1、Designation: E 2551 07Standard Test Method forHumidity Calibration (or Conformation) of HumidityGenerators for Use with Thermogravimetric Analyzers1This standard is issued under the fixed designation E 2551; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year 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.1. Scope1.1 This test method describes the humidity calibration (orconformance) of humidity
3、generators for use with thermogravi-metric analyzers and other thermal analysis apparatus. Thehumidity range covered is 5 to 95 % relative humidity (%RH)and the temperature range is 0 to 80 C.1.2 The values stated in SI units are to be regarded as thestandard.1.3 There are no ISO equivalents to this
4、 standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. 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. Re
5、ferenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 1142 Terminology Relating to Thermophysical PropertiesE 1582 Practice for Calibration of Temperature Scale forThermogravimetry3. Terminology3.1 Specific technical
6、 terms used in this standard are definedin Terminologies E 473 and E 1142. These terms includethermal curve and thermogravimetric analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 relative humidity, nthe ratio of actual partial pres-sure of water to the saturated water vapor pressure
7、 at the sametemperature, expressed as a percentage.3.2.2 water activity, nthe ratio of actual partial pressure ofwater to the saturated water vapor pressure at the sametemperature, expressed as a decimal fraction.3.2.2.1 DiscussionWater activity is also known as relativepressure in some applications
8、 areas.3.2.3 first-deviation-from-baseline, nthe relative humidityor water activity at which a deflection from the establishedbaseline is first observed.4. Summary of Test Method4.1 Humidity generators are devices aimed at producing aspecific level of humidity in the purge gas used by thermo-gravime
9、tric analyzers or other thermal analysis apparatus. Therequested humidity levels may be held constant (isohum) orincreased or decreased in a continuous or stepped fashion.4.2 The humidified purge gas is submitted to a thermogravi-metric analyzer in which the weight of a hygroscopic materialis observ
10、ed. The relative humidity (or activity) of the moisturein the purge gas is stepped or scanned through a humidityrange. At a fixed humidity of the purge gas, the test specimendeliquesces and gains weight. In MethodA, the humidity of theonset of this weight gain is taken as the humidity calibrationpoi
11、nt. In Methods B and C, the rate of weight change is zero atthe humidity calibration point.5. Significance and Use5.1 This test method calibrates or demonstrates conformityof the humidity level in a purge gas generated by a humiditygenerator at a fixed temperature. Such calibration or demon-stration
12、 of conformity may be required by quality initiatives.5.2 Conformance demonstrates that the humidified purgegas is within some established limits.5.3 Calibration provides an offset and or slope value thatmay be used for establishing the relative humidity scale of theapparatus.6. Interferences6.1 Tem
13、perature regulation of any solution-head space en-vironment to within 6 0.1 C is essential for realizinggenerated relative humidity values stable to within 6 1 %RH(expected).1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Su
14、bcommittee E37.01 on ThermalTest Methods and Practices.Current edition approved March 1, 2007. Published May 2007.2For 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 th
15、e standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Apparatus7.1 The humidity generator that is the focus of this standardmay be an accessory providing a humidified purge gas to som
16、eother thermal analysis apparatus (typically a thermogravimetricanalyzer) or it may be part of a self-contained instrument thatincludes both the humidity generator and the thermal analysisapparatus. In the former case, some of the components de-scribed below may be redundant.7.2 Humidity GeneratorTh
17、e essential instrumentation re-quired to provide the minimum humidity generator capabilityfor this method includes:7.2.1 Temperature Sensorto provide an indication of thepurge gas temperature readable to within 6 0.1 C.7.2.2 Temperature Controllercapable of executing a spe-cific temperature program
18、by operating heaters or coolersbetween selected temperature limits at a rate of temperaturechange of 0.5 C/min constant to 6 0.1 C/min or at anisothermal temperature constant to within 6 0.1 C.7.2.3 Humidity Sensorcapable of indicating the humidityof the purge gas over the range of 5 to 95 % relativ
