ISO 23976:2021
(Main)Plastics — Fast differential scanning calorimetry (FSC) — Chip calorimetry
Plastics — Fast differential scanning calorimetry (FSC) — Chip calorimetry
This document specifies the characteristics of non-adiabatic fast differential scanning calorimeters, also covered by the general abbreviation FSC having an open specimen geometry in which specimens are placed directly onto active measurement areas of chip sensors based on Micro-Electro-Mechanical Systems (MEMS) membrane technology, without encapsulation in closed crucibles and ovens. Due to the open specimen geometry, this document is applicable to very small specimens having masses of not greater than 1 µg only. The occurrence of high temperature gradients during measurements can be prevented by keeping specimen thicknesses as small as possible. The use of very low specimen masses enables achievement of very high scanning rates in the order of several thousand K/s, both in heating and cooling mode whereby lower specimen masses and thicknesses allow higher heating and cooling rates. Typically, low scanning rates of FSC overlap with high scanning rates of conventional DSC covered by ISO 11357‑1, thus enabling connection to conventional DSC results. NOTE 1 Due to the sensor layout FSC is also called chip calorimetry. NOTE 2 FSC stands for Fast Scanning Calorimetry but also for Fast Scanning Calorimeter. In practice from the context the choice can be made quite easily. FSC is suitable for thermal analysis of fast kinetic effects of polymers, polymer blends and composites, such as: — thermoplastics (polymers, moulding compounds and other moulding materials, with or without fillers, fibres or reinforcements); — thermosets (uncured or cured materials, with or without fillers, fibres or reinforcements); — elastomers (with or without fillers, fibres or reinforcements). This document specifies methods for qualitative and quantitative analysis of fast physical and chemical processes showing changes in heat flow rate. This includes measurement of characteristic temperatures as well as caloric values of both, solid and liquid materials. This document is particularly applicable for the observation of fast kinetics of thermal effects such as: — physical transitions (glass transition, phase transitions such as melting and crystallization, polymorphic transitions, etc.); — metastability and related processes like reorganization, (re)crystallization, annealing, ageing, amorphization; — chemical reactions (hydration, oxidation, polymerisation, crosslinking and curing of elastomers and thermosets, decomposition, etc.); — isothermal measurements of fast crystallising systems or chemical reactions. It is also applicable for the determination of heat capacity and related changes of thermodynamic functions. FSC provides a technique to analyse material behaviour at similarly high heating or cooling rates used in industrial polymer processing. FSC can also enable separation of overlapping thermal effects with different kinetics such as: — melting and decomposition: higher heating rates can shift decomposition to higher temperatures and allow unperturbed measurement of melting; — glass transition and cold crystallisation of polymers: higher heating rates can suppress cold crystallisation resulting in unperturbed measurement of glass transition as a function of cooling / heating rates; — reorganisation of amorphous or semi-crystalline polymers upon cooling and heating: depending on the cooling rate used specimens with different crystallinities can be generated and their reorganisation upon heating analysed using different scanning rates. This document establishes general aspects of FSC, such as the principle and the apparatus, sampling, calibration and general aspects of the procedure and test report.
Plastiques — Calorimétrie différentielle à balayage rapide (FSC) — Calorimétrie à balayage ultra-rapide
