ASTM E307-72(2019)
(Test Method)Standard Test Method for Normal Spectral Emittance at Elevated Temperatures
Standard Test Method for Normal Spectral Emittance at Elevated Temperatures
SIGNIFICANCE AND USE
5.1 The significant features are typified by a discussion of the limitations of the technique. With the description and arrangement given in the following portions of this test method, the instrument will record directly the normal spectral emittance of a specimen. However, the following conditions must be met within acceptable tolerance:
5.1.1 The effective temperatures of the specimen and blackbody must be within 1 K of each other. Practical limitations arise, however, because the temperature uniformities are often not better than a few degrees Kelvin.
5.1.2 The optical path length in the two beams must be equal, or the instrument should operate in a nonabsorbing atmosphere or a vacuum, in order to eliminate the effects of differential atmospheric absorption in the two beams. Measurements in air are in many cases important, and will not necessarily give the same results as in a vacuum, thus the equality of the optical paths for dual beam instruments becomes very critical.
Note 3: Very careful optical alignment of the spectrophotometer is required to minimize differences in absorptance along the two paths of the instrument, and careful adjustment of the chopper timing to reduce “cross-talk” (the overlap of the reference and sample signals) as well as precautions to reduce stray radiation in the spectrometer are required to keep the zero line flat. With the best adjustment, the “100 % line” will be flat to within 3 %; both of these measurements should be reproducible within these limits (see 7.3, Note 6).
5.1.3 Front-surface mirror optics must be used throughout, except for the prism in prism monochromators and the grating in grating monochromators, and it should be emphasized that equivalent optical elements must be used in the two beams in order to reduce and balance attenuation of the beams by absorption in the optical elements. It is recommended that optical surfaces be free of SiO2 and SiO coatings; MgF2 may be used to stabilize mirror surfaces for e...
SCOPE
1.1 This test method describes a highly accurate technique for measuring the normal spectral emittance of electrically conducting materials or materials with electrically conducting substrates, in the temperature range from 600 to 1400 K, and at wavelengths from 1 to 35 μm.
1.2 The test method requires expensive equipment and rather elaborate precautions, but produces data that are accurate to within a few percent. It is suitable for research laboratories where the highest precision and accuracy are desired, but is not recommended for routine production or acceptance testing. However, because of its high accuracy this test method can be used as a referee method to be applied to production and acceptance testing in cases of dispute.
1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
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 the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E307 − 72 (Reapproved 2019)
Standard Test Method for
Normal Spectral Emittance at Elevated Temperatures
This standard is issued under the fixed designation E307; 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 3.1.1 spectral normal emittance—the term as used in this
specification follows that advocated by Jones (1), Worthing
1.1 This test method describes a highly accurate technique
(2), and others, in that the word emittance is a property of a
for measuring the normal spectral emittance of electrically
specimen; it is the ratio of radiant flux emitted by a specimen
conducting materials or materials with electrically conducting
per unit area (thermal-radiant exitance) to that emitted by a
substrates,inthetemperaturerangefrom600to1400K,andat
blackbodyradiatoratthesametemperatureandunderthesame
wavelengths from 1 to 35 µm.
conditions. Emittance must be further qualified in order to
1.2 The test method requires expensive equipment and
convey a more precise meaning. Thermal-radiant exitance that
rather elaborate precautions, but produces data that are accu-
occurs in all possible directions is referred to as hemispherical
rate to within a few percent. It is suitable for research
thermal-radiant exitance. When limited directions of propaga-
laboratories where the highest precision and accuracy are
tion or observation are involved, the word directional thermal-
desired, but is not recommended for routine production or
radiantexitanceisused.Thus,normalthermal-radiantexitance
acceptance testing. However, because of its high accuracy this
is a special case of directional thermal-radiant exitance, and
test method can be used as a referee method to be applied to
means in a direction perpendicular (normal) to the surface.
production and acceptance testing in cases of dispute.
Therefore, spectral normal emittance refers to the radiant flux
1.3 The values stated in SI units are to be regarded as the emitted by a specimen within a narrow wavelength interval
standard. The values in parentheses are for information only. centered on a specific wavelength and emitted in a direction
normal to the plane of an incremental area of a specimen’s
1.4 This standard does not purport to address all of the
surface. These restrictions in angle occur usually by the
safety concerns, if any, associated with its use. It is the
method of measurement rather than by radiant flux emission
responsibility of the user of this standard to establish appro-
properties.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
NOTE 1—All the terminology used in this test method has not been
1.5 This international standard was developed in accor-
standardized. Terminology E349 contains some approved terms. When
dance with internationally recognized principles on standard-
agreement on other standard terms is reached, the definitions used herein
will be revised as required.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4. Summary of Test Method
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
4.1 The principle of the test method is a direct comparison
of the radiant flux from a specimen at a given temperature to
2. Referenced Documents
the radiant flux of a blackbody at the same temperature and
2.1 ASTM Standards:
under the same environmental conditions of atmosphere and
E349Terminology Relating to Space Simulation
pressure. The details of this test method are given by Harrison
et al (3) and Richmond et al (4).
