1、Designation: E 968 02Standard Practice forHeat Flow Calibration of Differential Scanning Calorimeters1This standard is issued under the fixed designation E 968; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. 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 practice covers the heat flow calibration of differ-ential scanning calorimeters over the temperature rangefrom 130C to +
3、800C.1.2 Values given in SI units are to be regarded as thestandard.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 to address all of thesafety concerns, if any, associated with its use. It i
4、s 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 Documents2.1 ASTM Standards:E 473 Terminology Relating to Thermal Analysis2E 793
5、Test Method for Heats of Fusion and Crystallizationby Differential Scanning Calorimetry2E 967 Practice for Temperature Calibration of DifferentialScanning Calorimeters and Differential Thermal Analyz-ers23. Terminology3.1 DefinitionsSpecific technical terms used in this prac-tice are in accordance w
6、ith Terminologies E 474 and E 1142.3.2 Definitions of Terms Specific to This Standard:3.2.1 coeffcient of variation, na measure of relativeprecision calculated as the standard deviation of a series ofvalues divided by their average. It is usually multiplied by 100and expressed as a percentage.NOTE 1
7、The term quantitative differential thermal analysis refers todifferential thermal analyzers that are designed to obtain quantitative orsemiquantitative heat flow results. This procedure may also be used tocalibrate such apparatus.4. Summary of Practice4.1 Differential scanning calorimeters measure h
8、eat flow1This practice is under the jurisdiction of ASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on ThermalAnalysis Methods.Current edition approved March 10, 2002. Published June 2002. Originallypublished as E 968 83. Last previous edition E 968
9、99.2Annual Book of ASTM Standards, Vol 14.02.TABLE 1 Sapphire (a Al2O3) Specific Heat CapacityATemperature,KSpecific HeatCapacity, J/gKTemperature, KSpecific HeatCapacity, J/gK140 0.2739 630 1.1184150 0.3133 640 1.1228160 0.3525 650 1.1272170 0.3912 660 1.1313180 0.4290 670 1.1353190 0.4659 680 1.13
10、93200 0.5014 690 1.1431210 0.5356 700 1.1467220 0.5684 710 1.1503230 0.5996 720 1.1538240 0.6294 730 1.1572250 0.6577 740 1.1604260 0.6846 750 1.1637270 0.7102 760 1.1667280 0.7344 770 1.1698290 0.7574 780 1.1727300 0.7792 790 1.1756310 0.7999 800 1.1784320 0.8194 810 1.1811330 0.8380 820 1.1839340
11、0.8555 830 1.1864350 0.8721 840 1.1890360 0.8878 850 1.1914370 0.9027 860 1.1939380 0.9168 870 1.1962390 0.9302 880 1.1986400 0.9429 890 1.2008410 0.9550 900 1.2031420 0.9665 910 1.2053430 0.9775 920 1.2074440 0.9879 930 1.2095450 0.9978 940 1.2115460 1.0073 950 1.2135470 1.0164 960 1.2155480 1.0250
12、 970 1.2174490 1.0332 980 1.2194500 1.0411 990 1.2212510 1.0486 1000 1.2230520 1.0559 1010 1.2249530 1.0628 1020 1.2266540 1.0694 1030 1.2284550 1.0758 1040 1.2301560 1.0819 1050 1.2318570 1.0877 1060 1.2335580 1.0934 1070 1.2351590 1.0988 1080 1.2367600 1.1039 1090 1.2383610 1.1090 1100 1.2400620 1
13、.1138AArcher, D.G., J. Phys. Chem. Ref. Data, Vol 22, No. 8, pp. 14411453 (1993).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(power) into or out of a test specimen and provide a signaloutput proportional to this measurement. This
14、 signal often isrecorded as a function 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 ar
15、ea under the curve scribed)must be multiplied 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
16、differential scanning calorimeterand recording 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 h
17、igh-purity standard material (where the heat offusion is known to better than 6 1.5 % (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 tempe
18、ra-tures other than that of the melting 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
19、 calibrationprovides an instrument calibration 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 Method
20、 E 793).5. 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 the resulting data to that of aknown standard is required.5.2
21、 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 unknowns.6. Apparatus6.1 Differential Scanning Calorimeter (DSC)Th
22、e essen-tial instrumentation required to provide the minimum differen-tial scanning 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 heating(cooling) of a specimen and reference to a constant tempe
