Fusionfire
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Discrepancy in density of graphite and anthracite coal
Hello folks,
Could someone please explain the large discrepancy between the densities of graphite and anthracite coal?
Graphite density: 2.09 - 2.23 g/cc
http://en.wikipedia.org/wiki/Graphite
Anthracite coal density: 1.3 - 1.4 g/cc
http://en.wikipedia.org/wiki/Anthracite
Anthracite is defined as 92 - 98% carbon content.
I don't think the discrepancy could be due to voids, because anthracite is formed under pressure and the upper limit of its density is still well
below that of graphite.
Thanks.
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gutter_ca
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Per Wiki:
| Quote: |
Anthracite may be considered to be a transition stage between ordinary bituminous and graphite, produced by the more or less complete elimination of
the volatile constituents of the former, and it is found most abundantly in areas that have been subjected to considerable earth-movements, such as
the flanks of great mountain ranges. Anthracite is a product of metamorphism and is associated with metamorphic rocks, just as bituminous is
associated with sedimentary rocks. For example, the compressed layers of anthracite that are deep mined in the folded (metamorphic) Appalachian
Mountains of the Coal Region of northeastern Pennsylvania are extensions of the layers of bituminous coal that are strip mined on the (sedimentary)
Allegheny Plateau of Kentucky and West Virginia, and Western Pennsylvania. In the same way the anthracite region of South Wales is confined to the
contorted portion west of Swansea and Llanelli, the central and eastern portions producing steam coal, coking coal and domestic house coals.
Structurally, it shows some alteration by the development of secondary divisional planes and fissures so that the original stratification lines are
not always easily seen. The thermal conductivity is also higher, a lump of anthracite feeling perceptibly colder when held in the warm hand than a
similar lump of bituminous at the same temperature. The chemical composition of some typical anthracites is given in the article coal.
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Fusionfire
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Sorry pardon me being slow but I don't see how the quoted text explains why graphite is 50% denser than anthracite coal.
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Xenoid
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Graphite is a hexagonal crystalline form of carbon (albeit very soft) comprising layers of carbon atoms in a regular hexagonal pattern.
Anthracite coal is an impure amorphous form of carbon, often containing ghostly relicts of the original plant material and spores from which it
formed!
Crystalline vs. amorphous!
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Fusionfire
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Wow, then the difference between the crystalline and amorphous densities is huge here. I don't think that happens even for cystalline vs. amorphous
metals and window glass.
So I presume graphite when made from pyrolisis of polymer fibre precursors, the fibres must be drawn first to ensure crystallinity of the starting
material and then the product?
Can the density of anthracite coal be made to approximiate graphite if it were hydraulically crushed or ball milled into a fine dust, and compressed
under high pressure + temperature?
Is it possible to convert anthracite coal into crystalline graphite?
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UnintentionalChaos
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Quote: Originally posted by Fusionfire  |
So I presume graphite when made from pyrolisis of polymer fibre precursors, the fibres must be drawn first to ensure crystallinity of the starting
material and then the product?...
Is it possible to convert anthracite coal into crystalline graphite? |
1) Nah, just chuck it in a graphitizing kiln. You get it hot enough and the carbon will rearrange itself into a proper lattice.
2) Yes, graphitizing kiln. Or sublime it with an arc or something.
[Edited on 1-21-12 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Fusionfire
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So does this mean that if you take a lump on anthracite coal of density 1.4 g/cc and put it in a kiln above its annealing temperature, you start
inducing crystallisation and an increase in density up to 2.23 g/cc?
Or will you just produce a mixed crystalline/amorphous lump of coal with cracks and thermal residual stresses due to phase changes inside it?
What is the annealing temperature of the amorphous -> crystalline phase transition?
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turd
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Simple: H atoms are very light and take a lot of space. C-C in aromatics is ~1.35 Å whereas non-bonded H-H is around 2.4 Å (VdW radius of hydrogen
is 1.2 according to Wikipedia).
Nonacosane has 85% C and has a density of 0.8. Then anthracite is certainly not densely packed, full of defects, and so on.
| Quote: | | Graphite is a hexagonal crystalline form of carbon |
Or trigonal.
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leu
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An old article on graphite synthesis:
Transformation of Other Forms of Carbon into Graphite.
