1、Designation: E968 02 (Reapproved 2014)Standard Practice forHeat Flow Calibration of Differential Scanning Calorimeters1This standard is issued under the fixed designation E968; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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.1. Scope1.1 This practice covers the heat flow calibration of differ-ential scanning calorimeters over the temperature range
3、from 130C to +800C.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 Computer or electronic based instruments, techniques ordata manipulation equivalent to this practice may also be used.1.4 This standard does not purport
4、to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of whoever uses this standard to consult andestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.See also Section 7.2. Referenced Docume
5、nts2.1 ASTM Standards:2E473 Terminology Relating to Thermal Analysis and Rhe-ologyE793 Test Method for Enthalpies of Fusion and Crystalliza-tion by Differential Scanning CalorimetryE967 Test Method for Temperature Calibration of Differen-tial Scanning Calorimeters and Differential Thermal Ana-lyzers
6、E1142 Terminology Relating to Thermophysical Properties3. Terminology3.1 DefinitionsSpecific technical terms used in this prac-tice are in accordance with Terminologies E473 and E1142.3.2 Definitions of Terms Specific to This Standard:3.2.1 coeffcient of variation, na measure of relative pre-cision
7、calculated as the standard deviation of a series of valuesdivided by their average. It is usually multiplied by 100 andexpressed as a percentage.NOTE 1The term quantitative differential thermal analysis refers todifferential thermal analyzers that are designed to obtain quantitative orsemiquantitati
8、ve heat flow results. This procedure may also be used tocalibrate such apparatus.4. Summary of Practice4.1 Differential scanning calorimeters measure heat flow(power) into or out of a test specimen and provide a signaloutput proportional to this measurement. This signal often isrecorded as a functio
9、n of a second signal proportional totemperature or time. If this heat flow signal is integrated overtime, the resultant value is proportional to energy (or enthalpyor heat).To obtain the desired energy information, the observedinstrument response (such as the area under the curve scribed)must be mul
10、tiplied by a proportionality constant that convertsthe units of instrument output into the desired energy units.This proportionality constant is called the instrument calibra-tion coefficient (E). The value and dimensions (units) of Edepend upon the particular differential scanning calorimeterand re
11、cording system being used and, moreover, may vary withtemperature.4.2 This practice consists of calibrating the heat flowresponse of a differential scanning calorimeter (that is, deter-mining the calibration coefficient) by recording the meltingendotherm of a high-purity standard material (where the
12、 heat offusion is known to better than 61.5 % (rel) as a function oftime. The peak is then integrated (over time) to yield an areameasurement proportional to the enthalpy of melting of thestandard material.4.3 Calibration of the instrument is extended to tempera-tures other than that of the melting
13、point of the standardmaterial through the recording of the specific heat capacity ofa (second) standard material over the temperature range ofinterest. The ratio of the measured specific heat capacity at thetemperature of interest to that of the temperature of calibrationprovides an instrument calib
14、ration coefficient at the newtemperature.4.4 Once the calibration coefficient at a given temperature isdetermined, it may be used to determine the desired energyvalue associated with an enthalpic transition in an unknownspecimen at that temperature (see Test Method E793).1This practice is under the
15、jurisdiction of ASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on Calo-rimetry and Mass Loss.Current edition approved March 15, 2014. Published April 2014. Originallyapproved in 1983. Last previous edition approved in 2008 as E968 02 (2008).DOI: 10.
