Micro-fissures

If the nuclides would diffuse into micro fissures of the rock, which seem to be the case for Cs and Am (see above), and not solely be adsorbed on the exposed fracture surfaces, the retention factors would be several orders of magnitude larger. 

Adhesive penetration into wood can be categorized (i) on micrometer level as a result of the hydrodynamic flow and capillary action of the liquid resin from the outer surface into the porous and capillary structure of wood, mostly filling cell lumens, as well as fractures and surface debris caused by processing [5], and (ii) on sub-micrometer level as diffusion penetration into cell walls and micro- fissures. Hydrodynamic flow is initiated by the external compression force as a result of pressure applied to the wood surface to be bonded. The flow then continues into the interconnected network of lumens and pits, with flow moving primarily in the direction of lowest resistance [6]. The extent of utilization of an adhesive may be limited due to excessive penetration into the substrate, since this portion of the applied adhesive is lost within porous substrate structures for the adhesion effect. 

Before immersion minor shrinkage cracks were observed in the cement paste specimens. These cracks were focused upon in detail because narrow micro-fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth [32], So, if crystallization is the mechanism of decay of cement paste, salt crystallization should first occur in the shrinkage cracks and sodium sulfate or magnesium sulfate crystals should be identified in these cracks. 

Martensite is inclined to stress corrosion. Micro-fissuring can easily occur in brittle areas of martensite on the surface of the specimen exposed to the potentially aggressive environment. Stress corrosion may start from this surface scratches and... 

The EDZ fracturing extends up to a distance of approximately two metres away from the tunnel walls. Within the EDZ, the disruption of the shale matrix is not complete, but rather propagates along macro- and micro-fissures (centimetre- to millimetre-scale) with no calcite sealing. Macroscopic crystals of gypsum occur on the fractured surfaces of the shales. But neither pyrite alteration nor neoformations of minerals such as iron oxyhydroxides or jarosite have been observed by optical and electron microscopes. 

Defects such as residual welding flux and micro-fissures create weld metal crevices that are easily corroded, particularly in chloride-containing environments. Some flux formulations on coated shielded metal arc or stick electrodes produce easily detached slags, and others give slags that are difficult to remove completely, even after grit-blasting. 

Micro-fissures or their larger counterparts, hot cracks, also provide easy initiation sites for crevice attack, which wiU drastically reduce the corrosion resistance of a weldment in a bleach plant. 

Micro-fissures are caused by thermal contraction stresses during weld solidification and are a problem that plagues austenitic stainless steel fabrications. These weld metal cracks are more likely to form when phosphorus and sulfur levels are higher (that is, more than 0.015% P and 0.015% S), with high heat input welding, and in austenitic weld metal in which the a-ferrite content is low (< 3%). 

Small-scale micro-fissures are often invisible to the naked eye, and their existence can readily explain the unexpectedly poor pitting performance of one of a gronp of weldments made with filler metals of apparently similar general composition. 

The micro-fissure provides a crevice that is easily corroded because stainless alloys are more susceptihle to crevice corrosion than to pitting. However, micro-fissure crevice corrosion is often mistakenly interpreted as self-irritiated pitting. 

Micro-fissure corrosion in austenitic stainless steel weldments containing 4 to 6% Mo is best avoided with the nickel-based Inconel 625, Inconel 112, or Avesta PI 2 filler metals, which are very resistant to crevice attack. Some stainless electrodes are suitable for welding 4% Mo steels, but they should be selected with low phosphorus and sulfur to avoid micro-fissure problems. 

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