Polishing and surface working of solids

The introduction of electron diffraction, a most powerful new tool5 for 

Crystalline solids other than metals examined, by electron diffraction, show some disturbance of the normal structure on polishing, but do not usually form a completely amorphous layer. Polishing tends to disintegrate the crystals at the surface, but not to the same extent as in metals and it often happens that continued polishing removes the 

1 Examination by means of X-rays does show lines corresponding to a finely divided crystalline structure on a polished metal (Boas and Schmid, Naturwiss., 20, 416 (1932) but this is almost certainly because the X-rays penetrate below the amorphous layer and reveal the microcrystalline structure below. Electrons do not penetrate to more than a few atoms depth. 

The amorphous Beilby layer (as it is often called) has properties markedly different from the rest of the solid. It is much harder, and is usually more soluble and electrolytically more anodic, a fact of considerable importance in the corrosion of metals, as it is often found that corrosion starts at those points (such as the neighbourhood of a punched hole) where some degree of surface flow, or damage to the crystalline structure, has taken place in the metal. It has, apparently, powers of dissolving other metals, not possessed by a crystalline surface. Thus Finch, Quarrell, and Roebuck1 found that if small amounts of metals were deposited by condensation from vapour on to a polished surface of another metal, patterns indicative of the crystalline structure of the deposited metal were obtained temporarily, but disappeared after a few minutes or even seconds. Permanent patterns of zinc on copper could only be obtained by very many successive depositions. If, however, metals were similarly deposited on crystalline surfaces of other metals, one deposition was always sufficient to give the pattern of the deposited metal. 

The actual mechanism by which the amorphous surface layer is produced is probably a combination of many processes very large shearing 

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