specimen(redirected from midstream specimen)
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a sample, usually metal, that may be studied macro-scopically (in macrosections) or microscopically (in microsections). Preparation of a specimen entails grinding the flat surface of a sample and, if microsections are to be examined, polishing the surface. The surface is then etched with chemical reagents or heated in a gaseous atmosphere or in a vacuum. Selective etching and evaporation occur as a result of the differences in the physi-cochemical properties both of the grains of different phases as well as of the different grain-boundary regions. This leads to the formation of a macrorelief, which is visible to the unaided eye, or a microrelief, which must be examined with a microscope.