ASTM_D_2284_-_11.pdf

Designation:D228411Standard Test Method forAcidity of Sulfur Hexafluoride1This standard is issued under the fixed designation D2284;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year 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 test method covers the determination of the acidicfluorides of sulfur hexafluoride(SF6).1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 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 applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent Water3.Summary of Test Method3.1 Acidic constituents of the sample are absorbed inslightly alkaline water containing an indicator and the excessbase titrated with a standard acid solution.The resultant acidityis expressed as equivalents of hydrofluoric acid(HF).4.Significance and Use4.1 Acidic fluorides are undesirable in SF6used as anelectrical insulating gas in that they may contribute to corro-sion or constitute dielectric hazard.4.2 This test method is valid for both new and used SF6.Inused SF6,it will only measure those active species which arehydrolyzable.5.Apparatus5.1 Gas Washing Bottles,500-mL capacity,two required.5.2 Microburet,graduated to 0.01 mL.5.3 Wet Test Meter.NOTE1The meter is used to measure the volume of dry gas in litersand hence the weight of SF6samples.The density of sulfur hexafluorideat 0C and 1 atm.of pressure(STP)is 6.52 g/L.The density of sulfurhexafluoride at 25C and 1 atm.of pressure(normal temperature andpressure)is 5.97 g/L.Alternatively,the sample weight may be determinedby weighing the sample cylinder before and after sampling.6.Reagents6.1 Purity of ReagentsUse reagent grade chemicals in alltests.Unless otherwise indicated,it is intended that all reagentsshall conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society,wheresuch specifications are available.3Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.6.2 Purity of WaterUnless otherwise indicated,referencesto water shall be understood to mean reagent grade waterconforming to Specification D1193.6.3 Phenolphthalein Indicator Solution(10 g/L)Dissolve1 g of phenolphthalein in 100 mL of ethanol(95%).6.4 Sodium Hydroxide Solution(0.01 N)Dissolve 0.4 60.01 g of sodium hydroxide(NaOH)in water and dilute to 1 L.Prepare a fresh solution weekly.Standardize by titratingagainst a weighed amount of potassium acid phthalate.6.5 Sulfuric Acid(0.01 N)Add 0.25 mL of concentratedsulfuric acid(H2SO4,sp gr 1.84)to water and dilute to 1 L.Standardize against standard 0.01 N NaOH solution.7.Sampling7.1 Take the sample as a liquid from the cylinder to besampled.This may be done by inverting the cylinder so that theoutlet valve is at the bottom.8.Preparation of Apparatus8.1 Place the cylinder to be sampled as suggested in Section7 and connect a needle valve to the cylinder outlet.Connect the1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.06 on Chemical Test.Current edition approved May 1,2011.Published May 2011.Originallyapproved in 1964 as D2284 64T.Last previous edition approved in 2002 asD2284 95(2002)which was withdrawn January 2011 and reinstated in May 2011.DOI:10.1520/D2284-11.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3Reagent Chemicals,American Chemical Society Specifications,AmericanChemical Society,Washington,DC.For Suggestions on the testing of reagents notlisted by the American Chemical Society,see Annual Standards for LaboratoryChemicals,BDH Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeiaand National Formulary,U.S.Pharmacopeial Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 inlet of one of the gas sampling bottles to the cylinder needlevalve and the outlet to the wet test meter.Flexible rubber orplastic tubing can be used.Set the meter to zero and note thereading.9.Procedure9.1 Boil 600 mL of deionized water in a 1-L beaker forabout 5 min and cool quickly to room temperature.Add 10drops of phenolphthalein indicator solution and enough 0.01 NNaOH solution to color the solution faintly pink.Pour half ofthe solution into each of the two gas washing bottles and add2.00 mL of 0.01 N NaOH solution to each.Replace