23、ratureor 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 A temperature sensor, to provide an indication of thespecimen/furnace temperature to 6 0.01 K.6.1
24、.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/min.NOTE 3Typically, 99.9+ % pure nitrogen, argon or he
25、lium are em-ployed when oxidation in air is a concern. Unless effects of moisture areto 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 aspecific temperature program by operating the furnace
26、(s)between selected temperature limits at a rate of temperaturechange of between 1 and 35 K/min constant to 6 1 % and at anisothermal temperature constant to 6 0.1 K.6.1.3 A recording device, either digital or analog, capable ofrecording and displaying the heat flow (DSC curve) signalversus temperat
27、ure, 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 thespecimen and reference.NOTE 4Most containers require
28、 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 provide constant cooling rates, or a combination thereo
29、f.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 weight speci-mens, or containers, or both, to 6 1 g,7. Precautions7.1 Toxic or corrosive effluents, or both, may be releasedwhen heating
30、 some material and could be harmful to personneland apparatus.8. Reagents and Materials8.1 For the temperature range covered by many applica-tions, the melting transitions of the following greater-than-99.9 % pure material may be used for calibration.Melting Tem-perature, K3Heat of Fusion,J/g4Indium
31、 429.75 28.58 6 0.078.2 Sapphire,(a Al2O3), 20 to 80 mg, solid disk.9. Calibration9.1 Perform any calibration procedures described by themanufacturer in the operations manual.9.2 Perform a temperature signal calibration according toPractice E 967.3PrestonThomas, H., Metrologia,Vol 27, 1990, p. 3.4St
32、olen, S., Gronvold, F., Thermochimica Acta, Vol 327, 1999, p.1.E96802210. 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 gas, and purge gas flow rate as will
33、 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 clean specimen holder.10.1.2 Seal t
34、he 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 endot-herm until the baseline is r
35、eestablished 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 if there isevidence of reaction wi
36、th 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 Calibration at other temperatures Once a c
37、alibrationcoefficient at a specific temperature has been obtained by theprocedure in 10.1, extension of the calibration coefficient toother temperatures may be accomplished using the interpola-tive technique described below.10.2.1 Select a temperature range for calibration of theinstrument. The rang
38、e 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 calibration material andspecimen holder by heatin
39、g 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 invalidate the test.10.2.3 Establish a baseline as
40、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 holder and lid at 10C/minthroughout the temperature
41、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 70 mg of the sapphireheat capacity reference mate
42、rial 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-mined in 10.2.1 and allow to equilibrate for 5 min.
43、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. Duplicate determination shall be made on the samespeci
44、men 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 connecting thetwo points at which the melting end
45、otherm 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 the standard reference material asfollows:E 5 Hm!
46、 / 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,A = melting endotherm peak area, in mJ,11.2 Calculate the calibration coefficient at other tempera-tures.11.2.1 Measure t
47、he 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 Dt and D used in (Eq 2) (see Fig. 2).11.2.2 Obtain specific he
48、at 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 desired temperature. These values are Ct and Cused in (Eq 2).F
49、IG. 1 Melting EndothermE96802311.2.3 Calculate the calibration coefficient at temperature Tas follows:Et5ECt D!/CDt! (2)where:Et = calibration coefficient at temperature T,E = calibration coefficient at the melting temperature ofthe standard reference material (Ts), as calculated in11.1.2,Ct = 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 referencematerial (Ts), in J/(g K),D = difference in recorder
