ISSN:
0142-2421
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Physics
Notes:
Type II carbon fibers have been oxidized to various extents in nitric acid, both with and without subsequent exposure to aqueous sodium hydroxide, and the resulting surface composition has been determined using angle-resolved x-ray photoelectron spectroscopy (ARXPS) and ion scattering spectroscopy (ISS). As-received fibers (unsized and commercially treated) contain substantial amounts of oxidized carbon, most of which is confined within the outermost 10-15 Å of the surface. Fiber treatment in 70% nitric acid at 115°C for 20-90 min alters the O/C atomic ratio as well as the depth distribution of oxidized carbon species. Evidence is presented suggesting that the fibers are oxidized primarily within the outermost surface region when the nitric acid exposure time is 〈40 min. As nitric acid treatment time is increased to 60 and 90 min, the fiber subsurface region near the maximum XPS sampling depth (60-100 Å) appears to be increasingly oxidized relative to further oxidation at the outermost surface region. This subsurface region is mostly the outer few graphitic layers which are exposed by pitting and roughening of the surface as oxidation continues. Exposing the nitric acid-oxidized carbon fibers to aqueous sodium hydroxide removes oxidized fragments from the outer fiber layers and consequently alters the depth profile of carbon/oxygen chemical groups. In most cases, after fiber exposure to sodium hydroxide, the relative O/C atomic ratio decreases by ∽10%, consistent with the removal of oxidized fiber fragments. Furthermore, ISS reveals that sodium hydroxide exposure enriches the outermost fiber layers with sodium, the concentration of which increases with increasing extent of prior nitric acid oxidation.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
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