Anodes, aluminum composite

FIG. 5-12 Variation of absorptivity with temperature of radiation source. (1) Slate composition roofing. (2) Linoleum, red brown. (3) Asbestos slate. (4) Soft rubber, gray. (5) Concrete. (6) Porcelain. (7) Vitreous enamel, white. (8) Red brick. (9) Cork. (10) White dutch tile. (11) White chamotte. (12) MgO, evaporated. (13) Anodized aluminum. (14) Aluminum paint. (15) Polished aluminum. (16) Graphite. The two dashed lines bound the limits of data on gray paving brick, asbestos paper, wood, various cloths, plaster of parts, lithopone, and paper. To convert degrees Ranldne to kelvins, multiply by (5.556)(10 ). 

XPS was used to determine the surface composition of the anodized aluminum substrate during exposure to warm, moist environments. The information obtained was used to construct surface behavior diagrams that showed that hydration of the surface involved three steps [38]. Step one, which was reversible, consisted of adsorption of water onto the AIPO4 monolayer. The second step, which was rate-controlling, involves dissolution of the phosphate followed by rapid hydration... 

In any event, practical solutions to the problem were found. The simplest solution is to coat the surfaces of polymeric composites and other sensitive surfaces with thin films of materials that resist corrosion. Among the coatings that appear to provide protection are anodized aluminum and thin layers of sputtered nickel. 

Aluminum spraying is used to coat less corrosion-resistant alloys. In the case of some composites, corrosion is due to the galvanic action between the aluminum matrix and the reinforcing material. Aluminum thermal spraying has been successfully used for the protection of the discontinous silicon carbide/aluminum composites, and continuous graphite/aluminum. Other protection procedures include sulfuric acid anodizing and iron vapor deposition on aluminum.44... 

Soil Clay, particulate, oil, grease Surface Painted, anodized aluminum Application Method Spray/brush/wipe Manufacture Ribbon or paddle blender Composition A % Wt... 

A number of factors have, however, been shown to be important, including (1) a stable oxide is important as this can prevent or minimize the formation of a relatively weakly bound inorganic layer (2) a topography that favors mechanical keying and provides an increased area over which interfacial interactions can occur is clearly beneficial. In the case of phosphoric acid anodized aluminum, the adhesive is thought to form a composite with the oxide structure. Strong interaction between the adhesive and the substrate is necessary to prevent the displacement of the adhesive by water. 

Corrosion Properties. In addition to corrosion problems such as pitting and exfoliation ced by conventional (monolithic) aluminum alloys, galvanic corrosion caused by the potential difference between the graphite fibers and the aluminum matrix is a reason for concern in these composites. As shown in Table 1, graphite appears at the cathodic (noble) end of the galvanic series while aluminum is at the anodic (active) end of the series. Graphite/aluminum composites have been shown to corrode 80 times faster than monolithic aluminum alloys in an aerated 3.15 wt% sodium chloride (NaCl) at room temperature (Ref 8). 

Anodized coatings on SiC/aluminum composites provide satisflictoiy corrosion protection, but they are not as effective as anodized coatings are for unieinfor-ced aluminum because the structure of the anodized layer is affected by the SiC particulates (the particulates interfere with the formation of a continuous barrier layer). TaUe 3 shows a comparison of pitting times and crevice times for sulfriric acid-an ized samples with a hot water seal with those of hard anodized SiCyahiminum. The corrosion resistance of the hard aiaxlized SiC/aluminum is less than that of the conventional anodized SiC/aluminum because the area fraction of the continuous barrier layer for hard anodized SiC/ahiminum is less than that for conventionally anodized SiC/alimiinum. 

Knoevenagel condensation of malonic acid with heptaldehyde [111-71-7] followed by ring closure, gives the fragrance y-nonanoic lactone [104-61-0] (6) (14). Beside organic synthesis, malonic acid can also be used as electrolyte additive for anodization of aluminum [7429-90-5] (15), or as additive in adhesive compositions (16). 

The anodized surface is often subjected to additional treatment before the radiation-sensitive coating is appHed. The use of aqueous sodium siUcate is well known and is claimed to improve the adhesion of diazo-based compositions ia particular (62), to reduce aluminum metal-catalyzed degradation of the coating, and to assist ia release after exposure and on development. Poly(viQyl phosphonic acid) (63) and copolymers (64) are also used. SiUcate is normally employed for negative-workiag coatings but rarely for positive ones. The latter are reported (65) to benefit from the use of potassium flu o r o zirc onate. 

Table 6-3 Composition (wt.%) and properties of aluminum alloys for anodes...

The quality control of galvanic anodes is reduced mainly to the analytical control of the chemical composition of the alloy, to the quality and coating of the support, to an adequate joint between support and anode material, as well as to restricting the weight and size of the anode. The standards in Refs. 6, 7, 22, 27, 31 refer to magnesium and zinc anodes. Corresponding specifications for aluminum anodes do not exist. In addition, the lowest values of the rest potentials are also given [16]. The analytical data represent the minimum requirements, which are usually exceeded. 

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