1、Designation: D 7542 09An American National StandardStandard Test Method forAir Oxidation of Carbon and Graphite in the Kinetic Regime1This standard is issued under the fixed designation D 7542; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、 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.1. Scope1.1 This test method covers the rate of oxidative weight lossper exposed nominal geometric surface
3、area, or per initialweight of machined test specimens of standard size and shape,or both. The test is valid in the temperature range where therate of air oxidation of graphite and manufactured carbon islimited by reaction kinetics.1.2 This test method also provides a standard oxidationtemperature (a
4、s defined in 3.1.7), and the kinetic parameters ofthe oxidation reaction, namely the activation energy and thelogarithm of pre-exponential factor in Arrhenius equation. Thekinetic parameters of Arrhenius equation are calculated fromthe temperature dependence of oxidation rates measured overthe tempe
5、rature range where Arrhenius plots (as defined in3.1.8) are linear, which is defined as the “kinetic” or “chemicalcontrol” oxidation regime. For typical nuclear grade graphitematerials it was found that the practical range of testingtemperatures is from about 500550C up to about 700750C.1.3 The valu
6、es stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 saf
7、ety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 559 Test Method for Bulk Density by Physical Measure-ments of Manufactured Carbon and Graphite ArticlesE 691 Practice for Conducting an Interlaboratory Study
8、toDetermine the Precision of a Test MethodE 898 Test Method of Testing Top-Loading, Direct-ReadingLaboratory Scales and BalancesE 1582 Practice for Calibration of Temperature Scale forThermogravimetryE 1970 Practice for Statistical Treatment of Thermoanalyti-cal Data3. Terminology3.1 Definitions:3.1
9、.1 Definitions are ordered by oxidation rates first, fol-lowed by activation energy as calculated from oxidation rates.3.1.2 area-normalized oxidation rate (ORa)rate of weightloss due to oxidation of a machined test specimen at a giventemperature, divided by the nominal geometric surface area ofthe
10、specimen.3.1.2.1 DiscussionThe rate of weight loss is determinedby a linear fit of the weight loss plotted against time in therange from 5% to 10% loss of original specimen weight. Theunits of area-normalized oxidation rate, ORa,aregh-1m-2.3.1.3 weight-normalized oxidation rate (ORw)rate ofweight lo
11、ss due to oxidation of a machined specimen at a giventemperature, divided by the initial weight of the specimen.3.1.3.1 DiscussionThe rate of weight loss is determinedby a linear fit of the weight loss plotted against time in therange from 5% to 10% loss of original specimen weight. Theunits of weig
12、ht-normalized oxidation rate, ORware:goxidized!# gspecimen!#21h21or, equivalent, h21! (1)3.1.4 nominal geometric surface areaexposed area (A)ofthe test specimen determined by measuring its diameter (D)and height (H) before testing and using the formula:A 5 2pD2/4 1pDH (2)The units of nominal geometr
13、ic surface area are m2.3.1.5 weight-normalized standard oxidation rate (SORw)value of weight-normalized oxidation rate corresponding to 1%weight loss in 24 h (equivalent to SORw= 4.17 3 10-4gg-1h-1).3.1.6 area-normalized standard oxidation rate (SORa)value of area normalized oxidation rate correspon
14、ding to 1%weight loss in 24 h. Area-normalized standard oxidation rate,SORa, depends on the initial specimen density. For carbon and1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.F0 on Manufact
15、ured Carbon and Graphite Products.Current edition approved June 15, 2009. Published July 2009.2For 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
16、 Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.graphite samples (density 1.2 2.2 g cm-3) SORavariesbetween 2 and4gh-1m-2.3.1.7 standard oxidation temperature (SOT)temperaturein degrees Celsius at whi
17、ch a sample would reach the standardoxidation rate, that is, it would lose by oxidation 1% of itsinitial weight in 24 h.3.1.7.1 DiscussionIn this procedure, SOT is estimated byplotting the decimal logarithm of oxidation rate data deter-mined at several temperatures against the reciprocal of theabsol
18、ute temperature (in Kelvin) of the measurement. The plotshould yield a straight line. The temperature at which the linepredicts a rate corresponding to 1% weight loss in 24 h(equivalent to SORw= 4.17 3 10-4gg-1h-1) is the standardoxidation temperature (SOT).3.1.8 activation energy (Ea)measure of tem
