G.H. Taylor

The cold-climate origin of inertinite-rich Gondwana coals

Abstract In the inertinite-rich Permian coals of Australian there occurs a close association between inertodetrinite and alginite of a kind which has been generally overlooked in the past. The association is believed to be a consequence of the environment of deposition and especially the climate, which is inferred to have been one of wet, cool summers and freezing winters. The inertodetrinite formed by drying out of a gelified, homogenised precursor; the algae lived at the periodically desiccated surface of the accumulating peat. Much of the evidence for these conclusions has come from the combined use of light microscopy and transmission electron microscopy.

DOMAIN STRUCTURE IN MP (MESOPHASE PITCH)-BASED FIBRES

Abstract The microstructure of a number of commercially available (Union Carbide, Thornel, or Amoco) mesophase pitch-based (MP) carbon fibres was investigated using light, scanning and transmission electron microscopy. Size, shape, and distribution of structure were examined in longitudinal and transverse sections. Because microtome sectioning methods produced considerable structural damage, a technique was developed for preparing ion-milled transverse sections for TEM. A domain structure is very common, perhaps ubiquitous, in MP fibres. Domains are long, thin needle-like or ribbon-like structural components of fibres that extend up to 100 μm parallel to the fibre axis and may be elongate in transverse section, the longer axis being 0.5 to 3 μm while the shorter axis is typically 0.2 μm. The fabric of domains is identified from textures in transverse polished and fractured sections. Many MP fibres examined have domains arranged in an oriented-core texture. This texture consists of polar zones where layering of domains is chaotic separated by an equatorial zone of layering continuous across each filament. PAC-man morphology can develop in some oriented-core filaments by radial failure in the flat equatorial regions. Not all domains are of the same kind. In dense domains, graphene layers are densely stacked with comparatively little void space, while microporous domains consist of thin walls of graphene sheets enclosing a high proportion of void space. Graphene layers within dense domains are oriented predominantly parallel both to the long axis of the domain in transverse section and to the fibre axis. Graphene layers in microporous domains have no preferred orientation. Dense domains represent former mesophase, while microporous domains represent a phase inferred to have been capable of forming at least some mesophase with generation of volatile substances. In some MP fibres, ordering in dense domains is turbostratic. In others, true graphite with three-dimensional crystal structure occurs, not as a separate domain type, but as a component of the domains described. All domains appear to originate at the time of pitch maturation (mesophase forming) and are considerably modified during spinning. Domains and their distribution influence mechanical properties. Factors such as the state of ordering within domains, volume fraction and distribution of microporous material and presence of folded and kinked layering and of flaws will modify processes like initiation and propagation of fracture and affect properties such as elastic modulus.

Micrinite — its nature, origin and significance

Abstract Transmission electron microscopy has been used in association with light microscopy to elucidate the nature of micrinite and micrinite-like macerals. Most occurrences of these consist of aggregates of much finer particles with either liptinitic or humic affinities. It is suggested that the term ‘micrinite‘ should be restricted to liptinite-related, micron-sized aggregates of particles about 50 nm in diameter. This micrinite occurs in close associated with, and forms from, liptinitic material during the generation of hydrocarbons. The 50-nm particles begin to form at the subbituminous stage of rank, but do not become visible as micrinite with light microscopy until the aggregates reach sufficient density and size. The progressive increase in the numbers of fine particles during diagenesis provides a guide to the generation of hydrocarbons from the liptinitic matter with which they are associated. Material which Shibaoka has termed ‘cavity-filling micrinite’ comprises finley particulate humic matter with affinity to vitrinite. Other ‘micrinite’ represents fine particles of inertodetrinite, and voids.

Biodegradation in coals and other organic-rich rocks

Abstract Biodegraded material and the remains of micro-organisms have been shown by transmission electron microscopy to be widespread in a range of Australian coals. Virtually all of this alteration, which has had significant effects on the properties subsequently attained by the coal, must have occurred at a very early stage of deposition. The micro-organisms appear to be mainly fungi and bacteria which have not only modified higher plant tissues but also represent significant amounts of added organic matter. Important amongst the latter are small but abundant occurrences of lipid-rich material of relevance in relation to the generation of hydrocarbons. The results suggest the need for reinterpretation of some light microscopic observations.

