G. E. Gadd

Novel rare gas interstitial fullerenes of C60 with Ar, Kr and Xe

Abstract In this paper we report the formation and characterisation of rare gas C 60 interstitial compounds of Ar, Kr and Xe. The materials were produced by hot isostatically pressing (HIP) the fullerene solid at temperatures between 200 and 550 °C and under rare gas pressures in the range 170–200 MPa. With this method, we have been able to make rare gas fullerene compounds with stoichiometries of Ar 1 C 60 , Kr 0.9 C 60 and Xe 0.66 C 60 . Thermal gravimetric analysis (TGA) showed that the HIPed materials contained rare gas after treatment, and gave a method for determining the stoichiometry. TGA also enabled the thermal stabilities of these materials with respect to rare gas loss to be investigated. The structure of the rare gas fullerenes was characterised by both X-ray and neutron powder diffraction. By Rietveld analysis of the diffraction data it has been shown that only the octahedral interstices of the fullerene face centred cubic (FCC) lattice were occupied by the rare gas, and the site occupancy of this site gave a stoichiometry agreeing within 5% of that obtained from TGA. The face centred to primitive cubic orientational ordering phase transition for these rare gas fullerenes was studied using neutron diffraction. The transition temperature was found to decrease as the size of the rare gas increases. This lowering is a result of the net weakening of the c 60 c 60 interaction potential, as the rare gas pushes the c 60 molecules slightly apart; a consequence of not only their size but also a result of their thermal motion (internal pressure) within the interstitial site. Differential scanning calorimetry (DSC) confirmed the transition temperatures obtained from neutron diffraction. In addition, transmission electron microscopy (TEM) and 13 C NMR studies have been performed on these materials and the results are discussed.

Endohedral fullerene formation through prompt gamma recoil

Abstract Neutron activation of rare gases trapped interstitially in the lattice of C 60 has been studied. Gamma spectroscopy of the neutron irradiated solids and solutions of them in toluene provided strong evidence that 1–2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission following neutron activation, become entrapped in what is most likely to be the C 60 molecule or some other fullerene derivative. From these results we postulate the formation of RN@C 60 where the radionuclide (RN) is 125g Xe, 133g Xe, 135g Xe, 41 Ar or 85m Kr.

The encapsulation of Ni in graphitic layers using C60 as a precursor

Abstract We have shown that Ni metal particles when melted in the presence of C 60 form graphitic layers around their outer surface with the Ni remaining as pure metal without any evidence of carbide formation. Particles over several orders of magnitude in size with diameters in the range of ∼10 nm to several microns have been successfully encapsulated in this manner. The process has been observed taking place in real time using transmission electron microscopy (TEM). The electron beam served a dual purpose in this case by providing a means of observation as well as the source of thermal energy. High resolution transmission electron microscopy (HRTEM) shows the nature of the encapsulation to be graphitic. The process does not occur when graphite powder is used instead of C 60 powder and the Ni similarly heated to melting point. The encapsulation method using C 60 as a carbon source also occurs on heating a mixture in a conventional manner and shows the effect is thermal in nature although the electron beam does offer the ability to control the process for individual particles. Further research has shown the encapsulation process to occur at temperatures as low as 800°C by a catalytic pathway.

Neutron irradiation of Ar1C60

Abstract Samples of Ar 1 C 60 (both powder and films) were produced by hot isostatically pressing C 60 in an atmosphere of Ar at 170 MPa. The prepared samples of Ar 1 C 60 were irradiated with neutrons in a high flux nuclear reactor for a period of 4 h. In each case, the material was exposed at 300 K to a thermal neutron flux of 5 × 10 13 neutrons cm −2 s −1 . The measured activity of the 41 Ar showed that there was no evidence of escape of the activated species from the lattice as a result of the neutron irradiation. IR spectroscopy, X-ray diffraction with Rietveld analysis, and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy showed that Ar in general was not lost from the lattice as a result of being exposed to the harsh nuclear reactor conditions associated with the neutron irradiation.

