OnSet 13 / 2014 - Netzsch

RESEARCH / DEVELOPMENT
POLYMERS
INSULATIONS
PHARMACY / CHEMISTRY
VEHICLE CONSTRUCTION
OnSet
ELECTRONICS / METALS
CERAMICS / GLASS
13
News, Facts and Professional Solutions for Thermal Analysis
Perseus TG 209 F1 – The Direct Combination
of Thermogravimetry with Spectroscopy
Dr. Ekkehard Füglein, Applications Laboratory
In this edition:
Page 6
A New Member for the
MMC 274 Nexus® – the HT
Coin Cell Module
Page 10
Measurement of Kinetics
and Thermodynamics of
Polymer Degradation Using
the STA 449 F3 Jupiter®
Page 14
PRECISE PRACTICE – DSC
Crucibles – More than Just
Sample Holders
Seite 17
TIPS & TRICKS – How to
Measure Rigid, Higher
Thermal Conductivity
Samples by Means of HFM
Page 19
International Symposium
Commemorating the 40th
Anniversary of GEFTA
Page 20
Events
TGA-MS
TGA-GC-MS TGA-FT-IR
TGA-FT-IR (Perseus)
TGA-FT-IR-MS
Evolved Gas
STA-FT-IR (Perseus) Analysis
STA-MS (SKIMMER®)
STA-FT-IR
(EGA)
STA-GC-MS
STA-MS
STA-FT-IR-MS
Fig. 1. Overview of the coupling methods
Introduction
Coupling Methods
The combination of thermoanalytical measuring instruments and gas
analysis methods such as mass spectrometry (MS) or Fourier Transform
Infrared Spectroscopy (FT-IR) has a
long tradition at NETZSCH. The first
coupling apparatus (STA-MS) was
introduced more than four decades
ago, and for more than twenty
years, we have had a very successful
collaboration with Bruker Optics in
the field of infrared spectroscopy.
Based on these many years of experience, we have established quite a
number of coupling possibilities on
the market, which are summarized
in the overview in figure 1.
Combining instruments in this way
is particularly valuable because
the information sets yielded by the
respective results complement one
another ideally. While thermoanalytical methods describe
EDITORIAL
Editorial
Dear Reader,
I am very pleased that you are
using this issue of OnSet13 to
catch up on the latest news
from the exciting world of thermal analysis. We will be presenting new instrument solutions,
an interesting report from the
research sector, and practicerelated tips.
This OnSet13 will be introducing
some powerful solutions from
the various NETZSCH Analyzing
& Testing product areas –
including thermal analysis,
thermophysical properties and
calorimetry.
The main article focuses on the
combination of evolved gas
analysis with thermogravimetry
and presents a coupling solution between a thermobalance
and FT-IR. The direct coupling
principle offered by the Perseus®
TG 209 F1 has a variety of
advantages over coupling by
means of a classical transfer line.
Along with a smaller footprint,
condensation effects are minimized and transfer times are
reduced. This increases the
efficiency of gas identification,
as shown by means of an
2
example using ethylene vinyl
acetate.
There has also been growth in
the MMC 274 Nexus® family, in
the form of a new measuring
module used for the quantitative determination of the temperature and energy released
during the charging and discharging of high-temperature
coin cells. This unique measuring module produces information relevant to battery development efforts about safety
in terms of possible thermal
reactions.
We are also pleased to present
a contribution by our customers
Jing Li and Stanislav I. Stoliarov
from the University of Maryland, USA. Their article discusses
the benefits of using an STA
449 F3 Jupiter® in describing
the decomposition kinetics of
polymer materials (e.g., PEEK)
in an anaerobic atmosphere by
means of simultaneous thermogravimetry (TGA) and Differential Scanning Calorimetry (DSC)
measurements.
In our PRECISE PRACTICE series,
the relevance to DSC measurements will be elucidated and
the influence of the crucible
material on DSC measurement
results will be described.
Under TIPS & TRICKS, you will
learn about determining a
material’s thermal conductivity using the new HFM 436
heat flow meter. Examples are
presented to show you how
samples with a very high and a
very low thermal conductivity
– such as concrete samples or
polymer foams – can be effectively characterized.
Finally, we would like to draw
your attention to the list of upcoming events in thermal analysis; in particular, the International Symposium commemorating
the 40th Anniversary of GEFTA
from September 16th through
19th, 2014 in Berlin.
I hope you enjoy your browse
through this issue of OnSet!
Dr. Andreas Spörrer
Polymers Business Segment
Manager
PERSEUS TG 209 F1
Continued from Page 1
changes to the chemical and physical properties of the sample itself
during the defined time/temperature program, spectroscopic and
spectrometric methods are able to
characterize the chemical composition of the gases evolved during
thermal treatment. Therefore, in
principle, for any given point in time
and at any given temperature, the
property changes in the samples
can be described, the released gases
quantified, and the type of gas
identified.
Couplings via Transfer Lines Or
Capillaries
The TGA-MS, TGA-FT-IR, TGA-FT-IRMS, STA-MS, STA-FT-IR and STA-FTIR-MS coupling methods presented
in the right half of figure 1 comprise
the instrument combinations which
connect the instruments mechanically by means of a capillary or
transfer line. All of these instrument combinations – including the
respective gas analysis method –
can be operated with an automatic
sample changer. The TGA-GC-MS
and STA-GC-MS instrument combinations can separate out individual
substances from the gas mixtures
via a chromatographic column and
analyze them in a mass spectrometer. The remaining three combinations can be described as direct
coupling solutions since they do not
require the transfer lines mentioned
above. These will be presented in
the following section.
STA. This solution is technically far
more sophisticated than a capillary coupling and has the decisive
advantage that all of the important
components can be kept at sample
temperature. This allows for the
transportation of large molecular
fragments and simultaneously helps
to prevent the evolved gases from
condensing.
The FT-IR analogous to this
SKIMMER® coupling was introduced
in 2012 as the Perseus STA 449 F1
[1]. A very compact FT-IR spectrometer, newly developed by Bruker Optics, connects directly to the furnace
outlet of the STA 449 F1 Jupiter®.
