1、Designation: E 537 02Standard Test Method forThe Thermal Stability Of Chemicals By Differential ScanningCalorimetry1This standard is issued under the fixed designation E 537; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONCommittee E-27 is currently enga
3、ged in developing methods to determine the hazard potential ofchemicals. An estimate of this potential may usually be obtained by the use of program CHETAH 7.0to compute the maximum energy of reaction of the chemical or mixture of chemicals.2The expression “hazard potential” as used by this committe
4、e is defined as the degree ofsusceptibility of material to ignition or release of energy under varying environmental conditions.The primary purpose of this test method is to detect enthalpic changes and to approximate thetemperature of initiation and enthalpies (heats) of these events. Differential
5、scanning calorimetry offersthe advantage of using very small specimens on the order of a few milligrams.1. Scope1.1 This test method covers the ascertainment of the pres-ence of enthalpic changes in a test specimen, using minimumquantities of material, approximates the temperature at whichthese enth
6、alpic changes occur and determines their enthalpies(heats) using differential scanning calorimetry or pressuredifferential scanning calorimetry.1.2 This test method may be performed on solids, liquids, orslurries.1.3 This test method may be performed in an inert or areactive atmsophere with an absol
7、ute pressure range from 100Pa through 7 MPa and over a temperature range from 300 to800 K (27 to 527C ).1.4 SI values are the standard.1.5 There is no ISO standard equivalent to this test method.1.6 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not pur
8、port toaddress all of the safety concerns associated with its use. It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to use. Specificsafety precautions are given in Section 8.2. Refe
9、renced Documents2.1 ASTM Standards:E 473 Terminology Relating to Thermal Analysis3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3E 967 Practice for Temperature Calibration of DifferentialScanning Calorimeters and Differential Thermal Analyz-ers3E 96
10、8 Practice for Heat Flow Calibration of DifferentialScanning Calorimeters3E 1445 Terminology Relating to Hazardous Potential ofChemicals3E 1860 Test Method for Elapsed Time Calibration of Ther-mal Analyzers33. Terminology3.1 Definitions:3.1.1 Specific technical terms used in this standard aredefined
11、 in Terminologies E 473 and E 1445.3.2 Definitions of Terms Specific to This Standard:3.2.1 DSC curvea record of a differential scanning calo-rimeter where the change in heat flow (Dq) is plotted on theordinate and temperature or time is plotted on the abscissa (seeFigs. 1 and 2 and Terminology E 47
12、3).3.2.2 peakthat portion of a thermal curve that is attribut-able to the occurrence of a single process. It is normallycharacterized by a deviation from the established baseline, a1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct res
13、ponsibility of Subcommittee E27.02 onThermal Stability and Condensed Phases.Current edition approved April 10, 2002. Published August 2002. Originallypublished as E 537 76. Last previous edition E 537 98.2A complete assessment of the hazard potential of chemicals must take intoaccount a number of re
14、alistic factors not considered in this test method or theCHETAH program.3Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.FIG.1TypicalDSCCurvewithExothermE537022FIG.2DSCCurveIllustratingaMeltin
15、gProcessImmediatelyFollowedbyanExothermicDecompositionE537023maximum deflection, and a reestablishment of a baseline notnecessarily identical to that before the peak (see Fig. 1).NOTE 1There will be instances when upon scanning in temperaturean endotherm will be observed that is immediately followed
16、 by or is inconjunction with an exotherm as shown in Fig. 2. These types ofcompeting reactions make it difficult and at times impossible to locate thetrue peak and onset temperatures.3.2.3 peak temperature (Tp)the temperature correspond-ing to the maximum deflection of the DSC curve.3.2.4 onset temp
17、erature (To)the temperature at which adeflection from the established baseline is first observed.3.2.5 extrapolated onset temperature (Te)empirically, thetemperature found by extrapolating the baseline (prior to thepeak) and the tangent at the inflection point on the leading sideof the peak to their
18、 intersection (see Fig. 1).3.2.6 reactionany transformation of material accompa-nied by a change of enthalpy that may be endothermic orexothermic.3.2.7 thermal stabilitythe absence of a reaction (for thepurposes of this test method only, see 3.2.6).4. Summary of Test Method4.1 In DSC, a measurement
