A. Hamwi

The reversible intercalation of tetrahydrofuran in some graphite-alkali metal lamellar compounds

Abstract Second and higher stage graphite derivatives of three alkali metals reversibly react with polar molecules such as tetrahydrofuran (THF). For the second stage binary derivatives the compounds formed are MC24Xp wher M is K, Rb or Cs and X is the organic molecule. When X is THF, p is 1 ( I c = 7.16 A ), 2( I c = 8.88 A ) or 3 ( I c = 8.95 A ) depending on the experimental conditions. Since the Ic values are practically independent of the nature of M it appears that in all cases the metal ion (or atom) is lodged within cavities between the organic molecules whose dimensions and orientations are solely responsible for the Ic values.

A real-time γ ray diffraction study of potassium intercalation into graphite

Abstract In-beam experiments have been performed on a γ ray diffractometer during potassium intercalation into highly oriented pyrolytic graphite. The evolution of the mosaic distribution during the formation of the first four stages was observed and the influence of pressure on the mosaic structure was studied for the second stage. Kinetic parameters were derived from the time dependence of the reflectivity during the intercalation process. The combination of the results obtained for the reflectivity and for the mosaic spread permitted detailed interpretations and demonstrated the efficiency of γ ray diffractometry in real-time studies of intercalation processes.

Intercalated pyrolytic graphite for neutron monochromatisation

Abstract Highly oriented pyrolytic graphite (HOPG) is actually the most efficient neutron monochromator for wavelengths, λ, from 2 A up to about 6 A. By means of intercalation its use can be extended to λ ∼ 10 A where, up to now, no monochromator crystals of high reflectivity have been available. Both theoretical and experimental results show that even though intercalation strongly increases the mosaic spread, the peak reflectivity of the intercalated HOPG compounds KC8, RbC8 and CsC8 is still about 70% for neutron wavelengths in the range from 7 to 9 A. The variation in d-spacing of these compounds allows enhancement of the neutron flux by increasing the bandwidth, Δλ/λ, up to about 10%. Typical applications are considered in three-axis spectrometry and in diffractometry.

Fluorine magnetic resonance and relaxation properties of stage I TaF5 intercalated graphite

Abstract First stage TaF 5 intercalated graphite ( C = 8.41 A ) has been synthesized in chlorine atmosphere and corresponds to an analytical formula of C 8.56 TaF 5.16 Cl 0.08 . Fluorine magnetic resonance has been investigated over the 150–350 K temperature range and shows well pronounced composite spectra below 250 K. T 1 and T 2 measurements, X-ray analysis patterns and infrared spectra are consistent with the existence of TaF 5 Cl − anions and heavier oligomeric anions in open chain conformation. A mechanism is proposed for the intercalation process.

A kinetic neutron diffraction study on the intercalation of deuterobenzene into KC24

Abstract The reaction of KC 24 with C 6 D 6 vapour was studied by neutron diffraction on a time scale of 5 min/spectrum. The reaction is initiated by the formation of a second-stage phase KC 24 (C 6 D 6 ) y . The CC spacing increases during the reaction which is explained by a charge transfer towards the graphite planes.

A real time neutron diffraction study on the intercalation of deuterobenzene into RbC24

Abstract The reaction of RbC24 with C6D6 vapour was studied by neutron diffraction on a time scale of 5 min/spectrum. As for the reaction of KC24, a second stage phase RbC24(C6D6)y is initially formed and subsequently transformed into a first stage phase. Model calculations indicate that the benzene rings are canted against the graphite planes both in the first and in the second stage phase.

A neutron diffraction study of the reaction of potassium with highly oriented pyrolytic graphite (HOPG)

Abstract The reaction of virgin HOPG with K vapour has been studied by real-time neutron diffractometry. A regular staging process appears to start at stage n = 5. At earlier times, a highly disordered phase exists. Evidence for the formation of stages with n = 3, 4 at the very onset of the reaction was also obtained. These observations agree with model calculations of the intercalation process.

De-intercalation and second intercalation of potassium into a highly oriented pyrolytic graphite

Abstract Staging has been studied during intercalation and de-intercalation of potassium vapor into HOPG. Kinetics, (001) peak broadening and apparent mosaic spread of the HOPG crystal have been studied. As intercalation/de-intercalation cycles occur, mosaic spread markedly increases while stage purity of graphite intercalation compounds improves. A mosaic spread minimum is observed close to the 3rd stage.