As with the SKIMMER® coupling,
the decisive advantages to connecting the instruments directly are the
shorter transfer times for the gases
and minimization of the risk of
condensation on the way from the
thermoanalytical instrument to the
spectrometer [2].
systems product spectrum (see figure 1). As with the Perseus STA 449
F1, the Bruker spectrometer in the
Perseus TG 209 F1 is also positioned
directly onto the thermobalance
and connected with its furnace outlet. The spectrometer is controlled
via the measurement software of
the TG 209 F1 – as is also the case
with all other NETZSCH-Bruker
couplings. The measured data
are transferred to the respective
software continuously during the
measurement.
Measurement Results
In order to illustrate the quality of
the data yielded by the Perseus TG
209 F1, an analysis of ethylene vinyl
acetate (EVA) was carried out. EVA is
used, for example, in the production
of films for a variety of applications
in horticulture, in the sanitary field,
or in the protection of photovoltaic systems against environmental
influences.
The Perseus TG 209 F1 (Figure 2)
completes the NETZSCH coupling
Direct Couplings
The direct coupling, known as the
SKIMMER®, was introduced in 1985.
This STA-MS coupling employs a
double orifice, allowing for direct
connection of the mass spectrometer with the furnace outlet of the
Fig. 2. Perseus TG 209 F1
PERSEUS TG 209 F1
As shown by the results of the TGA
data (black curve) in figure 3, EVA
decomposes at a thermal load
above 250°C under pyrolytic conditions in two steps. The measurement conditions are summarized in
table1 .
Tab. 1. Mesurement conditions for the analysis
on ethylene vinly acetate
Measurement
Perseus TG 209 F1
Measuring head
Standard
Crucible
Al2O3
Atmosphere
Nitrogen
Gas flow rate
40 ml/min
Heating rate
10 K/min
Sample mass
8.750 mg
Gas cell
200°C
Spectral range
4000 - 600 cm-1
The first derivative of the TGA data,
the DTG data (green curve), not
only yields information on the massloss rate – i.e., the reaction rate – of
the thermal degradation, but also,
by means of the maximum mass
loss rate, discloses the temperature
at which the reaction rate is at its
highest. Consequently, at 350°C
and 468°C, the maximum amounts
of gas for the two decomposition
reactions are released. These temperatures are in good agreement
with the maxima of what is known
as the Gram-Schmidt trace (GS,
blue). This data is a measure of the
intensity of the total IR absorption
by the evolved gases. Since these
maxima, at 351°C and 469°C, are
almost identical to the results of the
DTG data, they appear to indicate
that only a few seconds are required
to transfer the gases from the TGA
apparatus into the gas cell of the
spectrometer. Figure 4 shows all
4
Fig. 3. TGA, DTG and GS results on ethylene vinyl acetate
spectra recorded during the entire
measurement in a temperaturescaled, 3-dimensional presentation. The TGA data are additionally
displayed in the background.
To identify the gases released, the
respective individual spectra are
extracted from the 3-D cube and
then compared with IR spectra from
a gas phase library. The individual
spectrum during the first massloss step at 353°C (figure 5, red)
shows very good agreement with
the library spectrum for acetic acid
(figure 5, blue); the individual spectrum at 473°C (figure 6, red) shows
similar absorption bands to the
reference spectrum for the pyrolysis
of polyethylene (figure 6, blue).
It is thus confirmed that acetic acid
is released during the first mass-loss
step and that gases consistent with
those produced during the pyrolysis
of polyethylene are formed during
the second mass-loss step. With
consideration to the structure of
ethylene vinyl acetate (structural
formula see figure 3), these results
are chemically plausible. By splitting
the 3-D cube along the temperature
axis in the range of the absorption
maxima for acetic acid (1850 to
1700 cm-1) and for the degradation
products of polyethylene (3100 to
2800 cm-1), “traces” are obtained.
These traces depict the course of intensity for the respective substances
as a function of temperature and
thereby illustrate the temperature
at which they are released.
Fig. 4. Temperature-scaled 3-D presentation
of all IR spectra of the analysis on EVA
PERSEUS TG 209 F1
Fig. 5. Comparison of the measured individual spectrum at 355°C (red)
with the library spectrum for acetic acid (blue)
Figure 7 presents these traces along
with the thermogravimetric results.
It can clearly be seen that acetic
acid is formed exclusively during the
first release step and the degradation products of polyethylene
(CxHy fragments) exclusively during the second release step. Based
on this, the amounts released can
also be quantified with the help of
the mass-loss steps. The mass-loss
steps of 28.9% and 71.1% add up
to 100% and thus substantiate the
thermal degradation of ethylene
vinyl acetate quantitatively.
Summary
Fig. 6. Comparison of hte measured individual spectrum at 473°C (red)
with the library spectrum for the pyrolysis of polyethylene (blue)
In the Perseus TG 209 F1, a pure
thermobalance has been combined
directly with an FT-IR spectrometer
for the first time. The fact that no
transfer line is required to transport
gas from the thermobalance to the
spectrometer not only shortens the
transfer time of the gases released
but also minimizes the risk of condensation. The example using the
pyrolysis of ethylene vinyl acetate
demonstrates how efficiently the
Perseus TG 209 F1 can record the
measured data and use these data
to identify the gases released.
Literature
Fig. 7. Results of the analysis on EVA with the IR absorption intensities for
acetic acid (AC) and polyethylene (CH)
[1] A. Schindler, G. Neumann,
A. Rager, E. Füglein, J. Blumm, T.
Denner, “A novel direct coupling of
simultaneous thermal analysis and
Fourier transform-infrared (FT-IR)
spectroscopy”, J. Therm. Anal. Calorim. 2013, 113, 1091.
[2] www.netzsch-thermal-analysis.
com/literatur-digitale-medien/videoclips.html
HT COIN CELL MODULE
A New Member for the MMC 274 Nexus® –
the High-Temperature Coin Cell Module
Jean-Francois Mauger, R&D, NETZSCH Instruments, Burlington, USA
The new High-Temperature Coin
Cell Module for the multiple module
calorimeter MMC 274 Nexus® (RT to
300°C, figure 1) is specially designed
as a battery development tool. It
has the flexibility to cover two of
the three above-mentioned calorimetry modes: isothermal calorimetry
and differential scanning calorimetry, giving the user a wide array of
analysis opportunities.
