G. S. Kamali Kannangara

Unoccupied electronic structure of ball-milled graphite

Changes in electronic and vibrational structure of well characterised macrocrystalline graphite milled by a planetary ball-mill are investigated by Raman spectroscopy and Near Edge X-ray Absorption Fine structure (NEXAFS) measurements at the C K-edge. The electronic structure changes at the surface and in the sub-surface of the particles are examined by comparing two-different NEXAFS detection modes: total fluorescence yield (TFY) and partial electron yield (PEY) respectively. When the in-plane crystallite sizes of graphite are decreased to nanosized (from approximately 160 nm to approximately 9 nm), a new spectral structure appears in TFY at 284.1 eV which is not present in the macrocrystalline graphite. This feature is assigned to electronic states associated with zigzag edges. Further the TFY shows a shift of the main graphite pi* band from 285.5 to 285.9 eV, attributed to breaking the conjugation and hence the electron localization effect during milling, The TFY spectra also show strong spectral features at 287.5 and 288.6 eV, which suggest that the local environment of carbon atoms changes from sp(2) to more sp(3) due to physical damage of the graphite sheets and formation of structures other than aromatic hexagons. Complementary Raman spectroscopic measurements demonstrate an up-shift of the graphite G band from 1575 to 1583 cm(-1)en route to nanosize. The changes in TFY NEXAFS and Raman spectra are attributed to modification of the sub-surface electronic structure due to the presence of defects in the graphite crystal produced during milling. The discovery of the strong spectral feature at 284.1 eV in nanographite and the 0.4 eV up-shift of the pi* band may open up possibilities to influence the electronic transport properties of graphite by manipulation of defects during the preparation of the nanographite.

Macromolecules in the Bayer Process

This is the publishers version, also available electronically from http://www.degruyter.com/view/j/revce.2003.19.5/revce.2003.19.5.431/revce.2003.19.5.431.xml.

Potential of thermogravimetric analysis coupled with mass spectrometry for the evaluation of kerogen in source rocks

Abstract The molecular composition of oil and yield from a source rock depends on the temperature to which the source rock is subjected. However, the yield of oil and gas represents hydrocarbons generated over a range of temperatures. A technique that measures both volatile yields and bulk and molecular compositions during volatile evolution would determine the differential effects of temperature change, thereby giving information on the effect of thermal gradients. Attaching a mass spectrometer to a thermogravimetric analyser assists in this goal since it allows gases to be analysed during petroleum source rock evaluation by pyrolysis. Single ion monitoring allows unambiguous identification of thermal events. It reveals temperature at which water, methane and carbon dioxide evolve. This allows organic and inorganic transitions to be distinguished. Parameters that describe the yields of oil and gas can also be derived from thermogravimetric analysis (TGA) in much the same way as they can for Rock–Eval pyrolysis data and are useful when combined with solid state 13 C nuclear magnetic resonance (NMR) spectroscopy and Rock–Eval data for elucidating mineral matter effects.

Analysis of 3,4-Methylenedioxy-N-Methylamphetamine (MDMA) in “Ecstasy” Tablets by13C Solid State Nuclear Magnetic Resonance (NMR) Spectroscopy

The solution and solid state NMR spectra of 3,4-methylenedioxy-N-methylamphetamine hydrochloride (MDMA·HCl) and a number of illicitly manufactured tablets containing this material and marketed as “Ecstasy” have been obtained. We show solid state NMR to be a useful technique for the analysis of the impurities and excipients in “Ecstasy” tablets and with further development may be used quantitatively for determining the percentage carbon which is MDMA. Excipients detected include lactose, cellulose, stearate salts, sucrose, starch, polyvinylpyrrolidone and sodium croscarmellose. Two samples were found to contain 3,4-methylenedioxy-N-ethylamphetamine (MDEA), rather than MDMA. Some interesting conformational information is also observed. Differences in the chemical shifts of C-8 and C-10 carbons for 3,4-methylenedioxy-N-methylamphetamine hydrochloride in solution and solid state and in different “Ecstasy” samples are attributed to conformational freezing and hydrogen bonding. In the solid state, carbons 8 and 10 are restricted from free rotation and the methyl groups at carbon 10 and carbon 11 are held only in trans conformation unlike in solution. These results were confirmed by a crystal structure analysis. When excipients capable of hydrogen bonding are physically mixed with MDMA·HCl, the chemical shifts of carbons 8 and 10 in the resulting mixture changes such that they more closely resemble the shifts observed in solution.

