ASTM E698-99
(Test Method)Standard Test Method for Arrhenius Kinetic Constants for Thermally Unstable Materials
Standard Test Method for Arrhenius Kinetic Constants for Thermally Unstable Materials
SCOPE
1.1 This method covers the determination of the overall kinetic parameters for exothermic reactions.
1.2 The kinetic parameters are obtained from differential scanning calorimetry (DSC) curves (see Section 3).
1.3 This technique is applicable to reactions whose behavior can be described by the Arrhenius equation and the general rate law.
1.4 Limitations—There are cases where this technique is not applicable. Limitations may be indicated by curves departing from a straight line (see 11.2) or the isothermal aging test not closely agreeing with the results predicted by the calculated kinetic values. In particular, this method is not applicable to reactions that are partially inhibited. The technique may not work with reactions that include simultaneous or consecutive reaction steps. This method may not apply to materials that undergo phase transitions if the reaction rate is significant at the transition temperature.
1.5 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems 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.
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Designation: E 698 – 99
Standard Test Method for
Arrhenius Kinetic Constants for Thermally Unstable
Materials
This standard is issued under the fixed designation E 698; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The kinetics of exothermic reactions are important in assessing the potential of materials and
systems for thermal explosion. This method provides a means for determining Arrhenius activation
energies and pre-exponential factors using differential thermal methods. This method is one of several
methods being developed by ASTM Committee E-27 for chemical reactions. This method is to be used
in conjunction with other tests to characterize the hazard potential of chemicals.
1. Scope Scanning Calorimeters and Differential Thermal Analyz-
ers
1.1 This method covers the determination of the overall
E 968 Practice for Heat Flow Calibration of Differential
kinetic parameters for exothermic reactions.
Scanning Calorimeters
1.2 The kinetic parameters are obtained from differential
E 1142 Terminology Relating to Thermophysical Proper-
scanning calorimetry (DSC) curves (see Section 3).
ties
1.3 This technique is applicable to reactions whose behavior
E 1445 Terminology Relating to Hazardous Potential of
can be described by the Arrhenius equation and the general rate
Chemicals
law.
E 1860 Method for Elapsed Time Calibration of Thermal
1.4 Limitations—There are cases where this technique is not
Analyzers
applicable. Limitations may be indicated by curves departing
from a straight line (see 10.2) or the isothermal aging test not
3. Terminology
closely agreeing with the results predicted by the calculated
3.1 Technical terms used in this test method are defined in
kinetic values. In particular, this method is not applicable to
Terminologies E 473, E 1142, and E 1445.
reactions that are partially inhibited. The technique may not
work with reactions that include simultaneous or consecutive
4. Summary of Test Method
reaction steps. This method may not apply to materials that
4.1 A sample is placed in a suitable container and positioned
undergo phase transitions if the reaction rate is significant at
in a differential scanning calorimeter (DSC).
the transition temperature.
4.2 The sample equipment temperature is increased at a
1.5 This standard may involve hazardous materials, opera-
linear rate and any exothermic reaction peaks recorded.
tions, and equipment. This standard does not purport to
4.3 Steps 2.1 and 2.2 are repeated for several heating rates
address all of the safety problems associated with its use. It is
in the range from 1 to 10 K/min.
the responsibility of whoever uses this standard to consult and
4.4 Temperatures at which the reaction peak maxima occur
establish appropriate safety and health practices and deter-
are plotted as a function of their respective heating rates.
mine the applicability of regulatory limitations prior to use.
4.5 Kinetic values calculated from the peak temperature-
heating rate relationship are used to predict a reaction half-life
2. Referenced Documents
at a selected temperature.
2.1 ASTM Standards:
2 4.6 A sample is aged at the selected temperature for the
E 473 Terminology Relating to Thermal Analysis
predicted half-life time.
E 967 Practice for Temperature Calibration of Differential
4.7 The aged sample is temperature programmed in a
differntial scanning calorimetr and its reaction peak area
This method is under the jurisdiction of ASTM Committee E-27 on Hazard
compared with that for an unaged sample run under the same
Potential of Chemicals and is the direct responsibility of Subcommittee E27.02 on
conditions.
Hazard Potential of Chemicals.
Current edition approved May 10, 1999. Published August 2000.Originally 4.8 If the normalized area for the aged sample is approxi-
published as E 698–79. Last previous edition E698–93.
mately half that for the unaged sample, the kinetic values are
Discontinued, See 1984 Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 698
confirmed for the temperature selected. 6.4 A balance, wtih a capacity of at least 100 mg, to weigh
specimens and/or containers (pans, crucibles, vials, etc) to 10
5. Significance and Use
μg.
