1、Designation: E1641 15Standard Test Method forDecomposition Kinetics by Thermogravimetry Using theOzawa/Flynn/Wall Method1This standard is issued under the fixed designation E1641; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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 describes the determination of thekinetic parameters, Arrhenius activation energy, and preex
3、po-nential factor by thermogravimetry, based on the assumptionthat the decomposition obeys first-order kineticsusing theOzawa/Flynn/Wall isoconversional method (1, 2).21.2 This test method is generally applicable to materialswith well-defined decomposition profiles, namely, a smooth,continuous mass
4、change with a single maximum rate.1.3 This test method is normally applicable to decomposi-tion occurring in the range from 400 to 1300K (nominally 100to 1000C).The temperature range may be extended dependingon the instrumentation used.1.4 This test method is similar to ISO 11358-2 but differs inits
5、 mathematical treatment.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 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 st
6、andard 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:3E29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE473 Terminology Relating
7、to Thermal Analysis and Rhe-ologyE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1142 Terminology Relating to Thermophysical PropertiesE1582 Practice for Calibration of Temperature Scale forThermogravimetryE1877 Practice for Calculating Thermal Endura
8、nce of Ma-terials from Thermogravimetric Decomposition DataE1970 Practice for Statistical Treatment of ThermoanalyticalDataE2040 Test Method for Mass Scale Calibration of Thermo-gravimetric Analyzers2.2 Other Standard:4ISO 11358-2 Plastics Thermogravimetry (TG) of PolymersPart 2: Determination of Ki
9、netic Parameters3. Terminology3.1 DefinitionsTechnical terms used in this test methodare defined in Terminologies E473 and E1142 and includeactivation energy, Celsius, failure, failure criterion, and ther-mogravimetric analyzer.4. Summary of Test Method4.1 This test method is based upon the general
10、rate equationthat takes the form of:ddT 5 A1 2 ! exp2 E RT# (1)where: = fraction reacted (dimensionless),A = pre-exponential factor (min-1), = heating rate (K/min),E = activation energy (J/mol),R = gas constant (=8.316 J/(mol K),T = absolute temperature (K),exp = Eulers number exponential, andd/dT =
11、 rate of change of with T.4.2 Using the method of Ozawa, Flynn and Wall (1, 2), Eq1 may be solved for activation energy:E 5 R b! log#1T! (2)1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on Calo-rimetry
12、and Mass Loss.Current edition approved March 1, 2015. Published March 2015. Originallyapproved in 1994. Last previous edition approved in 2013 as E1641 13. DOI:10.1520/E1641-15.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standa
13、rds, 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.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor,
14、New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1where:E = the derivative of the Doyle approximation (3) withvalues tabulated in Table 1.4.3 Using a point of constant conversion from a series ofde
15、composition curves obtained at different heat rates,log#1 2 T! is obtained by linear regression.4.4 Assuming an initial value of b50.457, a first approxima-tion of activation energy (E) is obtained using Eq 2.4.5 This approximate activation energy is then used todetermine a new value of b using Tabl
16、e 1.4.6 This iterative process is continued until the value ofactivation energy no longer changes with the next iteration.4.7 For first order reactions (n51), the value of the pre-exponential factor (A) may be determined using Eq 3(4).A 5 2 R E!ln 1 2 #! 10a(3)where:a = the Doyle approximation value
17、 from Table 1.4.8 This test method consists of heating a series of four ormore test specimens, taken from the original sample, each at adifferent heating rate between 1 and 10 K/min, through theirdecomposition region. The specimen mass is recorded continu-ously as a function of temperature. The temp
18、eratures forconstant conversion are determined from the resultant massloss curves.TheArrhenius activation energy is then determinedfrom a plot of the logarithm of heating rate versus thereciprocal of the absolute temperature at constant conversionlevel.4.9 This activation energy may then be used to
19、calculatethermal endurance and an estimate of the lifetime of thematerial at a certain temperature using Test Method E1877.5. Significance and Use5.1 Thermogravimetry provides a rapid method for deter-mining the temperature-decomposition profile of a material.5.2 This test method can be used for est
