ISSN:
0142-2421
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Physics
Notes:
On Ni and low-chromium Ni—Cr alloys a surface graphitic carbon monolayer is formed when during carburization of the materials in carbon-containing atmospheres, e.g. in C2H2 or CH4-H2, at constant temperature the carbon activity aC exceeds a critical value aC,cr. On surface planes other than (111) and probably (110) and (311), carbon monolayer formation is accompanied by surface restructuring. The onset of formation and the growth of the carbon monolayer (two C atoms per one metal atom) on Ni and Ni—Cr alloys have been studied at 1150-1400 K directly by in situ AES analysis of the surface composition during carburization or indirectly by using the specific kinetic features of a subsequent decarburization of the materials in H2 as a sensitive probe. The fractional area f of the material surface which becomes covered with the carbon monolayer during carburization in CH4—H2 at carbon activities aC 〉 aC,cr has been determined as a function of the time ta of exposure of the samples to the carburizing atmosphere for various carbon activities aC, temperatures and alloy compositions. For carbon monolayer formation a growth law according to f = 1 - exp [ - ½δta2] with δ = δ(aC, T) has been established, indicating two-dimensional growth of the monolayer. The dissolution of the carbon monolayer during decarburization was found to be controlled by the separation of carbon atoms from the monolayer along the perimeter of the monolayer domains.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/sia.7401901106
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