ASTM_D_6558_-_00A_2015e1.pdf

Designation:D655800a(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 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 unit formatting was corrected editorially in December 2015.1.Scope1.1 This test method covers 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,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 correlatable.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 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 ofCarbon 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,nthat quantity of carbon that falls off thecarbon artifact while in the reaction chamber and 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 asmilligrams 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 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 milligrams 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 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 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 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 onPetroleum Products,Liquid Fuels,and Lubricantsand is the direct responsibility ofSubcommittee D02.05 on Properties of Fuels,Petroleum Coke and Carbon Material.Current edition 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 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 States1 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.5.2 Comparison of CO2reactivity and dusting rates is usefulin selecting raw material