ASTM D6559-00a(2010)
(Test Method)Standard Test Method for Determination of Thermogravimetric (TGA) Air Reactivity of Baked Carbon Anodes and Cathode Blocks
Standard Test Method for Determination of Thermogravimetric (TGA) Air Reactivity of Baked Carbon Anodes and Cathode Blocks
SIGNIFICANCE AND USE
The air reactivity rates are used to quantify the tendency of a carbon artifact to react with air. Carbon consumed by this unwanted side reaction is unavailable for the primary reactions of reducing alumina to the primary metal. Air reactivity dusting rate is used by some companies to quantify the tendency of the coke aggregate or binder coke of a carbon artifact to selectively react with these gases. Preferential attack of the binder coke or coke aggregate of a carbon artifact by these gases causes some carbon to fall off or dust, making the carbon unavailable for the primary reaction of reducing alumina and, more importantly, reducing the efficiency of the aluminum reduction cell.
Comparison of air reactivity and dusting rates is useful in selecting raw materials for the manufacture of commercial anodes for specific smelting technologies in the aluminum reduction industry.
Air reactivity rates are used for evaluating effectiveness and beneficiation processes or for research purposes.
SCOPE
1.1 This test method covers the thermogravimetric (TGA) determination of air reactivity and dusting of shaped carbon anodes and cathode blocks used in the aluminum reduction industry. The apparatus selection covers a significant variety of types with various thermal conditions, sample size capability, materials of construction, and procedures for determining the mass loss and subsequent rate of reaction. This test method standardizes the variables of sample dimensions, reaction temperature, gas velocity over the exposed surfaces, and reaction time such that results obtained on different apparatuses are correlatable.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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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Standards Content (Sample)
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Designation: D6559 − 00a(Reapproved 2010)
Standard Test Method for
Determination of Thermogravimetric (TGA) Air Reactivity of
Baked Carbon Anodes and Cathode Blocks
This standard is issued under the fixed designation D6559; 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 dusting, n—the quantity of carbon that falls off the
carbonartifactwhileinthereactionchamberandiscollectedin
1.1 This test method covers the thermogravimetric (TGA)
the container at the bottom of the reaction chamber.
determination of air reactivity and dusting of shaped carbon
anodes and cathode blocks used in the aluminum reduction
3.1.2 final air reactivity, n—the mass loss of the carbon
industry.Theapparatusselectioncoversasignificantvarietyof
artifactduringthefinal30minofexposuretoairinthereaction
types with various thermal conditions, sample size capability,
chamber divided by the initial geometric (right cylindrical)
materials of construction, and procedures for determining the 2
exposed surface area of the sample, expressed as mg/cm -h.
mass loss and subsequent rate of reaction. This test method
3.1.3 initial air reactivity, n—the mass loss of the carbon
standardizes the variables of sample dimensions, reaction
artifactduringthefirst30minofexposuretoairinthereaction
temperature, gas velocity over the exposed surfaces, and
chamber divided by the initial geometric (right cylindrical)
reactiontimesuchthatresultsobtainedondifferentapparatuses
are correlatable. exposed surface area of the sample, expressed as mg/cm -h.
1.2 The values stated in SI units are to be regarded as
3.1.4 total air reactivity, n—thetotalmasslossofthecarbon
standard. No other units of measurement are included in this
artifact(includingdusting)duringthetotaltimethatthesample
standard.
is exposed to air (180 min) in the reaction chamber divided by
1.3 This standard does not purport to address all of the the initial geometric (right cylindrical) exposed surface area of
safety concerns, if any, associated with its use. It is the the sample, expressed as mg/cm -h.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 4. Summary of Test Method
bility of regulatory limitations prior to use.
4.1 Initial, final, and total air reactivity and dusting are
determined by passing air at flow rates, giving a standard
2. Referenced Documents
velocity of reactant gas around cylindrically shaped carbon
2.1 ASTM Standards:
artifacts under nearly isothermal conditions for a specified
D6353Guide for Sampling Plan and Core Sampling for
length of time. The reactivity is determined by continuously
Prebaked Anodes Used in Aluminum Production
monitoring the sample mass loss. The dusting term is deter-
D6354Guide for Sampling Plan and Core Sampling of
mined by collecting and determining the mass of carbon
Carbon Cathode Blocks Used in Aluminum Production
particles that fall off the sample during reaction.
E691Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
5. Significance and Use
3. Terminology
5.1 Theairreactivityratesareusedtoquantifythetendency
3.1 Definitions of Terms Specific to This Standard:
of a carbon artifact to react with air. Carbon consumed by this
unwantedsidereactionisunavailablefortheprimaryreactions
1 ofreducingaluminatotheprimarymetal.Airreactivitydusting
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility of
rateisusedbysomecompaniestoquantifythetendencyofthe
SubcommitteeD02.05onPropertiesofFuels,PetroleumCokeandCarbonMaterial.
cokeaggregateorbindercokeofacarbonartifacttoselectively
Current edition approved May 1, 2010. Published May 2010. Originally
react with these gases. Preferential attack of the binder coke or
approved in 2000. Last previous edition approved in 2005 as D6559–00a (2005).