19、is made of the heat flow (Dq)associated with the observed change of enthalpy. Provisionsare made to measure the absolute temperature (T) of the sampleor reference or the average temperature of both.4.2 A sample of the material to be examined and of athermally inert reference material are placed in s
20、eparateholders.4.3 The sample and reference materials are simultaneouslyheated at a controlled rate of 2 to 20C/min under anequilibrated atmosphere. A record of Dq on the ordinate ismade as a function of temperature (T) on the abscissa.4.4 When the sample undergoes a transition involving achange of
21、enthalpy, that change is indicated by a departurefrom the initially established baseline of the heat flow record.4.5 The onset temperature (To), extrapolated onset tempera-ture (Te), and the integrated peak area (enthalpy) are deter-mined and reported.5. Significance and Use5.1 This test method is u
22、seful in detecting potentiallyhazardous reactions including those from volatile chemicalsand in estimating the temperatures at which these reactionsoccur and their enthalpies (heats). This test method is recom-mended as an early test for detecting the thermal hazards of anuncharacterized chemical su
23、bstance or mixture (see Section 8).5.2 The magnitude of the change of enthalpy may notnecessarily denote the relative hazard in a particular applica-tion. For example, certain exothermic reactions are oftenaccompanied by gas evolution that increases the potentialhazard. Alternatively, the extent of
24、energy release for certainexothermic reactions may differ widely with the extent ofconfinement of volatile products. Thus, the presence of anexotherm and its approximate temperature are the most signifi-cant criteria in this test method (see Section 3 and Fig. 1).5.3 When volatile substances are bei
25、ng studied, it is impor-tant to perform this test with a confining pressurized atmo-sphere so that changes of enthalpy that can occur above normalboiling or sublimation points may be detected. As an example,an absolute pressure of 1.14 MPa (150 psig) will generallyelevate the boiling point of a vola
26、tile organic substance 100C.Under these conditions exothermic decomposition is oftenobserved.5.4 For some substances the rate of enthalpy change duringan exothermic reaction may be small at normal atmosphericpressure, making an assessment of the temperature of instabil-ity difficult. Generally a rep
27、eated analysis at an elevatedpressure will improve the assessment by increasing the rate ofchange of enthalpy.NOTE 2The choice of pressure may sometimes be estimated by thepressure of the application to which the material is exposed.5.5 The four significant criteria of this test method are: thedetec
28、tion of a change of enthalpy; the approximate temperatureat which the event occurs; the estimation of its enthalpy and theobservance of effects due to the cell atmosphere and pressure.6. Limitations6.1 A host of environmental factors affect the existence,magnitude, and temperature of an exothermic r
29、eaction. Some,including heating rate, instrument sensitivity, degree of con-finement, and atmosphere reactivity, will affect the detectabil-ity of an exothermic reaction using this procedure. Therefore,it is imperative that the qualitative results obtained from theapplication of this test method be
30、viewed only as an indicationof the thermal stability of a chemical.7. Apparatus7.1 The equipment used in this test method shall be capableof displaying changes of enthalpy as a function of temperature(T), and shall have the capability of subjecting the sample cellto different atmospheres of equilibr
31、ated pressures.7.2 Differential Scanning Calorimeter (DSC)the essentialinstrumentation required to provide the minimum differentialscanning calorimetric capability for this test method include:7.2.1 A test chamber composed of:7.2.1.1 Furnace(s), to provide uniform controlled heating ofa specimen and
32、 reference to a constant temperature or at aconstant rate within the applicable temperature range of thismethod,7.2.1.2 Temperature sensor, to provide an indication of thespecimen/furnace temperature to 60.5 K,7.2.1.3 Differential sensor, to detect a temperature or heatflow difference between the sp
33、ecimen and reference equivalentto 0.2 mW,7.2.1.4 Means of sustaining a test chamber environment ofinert (for example, nitrogen, helium or argon) or reactive (forexample, air) gas at a purge rate of 50 6 5 mL/min,NOTE 3Typically, at least 99 % pure nitrogen, argon or helium isemployed when oxidation
34、in air is a concern. Unless effects of moistureare to be studied, use of dry purge gas is recommended and is essential foroperation at subambient temperatures.NOTE 4Other purge gas rates may be used but shall be reported.7.2.1.5 Temperature controller, capable of executing a spe-cific temperature pr
