1、Designation: D6558 00a (Reapproved 2015)1Standard Test Method forDetermination of TGA CO2Reactivity of Baked CarbonAnodes and Cathode Blocks1This standard is issued under the fixed designation D6558; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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 unit formatting was corrected editorially in December 2015.1. Scope1.1 This test method cover
3、s the thermogravimetric (TGA)determination 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, an
4、d 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 correlatable.1.2 The values
5、 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 appro-priate safet
6、y 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 ofCarbon Cathode Blo
7、cks 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, nthat quantity of carbon that falls off thecarbon artifact while in the reaction chamber and
8、is collected inthe container at the 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 asmi
9、lligrams per centimetre squared per hour.3.1.3 initial CO2reactivity, 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 asmilligrams per centimetre
10、squared per hour.3.1.4 total CO2reactivity, nthe total mass loss of thecarbon artifact (including dusting) 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 milli
11、grams percentimetre squared per hour.4. Summary of Test Method4.1 Initial, final, and total CO2reactivity and dusting aredetermined by passing carbon dioxide gas at flow rates givinga standard velocity of reactant gas around cylindrically shapedcarbon artifacts under isothermal conditions for a spec
12、ifiedlength 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 CO2reactivity rates are used to quantify
13、 thetendency of a carbon artifact to react with carbon dioxide.Carbon consumed by these unwanted side reactions is unavail-able for the primary reactions of reducing alumina to theprimary metal. CO2dusting rates are used to quantify thetendency of the coke aggregate or binder coke of a carbonartifac
14、t to selectively react with these gases. Preferential attack1This 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 Fuels, Petroleum Coke and Carbon Material.Current ed
15、ition approved Oct. 1, 2015. Published December 2015. Originallyapproved in 2000. Last previous edition approved in 2010 as D6558 00a (2010).DOI: 10.1520/D6558-00AR15E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu
16、al 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 States1of the binder coke or coke aggregate of a carbon artifact bythese gases cause
17、s 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.5.2 Comparison of CO2reactivity and dusting rates is usefulin selecting raw materials for the manufacture of comm
18、ercialanodes for specific smelting technologies in the aluminumreduction industry.5.3 CO2reactivity rates are used for evaluating effective-ness and beneficiation processes or for research purposes.6. Apparatus6.1 The apparatus to be used should be as simple as possibleand be commensurate with what
19、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 soforth). A typical appar
20、atus 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 controls to accom-p
21、lish 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 exothermic reactions, which occurd
22、uring air reactivity tests, if the furnace is also used for airreactivity testing. The control thermocouple shall be positioned4mm 6 1 mm from the side sample surface and centeredvertically within 5 mm of the center. The furnace shall be largeenough to accept the reaction chamber.6.1.1.1 Reaction Ch
23、amber, consisting of a vertical tubeconstructed of a material capable of withstanding the tempera-ture of the reaction (960 C 6 2 C) with sufficient insidediameter (ID) to accept the sample and sample holder while notaffecting the gas flow to and from the sample (100 mm 625 mm ID is recommended). Th
24、e reaction chamber is to beconstructed with a dust collection cup at the bottom that isremovable and capable of capturing all the dust that falls off thesample during the test. The most common materials of con-struction are quartz and Inconel.6.1.1.2 Sample Holders, capable of supporting the sample
25、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 accessible surface area ofthe test sample, or interfere with the free f
26、all 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 reaction chamber. The length and diameter of the tube canvary as long as the gases exiting the tu
