1、Designation: E 968 02 (Reapproved 2008)Standard 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
2、year 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 ran
3、gefrom 130 C to + 800 C.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
4、 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 Documents2.1 ASTM Standards:2E 473 Terminology Relating to The
5、rmal Analysis and Rhe-ologyE 793 Test Method 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 Propertie
6、s3. Terminology3.1 Definitions Specific technical terms used in this prac-tice are in accordance with Terminologies E 473 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 ofva
7、lues divided by their average. It is usually multiplied by 100and expressed as a percentage.NOTE 1The 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
8、 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 function of a second signal proportional totemperature or ti
9、me. 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 multiplied by a proportionality constant that convertsth
10、e 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 recording system being used and, moreover, may vary wi
11、thtemperature.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 heat offusion is known to better than 6 1.5 % (rel)
12、 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 point of the standardmaterial through the recording
13、 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 calibration coefficient at the newtemperature.4.4 Once t
14、he calibration coefficient at a given temperature isdetermined, it may be used to determine the desired energy1This practice is under the jurisdiction of ASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on ThermalTest Methods and Practices.Current edi
15、tion approved Sept. 1, 2008. Published October 2008. Originallyapproved in 1983. Last previous edition approved in 2002 as E 968 99(2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
16、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.value associated with an enthalpic transition in an unknownspecimen at that temperature (see Test Method E 7
17、93).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 Thi
18、s 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)The es
19、sen-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 temperatu
20、reor at a constant rate with the temperature range of 100 to 600C.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 indication of thespecimen/furnace temperature to 6 0.01 K.6.1.1.3
21、 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 helium
22、 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(s)b
23、etween 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 temperature,
24、 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 spe
25、cial 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 thereof.6.
26、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 som
27、e 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 429
28、.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 967.10. Procedure10.1 Calibration at a specific temperatureTh
29、e 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 be used for specimenmeasurement. A dry nitrogen purge gas with a flow rate of 10to 50 6 5 mL/min is recommended. Other purge g
30、ases 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 the specimen holder with a lid, minimizing thefree space between the specimen and the lid. Load thespecimen into the instrument.
31、10.1.3 Allow the specimen to equilibrate at a temperature30 C below the melting temperature.10.1.4 Heat the specimen at 10 C/min through the endot-herm until the baseline is reestablished above the meltingendotherm. Record the accompanying thermal curve of heatflow versus time.NOTE 5Other heating ra
32、tes 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 with the specimen holder.10.1.6 Calculate the calibration coefficient at the tempera-ture of measurement using the procedure de
33、scribed in Section11. Duplicate determinations shall be made on different speci-mens and the mean value determined and reported.3PrestonThomas, H., Metrologia, Vol 27, 1990, p. 3.4Stolen, S., Gronvold, F., Thermochimica Acta, Vol 327, 1999, p.1. E37E 968 02 (2008)210.2 Calibration at other temperatu
34、res Once a calibrationcoefficient 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 theinstrume
35、nt. The range should be at least 30 C below thelowest temperature of interest (to permit attainment of dynamicequilibrium) to 10 C above the highest temperature of interestand include the temperature of calibration established in 10.1.10.2.2 Condition the sapphire calibration material andspecimen ho
36、lder 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 invalidate the test.10.2.3 Establish
37、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 holder and lid at 10 C/minthroughout t
38、he 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 70 mg of the sapphireheat capacity
39、 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-mined in 10.2.1 and allow to equilib
40、rate for 5 min.10.2.7 Heat the specimen at 10 C/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
41、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 connecting thetwo points at which
42、 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 the standard reference material a
43、sfollows: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,A = melting endotherm peak area, in mJ,11.2 Calculate the calibration coefficient at other tempera-tures.
44、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 Dt and D used in (Eq 2) (see Table 1 and Fig. 2
45、).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 desired temperature. These values a
46、re Ct and Cused in (Eq 2).11.2.3 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
47、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 heat flow deflection betweenblank and calibration runs
48、at the melting temperatureof the reference material ( Ts), in mW, andDt = difference in recorder heat flow deflection betweenblank and calibration runs at the temperature ofinterest T,inmW.NOTE 8In cases where different specimen holders are used for thebaseline and calibration runs, the difference i
49、n recorder heat flowdeflections D and Dt may be corrected for small differences in specimenholder weight by adding the following value of D D to D and Dt:FIG. 1 Melting EndothermE 968 02 (2008)3DD 5cpb1000 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,in g,Wb= mass of the specimen holder for the blank run, in g,andb = heating rate, in K/s (C/s).12. Report12.1 The report shall contain the following:12.1.1
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