1、Designation: E2551 07E2551 13Standard Test Method forHumidity Calibration (or Conformation) of HumidityGenerators for Use with Thermogravimetric Analyzers1This standard is issued under the fixed designation E2551; the number immediately following the designation indicates the year oforiginal adoptio
2、n or, in the case of revision, the 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 test method describes the humidity calibration (or conformance) of hum
3、idity generators for use with thermogravimetricanalyzers and other thermal analysis apparatus. The humidity range covered is 5 to 95 % relative humidity (%RH) (% RH) andthe temperature range is 0 to 80 C.80C.1.2 The values stated in SI units are to be regarded as standard. No other units of measurem
4、ent are included in this standard.1.3 There are no ISO equivalents to this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and
5、 determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE473 Terminology Relating to Thermal Analysis and RheologyE691 Practice for Con
6、ducting an Interlaboratory Study to Determine the Precision of a Test MethodE1142 Terminology Relating to Thermophysical PropertiesE1582 Practice for Calibration of Temperature Scale for Thermogravimetry3. Terminology3.1 Specific technical terms used in this standard are defined in Terminologies E47
7、3 and E1142. These terms include thermalcurve and thermogravimetric analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 relative humidity, nthe ratio of actual partial pressure of water to the saturated water vapor pressure at the sametemperature, expressed as a percentage.3.2.2 water
8、activity, nthe ratio of actual partial pressure of water to the saturated water vapor pressure at the same temperature,expressed as a decimal fraction.3.2.2.1 DiscussionWater activity is also known as relative pressure in some applications areas.3.2.3 first-deviation-from-baseline, nthe relative hum
9、idity or water activity at which a deflection from the established baselineis first observed.1 This test method is under the jurisdiction ofASTM Committee E37 on Thermal Measurements and is the direct responsibility of Subcommittee E37.10 on Fundamental,Statistical and Mechanical Properties.Current
10、edition approved March 1, 2007April 1, 2013. Published May 2007 May 2013. Originally approved in 2007. Last previous edition approved in 2007 as E2551 07. DOI: 10.1520/E2551-07.10.1520/E2551-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at se
11、rviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version
12、. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International,
13、 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 Humidity generators are devices aimed at producing a specific level of humidity in the purge gas used by thermogravimetricanalyzers or other thermal analysis apparatus. The requested hum
14、idity levels may be held constant (isohum) or increased ordecreased in a continuous or stepped fashion.4.2 The humidified purge gas is submitted to a thermogravimetric analyzer in which the weight of a hygroscopic material isobserved. The relative humidity (or activity) of the moisture in the purge
15、gas is stepped or scanned through a humidity range. Ata fixed humidity of the purge gas, the test specimen deliquesces and gains weight. In Test Method A, the humidity of the onsetof this weight gain is taken as the humidity calibration point. In Methods B and C, the rate of weight change is zero at
16、 the humiditycalibration point.5. Significance and Use5.1 This test method calibrates or demonstrates conformity of the humidity level in a purge gas generated by a humiditygenerator at a fixed temperature. Such calibration or demonstration of conformity may be required by quality initiatives.5.2 Co
17、nformance demonstrates that the humidified purge gas is within some established limits.5.3 Calibration provides an offset and or slope value that may be used for establishing the relative humidity scale of theapparatus.6. Interferences6.1 Temperature regulation of any solution-head space environment
18、 to within 6 0.1 C 60.1C is essential for realizinggenerated relative humidity values stable to within 6 1 %RH61 % RH (expected).7. Apparatus7.1 The humidity generator that is the focus of this standard may be an accessory providing a humidified purge gas to some otherthermal analysis apparatus (typ