Figure 2 depicts the schematic of
a coin cell. The performance of
rechargeable batteries is highly
dependent on temperature and cycling conditions. Therefore, characterizing the heat generation during
charging and discharging is critical
for any battery designer in order to
improve the performance, lifetime
and safety of these secondary cells.
By accurately measuring the temperature, energy and rate of energy
released, quantitative data can be
determined that enable the scientists to consider possible chemical
reaction mechanisms and thereby
accelerate the development process.
Fig. 1. MMC 274 Nexus® with the High-Temperature Coin Cell Module
Calorimetry is the science of measuring the heat released or absorbed by any kind of material as a
function of temperature and time.
Existing calorimeters, among others,
are classified in different categories:
Adiabatic calorimeters prevent
small samples (mostly milligram
size) and are able to heat and
cool the sample very quickly.
(-)
Anode Cap (-)
Lithium anode
heat exchange between the
sample and the environment
and are mainly used for safety
applications
Isothermal calorimeters are usu-
ally used for large samples (multigram size) and require outstanding temperature stability
(+)
Gasket
MnO2 Cathode
Current collector
DSCs (Differential Scanning Calo-
rimeters) are mainly designed for
6
Fig. 2. Schematic illustration of a coin cell
Separator and electrolyte
Cell can (+)
HT COIN CELL MODULE
Innovative, Robust Instrument for
High-Quality Results
The sensor for measuring coin cells
(schematic figure 3, photo figure
4) has been designed to be symmetrical so it can be used as a true
differential system. One side is used
for the sample, the other side is for
the reference. In order to get better
precision and avoid any external
disturbance, the signal is derived
from the difference between the
two sides.
The heat measurement is performed by two custom-made heat
flux sensors – comprised of multiple
thermocouples that are connected
all together – and located on each
side of the sensor. The inner face
of the heat flux sensor is in direct
contact with the calorimetric block,
by which temperature is accurately
controlled and monitored. The
outer face is in direct contact with
the sample (entire coin cell or any
kind of material inserted inside a
coin-cell shaped crucible). When a
thermal event occurs in a sample,
energy is absorbed or released and,
consequently, the temperature of
the specimen changes. When, by
conduction, the temperature of the
inner face of the heat flux sensor
changes, a direct voltage proportional to the temperature difference
between the two faces of the heat
flux sensor (Seebeck effect) is generated.
The coin cell or the crucible is held
in position by a copper leaf spring,
which enables good thermal
contact between the sample and
the sensor and with the electrical
power supply needed to charge or
discharge the battery. Four electric
wires are connected to these copper
leaf springs in order to reduce the
Coin cell
Fig. 3. Schematic of HT coin cell sensor
electrical resistance of the conductor, improving the accuracy of the
electric measurement.
Heat flow measurement
Power
Calorimetric block
Fig. 4. Mounted sensor for coin cell
measurements
Heat flow sensor
Copper spring Aluminum film
HT COIN CELL MODULE
Different Operation Modes for
Different Applications
The main application for the isothermal mode is the charging and
discharging of batteries at constant
temperatures, as can be seen in figure 5. The design of the instrument
allows for the connection of a battery analyzer at the side of the top
hood of the instrument. The cycler
handles the battery management
with its own software. The NETZSCH
Proteus® software controls the coin
cell module. Once the experiment
is complete, all signals coming
from the battery analyzer (current,
voltage, power, resistance, etc.) are
easily imported into Proteus® and
merged with the temperature and
heat flux signals.
Fig.5. Charging/discharging experiment LiR2032 battery, CC/CV mode – 1C,
cycles between charging and discharging conditions: 3.0 V to 4.2 V, 40 mA
The plot reflects the good repeatability of the signal in multiple cycles.
The amount of heat released during
charging and discharging phases
is energy lost from the battery. The
ratio between this Joule effect loss
and the electrical energy used to
charge the battery or the amount
of electrical energy produced by the
battery is a measure of the battery’s
efficiency (figure 6).
The sensitivity of the instrument
allows the user to monitor even
very weak heat signatures (down to
20 µW) coming from low charge or
discharge currents in the mA range.
Figure 5 shows the evolution of the
heat released by the coin cell during
charging and discharging cycles.
Between 1720 and 1780 min, the
battery is discharged from 4.2 V to
3.0 V (green curve) with a 40 mA
load (red curve).
The discharge of the battery generates heat which rate fluctuates
along the process.
8
Fig. 6 Efficiency calculation LiR2032 battery CC/CV mode – 1C
The presented heat flow is a zoom of the first discharge/charge cycle of fig 5.
The efficiency of a battery depends on the charge-discharge rate but also on
temperature.
HT COIN CELL MODULE
From 1780 min to 1900 min, the
battery is discharged from 3.0 V to
4.2 V with the same 40 mA current.
Here, we can clearly notice a small
endotherm at the very beginning
of the process and then a smooth
exotherm.
By repeating the measurement two
times, the good repeatability of this
measurement can be seen.
Fig. 7. Typical DSC characteristics of Lithium-ion battery components [1]
In scanning mode e.g. (figure 7), the
instrument can be used as a standard DSC for investigating any kind
of material placed inside a coin-cell
shaped crucible, however, the primary application of this instrument
in this mode is to measure an entire
coin cell (figure 8) and obtain a full
heat signature over the entire temperature range (room temperature
to 300°C).
Conclusion
The only coin cell-dedicated DSC
on the market, the high-temperature coin cell module of the MMC
Nexus®, is able to improve the
throughput dramatically by measuring all thermal decompositions and
reactions of an entire coin cell in a
single run.
By contrast, standard DSC measurements require the user to prepare
and measure a sample of each battery component individually (Figure
7). Moreover, testing the entire coin
cell is the only way to accurately
study all possible interactions between components that can occur
in real life.
Fig. 8. DSC signature of an entire LiR2032 battery from RT to 300°C at 0.5 K/min
References
[1] Adams, D., & Matthies, B.
(2010). Best management practices
by age. Journal of Management,
14(3), 60-75.
