1、Designation: D 6559 00a (Reapproved 2005)An American National StandardStandard Test Method forDetermination of Thermogravimetric (TGA) Air Reactivity ofBaked Carbon Anodes and Cathode Blocks1This standard is issued under the fixed designation D 6559; the number immediately following the designation
2、indicates the year oforiginal 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 thermogra
3、vimetric (TGA)determination of air reactivity 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 f
4、or determining themass 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
5、units are to be regarded 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 p
6、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 6353 Guide for Sampling Plan and Core Sampling forPrebaked Anodes Used in Aluminum ProductionD 6354 Guide for Sampling Plan and Core Sampling ofCarbon Cathode Blocks Used in
7、Aluminum ProductionE 691 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, nthe quantity of carbon that falls off thecarbon artifact while in the reaction chamber and is collected
8、 inthe container at the bottom of the reaction chamber.3.1.2 final air reactivity, nthe mass loss of the carbonartifact during the final 30 min of exposure to air in the reactionchamber divided by the initial geometric (right cylindrical)exposed surface area of the sample, expressed as mg/cm2-h.3.1.
9、3 initial air reactivity, nthe mass loss of the carbonartifact during the first 30 min of exposure to air in the reactionchamber divided by the initial geometric (right cylindrical)exposed surface area of the sample, expressed as mg/cm2-h.3.1.4 total air reactivity, nthe total mass loss of thecarbon
10、 artifact (including dusting) during the total time that thesample is exposed to air (180 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 air reactivity an
11、d dusting aredetermined by passing air at flow rates, giving a standardvelocity of reactant gas around cylindrically shaped carbonartifacts under nearly isothermal conditions for a specifiedlength of time. The reactivity is determined by continuouslymonitoring the sample mass loss. The dusting term
12、is deter-mined by collecting and determining the mass of carbonparticles that fall off the sample during reaction.5. Significance and Use5.1 The air reactivity rates are used to quantify the tendencyof a carbon artifact to react with air. Carbon consumed by thisunwanted side reaction is unavailable
13、for the primary reactionsof reducing alumina to the primary metal.Air reactivity dustingrate is used by some companies to quantify the tendency of thecoke aggregate or binder coke of a carbon artifact to selectivelyreact with these gases. Preferential attack of the binder coke orcoke aggregate of a
14、carbon artifact by these gases causes somecarbon to fall off or dust, making the carbon unavailable for the1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.05 on Properties of Fuels, Petroleum Co
15、ke and Carbon Material.Current edition approved May 1, 2005. Published June 2005. Originallyapproved in 2000. Last previous edition approved in 2000 as D 655900a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book
16、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 Conshohocken, PA 19428-2959, United States.primary reaction of reducing alumina and, more importantly,reducing the efficiency o
17、f the aluminum reduction cell.5.2 Comparison of air reactivity and dusting rates is usefulin selecting raw materials for the manufacture of commercialanodes for specific smelting technologies in the aluminumreduction industry.5.3 Air reactivity rates are used for evaluating effectivenessand benefici
18、ation processes or for research purposes.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 chemicalp
19、roperties inherent to the apparatus (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
20、100-mm region centeredon the specimen. 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
21、within the reaction chambernear the surface of the test sample to allow the furnacecontroller to adjust to the exothermic reaction that occursduring the air reactivity test. The control thermocouple shall bepositioned 4 6 1 mm from the side sample surface andcentered vertically within 5 mm of the ce
22、nter. The furnace shallbe large enough to accept the reaction chamber.6.1.2 Reaction Chamber, consisting of a vertical tube con-structed of a material capable of withstanding the temperatureof the reaction with sufficient inside diameter (ID) to accept thesample and sample holder while not affecting
23、 the gas flow toand from the sample (100 6 25-mm ID is recommended). Thereaction chamber is to be constructed with a dust collection cupat the bottom, which is removable and capable of capturing allthe dust that falls off the sample during the test. The mostcommon materials of construction are quart