27、be are the sameFIG. 1 Typical CO2Reactivity ApparatusD6558 00a (2015)12temperature as the reaction chamber. The inlet gas shall exit thepreheat tube downward to prevent channeling of the gasthrough the reaction chamber and to prevent plugging of thepreheat tube with carbon dust.6.1.1.4 Balance, capa
28、ble of measuring the mass of thesample and sample holder (a maximum of approximately200 g) continuously throughout the duration of the test to thenearest 0.01 g.6.1.1.5 Gas Flow Meter, capable of monitoring the gas flowrate into the reaction chamber. All gas flow rates are to bemaintained at the rat
29、e 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 atmospheric pressure prior toentering the gas flow meter through the needle valve.6.1.1.8 Thermocoup
30、le(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 of value.6.1.1.9 Calipers, or other suitable device, cap
31、able 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,automatic control devices, multichannel line selector, andpersonal computer to automate data gath
32、ering, 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 Carbon Dioxide99.95 %.8. Sampling8.1 Shape the carbon specimen by coring and
33、cutting ormachining to a right cylindrical geometry, with a length of50 mm 6 1.0 mm and diameter of 50 mm 6 1.0 mm. Mostsample holders require a hole of about 3 mm diameter to bedrilled vertically through the center of the cylinder to accom-modate a hanger. The shaped specimen is to be smooth and fr
34、eeof visible cracks and gouges. Sampling plans for anodes andcathode blocks given in Guides D6353 and D6354 may be usedif desired.8.2 Dry the shaped specimen in an oven at 105 C 6 5Cto constant weight.8.3 Make the sample free of loose carbon dust and impuri-ties from the shaping process by blowing w
35、ith 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 of the zone to be calibratedis 100 mm (4 in.).NOTE 1For
36、single zone furnaces, the calibration probe shall be placedin center of where sample will be placed and confirm that the zone of100 mm 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 i
37、n.) above the tip; or a packetof thermocouples 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 thermocouple is connected to the maincon
38、troller setting, that is, 960 C 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 4 h for furnace to reach equilibrium undernitrogen purge (rate p
39、er 9.2).9.1.5 Adjust zones until all three (3) temperature indicatorsare 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 gas
40、velocity sweeping the reaction surfaces during the test. Thisrequires 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 r
41、eferenceflow rate (250 Lh) by the ratio of annular area of the systemFIG. 2 Typical Sample HolderD6558 00a (2015)13to the annular area of the reference system. For example, a tubewith ID of 75 mm and sample diameter of 50.8 mm wouldhave a flow rate calculated by:Ratio5 (1)FTube ID22 Sample OD2Ref Tu
42、be ID22 Ref Sample OD2G5F7522 50.8210022 502 G5304475005 0.406Flow Rate 5 250 L/h#0.406# 5 102L/h (2)10. Procedure10.1 Preheat the reactor tube to 960 C 6 2 C for CO2reactivity.10.2 Purge the reaction chamber with nitrogen at the flowrate determined in 9.2.10.3 Weigh and record the mass of the sampl
43、e 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 and su
44、spending 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 in the nitrogen preheat, andmaintai
45、n the flow rate as determined in 9.2.10.9 Record the mass 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 expired as the dustingparameter will be a
46、ffected. 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.10.12 Weig
47、h 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)$circumference1top and bottom surfaces 2 center hole!%,orA 5Hdsh124ds22 dh2!J/100 (4)where:A = exposed surface area, cm2,ds= sample di
48、ameter, mm,dh= diameter of central hole (if any), mm, andh = sample height, mm.11.2 Calculate total CO2reactivity rate (TRc) as follows:TRc51000Wi2 Wf!7A(5)where:TRc= total CO2reactivity rate, mg/cm2-h,Wi= initial sample mass, g, andWf= final sample mass, g.11.3 Calculate initial CO2reactivity rate
49、(IRc) as follows:IRc52000Wi2 W30!A(6)where:IRc= initial CO2reactivity rate, mg/cm2-h, andW30= sample mass after 30 min of test, g.11.4 Calculate final CO2reactivity rate (FRc) as follows:FRc52000W3902 Wf!A(7)where:FRc= final CO2reactivity rate, mg/cm2-h, andW390= sample mass 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= mass of dust collected during test, g.12. Report12.1 Report reactivity results to the nearest 0.1 mgcm2-h.13. Precision and Bia
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