SELF-RECURRING BEHAVIOR OF NANO-METAL COMPOUND PARTICLE -POROUS CARBON COMPOSITE Yusaku Sakata, Akinori MUTO, Md A. UDDIN; Takafumi Iwamoto, Yoshihoro Kusano*, Jun TAKADA Dept. of Applied Chemistry, Faculty of Engineering, Okayama University 3-1-1 Tsushima Naka, Okayama,700-8530, Japan * ) Dept. of Applied Art, College of the Arts, Kurashiki University of Science and the Arts, 2640 Nishinoura, Kurashiki, 712-8505, Japan Introduction Metal/porous carbon composites have intersting specialty, such as catalysts 1) and absorbents 2,3) , an electrode of electric double layer capacitor 4) . These porous carbon composites with highly dispersed ultrafine metal compounds were pre- pared by carbothermal reduction from metal ion exchanged resin (MIER-CTR) 5) . We have found that metallic Ni or Fe/ porous carbon composites by the MEIR-CTR method have “self-recurring” behavior 6,7) , that is, the trace created by a quadrangular pyramid shaped diamond needle gradually dis- appeared within few minutes for the cases of metallic nickel and iron oxide/porous carbon composites. The photographic images of this phenomenon are shown in Fig.l. In this work, the “self-recurring” phenomenon was exam- ined from in relation with the preparation conditions of the composite such as carbonization temperature, air treatment before carbonization, raw materials, metal content, etc. Experimental A commercial chelate resin (DIAION CRll, Mitsubishi Chemical, Japan) was used as a precursor of carbonized materials. Each of Ni 2+ , Fe 2+ and Fe 3+ was adsorbed into the resin by the conventional ion exchange procedure. The metal content of the carbonized material was controlled by the amount of metal ion adsorbed. After ion exchange, the resin was washed by distilled water and dried at room tempera- ture. An electric furnace was maintained at 120 o C for 1 hour then temperature was raised to carbonization temperature (400~700 o C) at a constant rate of 5 o C/min, and held for 3 hours in a gas streams of N 2 (300ml/min). In some cases, the resin was treated for 1 hour at 180~250 o C in a gas streams of air (300ml/min) before carbonization. Crystalline metal compounds in the composites were identi- fied by the powder X-ray diffraction (XD-3A, Shimadzu). The metal content in the composite was evaluated by thermogravimetric method (TG30, Shimadzu). The specific surface area (SJ was measured by the N 2 BET method at 77K (BELSORP28SP, Nippon BEL Co. Ltd). The micro- structure of the composites was observed by TEM (EM- 002B, Topcon Pleasanton, CA). Microvickers hardness (Hv) was measured (MVK-G2, Akashi) 12 times for each sample (load:1~300g, 10 seconds). Resuts and Discussion The preparation conditions and physico-chemical proper- ties of the Ni/C composites are shown in Table I. The microvickers hardness of some samples were not measured, because the needle trace disappeared after loading a dia- mond needle into the test sample. The needle trace faded out completely within 90 sec. This disappearance of the mark was observed when the needle load exceeded 25g. The for- mation of metallic nickel particles in the composites was confirmed by XRD. The disappearance of the needle trace was observed for the samples (Table 1, No. 8, 10, 11, 14) prepared under the following conditions: 1) Carbonization temperature was below soot. When car- bonization was done above 700 o C, the disappearance was not seen (Fig. 2). Graphitic carbon was formed and the structure of carbon matrix changed. 2) The nickel content of the composite was more than 13.5wt% ( See No.4-10) (Fig.3). 3) Heat treatment in air (at 200-220 o C) before carbonization was necessary even though Ni content was more than 13.5 wt% (Fig.3). The diameters of the crystalline compounds and specific surface area (Sg) of the composites are also shown in the Table I. These do not have any direct relationship with the disappearance of needle trace. The comparisons of the TEM images of the Ni/C compos- ites are shown in Figs. 4 (No.10) and 5 (No. 5). The diam- eter of the metallic nickel particle was about 10 nm in the composite of No.10, which showed the “self-recurring” phe- nomenon. However, when the particle diameter of nickel was distributed in the range of 10 - 60 nm (No.5), the disappear- ance phenomenon was not observed. These results indicate that the microstructure of the metal-porous carbon compos- ite correlates closely to the phenomenon of the needle trace disappearance.