19、perature ef-fects on the rate of oxidation in the kinetic, or chemical control,regime. Activation energy is calculated from the Arrheniusequation:OR 5 Z exp 2Ea/RT! (3)where:OR = oxidation rate,R = 8.314 J mole-1K-1is the universal gas constant,T = absolute temperature (in Kelvin), andZ = pre-expone
20、ntial factor.The activation energy and pre-exponential factor are calculatedfrom linearized form of Arrhenius equation, that is, from theslope and intercept of the linear plot of the logarithm ofoxidation rate versus the inverse of absolute temperature (1/T):log10OR! 5 log10Z Ea/ 2.303 RT! (4)Activa
21、tion energy is expressed in units of kJ/mol. Pre-exponential factor is expressed in the same units as theoxidation rates, namely g h-1m-2(for Zacalculated fromarea-normalized oxidation rates, ORa)orgg-1h-1(for Zwcalculated from weight-normalized oxidation rates, ORw).4. Summary of Test Method4.1 Thi
22、s test method provides the rate of oxidation in air ofcylindrical test specimens with standard size, machined ofcarbon and graphite. During tests, the specimens hang freelyfrom a continuously recording balance in a stream of dry airpreheated at a preselected test temperature. The nominalgeometrical
23、surface area of the specimen is determined beforetesting. The linear rate of weight loss between 5% and 10% ofthe specimens initial weight is determined during exposure.Experience has shown that this is the most linear part of thecurve because weight loss below 5% of the specimen startingweight incl
24、udes an induction period where reactive surface iscreated. For weight losses above 10% of the specimen startingweight, the sample dimensions become significantly distorted.The area-normalized oxidation rate (ORa) is calculated bydividing the rate of weight loss by the original nominalgeometric surfa
25、ce area of the specimen. The result is reportedingh-1m-2. The weight-normalized oxidation rate (ORw)iscalculated by dividing the rate of weight loss by the originalweight of the specimen. The result is reported in g g-1h-1. Theresults can be used to determine relative service life of samplesin a ser
26、ies, at a preselected temperature.4.2 In order to calculate the kinetic parameters of theoxidation reaction and the standard oxidation temperature, theprocedure is repeated with fresh specimens for a total of fourtemperatures. An Arrhenius plot is obtained as explained in3.1.8. Only those data point
27、s in the linear range of theArrhenius plot should be used for calculation of slope andintercept. If deviation from linearity of Arrhenius plots isobserved at high temperatures for certain materials, the dataoutside the linear segment should not be used, and moreoxidation rate measurements should be
28、performed at lowertemperatures. For typical nuclear graphite materials it wasfound that the practical range of testing temperatures is fromabout 500550C up to about 700750C.5. Significance and Use5.1 This test method can be used to measure the rate ofoxidation for various grades of manufactured carb
29、on andgraphite in standard conditions, and can be used for qualitycontrol purposes.5.2 This test method also provides kinetic parameters (ac-tivation energy and logarithm of pre-exponential factor) for theoxidation reaction, and a standard oxidation temperature. Theresults uniquely characterize the
30、effect of temperature onoxidation rates in air, and the oxidation resistance of machinedcarbon or graphite specimens with standard size and shape, inthe kinetic, or chemically controlled, oxidation regime. Thisinformation is useful for discrimination between materialgrades with different impurity le
31、vels, grain size, pore structure,degree of graphitization, or antioxidation treatments, or acombination thereof.5.3 Accurately determined kinetic parameters, like activa-tion energy and logarithm of pre-exponential factor, can beused for prediction of oxidation rates in air as a function oftemperatu
32、re in conditions similar to those of this test method.However, extrapolation of such predictions outside the tem-perature range where Arrhenius plots are linear (outside thekinetic or chemically controlled regime of oxidation) should bemade with caution. In conditions where oxidation rates becomecon
33、trolled by a mechanism other than chemical reactions, suchas in-pore diffusion or boundary transport of the oxidant gas,prediction of oxidation rates using kinetic parameters deter-mined with this test method may produce overestimatedresults.6. Interferences6.1 Specimens shall not be contaminated du
34、ring handling.They should be machined without oil, using diamond orcarbide tools, and handled with cotton gloves.6.2 The specimen and the air supply to the furnace shall befree of moisture. A desiccant column shall be used on the airsupply line.7. Apparatus7.1 Oxidation Apparatus, Shown schematicall
