1、Designation: D 6558 00a (Reapproved 2005)An American National StandardStandard Test Method forDetermination of TGA CO2Reactivity of Baked CarbonAnodes and Cathode Blocks1This standard is issued under the fixed designation D 6558; the number immediately following the designation indicates the year of
2、original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the thermogravimetric (TGA)determi
3、nation of CO2reactivity and dusting of shaped carbonanodes and cathode blocks used in the aluminum reductionindustry. The apparatus selection covers a significant variety oftypes with various thermal conditions, sample size capability,materials of construction, and procedures for determining themass
4、 loss and subsequent rate of reaction. This test methodstandardizes the variables of sample dimensions, reactiontemperature, gas velocity over the exposed surfaces, andreaction time such that results obtained on different apparatusesare correlatable.1.2 The values stated in SI units are to be regard
5、ed asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine
6、 the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 6353 Guide for Sampling Plan and Core Sampling ofPrebaked Anodes Used in Aluminum ProductionD 6354 Guide for Sampling Plan and Core Sampling ofCarbon Cathode Blocks Used in Aluminum ProductionE 69
7、1 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 dusting, nthat quantity of carbon that falls off thecarbon artifact while in the reaction chamber and is collected inthe container at th
8、e bottom of the reaction chamber.3.1.2 final CO2reactivity, nthe mass loss of the carbonartifact during the final 30 min of exposure to CO2in thereaction chamber divided by the initial geometric (right cylin-drical) exposed surface area of the sample, expressed asmg/cm2-h.3.1.3 initial CO2reactivity
9、, nthe mass loss of the carbonartifact during the first 30 min of exposure to CO2in thereaction chamber divided by the initial geometric (right cylin-drical) exposed surface area of the sample, expressed asmg/cm2-h.3.1.4 total CO2reactivity, nthe total mass loss of thecarbon artifact (including dust
10、ing) during the total time that thesample is exposed to CO2(420 min) in the reaction chamberdivided by the initial geometric (right cylindrical) exposedsurface area of the sample, expressed as mg/cm2-h.4. Summary of Test Method4.1 Initial, final, and total CO2reactivity and dusting aredetermined by
11、passing carbon dioxide gas at flow rates givinga standard velocity of reactant gas around cylindrically shapedcarbon artifacts under isothermal conditions for a specifiedlength of time. The reactivity is determined by continuouslymonitoring the sample mass loss. The dusting term is deter-mined by co
12、llecting and determining the mass of carbonparticles that fall off the sample during reaction.5. Significance and Use5.1 The CO2reactivity rates are used to quantify thetendency of a carbon artifact to react with carbon dioxide.Carbon consumed by these unwanted side reactions is unavail-able for the
13、 primary reactions of reducing alumina to theprimary metal. CO2dusting rates are used to quantify thetendency of the coke aggregate or binder coke of a carbonartifact to selectively react with these gases. Preferential attack1This test method is under the jurisdiction of ASTM Committee D02 onPetrole
14、um Products and Lubricants and is the direct responsibility of SubcommitteeD02.05 on Properties of Fuels, Petroleum Coke and Carbon Material.Current edition approved May 1, 2005. Published June 2005. Originallyapproved in 2000. Last previous edition approved in 2000 as D 655800a.2For referenced ASTM
15、 standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohoc
16、ken, PA 19428-2959, United States.of the binder coke or coke aggregate of a carbon artifact bythese gases causes some carbon to fall off or dust, making thecarbon unavailable for the primary reaction of reducing alu-mina and, more importantly, reducing the efficiency of thealuminum reduction cell.5.
