Anthony M. Vassallo

The dehydroxylation of the kaolinite clay minerals using infrared emission spectroscopy

The dehydroxylation of a series of the kaolinite clay minerals, kaolinite, halloysite and dickite, has been investigated by Fourier transform in situ infrared emission spectroscopy over a temperature range of 100 to 800°C at both 50 and 5° intervals. Excellent correspondence was obtained between the high temperature emission spectra and FTIR absorption spectra of the quenched clay mineral phases. The major advantage of the technique lies in the ability to obtain vibrational spectroscopic information in situ at the elevated temperature. Dehydroxylation at a number of temperatures was determined by the loss of intensity of hydroxyl bands as indicated by intensity changes of the 3550 cm−1 to 3750 cm−1 emission spectra. As with all clay minerals, kaolinite clay mineral dehydroxylation is structure dependent. No clay phase changes occur until after dehydroxylation takes place. The kaolinite clay mineral loses the inner sheet and inner hydroxyl groups simultaneously, whereas dickite and halloysites are shown to lose the outer hydroxyls, as evidenced by the intensity loss of the ~3684 cm−1 peak, before the inner hydroxyl groups as determined by the intensity loss of the 3620 cm−1 peak. Evidence for a high temperature stable hydroxyl band at 3730 cm−1 for dickite and halloysite was obtained. This band is attributed to the formation of a silanol group formed during the dehydroxylation process. It is proposed that the dehydroxylation process for kaolinite takes place homogenously and involves 2 mechanisms. The dehydroxylation of dickite and halloysite takes place in steps, with the first hydroxyl loss taking place homogenously and the second inhomogenously.

Measurement and modelling of the high-power performance of carbon-based supercapacitors

Abstract Supercapacitors are now being looked at for use in higher power applications such as mobile telecommunications and hybrid electric vehicles. We have examined two different supercapacitors, one is a commercial sample and the other is a supercapacitor of our own design. Four different testing methods including Impedance Spectroscopy, Constant Current Charging, Cyclic Voltammetry and Power Cycling were applied to each supercapacitor and the results are reviewed. Parameter values obtained from Impedance Spectroscopy are excellent for comparing supercapacitors under equilibrium conditions but correlate poorly with data obtained from the more useful Power Cycling Charts (PCC). The choice of the current step size in Constant Current Charging and the scan rate in Cyclic Voltammetry has a large bearing on the results obtained from these techniques. The strong voltage dependence of the parameters for the commercial sample prevented analysis using Cyclic Voltammetry. It was also clearly demonstrated by Power Cycling that the commercial sample had the poorer power performance of the two supercapacitors tested. It is concluded that for high-powered applications such as telecommunications and wireless protocols the most useful comparison of supercapacitor capability is through the PCC.

Infrared Emission Spectroscopy of Coal Minerals and their Thermal Transformations

An infrared (IR) emission cell which is capable of operation up to 1500°C is described. The cell is based on an atomic absorption graphite furnace and is coupled to a Fourier transform infrared spectrometer. The spectrometer has been used to measure the emission spectrum of quartz from 200 to 1400°C, and the changes in the spectrum occurring with temperature can be related to the formation of cristobalite; transitions between low and high forms (alpha and beta forms) can also be monitored. Aragonite has also been analyzed through the temperature range 100 to 600°C, and the aragonite/calcite transition is clearly evident. The transformation of kaolinite to metakaolinite and through to mullite and cristobalite has also been studied with this in situ technique. The formation of mullite is evident in the spectrum at temperatures as low as 900°C, and the formation of cristobalite is clearly seen at 1200°C.

Exploitation of relaxation in cross-polarization nuclear magnetic resonance spectroscopy of fossil fuels

Abstract The judicious choice of dipolar dephasing times or carbon magnetization holding times has been shown to improve resolution in solid state nuclear magnetic resonance (NMR) spectra of complex materials. Signals from protonated and alkylated aromatic carbons are reduced to enhance resolution of aromatic oxygenated groups. Rapidly rotating methyl groups can be resolved from other aliphatic carbon types. These techniques were used to investigate the structure of a brown coal, xylite fractions of a brown coal, a bituminous coal, an oil shale and a solvent-refined coal. The results allow estimates of the fraction of aromatic carbon that is protonated in coal to be made, and demonstrate that methyl groups in coal rotate rapidly at room temperature.

The chemical structure of highly aromatic humic acids in three volcanic ash soils as determined by dipolar dephasing NMR studies

Abstract Dipolar dephasing 13 C NMR studies of three highly aromatic humic acids, one from a modern soil and two from paleosols, have permitted the determination of the degree of aromatic substitution. From these data and the normal solid-state 13 C NMR data we have been able to develop a model for the average chemical structure of these humic acids that generally correlates well with permanganate oxidation data. The models depict these humic acids as benzene di- and tricarboxylic acids interconnected by biphenyl linkages. An increasing degree of substitution is observed with increasing geologic age. These structures may be characteristic of the resistant aromatic part of the “core” of humic substances that survives degradation.