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 23976
First edition
2021-02
Plastics — Fast differential scanning
calorimetry (FSC) — Chip calorimetry
Plastiques — Calorimétrie différentielle à balayage rapide (FSC) —
Calorimétrie à balayage ultra-rapide
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Principle . 3
5 Apparatus . 4
5.1 Chip calorimeter . 4
5.2 Microscope . 5
5.3 Tools for sample preparation . 5
5.4 Calibration materials . 5
5.5 Measuring atmosphere . 5
6 Specimens . 5
7 Test conditions and specimen conditioning . 6
7.1 Test conditions . 6
7.2 Conditioning of specimens . 6
8 Calibration . 6
8.1 Chip calorimeter performance . 6
[14],[17] 8
8.2 Temperature calibration .
8.2.1 General. 8
8.2.2 Correction for thermal lag due to scan rate . 9
8.2.3 Correction for thermal lag due to sample mass .10
8.2.4 Correction of measured temperature extrapolated to zero heating rate .10
[14],[17],[21] 12
8.3 Symmetry of temperature calibration .
8.3.1 General.12
8.3.2 Procedure .12
8.4 Calibration of heat and heat flow rate.13
9 Specimen measurement procedure .14
9.1 Preparation of apparatus .14
9.1.1 Starting the instrument.14
9.1.2 Purge gas . . .14
9.1.3 Preparation of sensor .14
[23] 14
9.1.4 Blank correction for heat loss .
9.2 Placement of specimens on the sensor .15
9.3 Performance of measurements .16
9.3.1 General.16
9.3.2 Running the instrument .17
9.3.3 Reuse of chip sensor .17
9.3.4 Evaluation of results .17
10 Investigation of physical-chemical effects .17
10.1 General .17
10.2 First Order phase transitions .17
10.3 Chemical reactions.17
10.4 Glass transitions.18
[24]
11 Determination of heat capacity .18
[14],[23]
12 Determination of specimen mass .20
12.1 General .20
12.2 Determination of specimen mass based on specific heat capacity of material .21
12.3 Determination of specimen mass based on specific heat capacity change at glass
transition .21
12.4 Determination of specimen mass based on specific enthalpy of fusion .22
12.5 Determination of specimen mass based on specimen dimensions and density .23
12.6 Use of FSC reference specimens .23
12.7 Criteria for selection of correct specimen mass .23
12.7.1 High specimen mass .23
12.7.2 Low specimen mass .24
13 Precision and bias .24
14 Test report .25
Bibliography .26
iv © ISO 2021 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Introduction
The development of fast scanning calorimetry (FSC) based on chip sensors with very high sensitivity
using ultrathin SiN membranes was initially driven by the objective to measure thermal properties of
very small amounts of sample such as thin films at very high scan rates in the order of magnitude of
4 [1] [2]
10 K/s . Shortly after, a differential scanning sensor was also introduced . These quasi-adiabatic
calorimeters could be used in heating mode only. The extension of sensors to fast cooling applications
was achieved upon operating at non-adiabatic conditions by using gas as thermally inert cooling agent.
To avoid the concomitantly strong increase of thermal lag with increasing scan rate, the sample mass is
decreased accordingly. Thus, reduction of specimens and heating elements to very small size enabled
sufficient temperature control upon fast cooling, see References [3] to [7]. Due to these developments,
the scan rate operating window of existing commercial DSCs is extended to more than 7 orders in
magnitude.
A break-through was the development of extremely fast-operating chip-calorimeters, see Table 1, based
on Micro-Electromechanical-Systems (MEMS) technology, as described in various publications (see, for
example, References [8], [9] and [10]). Until recently, results using chip calorimeters have been obtained
[11],[12]
by specific equipment located at universities , however, dedicated research has also led to the
development of commercially available FSC instrumentation.
For MEMS-sensor technology, power compensation-based twin-sensor microchip calorimeters,
commonly known as fast scanning calorimetry (FSC), and its capabilities have received a great deal of
[8]
attention in recent years . The reason that FSC has become increasingly popular is because, firstly, in
practice, some physical and chemical processes and processing techniques occur at much higher rates
than achievable using conventional DSC. Secondly, most nano-structures in materials and substances,
including polymers and pharmaceuticals, are in metastable states and these can be studied by FSC.
[8],[13],[14]
Finally, FSC is facilitated by the world-wide availability of the first commercial FSC instrument ,
[15]
followed by an advanced instrument achieving even higher scan rates and higher temperatures .