35、y in Fig. 1and consisting of the following:7.1.1 Vertical Tube FurnaceCapable of obtaining 900C.A three-zone furnace with proportionalintegralderivative(PID) controllers is recommended. Temperature control accu-racy should be 62C. The temperature of each zone should beD7542092independently controlle
36、d by its thermocouple. A separate testtemperature thermocouple should also be used; it is recom-mended that the test temperature thermocouple is located in thegas stream below the sample within maximum 5 mm of it. Itshould indicate the temperature of the gas stream just beforethe sample (sample temp
37、erature). Safety interlocks with ther-mocouples placed on the outside of the pipe are recommendedfor each zone.7.1.2 Oxidation Resistant Furnace TubeSuch as Inconel3212 in. schedule 40 pipe (7.30 cm outer diameter; 6.27 cm innerdiameter) should be used. Tubes of alumina or quartz withequivalent inne
38、r diameter may also be used. It is recommendedthat the ends extending from the furnace, especially the top endof the tube, are cooled by water circulating through coppertubing wrapped around the furnace tube (see Fig. 2).7.1.3 Top Cover BlockManufactured from a refractorymaterial, such as boron nitr
39、ide, and should be used as thermalshield protection for the analytical balance (Fig. 3).Alternately,a grooved copper plate can be used, having a copper tubethreaded through the grooves for water circulation. The role ofthermal shield is to ensure that the analytical balance placed ontop of the verti
40、cal furnace is maintained as constant tempera-ture, as close as possible to room temperature, as required forproper operation. The same effect can be obtained by allowingsufficient air gap between the top end of the furnace tube andthe analytical scale, and by removing the hot gases comingfrom the f
41、urnace tube through a snorkel connected to the localventilation system.7.1.4 Platinum Wire and Platinum BasketFor holdingsuspended specimen (Fig. 4).3Inconel is a trademark of Special Metals Corporation. The sole source of supplyof the apparatus known to the committee at this time is Special Metals
42、Corporation,4317 Middle Settlement Rd., New Hartford, NY 13413-5392. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.
43、FIG. 1 Oxidation ApparatusD75420937.2 Analytical BalanceWith weigh-below port feature, atleast 200-g capacity, 60.001 g resolution.7.3 Air Flow Meter0 to 10 L/min, 65% full-scale accu-racy.7.4 Nitrogen Flow Meter0 to 10 L/min, 65% full-scaleaccuracy.7.5 DesiccatorCharged with indicating desiccant fo
44、r stor-age of conditioned specimens before use.FIG. 2 Tube FurnaceD75420947.6 Cotton GlovesFor handling specimens.8. Reagents and Materials8.1 Alumina or Silica Beads or Spheres, 12 / +32 mesh.8.2 Air Supply, desiccated.8.3 Nitrogen Supply (99.99%), desiccated.8.4 Desiccant Column.9. Hazards9.1 Burn
45、sThe test involves high temperatures. Appropri-ate steps should be taken to avoid contact with hot surfaces.Guarding is recommended.9.2 FireHot surfaces could be a source of ignition.10. Sampling and Test Specimens10.1 At least four test specimens with standard size andshape are required. It is reco
46、mmended to prepare a total of 8 or10 specimens for duplicate measurements at a minimum offour temperatures.10.2 The standard size of test specimens for the oxidationtest is a cylinder with a 25.4-mm diameter and 25.4-mm length.Machining should be done with carbide or diamond tools. Themachining tole
47、rances should be 60.15 mm. Surface finish isnot critical.10.3 Wipe the specimens with lint-free paper to remove dustfrom machining.10.4 Condition the specimens at 110150C for a minimumof 3 h. Remove and cool in a desiccator for a minimum of 30min. Keep specimens in desiccator until ready to perform
48、test.11. Calibration and Standardization11.1 The recommended practice for calibration of tempera-ture scale for thermogravimmetry is Practice E 1582.11.2 The recommended test method for testing top-loading,direct-reading laboratory scales and balances is Test MethodE 898.12. Procedure12.1 Measure th
49、e diameter (D) and height (H)ofthespecimen to the nearest 60.03 mm.12.2 Assemble the furnace as shown in Fig. 1. Charge thebottom of the furnace with about 5-cm layer of alumina orsilica beads to act as a gas distributor.12.3 Hang the wire basket on the weigh-below hook of theanalytical balance. Ensure that the wire is in the middle of thefurnace chamber and does not touch the walls of the furnaceFIG. 3 Top CoverFIG. 4 Platinum Wire BasketD7542095tube. Tare the balance. Remove the wire basket and insert thespecimen. Re-hang the baske
