Anodic paints

Figure 3.86 UF of electrocoat paint-stability of anodic paint flux with XM-50 membrane.

Marking on bare metals is achieved by laser engraving with Nd YAG laser. The pulse or CW CO2 lasers described above cannot mark on bare metal because the beam is reflected off the surface without any absorption. Therefore, metals can only be marked if they are anodized, painted, or coated with an absorbing material. 

SECM can also be used to gain information about the quality of the insulation on the conical tips. An approach curve is obtained at the air/solution interface, where the solution contains a redox mediator such as Fe(CN)g . The potential sufficient to reduce Fe(CN)g is applied to the tip and the tip current is monitored as the tip is moved from air into the aqueous ferricyanide solution. Figure 6.3.4.5a shows the air/solution approach curve for a finite conical tip insulated with anodic paint. No current flows until the tip first enters the solution, where the current then rises sharply in an UME transient, which decays to a constant steady-state current value. This constant value is maintained as more of the tip is immersed in solution. Figure 6.3.4.5a indicates that the tip is completely insulated with only the very end of the tip uncovered. In contrast, a poorly insulated tip showed leaks along the sides as more of the tip is immersed into the solution (Figure 6.3.4.5b). The tip current increases stepwise as more of the tip enters the solution. This behavior is an indication of pinholes in the insulating film. 

Insulation of the probe was insured by electrophoretic deposition of an anodic paint. The natural tendency of this kind of paint to retract upon curing resulted in the spontaneous exposure of the tip extremity, which formed an approximately hemispherical microelectrode characterized by a tip radius in the submicron range. In that sense, this hand-made probe was the first AFM-SECM probe integrating an actual (sub)-microelectrode. Again no electrochemical current images were recorded but contact mode AEM images allowed the electrochemically induced etch pits to be visualized (see Figure 21.4). 

FIGURE 21.3 Combined AFM-SECM probe hand-fabricated from an etched, flattened, and bent platinum microwire. The probe is isolated by an electrophoretic anodic paint, (a) SEM micrograph of the probe, showing the cantilever and the tip. (b) and (c) Close-up SEM images of the tip extremity. Upon curing the insulating film shrunk, uncovering the tip apex, which behaved as a micrometer-sized (in b) or submicrometer-sized (in c) conical microelectrode. (Erom Macpherson, J.V. and Unwin, P.R., Anal. Chem., 72, 276, 2000. With permission.)... 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

When the spectral characteristics of the source itself are of primary interest, dispersive or ftir spectrometers are readily adapted to emission spectroscopy. Commercial instmments usually have a port that can accept an input beam without disturbing the usual source optics. Infrared emission spectroscopy at ambient or only moderately elevated temperatures has the advantage that no sample preparation is necessary. It is particularly appHcable to opaque and highly scattering samples, anodized and painted surfaces, polymer films, and atmospheric species (135). The interferometric... 

Anodic deposition is controlled by either fluid shear (cross-flow filtration) (48), similar to gel-polarization control, or by continual anode replacement (electrodeposited paints) (46). High fluid shear rates can cause deviations from theory when E > (49). The EUF efficiency drops rapidly... 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

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 ). 

The transition resistance between the surface of the metal and the electrolyte with uncoated iron anodes in coke backfill, the transition resistance is usually low. With metals in soil, it can be increased by films of grease, paint, rust or deposits. It contains in addition an electrochemical polarization resistance that depends on the current [see Eq. (2-35)]. 

If the rf source is applied to the analysis of conducting bulk samples its figures of merit are very similar to those of the dc source [4.208]. This is also shown by comparative depth-profile analyses of commercial coatings an steel [4.209, 4.210]. The capability of the rf source is, however, unsurpassed in the analysis of poorly or nonconducting materials, e.g. anodic alumina films [4.211], chemical vapor deposition (CVD)-coated tool steels [4.212], composite materials such as ceramic coated steel [4.213], coated glass surfaces [4.214], and polymer coatings [4.209, 4.215, 4.216]. These coatings are used for automotive body parts and consist of a number of distinct polymer layers on a metallic substrate. The total thickness of the paint layers is typically more than 100 pm. An example of a quantitative depth profile on prepainted metal-coated steel is shown as in Fig. 4.39. 

CoiTosion prevention is achieved by correct choice of material of construction, by physical means (e.g. paints or metallic, porcelain, plastic or enamel linings or coatings) or by chemical means (e.g. alloying or coating). Some metals, e.g. aluminium, are rendered passive by the formation of an inert protective film. Alternatively a metal to be protected may be linked electrically to a more easily corroded metal, e.g. magnesium, to serve as a sacrificial anode. 

Chromium and compounds SPA Chromic acid Sodium dichromate Anodizing Cement Dyes Electroplating Paint Tanneries... 

The anodic oxidation of the iron is usually localized in surface pits and crevices which allow the formation of adherent rust over the remaining surface area. Eventually the lateral extension of the anodic area undermines the rust to produce loose flakes. Moreover, once an adherent film of rust has formed, simply painting over gives but poor protection. This is due to the presence of electrolytes such as iron(II) sulfate in the film so that painting merely seals in the ingredients for anodic oxidation. It then only requites the exposure of some other portion of the surface, where cathodic reduction can take place, for rusting beneath the paint to occur. 

Louvers can be supplied in various materials and finishes, the most common being anodized or painted aluminum, since this provides good corrosion resistance and light weight. Other options are galvanized steel or, for more rigorous conditions, stainless steel. 

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