Subsurface damaged layer

Figure 8.12 Required CMP time and estimated depth of the subsurface damage layer introduced by the diamond abrasive as a function of the average abrasive size used in mechanical polishing as a CMP pretreatment.

Some injected wastes are persistent health hazards that need to be isolated from the biosphere indefinitely. For this reason, and because of the environmental and operational problems posed by loss of permeability or formation caving, well operators seek to avoid deterioration of the formation accepting the wastes and its confining layers. When wastes are injected, they are commonly far from chemical equilibrium with the minerals in the formation and, therefore, can be expected to react extensively with them (Boulding, 1990). The potential for subsurface damage by chemical reaction, nonetheless, has seldom been considered in the design of injection wells. 

Figure 5.18 Pictorial illustration of the subsurface damage induced by a primary ion as it travels beyond the sputtering front (this will occnr nnless the projectile is involved in a direct head-on collision or is scattered from the surface). The white circles represent atoms within the layer of interest.

Figure 11.12. (a) TEM micrograph showing the original silicate layer orientation in the sample and (b) micrograph taken after the scratch test showing subsurface damage beneath scratch track. White arrows point to the rotation of clay layers under the applied stress field. Scratch test conditions normal load 60 inN, scratch velocity 5 pm/s, spherical indenter and parallel to flow direction [107]... 

Figure 13.13 schematically summarizes the consequences for the four cases if scale damage has occurred, based on Figure 13.10. In case 1 protective crack healing can occur (Figure 13.13a). If in case 2 cracking takes places in the period where the Cr subsurface content is below the limit for protective scale formation then first a fast growing oxide nodule is formed at the defect, which may, however, later be "sealed" by a repassivation layer when the Cr content has increased again by rediffusion (Figure 13.13c). Final loss of the protective effect (Figure 13.13b) takes place in cases 3 and 4.

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