19、ically a thermogravimetric analyzer) or it may be part of a self-contained instrument that includesboth the humidity generator and the thermal analysis apparatus. In the former case, some of the components described below maybe redundant.7.2 Humidity GeneratorThe essential instrumentation required t
20、o provide the minimum humidity generator capability for thismethod includes:7.2.1 Temperature Sensorto provide an indication of the purge gas temperature readable to within 6 0.1 C.60.1C.7.2.2 Temperature Controllercapable of executing a specific temperature program by operating heaters or coolers b
21、etweenselected temperature limits at a rate of temperature change of 0.5 C/min 0.5C/min constant to 6 0.1 C/min 60.1C/min or atan isothermal temperature constant to within 6 0.1 C.60.1C.7.2.3 Humidity Sensorcapable of indicating the humidity of the purge gas over the range of 5 to 95 % relative humi
22、dity(%RH) (% RH) readable to within 6 0.1 %RH.60.1 % RH.7.2.4 Humidity Controllercapable of executing a specific humidity program by operating purge gas humidifiers betweenselected humidity limits at a rate of humidity change of 0.5 %RH/min 0.5 % RH/min constant to within 6 0.1 %RH60.1 % RHor at an
23、isohum relative humidity to within 6 0.1 %RH.60.1 % RH.7.2.5 Purge Gas Flow Sensorcapable of measuring purge gas flow readable to within 6 0.1 60.1 mL/min.7.2.6 Purge Gas Flow Controllercapable of controlling purge gas flow readable to within 6 0.1 60.1 mL/min.7.2.7 Humdifier elementcapable of gener
24、ating purge gases with relative humidity continuously over the range of 5 to95 %RH.95 % RH.7.3 Thermogravimetric Analyzer (TGA)The essential instrumentation required to provide the minimum thermogravimetricanalytical capability for this method includes:7.3.1 A furnace to provide uniform controlled h
25、eating or cooling of a specimen to a constant temperature or at a constant ratewithin the applicable temperature range of this method.7.3.2 A temperature sensor to provide an indication of the specimen or furnace temperature to within 6 0.1 C.60.1C.7.3.3 A continuously recording balance to measure t
26、he specimen weight with a minimum capacity of 100 mg and sensitivityof 6 10 610 g.7.3.4 A means of maintaining the specimen/container under atmospheric 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 specific t
27、emperature program by operating the furnace between selectedtemperature limits at a rate of temperature change of 0.5 C/min 0.5C/min constant to within 6 0.1 60.1 C/min or to anisothermal temperature that is maintained constant to within 6 0.1 C 60.1C for a minimum of 100 h.7.3.6 Containers (pans, c
28、rucibles, etc.) that are inert to the specimen and that will remain gravimetrically stable within thetemperature limits of this method.7.3.7 Data storage capable of storage of the weight and relative humidity signals.E2551 1327.3.8 A display capable of plotting a thermal curve with weight on the ord
29、inate (Y-axis) and relative humidity (or activity) onthe abscissa (X-axis) with a sensitivity of 10 g for weight and 0.1 %RH, 0.1 % RH, respectively.8. Reagents and Materials8.1 One or more inorganic salts taken from Table 1 selected to provide the humidity range of interest.8.2 Purity of ReagentsRe
30、agent grade chemicals (or better) shall be used for preparation of all standard solutions.8.3 Purity of WaterReagent water produced by distillation or by ion exchange, or reverse osmosis followed by distillationshall be used (see Specification D1193).9. Hazards9.1 Salt solutions are extremely corros
31、ive to apparatus if spilled. Care shall be taken in their preparation and handling to preventcontact with apparatus.10. Preparation of Apparatus10.1 Perform any setup or calibration procedures recommend by the apparatus manufacturer in the operations manual.10.2 Positioning of the Temperature Sensor
32、If the system employs a temperature sensor that is movable, it shall be located asclose to the specimen as possible without touching it or the balance pan. In addition, it must be located in exactly the same positionduring calibrations as used during analytical determinations.11. Calibration and Sta
33、ndardization11.1 Calibrate the temperature display of the apparatus according to Test Method E1582 using a heating rate of 0.5 6 0.2C/min.0.2C/min.12. Procedure12.1 Close the system, adjust the atmospheric flow rate of the purge gas to the selected rate, and zero (tare) the balance.12.2 Open the sys
34、tem and place 5 to 10 mg of the reference material in the specimen container in the same position as wouldbe placed for a test specimen. Close the system.12.3 Measure the weight of the reference material and report its value.TABLE 1 Humidity Fixed PointsL. Greenspan, L., “Humidity Fixed Points of Bi
