1、Designation: E 104 02Standard Practice forMaintaining Constant Relative Humidity by Means ofAqueous Solutions1This standard is issued under the fixed designation E 104; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This practice describes one method for
3、 generating con-stant relative humidity (rh) environments in relatively smallcontainers.1.2 This practice is applicable for obtaining constant rela-tive humidities ranging from dryness to near saturation attemperatures spanning from 0 to 50C.1.3 This practice is applicable for closed systems such as
4、environmental conditioning containers and for the calibrationof hygrometers.1.4 This practice is not recommended for the generation ofcontinuous (flowing) streams of constant humidity unlessprecautionary criteria are followed to ensure source stability.(See Section 9.)1.5 CautionSaturated salt solut
5、ions are extremely corro-sive, and care should be taken in their preparation andhandling. There is also the possibility of corrosive vapors in theatmospheres over the saturated salt solutions.21.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I
6、t 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. For more specificsafety precautionary information see 1.5 and 10.1.2. Referenced Documents2.1 ASTM Standards:3D 1193 Spec
7、ification for Reagent WaterD 1356 Terminology Relating to Sampling and Analysis ofAtmospheres2.2 Other Document:DIN50008 “Konstantklimate uber waesserigen Loseungen”(Constant Climates Over Aqueous Solutions).Part 1: Saturated Salt and Glycerol Solutions.43. Terminology3.1 non-hygroscopic materialmat
8、erial which neither ab-sorbs nor retains water vapor.3.2 For definitions of other terms used in this practice referto Terminology D 1356.4. Summary of Practice4.1 Standard value relative humidity environments are gen-erated using selected aqueous saturated salt solutions.5. Significance and Use5.1 S
9、tandard value relative humidity environments are im-portant for conditioning materials in shelf-life studies or in thetesting of mechanical properties such as dimensional stabilityand strength. Relative humidity is also an important operatingvariable for the calibration of many species of measuringi
10、nstruments.6. Interferences6.1 Temperature regulation of any solution-head space en-vironment to 60.1C is essential for realizing generatedrelative humidity values within 60.5 % (expected).6.2 Some aqueous saturated salt solutions change composi-tion following preparation by hydrolysis or by reactio
11、n withenvironmental components (for example, carbon dioxide ab-sorption by alkaline materials). These solutions should befreshly prepared on each occasion of use.7. Apparatus7.1 ContainerThe container, including a cover or lidwhich can be secured airtight, should be made of corrosionresistant, non-h
12、ygroscopic material such as glass. A metal or1This practice is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved October 10, 2002. Published December 2002. Origi-nally published as E 104 51. Last
13、 previous edition E 104 85(96).2Opila, R., Jr., Weschler, C. J., and Schubert, R., “Acidic Vapors AboveSaturated Salt Solutions Commonly Used for Control of Humidity,” IEEE Trans.Components, Hybrids and Manufacturing Technology, Vol 12, No. 1, March 1989,pp. 114120.3For referenced ASTM standards, vi
14、sit 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.4Published by Deutsches Institut fr Normung, 4-10 Burggrzfenstrasse Postfach1107, D-1000 Berlin
15、, Federal Republic of Germany. Also available from ANSIPublication Office, New York, NY.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.plastic container is acceptable if the solution is retained in adish or tray made of appropriate
16、material. Refer also to 9.2 forsize restrictions.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused for preparation of all standard solutions. Unless otherwiseindicated, it is intended that all reagents conform to thespecifications of the Committee on Analytical Reag
17、ents of theAmerican Chemical Society where such specifications areavailable.5Other grades may be used, provided it is firstascertained that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.8.1.1 Saturated salt solutions may be prepared
18、using eitheramorphous or hydrated reagents (that is, reagents containingwater of crystallization). Hydrated reagents are often preferredto amorphous forms for their solvating characteristics.8.2 Purity of WaterReagent water produced by distilla-tion, or by ion exchange, or reverse osmosis followed b
19、ydistillation shall be used. See Specification D 1193.8.3 Nomenclature for SaltsThe proper nomenclature forthe Humidity Fixed Point (HFP) salt chemicals and thecorresponding acceptable temperature ranges are provided inTable 1. The scale encompasses relative humidity ranges from2 % to 98.5 % and a t
20、emperature range from 5C to 80C.When the salt solutions are used at temperatures above 40C,the risk of salt crystals settling on the surface rather than beingimmersed in the solution must be taken into account.9. Technical Precautions9.1 Although a container capable of airtight closure isdescribed i
21、n Section 7, it may be desirable to have a vent undercertain conditions of test or with some kinds of containers(changes in pressure may produce undesirable cracks in sometypes of containers). The vent should be as small as practical tominimize loss of desired equilibrium conditions when in use.9.2
22、The container should be small to minimize the influenceof any temperature variations acting upon the container andcontents. A maximum proportion of 25 cm3volume/cm2ofsolution surface area is suggested, and overall containerheadspace volume should be no larger than necessary toconfine a stored item.9
