Parr Instrument 6200 - Manual (Page 33)

34
6200
Calorimeter Operating Instruction Manual
Use the following procedure when filling
and handling any of these tape-sealed
sample holders:
• Weigh the empty cup or capsule; then
cover the top with tape, trim with a knife
and press the trimmed edge firmly
against the metal rim. Also cut and
attach a small flag to the disc (see
Figure 5-7).
• Puncture the tape at a point below the
flag, then re-weigh the empty cup with
its tape cover.
• Add the sample with a hypodermic
syringe; close the opening with the flag
and re-weigh the filled cup.
• Set the cup in the capsule holder and
arrange the auxiliary fuse so that it
touches the center of the tape disc.
• Just before starting the test, prick the
disc with a sharp needle to make a
small opening which is needed to
prevent collapse of the disc when
pressure is applied.
•
Fill the bomb with the usual oxygen
charging pressure
.
• The calorimeter will fire the bomb and
complete the test in the usual manner.
Volatile samples are defined as one with
an initial boiling point below 180ºC per
ASTM D-2.
Low volatile samples with a high water
content, such as urine or blood, can be
burned in an open capsule by absorbing the
liquid on filter paper pulp or by adding a
combustion aid, such as ethylene glycol.
Because of the difference in combustion
characteristics of the many different materials
which may be burned in an oxygen bomb, it is
difficult to give specific directions which will
assure complete combustions for all samples.
The following fundamental conditions
should be considered when burning samples:
• Some part of the sample must be heated
to its ignition temperature to start the
combustion and, in burning, it must
liberate sufficient heat to support its own
combustion regardless of the chilling
effect of the adjacent metal parts.
• The combustion must produce sufficient
turbulence within the bomb to bring
oxygen into the fuel cup for burning the
last traces of the sample.
• Loose or powdery condition of the sample
which will permit unburned particles to be
ejected during a violent combustion.
• The use of a sample containing coarse
particles which will not burn readily.
Coal particles which are too large to
pass a 60 mesh screen may
not burn completely.
• The use of a sample pellet which has
been made too hard or too soft. Either
condition can cause spalling and the
ejection of unburned fragments.
• Insufficient space between the
combustion cup and the bottom of the
bomb. The bottom of the cup should
always be at least one-half inch above
the bottom of the bomb or above the
liquid level in the bomb to prevent
thermal quenching.
•
Excessive moisture or non-
combustible material in the sample. If
the moisture, ash and other non
combustible material in the sample
amounts to approximately 20% or
more of the charge, it may be difficult
to obtain complete combustion. This
condition can be remedied by adding a
small amount of benzoic acid or other
combustion aid.
Volatile
Sample
Holders
Continued
Poor
Combustion
5-8
5