ASTM E968-02(2008)

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:E968–99 Designation: E 968 – 02 (Reapproved 2008)
Standard Practice for
Heat Flow Calibration of Differential Scanning Calorimeters
This standard is issued under the fixed designation E968; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the heat flow calibration of differential scanning calorimeters over the temperature range from−130
°C to+800 °C.
1.2 Values given in SI units are to be regarded as the standard.
1.3 Computer or electronic based instruments, techniques or data manipulation equivalent to this practice may also be used.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of
regulatory limitations prior to use. See also Section 7.
2. Referenced Documents
2.1 ASTM Standards:
E473Terminology Relating to Thermal Analysis ASTM Standards:
E473 Terminology Relating to Thermal Analysis and Rheology
E793 Test Method for HeatsEnthalpies of Fusion and Crystallization by Differential Scanning Calorimetry
E967Practice for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers Test
Method for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers
E1142 Terminology Relating to Thermophysical Properties
3. Terminology
3.1 Definitions— Specific technical terms used in this practice are in accordance with Terminologies E474E473 and E1142.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 coeffıcient of variation, n—ameasureofrelativeprecisioncalculatedasthestandarddeviationofaseriesofvaluesdivided
by their average. It is usually multiplied by 100 and expressed as a percentage.
NOTE 1—The term quantitative differential thermal analysis refers to differential thermal analyzers that are designed to obtain quantitative or
semiquantitative heat flow results. This procedure may also be used to calibrate such apparatus.
4. Summary of Practice
4.1 Differential scanning calorimeters measure heat flow (power) into or out of a test specimen and provide a signal output
proportionaltothismeasurement.Thissignaloftenisrecordedasafunctionofasecondsignalproportionaltotemperatureortime.
If this heat flow signal is integrated over time, the resultant value is proportional to energy (or enthalpy or heat). To obtain the
desired energy information, the observed instrument response (such as the area under the curve scribed) must be multiplied by a
proportionality constant that converts the units of instrument output into the desired energy units. This proportionality constant is
called the instrument calibration coefficient ( E). The value and dimensions (units) of E depend upon the particular differential
scanning calorimeter and recording system being used and, moreover, may vary with temperature.
4.2 This practice consists of calibrating the heat flow response of a differential scanning calorimeter (that is, measuringdeter-
miningthecalibrationcoefficient)byrecordingthemeltingendothermofahigh-puritystandardmaterial(wheretheheatoffusion
is known to better than 6 1.5% (rel)) as a function of time.The peak is then integrated (over time) to yield an area measurement
proportional to the enthalpy of melting of the standard material.
ThispracticeisunderthejurisdictionofASTMCommitteeE-37onThermalMeasurementsandisthedirectresponsibilityofSubcommitteeE37.01onThermalAnalysis
Methods.
Current edition approved March 10, 1999. Published May 1999. Originally published as E968 – 83. Last previous edition E968 – 83 (1993).
This practice is under the jurisdiction of ASTM Committee E37 on Thermal Measurements and is the direct responsibility of Subcommittee E37.01 on Thermal Test
Methods and Practices.
Current edition approved Sept. 1, 2008. Published October 2008. Originally approved in 1983. Last previous edition approved in 2002 as E968 – 99(2002).
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
, Vol 14.02.volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 968 – 02 (2008)
4.3 Calibrationoftheinstrumentisextendedtotemperaturesotherthanthatofthemeltingpointofthestandardmaterialthrough
the recording of the specific heat capacity of a (second) standard material over the temperature range of interest. The ratio of the
measured specific heat capacity at the temperature of interest to that of the temperature of calibration provides an instrument
calibration coefficient at the new temperature.
4.4 Once the calibration coefficient at a given temperature is determined, it may be used to determine the desired energy value
associated with an enthalpic transition in an unknown specimen at that temperature (see Test Method E793).
5. Significance and Use
5.1 Differential scanning calorimetry is used to determine the heat or enthalpy of transition. For this information to be
meaningful in an absolute sense, heat flow calibration of the apparatus or comparison of the resulting data to that of a known
standard is required.
5.2 This practice is useful in calibrating the heat flow axis of differential scanning calorimeters or quantitative differential
thermal analyzers for subsequent use in the measurement of transition energies and specific heat capacities of unknowns.
