ASTM E1641-2007 Standard Test Method for Decomposition Kinetics by Thermogravimetry《用热重分析法的分解动力学用标准试验方法》.pdf

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1、Designation: E 1641 07Standard Test Method forDecomposition Kinetics by Thermogravimetry1This standard is issued under the fixed designation E 1641; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numbe

2、r in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 preexpo-nential factor by thermogra

3、vimetry, based on the assumptionthat the decomposition obeys first-order kinetics.1.2 This test method is generally applicable to materialswith well-defined decomposition profiles, namely, a smooth,continuous mass change with a single maximum rate.1.3 This test method is normally applicable to decom

4、posi-tion occurring in the range from 400 to 1300K (100 to 1000C). The temperature range may be extended depending on theinstrumentation used.1.4 Computer or electronic-based instruments, techniques,or data treatment equivalent to this test method may also beused.NOTE 1Users of this test method are

5、expressly advised that all suchinstruments or techniques may not be equivalent. It is the responsibility ofthe user of this test method to determine the necessary equivalency priorto use.1.5 SI units are the standard.1.6 This method is similar to ISO 113582 but differs in itsmathematical treatment.1

6、.7 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 Do

7、cuments2.1 ASTM Standards:2E 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 1142 Terminology Relating to Thermophysical PropertiesE 1582 Practice for Calibration of Temperature Scale forThermogravimetryE 1877 Practice for Calculating Thermal Endurance of Ma-terials from Thermogravimetri

8、c Decomposition Data2.2 Other Standard:3ISO) 113582 Plastics Thermogravimetry (TG) of PolymersPart 2: Determination of Kinetic Parameters3. Terminology3.1 Technical terms used in this test method are defined inTerminologies E 473 and E 1142.4. Summary of Test Method4.1 This test method consists of h

9、eating 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 temperatures forconstant conversion are determined f

10、rom 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. This activation energy may then be used to calculatethermal endurance and an estimate of the l

11、ifetime of thematerial at a certain temperature using Test Method E 1877.5. 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 estimating lifetimes ofmaterials, using Test Method E

12、 1877 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 testmethod includes:6.1.1 A thermobalance, composed of

13、 (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 to1This test method is under the jurisdiction ofA

14、STM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on ThermalTest Methods and Practices.Current edition approved March 1, 2007. Published April 2007. Originallyapproved in 1994. Last previous edition approved in 2004 as E 1641 04.2For referenced ASTM sta

15、ndards, 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.3Available from Available from American National Standards Institute (ANSI),25 W. 43r

16、d St., 4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.continuously measure the specimen mass with a minimumcapacity of 20 mg and a sensitivity of 650 g; and (d) a meansof sustaining the specimen/contain

17、er 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, capable of executing aspecific temperature program by operating the furnace betweenselected temperature limits at a rate of temperature changebetween 1 an

18、d 10 K/min to within 60.1 K/min.6.1.3 A recording device, capable of recording and display-ing any portion (including noise) of the change in mass and anyportion (including noise) of the temperature.6.1.4 Containers (pans, crucibles, and so forth) which areinert to the specimen and which will remain

19、 dimensionallystable over the temperature range from ambient to 900 K.6.2 High-Purity (99.99 %) Nitrogen Supply, for purge gas.NOTE 2Other atmospheres may be used but shall be specified.7. Precautions7.1 It is essential that the samples be representative sincemilligram quantities of specimen are to

20、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, although 20 % is justified in certain c

21、ases. It isstrongly suggested that calculations be made at several differ-ent levels of decomposition, for example, 5, 10, 15, and 20 %.Variations in the results among these determinations couldindicate the inapplicability of one of them. For instance,volatile, low-level impurities would affect the

22、results of thelowest conversion determination more than those at higherconversions. Consistent results for all conversions validate themethod 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 personnel

23、or apparatus.8. Sampling8.1 Powdered or granular specimens, which 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 ava

24、ilable, the specimensshould 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 represe

25、ntative sample forthe 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 9.5. Uniformity in particle

26、size can be achieved, withoutthe loss of volatiles, by using a liquid nitrogen mill to grind the sample toa fine powder. 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

27、 dry gas.8.2 In the absence 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 repor

28、t.8.3 Certain materials require more sophisticated condition-ing, such as maintaining the sample at a specified roomtemperature and relative humidity for an extended period oftime. Such conditioning may be conducted, but proceduraldetails shall be included in the report.9. Procedure9.1 Prepare the t

29、hermogravimetric analyzer 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 aft

30、er temperature calibration.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

31、residual oxygen is removed 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 E 15

32、82 usingthe same heating 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 Place 3 6 1 mg of the specimen under test into a clean,tared instrument specimen holder. Other spe