Simultaneous Thermal Analysis
Measurement of Kinetics and Thermodynamics of
Polymer Degradation Using the STA 449 F3 Jupiter®
Jing Li and Stanislav I. Stoliarov, University of Maryland, Department of Fire Protection Engineering,
Department of Mechanical Engineering, College Park, MD 20742, United States
Introduction
Polymers are ubiquitous in both
high technology and routine
household applications. An attractive combination of customizable
mechanical properties, low weight,
and easy processability makes them
an irreplaceable attribute of the
modern society. One of the main
disadvantages associated with a
widespread use of these materials
is their inherent flammability [1].
An important step towards flame
resistant polymeric structures and
design solutions is development
of models that relate chemical
and physical properties of these
materials to their performance in
various fire scenarios. A number
of such models have recently been
developed including Gpyro [2],
solid phase model in the NIST Fire
Dynamics Simulator [3] and
ThermaKin [4]. As an input, these
models require properties that describe kinetics and thermodynamics
of material thermal degradation
and define condensed-phase heat
transport.
Thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) are among the most frequently used techniques employed
for the measurement of the core
subset of these properties. The main
advantage of these techniques is
associated with the use of small
material samples (3 - 10 mg) and
relatively slow and steady heating
rates (3 - 30 K/min). These heating
conditions minimize the effects of
heat and mass transport inside the
sample on mass loss and heat flow,
which makes it possible to exclude
the transport from data analysis and
interpretation.
Heat of Decomposition Measurement Using DSC
DSC is used routinely to measure
heat capacities and heats of melting
of polymeric solids [5]. In this work,
this technique has been extended
to anaerobic thermal degradation
reactions. Measurement of the
heats of degradation is a challenging task because of instrumental
baseline instabilities caused by
volatile products [6] and the fact
that both sensible and reaction
heats contribute to the heat flow
as the material’s temperature is
raised through degradation. Several
research groups have attempted
to perform these measurements
with some degree of success [6-8].
The main distinguishing features
of the current approach are that it
employs a simultaneous thermal
Fig. 1. Experimental and simulated TGA of PEEK at 10 and 30 K/min
10
analysis (STA) instrument calibrated
using melting of organic and inorganic compounds and a unique DSC
data analysis methodology. This
methodology utilizes a TGA-derived
kinetic mechanism to generate sensible heat baseline for the reaction
region of the DSC curve and yields
a complete thermokinetic model
(including heat capacity of the
condensed-phase constituents, heat
of melting and heats of decomposition) that reproduces both TGA and
DSC experiments. This methodology
has been successfully applied to the
analysis of thermal decomposition
of both non-charring [9] and charring [10] polymers. Here, its application is demonstrated on poly(ether
ether ketone) (PEEK).
Experimental
A NETZSCH STA 449 F3 Jupiter® was
employed in this study. This apparatus combines a TGA instrument
equipped with 1 µg-resolution
microbalance and a heat flux DSC
implemented using a NETZSCH
TGA-DSC sample carrier equipped
with P-type thermocouples. An
anaerobic environment was created
inside the furnace by continuously
purging it with nitrogen at a rate of
50 cm3/min. TGA and DSC experiments were conducted simultaneously using the following heating
program. A sample was first heated
to 313 K and maintained at this
temperature for 25 minutes. Subsequently, the sample was heated
to 1223 K (873 K for non-charring
polymers) at a heating rate of
10 K/min. The mass and heat flow
data were collected only during the
second, linear heating phase of the
test. The selection of the heating
rate was based on a recent theoretical analysis [11] that indicated that
Simultaneous Thermal Analysis
using 10 K/min for <10 mg samples
ensures a uniform temperature inside the sample even when the heat
associated with decomposition processes is significant. Additional TGA
experiments were performed at
30 K/min. These experiments were
used to evaluate how well the mass
loss kinetics model developed using
10 K/min data performs at higher
heating rates. All thermal analysis
experiments were performed using
Platinum-Rhodium crucibles.
Seven thermal analysis experiments
(simultaneous TGA and DSC) were
performed on each polymer. Averaged mass and heat flow curves
were computed and used in further
analysis. Averaging of heat flow
curves from multiple experiments
was shown to significantly reduce
random errors and enable measurement of heat capacity [9]. Multiple
experiments also provided the data
necessary for the calculation of uncertainties in the extracted properties. Additional DSC experiments
were performed on char residue
produced in the polymer thermal
analysis experiments. These experiments were performed on 3 to 5 mg
samples at 10 K/min and were
repeated 3 times for char produced
from each material. The char was
compacted in the crucible prior to
DSC to ensure a good thermal contact with crucible bottom.
Data Analysis and Discussion
A numerical pyrolysis model, ThermaKin [4] , was used in this study to
analyze TGA and DSC experiments
and obtain a parametric description
of the kinetics and thermodynamics
of polymer degradation. ThermaKin
solves mass and energy conservation equations describing zero-,
one- or two-dimensional object
subjected to external (convective
and/or radiative) heat. The material of the object is represented by
a mixture of components, which
may interact chemically and physically. The components are assigned
individual temperature-dependent
properties and categorized as solids
or gases.
The results of 10 K/min TGA experiments performed on PEEK are
shown in Fig. 1. The experimental
mass loss rate (MLR) curve consists
of one major peak followed by an
extended shoulder. These features
of MLR can be modeled by a sequence of two first order reactions:
PEEK → θ1 PEEK_int,
PEEK_int → θ2 PPEK_char,
where PEEK_int and PEEK_char
denote condensed phase decom-
position products; and θ1 and θ2 are
the corresponding product yields.
Gas-phase products are not shown
because they are assumed to leave
the condensed phase and sample
container instantaneously. Note
that these reactions describe a semiglobal decomposition mechanism
formulated to capture key features
of the polymer mass loss dynamics.
Each reaction corresponds to tens
or, perhaps, hundreds of elementary
chemical processes occurring in the
corresponding temperature range.
