Quantitative characterization of coal by means of
microfocal X-ray Computed Microtomography (CMT)
and Color
Image Analysis (CIA)
Fysico-Chemische Geologie & Department of Civil
Engineering
Katholieke Universiteit Leuven (KUL)
Leuven,
Belgium
Int. J. Coal
Geol. 34, 69-88, 1997.
Abstract
Microfocal X-ray computed microtomography (CMT)
isa novel technique that produces three-dimensional maps of
the distribution of the linear attenuation coefficient inside
an object. In contrast to the more conventional medical
computerized tomography (CT) systems, a microfocal X-ray
source is used. This enables a far better spatial
resolution. The linear attenuation coefficient or tomodensity
is dependent on the physical density and the mineralogy of the
object to be imaged, and on the energy of the radiation
used. Earlier work by Verhelst et al. (1996) presented the
results of the correlation of the tomodensities obtained from
three-dimensional CT scans with two-dimensional data on the
composition of a coal sample acquired with color image
analysis (CIA), a camera technique. This analysis assumed the
linear proportionality of the tomodensity with the real
physical bulk density, which is true only for certain energy
ranges. In this paper, we use CMT-devices for a similar
correlation. For sake of comparison, the same core sample was
used. First, new CIA-data on the surface composition along two
profiles were sampled with greater detail (100 micron). These
data are subjected to a geostatistical analysis to quantify
the spatial dependence between the measurements. Second,
CMT-tomograms were made, yielding spatial resolutions twice as
high as medical CT. A multivariate correlation was carried
out, and two improved (geo)statistical methods are
suggested. The different energy range of the microfocal X-ray
source compared to medical CT, however, produces some bias in
the correlation of the tomodensities with the surface
percentages of the constituents. We therefore suggest that the
linear attenuation coefficient be treated as a separate
unit. No attempt was made to translate the linear attenuation
coefficient to the physical bulk density of the different
constituents of coal (e.g. macerals).
Figures
- Figure 01 Energy dependence of the linear attenuation coefficient for hexagonal carbon
- Figure 02 The microfocal X-ray tube
- Figure 03 Geometrical unsharpness
- Figure 04 Reduction of intrinsic unsharpness
- Figure 05 Schematic representation of Color Image Analysis (CIA)
- Figure 06 Photograph of the surface of the coal sample
- Figure 07 Computerized Micro Tomography tomodensities of the coal sample
- Figure 08 Cumulative normalized surface percentages of the five constituents (vitrinite, liptinite, inertinite, pyrite and binder) sampled along trace 1
- Figure 09 Cumulative normalized surface percentages of the five constituents (vitrinite, liptinite, inertinite, pyrite and binder) sampled along trace 2
- Figure 10 Filtered normalized surface percentages of trace 1
- Figure 11 Filtered normalized surface percentages of trace 2
- Figure 12 Results of the multiple regression for trace 1: predicted versus observed tomodensity
- Figure 13 Results of the multiple regression for trace 2: predicted versus observed tomodensity
- Figure 14 Predicted versus observed tomodensity after breakpoint regression
- Figure 15 Experimental semivariogram for the virtinite surface percentage of trace 1
- Figure 16 Experimental semivariogram for the virtinite surface percentage of trace 2
Frederik Simons
Last modified: Wed Apr 12 23:06:25 EDT 2023