Properties of cokes and graphites.
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
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
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
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
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