Corrosion poultice

In this regard, depending on the species, freshly cut wood contains over 50% moisture and organic acids that can be quite corrosive. Properly dried (kilned) wood is much more compatible. Wood treated against disease and insects may contain chemicals that can leach out and be corrosive. Some aerosol-type fungicides required for international shipment in wood containers can be particularly corrosive. 

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The mechanism of poultice corrosion is shown diagramatically in Figure 4. Corrosion initially occurs uniformly over the whole metal surface. However, as the process continues, the oxygen reduction cathodic reaction may become restricted to a band near the surface where oxygen is readily available. Corrosion of metal then takes place preferentially slightly below the band. The pH rises in the cathodic reaction area due to an increase in hydroxyl ion concentration while the anodic area decreases in pH due to the hydrolysis of metal chloride reaction products. 

Figure 4. Mechanism of poultice corrosion of auto steel showing initial and advanced stages.

To reproduce poultice corrosion in the lab, samples were immersed in washed sand saturated with a solution of interest, as described previously ( 8). When bare steel samples were tested in... 

Baboian, R. and Turcotte, R. C. "Development of Poultice Corrosion Tests for Automobiles" National Assoc, of Corrosion Eng. Paper Number 383, presented at N.A.C.E. Corrosion/85, March, 1985. 

CORROSION, DEPOSIT (also called poultice corrosion) - Corrosion occuring under or around a discontinous deposit on a metallic surface. 

Under-deposit attack or poultice corrosion may occur when a metal is locally covered by foreign, absorbent (organic or inorganic) materials [40,45]. In this case, attack can proceed even when the bulk of the system is dry due to retention of moisture in the poultice. The corrosion mechanism is similar to crevice corrosion in that the deposits act to limit the migration of oxygen to the covered area. This leads to acidic shifts in pH, concentration of Cl ions in the shielded area, and a shift to a more active corrosion potential under the deposit. Local corrosion rates can be very high due to the large cathode-to-anode area ratio. 

Probably the most common type of localized corrosion is pitting, in which small volumes of metal are removed by corrosion from certain areas on the surface to produce craters or pits that may culminate in complete perforation of a pipe or vessel wall (Fig. 6.8). Pitting corrosion may occur on a metal surface in a stagnant or slow-moving liquid. It may also be the first step in crevice corrosion, poultice corrosion, and many of the corrosion cells described in Chap. 7. 

Crevice and Poultice Corrosion In Cars. The average life of a car was... 

Poultice corrosion is a special form of crevice corrosion which forms when absorptive debris such as paper, wood, asbestos, sacking, cloth, and so forth., are in contact with a metal surface that becomes wetted periodically. No action occurs while the entire assembly is... 

Crevice corrosion, including corrosion under tubercles or deposits, filiform corrosion, and poultice corrosion... 

T3 Rolled surface Edges Crevices Deep pits No attack None Broad pits Pits coming from rolled surface 5 sites Extensive poultice corrosion... 

Corrosion occurring under or around a discontinuous deposit on a metalhc surface. Also called poultice corrosion. 

Poultice corrosion also occurs under deposits of road debris, such as mud that is deposited on the underside of automobile fenders and at other locations. These d osits hold corrosive substances such as road salt and abraded metal particles (e.g., brake dust) in... 

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