23、.3 Measurement accuracy is strongly dependent on theability to achieve and maintain temperature stability duringactual use of any solution system. Temperature instability of60.1C can cause corresponding instabilities in generatedvalues of relative humidity of 60.5 %.9.4 The compatibility of any cons
24、tant relative humiditysystem used for instrument calibration testing should beconfirmed by reference to the instrument manufacturers in-structions.9.5 Important considerations leading to stability shouldinclude (but are not necessarily limited to) the following:9.5.1 Elimination of leakage paths.9.5
25、.2 Elimination of heat sources or heat sinks, or both, fortemperature stability.9.5.3 Limiting flow rate to preclude source carry-over.10. Preparations of Aqueous Solutions10.1 CautionSome saturated salt-water systems shouldbe regarded as hazardous materials. Refer to 1.5 and 1.6 forguidelines.10.2
26、Saturated Salt-Water Systems:10.2.1 Select a salt of characteristic value from Annex A1.The reference document by Greenspan6contains informationon many other saturated salt solutions which may be used.These additional systems, however, are less accurately or lesscompletely defined in value. Also, so
27、me may only be usedwhen freshly prepared (to limit the influence of chemicalinstability such as hydrolysis or acid gas absorption). The saltslisted in Annex A1 can be used for a year or more.10.2.2 Place a quantity of the selected salt in the bottom ofa container or an insert tray to a depth of abou
28、t 4 cm for lowrh salts, or to a depth of about 1.5 cm for high rh salts.10.2.3 Add water in about 2-mL increments, stirring wellafter each addition, until the salt can absorb no more water asevidenced by free liquid. Although a saturated solution systemis defined when any excess quantity of undissol
29、ved solute ispresent, it is preferred to keep the excess liquid present to a5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for Laborato
30、ryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.6Greenspan, L., “Humidity Fixed Points of Binary Saturated Aqueous Solu-tions,” Journal of Research, National Institute of Standards and Tec
31、hnology, Vol.81A, 1977, pp. 8996.TABLE 1 Humidity Fixed Point (HFP) Salt SolutionsHFP Designation Salt Name Chemical Symbol Temperature Range (C)HFP 4 Caesium fluoride CsF 15 to 80HFP 7 Lithium bromide LiBr 5 to 80HFP 12 Lithium chloride LiCl 5 to 80HFP 23 Potassium acetate CH3COOK 10 to 30HFP 33 Ma
32、gnesium chloride MgCl25to80HFP 43 Potassium carbonate K2CO35to30HFP 59 Sodium bromide NaBr 5 to 80HFP 70 Potassium iodide KI 5 to 80HFP 75 Sodium chloride NaCl 5 to 80HFP 85 Potassium chloride KCl 5 to 80HFP 98 Potassium sulfate K2SO45to50E104022minimum for ease in handling and for minimal impact on
33、stability should temperature variations occur.10.2.4 Close the container and allow 1 h for temperaturestabilization.10.2.5 The container may be used as a reservoir from whichquantities of slush can be transferred for use, or the entirecontainer may be used for conditioning tests.11. Precision and Bi
34、as11.1 Under ideal conditions, the bias (accuracy) of thesources generated by this practice are equal to the uncertaintyfigures associated with each source value, as stated in theAnnex tables. In actual use, lack of temperature equilibrium(60.5C) and other functional losses can reduce the biasstatem
35、ent to 62.5 %. Precision is 60.5 % rh.12. Keywords12.1 aqueous solution; constant relative humidity; control ofrelative humidity; equilibrium relative humidity; humidity;relative humidity; saturated salt solutionsANNEX(Mandatory Information)A1. EQUILIBRIUM RELATIVE HUMIDITY VALUES FOR SELECTED SATUR
36、ATED AQUEOUS SALT SOLUTIONSE104023TABLEA1.1EqulibriumRelativeHumidityValuesforSelectedSaturatedAqueousSaltSolutionsHFPvaluesaccordingtoGreenspan(ref-morerefsneededfrompHtable)t(C)HFP4CaesiumfluorideHFP7LithiumbromideHFP12 LithiumchlorideHFP23PotassiumacetateHFP33MagnesiumchlorideHFP43Potassium carbo
37、nateHFP59Sodium bromideHFP70PotassiumiodideHFP75Sodium chlorideHFP85PotassiumchlorideHFP98Potassiumsulfate57.460.813(11.2-14.0)33.660.343.160.563.560.873.360.475.760.387.760.598.561.0107.160.713(11.3-14.3)23.460.633.560.343.160.462.260.672.160.475.760.386.860.498.260.8154.361.46.960.712(11.3-13.8)23
38、.460.433.360.343.260.460.760.671.060.375.660.285.960.497.960.7203.861.16.660.612(11.1-12.6)23.160.333.160.243.260.459.160.569.960.375.560.285.160.397.660.6253.461.16.460.611.360.322.560.432.860.243.260.457.660.468.960.375.360.284.260.397.360.5303.060.86.260.511.360.321.660.632.460.243.260.556.060.46
39、7.960.375.160.283.660.397.060.4352.760.76.060.511.360.332.160.254.660.467.060.374.960.283.060.396.760.4402.460.65.860.411.260.331.660.253.260.566.160.374.760.282.360.396.460.4452.260.55.760.411.260.331.160.252.060.565.360.374.560.281.760.396.160.4502.160.45.560.411.160.330.560.250.960.664.560.374.56
40、0.981.260.495.860.5552.060.45.460.311.060.329.960.250.260.763.860.374.560.980.760.4602.060.45.360.311.060.329.360.249.760.863.160.474.460.980.360.5652.160.55.360.310.960.328.560.349.561.062.560.474.260.979.960.5702.260.65.260.310.860.427.860.349.761.161.960.374.160.979.560.6752.460.75.260.310.660.42
41、6.960.350.361.361.460.574.060.979.260.7802.660.85.260.310.560.526.160.451.461.561.060.573.960.978.960.8E104024ASTM 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
42、 that determination of 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 rea
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44、u feel that your comments 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).E104025
