and resistance to abrasion or corrosion. 

Silver halide and thiocyanate membranes would respond in a similar way to a silver sulphide membrane, Ag+ ions being the mobile species, but by themselves make unsuitable membrane materials. A Nernstian response is, however, retained when they are incorporated into a Ag2S matrix, the membrane behaving as if it were a pure halide or thiocyanate conductor, i.e. 

Photochromic dyes, 20 516 Photochromic glass silver in, 22 658, 686 as a solar energy material, 23 5 Photochromic lenses, 6 588, 601-602 Photochromic materials, 6 587-606 inorganic, 6 589-592 organic, 6 592-601 polyoxometalates, 6 591-592 silver halide-containing glasses, 6 589-590... 

In order to circumvent this sensitivity limitation, the San Jose researchers sought to design resist materials that incorporate chemical amplification of the sort that characterizes the silver halide photographic emulsion system. In these systems a single photo event initiates a cascade of subsequent chemical reactions that ultimately result in the intended function. 

The use of ISEs in non-aqueous media(for a survey see [125,128]) is limited to electrodes with solid or glassy membranes. Even here there are further limitations connected with membrane material dissolution as a result of complexation by the solvent and damage to the membrane matrix or to the cement between the membrane and the electrode body. Silver halide electrodes have been used in methanol, ethanol, n-propanol, /so-propanol and other aliphatic alcohols, dimethylformamide, acetic acid and mixtures with water [40, 81, 121, 128]. The slope of the ISE potential dependence on the logarithm of the activity decreases with decreasing dielectric constant of the medium. With the fluoride ISE, the theoretical slope was found in ethanol-water mixtures [95] and in dimethylsulphoxide [23], and with PbS ISE in alcohols, their mixtures with water, dioxan and dimethylsulphoxide [134]. The standard Gibbs energies for the transfer of ions from water into these media were also determined [27, 30] using ISEs in non-aqueous media. 

The group of ion-selective electrodes with fixed ion-exchange sites includes systems with various membrane structures. The membranes are either homogeneous (single crystals, pressed pellets, sintered materials) or heterogeneous, set in an inactive skeleton of various polymeric materials. Important electrode materials include silver halides, silver and divalent metal chalcogenides, lanthanum trifluoride and various glassy materials. Here, the latter will be surveyed only briefly, for the sake of completeness. 

The light-sensitive layer of the present-day photographic material consists essentially of a large number (e.g., 108 per square centimeter) of tiny crystals of silver halide embedded in a layer of gelatin. The tiny crystals, or grains as they are commonly called, of the most sensitive photographic materials are composed of silver bromide, a small percentage of iodide, and a very small but very important amount of silver sulfide (Sheppard, 1) or possibly silver (Carroll and Hubbard, la) or both. The halide in the less sensitive materials may be simply bromide, chloride, or mixtures of the two. 

The mechanisms of the other methods of Intensification are more in doubt (cf. review by Sheppard el ah, 76). These methods include bathing the photographic material in a solution of silver salt, in a solution of hydrogen peroxide or sodium perborate (Vanselow et ah, 77), in a solution of aurous thiocyanate (James et ah, 31) or by fuming the material in the vapor of certain organic acids (Mueller and Bates, 78) or of ammonia. Such treatment may result in an increase in the effective size of the sub-nuclei, or simply in bringing about more favorable conditions for development at the silver/silver halide interface. 

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