19、e humidity(%RH) readable to within 6 0.1 %RH.7.2.4 Humidity Controllercapable of executing a specifichumidity program by operating purge gas humidifiers betweenselected humidity limits at a rate of humidity change of0.5 %RH/min constant to within 6 0.1 %RH or at an isohumrelative humidity to within
20、6 0.1 %RH.7.2.5 Purge Gas Flow Sensorcapable of measuring purgegas flow readable to within 6 0.1 mL/min.7.2.6 Purge Gas Flow Controllercapable of controllingpurge gas flow readable to within 6 0.1 mL/min.7.2.7 Humdifier elementcapable of generating purgegases with relative humidity continuously over
21、 the range of 5to 95 %RH.7.3 Thermogravimetric Analyzer (TGA)The essential in-strumentation required to provide the minimum thermogravi-metric analytical capability for this method includes:7.3.1 A furnace to provide uniform controlled heating orcooling of a specimen to a constant temperature or at
22、a constantrate within the applicable temperature range of this method.7.3.2 A temperature sensor to provide an indication of thespecimen or furnace temperature to within 6 0.1 C.7.3.3 A continuously recording balance to measure thespecimen weight with a minimum capacity of 100 mg andsensitivity of 6
23、 10 g.7.3.4 A means of maintaining the specimen/container underatmospheric control at a purge rate of 10 to 200 mL/min 6 10mL/min or 1 %, whichever is greater.7.3.5 A temperature controller capable of executing a spe-cific temperature program by operating the furnace betweenselected temperature limi
24、ts at a rate of temperature change of0.5 C/min constant to within 6 0.1 C/min or to an isothermaltemperature that is maintained constant to within 6 0.1 C fora minimum of 100 h.7.3.6 Containers (pans, crucibles, etc.) that are inert to thespecimen and that will remain gravimetrically stable within t
25、hetemperature limits of this method.7.3.7 Data storage capable of storage of the weight andrelative humidity signals.7.3.8 A display capable of plotting a thermal curve withweight on the ordinate (Y-axis) and relative humidity (oractivity) on the abscissa (X-axis) with a sensitivity of 10 g forweigh
26、t and 0.1 %RH, respectively.8. Reagents and Materials8.1 One or more inorganic salts taken from Table 1 selectedto provide the humidity range of interest.8.2 Purity of ReagentsReagent grade chemicals (or bet-ter) shall be used for preparation of all standard solutions.8.3 Purity of WaterReagent wate
27、r produced by distillationor by ion exchange, or reverse osmosis followed by distillationshall be used (see Specification D 1193).9. Hazards9.1 Salt solutions are extremely corrosive to apparatus ifspilled. Care shall be taken in their preparation and handling toprevent contact with apparatus.TABLE
28、1 Humidity Fixed PointsL. Greenspan, “Humidity Fixed Points of Binary Saturated Aqueous Solutions”, Journal of Research of the National Bureau ofStandards - A. Physics and Chemistry, 1977, 81A (1) pp. 89-96Temperature(C)LithiumChloridePotassiumAcetateMagnesiumChloridePotassiumCarbonateMagnesiumNitra
29、teSodiumBromideStrontiumChlorideSodiumChloridePotassiumChloride10 11.3 23.7 33.5 43.1 57.4 62.2 75.66 75.7 86.815 11.3 23.4 33.3 43.2 55.9 60.7 74.13 75.6 85.920 11.3 23.1 33.1 43.2 54.4 59.1 72.52 75.5 85.125 11.3 22.5 32.8 43.2 52.9 57.6 70.85 75.3 84.330 11.3 21.6 32.4 43.2 51.4 56.0 69.12 75.1 8
30、3.635 11.3 . 32.1 . 49.9 54.6 . 74.9 83.040 11.2 . 31.6 . 48.4 53.2 . 74.7 82.345 11.2 . 31.1 . 46.9 52.0 . 74.5 81.750 11.1 . 30.5 . 45.4 50.9 . 74.4 81.255 11.0 . 29.9 . . 50.2 . 74.4 80.760 11.0 . 29.3 . . 49.7 . 74.5 80.365 10.9 . 28.5 . . 49.5 . 74.7 79.970 10.8 . 27.8 . . 49.7 . 75.1 79.575 10
31、.6 . 26.9 . . 50.3 . 75.6 79.280 10.5 . 26.1 . . 51.4 . 76.3 78.9E255107210. Preparation of Apparatus10.1 Perform any setup or calibration procedures recom-mend by the apparatus manufacturer in the operations manual.10.2 Positioning of the Temperature SensorIf the systememploys a temperature sensor
32、that is movable, it shall belocated as close to the specimen as possible without touchingit or the balance pan. In addition, it must be located in exactlythe same position during calibrations as used during analyticaldeterminations.11. Calibration and Standardization11.1 Calibrate the temperature di
33、splay of the apparatusaccording to Test Method E 1582 using a heating rate of 0.5 60.2 C/min.12. Procedure12.1 Close the system, adjust the atmospheric flow rate ofthe purge gas to the selected rate, and zero (tare) the balance.12.2 Open the system and place 5 to 10 mg of the referencematerial in th
34、e specimen container in the same position aswould be placed for a test specimen. Close the system.12.3 Measure the weight of the reference material andreport its value.12.4 Method A12.4.1 Equilibrate the humidity for 60 min at a value that is5 %RH below the anticipated deliquescence point described