20、imating lifetimes ofmaterials, using Test Method E1877 provided that a relation-ship has been established between the thermal endurance testresults and actual lifetime tests.6. Apparatus6.1 The essential equipment required to provide the mini-mum thermogravimetric analytical capability of this testm
21、ethod includes:6.1.1 A thermobalance, composed of (a)afurnace toprovide uniform controlled heating of a specimen at a constantrate within the temperature range from ambient to 1300 K; (b)a temperature sensor to provide an indication of the specimen/furnace temperature to 60.1 K; (c)anelectrobalance
22、tocontinuously measure the specimen mass with a minimumcapacity of 20 mg and a sensitivity of 650 g; and (d) a meansof sustaining the specimen/container under atmospheric con-trol of an inert or reactive purge gas of 99.99 % purity at a rateof 20 to 50 6 5 mL/min.6.1.2 A temperature controller, capa
23、ble of executing aspecific temperature program by operating the furnace betweenselected temperature limits at a rate of temperature changebetween 1 and 10 K/min to within 60.1 K/min.NOTE 1The precision of results is strongly dependent upon theprecision of the heating rate; the greater the heating ra
24、te precision, thegreater the precision of results. The precision described here should beconsidered to be the minimum suitable for this test.6.1.3 A data collection device, to provide a means ofacquiring, storing, and displaying measured or calculatedsignals, or both. The minimum output signals requ
25、ired for thistest method are mass, temperature, and time.6.1.4 Containers (pans, crucibles, and so forth) which areinert to the specimen and that will remain dimensionally stableover the temperature range from ambient to 1300 K.TABLE 1 Numerical Integration ConstantsE/RT a b8 5.3699 0.53989 5.8980 0
26、.528110 6.4167 0.518711 6.928 0.51112 7.433 0.50513 7.933 0.50014 8.427 0.49415 8.918 0.49116 9.406 0.48817 9.890 0.48418 10.372 0.48219 10.851 0.47920 11.3277 0.477021 11.803 0.47522 12.276 0.47323 12.747 0.47124 13.217 0.47025 13.686 0.46926 14.153 0.46727 14.619 0.46628 15.084 0.46529 15.547 0.46
27、330 16.0104 0.462931 16.472 0.46232 16.933 0.46133 17.394 0.46134 17.853 0.45935 18.312 0.45936 18.770 0.45837 19.228 0.45838 19.684 0.45639 20.141 0.45640 20.5967 0.455841 21.052 0.45542 21.507 0.45543 21.961 0.45444 22.415 0.45445 22.868 0.45346 23.321 0.45347 23.774 0.45348 24.226 0.45249 24.678
28、0.45250 25.1295 0.451551 25.5806 0.451152 26.0314 0.450853 26.4820 0.450654 26.9323 0.450355 27.3823 0.450056 27.8319 0.449857 28.2814 0.449558 28.7305 0.449159 29.1794 0.448960 29.6281 0.4487E1641 1526.2 High-Purity (99.99 %) Nitrogen Supply, for purge gas.NOTE 2Other atmospheres may be used but sh
29、all be reported.6.3 Auxiliary apparatus considered necessary or useful inconducting this test method include:6.3.1 Cryogenic Mill to grind or mill test specimens to a finepowder at temperatures below 173 K (100C).7. Precautions7.1 It is essential that the samples be representative sincemilligram qua
30、ntities of specimen are to be used.7.2 The value of the calculated activation energy is inde-pendent of reaction order in the early stages of decomposition.This assumption does not hold for the later stages and shall beused with caution. An upper limit of 10 % decomposition issuggested. It is strong
31、ly suggested that calculations be made atseveral different levels of decomposition, for example, 5, 10,15, and 20 %. Variations in the results among these determi-nations could indicate the inapplicability of one of them. Forinstance, volatile, low-level impurities would affect the resultsof the low
32、est conversion determination more than those athigher conversions. Consistent results for all conversionsvalidate the method for the range of conversions examined.7.3 Toxic or corrosive effluents, or both, may be releasedduring the heating process and may be harmful to the personnelor apparatus.8. S
33、ampling8.1 Powdered or granular specimens that have a highsurface-to-volume ratio, are preferred, although films, fibers,and fabrics may be used providing that care is taken to make allof the specimens uniform in size and shape. Under circum-stances in which material parts are available, the specime
34、nsshould be prepared by filing or rasping the part. All specimensshould be mixed thoroughly prior to sampling if possible, andthey should be sampled by removing portions from variousparts of the container. These portions should in turn becombined and mixed well to ensure a representative specimenfor
