4. Results
4.1. Unconfined samples
20 measurements of each of the 219 unconfined samples were
taken parallel to the banding and averaged to receive comparable
results for each sample. Fig. 3 shows all 20 individual SSRH
measurements (blue dots) and the average SSRH for each sample
(coloured dots). The red lines indicate the standard deviation (SD)
for each average SSRH value. For a better visualisation the samples
are sorted regarding their SSRH value in ascending order for each
lithotype. Table 1 shows the average SSRH, average SD, the amount
of bright bands and number of samples tested for each lithotype of
the 219 unconfined samples.
To optimise the data set for determination of relationships
between SSRH and coal lithotype and rank, 53 samples with high
ash, tending towards carbonaceous mudstone, were eliminated
from the first data set. This was based on the overall density of the
entire sample. From the remaining 166 coal samples, 84 samples
with a relative density (RD) below 1.8 g/cm3, as this density value
is most representative of the cut off between coal and high ash
coal or carbonaceous mudstone, were used for further analysis and
presented in Table 2. A progressive increase of hardness with a
change of lithotype along with a decrease of the amount of bright
bands from bright banded (low SSRH) to dull (high SSRH) can be
seen in the first column of both tables (Tables 1 and 2). The
average SD for the banded samples could be slightly higher due to
about the same frequency of bright and dull bands in each banded
sample. During the measurement it was not recorded if the SSRH
tester hit a bright or dull band.
Fig. 4 shows the progress of optimising the data set from 219
samples to 84 coal samples with a RD below 1.8 g/cm3. The SSRH
values are divided into a cluster system of 5 (x-axis). The y-axis
indicates the frequency of each SSRH value for each data set. The
numbers above the columns illustrate the count of each SSRH
value in each cluster for all three data sets.
In order to determine if hardness was a factor of rank, available
vitrinite reflectance (VR) (%) data were plotted against each corre
sponding SSRH value of the cleaned data set (RDo1.8 g/cm3). VR is a
good indicator of high rank coals, since it is measured only on a
certain maceral type (band telovitrinite) and therefore avoids the
composition variability, that affects the chemical properties (e.g.
Volatile Matter either as received or on a dry ash free basis) [6].
Fig. 5 separates the samples into each different CM. Samples from the
FCCM and RCM show a decreasing hardness with increasing rank,
whereas the samples from the MCM indicate an increase in hardness
with increasing rank, as these are higher rank samples. Further all
samples with a VR above 1.8% show an increase in hardness with