1、Designation: E 698 05Standard Test Method forArrhenius Kinetic Constants for Thermally UnstableMaterials Using Differential Scanning Calorimetry and theFlynn/Wall/Ozawa Method1This standard is issued under the fixed designation E 698; the number immediately following the designation indicates the ye
2、ar 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 (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe kinetics of exothermic reactions are important in
3、 assessing the potential of materials andsystems for thermal explosion. This method provides a means for determining Arrhenius activationenergies and pre-exponential factors using differential thermal methods. This method is one of severalmethods being developed byASTM Committee E27 for chemical rea
4、ctions. This method is to be usedin conjunction with other tests to characterize the hazard potential of chemicals.1. Scope1.1 This method covers the determination of the overallkinetic parameters for exothermic reactions using the Flynn/Wall/Ozawa method and differential scanning calorimetry.1.2 Th
5、is 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 isothermal aging test n
6、otclosely agreeing with the results predicted by the calculatedkinetic values. In particular, this method is not applicable toreactions that are partially inhibited. The technique may notwork with reactions that include simultaneous or consecutivereaction steps. This method may not apply to material
7、s thatundergo phase transitions if the reaction rate is significant atthe transition temperature.1.4 SI units are the standard.1.5 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with i
8、tsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 473 Terminology Relating to Thermal AnalysisE 691 Practice for Conduct
9、ing an Interlaboratory Study toDetermine the Precision of a Test MethodE 968 Practice for Heat Flow Calibration of DifferentialScanning CalorimetersE 1142 Terminology Relating to Thermophysical PropertiesE 1445 Terminology Relating to Hazardous Potential ofChemicalsE 1860 Method for Elapsed Time Cal
10、ibration of ThermalAnalyzersE 1970 Practice for Statistical Treatment of Thermoanalyti-cal Data3. Terminology3.1 Technical terms used in this test method are defined inTerminologies E 473, E 1142, and E 1445.4. Summary of Test Method4.1 Asample is placed in a suitable container and positionedin a di
11、fferential 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 4.2 are repeated for several heating ratesin the range from 1 to 10 K min-1.1This test method is under the jurisdiction of ASTM Committ
12、ee E27 on HazardPotential of Chemicals and is the direct responsibility of Subcommittee E27.02 onHazard Potential of Chemicals.Current edition approved March 1, 2005. Published April 2005. Originallyapproved in 1979. Last previous edition approved in 2004 as E 698 01.2For referenced ASTM standards,
13、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942
14、8-2959, United States.4.4 Temperatures at which the reaction peak maxima occurare plotted as a function of their respective heating rates.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 i
15、s aged at the selected temperature for thepredicted half-life time.4.7 The aged sample is temperature programmed in adifferential scanning 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 appr
16、oxi-mately half that for the unaged sample, the kinetic values areconfirmed for the temperature selected.5. Significance and Use5.1 The Arrhenius parameters combined with the generalrate law and the reaction enthalpy can be used for thedetermination of thermal explosion hazards (1).36. Apparatus6.1
17、GeneralThe equipment used in this method should becapable of displaying quantitative changes of enthalpy as afunction of time (t) or temperature (T), should be linearlyprogrammable and have the capabilities of subjecting thesample cell to different atmospheres. The heat sensing elementshould be exte
18、rnal 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 provide 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.