By adjusting Arrhenius parameters
and product yields of these reactions in accordance with a procedure described elsewhere [9], the
reaction model was fit to the TGA
mass loss. As shown in Fig. 1, at
10 K/min, the model captures both
mass and MLR behaviors accurately
(R2 = 0.95). Simulation of 30 K/min
TGA experiments using the same
reaction model yields poorer agreement (see Fig. 1), which is likely to
be caused by deviations of the experimental conditions from spatial
isothermality assumed in the model.
Fig. 2 shows the result of DSC experiments performed on PEEK. The
heat flow normalized by the initial
Char samples produced in the thermal analysis experiments were further examined with a Hitachi S3400
scanning electron microscope. The
imaging was performed using 3 and
10 kV electrons. The purpose of this
exercise was to determine whether
there exist significant differences
in the microscale topology of chars
produced from different polymers.
Fig. 2. Determination of decomposition reaction contributions to the PEEK DSC signal
Simultaneous Thermal Analysis
mass is plotted as a function of
measurement time. There are three
distinct peaks in this curve. The lowest temperature peak is associated
with melting. The higher temperature peaks approximately match the
temperatures of the decomposition
reactions.
At the first stage of analysis, the
DSC curve was normalized by
instantaneous heating rate and
the regions of the curve not associated with melting or decomposition were fit with straight lines
representing heat capacities of the
solid and molten PEEK. PEEK_char
heat capacity was obtained from
separate experiments on the final
decomposition residue. Fig. 3 provides SEM images of this residue,
which appears to have relatively
homogeneous, solid-like structure
at micrometer scale. This structure
is fundamentally different from
that of intumescent polymer chars,
Fig 3. SEM images of chars produced as a
result of anaerobic thermal degradation
of PEEK
12
Fig 4. Experimental and simulated DSC of PEEK at 10 K/min
which show a fractal-like void pattern with an extremely wide range
of pore sizes [12].
The heat capacity of the intermediate component, PEEK_int, could not
be resolved because of the overlap
between the decomposition reactions. Therefore, the heat capacity
of this component was assumed to
be the mean of the heat capacity
of molten PEEK and PEEK_char. The
heat capacities weighted by a product of the corresponding compound
mass fraction and instantaneous
heating rate were added to obtain
a sensible heat flow baseline shown
in Fig. 2. The time evolution of the
mass fractions was computed using
Thermakin from the TGA-derived
reaction model.
Subtraction of this baseline from
the total heat flow and subsequent
integration of the difference in the
melting region produced the value
of the heat of melting (hm). Integration of the difference in the decomposition region produced the value
of the total heat of decomposition,
which was subsequently divided between the first (h1) and second (h2)
reactions. It should be noted that
what is referred to here as the heat
of decomposition reaction is actu-
ally a sum of heats of two processes:
chemical decomposition process,
which involves braking and formation of covalent chemical bonds and
vaporization of the decomposition
products, which involves braking of
the Van der Waals bonds. Both of
these processes change the system’s
enthalpy and cannot be separated
within the framework of the current
experiments.
At the last stage of analysis, the
thermodynamics of the parameterized reaction model was verified by
comparing ThermaKin calculated
heat flow with that observed in the
experiments. This comparison is
presented in Fig. 4 in a form of time
resolved heat flow and heat flow integral. The experimental and simulated heat flow integrals match very
well. The heat flow comparison is
not as favorable. The discrepancies
are thought to be due to the fact
that the model assumes that the set
heating rate (10 K/min) is always
followed; while in the experiments,
notable deviations from this heating rate are observed partiuclarly
at the end of the tests due to the
decompositon reaction.
Perhaps, the most significant outcome of this analysis is an observa-
Simultaneous Thermal Analysis
tion that PEEK, along with all other
examined high char yield (>40wt.%)
polymers [10], decomposes exothermically, while the rest of the
polymers, including seven analyzed
non-charring materials are characterized by an endothermic decomposition. The relationship between
the char yield and decomposition
exothermicity can be explained by
noting that a polymer char, which
molecular structure is likely to be
similar to that of graphite or soot
(i.e., multiple fused aromatic rings),
is highly thermodynamically stable.
When this char is produced in sufficient amount, its thermodynamic
stability compensates an increase
in enthalpy associated with the
formation of small molecular mass
volatiles.
Conclusion
A methodology for the measurement of kinetics and thermodynamics of anaerobic thermal degradation has been developed and
applied to non-charring as well as
charring polymers. This methodology utilizes carefully calibrated TGA
and DSC experiments that were
analyzed using a flexible numerical
pyrolysis modeling framework, ThermaKin. The parameter set developed for each material was shown
to capture both mass loss and heat
flow data. To the best of our knowledge, this is the first example of a
systematic approach that yields a
global reaction model that simultaneously reproduces both TGA and
DSC measurements.
The heats of decomposition of
highly charring polymers (char
yields >40wt.%) were found to be
exothermic. It is important to note
that this exothermicity does not
lead to spontaneous degradation.
As indicated by the right graph of
Fig. 4., it still takes a considerable
amount of energy to thermally
decompose such materials to char
and volatiles.
Literature
[1] C.F. Cullis, M.M. Hirschler, The
combustion of organic polymers,
Clarendon Press, Oxford University
Press, Oxford, New York, 1981.
[2] C. Lautenberger, C. FernandezPello, Fire Safety Journal, 44 (2009)
819-839.
[3] K. McGrattan, S. Hostikka, J.
Floyd, H. Baum, R. Rehm, W. Mell, R.
McDermott, Fire Dynamics Simulator (Version 5) Technical Reference Guide National Institute of
Standards and Technology Special
Publication, 2007.
[4] S.I. Stoliarov, I.T. Leventon, R.E.
Lyon, Fire and Materials, (2013) in
print.
[5] J.D. Menczel, R.B. Prime, Thermal
Analysis of Polymers - Fundamentals and Applications, John Wiley
& Sons, Inc., Hoboken, New Jersey,
2009, p.688.
[6] S.I. Stoliarov, R.N. Walters, Polymer Degradation and Stability, 93
(2008) 422-427.
[7] W.J. Frederick, C.C. Mentzer,
Journal of Applied Polymer Science,
19 (1975) 1799-1804.
[8] G. Agarwal, B. Lattimer, Thermochimica Acta, 545 (2012) 34-47.
