ASTM E1582-93
(Practice)Standard Practice for Calibration of Temperature Scale for Thermogravimetry
Standard Practice for Calibration of Temperature Scale for Thermogravimetry
SCOPE
1.1 This practice covers the temperature calibration of thermogravimetric analyzers over the temperature range from 25 to 1500oC and is applicable to commercial and custom-built apparatus. This calibration may be accomplished by the use of either melting point standards or magnetic transition standards.
1.2 The mass change curve in thermogravimetry results from a number of influences, some of which are characteristic of the specimen holder assembly and atmosphere rather than the specimen. The variations from instrument to instrument occur in the point of measurement of the temperature, the nature of the material, its size and packing, the geometry and composition of the specimen container, the geometry and design of the furnace, and the accuracy and sensitivity of the temperature sensor and displaying scales. These all contribute to differences in measured temperatures, which may exceed 20oC. In addition, some sample holder assemblies will show variations of measured temperature with sample size or heating/cooling rate, or both. Since it is neither practical nor advisable to standardize sample holders or thermobalance geometries, instruments may be calibrated by measurement of the deviation of a melting or magnetic (Curie Point) transition temperature from the standard reference temperature. This deviation can be applied as a correction term to subsequent measurements.
1.3 This practice assumes that the indicated temperature of the instrument is linear over the range defined by a two-point calibration and that this linearity has been verified. These two calibration temperatures should be as close to the experimental measurements to be made as possible.
1.4 This practice describes three procedures for temperature calibration of thermogravimetric analyzers using any type balance. Procedures A and B use melting point standards with vertical balances. Procedure C uses magnetic transition standards for calibration. Procedure A is designed specifically for use with horizontal-type balances using external furnaces. Procedure B is designed specifically for use with vertical hang-down balances using either internal or external furnaces. No procedure is restricted to the use of the furnace type described in that procedure.
1.5 Computer or electronic-based instruments, techniques, or data treatment equivalent to this procedure may be used.
Note 1--Since all electronic data treatments are not equivalent, the user shall verify equivalency prior to use.
1.6 The data generated by these procedures can be used to correct the temperature scale of the instrument by either a positive or negative amount using either a two-point temperature calibration procedure or a multi-point temperature calibration with best line fit for the generated data.
Note 2--A single-point calibration may be used where this is the only procedure possible or practical. The use of a single-point procedure is not recommended.
1.6.1 Many of the newer computer-controlled instruments have features for using calibration data of the latter type.
1.7 SI units are standard.
1.8 This practice is related to ISO 11358 but provides information and methods not found in ISO 11358 .
This standard does not purport to address all of the safety problems, 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.
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Designation: E 1582 – 93
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Calibration of Temperature Scale for Thermogravimetry
This standard is issued under the fixed designation E 1582; 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.
1. Scope or data treatment equivalent to this procedure may also be
used. Users of this practice are expressly advised that all such
1.1 This practice covers the temperature calibration of
instruments or techniques may not be equivalent. It is the
thermogravimetric analyzers over the temperature range from
responsibility of the user of this practice to determine the
25 to 1500°C and is applicable to commercial and custom-built
necessary equivalency prior to use. In the case of dispute, only
apparatus. This calibration may be accomplished by the use of
the manual procedures, described in this practice, are to be
either melting point standards or magnetic transition standards.
considered valid.