24、z and Inconel.6.1.3 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 the sample, limit the gas ac
25、cessible surface area ofthe test sample, or interfere with the free fall of dust from thesample. A typical sample holder is illustrated in Fig. 2.6.1.4 Gas Preheat Tube, extending into the first heat zone ofthe reaction chamber to preheat the gases prior to entering thereaction chamber. The length a
26、nd diameter of the tube can varyas long as the gases exiting the tube are the same temperatureFIG. 1 Typical Air Reactivity ApparatusD 6559 00a (2005)2as the reaction chamber. The inlet gas shall exit the preheattube downward to prevent channeling of the gas through thereaction chamber and to preven
27、t plugging of the preheat tubewith carbon dust.6.1.5 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.6.1.6 Gas Flow Meter, capable of monitoring the gas flowrate into the reacti
28、on chamber. All gas flow rates are to bemaintained at the rate determined for the particular testapparatus.6.1.7 Needle Valve, to make fine adjustments to the gas flowrate.6.1.8 Pressure Reducing Valve, to reduce the pressure of thecompressed gases to near atmospheric pressure prior to enter-ing the
29、 gas flow meter through the needle valve.6.1.9 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 of the internalreaction chamber to be
30、 of value.6.1.10 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.6.1.11 Optional Equipment, including but not limited to,automatic control devices, multichannel line
31、 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 Nitrogen99.95 %.7.1.2 Airless than 0.1 % moistu
32、re.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 the cylinder to accommodate a hanger
33、.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 The sample shall be made free of loose carbon dust
34、andimpurities 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 the specimen. The length to be
35、 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 sheath with probes located at the
36、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 located.9.1.2 The center thermo
37、couple is connected to the maincontroller setting, that is, 525C for air reactivity.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 4 h for furnace to reach equil
38、ibrium 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. Reactivities determinedwith this test
39、 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 flow rate for othergeometries is
40、determined by multiplying the reference flow rate(250 L/h) by the ratio of annular area of the system to theFIG. 2 Typical Sample HolderD 6559 00a (2005)3annular area of the reference system. For example, a 75-mm IDtube with 50.8-mm samples would have a flow rate calculatedby:Ratio 5 (1)FTube ID2 Sa
41、mple 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 525 6 2C for air reactivity.10.2 Purge the reaction chamber with nitrogen at the flowrate determined in 9.2.10.3 Weigh and record the mass of th
42、e 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 sample in the sample holder
43、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 air after 30 min in the nitrogen preheat, and
44、maintain 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 air reactivity is 3 h(180 min).10.10 Remove the sample from the reaction chamber assoon as possible after the test time has expired as the dustingparameter
45、 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 in a desiccator until cool
46、.10.12 Weigh the dust collected in the dust collection cup,and record as Wd.11. Calculation11.1 Calculate exposed surface area of the shaped sample asfollows:A 5 Area of (3)circumference 1 top and bottom surfaces center hole!,orA 5Hpdsh 12p4ds2 dh2!J/100 (4)where:A = exposed surface area, cm2,ds= sa
47、mple diameter, mm,dh= diameter of central hole (if any), mm, andh = sample height, mm.11.2 Calculate total air reactivity rate (TRa) as follows:TRa51000Wi Wf!3A(5)where:TRa= total air reactivity rate, mg/cm2-h,Wi= initial sample weight, g, andWf= final sample weight, g.11.3 Calculate initial air rea
48、ctivity rate (IRa) as follows:IRa52000Wi W30!A(6)where:IRa= initial air reactivity rate, mg/cm2-h, andW30= sample weight after 30 min of test, g.11.4 Calculate final air reactivity rate (FRa) as follows:FRa52000W150 Wf!A(7)where:FRa= final air reactivity rate, mg/cm2-h, andW150= sample weight after
49、150 min of test, g.11.5 Calculate air dusting rate (DRa) as follows:DRa51000Wd3A(8)where:DRa= dusting rate during 3 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 reproducibility are depend
