1、Designation: E 794 06Standard Test Method forMelting And Crystallization Temperatures By ThermalAnalysis1This standard is issued under the fixed designation E 794; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number 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 melting(and crystallization) temperatures of pure materials by differ-ential
3、 scanning calorimetry (DSC) and differential thermalanalysis (DTA).1.2 This test method is generally applicable to thermallystable materials with well-defined melting temperatures.1.3 The normal operating range is from 120 to 600 C forDSC and 25 to 1500 C for DTA. The temperature range canbe extende
4、d depending upon the instrumentation used.1.4 Computer or electronic based instruments, techniques,or data treatment equivalent to those in this test method may beused.1.5 SI units are the standard.1.6 This standard does not purport to address all of thesafety problems, if any, associated with its u
5、se. 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 Documents2.1 ASTM Standards:2E 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 793 Test Met
6、hod for Enthalpies of Fusion and Crystalli-zation by Differential Scanning CalorimetryE 967 Test Method for Temperature Calibration of Differ-ential Scanning Calorimeters and Differential ThermalAnalyzersE 1142 Terminology Relating to Thermophysical Properties3. Terminology3.1 DefinitionsSpecialized
7、 terms used in this test methodare defined in Terminologies E 473 and E 1142.4. Summary of Test Method4.1 The test method involves heating (or cooling) a testspecimen at a controlled rate in a controlled environmentthrough the region of fusion (or crystallization). The differencein heat flow (for DS
8、C) or temperature (for DTA) between thetest material and a reference material due to energy changes iscontinuously monitored and recorded. A transition is markedby absorption (or release) of energy by the specimen resultingin a corresponding endothermic (or exothermic) peak in theheating (or cooling
9、) curve.NOTE 1Enthalpies of fusion and crystallization are sometimes deter-mined in conjunction with melting or crystallization temperature measure-ments. These enthalpy values may be obtained by Test Method E 793.5. Significance and Use5.1 Differential scanning calorimetry and differential ther-mal
10、 analysis provide a rapid method for determining the fusionand crystallization temperatures of crystalline materials.5.2 This test is useful for quality control, specificationacceptance, and research.6. Interferences6.1 Test specimens need to be homogeneous, since milli-gram quantities are used.6.2
11、Toxic or corrosive effluents, or both, may be releasedwhen heating the material and could be harmful to personneland to apparatus.7. Apparatus7.1 Apparatus shall be of either type listed below:7.1.1 Differential Scanning Calorimeter (DSC) or Differen-tial Thermal Analyzer (DTA)The essential instrume
12、ntationrequired to provide the minimum differential scanning calori-metric or differential thermal analyzer capability for thismethod includes:7.1.1.1 Test Chamber composed of:1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of
13、Subcommittee E37.01 on TestMethods and Recommended Practices.Current edition approved March 1, 2006. Published March 2006. Originallyapproved in 1981. Last previous edition approved in 2001 as E 794 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
14、ice 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 19428-2959, United States.(1) A furnace or furnaces to provide uniform
15、 controlledheating (cooling) of a specimen and reference to a constanttemperature or at a constant rate within the applicable tempera-ture range of this method.(2) A temperature sensor to provide an indication of thespecimen or furnace temperature to within 6 0.01 C.(3) Differential sensors to detec
16、t a heat flow difference(DSC) or temperature difference (DTA) between the specimenand reference with a range of at least 100 mW and a sensitivityof 6 1 W (DSC) or 4 C and a sensitivity of 40 C (DTA).(4) Ameans of sustaining a test chamber environment witha purge gas of 10 to 100 6 5 mL/min.NOTE 2Typ
17、ically 99.9+% pure nitrogen, argon or helium is employedwhen oxidation in air is a concern. Unless effects of moisture are to bestudied, use of dry purge gas is recommended and is essential foroperation at subambient temperatures.7.1.1.2 A temperature controller, capable of executing aspecific tempe
18、rature program by operating the furnace orfurnaces between selected temperature limits at a rate oftemperature change of 10 C/min constant to within 6 0.1C/min or at an isothermal temperature constant to 6 0.1 C.7.1.2 A recording device, capable of recording and display-ing on the Y-axis any fractio
