1、Designation: D6559 00a (Reapproved 2016)1Standard Test Method forDetermination of Thermogravimetric (TGA) Air Reactivity ofBaked Carbon Anodes and Cathode Blocks1This standard is issued under the fixed designation D6559; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTESI units formatting was corrected editorially in May 2016.1. Scope1.1 This
3、test method covers the thermogravimetric (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 o
4、f construction, and procedures for 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 correlata
5、ble.1.2 The values stated in SI 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
6、appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D6353 Guide for Sampling Plan and Core Sampling forPrebaked Anodes Used in Aluminum ProductionD6354 Guide for Sampling Plan and Core Sampling of
7、Carbon Cathode Blocks Used in Aluminum ProductionE691 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 reac
8、tion chamber and is collected 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 sampl
9、e, expressed as milligramsper centimetre squared per hour.3.1.3 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 milligra
10、msper centimetre squared per hour.3.1.4 total air reactivity, nthe total mass loss of the carbonartifact (including dusting) during the total time that the sampleis exposed to air (180 min) in the reaction chamber divided bythe initial geometric (right cylindrical) exposed surface area ofthe sample,
11、 expressed as milligrams per centimetre squared perhour.4. Summary of Test Method4.1 Initial, final, and total air reactivity and dusting aredetermined by passing air at flow rates, giving a standardvelocity of reactant gas around cylindrically shaped carbonartifacts under nearly isothermal conditio
12、ns for a specifiedlength of time. The reactivity is determined by continuouslymonitoring the sample mass loss. The dusting term 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 us
13、ed to quantify the tendencyof a carbon artifact to react with air. Carbon consumed by thisunwanted side reaction is unavailable 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 bind
14、er coke of a carbon artifact to selectivelyreact with these gases. Preferential attack of the binder coke or1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility ofSubcommittee D02.05 on Properties of Fuel
15、s, Petroleum Coke and Carbon Material.Current edition approved April 1, 2016. Published May 2016. Originallyapproved in 2000. Last previous edition approved in 2010 as D6559 00a (2010).DOI: 10.1520/D6559-00AR16E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
16、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1coke aggregate of a carbon artifa
17、ct by these gases causes somecarbon to fall off or dust, making the carbon unavailable for theprimary reaction of reducing alumina and, more importantly,reducing the efficiency of the aluminum reduction cell.5.2 Comparison of air reactivity and dusting rates is usefulin selecting raw materials for t
18、he manufacture of commercialanodes for specific smelting technologies in the aluminumreduction industry.5.3 Air reactivity rates are used for evaluating effectivenessand beneficiation processes or for research purposes.6. Apparatus6.1 The apparatus to be used should be as simple as possibleand be co
19、mmensurate 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 apparatus (such as gas diffusionpatterns, gas temperature, exposed sample surface area, and sofo
20、rth). 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 62 C in the 100 mm region centeredon the specimen. The example apparatus of Fig. 1 employs athree zone heating element and associated
21、 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 the surface of the test sample to allow the furnacecontroller to adjust to the exothermic
22、 reaction that occursduring the air reactivity test. The control thermocouple shall bepositioned 4 mm 6 1 mm from the side sample surface andcentered vertically within 5 mm of the center. The furnace shallbe large enough to accept the reaction chamber.6.1.2 Reaction Chamber, consisting of a vertical
23、 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 the gas flow toand from the sample (100 mm 6 25 mm ID is recommended).The reaction chamber is to be constructed with
24、a dust collec-tion cup at the bottom, which is removable and capable ofcapturing all the dust that falls off the sample during the test.The most common materials of construction are quartz andInconel.6.1.3 Sample Holders, capable of supporting the sample inthe reaction chamber for the duration of th
25、e 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 accessible surface area ofthe test sample, or interfere with the free fall of dust from thesample. A typical sample
26、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 and diameter of the tube can varyas long as the gases exiting the tube are the same temperatureas the reaction cham
