ASTM D6558-00
(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<sub>2</sub> Reactivity of Baked Carbon Anodes and Cathode Blocks
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 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 6558 – 00 An American National Standard
Standard Test Method for
Determination of TGA CO Reactivity of Baked Carbon
Anodes and Cathode Blocks
This standard is issued under the fixed designation D 6558; 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 reaction chamber divided by the initial geometric (right cylin-
drical) exposed surface area of the sample, expressed as
1.1 This test method covers the thermogravimetric (TGA)
mg/cm -h.
determination of CO reactivity and dusting of shaped carbon
3.1.4 total CO reactivity, n—the total mass loss of the
anodes and cathode blocks used in the aluminum reduction
carbon artifact (including dusting) during the total time that the
industry. The apparatus selection covers a significant variety of
sample is exposed to CO (420 min) in the reaction chamber
types with various thermal conditions, sample size capability,
divided by the initial geometric (right cylindrical) exposed
materials of construction, and procedures for determining the
surface area of the sample, expressed as mg/cm -hr.
mass loss and subsequent rate of reaction. This test method
standardizes the variables of sample dimensions, reaction
4. Summary of Test Method
temperature, gas velocity over the exposed surfaces, and
4.1 Initial, final, and total CO reactivity and dusting are
reaction time such that results obtained on different apparatuses
determined by passing carbon dioxide gas at flow rates giving
are correlatable.
a standard velocity of reactant gas around cylindrically shaped
1.2 The values stated in SI units are to be regarded as the
carbon artifacts under isothermal conditions for a specified
standard.
length of time. The reactivity is determined by continuously
1.3 This standard does not purport to address all of the
monitoring the sample mass loss. The dusting term is deter-
safety concerns, if any, associated with its use. It is the
mined by collecting and determining the mass of carbon
responsibility of the user of this standard to establish appro-
particles that fall off the sample during reaction.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents 5.1 The CO reactivity rates are used to quantify the
tendency of a carbon artifact to react with carbon dioxide.
2.1 ASTM Standards:
Carbon consumed by these unwanted side reactions is unavail-
D 6353 Guide for Sampling Plan and Core Sampling of
2 able for the primary reactions of reducing alumina to the
Prebaked Anodes Used in Aluminum Production
primary metal. CO dusting rates are used to quantify the
D 6354 Guide for Sampling Plan and Core Sampling of
2 tendency of the coke aggregate or binder coke of a carbon
Carbon Cathode Blocks Used in Aluminum Production
artifact to selectively react with these gases. Preferential attack
3. Terminology of the binder coke or coke aggregate of a carbon artifact by
these gases causes some carbon to fall off or dust, making the
3.1 Definitions of Terms Specific to This Standard:
carbon unavailable for the primary reaction of reducing alu-
3.1.1 dusting, n—that quantity of carbon that falls off the
mina and, more importantly, reducing the efficiency of the
carbon artifact while in the reaction chamber and is collected in
aluminum reduction cell.
the container at the bottom of the reaction chamber.
5.2 Comparison of CO reactivity and dusting rates is useful
3.1.2 final CO reactivity, n—the mass loss of the carbon 2
in selecting raw materials for the manufacture of commercial
artifact during the final 30 min of exposure to CO in the
anodes for specific smelting technologies in the aluminum
reaction chamber divided by the initial geometric (right cylin-
reduction industry.
drical) exposed surface area of the sample, expressed as
5.3 CO reactivity rates are used for evaluating effectiveness
mg/cm -h. 2
and beneficiation processes or for research purposes.
3.1.3 initial CO reactivity, n—the mass loss of the carbon
artifact during the first 30 min of exposure to CO in the
6. Apparatus
6.1 The apparatus to be used should be as simple as possible
This test method is under the jurisdiction of ASTM Committee D02 on
and be commensurate with what is to be achieved, the principal
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
criteria being that the reaction rate is to be determined under
D02.05 on The Properties of Fuels, Petroleum Coke and Carbon Material.
Current edition approved June 10, 2000. Published July 2000.
isothermal conditions and unaffected by physical and chemical
Annual Book of ASTM Standards, Vol 05.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6558
properties inherent to the apparatus (such as gas diffusion capable of being reusable. The sample holder shall not change
patterns, gas temperature, exposed sample surface area, and so in mass during the test, affect the diffusion pattern of the gases
forth). A typical apparatus that has been found to be suitable is to or from the sample, limit the gas accessible surface area of
illustrated in Fig. 1. the test sample, or interfere with the free fall of dust from the
6.1.1 Furnace and Controller, capable of maintaining con- sample. A typical sample holder is illustrated in Fig. 2.
stant temperature, within 6 2°C in the 100-mm region centered 6.1.1.3 Gas Preheat Tube, extending into the first heat zone
on the specimen. The example apparatus of Fig. 1 employs a of the reaction chamber to preheat the gases prior to entering
three zone heating element and associated controls to accom- the reaction chamber. The length and diameter of the tube can
plish this, but other methods such as tapered windings or long vary as long as the gases exiting the tube are the same
linear heaters are also suitable. The control thermocouple is a temperature as the reaction chamber. The inlet gas shall exit the
grounded type and shall be located within the reaction chamber preheat tube downward to prevent channeling of the gas
near the surface of the test sample to allow the furnace through the reaction chamber and to prevent plugging of the
controller to adjust to exothermic reactions, which occur preheat tube with carbon dust.
during air reactivity tests, if the furnace is also used for air 6.1.1.4 Balance, capable of measuring the weight of the
reactivity testing. The control thermocouple shall be positioned sample and sample holder (approximately 200 g maximum)
4 6 1 mm from the side sample surface and centered vertically continuously throughout the duration of the test to the nearest
within 5 mm of the center. The furnace shall be large enough 0.01 g.
to accept the reaction chamber. 6.1.1.5 Gas Flow Meter, capable of monitoring the gas flow
6.1.1.1 Reaction Chamber, consisting of a vertical tube rate into the reaction chamber. All gas flow rates are to be
constructed of a material capable of withstanding the tempera- maintained at the rate determined for the particular test
ture of the reaction (960°C 6 2°C) with sufficient inside apparatus.
diameter (ID) to accept the sample and sample holder while not 6.1.1.6 Needle Valve, to make fine adjustments to the gas
affecting the gas flow to and from the sample (100 6 25-mm flow rate.
ID is recommended). The reaction chamber is to be constructed 6.1.1.7 Pressure Reducing Valve, to reduce the pressure of
with a dust collection cup at the bottom that is removable and the compressed gases to near atmospheric pressure prior to
capable of capturing all the dust that falls off the sample during entering the gas flow meter through the needle valve.
the test. The most common materials of construction are quartz 6.1.1.8 Thermocouple(s), inserted into the reaction chamber
and Inconel. to calibrate the furnace zone controllers. An optional thermo-
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