ASTM E1981-98
(Guide)Standard Guide for Assessing the Thermal Stability of Materials by Methods of Accelerating Rate Calorimetry
Standard Guide for Assessing the Thermal Stability of Materials by Methods of Accelerating Rate Calorimetry
SCOPE
1.1 This guide covers suggested procedures for the operation of a calorimetric device designed to obtain temperature and pressure data as a function of time for systems undergoing a physicochemical change under nearly adiabatic conditions.
1.2 This guide outlines the calculation of thermodynamic parameters from the time, temperature, and pressure data recorded by a calorimetric device.
1.3 The assessment outlined in this guide may be used over a pressure range from full vacuum to the rated pressure of the reaction container and pressure transducer. The temperature range of the calorimeter typically varies from ambient to 500&176C, but also may be user specified (see 6.6).
1.4 This statement does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific safety precautions are outlined in Section 7.
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Designation: E 1981 – 98
Standard Guide for
Assessing the Thermal Stability of Materials by Methods of
Accelerating Rate Calorimetry
This standard is issued under the fixed designation E 1981; 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
This guide is one of several standards being developed by ASTM Committee E-27 for determining
the physicochemical hazards of chemicals and chemical mixtures. This guide should be used in
conjunction with other test methods, as a complete assessment of the hazard potential of chemicals
must take into account a number of realistic factors not necessarily considered in this guide. The
expression hazard potential as used by this committee is defined as the degree of susceptibility of
material to ignition or release of energy under varying environmental conditions.
It is the intent of this guide to include any calorimetric device consistent with the principles of
adiabatic calorimetry. Device-specific information and specifications are located in appendices to the
guide. Any reference to specific devices in the guide are for purposes of illustration or clarity only.
1. Scope E 487 Test Method for Constant-Temperature Stability of
Chemical Materials
1.1 This guide covers suggested procedures for the opera-
E 537 Test Method for Assessing the Thermal Stability of
tion of a calorimetric device designed to obtain temperature
Chemicals by Methods of Differential Thermal Analysis
and pressure data as a function of time for systems undergoing
E 680 Test Method for Drop Weight Impact Sensitivity of
a physicochemical change under nearly adiabatic conditions.
Solid-Phase Hazardous Materials
1.2 This guide outlines the calculation of thermodynamic
E 698 Test Method for Arrhenius Kinetic Constants for
parameters from the time, temperature, and pressure data
Thermally Unstable Materials
recorded by a calorimetric device.
E 1231 Practice for Calculation of Hazard Potential
1.3 The assessment outlined in this guide may be used over
Figures-of-Merit for Thermally Unstable Materials
a pressure range from full vacuum to the rated pressure of the
reaction container and pressure transducer. The temperature
3. Terminology
range of the calorimeter typically varies from ambient to
3.1 Definitions of Terms Specific to This Standard:
500°C, but also may be user specified (see 6.6).
3.1.1 adiabatic calorimeter, n—an instrument capable of
1.4 This statement does not purport to address all of the
making calorimetric measurements while maintaining a mini-
safety concerns, if any, associated with its use. It is the
mal heat loss or gain between the sample and its environment,
responsibility of the user of this standard to establish appro-
which is verifiable by the capability to continuously measure
priate safety practices and to determine the applicability of
the temperature differential between the sample and its sur-
regulatory limitations prior to use. Specific safety precautions
roundings.
are outlined in Section 7.
3.1.2 autocatalytic reaction, n—a chemical reaction in
2. Referenced Documents which a product or reaction intermediate functions as a
catalyst.
2.1 ASTM Standards:
3.1.3 drift, n—a gradual unintended increase or decrease in
E 476 Test Method for Thermal Stability of Confined Con-
2 the system (sample container and surroundings) temperature
densed Phase Systems (Confinement Test)
due to limitations in the system calibration, or to changes
which occur in the system after calibration.
This guide is under the jurisdiction of ASTM Committee E27 on Hazard
Potential of Chemicals and is the direct responsibility of Subcommittee E27.02 on
Thermal Stability and Condensed Phases.
Current edition approved Oct. 10, 1998. Published February 1999.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1981
3.1.4 final temperature (T ), n—the observed system erroneously high time to maximum rates (TMR’s) (see 3.1.12).
final
temperature at the end of an exotherm, generally at the See also 10.1 for a mathematical formula definition of the
temperature where the self-heat rate of the reaction has thermal inertia factor.
decreased below the operator-defined slope sensitivity thresh-
3.1.11 thermal runaway reaction, n—a chemical reaction in
old.
which the heat generation rate in a system exceeds the heat
3.1.5 heat of reaction (DH), n—the net calculated heat
removal rate of that system.