19、6.2.1.2 A temperature sensor, to provide an indication of thespecimen/furnace temperature to 6 0.1 K.6.2.1.3 A differential sensor, 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
20、at a rate of 1050 6 mL/min.NOTE 1Typically, 99+ % pure nitrogen, argon, or helium are em-ployed when oxidation in air is a concern. 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, capa
21、ble of executing aspecific temperature program by operating the furnace(s)between selected temperature limits at a rate of temperaturechange between 0.5 and 10 K/min constant to 6 0.1 K/min orat an isothermal temperature constant to 6 0.1 K.6.2.3 A recording device, capable of recording and display-
22、ing any fraction of the heat flow signal including the signalnoise, on the Y-axis and any fraction of the temperature signal,including noise, on the X-axis.6.3 Containers (pans, crucibles, vials, etc), which are inertto the specimen and reference materials and which are suitablestructural shape and
23、integrity to contain the specimen andreference in accordance with the specific requirements of thismethod.6.4 A balance, with a capacity of at least 100 mg, to weighspecimens and/or containers (pans, crucibles, vials, etc) towithin 10 g.6.5 Auxiliary equipment useful for conducting this methodbelow
24、ambient temperature.6.5.1 A coolant system, which can be directly coupled withthe controller to the furnace to hasten its recovery fromelevated temperatures, to provide constant cooling rates, and/orto sustain an isothermal subambient temperature.7. Safety Precautions7.1 The use of this test method
25、on materials whose potentialhazards are unknown requires that precaution be taken duringsample preparation and testing.7.2 Where particle size reduction by grinding is necessary,the user of this method should presume that the material isdangerous.7.3 Toxic or corrosive effluents, or both, may be rel
26、easedwhen heating the material and could be harmful to thepersonnel or the apparatus. Use of an exhaused system toremove such 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 g
27、eneration of less than 8 mJ/s issatisfactory.8.2 Samples should 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
28、 The reference for the sample is normally an emptycontainer or one 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 weig
29、ht loss of unreacted material.8.6 The sample atmosphere should closely 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 E 968 an
30、d Method E 1860, respectively, using thesame type of specimen 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 E 968 and Method E
31、1860, respectively, using thesame type of specimen container 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
32、 ofthis standard.E698052(for example, pure indium metal) 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 us
33、edfor subsequent experiments following temperature calibration 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
34、initial sample of 5 mg or less to determineproper sample 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 and 10K/min from a point starting at least
35、50 K below the firstobserved exothermic peak deflection.10.4 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 determi
36、nations at heating rates between 1and 10 K/min are recommended.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
37、lag as in the example in Appendix X1.11.2 Plot log10b (heating rate, Kmin-1) versus 1/T, where Tis the corrected peak maximum in Kelvin. Calculate andconstruct a least squares “best fit” line through these points (seePractice E 1970). The slope of this “best fit” line is taken as thevalue for d log1
38、0b/d (1/T).11.3 Calculate an approximate value for E (activation en-ergy) as follows (2):E 22.19Rd log10b/d 1/T!# (1)11.4 Refine value of E by:11.4.1 Calculate E/RT approximately.11.4.2 Find corresponding value of D from Table X2.1.11.4.3 Calculate new value for E as follows:E 5 22.303R/D!d log10b/d
39、 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.FIG. 1 Arrangement for Good Sample Contact with ContainerFIG. 2 Sample Pan Collapsed and CollectedE69805311.5 TheArrhenius pre-exponential f
40、actor can be calculatedas follows:Z 5bEeE/RT/RT2(3)where:b = 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 eachtempe
41、rature.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 6 1 K control.Quench immediately to some temperature at least 50 K belowthe aging temperature so that no significant rea
42、ction occursduring 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 sh
43、ould be 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
44、 its purity (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 tes
45、t conditions, including the heatingrates and peak temperature range investigated.12.1.5 The specific dated version of this method used.13. Precision13.1 An interlaboratory study (ILS) was conducted in 2000involving participation by eight (8) laboratories using appara-tus from three (3) manufacturers
46、 and six (6) instrument models.Each laboratory characterized trityl azide (azidotriphenyl-methane) at 5 heating rates. The ILS results were treated byPractice E 691 and Practice E 1970. The results of this inter-laboratory study are on file at ASTM Headquarters.413.2 Precision:13.2.1 Within laborato
47、ry variability may be described usingthe repeatability value (r) obtained by multiplying the repeat-ability standard deviation by 2.8. The repeatability valueestimates the 95 % confidence limit. That is, two withinlaboratory results should be considered suspect if they differ bymore than the repeata
48、bility value (r).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 reprodu
49、cibility 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).13.2.2.1 The relative reproducibility standard deviation foractivation energy was 6.5 %.13.2.2.2 The relative reproducibility standard deviation forlogarithm of the pre-exponential factor was 8.4 %.13.3 Bias:13.3.1 Bias is the difference between a test result and anaccepted reference value. There
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