Gas storage in fullerenes

Abstract Fullerenes and in particular C60 have been shown to store effectively a wide range of gases from simple monatomic rare gases to diatomics and polyatomics. A review of the research in this area conducted at ANSTO is given. The trapping of Ar, Kr, Xe, and CO2 are discussed in detail whilst preliminary results pertaining to N2O, CH4, CF4, C2H6 and SF6 are also reported. A range of techniques have been used to elucidate both the structure of the new fullerene intercalated solid and the trapped gas itself. The preponderant techniques used, include infra-red absorption spectroscopy (IR), X-ray powder diffraction a (XRD), neutron powder diffraction (NRD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA).

Structural Characterization of the New Fullerene-Rare Gas Compound Ar1C60

Abstract We communicate how C60 Hot Isostatically Pressed (HIPed) at 200° or 400°C with a pressure of 1.7 kbar of Ar produces the new fullerene-rare gas compound Ar1C60. We have shown, using Xray powder diffraction and subsequent Rietveld analysis, that this solid can be characterised stoichiometrically as Ar1C60- The stoichiometry has also been confirmed by thermal gravimetric analysis (TGA) showing 5% by weight to be Ar (expected=5.25%). The presence of Ar is confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). This material is found to be remarkably stable to loss of Ar over several weeks at room temperature. This represents the first full characterisation of an interstitial rare gas fullerene compound. †Deceased. This letter is dedicated to the living memory of Dr. R. Lindsay Davis. His wisdom and encouragement are intangibly woven into this work

Endohedral Formation from Neutron Activation of Interstitial Rare Cas C60 Fullerides

Abstract Rare gas interstitial fullerenes, produced by hot isostatic pressing solid C60 in the presence of Ar, Kr or Xe, have been neutron irradiated and their behaviour investigated. The activity of the generated radionuclides was found to be in agreement with calculations and this combined with X-ray powder diffraction showed that both the activated radionuclides and the unactivated rare gas remained trapped in the solid after they have been subjected to the harsh conditions encountered in a nuclear reactor. Gamma spectroscopy of the irradiated solids and solutions of them in toluene provided strong evidence for endohedral compound formation. We estimate 1–2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission, end up in the centre of what is most likely too be the C60 molecule or some other fullerene derivative. On this basis, we postulate the formation of RN@C6o where the radionuclide (RN)is 125gXe, 133gXe, I35gXe, 41Ar or85mKr.

Novel rare gas interstitial fullerenes of C70

Abstract The formation and characterisation of the rare gas interstitial compounds of argon, krypton and xenon with C70 are presented. The materials were produced by hot-isostatically pressing (HIPing) powdered samples of C70 at a temperature of 400 °C and under a surrounding rare gas pressure between 170 and 200 MPa for ~ 12 h. The materials were analysed by thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). It appears that under the HIP conditions used we were able to saturate all octahedral sites of the C70 lattice (experimental error 5–10%), giving the rare gas stoichiometric materials Ar1C70, Kr1C70 and Xe1C70. The C70 rare gas fullerenes were found to be more susceptible to loss of rare gas, compared with the corresponding C60 materials, although the relative stabilities followed the same pattern, with heavier intercalated rare gases being lost more slowly. The argon is lost very easily (within a few days) whereas the krypton and xenon C70 fullerenes were found to be stable at room temperature for several months, with some loss from the krypton fullerene.

Fullerenes as precursors for nanocapsule formation

Abstract We have shown that Ni metal particles when melted in the presence of C60 form graphitic layers around themselves with the Ni remaining as pure metal and without any evidence of carbide formation. We have successfully encapsulated particles over several orders of magnitude of size from ∼10 nm to several microns. The process has been observed taking place in real time using transmission electron microscopy (TEM). The process was not observed when graphite powder was used instead of C60 powder and the Ni similarly heated to melting point, using the electron beam. Heating a mixture of Ni and C60 powders together in a conventional manner also produced encapsulated Ni particles. This suggests that the encapsulation method is thermal in nature although the electron beam does offer the ability to control the process for individual particles. Further research has shown that the encapsulation process can also occur at temperatures as low as 800° C by a catalytic route. We have extended the work of heating a metal in the presence of fullerenes and have effectively encapsulated other metals such as Fe, Co, Ho, Cu and Au.