35、inTable 1.NOTE 1Other humidity starting points may be used but shall bereported.12.4.2 Initiate either a humidity program with either0.2 %RH steps and 12 min soak times or 1 %RH/hr linearincrease to an ending humidity value that is 5 %RH higher thanthe anticipated deliquescence point in Table 1.NOTE
36、 2Other humidity ending points and rate of humidity changemay be used but shall be reported.12.4.3 Plot the results as weight of the reference material onthe ordinate (Y-axis) and the relative humidity on the abscissa(X-axis) of a thermal curve.12.4.4 Determine the first-deviation-from-baseline as t
37、hedeliquescence point of the reference material (see Fig. 1).Report the corresponding humidity as Mi.NOTE 3The rate of weight gain will increase with relative humidityabove the humidity at which the initial weight gain is observed. There isno inflection point. The use of extrapolate onset values sha
38、ll not be used.12.5 Method B12.5.1 Equilibrate the humidity for 60 min at 5 %RH abovethe anticipated deliquescence point described in Table 1.NOTE 4Other humidity starting points and equilibrium times may beused but shall be reported.12.5.2 Initiate decreasing humidity program with either0.2 %RH ste
39、ps and 12 min soak times or a linearly decreasingat 1 %RH/hr to an ending value that is 5 %RH lower than theanticipated deliquescence point in Table 1.NOTE 5Other humidity ending points and rates of change may beused but shall be reported.FIG. 1 First-Deviation-From-Baseline as the Deliquescence Poi
40、nt of the reference materialE255107312.5.3 Create a plot of the weight of the reference materialon the ordinate (Y-axis) versus the relative humidity on theabscissa (X-axis).12.5.4 Determine the relative humidity at the peak of thedeliquescence curve (see Fig. 2). Report this value as Mp.12.6 Method
41、 C12.6.1 Equilibrate the humidity for 60 min at 5 %RH abovethe anticipated deliquescence point described in Table 1.NOTE 6Other humidity starting points and equilibrium times may beused but shall be reported.12.6.2 Initiate a decreasing humidity program with either a0.2 %RH steps and 12 min soak tim
42、es or a linearly decreasingprogram at 1 %RH/hr to an ending value that is 5 %RH lowerthan the anticipated deliquescence point in Table 1.NOTE 7Other humidity ending points and rates of change may beused but shall be reported.12.6.3 Create a plot of the rate of weight change as afunction of a change
43、in humidity (dm/dRH) of the referencematerial on the ordinate (Y-axis) versus the relative humidityon the abscissa (X-axis).12.6.4 Determine the relative humidity at the point wheredm/dRH = 0 (see Fig. 3). Report this value as Mz.13. Calculation or Interpretation of Results13.1 Conformance (C) is th
44、e percent relative humiditydifference between an observed deliquescence value and that ofthe reference material (Ms) taken from Table 1 and is given byEq 1. Mi or Mp are taken as Mo for Methods A and B,respectively,C 5 Mo Ms or C 5 Mp Ms or C 5 Mz Ms (1)NOTE 8The conformance estimation is essentiall
45、y an estimate of biasand is suitable only for those humidities in the vicinity of the deliquescentof the reference material. More than one determination of conformancemay need to be performed to describe the humidity range from 5 to95 %RH.14. Report14.1 Report the following information:14.1.1 A comp
46、lete identification and description of thereference material used for calibration.14.1.2 Description of the humidity generator and thermo-gravimetric analyzer used.14.1.3 Experimental conditions including initial specimenweight, initial and final relative humidities and the rate ofhumidity change.14
47、.1.4 The values for Mi or Mp or both.15. Precision and Bias15.1 Precision15.1.1 The precision of this test method will be determinedin an interlaboratory test scheduled for 2008 to 2009. Anyonewishing to participate in this interlaboratory test should contactthe E37 Staff Manager at ASTM Internation
48、al Headquarters.15.1.2 The within laboratory standard deviation for thedetermination of Mi or Mp determined in two laboratories wasfound to be 0.26 %RH for MethodA, 0.20 %RH for Method B,and 0.12 %RH for Method C.15.2 Bias15.2.1 Bias is determined by this method as conformanceFIG. 2 Relative Humidit
49、y at the Peak of the Deliquescence CurveE255107415.2.2 The within laboratory conformance for the determi-nation of Mi or Mp determined in two laboratories at 25 C wasfound to be 1.0 %RH for Method A and 1.3 %RH for MethodB and C.16. Keywords16.1 humidity; moisture; thermal analysis; thermogravimet-ric analysisASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any su