1.2 The mass change curve in thermogravimetry results
1.6 The data generated by these procedures can be used to
from a number of influences, some of which are characteristic
correct the temperature scale of the instrument by either a
of the specimen holder assembly and atmosphere rather than
positive or negative amount using either a two-point tempera-
the specimen. The variations from instrument to instrument
ture calibration procedure or a multi-point temperature calibra-
occur in the point of measurement of the temperature, the
tion with best line fit for the generated data.
nature of the material, its size and packing, the geometry and
composition of the specimen container, the geometry and
NOTE 1—A single-point calibration may be used where this is the only
design of the furnace, and the accuracy and sensitivity of the
procedure possible or practical. The use of a single-point procedure is not
recommended.
temperature sensor and displaying scales. These all contribute
to differences in measured temperatures, which may exceed
1.6.1 Many of the newer computer-controlled instruments
20 K. In addition, some sample holder assemblies will show
have features for using calibration data of the latter type.
variations of measured temperature with sample size or
1.7 The values stated in SI units are to be regarded as the
heating/cooling rate, or both. Since it is neither practical nor
standard.
advisable to standardize sample holders or thermobalance
1.8 This standard does not purport to address all of the
geometries, instruments may be calibrated by measurement of
safety problems, if any, associated with its use. It is the
the deviation of a melting or magnetic (Curie Point) transition
responsibility of the user of this standard to establish appro-
temperature from the standard reference temperature. This
priate safety and health practices and determine the applica-
deviation can be applied as a correction term to subsequent
bility of regulatory limitations prior to use.
measurements.
2. Referenced Documents
1.3 This practice assumes that the indicated temperature of
the instrument is linear over the range defined by a two-point
2.1 ASTM Standards:
calibration and that this linearity has been verified. These two
E 472 Practice for Reporting Thermoanalytical Data
calibration temperatures should be as close to the experimental
E 473 Definitions of Terms Relating to Thermal Analysis
measurements to be made as possible.
E 691 Practice for Conducting an Interlaboratory Study to
1.4 This practice describes three procedures for temperature
Determine the Precision of a Test Method
calibration of thermogravimetric analyzers using any type
E 1142 Terminology Relating to Thermophysical Proper-
balance. Procedures A and B use melting point standards with
ties
vertical balances. Procedure C uses magnetic transition stan-
3. Terminology
dards for calibration. Procedure A is designed specifically for
use with horizontal-type balances using external furnaces.
3.1 Definitions—The term thermogravimetry is defined in
Procedure B is designed specifically for use with vertical
Definitions E 473. Thermal Curve is defined in Terminology
hang-down balances using either internal or external furnaces.
E 1142.
No procedure is restricted to the use of the furnace type
3.1.1 magnetic reference temperature—the observed tem-
described in that procedure.
perature at which a change in the magnetic properties of a
1.5 Computer or electronic-based instruments, techniques,
material in a magnetic field produces an apparent mass change.
This temperature is read from the dynamic TG curve as the
point of intersection of the extrapolated higher temperature
This practice is under the jurisdiction of ASTM Committee E-37 on Thermal
Measurements and is the direct responsibility of Subcommittee E37.01 on Test
Methods and Recommended Practices.
Current edition approved Nov. 15, 1993. Published January 1994. Annual Book of ASTM Standards, Vol 14.02.
E 1582
portion of the base line with a tangent drawn to the point of discontinuous mass loss. These events may be used to calibrate
greatest slope of apparent mass-change curve. This tempera- the thermogravimetric analyzer for the experimental conditions
ture most closely represents the Curie Point, that point on the used.
mass change curve where the magnetic effect of the standard 4.3 Calibration of Analyzers Using Magnetic Transition
material has disappeared completely (see Fig. 1). Standards:
4.3.1 In this procedure, the apparent mass change of one or
NOTE 2—The position of the magnet and the design of the instrument
more of the magnetic transition standards is obtained under the
will affect the direction of the mass change.
normal operating conditions of the instrument. The end tem-
perature, T (Fig. 1), is determined and compared with the
4. Summary of Practice
x
established transition temperature for the material. The differ-
4.1 This practice provides a set of different procedures since
ence provides an adjustment or calibration that may be applied
thermogravimetric apparatus is often of significantly differing
to the temperature scale of the instrument.
design.