19、n of the heat flow signal (DSCcurve) or differential temperature Signal (DTA Curve) includ-ing the signal noise as a function of any fraction of thetemperature (or time) signal on the X-axis including the signalnoise.7.2 Containers (pans, crucibles, vials, lids, closures, seals,etc.) that are inert
20、to the specimen and reference materials andthat are of suitable structural shape and integrity to contain thespecimen and reference in accordance with the requirements ofthis test method.NOTE 3DSC containers are commonly composed of aluminum orother inert material of high thermal conductivity. DTA c
21、ontainers arecommonly composed of borosilicate glass (for use below 500 C),alumina, or quartz (for use below 1200 C).7.3 Nitrogen, or other inert purge gas supply.7.4 Auxiliary instrumentation and apparatus considerednecessary or useful for conducting this method includes:7.4.1 Analytical Balance, w
22、ith a capacity greater than 100mg, capable of weighing to the nearest 0.01 mg.7.4.2 Cooling capacity to hasten cooling down from el-evated temperatures, to provide constant cooling rates or tosustain an isothermal subambient temperature.7.4.3 A means, tool or device, to close, encapsulate or sealthe
23、 container of choice.8. Sampling8.1 Powdered or granular materials should be mixed thor-oughly prior to sampling and should be sampled by removingportions from various parts of the container. These portions, inturn, should be combined and mixed well to ensure a repre-sentative specimen for the deter
24、mination. Liquid samples maybe sampled directly after mixing.8.2 In the absence of information, samples are assumed tobe analyzed as received. If some heat or mechanical treatmentis applied to the sample prior to analysis, this treatment shouldbe noted in the report. If some heat treatment is applie
25、d, recordany mass loss as a result of this treatment.9. Calibration9.1 Using the same heating rate, purge gas, and flow rate asthat to be used for analyzing the specimen, calibrate thetemperature axis of the instrument using the procedure inPractice E 967.10. Procedure10.1 Weigh 1 to 15 mg of materi
26、al to an accuracy of 0.01mg into a clean, dry specimen capsule. The specimen mass tobe used depends on the magnitude of the transition enthalpyand the volume of the capsule. For comparing multiple results,use similar mass (65 %) and encapsulation.10.2 Load the encapsulated specimen into the instrume
27、ntchamber, and purge the chamber with dry nitrogen (or otherinert gas) at a constant flow rate of 10 to 50 mL/min throughoutthe experiment. The flow rate should be measured and heldconstant for all data to be compared. The use of 99.99 % puritypurge gas and a drier is recommended.10.3 When a DSC is
28、used, heat the specimen rapidly to 30C (60 C in a DTA) below the melting temperature, and allowto equilibrate. For some materials, it may be necessary to startthe scan substantially lower in temperature, for example, belowthe glass transition in order to establish a baseline where thereis no evidenc
29、e of melting or crystallization.10.4 Heat the specimen at 10 C/min through the meltingrange until the baseline is reestablished above the meltingendotherm. Other heating rates may be used but shall be notedin the report. To allow the DSC system to achieve steady state,provide at least 3 min of scann
30、ing time both before and afterthe peak. For DTA instrumentation, allow at least 6 min toensure reaching a steady state. Record the accompanyingthermal curve.FIG. 1 Fusion and Crystallization Temperatures for PureCrystalline MaterialE79406210.5 Hold the specimen at this temperature for 2 min. Otherpe
31、riods may be used but shall be noted in the report.10.6 Cool the specimen at 10 C/min through the exothermuntil the baseline is reestablished below the crystallizationexotherm. Other cooling rates may be used but must beindicated in the report. To allow the system to achieve steadystate, provide at
32、least 3 min of scanning time (six for DTA)both before and after the peak. For some materials, it may benecessary to scan several tens of degrees below the peakmaximum in order to attain a constant baseline. Record theaccompanying thermal curve.10.7 Reweigh the specimen after completion of the analys
33、isand discard. Report any mass loss observed.NOTE 4Mass loss is only one indication of suspected sample degra-dation or decomposition. An accurate determination of mass loss may notbe easily accomplished for tests in which the measuring thermocouple isembedded in the specimen. For these cases, other
34、 decomposition indica-tions, such as color change, will suffice and should be reported.10.8 From the resultant curve, measure the temperatures forthe desired points on the curve: Tp,Tm,Tf,Tn,Tc. Report Tm,andTn, (see Fig. 1) for a pure crystalline, low molecular weightcompound. For such a material T