DOI: 10.1520/D6559-00AR10.
coke aggregate of a carbon artifact by these gases causes some
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
carbontofalloffor dust,makingthecarbonunavailableforthe
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
primary reaction of reducing alumina and, more importantly,
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. reducing the efficiency of the aluminum reduction cell.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6559 − 00a (2010)
5.2 Comparison of air reactivity and dusting rates is useful 6.1.2 Reaction Chamber, consisting of a vertical tube con-
in selecting raw materials for the manufacture of commercial structed of a material capable of withstanding the temperature
anodes for specific smelting technologies in the aluminum
ofthereactionwithsufficientinsidediameter(ID)toacceptthe
reduction industry.
sample and sample holder while not affecting the gas flow to
and from the sample (100 6 25-mm ID is recommended).The
5.3 Air reactivity rates are used for evaluating effectiveness
reactionchamberistobeconstructedwithadustcollectioncup
and beneficiation processes or for research purposes.
at the bottom, which is removable and capable of capturing all
6. Apparatus
the dust that falls off the sample during the test. The most
common materials of construction are quartz and Inconel.
6.1 Theapparatustobeusedshouldbeassimpleaspossible
andbecommensuratewithwhatistobeachieved,theprincipal
6.1.3 Sample Holders, capable of supporting the sample in
criteria being that the reaction rate is to be determined under
the reaction chamber for the duration of the test and should be
isothermal conditions and unaffected by physical and chemical
capable of being reusable. The sample holder shall not change
properties inherent to the apparatus (such as gas diffusion
in mass during the test, affect the diffusion pattern of the gases
patterns, gas temperature, exposed sample surface area, and so
to or from the sample, limit the gas accessible surface area of
forth).Atypical apparatus that has been found to be suitable is
the test sample, or interfere with the free fall of dust from the
illustrated in Fig. 1.
sample. A typical sample holder is illustrated in Fig. 2.
6.1.1 Furnace and Controller, capable of maintaining con-
6.1.4 Gas Preheat Tube,extendingintothefirstheatzoneof
stant temperature within 62°C in the 100-mm region centered
the reaction chamber to preheat the gases prior to entering the
on the specimen. The example apparatus of Fig. 1 employs a
reactionchamber.Thelengthanddiameterofthetubecanvary
three zone heating element and associated controls to accom-
as long as the gases exiting the tube are the same temperature
plish this, but other methods such as tapered windings or long
as the reaction chamber. The inlet gas shall exit the preheat
linear heaters are also suitable. The control thermocouple is a
tube downward to prevent channeling of the gas through the
groundedtypeandshallbelocatedwithinthereactionchamber
reaction chamber and to prevent plugging of the preheat tube
near the surface of the test sample to allow the furnace
with carbon dust.
controller to adjust to the exothermic reaction that occurs
6.1.5 Balance, capable of measuring the weight of the
duringtheairreactivitytest.Thecontrolthermocoupleshallbe
positioned 4 6 1 mm from the side sample surface and sample and sample holder (approximately 200 g maximum)
centeredverticallywithin5mmofthecenter.Thefurnaceshall continuously throughout the duration of the test to the nearest
be large enough to accept the reaction chamber. 0.01 g.
FIG. 1 Typical Air Reactivity Apparatus
D6559 − 00a (2010)
length and 50 6 1.0 mm in diameter. Most sample holders
require a hole of about 3-mm diameter to be drilled vertically
through the center of the cylinder to accommodate a hanger.
Theshapedspecimenistobesmoothandfreeofvisiblecracks
and gouges. Sampling plans for anodes and cathode blocks
given in Guides D6353 and D6354 may be used if desired.
8.2 Dry the shaped specimen in an oven at 105 6 5°C to
constant weight.
8.3 The sample shall be made free of loose carbon dust and
impurities from the shaping process by blowing with dry air.
9. Calibration
9.1 The purpose of this procedure is to establish a relation-
shipbetweenthecontrollersettingsforthreezonefurnacesand
the actual temperatures inside the reaction chamber in the
region of the specimen. The length to be calibrated is a
100-mm (4-in.) zone.
NOTE1—Forsinglezonefurnaces,thecalibrationprobeshallbeplaced
in center of where sample will be placed and confirm that the 100-mm
zone is within 62°C.
9.1.1 Insert a multiprobe thermocouple (for example, three
couples in same sheath with probes located at the tip and at 50
FIG. 2 Typical Sample Holder
and 100 mm (2 and 4 in.) above the tip, or a packet of
thermocouples with tips located at similar known distances)
6.1.6 Gas Flow Meter, capable of monitoring the gas flow
intothezonewherethesamplewillbelocated.Themultiprobe
rate into the reaction chamber. All gas flow rates are to be
thermocouple center probe shall be located where the center of
maintained at the rate determined for t
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