Filiform

Silver sulfide is exceptionally stable in air and sunlight, but decomposes when heated to 810°C. Moss silver (filiform silver), consisting of long hair-like growths of pure silver, is formed when silver sulfide is heated for a prolonged period at elevated temperatures below 810°C. 

Filiform Corrosion-type of corrosion that takes place under a film in the form of randomly distributed hairlines. 

Fades, m. thread filament, fiber (of wood) grain twine fathom (Sugar) string, faden-ahnlieh, -artig, -fSrmig, a. thread-like, filamentous, filiform. 

Faser-asbest, m. fibrous asbestos, -asche, /. fiber ash. -bildung, /. fiber formation, fibra-tion. -blende, /. fibrous sphalerite. Faserchen, n. little fiber, fibril, filament. Faserfarbung, /. coloration of the fiber, faserfdrmig, a. fibrous, filiform. 

The various types of localised corrosion have been enumerated in Table 1.2 in Section 1.1, and many of them are dealt with in some detail in other sections of this volume. For this reason this section will be confined to a consideration of the factors that give rise to crevice corrosion, filiform corrosion, pitting, selective leaching and erosion-corrosion and of the mechanisms of these forms of localised attack. 

The importance of occluded cells cannot be overemphasised, and Brown considers that pitting, crevice corrosion, intergranular attack, filiform corrosion and hydrogen cracking are characterised by local acidification due to hydrolysis of metal ions, and that this phenomenon is of major significance in the overall mechanism. 

Filiform corrosion is characterised by the formation of a network of threadlike filaments of corrosion products on the surface of a metal coated with a transparent lacquer or a paint him, as a result of exposure to a humid atmosphere. This phenomenon first attracted attention because of its formation on lacquered steel, and for this reason it is sometimes referred to as underfilm corrosion, but although it is most readily observed under a transparent lacquer it can also occur under an opaque paint film or on a bare metal surface. Filiform corrosion has been observed on steel, zinc, magnesium and aluminium coated with lacquers and paints, and with aluminium foil coated with paper. Surface treatment of the metal by phosphating or chromating lessens the tendency for filiform corrosion to occur, but it is not completely... 

The main factor in causing filiform corrosion is the relative humidity of the atmosphere, and if this is below 65% (the critical relative humidity for the atmospheric corrosion of most metals, see Section 2.2) it will not occur. As the relative humidity increases the thickness of the filaments increases at 65-80% relative humidity they are very thin, at 80-95% relative humidity they are much wider and at approximately 95% relative humidity they broaden sufficiehtly to form blisters. 

Fig. 1.52 Mechanism of filiform corrosion showing how atmospheric oxygen and watCT enter the active head through the film (lacquer) and how water leaves through the inactive tail. This results in a high concentration of oxygen at the V -shaped interface between the tail and the head, and to a differential aeration cell (after Uhlig )...

This appears as a random non-branching white tunnel of corrosion product either on the surface of non-protected metal or beneath thin surface coatings. It is a structurally insensitive form of corrosion which is more often detrimental to appearance than strength, although thin foil may be perforated and attack of thin clad sheet (as used in aircraft construction) may expose the less corrosion resistant aluminium alloy core. Filiform corrosion is not commonly experienced with aluminium, as reflected by the insignificance afforded it in reviews on the phenomena (Section 1.6). 

A patchy form of rust that attacks paint films from underneath, can be caused by sweaty hands, residues from fluxes, etc. Examples of the latter include residues from phosphating and soluble salts (including those from unsuitable rinsing water) and they can manifest themselves on steel in the form of a creeping filiform corrosion, i.e. as progressing threads of rust which loosen the coating. This can be followed visually through transparent films. It occurs, however, only when the relative humidity of the surround-... 

Even small traces of certain corrosion stimulants, notably soluble chlorides and sulphates, can maintain a continuing corrosion process under a paint film because the salts accelerate the initial dissolution of ferrous iron (and other metal ions) but are not immobilised in the hydrated oxide corrosion products. Filiform corrosion is the most spectacular example of this phenomenon, but progressive spread, preceded by blistering, is also observed from scratches or other breaks in a coating, for example during salt spray tests. 

Filiform Corrosion a form of corrosion under paint coatings on metals characterised by a thread-like form advancing by means of a growing head or point. 

D 2803 1982 (1987) Test method for filiform corrosion resistance of organic coatings... 

General rules for corrosion tests applicable to storage conditions Filiform corrosion test on steel Liquefied petroleum gases-corrosiveness to copper. Copper strip test Road vehicles-brake linings-resistance to water, saline solution, oil and brake fluid-test procedure... 

Filiform Corrosion corrosion in the form of hairs or filaments progressing across a metal surface. 

It resists pinpoint rust formation before enameling and filiform corrosion after enameling. 

Filament winding, 26 767, 768 of thermosetting resins, 19 558 Filament-winding resin-impregnated glass rovings, 20 117 Filament yarns, 11 250 acrylic, 11 212 Filiform corrosion, 7 174 Filled fibers, encapsulation spinning of, 16 26... 

Figure 1. The assignments of FTIR-RA spectra of unaged epoxy free and coated films on steel have been given previously ( ). It should be noted that this aged specimen exhibited extensive filiform corrosion after 7 months exposure. Figures 2 show the spectral changes at different exposure periods. These spectra have been normalized for the baseline shift resulting from the reflection change of the steel substrate due to exposure and corrosion.

In his recent book, Dietrich (1985) described the common habits of tourmaline as being acicular, filiform, asbestiform, and chalcedonylike, and as whiskers. This last term indicates that tourmaline composition fibers have been synthesized. The wide range of forms for minerals in this group probably accounts for some of the early confusion when samples of tourmaline were equated with asbestos. Schorl, now known to be NaFe Al6(B03)3Si60ig(0H)4, usually occurs as dark green or black acicular crystals. Based on their appearance alone, schorl could easily be mistaken for an amphibole. 

Filiform Having the shape of a thread or filiment, roughly 10 microns or less in thickness (=fine-fibrous). The term is often applied to wirelike growths of native metals. 

Sease C, Selwyn LS, Zubiate S, Bowers DF, Atkins DR (1997) Problems with coated silver whisker formation and possible filiform corrosion, Stud Conserv 42 1-10271. 

The absence of magnetic monopole implies the conditions V = 0 and B = -Vx = 0, which are consistent with the relations given above, since B =VAA =0. However, as with the A vector potential, the equality Bx = = Vx / 0 enables us to define a scalar potential x that can be calculated on the basis of Biot-Savart law for a filiform (filament-shaped) circuit... 

Description.—Gum-tragacanth, s wirite, yellowish, or yellowish-brown, and occurs either in moderately large, broad, thin pieces, marked with archod or concentric elevations—flaky tragacanth,—or in small, twisted, filiform, spil d fragments—vermiform tragacanth, The former is the kind usually found in this country, while the latter is common cn the Continent. 

Fry, G., 1989. 13c/12c ratios and the trophic importance of algae in Florida Syringodium filiforme seagrass meadows. Mar. Biol., 79 11-19. 

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