17、2 Comparison of CO2reactivity and dusting rates is usefulin selecting raw materials for the manufacture of commercialanodes for specific smelting technologies in the aluminumreduction industry.5.3 CO2reactivity rates are used for evaluating effectivenessand beneficiation processes or for research pu
18、rposes.6. Apparatus6.1 The apparatus to be used should be as simple as possibleand be commensurate with what is to be achieved, the principalcriteria being that the reaction rate is to be determined underisothermal conditions and unaffected by physical and chemicalproperties inherent to the apparatu
19、s (such as gas diffusionpatterns, gas temperature, exposed sample surface area, and soforth). A typical apparatus that has been found to be suitable isillustrated in Fig. 1.6.1.1 Furnace and Controller, capable of maintaining con-stant temperature, within 62C in the 100-mm region centeredon the spec
20、imen. The example apparatus of Fig. 1 employs athree zone heating element and associated controls to accom-plish this, but other methods such as tapered windings or longlinear heaters are also suitable. The control thermocouple is agrounded type and shall be located within the reaction chambernear t
21、he surface of the test sample to allow the furnacecontroller to adjust to exothermic reactions, which occurduring air reactivity tests, if the furnace is also used for airreactivity testing. The control thermocouple shall be positioned4 6 1 mm from the side sample surface and centered verticallywith
22、in 5 mm of the center. The furnace shall be large enoughto accept the reaction chamber.6.1.1.1 Reaction Chamber, consisting of a vertical tubeconstructed of a material capable of withstanding the tempera-ture of the reaction (960 6 2C) with sufficient inside diameter(ID) to accept the sample and sam
23、ple holder while not affectingthe gas flow to and from the sample (100 6 25-mm ID isrecommended). The reaction chamber is to be constructed witha dust collection cup at the bottom that is removable andcapable of capturing all the dust that falls off the sample duringthe test. The most common materia
24、ls of construction are quartzand Inconel.6.1.1.2 Sample Holders, capable of supporting the sample inthe reaction chamber for the duration of the test and should becapable of being reusable. The sample holder shall not changein mass during the test, affect the diffusion pattern of the gasesto or from
25、 the sample, limit the gas accessible surface area ofthe test sample, or interfere with the free fall of dust from thesample. A typical sample holder is illustrated in Fig. 2.6.1.1.3 Gas Preheat Tube, extending into the first heat zoneof the reaction chamber to preheat the gases prior to enteringthe
26、 reaction chamber. The length and diameter of the tube canvary as long as the gases exiting the tube are the sametemperature as the reaction chamber. The inlet gas shall exit theFIG. 1 Typical CO2Reactivity ApparatusD 6558 00a (2005)2preheat tube downward to prevent channeling of the gasthrough the
27、reaction chamber and to prevent plugging of thepreheat tube with carbon dust.6.1.1.4 Balance, capable of measuring the weight of thesample and sample holder (approximately 200 g maximum)continuously throughout the duration of the test to the nearest0.01 g.6.1.1.5 Gas Flow Meter, capable of monitorin
28、g the gas flowrate into the reaction chamber. All gas flow rates are to bemaintained at the rate determined for the particular testapparatus.6.1.1.6 Needle Valve, to make fine adjustments to the gasflow rate.6.1.1.7 Pressure Reducing Valve, to reduce the pressure ofthe compressed gases to near atmos
29、pheric pressure prior toentering the gas flow meter through the needle valve.6.1.1.8 Thermocouple(s), inserted into the reaction chamberto calibrate the furnace zone controllers. An optional thermo-couple may be used to monitor reaction temperatures. Someusers find continuous temperature measurement
30、 of the internalreaction chamber to be of value.6.1.1.9 Calipers, or other suitable device, capable of mea-suring to within 0.01 mm for determining the sample diameterand height to calculate geometric surface area exposed to thetest gases.6.1.1.10 Optional Equipment, including, but not limited to,au
31、tomatic control devices, multichannel line selector, andpersonal computer to automate data gathering, manipulation,reporting, and storage.7. Reagents7.1 Purity of ReagentsReagent grade, conforming to thespecifications of the Committee on Analytical Reagents of theAmerican Chemical Society.7.1.1 Nitr
32、ogen99.95 %.7.1.2 Carbon Dioxide99.95 %.8. Sampling8.1 Shape the carbon specimen by coring and cutting ormachining to a right cylindrical geometry, 50 6 1.0 mm inlength and 50 6 1.0 mm in diameter. Most sample holdersrequire a hole of about 3-mm diameter to be drilled verticallythrough the center of
33、 the cylinder to accommodate a hanger.The shaped specimen is to be smooth and free of visible cracksand gouges. Sampling plans for anodes and cathode blocksgiven in Guides D 6353 and D 6354 may be used if desired.8.2 Dry the shaped specimen in an oven at 105 6 5C toconstant weight.8.3 Make the sampl