16、1520/E0968-02R14.2For referenced ASTM standards, 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.Copyright ASTM International, 100 Barr Harbo
17、r Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 Differential scanning calorimetry is used to determinethe heat or enthalpy of transition. For this information to bemeaningful in an absolute sense, heat flow calibration of theapparatus or comparison of
18、 the resulting data to that of aknown standard is required.5.2 This practice is useful in calibrating the heat flow axis ofdifferential scanning calorimeters or quantitative differentialthermal analyzers for subsequent use in the measurement oftransition energies and specific heat capacities of unkn
19、owns.6. Apparatus6.1 Differential Scanning Calorimeter (DSC)The essentialinstrumentation required to provide the minimum differentialscanning calorimetric capability for this method includes:6.1.1 A DSC test chamber, composed of the following:6.1.1.1 A furnace(s) to provide uniform controlled heatin
20、g(cooling) of a specimen and reference to a constant temperatureor at a constant rate with the temperature range of 100 to600C.NOTE 2This temperature range may be extended to higher and lowertemperatures depending upon the capabilities of the apparatus.6.1.1.2 Atemperature sensor, to provide an indi
21、cation of thespecimen/furnace temperature to 60.01 K.6.1.1.3 A differential sensor, to detect a heat flow (power)difference between the specimen and reference equivalent to 1W.6.1.1.4 A means of sustaining a test chamber environment,of an inert purge gas at a purge gas rate of 10 to 100 mL/min6 5 mL
22、/min.NOTE 3Typically, 99.9+ % pure nitrogen, argon or helium areemployed when oxidation 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.6.1.2 A temperature controller, capable of executing
23、aspecific temperature program by operating the furnace(s)between selected temperature limits at a rate of temperaturechange of between 1 and 35 K/min constant to 61 % and at anisothermal temperature constant to 60.1 K.6.1.3 Arecording device, either digital or analog, capable ofrecording and display
24、ing the heat flow (DSC curve) signalversus temperature, displaying any fraction including thesignal noise.6.1.4 Containers, (pans, crucibles, vials, etc. and associatedlids), that are inert to the specimen and reference materials andthat are of suitable structural shape and integrity to contain thes
25、pecimen and reference.NOTE 4Most containers require special tool(s) for opening, closing orsealing. The specific tool(s) necessary to perform this action also arerequired.6.1.5 Cooling capability, to achieve and sustain cryogenictemperatures, to hasten cool down from elevated temperatures,or to prov
26、ide constant cooling rates, or a combination thereof.6.1.6 Computer and software capability to perform themathematical treatments of this method including peak inte-gration.6.2 A balance, with capacity of 100 mg to weightspecimens, or containers, or both, to 61 g,7. Precautions7.1 Toxic or corrosive
27、 effluents, or both, may be releasedwhen heating some material and could be harmful to personneland apparatus.8. Reagents and Materials8.1 For the temperature range covered by manyapplications, the melting transitions of the following greater-than-99.9 % pure material may be used for calibration.Mel
28、tingTemperature,KAHeat of Fusion,J/gBIndium 429.75 28.58 0.07APrestonThomas, H., Metrologia, Vol 27, 1990, p. 3.BStolen, S., Gronvold, F., Thermochimica Acta, Vol 327, 1999, p.1.8.2 Sapphire, ( Al2O3), 20 to 80 mg, solid disk.9. Calibration9.1 Perform any calibration procedures described by themanuf
29、acturer in the operations manual.9.2 Perform a temperature signal calibration according toPractice E967.10. Procedure10.1 Calibration at a Specific TemperatureThe followingprocedure is used to calibrate the heat flow response of theinstrument with the same type specimen holder, heating rate,purge ga
30、s, and purge gas flow rate as will be used for specimenmeasurement. A dry nitrogen purge gas with a flow rate of 10to 50 6 5 mL/min is recommended. Other purge gases andrates may be used but shall be reported.10.1.1 Placea5to106 0.001-mg weighed amount of melttransition calibration material into a c
31、lean specimen holder.10.1.2 Seal the specimen holder with a lid, minimizing thefree space between the specimen and the lid. Load thespecimen into the instrument.10.1.3 Allow the specimen to equilibrate at a temperature30C below the melting temperature.10.1.4 Heat the specimen at 10C/min through the
32、endo-therm until the baseline is reestablished above the meltingendotherm. Record the accompanying thermal curve of heatflow versus time.NOTE 5Other heating rates may be used but shall be reported.10.1.5 Cool and reweigh the specimen. Reject the data ifmass losses exceed 1 % of the original mass or
33、if there isevidence of reaction with the specimen holder.10.1.6 Calculate the calibration coefficient at the tempera-ture of measurement using the procedure described in Section11. Duplicate determinations shall be made on different speci-mens and the mean value determined and reported.10.2 Calibrat