35、ogram by operating the furnace(s) betweenE537024selected temperature limits (ambient temperature to 800 K) ata rate of temperature change of from 2 to 20 K/min constant to60.1 K/min, andNOTE 5The temperature range of the apparatus and the experimentmay be extended to 120 K with the use of appropriat
36、e cooling or to 1273K or greater with suitable apparatus.7.2.1.6 Recording device, either digital or analog, capable ofrecording and displaying any portion of the differential heatflow on the ordinate as a function of temperature on theabscissa, including the signal noise.7.2.2 If experiments are to
37、 be carried out under pressureconditions:7.2.2.1 Pressure vessel, or similar means of sealing the testchamber at any applied pressure within 0.10 to 1.27 MPa (0 to170 psig) pressure limits required by this test method,7.2.2.2 Pressurized gas source, capable of sustaining aregulated gas pressure in t
38、he test chamber between 0.10 and1.27 MPa (0 and 170 psig),7.2.2.3 Pressure transducer, or similar device to measurethe pressure inside the test chamber to 65 % including anytemperature dependence of the transducer,7.2.2.4 Pressure regulator, or similar device to adjust theapplied pressure in the tes
39、t chamber to 65 % of the desiredvalue,7.2.2.5 Ballast, or similar means to maintain the appliedpressure in the test chamber constant to 65%,7.2.2.6 Valves, to control pressurizing gas in the test cham-ber or to isolate components of the pressure system, or both.7.2.3 If subambient temperatures are d
40、esired:7.2.3.1 Cooling system, to hasten cool down from elevatedtemperatures and to sustain an isothermal subambient tempera-ture.7.3 Containers, (pans, crucibles, vials, etc.) which are inertto the specimen and reference materials and which are ofsuitable structural shape and integrity to contain t
41、he specimenand reference in accordance with the specific requirements ofthis method.7.4 Balance, with a capacity of 100 mg or greater to weighspecimens or containers, or both, to a sensitivity of 6 10 g.8. Safety Precautions8.1 The use of this test method as an initial test for materialwhose potenti
42、al hazards are unknown requires that precautionsbe taken during the sample preparation and testing.8.2 Where particle size reduction by grinding is necessary,the user of the test method should presume that the material issensitive to stimuli such as friction and electrostatic discharge.Accordingly,
43、appropriate test shall be conducted on thosematerials prior to grinding. Use of suitable protective equip-ment is always recommended when preparing materials ofunknown hazard. If a Material Safety Data Sheet is available,it shall be acquired and studied prior to handling unknownmaterials.8.3 The use
44、 of this test method may require operation atelevated temperatures and pressures.All precautions associatedwith such temperatures and pressures should be observed.8.4 Toxic or corrosive effluents, or both, may be releasedwhen heating the material and could be harmful to thepersonnel or the apparatus
45、. Use of an exhaust system to removesuch effluents is recommended.9. Calibration9.1 Perform any calibration procedures recommended bythe apparatus manufacturer as described in the Operatorsmanual.9.2 Calibrate the temperature signal within 62C usingPractice E 967.9.3 Calibrate the heat flow signal w
46、ithin 61 % using TestMethod E 968.9.4 Calibrate the time signal within 60.5 % using TestMethod E 1860.10. Sample and Reference Materials10.1 The selection of an adequate sample size will dependupon the availability of the material, the degree of dilutionrequired, the sensitivity of the instrument, t
47、he magnitude of thechange of enthalpy, and the heating rate. Additionally, samplesize must be compatible with the potential for a sudden largeenergy release. This test method should, therefore, be carriedout on as small a quantity of material as possible, typically 1 to50 mg.10.2 Samples should be r
48、epresentative of the material beingstudied including particle size and purity.10.3 The reference material must not undergo any thermaltransformation over the temperature range under study. Typicalreference materials include calcined aluminum oxide, glassbeads, silicone oil, or an empty container.11.
49、 Recommended Conditions of Tests11.1 Specimen Size A 5-mg specimen is generally consid-ered adequate. Decrease the specimen size if the response isgreater than 8 mW.NOTE 6For materials whose characteristics are unknown, it is safestto start with a specimen size of no more than 1 mg, and then increase thesize if the exothermic response is insufficiently large.11.2 Heating Rate A rate of 10 to 20C/min is considerednormal. If an endothermic response is immediately followed byan exotherm (see Note 1 and Fig. 2), then lower heating ratesof 2 to 6C/min are recommen
