ASTM D6559-00a(2005)
(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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D6559–00a (Reapproved 2005)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method covers the thermogravimetric (TGA) 3.1 Definitions of Terms Specific to This Standard:
determination of air reactivity and dusting of shaped carbon 3.1.1 dusting, n—the quantity of carbon that falls off the
anodes and cathode blocks used in the aluminum reduction carbonartifactwhileinthereactionchamberandiscollectedin
industry.The apparatus selection covers a significant variety of the container at the bottom of the reaction chamber.
types with various thermal conditions, sample size capability, 3.1.2 final air reactivity, n—the mass loss of the carbon
materials of construction, and procedures for determining the artifactduringthefinal30minofexposuretoairinthereaction
mass loss and subsequent rate of reaction. This test method chamber divided by the initial geometric (right cylindrical)
standardizes the variables of sample dimensions, reaction exposed surface area of the sample, expressed as mg/cm -h.
temperature, gas velocity over the exposed surfaces, and 3.1.3 initial air reactivity, n—the mass loss of the carbon
reactiontimesuchthatresultsobtainedondifferentapparatuses artifact during the first 30 min of exposure to air in the reaction
are correlatable. chamber divided by the initial geometric (right cylindrical)
1.2 The values stated in SI units are to be regarded as exposed surface area of the sample, expressed as mg/cm -h.
standard. No other units of measurement are included in this 3.1.4 total air reactivity, n—the total mass loss of the
standard. carbon artifact (including dusting) during the total time that the
1.3 This standard does not purport to address all of the sample is exposed to air (180 min) in the reaction chamber
safety concerns, if any, associated with its use. It is the divided by the initial geometric (right cylindrical) exposed
responsibility of the user of this standard to establish appro- surface area of the sample, expressed as mg/cm -h.
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
2. Referenced Documents
determined by passing air at flow rates, giving a standard
2.1 ASTM Standards: velocity of reactant gas around cylindrically shaped carbon
D6353 Guide for Sampling Plan and Core Sampling for artifacts under nearly isothermal conditions for a specified
Prebaked Anodes Used in Aluminum Production length of time. The reactivity is determined by continuously
D6354 Guide for Sampling Plan and Core Sampling of monitoring the sample mass loss. The dusting term is deter-
Carbon Cathode Blocks Used in Aluminum Production mined by collecting and determining the mass of carbon
E691 Practice for Conducting an Interlaboratory Study to particles that fall off the sample during reaction.
Determine the Precision of a Test Method
5. Significance and Use
5.1 The air reactivity rates are used to quantify the tendency
This test method is under the jurisdiction of ASTM Committee D02 on
of a carbon artifact to react with air. Carbon consumed by this
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
unwanted side reaction is unavailable for the primary reactions
D02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.
ofreducingaluminatotheprimarymetal.Airreactivitydusting
Current edition approved May 1, 2005. Published June 2005. Originally
rate is used by some companies to quantify the tendency of the
approved in 2000. Last previous edition approved in 2000 as D6559–00a. DOI:
10.1520/D6559-00AR05.
cokeaggregateorbindercokeofacarbonartifacttoselectively
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
react with these gases. Preferential attack of the binder coke or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
coke aggregate of a carbon artifact by these gases causes some
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. carbon to fall off or dust, making the carbon unavailable for the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6559–00a (2005)
primary reaction of reducing alumina and, more importantly, controller to adjust to the exothermic reaction that occurs
reducing the efficiency of the aluminum reduction cell. during the air reactivity test.The control thermocouple shall be
5.2 Comparison of air reactivity and dusting rates is useful
positioned 4 6 1 mm from the side sample surface and
in selecting raw materials for the manufacture of commercial
centeredverticallywithin5mmofthecenter.Thefurnaceshall
anodes for specific smelting technologies in the aluminum
be large enough to accept the reaction chamber.
reduction industry.
6.1.2 Reaction Chamber, consisting of a vertical tube con-
5.3 Air reactivity rates are used for evaluating effectiveness
structed of a material capable of withstanding the temperature
and beneficiation processes or for research purposes.
ofthereactionwithsufficientinsidediameter(ID)toacceptthe
sample and sample holder while not affecting the gas flow to
6. Apparatus
and from the sample (100 6 25-mm ID is recommended). The
6.1 Theapparatustobeusedshouldbeassimpleaspossible
reactionchamberistobeconstructedwithadustcollectioncup
andbecommensuratewithwhatistobeachieved,theprincipal
at the bottom, which is removable and capable of capturing all
criteria being that the reaction rate is to be determined under
the dust that falls off the sample during the test. The most
isothermal conditions and unaffected by physical and chemical
common materials of construction are quartz and Inconel.
properties inherent to the apparatus (such as gas diffusion
6.1.3 Sample Holders, capable of supporting the sample in
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
stant temperature within 62°C in the 100-mm region centered
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-
plish this, but other methods such as tapered windings or long 6.1.4 Gas Preheat Tube, extending into the first heat zone of
the reaction chamber to preheat the gases prior to entering the
linear heaters are also suitable. The control thermocouple is a
groundedtypeandshallbelocatedwithinthereactionchamber reaction chamber.The length and diameter of the tube can vary
near the surface of the test sample to allow the furnace as long as the gases exiting the tube are the same temperature
FIG. 1 Typical Air Reactivity Apparatus
D6559–00a (2005)
7. Reagents
7.1 Purity of Reagents—Reagent grade conforming to the
specifications of the Committee on Analytical Reagents of the
American Chemical Society.
7.1.1 Nitrogen—99.95 %.
7.1.2 Air—less than 0.1 % moisture.
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.
The shaped specimen is to be smooth and free of visible cracks
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
FIG. 2 Typical Sample Holder
9.1 The purpose of this procedure is to establish a relation-
ship between the controller settings for three zone furnaces and
the actual temperatures inside the reaction chamber in the
as the reaction chamber. The inlet gas shall exit the preheat
region of the specimen. The length to be calibrated is a
tube downward to prevent channeling of the gas through the
100-mm (4-in.) zone.
reaction chamber and to prevent plugging of the preheat tube
NOTE 1—For single zone furnaces, the calibration probe shall be placed
with carbon dust.
in center of where sample will be placed and confirm that the 100-mm
6.1.5 Balance, capable of measuring the weight of the
zone is within 62°C.
sample and sample holder (approximately 200 g maximum)
9.1.1 Insert a multiprobe thermocouple (for example, three
continuously throughout the duration of the test to the nearest
couples in same sheath with probes located at the tip and at 50
0.01 g.
and 100 mm (2
...
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