W. C. Arsem
Ind. Eng. Chem., 1911, 3 (11), pp 799–804
DOI: 10.1021/ie50035a002
which includes a discussion about the amorphous nature of carbon 
Attachment: ie50035a002.pdf (173kB)
This file has been downloaded 674 times
Chemistry is our Covalent Bond
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fledarmus
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Graphite is essentially large sheets of benzene rings, with the sheets stacked on top of each other. The fact that the sheets slide nicely across each
other gives it its slipperiness and use as a lubricant, and the fact that all the pi-electrons can be delocalized across the entire sheet gives it its
electrical conductivity. Under relatively normal conditions of heat and pressure, this is the most stable form that pure carbon can adopt. If the
pressure and temperature are extremely high, carbon can adopt a denser configuration, the adamantane (or diamond) structure, in which each carbon is
bonded to four other carbons at the points of a tetrahedron, rather than the benzene ring structure.
If you take any hydrocarbon and subject it to heat and pressure in the absence of oxygen, it will gradually adopt the graphite structure. This is
pyrolysis - oxygen gets eliminated as water, hydrogen gets eliminated either as water or methane, and so on. Typically structures such as starches,
sugars, resins, and cellulose, which give plant materials so much of their structure, are already laid out in mostly five and six membered rings, but
the hydrogens and hydroxyl groups take up a lot of space. As you compress and heat wood (excluding oxygen), you can remove all of the volatile
material and compress the remaining material into soft coal, and as the process continues and more hydrogen and oxygen are removed, the material will
get denser and denser until only the carbons remain and the material is all graphite.
I say "only the carbon", but that isn't quite true. Nitrogen and sulfur, in particular, can exist inside the graphite structure with only a small
energy cost, and most coal contains at least some nitrogen and sulfur. The amount of sulfur in the original organic material determines the amount of
sulfur in the final coal, and some coals are much sweeter than others due to the source of the original organic material.
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Fusionfire
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| Quote: Originally posted by fledarmus | Graphite is essentially large sheets of benzene rings, with the sheets stacked on top of each other. The fact that the sheets slide nicely across each
other gives it its slipperiness and use as a lubricant, and the fact that all the pi-electrons can be delocalized across the entire sheet gives it its
electrical conductivity. Under relatively normal conditions of heat and pressure, this is the most stable form that pure carbon can adopt. If the
pressure and temperature are extremely high, carbon can adopt a denser configuration, the adamantane (or diamond) structure, in which each carbon is
bonded to four other carbons at the points of a tetrahedron, rather than the benzene ring structure.
If you take any hydrocarbon and subject it to heat and pressure in the absence of oxygen, it will gradually adopt the graphite structure. This is
pyrolysis - oxygen gets eliminated as water, hydrogen gets eliminated either as water or methane, and so on. Typically structures such as starches,
sugars, resins, and cellulose, which give plant materials so much of their structure, are already laid out in mostly five and six membered rings, but
the hydrogens and hydroxyl groups take up a lot of space. As you compress and heat wood (excluding oxygen), you can remove all of the volatile
material and compress the remaining material into soft coal, and as the process continues and more hydrogen and oxygen are removed, the material will
get denser and denser until only the carbons remain and the material is all graphite.
I say "only the carbon", but that isn't quite true. Nitrogen and sulfur, in particular, can exist inside the graphite structure with only a small
energy cost, and most coal contains at least some nitrogen and sulfur. The amount of sulfur in the original organic material determines the amount of
sulfur in the final coal, and some coals are much sweeter than others due to the source of the original organic material. |
Thank you for your very useful description 
How are micrometric, very high purity graphite powders manufactured? E.g.
http://www.hpmsgraphite.com/micronsizegraphite.html
By pyrolysis of a suitable high carbon precursor like anthracite coal?
What are the necessary pressures and temperatures to achieve high purity graphite from coal?
What is the minimum size that can be accomplished with ball milling?
Am I correct in estimating that the density of a 99.95% carbon graphite particle would be about 2.23 g/cc, while the density of the loose bulk powder
would be reduced by 63.4% (random close packing of spheres) to 1.4 g/cc?
[Edited on 26-1-2012 by Fusionfire]
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