5.1 The Arrhenius parameters combined with the general 6.5 Auxiliary equipment useful for conducting this method
rate law and the reaction enthalpy can be used for the below ambient temperature.
determination of thermal explosion hazards (1). 6.5.1 A coolant system, which can be directly coupled with
the controller to the furnace to hasten its recovery from
6. Apparatus
elevated temperatures, to provide constant cooling rates, and/or
6.1 General—The equipment used in this method should be to sustain an isothermal subambient temperature.
capable of displaying quantitative changes of enthalpy as a
7. Safety Precautions
function of time (t) or temperature (T), should be linearly
7.1 The use of this test method on materials whose potential
programmable and have the capabilities of subjecting the
hazards are unknown requires that precaution be taken during
sample cell to different atmospheres. The heat sensing element
sample preparation and testing.
should be external to the sample.
7.2 Where particle size reduction by grinding is necessary,
6.2 Differential Scanning Calorimeter (DSC):
the user of this method should presume that the material is
6.2.1 A DSC test chamber composed of:
dangerous.
6.2.1.1 A furnace, to provide uniform controlled heating
7.3 Toxic or corrosive effluents, or both, may be released
(cooling) of a specimen and reference to a constant temperature
when heating the material and could be harmful to the
or at a constant rate within the applicable temperature range of
personnel or the apparatus. Use of an exhaused system to
this test method.
remove such effluents is recommended.
6.2.1.2 A temperature sensor, to provide an indication of the
specimen/furnace temperature to 6 0.1K. 8. Sampling
6.2.1.3 A differential sensor, to detect a difference in heat
8.1 Sample size is kept small to minimize temperature
flow between the specimen and reference equivalent to 10 μW.
gradients within the sample. In general, a sample weight
6.2.1.4 A means of sustaining a test chamber environ-
resulting in a maximum heat generation of less than 8 mJ/s is
ment,of an inert purge gas at a rate of 10–50 6 mL/min.
satisfactory.
8.2 Samples should be representative of the material being
NOTE 1—Typically, 99 +% pure nitrogen, argon, or helium are em-
ployed when oxidation in air is a concern. Unless effects of moisture are studied and should be prepared to achieve good thermal contact
to be studied, use of dry purge gas is recommended; especially for
between sample and container (see Fig. 1).
operation at subambient temperature.
8.3 The sample container should be nonreactive with the
6.2.2 A temperature controller, capable of executing a sample or reaction products.
8.4 The reference for the sample is normally an empty
specific temperature program by operating the furnace(s)
between selected temperature limits at a rate of temperature container or one filled with inert material.
8.5 Samples which have appreciable volatility over the
change between 0.5 and 10 K/min constant to 6 0.1K/min or
temperature range of interest may require sealing in hermetic
at an isothermal temperature constant to 6 0.1 K.
6.2.3 A recording device, either digital or analog, capable of containers or a high-pressure cell, or both, to prevent vapor-
ization interference and weight loss of unreacted material.
recording and displaying any fraction of the heat flow signal
including the signal noise. 8.6 The sample atmosphere should closely represent the
conditions of usage.
6.3 Containers (pans, crucibles, vials, etc), which are inert
to the specimen and reference materials and which are suitable
9. Calibration
structural shape and integrity to contain the specimen and
9.1 Perform any calibration procedures recommended by
reference in accordance with the specific requirements of this
the manufacturer as described in the Operator’s manual.
method.
9.2 Calibrate the heat flow and elapsed time signals using
Practice E 1860 and Method E 1860,respectively, using the
same type of specimen container to be used in the subsequent
The boldface numbers in parentheses refer to the list of references at the end of
this method. kinetic tests.
FIG. 1 Arrangement for Good Sample Contact with Container
E 698
E/RT 2
Perform any calibration procedures recommended by the
Z5bEe /RT (3)
manufacturer as described in the Operator’s manual.
where: b is a heating rate from the middle of the range.
9.3 Calibrate the temperature signal at 10 K/min using
11.6 For the confirming isothermal test, calculate k for
Practice E 967,using the same type of specimen container to be
various temperatures from the Arrhenius equation and the
used in the subsequent kinetic tests.
above E and Z values.
9.4 Determine the temperature calibration corrections for
11.7 From t 5 0.693/k, calculate aging times (t) for each
other heating rates by programming a sharply melting standard
temperature.
(for example, pure indium metal) at these heating rates and
11.8 Select a temperature requiring at least 1-h aging time,
observing the deviation of the known melt temperature as a
and age the sample isothermally for the calculated half-life in
function of the rate.
a thermal instrument or other facility capable of 61 K control.
NOTE 2—This table of temperature calibration correction values, once
Quench immediately to some temperature at least 50 K below
determined for a particular apparatus and specimen container, may be used
the aging temperature so that no significant reaction occurs
for subsequent experiments following temperature calibration at 10 K/min
during subsequent holding time.
heating rate in 9.3
11.9 Run the aged sample in a thermal instrument and
9.5 The thermal resistance of the instrument sample cell is
record its reaction peak.
determined by measuring the temperature lag observed for the
11.10 Run a similar but unaged sample in the same way and
melting of a pure metal standard. See Fig. X1.2 in Appendix
record its reaction peak.
X1.
11.11 On an equal weight basis,
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