Investigation on Structure Transition of Fullerene During Mechanical Alloying and Subsequent Treatments
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K. Masuyama Department of Mechanical Engineering, Toyama National College of Technology, 13 Hongoumachi, Toyama 939, Japan
K. Tsuchiya and M. Umemoto Department of Production Systems Engineering, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan (Received 22 January 2000; accepted 7 April 2000)
Mechanical milling of fullerene (soot containing C60 /C70 fullerenes in a 8:2 molar ratio) was investigated through various characterization methods. It was found that mechanical milling would not destroy the molecular structure of fullerene C60(C70), while the long-range order of the face-centered-cubic crystalline structure was easily modified and transformed into amorphous phase, a mixture of fullerene C60(C70) polymers and monomers. Differential scanning calorimetry analysis revealed a recovery of polymers to pristine fullerene molecules at 678 K, which is much higher than the reported depolymerization temperature of fullerene polymers induced by photo irradiation and by high-pressure–temperature processes. It is suggested that the contaminated Fe acts as a catalyst in the polymerization process.
I. INTRODUCTION
Since the discovery and macroscopic production of fullerene (mostly C60),1,2 much research has been devoted mainly to the chemical and physical properties and the possible applications of fullerene.3 Because of the unique molecular structure, a hollow core, and nanometerscale size, it is supposed to be a good dispersoid for metal to produce a new sort of composite with light weight and improved properties. Berrera and co-researchers had investigated the possibility of producing this kind of material.4,5 They tried several methods, such as sputtering, evaporation, and powder metallurgy, to disperse fullerene molecules into metal matrix. Although fullerene (C60) can withstand high temperature in inert atmosphere (∼900 °C in argon), it becomes unstable even at much lower temperature with the presence of oxidative substances (being oxidized to CO and CO2 at 500 °C in air).6–8 It is necessary for fullerene to remain stable during processing and to get uniform dispersion in the metal matrix. Therefore, a processing method that can disperse the fullerene molecules uniformly into the metal matrix at low temperature should be applied. Mechanical alloying (MA),9 a well-known solid-state alloying process for producing alloys at ambient temperature, is one of the suitable processes for producing metal– fullerene composite. 1528
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J. Mater. Res., Vol. 15, No. 7, Jul 2000 Downloaded: 25 Mar 2015
The basic process of MA is as follows: The repeated deformations, fractures, and cold weldings of the powders lead to the gradual refinement of the microstructure and finally the alloying of powders.10,11 Much previous work in metals had revealed that heavy plastic deformation in mechanical milling results in grain refinement,12–15 even amorphization.16 Consequently, to produce metal–fullerene composite by ball milling, one of the critical problems is that fullerene has to be
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