(energy) liberated during an exothermic reaction.
3.1.12 time to maximum rate (TMR), n—the amount of time
3.1.6 ideal adiabatic temperature rise (DT ), n—the tem-
ad
that is needed for a reaction to reach its maximum self-heating
perature rise which would be observed in an exothermic
rate or pressure rate in a thermal runaway reaction, normally
reaction if all of the heat liberated were used to increase the
referenced from the time corresponding to the onset tempera-
temperature of only the sample. It is conveniently calculated as
ture, but may also be referenced from any time-temperature
the product of the observed adiabatic temperature rise, DT ,
obs
point to the time at which the maximum self-heating or
and the thermal inertia factor, f.
pressure rate occurs. The experimentally-observed TMR is
3.1.7 observed adiabatic temperature rise (DT ), n—the
obs
normally divided by the thermal inertia factor (see 3.1.10) to
observed temperature rise in the system during an exotherm;
obtain a more conservative assessment of TMR. (TMR divided
mathematically, it is equal to the temperature difference be-
by the thermal inertia factor is often referred to as the
tween the final temperature and the onset temperature of an
“f-corrected” TMR).
exotherm.
3.1.8 onset temperature (T ), n—the observed system
start
4. Summary of Guide
temperature at the start of an exotherm where the self-heating
4.1 A sample is placed in a reaction container and posi-
rate first exceeds the operator-defined slope sensitivity thresh-
tioned in the calorimeter (see Fig. 1).
old, usually 0.02°C/min; the onset temperature is not a funda-
mental property of a substance, but is apparatus-dependent, 4.2 The bomb is heated to a user-specified initial tempera-
based upon the inherent sensitivity of the calorimetric system. ture and allowed to come to equilibrium, whereupon a search
3.1.9 self-heating, adj—any exothermic process which in- for evidence of an exothermic reaction is undertaken. An
creases the temperature of the system by the self absorption of exotherm is considered to have occurred when the user-
the liberated heat. specified rate of temperature rise is first exceeded. If no
3.1.10 thermal inertia factor (f), n— a correction factor exotherm is detected, the system temperature is raised a
applied to time and temperature differences observed in exo- specified increment and the system allowed to equilibrate
thermic reactions in the system (sample and container) under again. This heat-wait-search cycle is repeated until either an
test, which accounts for the sensible heat absorbed by the exotherm is detected or the upper temperature limit of the test
sample container that otherwise would lead to erroneously low is reached. If an exotherm is detected, the surroundings are
heats of reaction and adiabatic temperature rise, as well as to kept at the same temperature as the reaction container, allowing
FIG. 1 Example Calorimeter and Reaction Container
E 1981
the system to be maintained without heat loss as the tempera- lation is also dependent on the temperature tracking accuracy
ture of the system increases due to the heat evolved during the of the system (see 6.2).
exotherm. 6.5 The use of the equations specified for the determination
4.3 Time, temperature and pressure data are recorded at of kinetic parameters (see, for example, Appendix X1) may not
specified temperature intervals as a function of time. Addi- be suitable in many instances, especially when multiple reac-
tional user-selected parameters may also be recorded or stored. tions are involved.
4.4 The recorded data are used to calculate the time rates of 6.6 Data may be obtained in the temperature range consis-
changes of pressure and temperature. These data may also be tent with the calorimeter’s specifications and at pressures up to
used to calculate a time-to-maximum-rate (as defined in 3.1.12) those consistent with the limitation of the pressure transducer
and to obtain kinetic parameters (1-9) for simple, non- or the material of construction of the bomb.
autocatalytic exothermic reactions using the equations speci- 6.7 Modifications to the calorimeter can significantly alter
fied in the vendors’ manual (subject to the limitations of 6.5). the performance of the instrument. It is the user’s responsibility
These data may also be adjusted for the sample- and container- to assure that modifications do not alter the precision or
specific heats to calculate an adiabatic temperature rise and accuracy of the instrument.
heat of reaction. 6.8 If the thermal inertia (f) factor for the experiment
differs significantly from that of the system it is intended to
5. Significance and Use
simulate, any reaction mechanism observed experimentally
may not be the same as the true reaction mechanism that exists
5.1 The data from this test seldom, if ever, directly simulate
thermal and pressure events in the processing, storage and in the system being simulated.
