Pitting cross-sectional shapes

Figure 6.16 Frequent variations of the cross-sectional shape of the pits (ASTM G46-94)4...

Fig. 7.4 Cross-sectional shapes of pits [5]. Reprinted, with permission, from ASTM G 46-94, Standard Guide for Examination and Evaluation of Pitting Corrosion, copyright ASTM International, West Conshohocken, PA.

Figure 6.11 Typical cross-sectional shapes of corrosion pits.

Figure 5.3 Typical variations in the cross-sectional shape of pits,...

BIm 1 Variations in the cross-sectional shape of pits, (a) Narrow and deep. (1 Elliptical c) Wide and shallow. d Subsurface. d Undercutting. f Shapes deter mined by microstructural orientation. Source ASTM G 44... 

Copyright 1982, American Chemical Society.) (A) SEM of interfiber pits in earluwood as seen on the wood radial face. Note the donut-shaped borders. (B and C) SEM of pit pairs between adjacent fibers cross-sectional suiface. (D) SEM ofbordered-pit membranes (PM) in face view of a split wood radial surface. (E) Light micrograph of pit pairs as seen in cross section with a light microscope. Key PM, pit membranes PB, pit border and PA, pit aperture. 

High molar mass molecules as well as occlusions in the pits or lumens may inhibit flow. Since it can be assumed that the penetration depends on the ratio between the average diameter of the vessels in beech (earlywood 30 pm, latewood 67 pm) on the one hand and the average size of resin molecules on the other hand, the measured average depth of penetration (AP) can be correlated with the molar mass and with the viscosity of the resin. The same dependence can be expected also for fir, with an average size of the cross section of tracheids of 17 pm x 30 pm in earlywood and 10 pm X 17 pm in latewood, simplifying the cross section of such tracheids as the shape of a rectangle. 

We will consider only three types of cavities a crevice (an extended V shape, such as might be produced by a scratch) with a triangular cross section, a conical pit, and a reservoir with an arbitrary, but reentrant shape. These cases are schematically shown in Fig. 15. 

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