Thermal history – specifically cooling and heating rates – and sample/product treatment can change
the material behaviour drastically, leading to strongly deviating end properties. The significantly
extended range of achievable scan rates, increased instrument sensitivity and reduced time constant
of MEMS-sensors has resulted in strongly increased capabilities of studying the influence of thermal
history.
This document describes characteristic features of commercially available non-adiabatic FSCs,
calibration procedures and performance of measurements that deviate significantly from those of
conventional DSC outlined in the ISO 11357 series. See Reference [16].
vi © ISO 2021 – All rights reserved
Table 1 — Typical characteristics of some chip calorimeters
Achievable temperature at
Scan rate
constant rate
Purge gas
FSC
K/s °C
a a
heating cooling heating up to cooling down to type ml/min
20 000 5 000 410 40 N 20
Commercial
b
instrument 20 000 5 000 410 140 N 20
[13],[14],[15],[17]
20 000 5 000 200 -25 He 20
50 000 20 000 950 100 N 20
Commercial
[15]
instrument 2 b
50 000 20 000 950 250 N 20
University instrument 1 000 000 1 000 000 1 000 30 He 0
[8],[11],[12],[16]
1 000 000 1 000 000 1 000 -180 He 0
a
Cooling rate is determined by the cooling device (temperature difference to base temperature), magnitude of heat flow
rate, environmental conditions such as thermal conductivity of purge gas, etc.
b
Without cooling accessory.
INTERNATIONAL STANDARD ISO 23976:2021(E)
Plastics — Fast differential scanning calorimetry (FSC) —
Chip calorimetry
1 Scope
This document specifies the characteristics of non-adiabatic fast differential scanning calorimeters,
also covered by the general abbreviation FSC having an open specimen geometry in which specimens
are placed directly onto active measurement areas of chip sensors based on Micro-Electro-Mechanical
Systems (MEMS) membrane technology, without encapsulation in closed crucibles and ovens.
Due to the open specimen geometry, this document is applicable to very small specimens having masses
of not greater than 1 µg only. The occurrence of high temperature gradients during measurements can
be prevented by keeping specimen thicknesses as small as possible.
The use of very low specimen masses enables achievement of very high scanning rates in the order
of several thousand K/s, both in heating and cooling mode whereby lower specimen masses and
thicknesses allow higher heating and cooling rates. Typically, low scanning rates of FSC overlap
with high scanning rates of conventional DSC covered by ISO 11357-1, thus enabling connection to
conventional DSC results.
NOTE 1 Due to the sensor layout FSC is also called chip calorimetry.
NOTE 2 FSC stands for Fast Scanning Calorimetry but also for Fast Scanning Calorimeter. In practice from the
context the choice can be made quite easily.
FSC is suitable for thermal analysis of fast kinetic effects of polymers, polymer blends and composites,
such as:
— thermoplastics (polymers, moulding compounds and other moulding materials, with or without
fillers, fibres or reinforcements);
— thermosets (uncured or cured materials, with or without fillers, fibres or reinforcements);
— elastomers (with or without fillers, fibres or reinforcements).
This document specifies methods for qualitative and quantitative analysis of fast physical and chemical
processes showing changes in heat flow rate. This includes measurement of characteristic temperatures
as well as caloric values of both, solid and liquid materials.
This document is particularly applicable for the observation of fast kinetics of thermal effects such as:
— physical transitions (glass transition, phase transitions such as melting and crystallization,
polymorphic transitions, etc.);
— metastability and related processes like reorganization, (re)crystallization, annealing, ageing,
amorphization;
— chemical reactions (hydration, oxidation, polymerisation, crosslinking and curing of elastomers
and thermosets, decomposition, etc.);
— isothermal measurements of fast crystallising systems or chemical reactions.
It is also applicable for the determination of heat capacity and related changes of thermodynamic
functions.
FSC provides a technique to analyse material behaviour at similarly high heating or cooling rates used
in industrial polymer processing.
