ASTM D5032-19

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. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: D5032 − 11 D5032 − 19
Standard Practice for
Maintaining Constant Relative Humidity by Means of
Aqueous Glycerin Solutions
This standard is issued under the fixed designation D5032; 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
1.1 This practice describes a method for obtaining constant relative humidity ranging from 30 to 98 % at temperatures ranging
from 0 to 70°C in relatively small containers by means of an aqueous glycerin solution.
1.2 This practice is applicable for closed systems such as environmental conditioning containers.
1.3 This practice is not recommended for the generation of continuous (flowing) streams of constant humidity unless
precautionary criteria are followed to ensure source stability.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D4023 Terminology Relating to Humidity Measurements (Withdrawn 2002)
D6054 Practice for Conditioning Electrical Insulating Materials for Testing (Withdrawn 2012)
E104 Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
2.2 Other Documents:
DIN50008 Constant Climates over Aqueous Solutions
Part 1: Saturated Salt and Glycerol Solutions
Part 2: Sulfuric Acid Solutions (1981)
3. Summary of Practice
3.1 Controlled relative humidity environments are generated using mixtures of glycerin and water.
3.2 Practice E104 contains methods for maintaining constant relative humidity environments using aqueous saturated salt
solutions or various strength sulfuric acid-water systems.
4. Significance and Use
4.1 Controlled relative humidity environments are important for conditioning materials for shelf-life studies or for investigating
the change in physical or dielectric properties after exposure.
This practice is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee D09.12
on Electrical Tests.
Current edition approved Aug. 1, 2011March 1, 2019. Published September 2011March 2019. Originally approved in 1990. Last previous edition approved in 20032011
as D5032 – 97D5032 – 11.(2003). DOI: 10.1520/D5032-11.10.1520/D5032-19.
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.
The last approved version of this historical standard is referenced on www.astm.org.
Available from Deutsches Institut fur Normung, 4-10 Burggrenzenstrasse Postfach 1107, D-1000 Berlin, Germany. Also available from American National Standards
Institute, 25 W. 43rd St., 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5032 − 19
4.2 The use of aqueous-glycerin solutions reduces the possibility of contamination of the materials or corrosion of electrode
systems which would be more likely to result from saturated salt or acid water solutions.
4.3 Applicable material specifications shouldshall state the exposure conditions, including time, temperature and relative
humidity that a material should is to be subjected to before subsequent testing. Typical conditions are given in Practice D618 or
D6054.
5. Apparatus
5.1 Container, airtight, of a material not acted upon by copper sulfate (or with the glycerin solution contained in a tray made
of a material not acted upon by copper sulfate).
5.2 Refract meter, covering the range of 1.33 to 1.47 (sodium) with an accuracy of 0.0003.
6. Glycerin Solution
6.1 Use a good industrial grade of glycerin (“high gravity” and “dynamite” grades have been found to be satisfactory) in
distilled water. Calculate the concentration in terms of the refractive index, (R), at 25°C for the desired relative humidity at any
temperature between 0 and 70°C as follows:
2 2 2
R 5~=~1001A! 1A 2 ~H1A! 2 A! 11.3333 (1)
715.3
where:
T = temperature of the solution, °C,
A = 25.60 − 0.1950T + 0.0008T , and
H = relative humidity, percent.
6.1.1 This will give the desired relative humidity with an accuracy of 60.2 % at a constant temperature of 25°C. At other
constant temperatures, the error, if any, may it is possible the error can increase with the deviation of the temperature from 25°C.
The relative humidity values at 0, 25, 50, and 70°C for a number of refractive index values are given in Table 1. Obtain the
refractive index for intermediate values of relative humidity and temperature by plotting curves from the values in the table or by
calculating from the above formula.
6.2 To prevent fungus growth in the solution, add about 0.1 % by weight of copper sulfate to the glycerin solution. The most
convenient way of measuring the copper sulfate is to prepare a saturated solution in water and add four drops of the saturated
solution per 100 mL of the glycerin solution. Use a container, or tray holding the glycerin solution, made of a material that will
not react with the copper in the copper sulfate. If the copper is removed, fungus growth can occur, which will cause lowering of
the humidity value of the glycerin solution.
6.3 Loss of water through evaporation when the container is opened can reduce the humidity value of the solution. The rate of
loss with the container open is quite low and is negligible for the normal time the container would be opened for loading and
unloading (Note 1).
NOTE 1—A solution adjusted to produce a 96 % relative humidity atmosphere at 25°C in an open container, in a still atmosphere of 50 % relative
humidity at 25°C, will lose water at the rate of approximately 0.01 0.01 mL mL/h/in.⁄h ⁄in. of solution surface area. This rate will reduce the relative
humidity value of a 96 % solution having a depth of 1 in. by 0.5 % relative humidity in 26 h.
6.4 Loss of water by absorption by the material being conditioned, can reduce the humidity value of the solution. Proper
precaution must be taken to prevent the reduction of humidity by a material being conditioned that will absorb a large amount of
TABLE 1 Relative Humidity Over Glycerin Solutions
Refractive Relative Humidity, %
Index
0°C 25°C 50°C 70°C
at 25°C
1.3463 97.7 98.0 98.2 98.4
1.3560 95.6 96.0
...