108 T. Takakura et al. Research paper Thermal reactivity of fullerene Tsuyoshi Takakura*†, Atsushi Uramoto*, Gou Kawano*, Hidetsugu Nakamura, and Kazuo Iwamoto** *Department of Applied Science for Integrated System Engineering, Graduate School of Engineering, Kyushu Institute of Technology, 1-1 Sensui, Tobata, Kitakyushu, Fukuoka 804-8550, JAPAN †Corresponding address: [email protected] **Frontier Carbon Corporation Production Center 1-1, Kurosaki Shiroishi Yahatanishi-ku, Kitakyushu-shi 806-0004, JAPAN Received: February 5, 2008 Accepted: June 6, 2008 Abstract Fullerene is a typical nano-carbon material with interesting properties. Though a great deal of research has been per- formed on the basic properties of fullerene to the present, little thermal research has been reported. This study examined the physical and chemical properties, thermal reactivity, and combustion reactivity of fullerene. The results obtained were as follows. Fullerene is a carbon material with high crystallinity which has higher carbon content compared to the other carbon materials. Fullerene C60 and Mixed fullerene(MF) caused sublimation and suffered oxidation in air at lower temperature compared standard carbon black. And C60 was more thermally stable than MF, which contained higher fullerenes includ- ing C70, according to the oxidation reaction in air. Fullerenes burn, while the carbon black does not burn. However, in the burning rate test by the U N ,fullerenes are not a flammable materials. Keywords: Fullerene, Nano-carbon, TG-DTA, Burning test, Inflammability 1. Introduction pated in 1970 1), and it was experimentally confirmed for Fullerene consists only of carbon atoms, and it is a nano- the first time in research on the interstellar molecule in 2) 3) sized “carbon molecule” with a hollow structure. C60 is one 1985 . Since its successful artificial creation in 1990 , example of a fullerene. Its structure is shown in Fig. 1. energetic research has been carried out in Japan, the U.S. As a representative nano-carbon material, fullerene is and Europe, and the characteristic properties of globu- expected to find applications in various fields. The exis- lar carbon molecules have been successively clarified. tence of carbon molecules such as fullerene was antici- Fullerenes have various carbon numbers, including C60, and many research reports have been published on their properties, but research on its thermal stability has not been carried out to a large extent. This study examined the physical and chemical properties, thermal reactivity, and combustion reactivity of fullerene. 2. Experimental 2.1 Samples The species of fullerene used in this study were fullerene C60 (1), mixed fullerene (2), and fullerene-similar carbon powder (3) produced under a reduced atmosphere using the combustion method by the Frontier Carbon Co.(FCC). In order to examine the effect of particle size on reactiv- ity, the samples were pulverized and abbreviated as sam- ples (4)-(6). Standard carbon black (7) made by the Sid Fig. 1 Carbon structure of fullerene (C60). Richardson Carbon Company was used for comparison. Sci. Tech. Energetic Materials, Vol.69, No.4, 2008 109 (1) Fullerene C60 (abbreviation: C60, trade name: Nanom 2.2.3 Thermal analysis puple ST, C60: over 96 %) Thermal analysis was carried out using the thermal ana- (2) Mixed fullerene (abbreviation: MF, trade name: lyzer Thermo Plus 2 made by the Rigakudenki Co. under Nanom mix ST, C60: about 60 %, C70: about 20 %. In heating up to 1000 °C in air. The measurement process addition, mixed fullerene included the higher fuller- consisted of weighting about 2 mg of the sample in an enes.) open container made of alumina with a heating rate of 20 (3) Fullerene-similar carbon (abbreviation: FB, trade °C min–1. Thermal analysis in a nitrogen atmosphere was name: Nanom black ST, the solvent insoluble of soot carried out under heating up to 1000 °C using a thermal including the fullerene ) analysis device Exstar 6000 made by the SII nanotechnol- (4) Fullerene C60 fine powder (abbreviation: C60-F, ogy Co. A 5-mg sample was weighted in an open plati- resulting from grinding (1)) num container and heated at a rate of 20 °C min–1. (5) Mixed fullerene fine powder (abbreviation: MF-F, The isothermal oxidation reaction was carried out in air trade name, Nanom mix ST-F, resulting from grinding using the thermal analyser Thermo Plus 2 made by the (2)) Rigakudenki Co. An approximately 2-mg sample was (6) Fullerene-similar carbon fine powder (abbreviation: placed in an alumina container. The oxidation tempera- FB-F, trade name: Nanom black ST-F, resulting from tures at 4 points ranged from 365-400 °C