1、Designation: E698 11Standard Test Method forArrhenius Kinetic Constants for Thermally UnstableMaterials Using Differential Scanning Calorimetry and theFlynn/Wall/Ozawa Method1This standard is issued under the fixed designation E698; the number immediately following the designation indicates the year
2、 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.INTRODUCTIONThe kinetics of exothermic reactions are important in as
3、sessing the potential of materials andsystems for thermal explosion. This test method provides a means for determining Arrheniusactivation energies and pre-exponential factors using differential thermal methods. This test method isone of several test methods being developed by ASTM Committee E27 for
4、 chemical reactions. Thistest method is to be used in conjunction with other tests to characterize the hazard potential ofchemicals.1. Scope1.1 This test method covers the determination of the overallkinetic parameters for exothermic reactions using the Flynn/Wall/Ozawa method and differential scann
5、ing calorimetry.1.2 This technique is applicable to reactions whose behaviorcan be described by theArrhenius equation and the general ratelaw.1.3 LimitationsThere are cases where this technique is notapplicable. Limitations may be indicated by curves departingfrom a straight line (see 11.2) or the i
6、sothermal aging test notclosely agreeing with the results predicted by the calculatedkinetic values. In particular, this test method is not applicableto reactions that are partially inhibited. The technique may notwork with reactions that include simultaneous or consecutivereaction steps. This test
7、method may not apply to materials thatundergo phase transitions if the reaction rate is significant atthe transition temperature.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 may involve hazardous materia
8、ls, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations pr
9、ior to use.2. Referenced Documents2.1 ASTM Standards:2E473 Terminology Relating to Thermal Analysis and Rhe-ologyE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE968 Practice for Heat Flow Calibration of DifferentialScanning CalorimetersE1142 Terminolo
10、gy Relating to Thermophysical PropertiesE1445 Terminology Relating to Hazard Potential of Chemi-calsE1860 Test Method for Elapsed Time Calibration of Ther-mal AnalyzersE1970 Practice for Statistical Treatment of Thermoanalyti-cal Data3. Terminology3.1 Technical terms used in this test method are def
11、ined inTerminologies E473, E1142, and E1445.4. Summary of Test Method4.1 Asample is placed in a suitable container and positionedin a differential scanning calorimeter (DSC).4.2 The sample equipment temperature is increased at alinear rate and any exothermic reaction peaks recorded.4.3 Steps 4.1 and
12、 4.2 are repeated for several heating ratesin the range from 1 to 10 K min1.1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct responsibility of Subcommittee E27.02 onThermal Stability and Condensed Phases.Current edition approved Marc
13、h 1, 2011. Published March 2011. Originallyapproved in 1979. Last previous edition approved in 2005 as E698 05. DOI:10.1520/E0698-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume infor
14、mation, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.4 Temperatures at which the reaction peak maxima occurare plotted as a function of their respective heating rat
15、es.4.5 Kinetic values calculated from the peak temperature-heating rate relationship are used to predict a reaction half-lifeat a selected temperature.4.6 A sample is aged at the selected temperature for thepredicted half-life time.4.7 The aged sample is temperature programmed in adifferential scann
16、ing calorimeter and its reaction peak areacompared with that for an unaged sample run under the sameconditions.4.8 If the normalized area for the aged sample is approxi-mately half that for the unaged sample, the kinetic values areconfirmed for the temperature selected.5. Significance and Use5.1 The
17、 Arrhenius parameters combined with the generalrate law and the reaction enthalpy can be used for thedetermination of thermal explosion hazards (1).36. Apparatus6.1 GeneralThe equipment used in this test methodshould be capable of displaying quantitative changes of en-thalpy as a function of time (t
18、) or temperature (T), should belinearly programmable and have the capabilities of subjectingthe sample cell to different atmospheres. The heat sensingelement should be external to the sample.6.2 Differential Scanning Calorimeter (DSC):6.2.1 A DSC test chamber composed of:6.2.1.1 A furnace, to provid
