Carbons and graphites have many industrial applications e.g. synthetic graphite (as moderators in the nuclear industry), natural flake graphites (for application in the manufacture of anti-piping agents) and metallurgical coke (for use in the blast furnace). The overall objective of this Thesis is to study effects of changes in properties of graphites and cokes by (i) radiolytic gasification of graphite, (ii) intercalation of natural flake graphites by sulphuric acid and (iii) intercalation of metallurgical cokes by potassium. (i) Radiolytic gasification Methods of image analysis have been developed to study the pore structure of graphite. These methods have been used to investigate the change in pore structure of a series of radiolytically gasified graphites. To examine the pore structure of the graphites by optical and scanning electron microscopy, each sample was vacuum-impregnated with a slow-setting resin containing a yellow dye. A semi-automatic image analysis system (Micromeasurements VrDS) linked to the optical microscope, enabled data on porosity to be obtained. The pore outline data, so obtained, were used by programmes on the controlling microcomputer to provide pore parameters such as cross-sectional areas, perimeters, Feret's diameters and shape factors. The results show that pores less than 100 ~m2 cross-sectional area are gasified because of the inability of the inhibitors (carbon monoxide and methane) to deactivate activated CO2* species before reaching the pore wall. Pores >1000 ~m2 cross-sectional area show only small changes in size and shape because of the deposition of carbon from methane inhibitor in these pores and are only developed at weight losses >17.0 wt.% by coalescence of open porosity <100 ~m2 cross-sectional area. (ii) Intercalation of natural flake graphite's Techniques have been developed to distinguish between natural flake graphite's and establish those suitable for use as anti-piping agents. Techniques used to examine the structure of natural flake graphite's include EDAX analysis to monitor amounts and distributions of elements, bromine intercalation to assess crystallographic ordering and image analysis to examine size and shape of the natural flake graphite's before and after intercalation. Results indicated that performances of the natural flake graphite's for use in intercalation studies can be predicted by assessing morphology and extents of fissures, bromine uptake, and mineral distribution of the flakes. Flakes suitable for intercalation studies have a mean flake thickness of ~25 ~m. Bromine uptake can be used to give an indication of the perfection of stacking. A high bromine uptake is desirable indicating a high stacking order i.e. good crystal perfection. Fissures in the natural flake graphite's are advantageous particularly in flakes of 40-70 ~m thick, by facilitating, a mean flake thickness of ~25 ~m. Fissures in the intercalated flake are detrimental as they may allow an 'escape route' to desorbing intercalate. Mineral impurities in the graphite flakes are of importance as they influence the flake thickness and cleavage properties. (iii) Intercalation of metallurgical cokes by potassium It is considered that the alkali metals, particularly potassium, have a crucial role in the breakdown of coke material during blast furnace operation. Extents of degradation, related to coke structure (optical texture) are examined to identify those structural aspects of cokes which are susceptible to alkali attack. The mechanism of potassium entering into metallurgical coke is investigated, ~. solid state diffusion, intercalation, absorption and adsorption. Metallurgical cokes, with a range of heat-treatment temperatures, graphitic carbon, and a shot-coke of small sized optical texture were heated with potassium vapour, either from direct addition of metal, or formed by heating a mixture of potassium carbonate with carbon black.Results of the study indicate that the rank of coking coal, and hence the optical texture of the derived coke, influenced the extents of degradation of the metallurgical cokes. Cokes from high rank coals (204 and 30lb) were consistently less degraded than those from lower rank coals (401 and 502 rank). Optical texture studies indicated that those optical textures most resistant to degradation by potassium vapour were of single component textures (flow anisotropy and isotropic). Multi-component textures as found in metallurgical cokes were less resistant to alkali attack. Heat-treatment of metallurgical cokes increased their resistance to degradation (2800 > 2400 > 2000 > 1500 > 11000C HTT). Degradation of metallurgical coke is thought to be due to mixed staging (yellow/blue/black colouration) of intercalates in graphitizable carbons because of non-uniform concentration of potassium causing high stresses and leading to break-up by macro-crack formation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:353772 |
| Date | January 1985 |
| Creators | Murdie, Neil |
| Publisher | University of Newcastle upon Tyne |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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