Measuring Time for Thermal
High Speed Furnaces
for Thermal Analysis
The High Speed
Effect of Heating
The estimated measuring time – along with the reliability and significance of
the results – often plays an important role in almost any analytical question.
The more intensively analysis methods are linked to production processes, the
more important this becomes. While in the research and development of new
materials, measuring times for the characterization of properties are scheduled
as a matter of course, in in-process analysis, it is the capacity of production
plants which determines the intervals at which product properties and product
quality must be verified. Analyses for quality assurance must therefore often be
realized on-line during the production process, or it must at least be possible
to carry them out within the space of a few minutes for random sampling
Measuring Time for Thermal Analysis
In the past, it had been difficult to cover these areas by means of Thermal Analysis
since conventional analyses take from 30 minutes to several hours, depending
upon the measuring program. The measuring time depends primarily on the material
to be tested and/or the temperature range which must be investigated for the
characteristic material properties. Decisive parameters here are also the
heating and cooling rates employed. These, in turn, are essentially dependent on
the constructional design of the furnaces and analytical instruments. And that
is where the newly developed highspeed furnace sets new standards.
High Speed Furnaces for Thermal Analysis
With conventional thermoanalytical instruments, heating and cooling rates from 1
K/min to 20 K/min are common while the potential range is from 0.001 K/min to
100 K/min; the new high-speed furnace, on the other hand, allows for heating
rates up to 1000 K/min. A heating rate of 500 K/min already reduces the
measuring time from room temperature to 1000°C to under two minutes and thus
increases the sample throughput tremendously.
The High Speed Furnace Concept
The new high-speed furnace does not require a stand-alone instrument but
extends the well-established 400 platform by another furnace type. The platform
concept allows for equipping a measuring instrument with a double-furnace
hoisting device for two furnaces. The high-speed furnace can therefore be
mounted on the doublehoisting device combined with other furnaces. Instead of a
second furnace, an automatic sample changer (ASC) can optionally be used for the
high-speed furnace. Modular flexibility and particularly the combinability of
the high-speed furnace with the ASC saves a great amount of time and thus
directly results in an increased sample throughput.
Available Furnace Types
The following furnace types for the instrument series DSC 404
F1, DSC 404 F3, STA 449
F1 and STA 449 F3 are now available.
Figure 1. Different furnace types for the STA 449 and DSC
Figure 2 shows a cross section of the high-speed furnace. It can be seen that
the high-speed furnace does not differ from the other furnaces of the 400
platform with regard to the main design points such as measuring heads, position
of the sample temperature determination, gas flow, and separation of the sample
and weighing chambers.
Figure 2. Cross section of the high-speed furnace
The great variety of crucible types and materials can also be used in the
high-speed furnace. This guarantees ideal comparability of the test results,
even when obtained with different furnace types. The actual heating element of
the high-speed furnace consists of a resistance-heated platinum mesh (Fig. 3).
The protective tube separates the sample chamber from the exterior and renders
it possible to work in pure sample atmospheres by means of evacuating and
flooding of the sample chamber.
Figure 3. Heating element with sample holder and
In addition to the measurements at high heating rates, measurements at
conventional heating rates of 10 K/min and 20 K/min were also carried out with
the high-speed furnace in order to guarantee the comparability of test results
with those obtained using other thermoanalytical instruments.
The presentation of the measured sample temperature versus time in Figure 4
shows linear heating rates in the range from 10 K/min to 500 K/min.
It was thereby confirmed that the high-speed furnace need not be limited to
fast heating rates but that it is also perfectly capable of handling more
Figure 4. Recording of the measured sample temperature
versus time confirms linear heating rates of 10, 20, 50, 100, 200 and 500
Effect of Heating Rate
Varying the heating rate under otherwise identical test conditions shifts the
results to higher temperatures as the heating rate increases. This is a
well-known correlation which further allows for the kinetic evaluation of the
measured data by means of the specially developed NETZSCH
Thermokinetics® software. If the correlation between the variation in the
heating rates and the effects on the measured data is known and can be
mathematically described, measurements can be carried out rapidly without having
to forego the traceability of the measurement data to known sample properties,
as are listed in the NETZSCH annuals, for example.
Pyrolysis of Polypropylene
Using the pyrolysis of polypropylene (PP) as an example, the dependence of
the results on the heating rate shall be pointed out.