[9] J. Li, S.I. Stoliarov, Combust
Flame, 160 (2013) 1287-1297.
[10] J. Li, S.I. Stoliarov, Polymer
Degradation and Stability, (2013) in
print.
[11] R.E. Lyon, N. Safronava, J. Senese, S.I. Stoliarov, Thermochimica
Acta, 545 (2012) 82-89.
[12] J.E.J. Staggs, Fire Safety Journal,
45 (2010) 228-237.
The Authors
Jing Li is a PhD candidate
in the Department of Mechanical Engineering and Fire
Protection Engineering of
the University of Maryland,
College Park (USA). His PhD
project is focus on developing a multiscale approach to
parameterization of burning
models for charring polymers.
He has been working with
NETZSCH equipment for thermal analysis needs (STA 449
F3 Jupiter®) for more than
three years.
Stanislav I. Stoliarov is an
Assistant Professor in the
Department of Fire Protection
Engineering of the University
of Maryland, College Park
(USA). His research interests
include material flammability, pyrolysis and smoldering
mechanisms, thermophysical
properties, flame structure
and spread. He has authored
close to 50 peer-reviewed
publications and patents.
PRECISE PRACTICE
PRECISE PRACTICE
DSC Crucibles – More than Just Sample Holders
Dr. Gabriele Kaiser, Scientific & Technical Communication
The quality of DSC results is often
determined as early as the sample
preparation and measurement
parameter selection phase. The
crucible chosen plays an important role here. Variables such as
the material, form, volume and
mass of the crucible, as well as the
status of the lid (yes/no/pierced/
closed), are important influential
factors. The first two of these –
crucible material and form – will
be discussed in more detail in this
article.
For DSC investigations, the crucible
serves primarily as a container
for the sample and the reference
material and – just as with a pot on
a stove – must protect the sensor
from contamination and distribute
the heat to the sample or reference
material as evenly as possible without reacting with it. Additionally,
the crucible should provide good
heat transfer to the sensor so that
even the slightest change in the
sample can be detected. Crucial factors here are the thermal conductivity of the crucible material and
the degree of contact between the
crucible bottom and sensor.
High Thermal Conductivity
Provides Good Heat Transport
The thermal conductivity of a
material (symbol: λ) describes the
transport of energy – in the form
of heat – through a body based
upon a temperature gradient. The
higher the thermal conductivity, the
greater the amount of energy transported and thus the more effective
the heat exchange.
The thermal conductivities of various crucible materials are summarized in table. 1. It confirms that
metals have a higher λ value than,
for example, ceramics (alumina) and
are therefore better heat conductors. The thermal conductivity of
aluminum, at 237 W/(m·K), is higher
than that of platinum and far higher
than that of alumina, but still considerably lower than that of gold,
copper and silver.
Table 1. Thermophysical data for some typical crucible materials at RT
Material
14
Thermal conductivity λ
(W/(m·K))
Thermal diffusivity a
(mm²/s)
Specific heat capacity cp
(J/(g·K))
Aluminum
237(1)
98.8(3)
0.9(1)
Platinum
71.6(1)
25(3)
0.13(1)
Al2O3 (α)
28(3)
10.2(2)
0.76(2)
Copper
404(1)
117(3)
0.39(1)
Silver
429(1)
173(3)
0.23(1)
Gold
317(1)
127.2(3)
0.13(1)
PRESICE PRACTICE
figure 1 that the slope following
the melting peak declines much
less sharply for the measurement
conducted in the Al2O3 crucible than
for those conducted in the metal
crucibles. The narrower a peak (e.g.,
the shorter the time constant), the
better neighboring effects are separated, and therefore, the better the
resolution. Pivotal factors here are
the thermal diffusivity (symbol: a),
which indicates how fast a material
reacts to a temperature change, and
the thermal mass (m·cp) (for a and
cp, also see table 1).
Fig. 1. DSC measuremenst on indium, sample mass: approx. 7.2 mg, heating rate: 10 K/min,
N2 atmosphere; presented here are the 2nd heating runs (of 4) for each
Figure 1 illustrates the abovementioned differences by means
of three different measurements
on indium in aluminum, Al2O3
and platinum/rhodium crucibles.
With the same sample mass and
otherwise identical conditions, the
measurement carried out in the
aluminum crucible (red curve) exhibited the largest peak followed by
the one in the Pt/Rh crucible (blue).
The dotted black curve exhibits the
smallest peak and represents the
measurement in the Al2O3 crucible.
Silver and gold create alloys when
coming into contact with indium
and were therefore not included in
this test series.
The good heat transfer properties
of the metals are reflected not
only in the corresponding peak
heights, but also in the so-called
time constant. This is defined as the
amount of time a measuring signal
needs to decrease from the top
of its peak to 1/e of the intensity
(corresponds to a decline of approx. 63 %). Even without precise
numerical data, it can be seen in
Figure 2 shows a real sample measurement on PET, carried out in aluminum crucibles (here in Concavus
crucibles, blue curve) and in Al2O3
crucibles (red dotted line). The DSC,
reflecting the test in aluminum crucibles, is superior here to the measurement in Al2O3 crucibles both in
terms of peak intensity (higher) and
peak width (narrower).
Fig. 2. DSC measurements on polyethlyene terephthalate (PET), sample mass: approx. 7.4 mg to
8.2 mg, heating rate: 20 K/min, N2 atmosphere; presented are the 2nd and 3rd heating runs (of 4)
PRECISE PRACTICE
DSC or STA instrument with a DSC
sample carrier.
At only a few millimeters high, DSC
crucibles are generally quite flat.
Therefore, only a small amount of
heat can be lost to the surrounding gas atmosphere, and the effect
on the system’s sensitivity is correspondingly positive.
Fig. 3. Schematic of a Concavus crucible on a Corona sensor.
The concavity of the aluminum crucible is exaggerated here
(in reality, it only amounts to 10 µm).
The fact that aluminum is considerably less expensive than the
precious metals gold and silver
and that it also does not have a
catalytic effect on organic materials, as would copper (buzz phrase:
oxidative stability of cable sheathing in copper crucibles), have made
aluminum to the standard crucible
material for polymers, many pharmaceuticals and food. The melting
point of pure aluminum is 660.3°C,
so the temperature range for the
use of Al crucibles is limited to a
maximum of 610°C.