33、cimen sizes maybe used but shall be indicated in the report.NOTE 6The specimen holder should be tared in the fully assembledsystem, with the purge gas flowing.NOTE 7Powdered or granular specimens should be distributed evenlyover the specimen holder so as to maximize the exposed surface. Aone-grain t

34、hick layer would be optimal.9.6 Equilibrate the specimen at a temperature, in kelvins(K), of ten times the heating rate in kelvins per minute belowthe known decomposition temperature. If the percentage massloss is to be recorded, establish zero percent loss at this time.NOTE 8If zero percent mass lo

35、ss is established at the time at whichthe specimen is placed into the instrument, the specimen mass at theequilibration temperature can be greater than 100 % due to buoyancyeffects. A blank should be run for accurate determination of the buoyancyeffect throughout the temperature range of the experim

36、ent. 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.9.7 Heat the specimen at a constant rate through thedecomposition profile until a constant mass is obtained or thetemperature is well beyond

37、 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.9.8 Once the decomposition of the test specimen is com-plete, cool the instrument to room temperature, remove

38、, clean,E 1641 072and replace the specimen holder, and retare the instrument inpreparation for additional experiments. Use the same specimenholder for the entire series of runs to eliminate buoyancyproblems.9.9 Repeat the procedures described in 9.4-9.8 at threeadditional heating rates covering the

39、range from 1 to 10 K/min.Other heating rates, and more than four, may be used but shallbe noted in the report.NOTE 9The use of heating rates greater than 10 K/min affects both theprecision of the temperature measurement and the kinetics of thedecomposition. Diffusion of volatiles from the sample may

40、 become therate-controlling process at high heating rates.10. Calculation10.1 From each of the thermal curves obtained in 9.5-9.9,determine the absolute temperature at constant conversion, a,for each of the constant conversion values to be used in thecalculations as noted in 7.2. For example, see Fi

41、g. 1. Thetemperature corresponding to other conversion levels (notgreater than 20 %) may be used in the determination, but itmust be noted in the report.NOTE 10These calculations are simplified if the percent mass lossrather than actual mass is recorded on the ordinate.NOTE 11The value is determined

42、 from the difference of the initial andfinal sample conversion, with the initial mass taken as the mass at theequilibration temperature and the final mass taken once the plateau hasbeen reached at the end of weight loss. For example, if the initial mass is100.3 % and the final mass is 80 %, 100 % de

43、composition corresponds to(100.3 to 80.0) or 20.3 % mass loss. Thus, 5 % decomposition occurs at(0.05 3 20.3) or 1.02 % mass loss, which occurs on the ordinate at 99.3 %(100.3 % 1.02 % = 99.28 %).10.2 Plot the logarithm of the heating rate expressed askelvins per minute against the reciprocal of the

44、 absolutetemperature at which the conversion level, selected in 10.1,was reached. A straight line, similar to that in Fig. 2, shouldresult. This test procedure is not applicable if the curve isnonlinear.FIG. 1 Examples of Mass Loss Curves at the Following Heating Rates: 1C/min, 2C/min, 5C/min, 10C/m

45、inFIG. 2 Arrhenius Plot of Heating Rate, Temperature of Constant Conversion DataE 1641 073NOTE 12An apparent nonlinearity may result from erroneous deter-minations. It is recommended that any nonlinear points be repeated forverification.10.3 Using the least-squares method fit a straight line tothese

46、 data without weighing factors, and determine the slopeDlogb!/D1/T!NOTE 13If the values obtained from this test method are to be used inTest Method E 1877, an estimation of the uncertainty for activation energy(E) and preexponential factor (A) is required. These uncertainties may bederived from the

47、uncertainty in the slope value of m = D (log b)/D (1/T).If the calculation tool used to obtain the slope of the straight line providesan estimation of uncertainty in the determined slope (dm), record it.Otherwise, the uncertainty in the slope may be obtained using theprocedure in Appendix X1.10.4 Th

48、e following definitions apply to 10.2-10.9:E = refined Arrhenius activation energy,J/mol,A = pre-exponential factor, min1,R = gas constant, 8.314 J/(molK),D(logb)/D(1/T) = slope of the line obtained in 10.2,b = heating rate, K/min,b8 = heating rate nearest the midpoint of theexperimental heating rat

49、es, K/min,T = temperature (K) at constant conversion,b = approximation derivative from Table 1(use b = 0.457/K on first iteration),a = approximation integral taken from Table1,a = conversion value of decomposition, andTc= temperature for point of constant conver-sion for b8,K.10.5 Calculate an estimation of the activation energy usingEq 1(1, 2),4making use of the value of D(logb)/D(1/T)determined in 10.2 and a value of 0.457/K for b in this firstiteration:E 52R/b!*Dlogb!/D1/T! (1)10.6 Calculate the value for E/RTc, where Tc= the tempera-ture at consta