35、nary Saturated Aqueous Solutions”,Solutions,”Journal of Research of theNational Bureau of Standards - A. Physics and Chemistry, 1977, 81A (1) Vol 81A, No. 1, 1977, pp. 8996.Temperature(C)LithiumChloridePotassiumAcetateMagnesiumChloridePotassiumCarbonateMagnesiumNitrateSodiumBromideStrontiumChlorideS
36、odiumChloridePotassiumChloride10 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 83.635 11.3 . 32.1 . 49.9 54.6 . 7
37、4.9 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 10.6 . 26.9 . . 50.3 . 75.6 79.280
38、10.5 . 26.1 . . 51.4 . 76.3 78.9E2551 13312.4 Test Method A:12.4.1 Equilibrate the humidity for 60 min at a value that is 5 %RH 5 % RH below the anticipated deliquescence point describedin Table 1.NOTE 1Other humidity starting points may be used but shall be reported.12.4.2 Initiate either a humidit
39、y program with either 0.2 %RH 0.2 % RH steps and 12 min soak times or 1 %RH/hr 1 % RH/hrlinear increase to an ending humidity value that is 5 %RH 5 % RH higher than the anticipated deliquescence point in Table 1.NOTE 2Other humidity ending points and rate of humidity change may be used but shall be
40、reported.12.4.3 Plot the results as weight of the reference material on the 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 the deliquescence point of the reference material (see Fig. 1). Report thecorrespon
41、ding humidity as Mi.NOTE 3The rate of weight gain will increase with relative humidity above the humidity at which the initial weight gain is observed. There is noinflection point. The use of extrapolate onset values shall not be used.12.5 Test Method B:12.5.1 Equilibrate the humidity for 60 min at
42、5 %RH 5 % RH above the anticipated deliquescence point described in Table 1.NOTE 4Other humidity starting points and equilibrium times may be used but shall be reported.12.5.2 Initiate decreasing humidity program with either 0.2 %RH 0.2 % RH steps and 12 min soak times or a linearly decreasingat 1 %
43、RH/hr 1 % RH/hr to an ending value that is 5 %RH 5 % RH lower than the anticipated deliquescence point in Table 1.NOTE 5Other humidity ending points and rates of change may be used but shall be reported.12.5.3 Create a plot of the weight of the reference material on the ordinate (Y-axis) versus the
44、relative humidity on the abscissa(X-axis).12.5.4 Determine the relative humidity at the peak of the deliquescence curve (see Fig. 2). Report this value as Mp.12.6 Test Method C:12.6.1 Equilibrate the humidity for 60 min at 5 %RH 5 % RH above the anticipated deliquescence point described in Table 1.N
45、OTE 6Other humidity starting points and equilibrium times may be used but shall be reported.FIG. 1 First-Deviation-From-Baseline as the Deliquescence Point of the reference materialE2551 13412.6.2 Initiate a decreasing humidity program with either a 0.2 %RH 0.2 % RH steps and 12 min soak times or a
46、linearlydecreasing program at 1 %RH/hr 1 % RH/hr to an ending value that is 5 %RH 5 % RH lower than the anticipated deliquescencepoint in Table 1.NOTE 7Other humidity ending points and rates of change may be used but shall be reported.12.6.3 Create a plot of the rate of weight change as a function o
47、f a change in humidity (dm/dRH) of the reference material onthe ordinate (Y-axis) versus the relative humidity on the abscissa (X-axis).12.6.4 Determine the relative humidity at the point where dm/dRH = 0 (see Fig. 3). Report this value as Mz.13. Calculation or Interpretation of Results13.1 Conforma
48、nce (C) is the percent relative humidity difference between an observed deliquescence value and that of thereference material (Ms) taken from Table 1 and is given by Eq 1. Mi or Mp are taken as Mo for Methods A and B, respectively,C5Mo2Ms or C5Mp2Ms or C5Mz2Ms (1)NOTE 8The conformance estimation is
49、essentially an estimate of bias and is suitable only for those humidities in the vicinity of the deliquescent ofthe reference material. More than one determination of conformance may need to be performed to describe the humidity range from 5 to 95 %RH.95 %RH.14. Report14.1 Report the following information:14.1.1 A complete identification and description of the reference material used for calibration.14.1.2 Description of the humidity generator and thermogravimetric analyzer used.14.1.3 Experimental conditions including initial s
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