4.3.2 The apparent mass change of the magnetic transition
4.2 Calibration of Analyzers Using Melting Point
materials is caused by the magnetic to nonmagnetic transition
Standards—The calibration material is heated at a controlled
in the presence of a magnetic field.
rate in a controlled atmosphere through its melting region. The
temperature of the standard is monitored and recorded continu-
5. Significance and Use
ously. In this practice, a small platinum mass is suspended
5.1 Thermogravimetric analyzers are used to characterize a
within a thermogravimetric analyzer specimen boat or pan
broad range of materials. In most cases, one of the desired
from a fusible link of the standard calibration material. As the
values to be assigned in thermogravimetric measurements is
standard specimen is heated through the melting region, the
the temperature at which significant changes in specimen mass
platinum mass is released. The mass is either caught in the
occur. Therefore, the temperature axis (abscissa) of all
specimen boat or pan, producing an “action/reaction” blip on
apparent-mass-change curves must be calibrated accurately,
the thermal curve, or is allowed to drop through a hole in the
either by direct reading of a temperature sensor, or by adjusting
bottom of the specimen boat or pan, producing a sharp,
the programmer temperature to match the actual temperature
over the temperature range of interest. In the latter case, this is
accomplished by the use of either melting point or magnetic
transition standards.
5.2 This practice permits interlaboratory comparison and
intralaboratory correlation of instrumental temperature scale
data.
6. Interferences
6.1 The reference metals are sensitive to impurities and may
oxidize at elevated temperatures. All runs shall be conducted in
an oxygen-free inert purge gas of the same type to be used in
the experimental procedures.
6.2 Care must be taken to stay below temperatures at which
the magnetic transition standard will react with the specimen or
its holder.
7. Apparatus
7.1 Thermogravimetric Analyzer—A system of related in-
struments that are capable of continuously measuring the mass
of a specimen in a controlled atmosphere and in a controlled
temperature environment ranging from ambient to at least
25°C above the temperature range of interest over a selected
time period. This instrument shall consist of the following:
7.1.1 Electrobalance, sensitive to 5 μg.
7.1.2 Furnace, controllable from 25°C to the upper tem-
perature limit of the instrument.
7.1.3 Temperature Programmer, capable of providing a
linear rate of rise from 0.5 to 20°C/min (programmed rates in
addition to those listed may be used).
7.1.4 Temperature Measurement System, consisting of a
sensor, usually a thermocouple and a readout/recording device.
7.1.5 Recording Device, for example, X-Y or strip chart
recorder, printer-plotter.
7.2 Inert Atmosphere (Gas Purge)—Purified grade N or
FIG. 1 Magnetic Reference Temperature other inert gas.
E 1582
TABLE 1 Melting Point Standards
employs a temperature sensor that is movable, it must be
Calibration Material Melting Temperature, °C (K) located as close to the specimen as possible without touching
A
it or the balance pan. In addition, it must be located in exactly
Indium 156.6 (429.8)
A
Tin 232.0 (505.1)
the same position during calibrations as used during analytical
B
Lead 327.5 (600.6)
determinations.
A
Zinc 419.6 (692.7)
A
Aluminum 660.4 (933.5)
NOTE 6—This position may be inside or outside the balance pan.
A
Silver 961.9 (1235.1)
A
Gold 1064.4 (1337.6)
9.2 Action-Reaction Procedure:
A
Copper 1084.5 (1357.6)
9.2.1 Flatten one end of a fine platinum wire (approximately
C
Nickel 1455 (1728)
C 0.34-mm diameter and 2 cm in length), and spot weld it to the
Palladium 1554 (1827)
C
Platinum 1769 (2042) outside of a specimen boat or pan as shown in Fig. 2. Carefully
A
bend the wire into a U shape so that the cantilevered end is
Primary fixed points.
B
Secondary reference points.
located in the center of the specimen boat or pan.
C
From Ref (2).
9.2.2 Suspend this specimen boat or pan from the balance
mechanism so that it hangs freely, and locate the temperature
TABLE 2 Curie Point Standards
sensor as outlined in 9.1.
