can be carried out in sequence using the
same test specimen. Alternatively, the determination of moisture,
volatile matter, or ash can be carried out separately on test
specimens of coal or coke.
13.2 Sequential Determination of Moisture, Volatile Matter
and Ash:
13.2.1 After verifying instrument setup according to Section
11 on the preparation of apparatus, load and tare the crucibles.
Add 1 g 6 0.1 g of coal or coke to the crucible in the balance
position and weigh immediately before advancing the next
crucible. Transfer the test specimen from the sample bottle to
the crucible quickly to minimize the exposure of the test
specimen to the atmosphere during the initial weighing process.
13.2.2 For moisture determinations, heat the weighed test
specimens in crucibles without the covers at 107 6 3 °C. Use
a drying gas flow rate of 0.4 to 1.4 furnace volume changes per
minute (see 8.1). Program the instrument to terminate the test
when the test specimens and crucibles have reached a constant
mass (see 11.3). Alternatively, program the instrument to allow
for moisture determination by heating the test specimens for 1
h.
13.2.3 For volatile matter determinations following the
moisture analysis, place covers on the crucibles in the TGA
carousel (the crucibles are placed automatically in some
systems and manually in others). Program the instrument to
reweigh the crucibles, with specimens inside, and covers in
place before initiating the volatile matter part of the cycle.
13.2.3.1 To provide an inert atmosphere, use nitrogen or
argon with a flow rate of 0.7 to 1.4 furnace volume changes per
minute to sweep away the volatile components. Raise the
furnace temperature at a rate such that the temperature is raised
from 107°C to 950 6 10°C in a 26-30 min time period (See
Note 2). Program the instrument to hold at this temperature for
7 min. The TGA weighs the covered crucibles at regular
intervals while the temperature of the furnace is raised. The
weights of the crucibles and covers at the end of the 7-min hold
period are used in the calculation of the volatile matter.
NOTE 2—It is the nature of resistance furnaces to start heating slowly
with a gradual increase in heating rate until the furnace heating element
controller reduces the power to moderate the heating rate. As a result, high
furnace ramp rates are seldom ever uniform over the temperature range
selected. Selecting a heating time (26-30 min) with a high heating ramp
rate accomplishes the desired result, to duplicate the conditions (Macro
TGA furnaces set at 30-45°C/min ramp rate) that were used by the
laboratories in the interlaboratory study. At the same time, it allows the
Macro TGA furnaces to moderate the heating rate enough to avoid
overshooting the selected high temperature of 950°C.
13.2.3.2 With strongly caking low-volatile and mediumvolatile
bituminous coals, the coke button can burst as a result
of the rapid liberation of volatile matter within the button. This
is designated as popping. Such popping can blow the lid off the
crucible and cause mechanical loss of the coked material.
When evidence of such popping is observed, reject the determination
and repeat the test with smaller test specimen sizes
until popping is no longer evident. Also, some high swelling
coals can expand beyond the volume of the crucible such that
they raise the crucible cover and stick to the underside of the
cover. This material can be lost when the crucible cover is
removed. For swelling coals examine the crucible covers as
D7582 – 10
3
they are removed.