ASTM_E_2551_-_13.pdf

Designation:E255113Standard 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 adoption 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(orconformance)of humidity generators for use with thermogra-vimetric analyzers and other thermal analysis apparatus.Thehumidity range covered is 5 to 95%relative humidity(%RH)and the temperature range is 0 to 80C.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 There are no ISO equivalents to this 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.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE473 Terminology Relating to Thermal Analysis and Rhe-ologyE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1142 Terminology Relating to Thermophysical PropertiesE1582 Practice for Calibration of Temperature Scale forThermogravimetry3.Terminology3.1 Specific technical terms used in this standard are definedin Terminologies E473 and E1142.These terms include ther-mal 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 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 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 thermogra-vimetric 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 thermogra-vimetric analyzer in which the weight of a hygroscopicmaterial is observed.The relative humidity(or activity)of themoisture in the purge gas is stepped or scanned through ahumidity range.At a fixed humidity of the purge gas,the testspecimen deliquesces and gains weight.In Test Method A,thehumidity of the onset of this weight gain is taken as thehumidity calibration point.In Methods B and C,the rate ofweight change is zero at the 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 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.1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.10 onFundamental,Statistical and Mechanical Properties.Current edition approved April 1,2013.Published May 2013.Originallyapproved in 2007.Last previous edition approved in 2007 as E2551 07.DOI:10.1520/E2551-13.2For 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 Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Interferences6.1 Temperature regulation of any solution-head space en-vironment to within 60.1C is essential for realizing generatedrelative humidity values stable to within 61%RH(expected).7.Apparatus7.1 The humidity generator that is the focus of this standardmay be an accessory providing a humidified purge gas to someother 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