ASTM D6558-00a(2010)
(Test Method)Standard Test Method for Determination of TGA CO2 Reactivity of Baked Carbon Anodes and Cathode Blocks
Standard Test Method for Determination of TGA CO<inf>2</inf> Reactivity of Baked Carbon Anodes and Cathode Blocks
SIGNIFICANCE AND USE
The CO2 reactivity rates are used to quantify the tendency of a carbon artifact to react with carbon dioxide. Carbon consumed by these unwanted side reactions is unavailable for the primary reactions of reducing alumina to the primary metal. CO2 dusting rates are used 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 CO2 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.
CO2 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 CO2 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: D6558 − 00a(Reapproved 2010)
Standard Test Method for
Determination of TGA CO Reactivity of Baked Carbon
Anodes and Cathode Blocks
This standard is issued under the fixed designation D6558; 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—that 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 CO reactivity and dusting of shaped carbon
3.1.2 final CO reactivity, n—the mass loss of the carbon
anodes and cathode blocks used in the aluminum reduction
artifact during the final 30 min of exposure to CO in the
industry.Theapparatusselectioncoversasignificantvarietyof
reaction chamber divided by the initial geometric (right cylin-
types with various thermal conditions, sample size capability,
drical) exposed surface area of the sample, expressed as
materials of construction, and procedures for determining the
mg/cm -h.
mass loss and subsequent rate of reaction. This test method
standardizes the variables of sample dimensions, reaction
3.1.3 initial CO reactivity, n—the mass loss of the carbon
temperature, gas velocity over the exposed surfaces, and
artifact during the first 30 min of exposure to CO in the
reactiontimesuchthatresultsobtainedondifferentapparatuses
reaction chamber divided by the initial geometric (right cylin-
are correlatable.
drical) exposed surface area of the sample, expressed as
mg/cm -h.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3.1.4 total CO reactivity, n—the total mass loss of the
standard.
carbonartifact(includingdusting)duringthetotaltimethatthe
sample is exposed to CO (420 min) in the reaction chamber
1.3 This standard does not purport to address all of the 2
divided by the initial geometric (right cylindrical) exposed
safety concerns, if any, associated with its use. It is the
surface area of 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 CO reactivity and dusting are
2. Referenced Documents
determined by passing carbon dioxide gas at flow rates giving
a standard velocity of reactant gas around cylindrically shaped
2.1 ASTM Standards:
carbon artifacts under 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 The CO reactivity rates are used to quantify the
tendency of a carbon artifact to react with carbon dioxide.
3.1 Definitions of Terms Specific to This Standard:
Carbon consumed by these unwanted side reactions is unavail-
able for the primary reactions of reducing alumina to the
This test method is under the jurisdiction of ASTM Committee D02 on
primary metal. CO dusting rates are used to quantify the
Petroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility of
tendency of the coke aggregate or binder coke of a carbon
SubcommitteeD02.05onPropertiesofFuels,PetroleumCokeandCarbonMaterial.
artifact to selectively react with these gases. Preferential attack
Current edition approved May 1, 2010. Published June 2010. Originally
of the binder coke or coke aggregate of a carbon artifact by
approved in 2000. Last previous edition approved in 2005 as D6558–00a (2005).
DOI: 10.1520/D6558-00AR10.
these gases causes some carbon to fall off or dust, making the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
carbon unavailable for the primary reaction of reducing alu-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mina and, more importantly, reducing the efficiency of the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. aluminum reduction cell.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6558 − 00a (2010)
5.2 ComparisonofCO reactivityanddustingratesisuseful within 5 mm of the center. The furnace shall be large enough
in selecting raw materials for the manufacture of commercial to accept the reaction chamber.
anodes for specific smelting technologies in the aluminum
6.1.1.1 Reaction Chamber, consisting of a vertical tube
reduction industry.
constructed of a material capable of withstanding the tempera-
5.3 CO reactivity rates are used for evaluating effective- tureofthereaction(960 62°C)withsufficientinsidediameter
ness and beneficiation processes or for research purposes. (ID)toacceptthesampleandsampleholderwhilenotaffecting
the gas flow to and from the sample (100 6 25-mm ID is
6. Apparatus
recommended).Thereactionchamberistobeconstructedwith
a dust collection cup at the bottom that is removable and
6.1 Theapparatustobeusedshouldbeassimpleaspossible
andbecommensuratewithwhatistobeachieved,theprincipal capableofcapturingallthedustthatfallsoffthesampleduring
criteria being that the reaction rate is to be determined under
thetest.Themostcommonmaterialsofconstructionarequartz
isothermal conditions and unaffected by physical and chemical
and Inconel.
properties inherent to the apparatus (such as gas diffusion
6.1.1.2 Sample Holders,capableofsupportingthesamplein
patterns, gas temperature, exposed sample surface area, and so
the reaction chamber for the duration of the test and should be
forth).Atypical apparatus that has been found to be suitable is
capable of being reusable. The sample holder shall not change
illustrated in Fig. 1.
in mass during the test, affect the diffusion pattern of the gases
6.1.1 Furnace and Controller, capable of maintaining con-
to or from the sample, limit the gas accessible surface area of
stanttemperature,within 62°Cinthe100-mmregioncentered
the test sample, or interfere with the free fall of dust from the
on the specimen. The example apparatus of Fig. 1 employs a
sample. A typical sample holder is illustrated in Fig. 2.
three zone heating element and associated controls to accom-
6.1.1.3 Gas Preheat Tube, extending into the first heat zone
plish this, but other methods such as tapered windings or long
of the reaction chamber to preheat the gases prior to entering
linear heaters are also suitable. The control thermocouple is a
the reaction chamber. The length and diameter of the tube can
groundedtypeandshallbelocatedwithinthereactionchamber
vary as long as the gases exiting the tube are the same
near the surface of the test sample to allow the furnace
temperatureasthereactionchamber.Theinletgasshallexitthe
controller to adjust to exothermic reactions, which occur
preheat tube downward to prevent channeling of the gas
during air reactivity tests, if the furnace is also used for air
reactivitytesting.Thecontrolthermocoupleshallbepositioned through the reaction chamber and to prevent plugging of the
4 61mmfromthesidesamplesurfaceandcenteredvertically preheat tube with carbon dust.
FIG. 1 Typical CO Reactivity Apparatus
D6558 − 00a (2010)
8. Sampling
8.1 Shape the carbon specimen by coring and cutting or
machining to a right cylindrical geometry, 50 6 1.0 mm in
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 Make the sample free of loose carbon dust and impuri-
ties 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.
FIG. 2 Typical Sample Holder
9.1.1 Insert a multiprobe thermocouple (for example, three
couplesinsamesheathwithprobeslocatedatthetip,andat50
6.1.1.4 Balance, capable of measuring the weight of the
and 100-mm (2 and 4 in.) above the tip; or a packet of
sample and sample holder (approximately 200 g maximum)
thermocouples with tips located at similar known distances)
continuously throughout the duration of the test to the nearest
intothezonewherethesamplewillbelocated.Themultiprobe
0.0
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