FSC can also enable separation of overlapping thermal effects with different kinetics such as:
— melting and decomposition: higher heating rates can shift decomposition to higher temperatures
and allow unperturbed measurement of melting;
— glass transition and cold crystallisation of polymers: higher heating rates can suppress cold
crystallisation resulting in unperturbed measurement of glass transition as a function of cooling /
heating rates;
— reorganisation of amorphous or semi-crystalline polymers upon cooling and heating: depending
on the cooling rate used specimens with different crystallinities can be generated and their
reorganisation upon heating analysed using different scanning rates.
This document establishes general aspects of FSC, such as the principle and the apparatus, sampling,
calibration and general aspects of the procedure and test report.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 11357-1, Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles
ISO 11357-2, Plastics — Differential scanning calorimetry (DSC) — Part 2: Determination of glass transition
temperature and step height
ISO 11357-3, Plastics — Differential scanning calorimetry (DSC) — Part 3: Determination of temperature
and enthalpy of melting and crystallization
ISO 11357-4, Plastics — Differential scanning calorimetry (DSC) — Part 4: Determination of specific heat
capacity
ISO 11357-5, Plastics — Differential scanning calorimetry (DSC) — Part 5: Determination of characteristic
reaction-curve temperatures and times, enthalpy of reaction and degree of conversion
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11357-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
chip sensor
symmetric power-compensated sample holder having low addenda heat capacity (3.6) in the order of
nJ/K based on a silicon nitride membrane with a thickness in the µm range
Note 1 to entry: Electronic components for heater and temperature sensor are attached to the membrane. The
sample holder has separate areas for sample and reference specimen onto which specimens are placed directly
and openly in a purge gas environment without encapsulation in crucibles.
2 © ISO 2021 – All rights reserved
3.2
chip calorimetry
non-adiabatic technique in which the difference between the heat flow rate into the sample (3.3) and
reference side of a symmetric chip sensor (3.1) with open specimen geometry is derived as a function of
temperature or time
Note 1 to entry: The temperature difference between sample and reference side of the sensor, both subjected to
the same temperature program, is regulated to almost zero by increasing or decreasing the heating power on
both sides of the sensor while maintaining the controlled temperature program in a specified atmosphere.
Note 2 to entry: The required differential power is measured as a function of temperature or time. Chip
calorimetry enables direct measurement of caloric values and characteristic temperatures.
Note 3 to entry: Information on graphical representation of results can be found in ISO 11357-1.
3.3
sample
small portion of a material taken from a larger quantity of material and intended to be representative
of the whole or to represent a particular section of a manufactured part, such as the skin
3.4
specimen
test piece taken from the sample (3.3) placed on the sample area of the chip sensor (3.1) and analysed
3.5
reference
comparative specimen placed on the reference area of the chip sensor (3.1)
Note 1 to entry: The reference area of the chip sensor is usually left empty.
3.6
addenda heat capacity
additional heat capacity contribution of the sensor not related to the specimen
4 Principle
Very small amounts (typically in the order of 10 ng and not more than 1 µg) of sample and, if applicable,
reference material are placed directly on the corresponding active areas of the chip sensor. The
difference between the heat flow rate into the specimen and that into the reference is measured as
a function of temperature and/or time while specimen and reference are subjected to the same
temperature-controlled programme under a specified atmosphere.
NOTE Suitable heating and cooling rates can vary depending on the characteristics of particular chip
sensors.
Due to the open sample geometry of fast scanning calorimetry the limitation of sample masses to above
indicated values is important to prevent significant temperature gradients in sample and, if applicable,
reference specimens. Figure 1 shows a schematic picture of a typical chip sensor which consists of
two identical siliconnitride/-oxide membranes having lateral dimensions in the mm range or smaller
and a thickness in the µm range or smaller coated with a thin metal layer for improved temperature
distribution that are mounted in a ceramic plate. The sensor layout is symmetrical where both sides,
sample and reference, have identical separate thermal resistance heaters. The temperature is measured
by means of thermocouples arranged symmetrically around the measurement areas of the sample and
reference side, of the chip sensor, respectively. The measurement principle is power-compensation
DSC, i.e. individual heaters are used for sample and reference area. The difference in electrical power
required to maintain both the sample position and the reference position at the same temperature
is recorded against temperature or time, while each position is subjected to the same temperature-
controlled programme. This enables direct measurement of characteristic temperatures and caloric
values of thermal effects.
