1、Designation: D7542 15 An American National StandardStandard Test Method forAir Oxidation of Carbon and Graphite in the Kinetic Regime1This standard is issued under the fixed designation D7542; 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. Scope*1.1 This test method recommends a standard procedure formeasuring oxidation rates in air of various
3、 grades of nucleargraphite and/or manufactured carbon. Following the standardprocedure recommended here, one can obtain kinetic param-eters that characterize the oxidation resistance of tested mate-rials and that can be used to for materials selection andqualification, and for quality control purpos
4、es in the fabricationprocess.1.2 This test method covers the rate of oxidative weight lossper exposed nominal geometric surface 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 graph
5、ite and manufactured carbon islimited by reaction kinetics.1.3 This test method also provides a standard oxidationtemperature (as 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. The
6、kinetic parameters of Arrhenius equation are calculated fromthe temperature dependence of oxidation rates measured overthe temperature 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 graph
7、itematerials it was found that the practical range of testingtemperatures is from about 500 C to 550 C up to about700 C to 750 C.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address a
8、ll 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:2C559 Test Method fo
9、r Bulk Density by Physical Measure-ments of Manufactured Carbon and Graphite ArticlesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE898 Test Method of Testing Top-Loading, Direct-ReadingLaboratory Scales and BalancesE1582 Practice for Calibration of
10、Temperature Scale forThermogravimetryE1970 Practice for Statistical Treatment of ThermoanalyticalData3. Terminology3.1 Definitions:3.1.1 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
11、of weightloss due to oxidation of a machined test specimen at a giventemperature, divided by the nominal geometric surface area ofthe 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
12、specimen weight. Theunits of area-normalized oxidation rate, ORa,aregh-1m-2.3.1.3 weight-normalized oxidation rate (ORw)rate ofweight loss 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 determi
13、nedby a linear fit of the weight loss plotted against time in therange from 5 % to 10 % loss of original specimen weight. Theunits of weight-normalized oxidation rate, ORware:goxidized!#gspecimen!#21h21or, equivalent, h21! (1)3.1.4 nominal geometric surface areaexposed area (A)ofthe test specimen de
14、termined by measuring its diameter (D)and height (H) before testing and using the formula:A 5 2D2/41DH (2)The units of nominal geometric surface area are m2.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsi
15、bility ofSubcommittee D02.F0 on Manufactured Carbon and Graphite Products.Current edition approved Oct. 1, 2015. Published November 2015. Originallyapproved in 2009. Last previous edition approved in 2009 as D7542 09. DOI:10.1520/D7542-15.2For referenced ASTM standards, visit the ASTM website, www.a
16、stm.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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO B
17、ox C700, West Conshohocken, PA 19428-2959. United States13.1.5 weight-normalized standard oxidation rate (SORw)value of weight-normalized oxidation rate corresponding to1 % weight loss in 24 h (equivalent to SORw= 4.17 10-4gg-1h-1).3.1.6 area-normalized standard oxidation rate (SORa)value of area no
18、rmalized oxidation rate corresponding to 1 %weight loss in 24 h. Area-normalized standard oxidation rate,SORa, depends on the initial specimen density. For carbon andgraphite samples (density 1.2 to 2.2 g cm-3) SORavariesbetween 2 and4gh-1m-2.3.1.7 standard oxidation temperature (SOT)temperaturein d
19、egrees Celsius at which 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
20、reciprocal of theabsolute 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=4.1710-4gg-1h-1) is the standardoxidation temperature (SOT).3.1.8 activation energy
21、 (Ea)measure of temperature ef-fects on the rate of oxidation in the kinetic, or chemical control,regime. Activation energy is calculated from the Arrheniusequation:OR 5 Zexp2Ea/RT! (3)where:OR = oxidation rate,R = 8.314 J mole-1K-1is the universal gas constant,T = absolute temperature (in Kelvin),
22、andZ = pre-exponential factor.The activation energy and pre-exponential factor are calcu-lated from linearized form of Arrhenius equation, that is, fromthe slope and intercept of the linear plot of the logarithm ofoxidation rate versus the inverse of absolute temperature (1/T):log10OR! 5 log10Z 2 Ea
23、/2.303 RT! (4)Activation energy is expressed in units of kJ/mol. Pre-exponential factor is expressed in the same units as the oxi-dation rates, namely g h-1m-2(for Zacalculated from area-normalized oxidation rates, ORa)orgg-1h-1(for Zwcalculated from weight-normalized oxidation rates, ORw).4. Summar
24、y of Test Method4.1 This 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.