6.9 In the determination of kinetic parameters, the possibil-
shipping of chemicals. However, the data obtained from this
test may be used, with suitable precautions, to predict the ity of autocatalytic reaction mechanisms must be considered.
thermal and pressure hazards associated with processing,
7. Hazards
storage and shipping of a chemical or mixture of chemicals
after appropriate scaling of the data. This has been addressed in
7.1 The thermal stability characteristics, impact character-
the literature (1-9) but is beyond the scope of this guide.
istics, (see Test Method E 476, E 487, E 537, E 680, and E 698,
5.2 This test is suitable, under the proper conditions, for the
Practice E 1231 and Ref. 12) or friction sensitivity character-
investigation of the effects of catalyst, inhibitors, initiators,
istics of the sample, or combination thereof, should be as-
reaction atmospheres, materials of construction, or, if avail-
sessed, as it is often necessary to grind (see Note 1) or compact
able, agitation (see 6.1.2).
the sample prior to or during loading into the sample container.
5.3 Interpretation of the time-temperature or time-pressure
Additional physical properties of the sample may also need to
data may be possible for relatively simple systems through the
be determined, such as sensitivity to electrostatic discharge.
use of suitable temperature-dependent kinetic theories such as
NOTE 1—Caution should be used in grinding sample materials, as
the Arrhenius and Absolute Reaction Rate theories (10-11).
polymorphic changes can occur, thus altering the nature of the sample.
6. Limitations
7.2 If the device incorporates a pressure relief device, it
should be periodically inspected for possible corrosion or
6.1 This test method requires good heat transfer within the
physical damage which may result in improper operation.
sample and between the sample and the container and therefore
7.3 Operation of the relief device or rupture of the bomb
is subject to the following limitations:
may result in the release of toxic or noxious fumes which may
6.1.1 Solid samples or systems where heat transfer could
escape into the immediate operating area. The calorimeter,
become rate-limiting may not yield quantitatively reliable or
therefore, should be properly vented.
consistent results, and
7.4 When venting the sample container at the end of the test,
6.1.2 Heterogeneous systems may not give meaningful
suitable precautions should be taken prior to lifting the top
results. A qualitative indication of change in reaction rate may
cover of the calorimeter in order to prevent exposure of the
be obtained by (optional) agitation, but the observed reaction
operator to a potentially highly pressurized container capable
rates may be strongly dependent on the rate and efficiency of
of rupture without warning.
the agitation. Loss of agitation may also affect observed
7.5 Bombs and transducer lines may become plugged,
reaction rates.
preventing normal operation of any relief device or vent valve.
6.2 Accurate tracking of very high or very low self-heat
Therefore, exercise caution and use appropriate personal pro-
rates may not be quantitatively reliable and is equipment
tective equipment and shielding devices prior to attempts to
dependent.
relieve the pressure. Depressurization and subsequent opening
6.3 Endothermic reactions can be observed but generally are
of the sample container at the end of the test should be
not quantitatively measured.
performed in a safe manner, taking into consideration potential,
6.4 The determination of enthalpies of reaction is based on
unanticipated pressure releases or exposure to the operator, or
an accurate knowledge of the (temperature-dependent) heat
both.
capacities of the reactants, products and container. The calcu-
7.6 The toxicity of the contents of the sample container,
especially after reaction, should be considered and handled in
a manner consistent with local safety and regulatory proce-
The boldface numbers in parentheses refer to the list of references found at the
end of this practice. dures.
E 1981
7.7 Material incompatibilities, including that with the sili- round robin testing for these compounds using an ARC . Other
cone oil or other fluids in the pressure transducer or lines, suitable devices may use the same or different calibration
should be considered in any test. compounds.
7.8 The mass of the sample and total energy release poten-
9.2 Operating Procedure
tial (see Test Methods E 476, E 487, E 537, E 680, and E 698,
9.2.1 The sample to be tested is loaded into a sample
Practice E 1231, and Ref. 12) should always be sufficiently
container. Sample containers may be reused; however, it is the
limited so as to minimize the potential for rupture of the sample
responsibility of the user to assure that the containers are
container due to overpressurization.
properly cleaned prior to reuse. If stirring is to be carried out,
7.9 Any safety interlock on the de
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