ASTM E2551-20

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Designation: E2551 − 18 E2551 − 20
Standard Test Methods for
Humidity Calibration (or Conformation) of Humidity
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Generators for Use with Thermogravimetric Analyzers
This standard is issued under the fixed designation E2551; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 These test methods describe the humidity calibration (or conformance) of humidity generators for use with thermogravi-
metric analyzers and other thermal analysis apparatus. The humidity range covered is 5 % relative humidity (% RH) to 95 % RH
and the temperature range is 0 °C to 80 °C.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
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2.1 ASTM Standards:
D1193 Specification for Reagent Water
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E473 Terminology Relating to Thermal Analysis and Rheology
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E1142 Terminology Relating to Thermophysical Properties
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These test methods are under the jurisdiction of ASTM Committee E37 on Thermal Measurements and are the direct responsibility of Subcommittee E37.10 on
Fundamental, Statistical and Mechanical Properties.
Current edition approved Oct. 1, 2018March 15, 2020. Published October 2018April 2020. Originally approved in 2007. Last previous edition approved in 20132018 as
E2551 – 13.18. DOI: 10.1520/E2551-18.10.1520/E2551-20.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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E2551 − 20
E1582 Test Method for Temperature Calibration of Thermogravimetric Analyzers
3. Terminology
3.1 Specific technical terms used in this standard are defined in Terminologies E473 and E1142. These terms include
first-deviation-from-baseline, isohume, relative humidity, thermal curve, and thermogravimetric analysis.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 water activity, n—the ratio of actual partial pressure of water to the saturated water vapor pressure at the same temperature,
expressed as a decimal fraction.
3.2.1.1 Discussion—
Water activity is also known as relative pressure in some applications areas.
4. Summary of Test Method
4.1 Humidity generators are devices aimed at producing a specific level of humidity in the purge gas used by thermogravimetric
analyzers or other thermal analysis apparatus. The requested humidity levels may be held constant (isohume) or increased or
decreased 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 is
observed. The relative humidity (or activity) of the moisture in the purge gas is stepped or scanned through a humidity range. At
a fixed humidity of the purge gas, the test specimen deliquesces and gains weight. In Test Method A, the humidity of the onset
of this weight gain is taken as the humidity calibration point. In Test Methods B and C, the rate of weight change is zero at the
humidity calibration point.
5. Significance and Use
5.1 These test methods calibrate or demonstrate conformity of the humidity level in a purge gas generated by a humidity
generator at a fixed temperature. Such calibration or
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