Key
1 ceramic plate 5 thermocouple
2 silicon frame 6 resistance heater
3 bonding wire 7 metal plate for improved temperature homogeneity
4 siliconnitride/-oxide membrane
[15]
Figure 1 — Example of chip sensor layout
5 Apparatus
5.1 Chip calorimeter
The instrument shall have the following features:
— chip sensor with designated active areas for placement of sample and reference, for measurements
of liquid samples specifically designed sensors may be used;
— capability of generating constant heating and cooling rates up to 1 000 K/s or higher, the upper
scanning rate limit shall be sufficiently high for intended measurements;
— capability to maintain the test temperature constant to within ±0,5 K or less for at least 60 min;
— capability to perform step heating or step cooling measurements;
NOTE 1 Normally, this is achieved by a suitable combination of linear heating or cooling steps and
constant temperature steps.
— capability to provide a controlled static or purging gas environment of the sample holder. When
using continuous purging of the sample holder, the purge gas flow shall be laminar and the flow rate
controllable to within ±10 %;
NOTE 2 The actual gas flow rate depends on the design of the instrument used and the purpose of
measurement.
— capability of generating a temperature range in line with the experimental requirements;
— capability of achieving a heat flow rate range and sensitivity adapted to the designated sample size
range of the chip sensor;
NOTE 3 For a chip sensor designed for specimen masses between 10 ng and 1 µg, typical values of max.
heat flow rate signal and sensitivity are approximately 20 mW and 1 µW, respectively.
— an adequate time constant of the sensor to achieve sufficiently high heating and cooling rates;
— a recording device capable of automatically recording the measured curve of heat flow rate against
temperature and/or time;
4 © ISO 2021 – All rights reserved
— suitable software for evaluation and interpretation of results.
5.2 Microscope
The instrument shall be equipped with a microscope with sufficient magnification for preparation and
correct positioning of sample and, if applicable, reference in the active sensor area, respectively.
For removable chip sensors, preparation and positioning may be done outside of the instrument and the
sensor(s) with attached specimen(s) installed in the instrument prior to measurements.
5.3 Tools for sample preparation
Depending on the properties of the material to be analysed and the desired sample size the following
tools are recommended for sample preparation:
— a pair of tweezers for holding and moving samples;
— microtome for cutting samples to desired thickness;
— abrasive material for preparation of sample powder;
— glass support slides and knife for cutting samples;
— hair or thin soft wire to position specimens on the sensor area;
— silicone oil, graphite, grease or other suitable contact media for improved thermal contact or
wetting.
Other tools may be used as appropriate for particular sample preparation requirements.
5.4 Calibration materials
Calibration materials shall be in accordance with ISO 11357-1.
Stable substances may be archived for later use for additional experiments, as the typical repeatability
of measurements using removable commercially available chip sensors is excellent.
Also, volatile organic compounds may be used if they are easily removable from the sensor without any
residues and do no interact with the membrane.
5.5 Measuring atmosphere
Measuring atmosphere shall be in accordance with ISO 11357-1.
Normally, nitrogen is used as purge gas. It shows a balanced behaviour in heating and cooling mode and
for most samples and experimental conditions nitrogen is sufficiently inert.
Higher cooling rates can be achieved with purge gas of high thermal conductivity such as Helium.
However, due to higher thermal loss the maximum temperature at the same purge gas flow rate will
be significantly reduced compared to nitrogen. The achievable temperature may be increased using
[14]
reduced flow rates .
The flow rate should be optimized in order to prevent contamination with oxygen on the one hand and
maintain laminar flow on the other hand. Alternatively, static atmosphere may be used.
