Experiments have shown that carbon-based materials containing pure metallic iron, alloys of iron, halides of iron, and/or oxides of iron can be synthesized from precursors of general composition CFx, denoted loosely as graphite fluoride. Typical samples of the product materials contain 1 iron atom per 3.5 to 5 carbon atoms. Those product materials that contain iron in the pure, alloy, and/or Fe3O4 forms are magnetic (see figure).
Some earlier related experiments were reported in "Storing Fluorine in Graphitelike Carbon Fibers" (LEW-15359), NASA Tech Briefs, Vol. 19, No. 12 (December 1995), page 63 and "Modification of Carbon Fibers for Higher Young's Modulus" (LEW-15847) NASA Tech Briefs, Vol. 21, No. 4 (April 1997), page 56. In other earlier related experiments not reported in NASA Tech Briefs, it was found that FeCl3 reacts with CFx at temperatures between 300 and 400 °C to yield graphite intercalation compounds containing iron chloride or mixtures of iron chloride and fluoride; this finding constitutes the point of departure for the experiments reported here.
The precursor materials used in these experiments were CFx (x ranging from 0.68 to 1.0) made, variously, from highly graphitized carbon fibers, less-graphitized carbon fibers, nongraphitized carbon fibers, and crystalline graphite powders. The experiments included exposure of CF0.68 to FeCl3 at temperatures between 280 and 420 °C to study the details of the overall general reaction CFx + FeCl3 → C (iron halides). Between 280 and 295 °C, FeCl3 quickly entered the molecular structure of CF0.68 and broke the carbon-fluorine bonds; within 10 to 30 minutes, the CF0.68 was completely converted to carbon made of graphite planes, between which particles of crystalline FeF3 and noncrystalline FeCl2 were located. Longer reaction times (e.g., 28 hours) or higher reaction temperatures (e.g., 420°C) yielded materials that contained graphite, an FeCl3/graphite intercalation compound, FeCl2·4H2O, and FeCl2·2H2O.
Materials produced in the foregoing reactions were subjected to various further heat treatments - some in air, some in nitrogen. When the heating temperatures were kept between 750 and 850 °C and the oxygen supply was kept at the optimum level, the iron halides were converted to iron oxides. When the heating temperature was increased to 900°C, the iron oxides were reduced to iron metal. These observations led to further experiments in which, prior to the heat treatments, the materials were mixed with NiO or NiCl2 in attempts to induce the formation of Fe/Ni alloys. In one successful experiment along this line, a commercial CF0.7 powder that had been reacted with FeCl3 was mixed with NiO, then the mixture was heated to a temperature of 1,200 °C for 45 minutes in quartz tubes in a nitrogen atmosphere. The product of this experiment was examined by x-ray diffraction and found to be carbon containing an Fe/Ni alloy.
This work was done by Ching-cheh Hung of Lewis Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Materials category, or circle no. 102 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).
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