35、 the determination.NOTE 3Care should be exercised during sample preparation to avoidcontamination.NOTE 4The specimen size and surface-to-volume ratio are known toaffect the results of this test. A narrow range of specimen sizes should beused, as noted in 10.1. Uniformity in particle size can be achi
36、eved, withoutthe loss of volatiles, by using a cryogenic mill to grind the sample to a finepowder. To prevent the condensation of moisture, the mill should beopened only after returning fully to ambient temperature, or the operationshould be performed in a glove box filled with dry gas.8.2 In the ab
37、sence of other information, the samples areassumed to be analyzed as received except for the mechanicaltreatment noted in 8.1. If some heat treatment, such as drying,is applied to the sample prior to analysis, this treatment and anyresulting mass loss must be noted in the report.8.3 Certain material
38、s require more sophisticatedconditioning, such as maintaining the sample at a specifiedroom temperature and relative humidity for an extended periodof time. Such conditioning may be conducted, but proceduraldetails shall be included in the report.9. Calibration9.1 Prepare the thermogravimetric analy
39、zer using any pro-cedures described in the manufacturers Operations manual.9.2 Place the temperature sensor within 2 mm of the outsideof the specimen holder. Care must be taken to ensure that thespecimen holder is not touched in any way by the sensor andthat it is not moved after temperature calibra
40、tion.9.3 Maintain a constant flow rate of purge gas in the rangefrom 20 to 50 mL/min throughout the experiment.NOTE 5In the case of samples that may be sensitive to oxidativedegradation, it will be necessary to maintain inert gas purging for a timesufficient to ensure that all residual oxygen is rem
41、oved from the systemprior to the start of the temperature program. It may be necessary toevacuate the system prior to initiating inert gas purging for someinstruments.9.4 Calibrate the instrument furnace temperature in accor-dance with the calibration procedure in Practice E1582 usingthe same heatin
42、g rate, purge gas, and flow rate to be used forthe specimens. The temperature calibration shall be performedboth prior to every change in heating rate and at that heatingrate.9.5 Calibrate the mass signal using Test Method E2040.10. Procedure10.1 Place 3 6 1 mg of the specimen under test into a clea
43、n,tared instrument specimen holder.NOTE 6Other specimen sizes may be used but shall be indicated in thereport.NOTE 7The specimen holder should be tared in the fully assembledsystem, with the purge gas flowing.NOTE 8Powdered or granular specimens should be distributed evenlyover the specimen holder s
44、o as to maximize the exposed surface. Aone-grain thick layer would be optimal.10.2 Select an equilibrium temperature based upon theheating rate and known decomposition temperature of thespecimen, where the equilibrium temperature equals the de-composition temperature (10 min heating rate). If theper
45、centage mass loss is to be recorded, establish zero percentloss at this time.NOTE 9If zero percent mass loss is established at the time at which thespecimen is placed into the instrument, the specimen mass at theequilibration temperature can be greater than 100 % due to buoyancyeffects. A blank shou
46、ld be run for accurate determination of the buoyancyeffect throughout the temperature range of the experiment. The blank canbe a piece of platinum of approximately the same volume as the specimen.The balance drift at any temperature can be determined in this manner.10.3 Heat the specimen at a consta
47、nt rate through thedecomposition profile until a constant mass is obtained or thetemperature is well beyond the useful temperature range of thematerial tested. Record the accompanying thermal curve, withmass or percentage mass loss displayed on the ordinate andspecimen temperature on the abscissa.10
48、.4 Once the decomposition of the test specimen iscomplete, cool the instrument to room temperature, remove,clean, and replace the specimen holder, and re-tare the instru-ment in preparation for additional experiments. Use the samespecimen holder for the entire series of runs to eliminatebuoyancy pro
49、blems.E1641 15310.5 Repeat the procedures described in 10.1 10.4 at threeadditional heating rates covering the range from 1 to 10 K/min.NOTE 10Other heating rates, and more than four, may be used butshall be noted in the report.NOTE 11The use of heating rates greater than 10 K/min affects boththe precision of the temperature measurement and the kinetics of thedecomposition. Diffusion of volatiles from the sample may become therate-controlling process at high heating rates.11. Calculation11.1 Select some mass loss (
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