for MF and grinding (3)) C60, 350-425 °C for FB ,and 450-510 °C for IRB#7. (7) Standard carbon black (abbreviation: IRB#7) 2.2.4 Combustion test 2.2 Experimental The small gas flame test was followed by the “the small 2.2.1 Purity analysis gas flame test” on dangerous object 2 (the combustible Fullerene content was determined using high-pressure solid) based on Japanese fire protection law, and it was liquid chromatography (HPLC) 4). For the HPLC separa- carried out 10 times 5). tion of fullerenes, a YMC-Pack ODS-AM (3 μm, 75 × The burning rate test was carried out twice for every 4.6 mmID, YMC Co.Ltd., Kyoto, Japan) was used. The sample, correspondent to the United Nations’ hazardous mobile phase was toluen/methanol = 48 / 52(vol %) and materials transportation advice on “burning rate testing the elution rate was 0.8 ml · min–1. method 6). Calibration curves were obtained using pure fullerenes C60 and C70, which were refined separately using the sub- 3. Results and discussion limation method on the MF raw material made by the FCC. 3.1 Physical and chemical properties of fullerene Elemental analysis was carried out by measuring 3.1.1 Purity nitrogen, hydrogen, and carbon using the CHNS/O Fullerene is the only carbon material which is soluble in aro- Analyzer2400 made by the PERKIN ELMER Co., and matic solvents such as toluene and xylene. A chromatogram oxygen using an oxygen nitrogen simultaneous analysis of C60 is shown in Fig. 2-1, 2. The purity of C60 was con- device TC-436 made by the LECO Co. firmed to be 99.6 % by the lack of other peaks in the HPLC Water content was determined by the coulometric titration when toluene / methanol was used as an eluate. A chromato- method using an aquameter CA-200 and a moisture vapor- gram of MF is shown in Fig. 2-3, 4. C60 and C70 were the ization device VA-200 made by the Dia Instrument Co. main components of MF, and the total amount of fullerene Ash content was determined following by JIS K1474 composed of C60, C70, and higher fullerenes was 97 %. after heating for 2 hours at 815 °C in air. The results of fullerene purity and elemental analysis for each sample are shown in Table 1. IRB#7 was used as the 2.2.2 Physical property measurement standard carbon black in this experiment, and its carbon con- IR spectra were obtained using FT-IR and IRA-2, made tent was 96.75 %. The carbon content of C60 is 99.6 %. The by the Japan Spectral Diffraction Industry Co., and quali- hydrogen, nitrogen, and oxygen contents were about 0.3 % tative analysis was carried out using the KBr tablet mold- or less, less than in standard carbon black. C60 is also a high- ing method. purity carbon material with an ash content of 0.1 % or less. SEM images were measured using a fully automatic MF showed a high carbon content of 99.3 %, but its carbon microanalysis device JCXA-733 made by the JEOL Co. content was still lower than that of C60. Additionally, hydro- X-ray powder diffraction analysis was carried out using gen, nitrogen, and oxygen each had a value under 0.3 %, less a particular status environmental X-ray diffraction device than that of the standard carbon black, and MF is also a high- DX-3500K made by the JEOL Co. The measurement was purity carbon material with an ash content of 0.1 % or less. carried out using the powder method. However, FB which is insoluble in all solvents and con- The particle size distribution was measured using a laser tains slight amounts of fullerene, has a low carbon content diffraction/scattering-style particle size distribution mea- compared to those of the fullerenes. surement device LA-920 made by the HORIBA Co. C60 and MF together adhered 0.1 % or less with water. The specific surface area was measured using an auto- The water adhesion value of FB is about 0.1 %. Thus, C60 matic specific surface measuring device Gemini 2360 and MF are materials with lower hygroscopicities than the made by the Micrometrics Co. standard carbon black, which has a water adhesion value of 1.3 %. 110 T. Takakura et al. 300 250 1 200 U C60 䠝 150 m 100 solvent 50 0 0510 15 20 RT (min) 30 䠅 25 2 20 C60 U solvent 䠝 15 m 10 C -O 5 60 0 0510 15 20 RT (min) 300 C60 250 3 200 U 䠝 150 m C 100 70 solvent 50 C84 C䠓6C82 0 0510 15 20 RT (min) 30 25 20 4 C60 C70 U solvent 䠝 15 m C 10 84 C76 5 C60-O C82 C86 C90 C -O C70-O C C92 C94 0 60 2 88 0510 15 20 RT (min) Fig. 2 HPLC of fullerene (C60) and mixed fullerene (MF). 1: C60 2: The scale of the vertical line is expanded at 10 times of C60 3: MF 4: The scale of the vertical line is expanded at 10 times of MF The condition of HPLC, eluant: 48 vol % toluene/methanol 0.8 ml·min–1, column: YMC-Pack ODS-AM, S-3 μm, 75* 4.6 mm I.D.