Figure 5 initially shows that there are no significant differences in the
measurement results when polypropylene is investigated under identical
conditions using two different thermogravimetric instruments (TG 209
F1 and STA 449 F1). This is noteworthy since the
furnace geometry and therefore also the flow conditions of the purge gases are
Figure 5. Comparison of the measurement results of the
pyrolysis of polypropylene (PP) with the TG 209 F1 Iris®
(red) and STA 449 F1 Jupiter® (black)
In addition to the results of the relative mass change (TG), figure 5 shows
its first derivative, i.e. the mass-change rates, as dashed lines (DTG). When
evaluating the temperatures for the heating rates 10, 20, 50, 100, 200 and 500
K/min, where the mass-loss rate is at maximum (minimum of the DTG curve), the
heating-rate dependence of the pyrolysis of propylene is obtained. This is
presented in figure 6.
Figure 6. Variation of the pyrolysis temperature of
polypropylene for the heating rates 10, 20, 50, 100, 200 and 500 K/min
The logarithmic scaling of the heating rates yields a straight line, as can
be seen in figure 7. The error bars shown in both figures 6 and 7 in the
y-direction do not display real errors, but only depict a confidence interval of
± 2.5 K.
Figure 7. Variation of the pyrolysis temperature of
polypropylene for the heating rates 10, 20, 50, 100, 200 and 500 K/min
The thermal treatment of calcium carbonate (CaCO3) results in a
decomposition reaction above temperatures of 600°C where calcium oxide (CaO) and
carbon dioxide (CO2) are formed according to the following
While the solid CaO remains in the sample crucible, the CO2 and
the purge gas flow are both leaving the instrument via the outlet. The amount of
CO2 accrued can be quantified as a mass loss.
Figure 8 presents the results of a test series which was carried out with the
same measurement conditions as described for PP. Both the mass-loss steps and
the temperatures of the maximum decomposition speed (DTG minimum) are shifted to
higher temperatures as the heating rates increase.
Figure 8. TG-DTG results for CaCO3 with
varying heating rates from 10 K/min to 500 K/min.
The mass-loss rate increases from 5.1% to 128.8% when the heating rate is
increased from 10 K/min to 500 K/min (Figure 9).
Figure 9. Change of the mass-loss rate as a function of
the heating rate.
This shows that the influence of the heating rate on the measurement results
follows a traceable law.
Analysis of Brake Pads
Materials for products such as brake pads can now be analyzed under operating
conditions. During braking, kinetic energy is transferred into heat by means of
friction. The material can thereby be exposed to very high temperatures within a
very short time frame.
Heating rates of 500 K/min allow these extreme operating conditions to be
analytically reproduced (figure 10).
Figure 10. Measurement result of a brake pad at a heating
rate of 500 K/min.
Table 1. Technical data high-speed furnace
|Maximum heating rate (linear)
|Maximum sample temperature
The new high-speed furnace constitutes an extension to the well established
400 platform which enhances its already versatile potential. Some of this
entails the possibility of combining the high speed furnace with other furnaces
on a double-hoist device or with an automatic sample changer (ASC).
The comparability of the measurement results of the high-speed furnace with
those of other thermogravimetric instruments was demostrated using the pyrolysis
of polypropylene as an example. This is an important prerequisite for
unrestricted utilization and for the information content of measurements at
heating rates of up to 500 K/min.
The dependence of the measurement results on the variation of the heating
rate shows a linear correlation under logarithmic scaling of the heating rate.
Therefore, comparisons with measurements at conventional heating rates are also
Also, using the thermal decomposition of CaCO3 as an example, it
was shown clearly that although the heating rate does have an influence on the
measurement results, it also follows a very traceable law. Using fast heating
rates therefore does not result in any loss of information, and the fact that
each measurement only takes a few minutes yields a tremendous gain in time which
greatly increases the sample throughput and thus also the efficiency of the
The thermogravimetric investigation of a brake pad at 500 K/min also allowed
– in addition to the greatly increased throughput – for materials being exposed
to extreme thermal conditions to be analyzed under operating conditions for the
Source: High-Speed Furnace
Author: Dr. Ekkehard
For more information on this source visit NETZSCH-Gerätebau