Terry D. Rantell

Load transfer and deformation mechanisms in carbon nanotube-polystyrene composites

Multiwall carbon nanotubes have been dispersed homogeneously throughout polystyrene matrices by a simple solution-evaporation method without destroying the integrity of the nanotubes. Tensile tests on composite films show that 1 wt % nanotube additions result in 36%–42% and ∼25% increases in elastic modulus and break stress, respectively, indicating significant load transfer across the nanotube-matrix interface. In situ transmission electron microscopy studies provided information regarding composite deformation mechanisms and interfacial bonding between the multiwall nanotubes and polymer matrix.

Fabrication of Carbon Multiwall Nanotube/Polymer Composites by Shear Mixing

The dispersion of nanotubes in polymer matrices has been investigated as a means of deriving new and advanced engineering materials. These composite materials have been formed into fibers and thin films and their mechanical and electrical properties determined. The nanotube concentration at which conductivity was initiated (the percolation threshold) varied with host polymer. In poly(propylene), this was as low as 0.05 vol.-%, while higher concentrations were required for polystyrene and particularly for ABS. There was a small increase in elastic modulus and decrease in tensile strength at low nanotube loading, but as the concentration was increased there was a progressive increase in both strength and stiffness.

Estimation of the concentration of donatable hydrogen in a coal solvent by n.m.r.

Abstract 1 H and 13 C nuclear magnetic resonance (n.m.r.) spectroscopies have been used to study the changes in composition of a hydrogenated anthracene oil solvent that occur during extraction of a UK bituminous coal. It has been shown that the principal hydrogen donor groups in the solvent are hydroaromatic and naphthenic rings in hydroaromatic species. Good agreement was achieved between the concentration of donatable hydrogen estimated from n.m.r., and the amount of hydrogen transferred from the solvent during exhaustive extraction.

Synthesis of isotropic carbon fibers and activated carbon fibers from pitch precursors

The influence of pitch precursor composition on the formation and properties of isotropic pitch fibers from non-conventional precursors has been examined. Changes in fiber weight that occur during the oxidative stabilization of green fibers are inversely related to the observed axial contraction. The weight gain upon stabilization also increases, and the contraction decreases with increasing pitch carbon content and aromaticity while the opposite occurs with increasing hydrogen and hetero-atom (H, N, O and S) content. Similar trends are found for fiber carbonization. The combined effects of stabilization and carbonization give a fiber yield of between 50 to 86% of the green fibers, with axial contractions of 12 to 28%, the highest yield corresponding to the smallest contraction. The net yield increases with pitch carbon content and aromaticity, and decreases with hetero-atom content, while the overall axial contraction decreases. The fiber tensile strength was found to increase with precursor carbon content, carbon yield and aromaticity. The activation rate of the derived fibers increased with increasing heteroatom content, especially oxygen content. While most fibers were microporous upon activation, fibers from shale oil and the sub-bituminous coal extract, developed a more mesoporous structure.

Filtration in coal liquefaction. Influence of digestion conditions in the filtration of non-hydrogenated coal digests

Abstract A series of experiments has been carried out to study the way in which preparation conditions of coal digests influence filtration rate. It was shown that a relation exists between cake resistivity and digestion temperature and time, and therefore good control over digestion conditions is important for rapid filtration. Particular attention must be paid to the design of the reactor to ensure that all the material is given the same heat-treatment. The optimum residence time occurs when repolymerization of the dissolved coal commences.

Filtration in coal liquefaction. Influence of filtration conditions in non-hydrogenated systems

Abstract A series of experiments has been carried out to study the effects of filtration conditions upon the rate of filtration of non-hydrogenated coal digests. The results show the dependence of cake resistivity on both the filtration temperature and pressure. Filter cakes were found to be compressible, resulting in smaller increases in rate with increasing pressure than with incompressible cakes. The filtration temperature determines the packing of residual solids in the cake which in turn affects the cake resistivity. An empirical relation has been derived between filtration temperature and resistivity. With increasing temperature there is an increase in filtration rate due to the reduced viscosity, but a reduction owing to a higher packing density of solids in the filter cake.

Kinetics of coke formation from coal solutions

Abstract The reaction kinetics for the formation of mesophase from coal solutions has been studied under conditions similar to those experienced in a delayed coker preheater coil, i.e. at temperatures from 475 to 525 °C approached at high heating rates. The degree of polymerization of the heat-treated materials has been assessed by their solubility in two solvents, cyclohexane and quinoline. An approximation has been made in order to make a kinetic analysis for the formation of insolubles in a non-isothermal system. It has been found that the polymerization of the dissolved coal component, as evidenced by the formation of quinoline insolubles during the heat-treatment of concentrated coal solutions, is essentially a second-order reaction with an apparent activation energy of ≈190 kJ mol−1. The formation of cyclohexane insolubles from the diluent oil is a slower reaction showing first-order kinetics.

Reactivity of cycloalkanes during the solvent extraction of coal

Abstract The reactivity of cycloalkanes, either alone or as part of a solvent mixture, during the solvent extraction of coal at 430 °C has been studied. When used with polyaromatic compounds (⩾ 3 rings) as solvents, cycloalkanes participate in hydrogen donation reactions giving rise to high extraction yields of the coal.

Carbonization and liquid-crystal (mesophase) development. 18. carbonization of coal-extract solutions (non-hydrogenated): influence of digestion conditions upon optical texture of cokes

Abstract Coal-extract solutions have been produced by the dissolution of a prime coking coal in anthracene oil followed by the removal of the undissolved solids. A range of coal-extract solutions prepared under different conditions was carbonized and the optical texture of the polished surfaces of the resultant cokes were assessed. The coal-extract solution prepared with the longest digestion time and at the highest temperature produced a coke with the largest anisotropic domains with some flow structure. Removal of the anthracene oil component of the coal-extract solution by extraction with selected solvents modified the carbonization behaviour such that although the coke yield increased substantially there was a significant decrease in the size of the anisotropic domains of the resultant cokes.

Filtration in coal liquefaction.: 2. Relation between digestion conditions and filtration rate

Abstract In systems for the liquefaction of coal by solvent extraction, removal of the undissolved solids from the liquefaction products is a fundemental part of the process. For separation of solids by filtration to be economically viable, it is essential to achieve high filtration rates. The influence of the extraction conditions, temperature, residence time and coal feed size, on the rate of filtration has been investigated. It has been shown that the rate of filtration is sensitive to the presence of a gel-like intermediate formed during the dissolution of the coal. The formation of this intermediate imposes limitations on the choice of digestion conditions, in particular the coal feed size. However, by inducing polymerization, the gel can be stabilized, thus allowing significantly improved filtration rates to be achieved.