Parr Instrument 6200 - Manual (Page 31)

32
6200
Calorimeter Operating Instruction Manual
Combustion
Capsules
Coarse
Samples
Non-volatile samples to be tested in
Parr oxygen bombs are weighed and
burned in shallow capsules measuring
approximately 1" diameter and 7/16" deep.
These are available in stainless steel, fused
silica and platinum alloyed with 3-1/2%
rhodium.
Stainless steel capsules (43AS) are
furnished with each calorimeter. When
combusting samples that contain metal
particles such as aluminum or magnesium,
the non-metallic (fused silica) 43A3 Capsule
is required. When superior corrosion
resistance is needed, the Platinum Rhodium
43A5 Capsule is required.
The stainless steel capsules will acquire
a dull gray finish after repeated use in an
oxygen bomb due to the formation of a
hard, protective oxide film. This dull finish
not only protects the capsule, but it also
promotes combustion and makes it easier to
burn the last traces of the sample.
Capsules should be monitored for
wear. Do not use the capsule if the
wall or base thickness is less than 0.025”.
New capsules are heated in a muffle
furnace at 500ºC for 24 hours to develop
this protective coating uniformly on all
surfaces. This treatment should be repeated
after a capsule has been polished with an
abrasive to remove any ash or other surface
deposits. Heating in a muffle is also a good
way to destroy any traces of carbon or
combustible matter which might remain in
the capsule from a previous test.
Note:
After heating, place the capsules in a
clean container and handle them only
with forceps when they are removed to
be weighed on an analytical balance.
Fibrous and fluffy materials generally
require one of three modes of controlling the
burn rate. Fibrous materials do not pelletize
readily and generally require either moisture
content of combustion aid such as mineral
oil to retard the burn rate and avoid
development of high pressures.
Partial drying may be
necessary if the moisture content
is too high to obtain ignition, but if
the sample is heat sensitive and
cannot be dried, a water soluble
combustion aid such as ethylene
glycol can be added to promote
ignition.
In most cases it may be necessary to
burn coarse samples without size reduction
since grinding or drying may introduce
unwanted changes. There is no objection to
this if the coarse sample will ignite and burn
completely. Whole wheat grains and
coarse charcoal chunks are typical of
materials which will burn satisfactorily
without grinding and without additives or a
special procedure.
Foodstuffs and
Cellulosic
Materials
5-6
5