Curie Point (Magnetic) Transition,
9.2.3 Bend a 5-mm length (0.25-mm diameter) of the wire
Metal
°C (K)
temperature standard into a sigmoid shape, and suspend it from
A
Alumel 163 (436)
the end of the platinum wire in the middle of the specimen boat
B
Permanorm 3 259 (539)
A
or pan.
Nickel 354 (627)
B
MuMetal 381 (659)
B
NOTE 7—The selection of wire standard depends on the part of the
Permanorm 5 454 (732)
A
Perkalloy 596 (869) temperature axis that is to be calibrated. Two or more standards may be
B
Trafoperm 750 (1027)
run consecutively to enable one to obtain a calibration curve.
A
Iron 780 (1053)
A 9.2.4 Close the balance assembly, and purge the system with
Hisat-50 1000 (1273)
C
Cobalt 1120 (1393)
the desired atmosphere at the selected rate. Select the appro-
A
priate heating rate.
Primary fixed points.
B
Secondary reference points.
C
NOTE 8—The atmosphere, flow rate, and heating rate will affect the
From Ref (2).
calibration. These rates and conditions must be the same for both
8. Calibration and Standardization
calibration and analysis. In addition, fast heating rates should be avoided,
if possible, Due to the differing heat exchange (emissivity and heat
8.1 Calibration of Apparatus—If necessary, calibrate the
capacity) during the calibration and analysis, higher heating rates increase
temperature sensor of the instrument at room temperature using
the error in the temperature measurement. The ICTA Sixth International
the procedure described in the instrument manual.
Test Program Protocol (4) warns that heating rates above 6°C/min can
8.2 Calibration Materials:
produce errors in the temperature calibration.
8.2.1 Melting Point Standards—For the temperature range
9.2.5 Zero the balance and the recorder.
covered by many applications, the melting transition of the
9.2.6 Open the system and carefully suspend a platinum
99.9+ % pure materials listed in Table 1 may be used for
mass of approximately 50 mg from the end of the wire
calibration.
standard.
NOTE 3—It is recommended that the size of the wire used be 0.25 mm
NOTE 9—This mass can be prepared by tightly winding approximately
in diameter. For sources of very pure fine metal wire, contact the ASTM
50 mm of 0.25-mm diameter platinum wire and distending one loop of the
Information Center, 1916 Race St., Philadelphia, PA 19103-1187.
wire to provide a convenient connecting loop.
NOTE 4—The melting temperatures of the first eight materials given in
9.2.6.1 Close the system.
this table are taken from T. J. Quinn (1) and have been selected either as
9.2.7 For analog systems using a chart recorder, adjust the
primary fixed points or as secondary reference points for the International
Practical Temperature Scale 1990. The remaining melting point tempera-
y-axis pen recorder control sensitivity so that the pen is located
tures given in this table are taken from I. Barin (2).
about the middle of the chart paper.
9.2.8 Rapidly heat the system to 50°C below the theoretical
8.2.2 Magnetic Transition Standards.
melting temperature, and allow the system to equilibrate for 5
NOTE 5—Materials with known magnetic transitions determined with
min. Then heat at the selected programmed rate up through the
high precision are required. The Perkin-Elmer Co. supplies such materials.
melting temperature of the standard. When the standard melts,
Materials are also available from the National Institute for Standards and
the platinum mass falls into the specimen boat or pan. This
Technology. The materials available from these sources are presented in
Table 2. These values may change from lot to lot of the material. Curie produces an action-reaction blip on the recorded thermal curve
Point temperatures given in the table were obtained from Refs. (3-5).
without any mass loss. A typical thermal curve is shown in Fig.
3.
9. Procedure A—Melting Point Standard Test for
NOTE 10—The recorder action is fast and must ordinarily be observed
Horizontal Balance Types
at high sensitivity and data acquisition rates. The meas
...
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