3. Terminology
3.1 Definitions of Terms Specific to This Standard: 4.2 The essential features of the test method are the use of
adouble-beamratio-recordinginfraredspectrophotometerwith
variable slit widths, which combines and compares the signals
This test method is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of SpaceTechnology and is the direct responsibility of
from the specimen and the reference blackbody through a
Subcommittee E21.04 on Space Simulation Test Methods.
monochromator system which covers the wavelength range
Current edition approved Oct. 1, 2019. Published October 2019. Originally
from1to35µm(Note 2). According to Harrison et al (3) a
approvedin1968.Lastpreviouseditionapprovedin2014asE307–72(2014).DOI:
10.1520/E0307-72R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E307 − 72 (2019)
differential thermocouple with suitable instrumentation is used 6. Apparatus
to maintain a heated specimen and the blackbody at the same
6.1 The spectrophotometer used for the measurement of
temperature.
spectral normal emittance is equipped with a wavelength drive
that provides automatic scanning of the spectrum of radiant
NOTE 2—An electronic-null, ratio-recording spectrophotometer is pre-
flux and a slit servomechanism that automatically opens and
ferred to an optical-null instrument for this use. It may be difficult to
obtain and maintain linearity of response of an optical-null instrument if
closes the slits to minimize the variations of radiant flux in the
the optical paths are not identical to those of the instrument as manufac-
comparison beam. For most materials the wavelength band-
tured.
pass of the instrument is generally smaller than the width of
any absorption or emission band in the spectrum to be
5. Significance and Use
measured. Operation of the spectrophotometer at a higher
5.1 The significant features are typified by a discussion of sensitivity level or in a single-beam mode can be used to
the limitations of the technique. With the description and evaluate band-pass effects. In a prism instrument, several
arrangement given in the following portions of this test prisms compositions can be used to cover the complete
method, the instrument will record directly the normal spectral wavelength range; however, a sodium chloride prism is typi-
emittance of a specimen. However, the following conditions cally used to cover the spectral range from 1.0 to 15 µm, and
must be met within acceptable tolerance: a cesium bromide prism used to cover the spectral range from
15 to 35 µm. As a detector, a vacuum thermocouple with a
5.1.1 The effective temperatures of the specimen and black-
sodiumchloridewindowisusedinthespectralrangefrom1to
body must be within1Kof each other. Practical limitations
15 µm, and a vacuum thermocouple with a cesium bromide
arise, however, because the temperature uniformities are often
window in the spectral range from 1 to 35 µm. A black
not better than a few degrees Kelvin.
polyethylene filter is used to limit stray radiation in the 15 to
5.1.2 The optical path length in the two beams must be
35-µm range.
equal, or the instrument should operate in a nonabsorbing
atmosphere or a vacuum, in order to eliminate the effects of 6.2 In order to reduce the effects of absorption by atmo-
differentialatmosphericabsorptioninthetwobeams.Measure-
spheric water vapor and carbon dioxide, especially in the 15 to
ments in air are in many cases important, and will not 35-µm range, the entire length of both the specimen and
necessarily give the same results as in a vacuum, thus the
reference optical paths in the instrument must be enclosed in
equality of the optical paths for dual beam instruments be- dry air (dew point of less than 223 K) by a nearly gas-tight
comes very critical.
enclosuremaintainedataslightpositivepressurerelativetothe
surrounding atmosphere.
NOTE 3—Very careful optical alignment of the spectrophotometer is
requiredtominimizedifferencesinabsorptancealongthetwopathsofthe 6.3 The design of the reference blackbody is very critical
instrument, and careful adjustment of the chopper timing to reduce
when accurate measurements are to be made. Several designs
“cross-talk” (the overlap of the reference and sample signals) as well as
are possible and a complete description of the one used at the
precautions to reduce stray radiation in the spectrometer are required to
National Institute of Standards and Technology is presented in
keep the zero line flat. With the best adjustment, the “100% line” will be
Ref (3). Several points should be emphasized in the design of
flat to within 3%; both of these measurements should be reproducible
within these limits (see 7.3, Note 6). the blackbody reference. The temperature of the blackbody
furnace is measured by means of a platinum, platinum-10%
5.1.3 Front-surface mirror optics must be used throughout,
rhodium thermocouple, the bare bead of which extends about
except for the prism in prism monochromators and the grating
6mm( ⁄4 in.) into the cavity from the rear. The thermocouple
in grating monochromators, and it should be emphasized that
leads are insulated from the core by high-alumina refractory
equivalent optical elements must be used in the two beams in
tubing, which is surrounded by a grounded platinum tube to
order to reduce and balance attenuation of the beams by
prevent pickup by the thermocouple of spurious signals due to
absorption in the optical elements. It is recommended that
electrical leakage from the winding.The effective emittance of
optical surfaces be free of SiO and SiO coatings; MgF may
2 2
any blackbody furnace which is to be used as a reference,
be used to stabilize mirror surfaces for extended periods of
computed by the DeVos’ (5) or the Gouffé (6) equation as the
time. The optical characteristics of these coatings are critical,
situation dictates, should not be less than 0.995 assuming that
but can be relaxed if all optical paths are fixed during
the interior of the cavity is at a uniform temperature, within 3°
measurements or the incident angles are not changed between
and is a completely diffuse reflector.
