1、Designation: D 5032 97 (Reapproved 2003)An American National StandardStandard Practice forMaintaining Constant Relative Humidity by Means ofAqueous Glycerin Solutions1This standard is issued under the fixed designation D 5032; the number immediately following the designation indicates the year ofori
2、ginal adoption or, 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 practice describes a method for obtaining constantrelati
3、ve humidity ranging from 30 to 98 % at temperaturesranging from 0 to 70C in relatively small containers by meansof an aqueous glycerin solution.1.2 This practice is applicable for closed systems such asenvironmental conditioning containers.1.3 This practice is not recommended for the generation ofco
4、ntinuous (flowing) streams of constant humidity unlessprecautionary criteria are followed to ensure source stability.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-priat
5、e safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 618 Practice for Conditioning Plastics for Testing2D 4023 Terminology Relating to Humidity Measurements3E 104 Practice for Maintaining Constant Relative H
6、umidityby Means of Aqueous Solutions32.2 Other Documents:DIN50008 Constant Climates Over Aqueous Solutions4Part 1: Saturated Salt and Glycerol SolutionsPart 2: Sulfuric Acid Solutions (1981)3. Summary of Practice3.1 Controlled relative humidity environments are gener-ated using mixtures of glycerin
7、and water.3.2 Practice E 104 contains methods for maintaining con-stant relative humidity environments using aqueous saturatedsalt solutions or various strength sulfuric acid-water systems.4. Significance and Use4.1 Controlled relative humidity environments are impor-tant for conditioning materials
8、for shelf-life studies or forinvestigating the change in physical or dielectric propertiesafter exposure.4.2 The use of aqueous-glycerin solutions reduces the pos-sibility of contamination of the materials or corrosion ofelectrode systems which would be more likely to result fromsaturated salt or ac
9、id water solutions.4.3 Applicable material specifications should state the ex-posure conditions, including time, temperature and relativehumidity, that a material should be subjected to before subse-quent testing. Typical conditions are given in Practice D 618.5. Apparatus5.1 Container, airtight, of
10、 a material not acted upon bycopper sulfate (or with the glycerin solution contained in a traymade of a material not acted upon by copper sulfate).5.2 Refractometer, covering the range of 1.33 to 1.47(sodium) with an accuracy of 0.0003.6. Glycerin Solution6.1 Use a good industrial grade of glycerin
11、(“high gravity”and “dynamite” grades are satisfactory) in distilled water.Calculate the concentration in terms of the refractive index,(R), at 25C for the desired relative humidity at any tempera-ture between 0 and 70C as follows:R 5 =100 1 A!21 A22 H 1 A!22 A!1715.31 1.3333(1)where:T = temperature
12、of the solution, C,A = 25.60 0.1950T + 0.0008T2, andH = relative humidity, percent.6.1.1 This will give the desired relative humidity with anaccuracy of 60.2 % at a constant temperature of 25C. At otherconstant temperatures, the error, if any, may increase with thedeviation of the temperature from 2
13、5C. The relative humidityvalues at 0, 25, 50 and 70C for a number of refractive indexvalues are given in Table 1. Obtain the refractive index forintermediate values of relative humidity and temperature by1This practice is under the jurisdiction of ASTM Committee D09 on Electricaland Electronic Insul
14、ating Materials and is the direct responsibility of SubcommitteeD09.12 on Electrical Tests.Current edition approved March 10, 2003. Published April 2003. Originallyapproved in 1990. Last previous edition approved in 1997 as D 5032 97.2Annual Book of ASTM Standards, Vols 08.01 and 10.01.3Annual Book
15、of ASTM Standards, Vol 11.03.4Available from Deutsches Institut fur Normung, 4-10 BurggrenzenstrassePostfach 1107, D-1000 Berlin, Germany. Also available from American NationalStandards Institute, 25 W. 43rd St., 4th Floor, New York, NY 100361Copyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959, United States.plotting curves from the values in the table or by calculatingfrom the above formula.6.2 To prevent fungus growth in the solution, add about0.1 % by weight of copper sulfate to the glycerin solution. Themost convenient way of measuring the cop
17、per sulfate is toprepare a saturated solution in water and add four drops of thesaturated solution per 100 mL of the glycerin solution. Use acontainer, or tray holding the glycerin solution, made of amaterial that will not react with the copper in the coppersulfate. If the copper is removed, fungus
18、growth can occur,which will cause lowering of the humidity value of the glycerinsolution.6.3 Loss of water through evaporation when the container isopen, or by absorption by the material being conditioned, willreduce the humidity value of the solution. The rate of loss withthe container open is quit
19、e low and is negligible for the normaltime the container would be open for loading and unloading(Note 1). A material being conditioned that will absorb a largeamount of water may seriously reduce the humidity unlessproper precautions are taken. For example, a loss of 0.26 mLwater/cubic in.3of a glyc
20、erin-water solution adjusted to pro-duce a 96 % relative humidity at 25C will reduce the humidityby 0.5 % relative humidity. If it is estimated that the reductionin humidity will be greater than desired, one or both of thefollowing may be done: the loading may re reduced below thatsuggested in 7.5 o