27、ber. The inlet gas shall exit the preheatFIG. 1 Typical Air Reactivity ApparatusD6559 00a (2016)12tube downward to prevent channeling of the gas through thereaction chamber and to prevent plugging of the preheat tubewith carbon dust.6.1.5 Balance, capable of measuring the weight of thesample and sam
28、ple 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 reaction chamber. All gas flow rates are to bemaintained at the rate determined for the particular testapparatus.6.1.7 N
29、eedle 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 gas flow meter through the needle valve.6.1.9 Thermocouple(s), inserted into the reaction chamberto calibrate the
30、 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 of value.6.1.10 Calipers, or other suitable device, capable of mea-suring to within 0.01 mm for determining the s
31、ample 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 selector, andpersonal computer to automate data gathering, manipulation,reporting, and storage.7. Reagents7.1 Pur
32、ity 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 % moisture.8. Sampling8.1 Shape the carbon specimen by coring and cutting ormachining to a right cylindrical geometry, 50
33、mm 6 1.0 mm inlength and 50 mm 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.The shaped specimen is to be smooth and free of visible cracksand gouges. Sampling plans for anodes and cat
34、hode blocksgiven in Guides D6353 and D6354 may be used if desired.8.2 Dry the shaped specimen in an oven at 105 C 6 5Cto constant weight.8.3 The sample shall be made free of loose carbon dust andimpurities from the shaping process by blowing with dry air.9. Calibration9.1 The purpose of this procedu
35、re 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 calibrated is a 100 mm(4 in.) zone.NOTE 1For single zone furnaces, the calibration probe shall be placedin
36、center of where sample will be placed and confirm that the 100 mmzone is within 62 C.9.1.1 Insert a multiprobe thermocouple (for example, threecouples in same sheath with probes located at the tip and at50 mm and 100 mm (2 in. and 4 in.) above the tip, or a packetof thermocouples with tips located a
37、t 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 thermocouple is connected to the maincontroller setting, that is, 525 C for air reactivity.9.1.3 Connect t
38、he 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 equilibrium undernitrogen purge (rate per 9.2).9.1.5 Adjust zones until all three (3) temperature indica
39、torsare 62 C.9.2 Gas Flow Rates, for this test are based on 250 Lh 65 Lh (ambient temperature) for a sample diameter of 50 mmand a reaction tube with an ID of 100 mm. Reactivitiesdetermined with this test method are affected by the gasvelocity sweeping the reaction surfaces during the test. Thisrequ
40、ires gas flow rates to be such that the velocity through theannular space between the sample and reaction tube wall isconstant for various size reaction tubes. The proper flow ratefor other geometries is determined by multiplying the referenceflow rate (250 Lh) by the ratio of annular area of the sy
41、stemFIG. 2 Typical Sample HolderD6559 00a (2016)13to the annular area of the reference system. For example, a75 mm ID tube with 50.8 mm samples would have a flow ratecalculated by:Ratio5 (1)FTube ID22 Sample OD2Ref Tube ID22 Ref Sample OD2G5F7522 50.8210022 502 G5304475005 0.406Flow Rate 5 250 L/h#0
42、.406# 5 102L/h (2)10. Procedure10.1 Preheat the reactor tube to 525 C 6 2 C for airreactivity.10.2 Purge the reaction chamber with nitrogen at the flowrate determined in 9.2.10.3 Weigh and record the mass of the sample to the nearest0.01 g as Wi.10.4 Measure the sample diameter (ds), sample height (
43、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 and suspending the sampleholder from the balance.10.6 Preheat the sample under nitrogen pu
44、rge 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, andmaintain the flow rate as determined in 9.2.10.9 Record the weight of the sample every min
45、ute 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 will be affected. Exercise care so that the sampledoes not strike the sides of the reacti
46、on 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.10.12 Weigh the dust collected in the dust collection cup,and record as Wd.11. Calculatio
47、n11.1 Calculate exposed surface area of the shaped sample asfollows:A 5 Area of (3)circumference1top and bottom surfaces 2 center hole!,orA 5Hdsh124ds22 dh2!J/100 (4)where:A = exposed surface area, cm2,ds= sample diameter, mm,dh= diameter of central hole (if any), mm, andh = sample height, mm.11.2 C
48、alculate total air reactivity rate (TRa) as follows:TRa51000Wi2 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 reactivity rate (IRa) as follows:IRa52000Wi2 W30!A(6)where:IRa= initial air reactivity rate, m
49、g/cm2-h, andW30= sample weight after 30 min of test, g.11.4 Calculate final air reactivity rate (FRa) as follows:FRa52000W1502 Wf!A(7)where:FRa= final air reactivity rate, mg/cm2-h, andW150= sample weight after 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 mgcm2-h.13. Precision and Bias313.1 PrecisionThe precision was determined by an inter-laborator
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