19、e uniform controlled heating(cooling) of a specimen and reference to a constant temperatureor at a constant rate within the applicable temperature range ofthis test method.6.2.1.2 A temperature sensor, to provide an indication ofthe specimen/furnace temperature to 60.1 K.6.2.1.3 A differential senso
20、r, to detect a difference in heatflow between the specimen and reference equivalent to 10 W.6.2.1.4 A means of sustaining a test chamber environment,of an inert purge gas at a rate of 10 50 6 mL/min.NOTE 1Typically, 99+ % pure nitrogen, argon, or helium are em-ployed when oxidation in air is a conce
21、rn. Unless effects of moisture areto be studied, use of dry purge gas is recommended; especially foroperation at subambient temperature.6.2.2 A temperature controller, capable of executing a spe-cific temperature program by operating the furnace(s) betweenselected temperature limits at a rate of tem
22、perature changebetween 0.5 and 10 K/min constant to 60.1 K/min or at anisothermal temperature constant to 60.1 K.6.2.3 A data collection device, to provide a means ofacquiring, storing, and displaying measured or calculatedsignals, or both. The minimum output signals required fordifferential scannin
23、g calorimetry are heat flow, temperature,and time.6.3 Containers (pans, crucibles, vials, etc), which are inertto the specimen and reference materials and which are suitablestructural shape and integrity to contain the specimen andreference in accordance with the specific requirements of thistest me
24、thod.6.4 A balance, with a capacity of at least 100 mg, to weighspecimens or containers (pans, crucibles, vials, etc), or bht, towithin 10 g.6.5 Auxiliary equipment useful for conducting this testmethod below ambient temperature.6.5.1 A coolant system, which can be directly coupled withthe controlle
25、r to the furnace to hasten its recovery fromelevated temperatures, to provide constant cooling rates, or tosustain an isothermal subambient temperature, or a combina-tion thereof.7. Safety Precautions7.1 The use of this test method on materials whose potentialhazards are unknown requires that precau
26、tion be taken duringsample preparation and testing.7.2 Where particle size reduction by grinding is necessary,the user of this test method should presume that the material isdangerous.7.3 Toxic or corrosive effluents, or both, may be releasedwhen heating the material and could be harmful to theperso
27、nnel or the apparatus. Use of an exhaust system to removesuch effluents is recommended.8. Sampling8.1 Sample size is kept small to minimize temperaturegradients within the sample. In general, a sample weightresulting in a maximum heat generation of less than 8 mJ/s issatisfactory.8.2 Samples should
28、be representative of the material beingstudied and should be prepared to achieve good thermal contactbetween sample and container (see Figs. 1 and 2).8.3 The sample container should be nonreactive with thesample or reaction products.8.4 The reference for the sample is normally an emptycontainer or o
29、ne filled with inert material.8.5 Samples which have appreciable volatility over thetemperature range of interest may require sealing in hermeticcontainers or a high-pressure cell, or both, to prevent vapor-ization interference and weight loss of unreacted material.8.6 The sample atmosphere should c
30、losely represent theconditions of usage.9. Calibration9.1 Perform any calibration procedures recommended bythe manufacturer as described in the operators manual.9.2 Calibrate the heat flow and elapsed time signals usingPractice E968 and Test Method E1860, respectively, using thesame type of specimen
31、 container to be used in the subsequentkinetic tests. Perform any calibration procedures recommendedby the manufacturer as described in the operators manual.9.3 Calibrate the temperature signal at 10 K/min usingPractice E968 and Test Method E1860, respectively, using thesame type of specimen contain
32、er to be used in the subsequentkinetic tests.9.4 Determine the temperature calibration corrections forother heating rates by programming a sharply melting standard3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E698 112(for example, pure indium metal)
33、at these heating rates andobserving the deviation of the known melt temperature as afunction of the rate.NOTE 2This table of temperature calibration correction values, oncedetermined for a particular apparatus and specimen container, may be usedfor subsequent experiments following temperature calibr
34、ation at 10 K/minheating rate in 9.3.9.5 The thermal resistance of the instrument sample cell isdetermined by measuring the temperature lag observed for themelting of a pure metal standard. See Fig. X1.2 in AppendixX1.10. Procedure10.1 Run an initial sample of 5 mg or less to determineproper sample