6 Specimens
The specimen shall be in the liquid or solid state. Solid-state specimens may be in any form suitable for
the chip sensor area or may be cut from bigger pieces to a suitable size. The specimen thickness shall
be kept as low as possible in order to prevent the occurrence of high temperature gradients during
measurements.
The specimen shall be representative of the sample being examined and shall be prepared and handled
with care. Particular care shall be taken to avoid any contamination of the specimen. If the specimen
is taken from larger pieces by cutting, care shall be taken to prevent heating, polymer orientation or
any other effect that may alter the specimen properties. Operations such as grinding that could cause
heating or reorientation and could therefore change the thermal history of the specimen shall be
avoided.
The method of sampling and specimen preparation shall be stated in the test report.
Contact media, such as silicone oil, may be used to improve the thermal contact between specimen and
sensor. Care shall be taken to prevent adverse effects of the contact medium to test results.
Specimen thicknesses and masses shall be adapted to test conditions and instrument, or chip sensor used.
7 Test conditions and specimen conditioning
7.1 Test conditions
The instrument shall be maintained and operated in an atmosphere suitable for the intended test.
It is recommended that the instrument be protected from air draughts, exposure to direct sunlight and
abrupt changes in temperature, pressure or mains voltage.
7.2 Conditioning of specimens
Specimens shall be conditioned prior to the measurement run as specified in the relevant material
standard or by a method agreed between the interested parties.
Unless otherwise specified, specimens shall be dried to constant mass before performing measurements.
Care shall be taken to choose suitable drying conditions to prevent physical changes, such as ageing or
changes in crystallinity, of the specimens.
NOTE Depending on the material and its thermal history, the methods of preparation and conditioning of the
sample and specimens can be crucial to the values obtained, the consistency of the results and their significance.
8 Calibration
8.1 Chip calorimeter performance
Prior to any measurement a performance check of the instrument with empty sensor shall be done
with respect to its scan rate capabilities depending on heating and cooling mode and environment
(cooling accessory, purge gas type and flow rate). This performance check shall be repeated each time
the testing environment conditions are changed.
For this performance check, the achieved heating or cooling rates are obtained by plotting the derivative
of the achieved sample temperature as a function of achieved temperature as shown in Figure 2 and
Figure 3. The instrument shall be used for measurements only within temperature ranges and scan
rates where the achieved heating and cooling rates are constant.
Environmental gases with higher thermal conductivity, such as helium, provide higher cooling rates or
extended temperature ranges in cooling, but may limit the upper temperature limit upon heating (see
[14]
Figure 2 and Figure 3). They may also show a higher sensitivity to purge gas flow rate changes .
6 © ISO 2021 – All rights reserved
Key
Y achieved scan rate in K/s 5, 5′ ±5 000 K/s
X programmed temperature in °C 6, 6′ ±3 000 K/s
1, 1′ ±20 000 K/s 7, 7′ ±1 000 K/s
2, 2′ ±15 000 K/s without cooling accessory
3, 3′ ±10 000 K/s with IntraCooler set to -95 °C
4, 4′ ±8 000 K/s
NOTE Measured using a commercial FSC instrument at scan rates from 20 000 K/s to 1 000 K/s with
empty sensor.
[14]
Figure 2 — Achieved scan rates vs. sample temperature purged with 20 ml/min N
Key
Y achieved scan rate in K/s 5, 5′ ±5 000 K/s
X programmed temperature in °C 6, 6′ ±3 000 K/s
1, 1′ ±20 000 K/s 7, 7′ ±1 000 K/s
2, 2′ ±15 000 K/s
without cooling accessory
3, 3′ ±10 000 K/s with IntraCooler set to -95 °C
4, 4′ ±8 000 K/s
NOTE Measured using the same instrument and scan rates as in Figure 2 with empty sensor.