Studies of angiospermous wood in Australian brown coal by nuclear magnetic resonance and analytical pyrolysis: new insights into the early coalification process

Abstract Many Tertiary coals contain abundant fossilized remains of angiosperms that often dominated some ancient peat-swamp environments; modern analogs of which can be found in tropical and subtropical regions of the world. Comparisons of angiospermous woods from Australian brown coal with similar woods buried in modern peat swamps of Indonesia have provided some new insights into coalification reactions. These comparisons were made by using solid-state 13 C nuclear magnetic resonance (NMR) techniques and pyrolysis-gas chromatography-mass spectrometry (py-gc-ms), two modern techniques especially suited for detailed structural evaluation of the complex macromolecules in coal. From these studies, we conclude that the earliest transformation (peatification) of organic matter in angiospermous wood is the degradation of cellulosic components. The efficiency of removal of cellulosic components in the wood varies considerably in peat, which results in variable levels of cellulose in peatified wood. However, the net trend is towards eventual removal of the cellulose. The angiospermous lignin that becomes enriched in wood as a result of cellulose degradation also is modified by coalifications reactions; this modification, however, does not involve degradation and removal. Rather, the early coalification process transforms the lignin phenols (guaiacyl and syringyl) to eventually yield the aromatic structures typically found in brown coal. One such transformation, which is determined from the NMR data, involves the cleavage of aryl ether bonds that link guaiacyl and syringyl units in lignin and leads to the formation of free lignin phenols. Another transformation, which is also determined from the NMR data, involves the loss of methoxyl groups, probably via demethylation, to produce catechol-like structures. Coincident with ether-cleavage and demethylation, the aromatic rings derived from lignin phenols become more carbon-substituted and cross-linked, as determined by dipolar-dephasing NMR studies. This cross-linking is probably responsible for preventing the lignin phenols, which are freed from the lignin macromolecule by ether cleavage and from being removed from the coal by dissolution. Pyrolysis data suggest that the syringyl units are altered more readily than are guaiacyl units, which leads to an enrichment of the guaiacyl units in fossil angiospermous woods. Although many of the coalification reactions noted above occur to some degree in all angiospermous fossil woods examined, some significant differences are observed in the degree of coalification of the fossil woods from the same burial depth in the brown coal. This indicates that the depth and the duration of burial are probably not entirely responsible for the variations in degree of coalification. It is likely that different rates of degradation in peat may have contributed to the variations in the apparent degree of coalification, considering the fact that some woods may have been altered more rapidly at the peat stage than others. Although preliminary, it is clear that a systematic study of botanically related woods in peat and coal leads to a more detailed differentiation of coalification reactions than have previous investigations. The combined use of solid-state 13 C NMR and py-gc-ms has facilitated this detailed new insight into coalification of angiospermous wood.

Infrared spectroscopy of coal maceral concentrates at elevated temperatures

Abstract Resinite, vitrinite and inertinite from three Chinese and one Australian coal were pyrolysed under nitrogen at temperatures up to 625 °C in a Fourier transform infrared (FT-i.r.) spectrometer. During pyrolysis the infrared spectra were obtained at increments of 25 °C. For the resinites, the main changes in chemical structure were the loss of protonated aliphatic carbon and a change in the distribution of carboxyl functional groups. Pyrolysis of vitrinite produced increased absorption from protonated aromatic carbon, particularly in the 700–900 cm −1 region, but a steady decrease in intensity of the 1600 cm −1 band. Formation of carbon dioxide was evident at temperatures as low as 150 °C and is postulated to arise from the potassium catalysed decomposition of carboxylic acids formed during pyrolysis. Inertinite showed no appreciable change in its i.r. spectrum until 300 °C. Above this temperature, increased absorption in the carbonyl region showed that some oxidation had occurred.

The nature of olefins and carboxyl groups in an Australian brown coal resin

The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (13C CP MAS NMR). Some additional solution 1H and 13C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C15 carbon atoms in the diterpenoids without cyclization of the methylene units at C8.

Developments in high-resolution solid-state13C NMR spectroscopy of coals

Abstract The recent development of “second generation” NMR experiments on coals is discussed in this paper. Such experiments have three aims: (1) To determine the extent to which quantitative aromaticity measurements can be made on coals by cross polarization-magic angle spinning (CP/MAS); (2) To obtain more detailed information on coal structure and reactivity than that given by the simple aromaticity measurements possible at the time; (3) To follow reaction pathways when coal is chemically modified. In this plenary lecture the relevant literature is reviewed, and new experimental work in all three areas outlined above is reported. Experimental evidence is presented which shows that aromaticity measurements on a bituminous coal by cross polarization (CP) or single pulse techniques give identical results. Relaxation data for naphthalene polymers suggest that these structures in coal are seen in CP experiments. Dipolar dephasing experiments suggest that the average size of the coal vitrinite molecule does not increase with increase in coal rank due to aromatic substitution reactions. Various relaxation experiments demonstrate how different carbon types can be distinguished in both13C-labelled and unlabelled coals.

Selective loss of carbohydrates from plant remains during coalification

Fossil leaves ofOleinites willsii, Banksieaephyllum angustum, associated organic matter and rhizomes ofGleichenia sp. isolated from Yallourn brown coal deposits, Latrobe Valley, Victoria, Australia and their living relatives have been analysed by high-resolution solid-state13C nuclear magnetic resonance spectroscopy, infrared spectroscopy and pyrolysis—gas chromatography—mass spectrometry. The fossil leaves and rhizomes retain carbohydrates and, on a carbon basis, the amounts of carbohydrates in the fossil rhizomes and their living relatives appear to be similar. On the other hand, the amount of carbohydrates in the fossil leaves is substantially less than in the living relatives. The organic matter found intimately associated with the fossil leaves is quite different in structure from the fossil leaves themselves and bears a closer resemblance to humic acids and the smallest (<75μm) fractions of Yallourn brown coal. Since the fossil leaves are found in stratified beds, interfolded with associated organic matter, it is suggested that during coalification the leaves and associated organic matter undergo independent transformations and are brought together by water transport.