34、e free of loose carbon dust and impuri-ties from the shaping process by blowing with dry air.9. Calibration9.1 The purpose of this procedure is to establish a relation-ship between the controller settings for three zone furnaces andthe actual temperatures inside the reaction chamber in theregion of
35、the specimen. The length to be calibrated is a100-mm (4-in.) zone.NOTE 1For single zone furnaces, the calibration probe shall be placedin center of where sample will be placed and confirm that the 100-mmzone is within 62C.9.1.1 Insert a multiprobe thermocouple (for example, threecouples in same shea
36、th with probes located at the tip, and at 50and 100-mm (2 and 4 in.) above the tip; or a packet ofthermocouples with tips located at similar known distances)into the zone where the sample will be located. The multiprobethermocouple center probe shall be located where the center ofthe sample will be
37、located.9.1.2 The center thermocouple is connected to the maincontroller setting, that is, 960C for CO2reactivity.9.1.3 Connect the other two (2) thermocouples to anytemperature indicating device. For determining actual tempera-ture profile, a recording temperature indicator is required.9.1.4 Allow
38、4 h for furnace to reach equilibrium undernitrogen purge (rate per 9.2).9.1.5 Adjust zones until all three (3) temperature indicatorsare 62C.9.2 Gas Flow Rates, for this test are based on 250 6 5 L/h(ambient temperature) for a sample diameter of 50 mm and areaction tube with an ID of 100 mm. Reactiv
39、ities determinedwith this test method are affected by the gas velocity sweepingthe reaction surfaces during the test. This requires gas flowrates to be such that the velocity through the annular spacebetween the sample and reaction tube wall is constant forvarious size reaction tubes. The proper flo
40、w rate for othergeometries is determined by multiplying the reference flow rate(250 L/h) by the ratio of annular area of the system to theannular area of the reference system. For example, a 75-mm IDtube with 50.8-mm samples would have a flow rate calculatedby:FIG. 2 Typical Sample HolderD 6558 00a
41、(2005)3Ratio 5 (1)FTube ID2 Sample OD2Ref Tube ID2 Ref Sample OD2G5F752 50.821002502G5304475005 0.406Flow Rate 5 250 L/h 0.406 5 102 L/h (2)10. Procedure10.1 Preheat the reactor tube to 960 6 2C for CO2reactivity.10.2 Purge the reaction chamber with nitrogen at the flowrate determined in 9.2.10.3 We
42、igh and record the mass of the sample to the nearest0.01 g as Wi.10.4 Measure the sample diameter (ds), sample height (h),and diameter of the center hole (dh)to60.01 mm to calculategeometric surface area for the reaction as given in 11.1.10.5 Insert the sample into the reaction chamber by placingthe
43、 sample in the sample holder and suspending the sampleholder from the balance.10.6 Preheat the sample under nitrogen purge for 30 min.10.7 Tare the balance in accordance with the balancemanufacturers instructions.10.8 Switch the gas introduced to the reaction chamber fromnitrogen to CO2after 30 min
44、in the nitrogen preheat, andmaintain the flow rate as determined in 9.2.10.9 Record the weight of the sample every minute for theduration of the test. The test duration for CO2reactivity is 7 h(420 min).10.10 Remove the sample from the reaction chamber assoon as possible after the test time has expi
45、red as the dustingparameter will be affected. Exercise care so that the sampledoes not strike the sides of the reaction chamber upon removal,which could result in dislodging particles and adding to themass of dust.10.11 Remove the dust collection cup from the bottom ofthe reaction chamber and place
46、in a desiccator until cool.10.12 Weigh the dust collected in the dust collection cup,and record as Wd.11. Calculation11.1 Calculate the exposed surface area of the shapedsample as follows:A 5 Area of (3)$circumference 1 top and bottom surfaces center hole!%,orA 5Hpdsh 12p4ds2 dh2!J/100 (4)where:A =
47、exposed surface area, cm2,ds= sample diameter, mm,dh= diameter of central hole (if any), mm, andh = sample height, mm.11.2 Calculate total CO2reactivity rate (TRc) as follows:TRc51000Wi Wf!7A(5)where:TRc= total CO2reactivity rate, mg/cm2-h,Wi= initial sample weight, g, andWf= final sample weight, g.
48、11.3 Calculate initial CO2reactivity rate (IRc) as follows:IRc52000Wi W30!A(6)where:IRc= initial CO2reactivity rate, mg/cm2-h, andW30= sample weight after 30 min of test, g.11.4 Calculate final CO2reactivity rate (FRc) as follows:FRc52000W390 Wf!A(7)where:FRc= final CO2reactivity rate, mg/cm2-h, and
49、W390= sample weight after 390 min of test, g.11.5 Calculate CO2dusting rate (DRc) as follows:DRc51000Wd7A(8)where:DRc= dusting rate during 7 h test, mg/cm2-h, andWd= weight of dust collected during test, g.12. Report12.1 Report reactivity results to the nearest 0.1 mg/cm2-h.13. Precision and Bias313.1 PrecisionThe precision was determined by an inter-laboratory study conducted in accordance with Practice E 691.Six laboratories tested nine materials (seven anodes and twocathodes). It was found, by linear regression, that the repeat-ability and re
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