[14]
Figure 3 — Achieved scan rates vs. temperature purged with 20 ml/min He
[14],[17]
8.2 Temperature calibration
8.2.1 General
A certified or otherwise acknowledged calibration material shall be selected. Suitable calibration
materials can be found in ISO 11357-1, but also other calibration materials may be used as appropriate.
The calibration sample shall be placed as close as possible to the centre of the active area of the sample
[18] [14]
holder to prevent significant shift or broadening of transition peaks , as shown in Figure 4 .
A sufficient number of calibration materials shall be used to cover the temperature range required for
measurements.
The temperature calibration shall be done for each purge gas separately. If required, the influence of
the purge gas flow rate (e.g. for He) shall be taken into account.
8 © ISO 2021 – All rights reserved
a) Sample positions b) Melting curves
Key
Y heat flow rate side position (1.)
X temperature in °C centre position (2.)
A 10 K/s opposite side position (3.)
a
B 100 K/s Endothermic direction.
C 300 K/s
D 500 K/s
Figure 4 — Melting curves obtained at different heating rates with a sample of 1 µg of indium
[14]
placed at different positions of the active area of the sample holder
The temperature calibration of the sensor shall establish the following three corrections:
— correction for thermal lag due to scan rate;
— correction for thermal lag due to sample mass;
— correction of the measured temperature extrapolated to zero heating rate indicated by the
instrument towards the true transition temperature of the calibration material.
In addition, the influence of static temperature gradients caused by low thermal conductivity of
specimens or bad thermal contact to the sensor should be taken into account. This can not only
cause significant temperature lag at higher scanning rates but can also yield constant temperature
[19],[20]
offset .
As specimens cannot be easily removed from chip sensors, temperature calibration is generally not
done on the very same chip sensor used for measurements but on similar sensors coming from the
same production batch. This problem can be eliminated by using volatile calibration substances that
can be removed from the sensor without residues.
8.2.2 Correction for thermal lag due to scan rate
For the scan rate correction, a suitable range of scan rates shall be selected for the type of chip
calorimeter or sensor used. Calibration runs shall be done at a minimum of five scan rates: the minimum
rate β , the maximum scan rate β and at least three rates evenly spread in between. The minimum
min max
and maximum heating rates shall be selected to cover the scan rate range required for measurements.
8.2.3 Correction for thermal lag due to sample mass
Depending on the type of chip calorimeter or sensor, suitable masses differing by at least two orders of
magnitude shall be selected for each scan rate run specified in 8.2.2. At least three sample masses shall
be used: one having an optimal mass for the type of instrument or sensor used and two samples having
lower and higher mass, respectively.
Key
Y measured extrapolated peak onset temperature in °C m = 2,508 μg
X heating rate in K/s m = 1,997 μg
m sample mass
m = 1,567 μg
m = 0,408 μg
m = 0,285 μg
m = 0,103 μg
m = 0,016 μg
Figure 5 — Extrapolated peak onset temperatures of indium as a function of heating rate and
[14],[17]
sample mass
An example of extrapolated peak onset temperatures of indium extrapolated to zero heating rate at
different sample masses is shown in Figure 5.
8.2.4 Correction of measured temperature extrapolated to zero heating rate
The measured extrapolated peak onset temperatures, obtained by the intersection point of the baseline,
i.e. that lower temperature part of the curve that represents the non-transition part of the measurement,
10 © ISO 2021 – All rights reserved
with that part of the curve that shows the steepest slope and thus represents the measured transition.
These extrapolated peak onset temperatures shall be fitted by Formula (1):
aa
Tm()ββ, =+aa ⋅+am⋅⋅β (1)
ei,p 01 3
For some types of chip calorimeters or sensors, Formula (1) can be simplified to:
Tmββ, =+aa ⋅⋅m (2)
()
ei,p 01
where
Tm()β , is the extrapolated peak onset temperature extrapolated to zero heating rate and
ei,p
dependent on sample mass;
β
is the heating rate in K/s;
m
is the is the sample mass;
aa,,aa,,a are the fitting parameters of Formulae (1) or (2).