25、The nominalgeometrical 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 sp
26、ecimen startingweight includes 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 orig
27、inal nominalgeometric surface 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 serv
28、ice life of samplesin a series, 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
29、.1.8. Only those data points 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 r
30、ate measurements should be performed at lowertemperatures. For typical nuclear graphite materials it wasfound that the practical range of testing temperatures is fromabout 500 C to 550 C up to about 700 C to 750 C.5. Significance and Use5.1 This test method can be used to measure the rate ofoxidatio
31、n for various grades of manufactured carbon andgraphite in standard conditions, and can be used for qualitycontrol purposes.5.2 The following conditions are standardized in this testmethod: size and shape of the graphite specimens; theirplacement in the vertical furnace with upwards air flow; themet
32、hod for continuous weight variation measurement using ananalytical scale with under-the-scale port; the air flow rate,which is high enough to ensure that oxidation is not oxygen-starved at the highest temperature used; the initial and finalpoints on the weight loss curve used for calculation ofoxida
33、tion rate.5.3 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 effect of temperature onoxidation rates in air, and the oxidation resista
34、nce 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 levels, grain size, pore structure,degree of graphitization, or antioxidati
35、on treatments, or acombination thereof.5.4 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 oftemperature in conditions similar to those of this test method.However, extrapolat
36、ion of such predictions outside the tem-perature range where Arrhenius plots are linear (outside thekinetic or chemically controlled regime of oxidation) should bemade with extreme caution. In conditions where oxidationrates become controlled by a mechanism other than chemicalreactions, such as in-p
37、ore diffusion or boundary transport of theD7542 152oxidant gas, prediction of oxidation rates using kinetic param-eters determined with this test method will produce overesti-mated results.6. Interferences6.1 Specimens shall not be contaminated during handling.They should be machined without oil, us
38、ing 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 schematically in Fig. 1and consisting of the following:7.1.1 Vert
39、ical Tube FurnaceCapable of obtaining 900 C.A three-zone furnace with proportionalintegralderivative(PID) controllers is recommended. Temperature control accu-racy should be 62 C. The temperature of each zone should beindependently controlled by its thermocouple. A separatesample temperature thermoc
40、ouple should also be used; it isrecommended that the sample temperature thermocouple islocated in the gas stream below the sample within maximum5 mm of it. It should indicate the temperature of the gas streamjust before the sample (sample temperature). Safety interlockswith thermocouples placed on t
41、he outside of the pipe arerecommended for each zone.7.1.2 Oxidation Resistant Furnace TubeSuch as Inconel3212 in. schedule 40 pipe (7.30 cm outer diameter; 6.27 cminner diameter) should be used. Tubes of alumina or quartzwith equivalent inner diameter may also be used. It is recom-mended that the en
42、ds extending from the furnace, especially3Inconel is a trademark of Special Metals Corporation. The sole source of supplyof the apparatus known to the committee at this time is Special Metals Corporation,4317 Middle Settlement Rd., New Hartford, NY 13413-5392. If you are aware ofalternative supplier
43、s, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.FIG. 1 Oxidation ApparatusD7542 153the top end of the tube, are cooled by water circulating throughcopper tu
44、bing wrapped around the furnace tube (see Fig. 2).7.1.3 Top Cover BlockManufactured from a refractorymaterial, such as boron nitride, 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 throug
45、h the grooves for water circulation. The role ofthermal shield is to ensure that the analytical balance placed ontop of the vertical furnace is maintained as constanttemperature, as close as possible to room temperature, asrequired for proper operation. The same effect can be obtainedby allowing suf
46、ficient air gap between the top end of thefurnace tube and the analytical scale, and by removing the hotgases coming from the furnace tube through a snorkel con-nected to the local ventilation system.FIG. 2 Tube FurnaceD7542 1547.1.4 Platinum Wire and Platinum BasketFor holdingsuspended specimen (Fi
47、g. 4).7.2 Analytical BalanceWith weigh-below port feature, atleast 200 g capacity, 60.001 g resolution.7.3 Air Flow Meter0 Lmin to 10 Lmin, 65 % full-scaleaccuracy.7.4 Nitrogen Flow Meter0 Lmin to 10 Lmin, 65%full-scale accuracy.7.5 DesiccatorCharged with indicating desiccant for stor-age of conditi
48、oned specimens before use.7.6 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 BurnsThe test involves high temperatures. Appropri-
49、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 recommended 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 too