Crucible Shape — Form Follows
Function
Another factor in optimizing heat
transfer is good contact between
the crucible bottom and the sensor. Theoretically, a perfectly plane
crucible bottom positioned onto
a perfectly plane sensor would be
the ideal combination. One must
take into consideration, however,
that even metal surfaces which are
macroscopically plane consist of
microscopic elevations and depressions attributable to surface rough-
16
ness – so where the plane surfaces
of a crucible and a sensor come together, contact is only ever actually
made at certain points. The more
such points there are, the better the
heat transfer will be.
In addition, particularly for crucibles with a relatively thin bottom,
manufacturing tolerances must not
be disregarded. Even small anomalies in the plane surface of a crucible
bottom can considerably reduce the
reproducibility of the measurement
results for such crucibles.
A new approach for meeting these
challenges is to lend a concave
shape to the crucible bottom, i.e.,
to deliberately create an inward
concavity of the outer crucible bottom, as realized in the Concavus
crucible made of aluminum (figure
3). When placed upon a flat sensor,
this results in an even, ring-shaped
contact zone and considerably improves reproducibility.
The Concavus crucible was designed
especially for the Corona sensor
of the DSC 214 Polyma, but it can
also be used in any other NETZSCH
Summary
Aluminum is the ideal crucible
material for most measuring tasks
in the temperature range to 610°C
since its material and production
costs are relatively low while its material properties are still very good.
The special shape of the Concavus
crucible in combination with the
Corona sensor sets new standards in
this realm.
As a general rule, it is important
to always select crucible materials which will not interact with the
sample. Whenever possible, metal
crucibles should be favored for DSC
investigations due to their superior
heat transfer properties.
References
(1) NETZSCH poster: Thermal
Properties of the Elements
(2) Values of the NETZSCH Al2O3
reference materials
(3) www.Wikipedia.de
(4) Special thanks to my colleagues
Andrea Kesselboth and Claire
Straßer for providing the measurements.
40 YEARS OF GEFTA
International Symposium Commemorating
the 40th Anniversary of GEFTA
Dr. Michael Feist, Chairman of GEFTA (the German Association of Thermal Analysis)
Since 1978, the NETZSCH-GEFTA
Award has been conferred every
two years – and in 2014, the anniversary year, Professor Jaroslav
Šesták from the Czech Academy of
Sciences in Prague will be receiving
this honor. For decades, he has been
working on the kinetics of solidstate reactions and thermophysical
properties of solids, and has gained
particular recognition in these
fields.
Forum in front of the Erwin-Schrödinger-Zentrum on the Berlin-Adlershof campus – the venue
for the GEFTA anniversary symposium from September 16th - 19th, 2014.
In the foreground is a kinetic installation, Heads, shifting, by Berlin artists Josefine Günschel
und Margund Smolka.
This year, the Gesellschaft für Thermische Analyse e.V. (GEFTA, German
Association for Thermal Analysis)
commemorates its 40th anniversary
with an international symposium at
the Institute of Chemistry at Humboldt University in Berlin:
Thermal Analysis and Calorimetry
in Industry and Research
40 Years of GEFTA
September 16th-19th, 2014
This will be taking place at the
Erwin-Schrödinger-Zentrum on the
Berlin Adlershof campus. An instrument exhibition is also planned.
GEFTA is the association of scientific
experts in the German-speaking
region who work in the field of
thermal an calorimetric materials
characterization, materials science
and properties testing as well as
in subsets of these areas such as
chemistry, physics and pharmacy.
It brings scientists, engineers, lab
assistants and technicians together
and is a sub-organization of the
International Union for Pure and Applied Chemistry (IUPAC).
For 40 years, GEFTA has been in a
convivial scientific exchange with
partner companies in neighboring
European countries and has organized many bi- and trilateral seminars with them. Delegations from
seven countries were thus invited
to join the anniversary celebration:
from France, the Netherlands, Poland, the Czech Republic, Hungary,
Scandinavia and Switzerland. Six of
them have already confirmed their
participation.
The GEFTA Science Award, which is
awarded at irregular intervals, will
be conferred to Professor Christoph Schick (University of Rostock)
this year for his research work in
polymer characterization by means
of TMDSC as well as for his development accomplishments with
chip calorimeters. In addition, the
TAInstruments Industrial Award will
be conferred for the third time. The
Awardee 2014 will be Dr. Leon Olde
Damink from Matricel GmbH.
We cordially invite you to participate and look forward to receiving
your registration for the lectures
or poster presentations which are
relevant to your current research
work. More on the conference sections and all other information can
be found at:
www.gefta.org
TIPS & TRICKS
How to Measure Rigid, Higher Thermal
Conductivity Samples by Means of HFM
Rob Campbell, Applications Laboratory, NETZSCH Instruments, Burlington, USA
(ΔT) as measured by the thermocouples embedded in the hot plate
and cold plate surfaces can be used
for the thermal conductivity calculation. Although there is always a
small thermal resistance and temperature drop present at the plate
to sample interfaces, they can be
neglected compared to the much
larger sample thermal resistance
and ΔT. For compressible insulating
materials, good thermal contact is
ensured if the sample is compressed
slightly by the plates. For more
rigid materials such as plastic foam,
these contact resistances can still
be neglected as long as the sample
surfaces are flat and parallel and
sufficient pressure is applied by the
HFM plates.
Fig. 1. HFM 436 Lambda
Introduction
The heat flow meter (NETZSCH HFM
436 Lambda in Figure 1) method is
most commonly applied to thermal
conductivity measurements of insulating materials such as fiberglass,
mineral fiber and polymer foams in
the approximate range of 0.02 to
0.1 W/(m·K) and 20 to100 mm
thickness. With special precautions
regarding sample preparation,
temperature measurement and in-
strument settings, the HFM method
range can be extended to measurements of building materials such
as concrete, masonry and wood,
as well as plastics, composites and
glass with thermal conductivity
as high as 2 W/(m·K) and thermal
resistance as low as 0.02 (m2·K)/W
(see example in Table 1).