35、mis the best determination ofthe discrete thermodynamic melting temperature, and Tnindi-cates the onset of crystallization. For polymers, alloys ormixtures of materials, report the relevant descriptive parameter(see Fig. 2). Report multiple Tps and Tcs, if observed.where:Tm= melting temperature,Tp=
36、melting peak maximum, C,Tf= return to baseline, C,Tn= extrapolated crystallization onset C, andTc= crystallization onset, C.NOTE 5For certain DTA instrumentation, the peak shape obtainedfrom melting a pure, low molecular weight crystalline material (such as amelting point standard) may look quite di
37、fferent from that shown in Fig.1. If this is the case, report all of the above parameters for any materialanalyzed. In this case the Tpand Tcvalues are often taken as the meltingand crystallization temperatures, respectively.NOTE 6Samples of high purity materials may crystallize with varyingamounts
38、of supercooling; therefore, the use of crystallization temperaturesshould be established prior to use. In general, crystallization temperaturesare useful for polymeric, alloy, and impure organic and inorganicchemicals having sufficient nucleation sites for repeatable determinationsof crystallization
39、 temperatures.11. Report11.1 Report the following information:11.1.1 Complete identification and description of the mate-rial tested including source, manufacturers code, and anythermal or mechanical pretreatment.11.1.2 Description of instrument (such as manufacturer andmodel number) used for test.1
40、1.1.3 Statement of the mass, dimensions, geometry, andmaterial of specimen encapsulation, and temperature program.11.1.4 Description of temperature calibration procedure.11.1.5 Identification of the specimen environment by gasflow rate, purity, and composition.11.1.6 Results of the transition measur
41、ements using thetemperature parameters (Tp, etc.) cited in Figs. 1 and 2.Ingeneral, temperature results should be reported to the nearest0.1 C.11.1.7 Any side reaction (for example, thermal degradationand oxidation) shall also be reported and the reaction identi-fied, if possible.11.1.8 The specific
42、 dated version of this standard used.12. Precision and Bias312.1 The precision and bias were determined by an inter-laboratory study in which 17 laboratories participated using3Supporting data for this test method have been filed at ASTM HeadquartersRequest RR:E37-1002.FIG. 2 Fusion and Crystallizat
43、ion Temperatures for Polymeric MaterialE794063five instrument models. The testing was performed on polymer,pure organic, and inorganic materials.12.2 Based on the results of this study, the following criteriaare recommended for judging the acceptability of results:12.2.1 Repeatability (Single Analys
44、t)The standard devia-tion of results, obtained by the same analyst on different days,is estimated for the:12.2.1.1 Melting Temperature (Me), Melting Peak Maximum(Tp), Extrapolated Crystallization onset (Tn), and Peak maxi-mum (Tc) to be 1.1 C at 400 degrees of freedom. Two suchresults should be cons
45、idered suspect (95 % confidence level) ifthey differ by more than 3.1 C.12.2.2 Reproducibility(Multilaboratory)The standard de-viation of results, obtained by analysts in different laboratories,has been estimated for the:12.2.2.1 Melting Temperature (Tm), Melting Peak maximum(Tp), Extrapolated Cryst
46、allization onset (Tn), and Crystalliza-tion Peak maximum (Tc) to be 2.1 C at 168 degrees offreedom. Two such results should be considered suspect (95 %confidence level) if they differ by more than 5.9 C.12.3 An estimation of the accuracy of the melting tempera-ture measurement was obtained by compar
47、ing the overall meanvalue obtained during the interlaboratory testing with valuesreported in the literature.Melting Temperatures, CMaterial Interlaboratory Test LiteratureLeadA326.4 6 2.0 327.5 6 0.03Adipic acidB151.1 6 0.7 151.4 6 0.003ARossini, F.O., Pure and Applied Chemistry, Vol 22, 1972, p. 55
48、7.BColarusso, V.G., et al, Analytical Chemistry, Vol 40, 1968, p. 1521.12.4 A second interlaboratory test (ILT) was carried out in1997 to determine the extent to which more modern instru-mentation and computer calculations have improved the pre-cision and bias over the original ILT. The tests were c
49、arried outon two materials, one pure material which melts completely ata single temperature, and one polymer which melts over atemperature range. A total of 10 laboratories using 6 differentDSC models from 4 manufacturers participated. The resultsshowed substantial improvement for the onset temperature fora pure material where sample thermal contact is good, but theyshowed no improvement for the polymer where sample contactvariability may effect the peak temperature.12.5 Precision results for melting tin, and for melting andcrystallization of pol
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