IKA C 3000 isoperibol, Руководство по эксплуатации

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Complete combustion
To correctly determine the gross calorific value, it is of fundamen-
tal importance that the sample undergoes complete combustion.
After each experiment, the crucible and all solid residues must be
examined for any signs that combustion was not complete.
In case of using substances tending to squirt it is not possible to
ensure complete combustion. Substances with low flammabil-
ity ( substances with a high content of mineral matter and low-
calorific substances) will often undergo complete combustion only
with the aid of combustion capsules or combustion bags (C 10/
C 12 see “Accessories“).
It is also possible to use liquid combustion aids such as paraffin oil.
The combustion aids as well (for example the cotton thread) must
undergo complete combustion. If unburned residues are left over,
the experiment must be repeated.
Calibration
To ensure precise, reproducible results of the measurement, the
calorimeter system is calibrated after it is initially placed in ser-
vice, after service jobs, after parts are replaced and at specific time
intervals. During calibration, the heat capacity of the calorimeter
system is redetermined.
Regular calibration is absolutely essential to obtain accurate
measurements!
For this purpose, a specific quantity of a reference substance un-
dergoes combustion in the IKA
®
C 3000 isoperibol under the con-
ditions of the experiment. Since the gross calorific value of the
reference substance is known, it is possible after combustion has
occurred to calculate the heat capacity based on the increase in
temperature of the calorimeter system.
The reference substance for calorimetry on an international level
is benzoic acid of the National Bureau of Standards (NBS Standard
Sample 39 J) with a guaranteed gross calorific value.
The thermal capacity is derived from the formula for the calorific
value.
CV = (Ho * m + Qext) / DT
Depending on the standard used, determination of the thermal
capacity may require performance of several measurements. Us-
ing various statistical criteria the average value is calculated and
is used as the thermal capacity for subsequent determinations of
calorific values.
For more detailed information on calibration please see the rele-
vant standards. If the IKA
®
C 3000 isoperibol is operated with sev-
eral different decomposition vessels, you will need to determine
the heat capacity of the system for each decomposition vessel.
The parts of each decomposition vessel must then not be swapped
with parts from other vessels.
In addition the thermal capacity depends to a small extent on the
measurement procedure used. The thermal capacity determined
for each measurement procedure that is used.
Instructions on calibration
Ensure that calibration is carried out under the same conditions as
the subsequent tests. If substances are used in the decomposition
vessel in combustion tests (e.g. distilled water or solutions), you
must use exactly the same amount of this substance for calibra-
tion.
For determination of calorific values the increase in temperature
must be about as great as for the calibration (e.g.: 2 tablets = ap-
prox. 1 g benzoic acid =˜ 3 K). The optimum sample quantity must
de determined by several trials where necessary.
• For substances with low flammability or low calorific sub-
stances use combustion aids (see “Accessories“). Before the
capsules or the combustion bag is filled with the substance
to be determined, it must be weighed in order to determine
the additional extraneous energy introduced into the system
from the weight and the gross calorific value. This is taken
into consideration with QExtern2. The amount of combustion
aid should be as little as possible.
• Under the conditions that prevail during calorimetric mea-
surements, sulfur and nitrogen undergo combustion and
form SO
2
, SO
3
and NO
X
. Sulfuric and nitric acid arise in com-
bination with the water resulting form combustion. Heat of
solution is also generated. This heat of solution is taken into
consideration in calculating the gross calorific value. In or-
der to quantitatively record and determine all acids that have
been formed, about 5 ml of distilled water or another suit-
able substance can be added to the decomposition vessel
before the experiment.
The calibration of the system must have been performed in
accordance with the instructions!
After combustion, the water that was added, is collected and the
decomposition vessel is rinsed thoroughly with distilled water. The
rinsing water and the solution formed from the water that was
added are combined and the acid content of the combined solu-
tion is examined. If the sulfur content of the combustion aid and
the nitric acid correction are known, the water does not need to
be analyzed.
To increase the service life of parts to wear and tear (O rings, seals
etc.) we recommend to work with water added to the experiment
as a matter of general principle.
WARNING
Caution! Risk of corrosion! Sub-
stances with high halogen content
must not be combusted in the C
6010 decomposition vessel; in-
stead use the C 6012 decomposi-
tion vessel.