ASTM D6745-06(2011)
(Test Method)Standard Test Method for Linear Thermal Expansion of Electrode Carbons
Standard Test Method for Linear Thermal Expansion of Electrode Carbons
SIGNIFICANCE AND USE
Coefficients of linear thermal expansion are used for design and quality control purposes and to determine dimensional changes of parts and components (such as carbon anodes, cathodes, and so forth) when subjected to varying temperatures.
SCOPE
1.1 This test method covers the determination of the coefficient of linear thermal expansion (CTE) for carbon anodes and cathodes used in the aluminum industry, in baked form, by use of a vitreous silica dilatometer.
1.2 The applicable temperature range for this test method for research purposes is ambient to 1000°C. The recommended maximum use temperature for product evaluation is 500°C.
1.3 This test method and procedure is based on Test Method E 228, which is a generic all-encompassing method. Specifics dictated by the nature of electrode carbons and the purposes for which they are used are addressed by this procedure.
1.4 Electrode carbons in the baked form will only exhibit primarily reversible dimensional changes when heated.
1.5 The values stated in SI units are to be regarded as standard.
1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D6745–06 (Reapproved 2011)
Standard Test Method for
Linear Thermal Expansion of Electrode Carbons
This standard is issued under the fixed designation D6745; 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 specimens lengths at reference temperature T and test tem-
perature T , respectively. Linear thermal expansion is often
1.1 This test method covers the determination of the coef- 1
expressed as a percentage or in parts per million (such as
ficient of linear thermal expansion (CTE) for carbon anodes
µm/m).
andcathodesusedinthealuminumindustry,inbakedform,by
3.1.2 mean coeffıcient of linear thermal expansion (CTE)—
use of a vitreous silica dilatometer.
The linear thermal expansion per change in temperature; the
1.2 The applicable temperature range for this test method
mean coefficient of linear thermal expansion is represented by:
forresearchpurposesisambientto1000°C.Therecommended
maximum use temperature for product evaluation is 500°C. DL/L 1 DL 1 L 2 L
0 1 0
a 5 5 · 5 (1)
T
DT L DT L T 2 T
1.3 ThistestmethodandprocedureisbasedonTestMethod
0 0 1 0
E228, which is a generic all-encompassing method. Specifics
3.1.2.1 Thishastobeaccompaniedbythevaluesofthetwo
dictatedbythenatureofelectrodecarbonsandthepurposesfor
temperatures to be meaningful; the reference temperature (T )
which they are used are addressed by this procedure.
is 20°C, and the notation may then only contain a single
1.4 Electrode carbons in the baked form will only exhibit
number, such as a¯ , meaning the mean coefficient of linear
primarily reversible dimensional changes when heated.
thermal expansion between 20 and 200°C.
1.5 The values stated in SI units are to be regarded as
3.2 Definitions of Terms Specific to This Standard:
standard.
3.2.1 reference specimen—a particularly identified or pedi-
1.6 This standard does not purport to address all of the
greed material sample, with well-characterized behavior and
safety concerns, if any, associated with its use. It is the
independently documented performance.
responsibility of the user of this standard to establish appro-
3.2.2 specimen—a representative piece of a larger body
priate safety and health practices and determine the applica-
(anode, cathode, and so forth) that is considered to be fairly
bility of regulatory limitations prior to use.
typical of a portion or of the entire piece.
3.2.3 vitreous silica dilatometer—a device used to deter-
2. Referenced Documents
mine linear thermal expansion, by measuring the difference in
2.1 ASTM Standards:
linear thermal expansion between a test specimen and the
E228 Test Method for Linear Thermal Expansion of Solid
vitreous silica parts of the dilatometer.
Materials With a Push-Rod Dilatometer
4. Summary of Test Method
3. Terminology
4.1 Arepresentativespecimenisplacedintoavitreoussilica
3.1 Definitions:
dilatometer and heated, while its linear expansion is continu-
3.1.1 linear thermal expansion—the change in length per
ously recorded.The change of the specimen length is recorded
unit length resulting from a temperature change. Linear ther-
as a function of temperature. The coefficient of linear thermal
malexpansionissymbolicallyrepresentedby DL/L ,where DL
expansion is then calculated from these recorded data.
isthelengthchangeofthespecimen(L −L ), L and L arethe
1 0 0 1
5. Significance and Use
1 5.1 Coefficients of linear thermal expansion are used for
This test method is under the jurisdiction of ASTM Committee D02 on
design and quality control purposes and to determine dimen-
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.
sional changes of parts and components (such as carbon
CurrenteditionapprovedMay1,2011.PublishedJuly2011.Originallyapproved
anodes, cathodes, and so forth) when subjected to varying
in 2001. Last previous edition approved in 2006 as D6745–06. DOI: 10.1520/
temperatures.