modes of operation (during “0% line,” “100% line,” and
6.4 TheNationalInstituteofStandardsandTechnologyuses
sample measurements). It is recommended that all optical
elements be adequately filled with energy. specimensintheshapeofstrips,6mm( ⁄4in.)wideby200mm
(8 in.) long, of any convenient thickness. These specimens are
5.1.4 The source and field apertures of the two beams must
heated by passing a current through the length of the strip.
be equal in order to ensure that radiant flux in the two beams
Specimen geometry is such that temperature uniformity can be
compared by the apparatus will pertain to equal areas of the
adequately maintained.
sources and equal solid angles of emission. In some cases it
may be desirable to define the solid angle of the source and
6.5 The specimen enclosure should have certain design
sample when comparing alternative measurement techniques.
characteristicstoallowforaccurateandprecisemeasurements.
5.1.5 The response of the detector-amplifier system must 6.5.1 The enclosure should be water cooled when measure-
vary linearly with the incident radiant flux. ments are being made at the higher end (1400 K) of the
E307 − 72 (2019)
temperature range. Provisions should be made to cool the less than 223 K in order to avoid serious absorption in the 15
enclosure to 200 K or liquid nitrogen temperatures during to35-µmrange.Becauseofthisrelativelylongperiodrequired
measurements at the low end (600 K) of the temperature range for purging, it is recommended that the dry atmosphere be
especially when measuring low emittance specimens. maintained continuously, except when the enclosure must be
6.5.2 The inner surface of the enclosure should have a openedtopermitadjustmentofequipmentorinsertionofanew
reflectanceoflessthan0.05attheoperatingtemperatureofthe specimen.
water cooled walls. Several black paints may be used; or
NOTE 5—When standardizing the measurements using emittance
alternatively, the inner surface may be constructed from a
standards, the nitrogen purge should be accomplished before the standard
nickel-chromium-iron alloy which has been threaded with a
isheated.AtmosphericairpassedthroughadryingtowerfilledwithaCO
absorberthendriedtoadewpointof173Kmaybeusedinsteadofthedry
No. 80 thread and then oxidized in air at a temperature above
nitrogen.
1350Kfor6hto obtain the desired reflectance.
6.5.3 For cylindrically shaped enclosures the specimen 7.2 In making a wavelength calibration of the monochro-
should be positioned off-center so that any radiant flux specu- mator use standard calibration techniques in accordance with
larly reflected from the walls will be reflected twice before Plyler et al (7) and Blaine (8). Typical techniques use the
hitting the specimen. emission spectra of a helium arc, a mercury arc, and the
absorption spectra of didymium glass or the atmosphere (9),
6.5.4 With resistance heating techniques, the electrodes
holding the specimen are water cooled and insulated from the and a polystyrene film. The emission and absorption peaks
having known wavelengths are identified in the respective
ends of the enclosure. The lower electrode and enclosure
configuration are designed to permit the specimen to expand curves, and for each peak the observed chart indication or
wavelengthdrumpositionatwhichthepeakoccurredisplotted
without buckling when heated.
6.5.5 Adjustable baffles above and below the viewing win- as a function of the known wavelength of the peak.
dow are used to reduce convection and the resulting tempera-
7.3 The linearity of response of the spectrophotometer must
ture fluctuations and thermal gradients.Adjustable telescoping
be established (within the varying wavelength interval encom-
cylindrical reflectors surround the specimen at each end to
passed by the exit slit) when the instrument is operated
reduce heat loss at the ends of the specimen, and the thermal
double-beam in ratio mode. In order to check linearity, two
gradients along the specimen.
blackbody furnaces, controlled very closely to the same tem-
6.6 The temperatures of the specimen and blackbody are perature(about1400K),areusedassourcesforthetwobeams.
Adjust the instrumen
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