Preliminary analysis of pore distributions using NMR in natural coral and hydrothermally prepared hydroxyapatite

Pore size distributions in an Australian coral from Goniopora sp have been measured by mercury intrusion, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). A significant result is that NMR predicts nanopores which could be seen visibly. The methods give similar results as mercury intrusion for large pores around 100 μm but differ for smaller pores. Differences between NMR and mercury intrusion are equated using a non linear sigmoidal regression model. The NMR method was also compared with mercury intrusion methods to measure pore sizes on hydroxyapatite conversion products which have promise as bio-implants. Differences between samples due to errors in the methodology are discussed. Together all three methods are shown to complement each other.

Isothermal evaporation of ethanol in a dynamic gas atmosphere

Optimization of evaporation and pyrolysis conditions for ethanol are important in carbon nanotube (CNT) synthesis. The activation enthalpy (ΔH(‡)), the activation entropy (ΔS(‡)), and the free energy barrier (ΔG(‡)) to evaporation have been determined by measuring the molar coefficient of evaporation, k(evap), at nine different temperatures (30-70 °C) and four gas flow rates (25-200 mL/min) using nitrogen and argon as carrier gases. At 70 °C in argon, the effect of the gas flow rate on k(evap) and ΔG(‡) is small. However, this is not true at temperatures as low as 30 °C, where the increase of the gas flow rate from 25 to 200 mL/min results in a nearly 6 times increase of k(evap) and decrease of ΔG(‡) by ~5 kJ/mol. Therefore, at 30 °C, the effect of the gas flow rate on the ethanol evaporation rate is attributed to interactions of ethanol with argon molecules. This is supported by simultaneous infrared spectroscopic analysis of the evolved vapors, which demonstrates the presence of different amounts of linear and cyclic hydrogen bonded ethanol aggregates. While the amount of these aggregates at 30 °C depends upon the gas flow rate, no such dependence was observed during evaporation at 70 °C. When the evaporation was carried out in nitrogen, ΔG(‡) was almost independent of the evaporation temperature (30-70 °C) and the gas flow rate (25-200 mL/min). Thus the evaporation of ethanol in a dynamic gas atmosphere at different temperatures may go via different mechanisms depending on the nature of the carrier gas.

Microstructural Changes upon Milling of Graphite in Water and Subsequent MWCNT Formation During High Temperature Annealing

The method of preparing carbon nanotube (CNT) by milling of graphite particles in water followed by high temperature annealing is proposed and the mechanism discussed. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) line broadening analysis reveal that cleavage of the graphite particles occurs preferentially along the out‐of‐plane π bonds. Carbon K‐edge near edge X‐ray absorption fine structure (NEXAFS) of the milled graphite shows an increased sp3 character of the C=C bonds, but no major bonds rupture in the graphene sheets. The annealing at 1400 °C for 4 h of the milled graphite in argon results in formation of multiwalled carbon nanotubes accompanied with a number of coiled and twisted stacks of graphene sheets. The increased structural disorder of the milled graphite and presence of iron contaminations facilitate the rolling up of the cleaved graphene sheets during annealing.

Stereochemistry of carbon nanotubes for electronic applications

Results are presented from studies to prepare carbon nanotubes of single geometry. Carbon nanotubes of certain stereochemistry have been found to be conductive. Others have been found to be excellent transistors, and together nanoelectronic devices have already been formed from them including logic gate circuits. Two synthetic approaches have been tried, namely plasma arcing in the presence of additives and ball milling. In plasma arcing, cathode deposits are altered by the presence of naphthalene in the feed material. The mixture of nanotubes so formed has a larger average void size than that formed in the absence of naphthalene. The results support proposed mechanisms of nanotube formation which involve growth by incorporation of carbon atoms into open tubes. They also show that naphthalene can be directly incorporated into fullerene black and thereby increase the number of hexagonal sheet structures in the carbon deposit. Work so far in ball milling has been confined to studies of the destruction of graphite crystalline phases.