D6745-06R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6. Apparatus
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
6.1 Dilatometer—Thedilatometerconsistsofthefollowing:
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6745–06 (2011)
6.1.1 Specimen Holder and Push-rod,bothmadeofvitreous 6.2.3 Computerized recording may be used with similar
silica. The design of the device shall ensure that the push-rod restriction to 6.2.2. Calculations and corrections may be done
load on the specimen by itself is not causing deformation. The using suitable software.
use of pressure distribution quartz plates on top of the 6.3 Furnace—Thefurnaceisusedforuniformlyheatingthe
specimen is permissible. specimen over the temperature range of interest, but not above
1000°C. Temperature uniformity shall be at least 6 0.5°C per
NOTE 1—Dilatometers are usually constructed in horizontal or vertical
50 mm of sample length. The temperatures shall be controlled
configurations (1) Vertical devices are preferred for very large samples
as a function of time. The furnace may have a muffle (quartz,
and when extensive shrinkage is expected. Horizontal configurations
mullite, alumina, inconel, monel, or stainless steel are most
usually afford better temperature uniformity over the specimen, but are
subject to drooping when large specimens are employed. Horizontal
common) or other provisions to provide a protective atmo-
devices, when used with very large specimens, require special provisions
sphere for the specimen. The furnace shall have provisions for
to reduce friction between the specimen and the dilatometer tube to
continuous purging with an inert gas at a sufficient rate, and
minimizepush-rodpressurerequiredtokeepthespecimenincontactwith
exclude air from the specimen while a purge is maintained.
the end plate. For this application, either configuration is acceptable.
6.4 Caliper—Thecaliper(micrometerorVerniertype)isfor
NOTE 2—For basic construction details and fused silica annealing
measuring the initial length of the specimen, L , with an
schedule, consult Test Method E228.
NOTE 3—Multiplerodssupportingaplatforminplaceoflargediameter accuracy within 6 25 µm, and a capacity to open to the length
tubes have been also used successfully in the vertical configuration.
of the specimen plus 1 mm.
6.1.2 Transducer or Indicator, for measuring the difference
7. Test Specimen
in length between the specimen and the dilatometer with an
accuracy within 6 2 µm. The transducer shall translate these
7.1 Specimens shall be cylindrical, preferably with a 50 6
movements into an electrical signal suitable for displaying or
2mmdiameter.Slightlysmallerorlargerdiameterscanalsobe
recording. The non-linearity of this conversion must be less
accommodated without degradation of data. The length of the
than0.25%ofthefullscalevalueoftheoutput.Thetransducer
specimensshallbebetween50and130mminlengthandhave
shall be protected or mounted so that the maximum tempera-
flat and parallel ends to within 6 25 µm.
ture change observed in the transducer during a test will affect
7.2 It is permissible to stack up to five disks of smaller
the transducer readings by less than 1 µm.
lengths to obtain a proper length specimen. The interfaces,
6.1.3 Temperature Sensors, for determining the mean tem-
however, must be flat and parallel within 6 25 µm to prevent
perature of the specimen with an accuracy within 6 0.5°C.
rocking.
When a thermocouple is used, it shall be referenced (cold
7.3 The dimensions of the specimens should be ordinarily
junction compensated) to the ice point with an ice-water bath
measured as received.
or an equivalent system.
7.4 If water was used in conjunction with their preparation,
6.1.3.1 Duetothelargesizeofthespecimen,aminimumof
each specimen must be kept in an oven at 110 6 5°C for at
one thermocouple per 40 mm specimen length must be
least 6 h and allowed to cool down thereafter, prior to testing.
employed. It is permissible to read the output of each thermo-
If any heat or mechanical treatment is applied to the specimen
couple independently and average the readings or to connect
prior to testing, this treatment should be noted in the report.
them in series and divide the single reading by the number of
thermocouples to obtain the average. In the latter case, inter-
8. Calibration
connections must be made at or beyond the point of cold
8.1 Thetransducershouldbecalibratedbyimposingaseries
junction compensation.
of known displacements with a precision screw micrometer,
6.1.3.2 The temperature sensors shall be in close proximity
gageblocks,orequallyaccuratedevice.Forabsolutetransduc-
to the specimen, preferably in between the quartz dilatometer
ers (such as digital encoders, and so forth), this procedure is
tube and the specimen. The temperature sensors shall not be
omitted and periodic verification is sufficient.
directly exposed to the furnace walls.