01 23 4
The selection of the formula to be used for fitting shall be justified based on the correlation factor.
The peak onset temperatures extrapolated to zero heating rate Tmβ , shall be shifted by a
()
ei,p
correction factor C obtained by comparison with the true transition temperature T of the
T cal
ei
calibration material, shown as Formula (3):
TT= ()β ,mC+ (3)
calei,p T
ei
Following this procedure, all corrected temperatures extrapolated to zero scan rate will be equal to the
true transition temperature, T .
cal
In addition, a correction matrix for the extrapolated peak onset temperature Tm()β , may be
ei,p
calculated based on the fitting by Formula (1) or Formula (2) and the correction factor C as shown in
T
ei
Table 2.
Table 2 — Correction matrix for the extrapolated onset temperatures of indium as a function of
[14],[17]
heating rate and sample mass
C
T
ei
K
Mass
β
µg
K/s 0,05 0,1 0,5 1 1,5 2 4
0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
1 0,0 0,0 0,0 0,0 0,0 0,0 0,0
10 0,0 0,0 0,0 0,0 0,0 0,0 0,0
30 0,0 0,0 0,0 0,0 -0,1 -0,1 -0,1
50 -0,1 -0,1 -0,1 -0,1 -0,1 -0,1 -0,1
80 -0,1 -0,1 -0,1 -0,1 -0,1 -0,1 -0,2
100 -0,1 -0,1 -0,2 -0,2 -0,2 -0,2 -0,2
200 -0,2 -0,2 -0,2 -0,2 -0,2 -0,3 -0,3
Table 2 (continued)
C
T
ei
K
Mass
β
µg
300 -0,2 -0,2 -0,2 -0,3 -0,3 -0,3 -0,4
400 -0,4 -0,5 -0,5 -0,6 -0,6 -0,7 -0,9
500 -0,6 -0,6 -0,7 -0,8 -0,9 -1,0 -1,4
800 -0,8 -0,8 -1,0 -1,2 -1,3 -1,5 -2,1
1 000 -0,9 -1,0 -1,2 -1,4 -1,6 -1,8 -2,6
[14],[17],[21]
8.3 Symmetry of temperature calibration
8.3.1 General
The symmetry of temperature calibration between heating and cooling of the chip sensor shall be
verified within the scan rates of interest. Symmetrical behaviour of the chip sensor with respect to
extrapolated peak onset temperatures means that the correction factors established in heating mode
in 8.2 apply for cooling mode, too, with opposite sign. If such verification is not achieved, separate
correction factors and a separate correction factor matrix shall be obtained for cooling.
Three liquid crystals have been reported in literature for checking the symmetry of fast scanning
1)
calorimeters :
— 4-cyano-4’-octyloxybiphenyl (8OCB or M-24);
— 4-(4-pentyl cyclohexyl)-benzoicacid-4-propyl-phenylester (HP-53);
— 4’-ethyl-4(4-propylcyclohexyl)-biphenyl (BCH-52).
Calibration symmetry measurements shall be done based on extrapolated peak onset temperatures
or peak temperatures, whatever can be determined more accurately, of liquid crystal transitions. The
transition peaks shall be continuous and symmetric and shall not show multiple peaks within the
scan rate range required for measurements in both, heating and cooling mode. In order to prevent
structural reorganisation during heating calibration samples may need to be conditioned to achieve
[21]
full crystallisation and sufficiently stable crystals .
8.3.2 Procedure
The sample used for checking the symmetry of temperature calibration shall have a mass typical for
the selected type of chip calorimeter or sensor, and the intended application.
The extrapolated peak onset temperatures T or peak maximum temperatures T shall be determined
ei p
as a function of heating and cooling rate covering the scan rate range required for measurements.
Temperatures or temperature differences vs. known transition temperatures shall be plotted as a
function of cooling and
...
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