HIGH TEMPERATURE OXIDATION OF THE GRAPHITE FLUORIDE-METAL CHLORIDE REACTION PRODUCTS

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1 HIGH TEMPERATURE OXIDATION OF THE GRAPHITE FLUORIDE-METAL CHLORIDE REACTION PRODUCTS Ching-cheh Hung NASA Glenn Research Center, Cleveland OH Corresponding author address: Introduction It was previously observed that reactions between metal chlorides (MCl n ) and graphite fluoride (CF x ) resulted in carbon containing metal halides (fluoride and chloride) compounds if the CF x can be wetted by the metal chlorides at a temperature lower than the decomposition temperature of CF x, at C [1.2]. In this report, the format C(MX n ) is used to represent this product. The size of the metal halides in C(MXn) was found to be in the range of < 20 to 1000 Å by a TEM [3]. The nanoparticles of metal halides in carbon were oxidized when heating this carbon-metal halides composites in air at C. Further oxidation at C in air removed all carbon, resulting in metal oxide nanoparticles. However, if the heating was conducted in an inert environment, the metal oxides were reduced by some of the carbon host, resulted in metal in carbon [3], with the format C(M) in this report. This report describes further study of the formation and oxidation of C(MX n ).The objective was to produce mixed metal oxides or alloys that was made from the nanoparticles in carbon and had the shape of its carbon. Also, in order to reduce the sizes of the nanoparticles, some of the carbon-metal halides composites were rinsed in distilled water before the subsequent heating process. Experimental (1) A graphite fluoride fiber sample CF 0.45 (made from graphitized carbon fibers) in the form of fabric was exposed to ZnCl 2 at 300 C. A small portion of the product, ZnF 2 in carbon, was rinsed in distilled water. Both parts were than heated in air for a period that start at 500 C and end at 900 C, until the black color of carbon disappeared. (2) A sample of graphite fluoride powder CF 0.7 was exposed to 300 C FeCl 3 for 80 minutes and then 380 C for 45 minutes. The product C(FeX n ) was then mixed with an excess of NiO in a quartz tube and heated in 1200 C in nitrogen for 45 minutes. In this experiment, the use of NiO as an oxidation agent was tested. (3) Four samples of graphite fluoride fiber strands CF 0.68 (made from graphitized carbon fibers) were separately exposed to metal halides. One of them were exposed to AlCl 3 at 190 C. Two of them were exposed to a mixture of AlCl 3 and FeCl 3 at 190 C. The other

2 one was exposed to FeCl 3 at 290 C. One of the products from the reactions to the mixed chlorides was rinsed in distilled water for 15 seconds in order to reduce the amounts of metal halides in the carbon materials. All 4 samples were than heated in air at 450 C for 10 days, 500 C for 36 hours, and then 550 C for 22 hours, until the black color of carbon disappeared. Results and Discussion (1) The graphite fluoride fabric (made from graphitized carbon fibers) became zinc oxide fabric after the fluorination in fluorine, ZnCl 2 exposure at 300 C, and heating in air at a temperature of up to 900 C. A picture of this fabric is shown in Figure 1. Both x-ray diffraction (XRD) and energy dispersive spectrum (EDS) indicated the product was ZnO with a small amount of carbon. The product was fragile. It was greenish-white in color. It was not an insulator, possibly because of the presence of carbon. The electrical resistivity was in the KΩ-cm range. The small portion that was rinsed after ZnCl 2 treatment but before air heating resulted in a cotton-like ZnO product. (Figure 2). The fibers were not as fragile. It was an electrical insulator and was white in color. The diameter of the fibers was 2 µm, while the size of its carbon precursor was 10 µm. (2) The graphite fluoride powder became carbon containing magnetic Ni-Fe alloy (XRD and EDS data) after the sequential treatments of FeCl 3 at C and NiO at 1200 C. Figure 3 show the powder sample arranges itself along the magnetic field on a magnet. The reactions were believed to be between NiO and both the FeX n nanoparticles and its carbon host. (3) The graphite fluoride fiber strands (made from graphitized carbon fibers) became Fe 2 O 3, Fe 2 O 3 and γ-al 2 O 3 mixture, and γ-al 2 O 3 fiber strands after exposure to FeCl 3, FeCl 3 and AlCl 3 mixture, and AlCl 3, respectively, followed by heating in air (Figures 4, 5 and 6). All of these oxide fiber strands were very fragile. Electrical resistivity for the γ- Al 2 O 3 final products after 550 C heating was in the KΩ-cm range. The other two products were electrical insulators. The 4 th sample that was rinsed after the mixed-chloride treatment but before air heating resulted in a cotton-like product. (Figure 7). It was very light, but not as fragile as the one without the rinsing process. The color indicated it contained nonuniformly distributed Fe 2 O 3 and γ-al 2 O 3. Conclusions In the previous reports the process to produce nanoparticles in carbon were described. This report demonstrates the process to use the nanoparticles of mixed halides in carbon to produce mixed metal oxides or alloys that had the shape of the carbon host. The process involves exposing the C(MX n ) to either air or metal oxide (e.g., NiO). The

3 products fabricated in this study included nickel-iron alloy (a magnetic material) in carbon, mixed aluminum oxide-iron oxide fibers, and zinc oxide fabric. References [1] Hung C. Ferric Chloride-Graphite Intercalation Compounds Prepared from Graphite Fluoride, Carbon 1995:33(3) [2] Hung C., Process and Products of the reactions Between Graphite Fluoride and a Few Selected Metal Halides, Extended abstracts, 22 nd biennial conference on carbon, UC San Diego (California, USA): American Carbon Society, 1995, [3]Hung C., Corbin J., From Graphite to Porous Carbon Containing Nanoparticles Through Chemical Reactions, Mat. Res. Soc. Symp. Proc Vol. 431,

4 Figure 1. The zinc oxide fabric (fragile) made from graphite fluoride fabric after ZnCl2 exposure at 300 C, and heated in air at a temperature of up to 900 C Figure 2. Scanning electron micrograph of ZnO filaments (flexible) obtained from graphite fluoride fabric after ZnCl2 exposure at 300 C, rinsed in distilled water, and heated in air at a temperature of up to 900 C

5 Figure 3: Nickel and iron-containing carbon materials on magnets Figure 4. The Fe 2 O 3 fiber strand (fragile) made from graphite fluoride fiber strand after exposing the graphite fluoride fibers to FeCl 3 at 300 C, followed by heating in 450 C air

6 Figure 5. The γ-al2o3-fe2o3 fiber strands (fragile) made from graphite fluoride fiber strands after exposing the graphite fluoride fibers to AlCl3-FeCl3 mixture at 190 C, followed by heating in 650 C air Figure 6. The γ-al2o3 fiber strands (fragile) made from graphite fluoride fiber strands after exposing the graphite fluoride fibers to AlCl3 at 190 C, followed by heating in 650 C air

7 Figure 7. γ-al 2 O 3 -FeCl 3 fibers (flexible and very fine) made from graphite fluoride fiber strands after exposing the graphite fluoride fibers to AlCl 3 -FeCl 3 mixture at 190 C, followed by rinsing in distilled water and heating in 650 C air