21、r the depth of the solution may be increased.NOTE 1A solution adjusted to produce a 96 % relative humidityatmosphere at 25C in an open container, in a still atmosphere of 50 %relative humidity at 25C, will lose water at the rate of approximately 0.01mL/h/in.2of solution surface area. This rate will
22、reduce the relativehumidity value of a 96 % solution having a depth of 1 in. by 0.5 % relativehumidity in 26 h.7. Precautions7.1 Container:7.1.1 Make the container small so that the temperaturethroughout the container will be the same as that of thesolution. Keep the volume of the air space per unit
23、 area ofsurface of solution low. Ten cubic inches or less per in.2ofsolution surface is advisable unless a larger volume is neces-sary because of the device to be conditioned.7.1.2 Although an airtight container is recommended, it isdesirable to have a vent under certain conditions of test or withso
24、me kinds of containers. (Changes in pressure may produceundesirable cracks in some types of containers. ) Make the ventas small as practical as there will be a continual loss of vaporthrough the vent. Check the concentration of the solutionperiodically and adjust if necessary in this case.7.1.3 Make
25、 the surface creepage distance between thesolution and the material being conditioned long enough toprevent the solution creeping to the material being conditioned.7.2 Temperature Fluctuations:7.2.1 Avoid temperature fluctuations. Best results are ob-tained in a controlled temperature room where the
26、 averagetemperature is constant and the fluctuations are of relativelyshort duration. Cover the container to shield from drafts. Draftsmay cause temperature differences inside the container. Chang-ing ambient temperature causes a temperature difference be-tween that of the solution and the air above
27、 it. As a rule,changes in the solution temperature lag behind that of the air inthe container. This results in a low humidity with risingtemperature and a high humidity with falling temperature.7.2.2 If a controlled temperature room is not available, fairresults may be obtained by placing the contai
28、ner in a locationhaving the minimum change in temperature and thermallyinsulating the container with at least 1 in. of glass wool, or theequivalent. Reducing the volume of air space in the containerper unit area of solution surface will also reduce the effect ofchanging temperature.7.2.3 A glass des
29、iccator covered with a corrugated paperbox will stand short time (30 min or less) fluctuations oftemperature of 61C without changing the relative humidityover 60.1 %. Where larger fluctuations or long time fluctua-tions are encountered, thermally insulate the container. It isestimated that a thermal
30、ly insulated container will withstandfluctuations of temperature of 63C without changing therelative humidity over 60.1 %.7.2.4 A thick aluminum cover or base plate, or both, on thecontainer will also effectively dampen temperature fluctua-tions.7.3 Temperature Above Room TemperatureOperating attemp
31、eratures above or below room temperature is not assatisfactory as operating at room temperature, because of thegreater possibility of the air in the container not being at thesolution temperature and not being the same throughout thecontainer. For example, with a solution for a relative humidityof 9
32、6 %, a spot having a temperature 0.3C higher than that ofthe solution would have a relative humidity of 94 %, while thathaving a temperature 0.3C lower would have a relativehumidity of 98 %. However, with proper care, humidities attemperatures above room temperature are attainable by heatingthe cont
33、ainer in an oven. Thermally insulate the container asdescribed in 7.2 and adjust the oven air circulation so as tohave as nearly uniform temperature throughout the container aspossible. Load the container while at room temperature.7.4 Temperatures Below Room TemperatureFollow thesame precautions as
34、for temperatures above room temperatureexcept reduce the temperature of the container (open) belowthe conditioning temperature before loading.7.5 LoadingAvoid overloading as this may decrease therate of rise of the humidity in the container to such an extentTABLE 1 Relative Humidity Over Glycerin So
35、lutionsRefractiveIndexat 25CRelative Humidity, %0C 25C 50C 70C1.3463 97.7 98.0 98.2 98.41.3560 95.6 96.0 96.4 96.71.3602 94.5 95.0 95.5 95.81.3773 89.2 90.0 90.7 91.21.3905 84.0 85.0 85.9 86.61.4015 78.8 80.0 81.1 81.81.4109 73.7 75.0 76.2 77.01.4191 68.6 70.0 71.3 72.21.4264 63.4 65.0 66.4 67.31.43
36、29 58.4 60.0 61.4 62.51.4387 53.3 55.0 56.5 57.61.4440 48.3 50.0 51.5 52.61.4486 43.3 45.0 46.6 47.71.4529 38.3 40.0 41.6 42.7D 5032 97 (2003)2that an unreasonably long time is required for the humidity toreach a steady state. The limit of loading cannot very well bespecified as this depends upon th
37、e amount of moisture thematerial will absorb; this differs for different materials. As ageneral rule, make the over-all area of the material less than thesurface area of the solution.7.6 Opening of the Chamber During Test Avoid openingthe chamber during a test since the rate of establishingequilibri
38、um after reclosing the chamber is not known. Equilib-rium in the chamber depends on the ratio of chamber volumeto solution surface area, type of material in thechamber,amount of material in the chamber and temperature differencebetween the solution and the chamber atmosphere.8. Keywords8.1 aqueous g
39、lycerin solutions; conditioning; constant rela-tive humidity; glycerin; relative humidityASTM 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 o
40、f the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn.
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42、ents have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 5032 97 (2003)3