34、ion at Other TemperaturesOnce a calibra-tion coefficient at a specific temperature has been obtained bythe procedure in 10.1, extension of the calibration coefficient toE968 02 (2014)2other temperatures may be accomplished using the interpola-tive technique described below.10.2.1 Select a temperatur
35、e range for calibration of theinstrument. The range should be at least 30C below the lowesttemperature of interest (to permit attainment of dynamicequilibrium) to 10C above the highest temperature of interestand include the temperature of calibration established in 10.1.10.2.2 Condition the sapphire
36、 calibration material andspecimen holder by heating to the maximum temperaturedetermined in 10.2.1 and holding for 2 min. Cool to roomtemperature and store in a desiccator until needed.NOTE 6Any volatilization (such as from absorbed moisture) from thecalibration material during the experiment will i
37、nvalidate the test.10.2.3 Establish a baseline as follows:10.2.3.1 Load the instrument with the specimen pan and lid(from 10.2.2) to be used in 10.2.5.10.2.3.2 Establish the initial temperature conditions of theexperiment (determined in 10.2.1) and equilibrate for 5 min.10.2.3.3 Heat the specimen ho
38、lder and lid at 10C/minthroughout the temperature range established in 10.2.1. Recordthe accompanying thermogram of heat flow versus tempera-ture.NOTE 7Other heating rates may be used but shall be reported.10.2.4 After cooling the specimen holder and lid to roomtemperature, introduce and weigh 20 to
39、 70 mg of the sapphireheat capacity reference material from 10.2.2 to an accuracy of0.01 mg.10.2.5 Cover the specimen holder with the same lid mini-mizing the free space between the specimen and the lid. Loadthe specimen into the instrument.10.2.6 Take the specimen to the initial temperature deter-m
40、ined in 10.2.1 and allow to equilibrate for 5 min.10.2.7 Heat the specimen at 10C/min through the tempera-ture range of test recording the accompanying thermal curve.10.2.8 Calculate the calibration coefficient at any tempera-ture of interest within the temperature range described inSection 11. Dupl
41、icate determination shall be made on the samespecimen and the mean value determined and reported.11. Calculation11.1 Calculate the calibration coefficient at a specific tem-perature as follows:11.1.1 Using the thermal curve obtained in 10.1, construct abaseline on the differential heat flow curve by
42、 connecting thetwo points at which the melting endotherm deviates from thebaseline before and after the melt (see Fig. 1). Integrate thisarea as a function of time to achieve the melting endothermicpeak area in mJ.11.1.2 Calculate the experimental calibration coefficient atthe melting temperature of
43、 the standard reference material asfollows:E 5 Hm!/A! (1)where:E = calibration coefficient at the temperature of the meltingendotherm,H = enthalpy of fusion of the standard material, in J/g(mJ/g),m = mass of the standard, in g, andA = melting endotherm peak area, in mJ.11.2 Calculate the calibration
44、 coefficient at other tempera-tures.11.2.1 Measure the heat flow difference between the sap-phire and baseline trace on the heat flow recorder axis in thethermal curve obtained in 10.2 at the temperature of interest Tand the melting temperature Tsof the reference material.Thesevalues are D and D use
45、d in (Eq 2) (see Table 1 and Fig. 2).11.2.2 Obtain specific heat capacity values of the sapphire atthe temperature of interest (T) and at the melting temperatureof the reference material (Ts) from Table 2. Interpolate betweenthose values given in the table to obtain the specific heatcapacity at the
46、desired temperature. These values are C and Cused in (Eq 2).11.2.3 Calculate the calibration coefficient at temperature Tas follows:E 5 EC D!/CD! (2)where:E = calibration coefficient at temperature T,E = calibration coefficient at the melting temperature of thestandard reference material (Ts), as ca
47、lculated in11.1.2,C = specific heat capacity of sapphire reference material attemperature of interest T, in J/(g K),C = specific heat capacity of the sapphire reference mate-rial at the melting temperature of the reference material(Ts), in J/(g K),D = difference in recorder heat flow deflection betw
48、eenblank and calibration runs at the melting temperatureof the reference material (Ts), in mW, andD = difference in recorder heat flow deflection betweenblank and calibration runs at the temperature of interestT,inmW.NOTE 8In cases where different specimen holders are used for thebaseline and calibr
49、ation runs, the difference in recorder heat flowdeflections D and D may be corrected for small differences in specimenholder weight by adding the following value of D to D and D:FIG. 1 Melting EndothermE968 02 (2014)3D 5cp1000 EWc2 Wb!(3)where:cp= specific heat of aluminum (or other specimen holdermaterial of construction), in J/(g K) for aluminum),Wc= mass of the specimen holder for the calibration run, ing,Wb= mass of the specimen holder for the blank run, in g,and = heating rate, in K/s (C/s).12. Report12.1 The report