Microstructure in a series of mesophase pitch-based fibers from du pont: zones, folds, and disclinations

Abstract The microstructure of seven types of Du Pont fibers were studied using light, scanning, and transmission electron microscopy. The dominant microstructure in transverse section is of an oriented core region and a banded sheath. The orientation of layering within the sheath zig-zags about the radial direction in a regular pattern of folding corresponding to the banded structure. A transition zone occurs between the core and the sheath, and layering is often quite convoluted. An irregular pattern of finer scale folding, and a high density of splays and disclinations, also occur throughout the fiber. The microporous phase is absent and there is no evidence of abutments in the layering. It is concluded that these fibers were spun from mesophase containing no isotropic phase. The pattern of flow during spinning probably causes the regularly folded structure and modifies any pre-existing fine-scale folds and disclination structure. Consideration of the effects of all of these fine-scale microstructures upon fiber strength suggests that fold separation is the feature which critically controls strength. The microstructures in the Du Pont fibers may all help to give improved strength compared to other fibers, but other factors, such as reduced size and density of inherent flaws, cannot be discounted.

Influence of QI on mesophase structure

Abstract The influence of quinoline insoluble (QI) particles on the transformation of isotropic pitch to mesophase has been studied using light microscopy, scanning electron microscopy, and transmission electron microscopy. The authors conclude that QI does not significantly affect either the nucleation of mesophase spheres or the rate at which mesophase forms. However, QI does profoundly affect the structure of the pitch at all stages of conversion and the structure of carbons derived from mesophase. QI particles appear to “pin” the mesophase structures in their vicinity, making the mesophase behave as a much more viscous material than would otherwise be the case; this is consistent with the many changes of layer plane orientation observed within QI-rich mesophase. The complex structure caused by the QI persists through to the stage of solidification so that some properties of the carbon product may be much modified by controlling the occurrence of QI in the parent pitch. All as-received pitch samples, including nominally “QI-free pitches” contain significant numbers of QI particles.

Bituminite — A TEM view

Abstract An Illinois coal (high-volatile Bituminous B, of Carboniferous age) containing typical bituminite has been examined by transmission electron microscopy (TEM) to supplement observations with the light microscope. With TEM, the bituminite has a fine, fairly regular structure including voids of a characteristic shape. This structure is almost certainly inherited from a botanical precursor, and is thought to represent much-altered remains of former colonies of algae, probably green algae. The present remains contain abundant lipid-rich globules, and probably also include matter of algal and bacterial origin which cannot be resolved even at TEM resolutions.

Cathode deposits in fullerene formation — microstructural evidence for independent pathways of pyrolytic carbon and nanobody formation

Abstract Microstructures in cathode deposits formed during fullerene production by electrical arcing in helium have been examined in detail. This has provided new information about the mechanisms by which nanobodies (nanotubes and nanoparticles) and pyrolytic carbon are deposited. Nanobodies and pyrolytic carbon form independently; the former probably grow in the plasma then deposit on the electrode but much of the latter deposits directly on the electrode surface.

TEM OBSERVATIONS ON TYPE III KEROGEN, WITH SPECIAL REFERENCE TO COAL AS A SOURCE ROCK

Abstract Type III kerogen follows the coalification track of vitrinite or a bulk coal. It is often inferred that, because this organic matter is of comparatively low hydrogen and high oxygen content, it cannot be more than a marginal source of petroleum. This is not a correct approach because the actual source material is not the whole coal but only a small fraction. Some, at least, of this small fraction appears likely to be just as rich a source as much of Type I or Type II kerogen. There is no doubt that the liptinite macerals are important source materials. However, with TEM it can be shown that there are additional, and in some cases more significant, sources with varying degrees of thermal reactivity. These include: • -in vitrinite, the remains of fungi and bacteria, other fine lipid-rich matter, and suberin; • -in vitrinitic and especially in inertinitic coal, algal and algae-like material. Micrinite consists of aggregates of very fine spherical bodies which are formed when hydrocarbons are generated. The presence of such aggregates within the coal texture confirms the generative role of the lipid-rich components and provides an important indication as to whether generation has occurred.

Characterization of huminite macerals

Abstract The first results of an electron microscopy study of soft brown coals include observations of various cell structures not normally resolved with light microscopes. There is widespread evidence of gelification having occurred to produce spherical aggregates of huminitic material. Some macerals, especially attrinite, are revealed as highly heterogeneous in both component materials and in texture. Differential uptake of heavy metal ‘stains’ confirms that the huminitic macerals vary considerably in fine physical structure.