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Mechanically Stimulated Gas Emission == Phenomenology == Mechanically stimulated gas emission (MSGE) is a complex phenomenon embracing various physical and chemical processes occurring on the surface and in the bulk of a solid under applied mechanical stress and resulting in emission of gases. MSGE is a part of a more general phenomenon of Mechanically Stimulated Neutral Emission (MSNE).〔Dickinson J.T. Atomic and molecular emission following fracture of alkali halides: a dislocation driven process. J. Mat. Res. 1991. V. 6. P. 112 .〕 The specific characteristics of MSGE as compared with MSNE is that the emitted neutral particles are limited to gas molecules. MSGE is opposite to Mechanically Stimulated Gas Absorption that usually occurs under fretting corrosion of metals, exposure to gases at high pressures, etc. There are three main sources of MSGE:〔Řepa P. Mechanically induced desorption. Vacuum. 1992. V.43. P. 367-371〕〔Řepa P., Rott, M. Outgassing of metals stimulated by friction. Vacuum. 1997. V.48. P. 775-778〕〔Řepa P., Orálek D. Outgassing stimulated by deformation. Vacuum. 1999. V. 53. P. 299-302〕〔Nevshupa R., de Segovia J.L., Roman E. The origin of gas desorption during friction in an ultrahigh vacuum. J. Vac. Sci Technol A , v 26. 2008. – P. 1218-1223.〕 : I. Gas molecules adsorbed on the surface of a solid : IIa. Gases dissolved in the material bulk : IIb. Gases occluded or trapped in micro- and nanovoids, discontinuties and on defects in the material bulk : III. Gases generated as a result of mechanical activation of chemical reactions.〔Urakaev F. K. Mechanodestruction of minerals at the crack tip (Overview): 1. Experiment.Physics and Chemistry of Minerals. 2007. V.34. P. 351-361〕〔Mori S., Shitara Y. Tribochemical activation of gold surface by scratching. Applied Surface Science. 1994. V. 78. P. 269-273.〕 Generally, for producing MSGE, the mechanical action on the solid can be of any type including tension, compression, torsion, shearing, rubbing, fretting, rolling, indentation, etc. In previous studies carried out by various groups it was found that MSGE is associated mainly with plastic deformation, fracture, wear and other irreversible modifications of a solid.〔Frisch B., Thiele W.-R. The tribologically induced effect of hydrogen effusion and penetration in steels. Wear. 1984. V.95. P. 213-227.〕〔Louthan M.R., et al. Hydrogen embrittlement of metals, Material Science and Engineering. 1972. V. 10. P. 357-368.〕 Under elastic deformation MSGE is almost negligible and only was observed just below elastic limit due to possible microplastic deformation. In accordance to the main sources, the emitted gases usually contain hydrogen (source type IIa), argon (for coatings obtained using PVD in Ar plasma - source type IIb), methane (source type III), water (source type I and/or III), carbon mono- and dioxide (source type I/III). The knowledge on the mechanisms of MSGE is still vague. On the basis of the experimental findings it was speculated that the following processes can be related with MSGE: # Transport of gas atoms by moving dislocations # Gas diffusion in the bulk driven by gradient of mechanical stress # Phase transformation induced by deformation # Removal of oxide and other surface layers, which prevent exit of dissolved atoms on the surface # Extension of free surface Thermal effect seems to be irrelevant to the gas emission under light load conditions.〔Nevshupa R.A., Roman E., de Segovia J.L. Model of the effect of local frictional heating on the tribodesorbed gases from metals in ultra-high vacuum. International Journal of Materials and Product Technology. 2010. V. 38, N.1, pp. 57-65〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mechanically stimulated gas emission」の詳細全文を読む スポンサード リンク
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