1、Designation: D5032 11Standard Practice forMaintaining Constant Relative Humidity by Means ofAqueous Glycerin Solutions1This standard is issued under the fixed designation D5032; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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 practice describes a method for obtaining constantrelative humidity ranging from 30 to 98 % at temperature
3、sranging 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 ofcontinuous (flowing) streams of constant humidity un
4、lessprecautionary 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-priate safety and health practices and determine the ap
5、plica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD4023 Terminology Relating to Humidity Measurements(Withdrawn 2002)3D6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing (Withdraw
6、n 2012)3E104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Solutions2.2 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
7、 environments are gener-ated using mixtures of glycerin and water.3.2 Practice E104 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
8、environments are impor-tant for conditioning materials 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
9、would be more likely to result fromsaturated salt or acid 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
10、Practice D618 orD6054.5. Apparatus5.1 Container, airtight, of 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 Refract meter, covering the range of 1.33 to 1.47(sodium) with an accuracy of 0.0003.6.
11、Glycerin Solution6.1 Use a good industrial grade of glycerin (“high gravity”and “dynamite” grades have been found to be satisfactory) indistilled water. Calculate the concentration in terms of therefractive index, (R), at 25C for the desired relative humidityat any temperature between 0 and 70C as f
12、ollows:R 5 =1001A!21A22 H1A!22 A!1715.311.3333 (1)1This practice is under the jurisdiction of ASTM Committee D09 on Electricaland Electronic Insulating Materials and is the direct responsibility of SubcommitteeD09.12 on Electrical Tests.Current edition approved Aug. 1, 2011. Published September 2011
13、. Originallyapproved in 1990. Last previous edition approved in 2003 as D5032 97(2003).DOI: 10.1520/D5032-11.2For 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 sta
14、ndards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from Deutsches Institut fur Normung, 4-10 BurggrenzenstrassePostfach 1107, D-1000 Berlin, Germany. Also available from American NationalStandards Institute,
15、25 W. 43rd St., 4th Floor, New York, NY 10036Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1where:T = temperature of the solution, C,A = 25.60 0.1950T + 0.0008T2, andH = relative humidity, percent.6.1.1 This will give the desired rel
16、ative 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 25C. The relative humidityvalues at 0, 25, 50 and 70C for a number of refractive indexvalues are given in Table 1. Obtain
17、 the refractive index forintermediate values of relative humidity and temperature byplotting 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 convenie
18、nt way of measuring the copper 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
19、 copper is removed, fungus growth can occur,which will cause lowering of the humidity value of the glycerinsolution.6.3 Loss of water through evaporation when the container isopened can reduce the humidity value of the solution. The rateof loss with the container open is quite low and is negligible
20、forthe normal time the container would be opened for loading andunloading (Note 1).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
21、solution surface area. This rate will reduce the relativehumidity value of a 96 % solution having a depth of 1 in. by 0.5 % relativehumidity in 26 h.6.4 Loss of water by absorption by the material beingconditioned, can reduce the humidity value of the solution.Proper precaution must be taken to prev
22、ent the reduction ofhumidity by a material being conditioned that will absorb alarge amount of water. If it is estimated that the reduction inhumidity will be greater than desired, one or both of thefollowing options must be done: Reduce the loading below thatsuggested in 7.5 or increase the depth o
23、f the solution.NOTE 2For example, a loss of 0.26 mL water/in.3of a glycerin-watersolution adjusted to produce a 96 % relative humidity at 25C will reducethe humidity by 0.5 % relative humidity.7. Precautions7.1 Container:7.1.1 Make the container small so that the temperaturethroughout the container
24、will be the same as that of thesolution. Keep the volume of the air space per unit 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 rec
25、ommended, it isdesirable to have a vent under certain conditions of test or withsome 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 concentr
26、ation of the solutionperiodically and adjust if necessary in this case.7.1.3 Make the surface creepage distance between thesolution and the material being conditioned long enough toprevent the solution from creeping on to the material beingconditioned.7.2 Temperature Fluctuations:7.2.1 Avoid tempera
27、ture fluctuations. Best results are ob-tained in a controlled temperature room where the 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 tem
28、perature causes a temperature difference be-tween that of the solution and the air above 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 control
29、led temperature room is not available, placethe container in a location having the minimum change intemperature and thermally insulating the container with aminimum of 1 in. of glass wool, or the equivalent. Reducingthe volume of air space in the container per unit area ofsolution surface will also
30、reduce the effect of changing tem-perature.7.2.3 A glass desiccator 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, the
31、rmally insulate the container. It isestimated that a thermally 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-
32、tions.7.3 Temperature Above Room TemperatureOperating attemperatures above room temperature is not as satisfactory asoperating at room temperature, because of the greater possi-bility of the air in the container not being equivalent to theTABLE 1 Relative Humidity Over Glycerin SolutionsRefractiveIn
33、dexat 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 67.31.4329 58.4 60.0 61.4 6
34、2.51.4387 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 42.7D5032 112solution temperature and not being the equivalent throughoutthe container. However, with proper care, humidities at tem-peratures above room temperature are attainable by heating theco
35、ntainer 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.NOTE 3For example, with a solution for a relative humidity of 96 %,
36、a spot having a temperature 0.3C higher than that of the solution wouldhave a relative humidity of 94 %, while that having a temperature 0.3Clower would have a relative humidity of 98 %.7.4 Temperatures Below Room TemperatureOperating attemperatures below room temperature is not as satisfactory asop
37、erating at room temperature, because of the greater possi-bility of the air in the container not being equivalent to thesolution temperature and not being the equivalent throughoutthe container. However, with proper care, humidities at tem-peratures below room temperature are attainable by cooling t
38、hecontainer in a chamber. Thermally insulate the container asdescribed in 7.2 and adjust the chamber air circulation so as tohave as nearly uniform temperature throughout the container aspossible. Load the container by reducing the temperature of thecontainer below the conditioning temperature befor
39、e loading.7.5 LoadingDo not overload the container as this willdecrease the rate of rise of the humidity in the container to suchan extent that an unreasonably long time is required for thehumidity to reach a steady state. The limit of loading cannotvery well be specified as this depends upon the am
40、ount ofmoisture the material will absorb and this will differ bymaterial. As a general rule, make the overall area of thematerial less than the surface area of the solution.7.6 Opening of the Chamber During TestAvoid openingthe chamber during a test since the rate of establishingequilibrium after re
41、closing the chamber is not known. Equilib-rium in the chamber depends on the ratio of chamber volumeto solution surface area, type of material in the chamber,amount of material in the chamber and temperature differencebetween the solution and the chamber atmosphere.8. Keywords8.1 aqueous glycerin so
42、lutions; 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 of the vali
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