8.2 Verificationofthecalibrationofthetemperaturesensors
6.2 Readout or Recording of Data:
separately from the dilatometer is to be performed periodically
6.2.1 Manual recording of expansion and temperature val-
or when contamination of the junction is suspected.
uesindicatedatselectedtemperaturepointsmaybemadeifthe
8.3 Regardlessofindependentcalibrationsofthetransducer
transducer is equipped with or connected to a suitable display
and the thermocouples, the dilatometer, as a total system, shall
and the thermocouples outputs are determined with a potenti-
be calibrated by determining the thermal expansion of at least
ometer or millivolt meter.
one reference material of known thermal expansion. Recom-
6.2.2 Chart or data logger recording of the expansion and
mended reference materials are listed in Annex A1.
temperature signals may be accomplished using a device
8.3.1 The calibration should be done using approximately
whoseresolutionisatleast1000timeshigherthantheexpected
the same thermal cycle as that used for testing (see 9.7 and
maximum output signal. All calculations and corrections (see
9.8).
Section 10) must be done externally based on the recorded
8.3.2 The calibration constant may be derived as follows:
values.
DL DL
A 5 2 (2)
S D S D
L L
0 0
t m
Hidnert, P. and Krider, H.S., “Thermal Expansion Measurements,” Journal of
where:
Research, National Bureau of Standards, Vol 48, 1952, p. 209.
D6745–06 (2011)
9. Procedure
m = measured expansion of the reference material, and
t = true or certified expansion of the reference material.
9.1 Measure the initial (room temperature) length of the
8.4 Ifthecalibrationspecimenisconsiderablysmallerinthe
specimen, and record it as L .
cross section than the specimen, it is necessary to provide a
9.2 Place the specimen into the dilatometer after making
thermaljacketaroundittopreventerrorscausedbyconvective
certain that all contacting surfaces are free of foreign material.
currents. A thermal jacket may be produced by drilling a hole
It is important to have good seating of the specimen in a stable
in the axis of a carbon specimen and loosely fitting the
position. (Warning—Alkali contamination will adversely af-
calibrationspecimenintoit.Thecarbonjacketmustbeabout1
fect fused silica parts. Avoid touching them with hands.)
mm shorter than the calibration specimen.
9.3 Ensure that the temperature sensors shall not restrict
8.5 The use of published values of thermal expansion for
movement of the specimen in the dilatometer. Do not allow an
quartz may not be used to compute a correction factor.
exposed junction to contact any carbonaceous materials.
Accounting for the expansion of the dilatometer parts through
9.4 Make certain that the push-rod is in stable contact with
calculationsinplaceofacalibrationproceduredescribedabove
thespecimen.Apressuredistributionplatemadeoffusedsilica
is not permitted.
may be used between the push-rod and the specimen.
8.6 Materials usable for calibration or verification of opera-
9.5 Insert the loaded dilatometer into the furnace (at ambi-
tion fall into four categories.
ent temperature) and allow the temperature of the specimen to
8.6.1 Standard Reference Materials—These are actual
come to equilibrium.
specimens supplied with a certificate by NIST , or a similar
9.6 Record the initial readings of the temperature sensors,
,
national standards organization of another country.
T , and the transducer, X .
0 0
9.7 Heat the furnace to 300 or 500 6 10°C at a rate not
NOTE 4—These materials are very few and NIST supplies have been
exceeding 10°C/min. Allow the furnace and specimen to
exhausted in some cases. To determine the absolute accuracy of a device,
materials in this category are the most preferred. stabilizeatthattemperaturefor60min.Recordreadingsofthe
temperaturesensors, T ,andthetransducer, X .Ifdataobtained
1 1
8.6.2 Traceable Reference Materials—These are exten-
during ramping is to be used, heating rates above 1°C/min are
sively investigated materials, substantially described in pub-
not permitted.
lished literature and considered stable. Often they are generi-
9.8 Alternate to 9.7. Heat the furnace at rates up to 10°C/
cally identical to Standard Reference Materials. Specific lots
min. Hold the furnace and specimen at a single or series of
when tested in a systematic fashion using a dilatometer
constant temperatures until the transducer reading reaches a
calibrated with a certified Standard Reference Material can be
constant value (variation < 6 2.6 µm), At that point, the
referred to as Traceable Reference Materials. They may also
indicated temperature of the specimen shall not vary by more
serve well in comparing equipment or test procedures at
than 6 2°C and the temperature gradient in the specimen shall
different laboratories and to arbitrate disputes and differences.
not exceed 2% of its actual temperature. The dwell time is a
8.6.3 Reference Materials—These are widely investigated,
function of the thermal mass of the dilatometer and the
well-characterized materials that were found to be stable with
specimen. It will vary with temperature and heating rate. The
time and temperature exposure and performance data are
length of the dwell shall be sufficient as to limit consecutive
readilyavailableintheliterature;forexample,platinum.These
length change readings taken in 5 min intervals to less than 4
materials are well suited for r
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