Filament silver

Enclosed nitrate filaments can be thermally decomposed to silver by a simple heat treatment. In opposition to electron irradiation that fragments the filaments, the simple heating yields continuous metal nanorods (see Fig. 6 for a silver filament generated by a 60 min. treatment at 400°C, pressure lO Torr). 

Gold, silver Filaments Precious metals (silver or gold)... 

Developed silver is usually filamentary in nature and often occupies about the same volume as the original silver halide grain but as a complex tangle of silver filaments (Figure 2). 

The spherical growth of the latent image will accelerate because of the increase in surface area and Berry [98] suggested that once the rate reaches a value such that the rate of diffusion of silver atoms on the surface of the growing speck is unable to maintain a spherical shape, silver filaments move out from the grain surface. 

Gorbunova KM, Pankov PD (1949) Regularities in the crystallization of thin silver filaments. Zh Fiz Khim 23 616-624 (in Russian)... 

Electrol5dic silver is not practical for most PWB applications because of the high cost of plating a relatively thick silver deposit, and because of the reliability concerns associated with silver migration. Under certain conditions of temperature, humidity, and electrical bias, silver migrates from one pad to another as shown in Fig. 14. The silver filaments that form as a result of the migration are conductive and can cause electrical failures due to short circuits. 

There are, however, technical limitations to substitution. Some materials are used in ways not easily filled by others. Platinum as a catalyst, liquid helium as a refrigerant, and silver on electrical contact areas cannot be replaced they perform a unique function - they are, so to speak, the vitamins of engineering materials. Others - a replacement for tungsten for lamp filaments, for example - would require the development of a whole new technology, and this can take many years. Finally,... 

Much care had to be taken during the TEM observations of silver nitrate filled tubes, because this salt is very sensitive to electron irradiation and the continuous filaments transformed quickly into a chain of silver particles (see Fig. 5) [22]. 

Figure 18.1 Typical tangle (T) and plaque (P) as visualised by silver impregnation in the cerebral cortex of a case of Alzheimer s disease. The extracellular plaque (10-50 pm diameter) consists of a central core of amyloid surrounded by glial processes and a number of neurites in a ring formation. The intracellular cytoplasmic tangle is composed of helical filaments in a paired format. (Reproduced with permission of Academic Press from Wischik and Crowther 1986)...

Fig. 6.11. The schematics of experimental set-up to study emission of atomic oxygen. 1 — sensor of oxygen atoms 2 samples of reduced silver 3 shutter 4 weights to brake membranes 5 platinum filament to calibrate sensor against the concentration of oxygen atoms.

The above conclusion was confirmed by control experiment. It is well known [47] that freshly deposited silver films are very efficient in adsorption of atomic oxygen at room temperature. Therefore, the attachment covered by Ag-film similar to that with a Co304-covering should completely stop the flux of oxygen atoms. (The experiment with the known source of oxygen atoms - hot Pt-filament - confirms the efficiency of above attachment). It occurred [44] that in case of particles leaving the Ag surface such an attachment completely shuts down the flux of particles from the surface of the sample under investigation. 

The first fibers used by humans were probably those that occur naturally as tissues or excretions of either vegetables or animals (see Table 87). At much later times, after metals had been discovered, humans also learned to manufacture - from some of the ductile metals, mainly gold, silver, and their alloys - thin filaments (not fibers, however), which have since been used to decorate textile fabrics. It was only during the twentieth century, after synthetic plastics were discovered, that it became possible to make artificial human made fibers. The great majority of the natural fibers, such as cotton and wool, occur as staple fibers, short fibers whose length is measured in centimeters. Silk is different from all other natural fibers in that it occurs as extremely long and continuous filaments several hundred meters long. 

Metal Threads. Metal threads, not really metal fibers but metal filaments, are human-made. In antiquity, metal threads were made for ornamental or decorative purposes from precious, ductile metals or alloys, particularly silver and gold and their alloys. Such threads were either applied with adhesives to finished fabrics or wound around ordinary textile yam cores the metal-covered yarn was then either woven into textile fabrics or embroidered on the textile fabric (Jaro and Toth 1991 Lee-Whitmann and Skelton 1984). 

KU, in co-operation with a German battery manufacturer, managed within a short time to produce silver GDE with a low PTFE content and to adapt them to the chlor-alkali technology in test cells. An examination of the GDE manufactured using a special process shows that the active silver centres of the GDE are held together by PTFE filaments in the form of a spider s web (Fig. 16.14). 

Data on the critical temperature of deposition of silver on glass are unsatisfactory. Knudsen (47) gives the critical temperature as above 575°. Cockcroft, however, reports critical temperatures ranging from —90 to —15°, depending on the filament temperature, for deposition of silver on mica. 

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