6. Apparatus
6.1 Differential Scanning Calorimeter (DSC)—The essential instrumentation required to provide the minimum differential
scanning calorimetric capability for this method includes:
6.1.1 A DSC test chamber, composed of the following:
6.1.1.1 Afurnace(s) to provide uniform controlled heating (cooling) of a specimen and reference to a constant temperature or
at a constant rate with the temperature range of –100 to 600 °C.
NOTE 2—This temperature range may be extended to higher and lower temperatures depending upon the capabilities of the apparatus.
6.1.1.2 A temperature sensor, to provide an indication of the specimen/furnace temperature to 6 0.01 K.
6.1.1.3 A differential sensor, to detect a heat flow (power) difference between the specimen and reference equivalent to 1 µW.
6.1.1.4 Ameans of sustaining a test chamber environment, of an inert purge gas at a purge gas rate of 10 to 100 mL/min 6 5
mL/min.
NOTE 3—Typically, 99.9+% pure nitrogen, argon or helium are employed when oxidation in air is a concern. Unless effects of moisture are to be
studied, use of dry purge gas is recommended and is essential for operation at subambient temperatures.
6.1.2 A temperature controller, capable of executing a specific temperature program by operating the furnace(s) between
selected temperature limits at a rate of temperature change of between 1 and 35 K/min constant to 6 1% and at an isothermal
temperature constant to 6 0.1 K.
6.1.3 A recording device, either digital or analog, capable of recording and displaying the heat flow (DSC curve) signal versus
temperature, displaying any fraction including the signal noise.
6.1.4 Containers,(pans,crucibles,vials,etc.andassociatedlids),thatareinerttothespecimenandreferencematerialsandthat
are of suitable structural shape and integrity to contain the specimen and reference.
NOTE 4—Most containers require special tool(s) for opening, closing or sealing.The specific tool(s) necessary to perform this action also are required.
6.1.5 Cooling capability, to achieve and sustain cryogenic temperatures, to hasten cool down from elevated temperatures, or to
provide constant cooling rates, or a combination thereof.
6.1.6 Computer and software capability to perform the mathematical treatments of this method including peak integration.
6.2 A balance, with capacity of 100 mg to weight specimens, or containers, or both, to 6 1 µg,
7. Precautions
7.1 Toxic or corrosive effluents, or both, may be released when heating some material and could be harmful to personnel and
apparatus.
8. Reagents and Materials
8.1 For the temperature range covered by many applications, the melting transitions of the following greater-than-99.9% pure
material may be used for calibration.
Melting Tem- Heat of Fusion,
3 4
perature, K J/g
Indium 429.8 28.42 6 0.36
Indium 429.75 28.58 6 0.07
8.2 Sapphire,(a−Al O ), 20 to 80 mg, solid disk.
2 3
Rossini, F. D., Pure Applied Chemistry, Vol 22, 1970, p. 557.
Preston–Thomas, H., Metrologia,, Vol 27, 1990, p. 3.
Hultgren, R. et al, Selected Values of Thermodynamic Properties of the Elements, American Society of Metals, Metals Park, OH, 1973.
Stolen, S., Gronvold, F., Thermochimica Acta, Vol 327, 1999, p.1. E37
E 968 – 02 (2008)
9. Calibration
9.1 Perform any calibration procedures described by the manufacturer in the operations manual.
9.2 Perform a temperature signal calibration according to Practice E967.
10. Procedure
10.1 Calibration at a specific temperature—The following procedure is used to calibrate the heat flow response of the
instrument with the same type specimen holder, heating rate, purge gas, and purge gas flow rate as will be used for specimen
measurement. A dry nitrogen purge gas with a flow rate of 10 to 50 6 5 mL/min is recommended. Other purge gases and rates
may be used but shall be reported.
10.1.1 Placea5to10 6 0.001-mg weighed amount of melt transition calibration material into a clean specimen holder.
10.1.2 Sealthespecimenholderwithalid,minimizingthefreespacebetweenthespecimenandthelid.Loadthespecimeninto
the instrument.
10.1.3 Allow the specimen to equilibrate at a temperature 30 °C below the melting temperature.
10.1.4 Heat the specimen at 10 °C/min through the endotherm until the baseline is reestablished above the melting endotherm.
Record the accompanying thermal curve of heat flow versus time.
NOTE 5—Other heating rates may be used but shall be reported.
10.1.5 Cool and reweigh the specimen. Reject the data if mass losses exceed 1% of the original mass or if there is evidence
of reaction with the specimen holder.
10.1.6 Calculate the calibration coefficient at the temperature of measurement using the procedure described in Section 11.
Duplicate determinations shall be made on different specimens and the mean valu
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