35、sizes and starting temperatures.10.2 Place the sample and reference materials in the instru-ment heating unit. Use a sample size as recommended in 8.1.10.3 Program the temperature at a rate between 1 and10 K/min from a point starting at least 50 K below the firstobserved exothermic peak deflection.1
36、0.4 Record the differential heat flow signal as a function oftemperature. Continue heating until the peak maximum ofinterest is recorded.10.5 Repeat 10.2-10.4 for various heating rates betweenabout 1 and 10 K/min.NOTE 3Aminimum of four determinations at heating rates between 1and 10 K/min are recomm
37、ended.NOTE 4Reaction curve baselines should be level to minimize slopeerror in peak maxima measurements.11. Calculation11.1 Temperatures of reaction peak maxima are correctedfor temperature scale nonlinearity, heating rate changes, andthermal lag as in the example in Appendix X1.11.2 Plot log10b (he
38、ating rate, Kmin1) versus 1/T, where Tis the corrected peak maximum temperature in Kelvin. Calcu-late and construct a least squares “best fit” line through thesepoints (see Practice E1970). The slope of this “best fit” line istaken as the value for d log10b/d (1/T).11.3 Calculate an approximate valu
39、e for E (activation en-ergy) as follows (2):E 22.19Rd log10b/d 1/T!# (1)where R = gas constant (=8.314 J mol1K1)11.4 Refine value of E by:11.4.1 Calculate E/RT approximately.11.4.2 Find corresponding value of D from Table X2.1.FIG. 1 Arrangement for Good Sample Contact with ContainerFIG. 2 Sample Pa
40、n Collapsed and CollectedE698 11311.4.3 Calculate new value for E as follows:E 5 2.303R/D!d log10b/d 1/T!# (2)Refining the value of E a second time usually results in aclose approach to its final value. An alternative calculationmethod is shown in Appendix X3.11.5 TheArrhenius pre-exponential factor
41、 can be calculatedas follows:Z 5bEeE/RT/RT2(3)whereb = a heating rate from the middle of the range.11.6 For the confirming isothermal test, calculate k forvarious temperatures from the Arrhenius equation and theabove E and Z values.11.7 From t = 0.693/k, calculate aging times (t) for eachtemperature
42、.11.8 Select a temperature requiring at least 1-h aging time,and age the sample isothermally for the calculated half-life ina thermal instrument or other facility capable of 61 K control.Quench immediately to some temperature at least 50 K belowthe aging temperature so that no significant reaction o
43、ccursduring subsequent holding time.11.9 Run the aged sample in a thermal instrument andrecord its reaction peak.11.10 Run a similar but unaged sample in the same way andrecord its reaction peak.11.11 On an equal weight basis, the peak area or displace-ment from baseline of the aged sample should be
44、 one half thatof the unaged sample. If so, the reaction kinetics are confirmedfor the temperature range explored.12. Report12.1 The report shall include the following:12.1.1 Identification of the sample by name or composition,stating the source, past history, and weight of sample togetherwith its pu
45、rity (if available).12.1.2 Description of apparatus and type of container used.12.1.3 Identification of sample environment as to degree ofconfinement, composition of atmosphere, and whether theatmosphere is static, self-generated, or dynamic through orover the sample.12.1.4 Description of test condi
46、tions, including the heatingrates and peak temperature range investigated.12.1.5 The specific dated version of this test method used.13. Precision13.1 An interlaboratory study (ILS) was conducted in 2000involving participation by eight laboratories using apparatusfrom three manufacturers and six ins
47、trument models. Eachlaboratory characterized trityl azide (azidotriphenylmethane) atfive heating rates. The ILS results were treated by PracticeE691 and Practice E1970. The results of this interlaboratorystudy are on file at ASTM Headquarters.413.2 Precision:13.2.1 Within laboratory variability may
48、be described usingthe repeatability value (r) obtained by multiplying the repeat-ability standard deviation by 2.8. The repeatability value esti-mates the 95 % confidence limit. That is, two within laboratoryresults should be considered suspect if they differ by more thanthe repeatability value (r).
49、13.2.1.1 The pooled repeatability relative standard deviationfor activation energy (E) was 3.7 %.13.2.1.2 The pooled repeatability relative standard deviationfor logarithm of the pre-exponential factor was 4.1 %.13.2.2 Between laboratory variability may be describedusing the reproducibility value (R) obtained by multiplying thereproducibility standard deviation by 2.8. The reproducibilityvalue estimates the 95 % confidence limit. That is, twobetween laboratory results should be considered suspect if theydiffer by more than the reproducibility value (R).13.2.2
