ASTM D6559-00
(Test Method)Standard Test Method for Determination of TGA Air Reactivity of Baked Carbon Anodes and Cathode Blocks
Standard Test Method for Determination of TGA Air Reactivity of Baked Carbon Anodes and Cathode Blocks
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 the 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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Designation: D 6559 – 00 An American National Standard
Standard Test Method for
Determination of TGA Air Reactivity of Baked Carbon
Anodes and Cathode Blocks
This standard is issued under the fixed designation D 6559; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope chamber divided by the initial geometric (right cylindrical)
exposed surface area of the sample, expressed as mg/cm -h.
1.1 This test method covers the thermogravimetric (TGA)
3.1.4 total air reactivity, n—the total mass loss of the
determination of air reactivity and dusting of shaped carbon
carbon artifact (including dusting) during the total time that the
anodes and cathode blocks used in the aluminum reduction
sample is exposed to air (180 min) in the reaction chamber
industry. The apparatus selection covers a significant variety of
divided by the initial geometric (right cylindrical) exposed
types with various thermal conditions, sample size capability,
surface area of the sample, expressed as mg/cm -h.
materials of construction, and procedures for determining the
mass loss and subsequent rate of reaction. This test method
4. Summary of Test Method
standardizes the variables of sample dimensions, reaction
4.1 Initial, final, and total air reactivity and dusting are
temperature, gas velocity over the exposed surfaces, and
determined by passing air at flow rates, giving a standard
reaction time such that results obtained on different apparatuses
velocity of reactant gas around cylindrically shaped carbon
are correlatable.
artifacts under nearly isothermal conditions for a specified
1.2 The values stated in SI units are to be regarded as the
length of time. The reactivity is determined by continuously
standard.
monitoring the sample mass loss. The dusting term is deter-
1.3 This standard does not purport to address all of the
mined by collecting and determining the mass of carbon
safety concerns, if any, associated with its use. It is the
particles that fall off the sample during reaction.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. Significance and Use
bility of regulatory limitations prior to use.
5.1 The air reactivity rates are used to quantify the tendency
of a carbon artifact to react with air. Carbon consumed by this
2. Referenced Documents
unwanted side reaction is unavailable for the primary reactions
2.1 ASTM Standards:
of reducing alumina to the primary metal. Air reactivity dusting
D 6353 Guide for Sampling Plan and Core Sampling of
2 rate is used by some companies to quantify the tendency of the
Prebaked Anodes Used in Aluminum Production
coke aggregate or binder coke of a carbon artifact to selectively
D 6354 Guide for Sampling Plan and Core Sampling of
2 react with these gases. Preferential attack of the binder coke or
Carbon Cathode Blocks Used in Aluminum Production
coke aggregate of a carbon artifact by these gases causes some
3. Terminology carbon to fall off or dust, making the carbon unavailable for the
primary reaction of reducing alumina and, more importantly,
3.1 Definitions of Terms Specific to This Standard:
reducing the efficiency of the aluminum reduction cell.
3.1.1 dusting, n—the quantity of carbon that falls off the
5.2 Comparison of air reactivity and dusting rates is useful
carbon artifact while in the reaction chamber and is collected in
in selecting raw materials for the manufacture of commercial
the container at the bottom of the reaction chamber.
anodes for specific smelting technologies in the aluminum
3.1.2 final air reactivity, n—the mass loss of the carbon
reduction industry.
artifact during the final 30 min of exposure to air in the reaction
5.3 Air reactivity rates are used for evaluating effectiveness
chamber divided by the initial geometric (right cylindrical)
and beneficiation processes or for research purposes.
exposed surface area of the sample, expressed as mg/cm -h.
3.1.3 initial air reactivity, n—the mass loss of the carbon
6. Apparatus
artifact during the first 30 min of exposure to air in the reaction
6.1 The apparatus to be used should be as simple as possible
and be commensurate with what is to be achieved, the principal
criteria being that the reaction rate is to be determined under
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
isothermal conditions and unaffected by physical and chemical
D02.05 on The Properties of Fuels, Petroleum Coke and Carbon Material.
properties inherent to the apparatus (such as gas diffusion
Current edition approved June 10, 2000. Published July 2000.
2 patterns, gas temperature, exposed sample surface area, and so
Annual Book of ASTM Standards, Vol 05.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6559
forth). A typical apparatus that has been found to be suitable is sample. A typical sample holder is illustrated in Fig. 2.
illustrated in Fig. 1.
6.1.4 Gas Preheat Tube, extending into the first heat zone of
6.1.1 Furnace and Controller, capable of maintaining con-
the reaction chamber to preheat the gases prior to entering the
stant temperature within 6 2°C in the 100-mm region centered
reaction chamber. The length and diameter of the tube can vary
on the specimen. The example apparatus of Fig. 1 employs a
as long as the gases exiting the tube are the same temperature
three zone heating element and associated controls to accom-
as the reaction chamber. The inlet gas shall exit the preheat
plish this, but other methods such as tapered windings or long
tube downward to prevent channeling of the gas through the
linear heaters are also suitable. The control thermocouple is a
reaction chamber and to prevent plugging of the preheat tube
grounded type and shall be located within the reaction chamber
with carbon dust.
near the surface of the test sample to allow the furnace
6.1.5 Balance, capable of measuring the weight of the
controller to adjust to the exothermic reaction that occurs
sample and sample holder (approximately 200 g maximum)
during the air reactivity test. The control thermocouple shall be
continuously throughout the duration of the test to the nearest
positioned 4 6 1 mm from the side sample surface and
0.01 g.
centered vertically within 5 mm of the center. The furnace shall
6.1.6 Gas Flow Meter, capable of monitoring the gas flow
be large enough to accept the reaction chamber.
rate into the reaction chamber. All gas flow rates are to be
6.1.2 Reaction Chamber, consisting of a vertical tube con-
maintained at the rate determined for the particular test
structed of a material capable of withstanding the temperature
apparatus.
of the reaction with sufficient inside diameter (ID) to accept the
6.1.7 Needle Valve, to make fine adjustments to the gas flow
sample and sample holder while not affecting the gas flow to
rate.
and from the sample (100 6 25-mm ID is recommended). The
6.1.8 Pressure Reducing Valve, to reduce the pressure of the
reaction chamber is to be constructed with a dust collection cup
compressed gases to near atmospheric pressure prior to enter-
at the bottom, which is removable and capable of capturing all
ing the gas flow meter through the needle valve.
the dust that falls off the sample during the test. The most
6.1.9 Thermocouple(s), inserted into the reaction chamber
common materials of construction are quartz and Inconel.
to calibrate the furnace zone controllers. An optional thermo-
6.1.3 Sample Holders, capable of supporting the sample in
couple may be used to monitor reaction temperatures. Some
the reaction chamber for the duration of the test and should be
users find continuous temperature measurement of the internal
capable of being reusable. The sample holder shall not cha
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