With typical HFM measurements of
insulating materials, the temperature difference across the sample
For higher thermal conductivity
materials, generally with thermal
conductivity > 0.5 W/(m·K) and
thermal resistance < 0.1 (m2·K)/W,
the plate to sample contact resistances can no longer be neglected.
Also, since these materials are generally rigid and incompressible and
may have rough surfaces, thermal
contact with the HFM plates may be
even further reduced by gaps and
air films. To overcome these effects,
sample surface mounted thermocouples and rubber interface sheets
are employed as described below.
Table 1. Measurement of cement thermal conductivity using HFM 436/3 with instrumentation kit (rubber sheets and sample thermocouples)
Sample
Cement
18
Sample
thickness
(mm)
76.25
Stack
pressure
(PSI)
k(PA)
2.0
13.8
Temp. mean
(°C)
26.1
Temp. Δ
plates
sample
(K)
19.2
14.3
Sample
density
(kg/m³)
Thermal
resistance
(m²·K/W)
Thermal
conductivity
(W/m·K)
1959
0.0617
1.24
TIPS & TRICKS
Sample Preparation
To give sufficient sample thermal resistance and Δ T, a minimum sample
thickness of 50 mm is recommended. Maximum thickness is approximately 90 mm to allow space for
the interface pads and installation
and removal of the sample.
Prepare the sample surfaces in contact with the plates to be as smooth
as possible and flat and parallel
within approximately 0.3 mm. While
this may be challenging for many
building materials such as concrete,
it is necessary for good thermal
contact with the HFM plates even
when these special procedures are
followed.
Before installation in the HFM, the
sample thickness should be carefully
measured in several locations near
the central metering area and the
average calculated.
is valid over a large range of thermal
resistance.
Procedure – NETZSCH HFM 436/3
with Optional Instrumentation
Kit
Two thermocouples and two
silicone rubber interface sheets
are supplied (Figure 2). Mark
the center point of each sample
surface, lay the upper and lower
thermocouple probes
with the end placed near the
center mark and tape in place as
shown in Figure 3.
Place the rubber sheets on each
side of the sample over the
surface thermocouples and tape
them in position around the
sample edges as shown in Figure
4. The tape will keep the sheets
from shifting or folding during
sample loading.
Load the sample in the HFM
HFM Calibration
A normal calibration using the
supplied fiberglass board standard
is sufficient. It is not necessary to
calibrate using the sample thermocouples and interface sheets or with
a higher thermal conductivity standard sample. Testing has shown that
the heat flux transducer calibration
using the fiberglass board standard
Fig. 2. Instrumentation kit
chamber and lower the plate
until it stops automatically (maximum plate load applied). If using
the optional stack loading feature, a plate pressure of about 2
PSI (about 14 kPa) is recommended to improve thermal contact.
Plug the upper sample thermo-
and the lower sample thermocouple connector into the right
position. Close the HFM door.
In Q-Lab software:
For sample definition User Thickness must be selected and the
sample thickness in cm entered
in the window. The sample thickness will be used to calculate
thermal conductivity. Note that
the Gauge Thickness now includes the thickness of the rubber
interface sheets.
Depending on the thermal resistance of the sample a smaller
temperature Δ will normally
need to be defined to avoid saturation of the heat flux transducer
readings, Q Upper and Q Lower.
For samples such as concrete
(thickness of 50 mm, thermal
conductivity > 1 W/m·K) a Δ of
10 K or less (across the sample) is
typically required. The Δ must be
selected to keep the Q Upper and
Q Lower readings at equilibrium
at or below approximately 32000
uV. This may require setting
several setpoints with different Δ
when testing unknown samples.
The minimum recommended
Delta is approximately 4 K.
couple connector into the left
position (Instrumentation Kit)
Fig. 3. Sample thermocouple mounting
Fig. 4. Mounting of interface rubber sheets
GENERAL
Our Events:
www.netzsch.com/n74902
Event
Date
Location
40 Years of GEFTA
Sep 16 - 19, 2014
Berlin, Germany
LabAfrica 2014
Sep 16 - 18, 2014
Kapstadt, South Africa
MID European Clay Conference 2014
Sep 16 - 19, 2014
Radebeul, Dresden, Germany
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4INSULATION
Sep 18 - 19, 2014
Cracow, Poland
DMG
Sep 21 - 24, 2014
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Tecnargilla
Sep 22 - 26, 2014
Rimini, Italy
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Sep 23 - 26, 2014
Hamburg, Germany
Analytica China 2014
Sep 24 - 26, 2014
Shanghai, China
Kunststoffenbeurs Veldhoven 2014
Sep 24 - 25, 2014
Veldhoven, Netherlands
12th European Conference on Thermoelectrics Sep 24 - 26, 2014
Madrid, Spain
XII SBPMat 2014
Sep 8 - Oct 2, 2014
João Pessoa, Brazil
Brno Trade Fair 2014
Sep 29 - Oct 2, 2014
Brno, Czech Republic
Interplas 2014
Sep 30 - Oct 2, 2014
Birmingham, UK
Expoquimica 2014
Sep 30 - Oct 3, 2014
Barcelona, Spain
IOC 2014
Oct 1 - 4, 2014
Belgrade, Serbia
RAMSPEC 2014
Oct 2 - 4, 2014
Modena, Italy
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Oct 7 - 9, 2014
Düsseldorf, Germany
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Oct 11 - 16, 2014
Orlando, FL, USA
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Oct 12 - 16, 2014
Pittsburgh, PA, USA
testXpo 2014
Oct 13 - 16, 2014
Ulm, Germany
Editor:
NETZSCH-Gerätebau GmbH
Wittelsbacherstraße 42
95100 Selb, Germany
Tel.: +49 9287 881-0
Fax: +49 9287 881-505
at@netzsch.com
www.netzsch.com
20
Editorial Staff:
Dr. Gabriele Kaiser, Dr. Ekkehard Füglein,
Dr. Elisabeth Kapsch, Dr. Andreas Spörrer, Doris Steidl
Translations:
Doris Steidl, Nicole Huss
Copyright:
NETZSCH-Gerätebau GmbH, 08/14
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