1、Designation: C 1108 99 (Reapproved 2006)Standard Test Method forPlutonium by Controlled-Potential Coulometry1This standard is issued under the fixed designation C 1108; 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.1. Scope1.1 This test method describes the determination of pluto-nium in solutions of unirradiated nuclear-grade (that is, high-pu
3、rity) materials by controlled-potential coulometry.Controlled-potential coulometry may be performed in a choiceof supporting electrolytes, such as 0.9 M HNO3,1M HClO4,1M HCl, 5 M HCl, and 0.5 M H2SO4. Limitations on the use ofselected supporting electrolytes are discussed in Section 5.Optimum quanti
4、ties of plutonium for this procedure are 5 to 10mg.1.2 Plutonium-bearing materials are radioactive and toxic.Adequate laboratory facilities, such as gloved boxes, fumehoods, controlled ventilation, etc., along with safe techniquesmust be used in handling specimens containing these materials.1.3 The
5、values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.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
6、e safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemistry Laboratories Within theNuclear IndustryC 1068 Guide for Qualification o
7、f Measurement Methodsby a Laboratory Within the Nuclear IndustryC 1128 Guide for Preparation of Working Reference Mate-rials for Use in the Analysis of Nuclear Fuel CycleMaterialsC 1156 Guide for Establishing Calibration for a Measure-ment Method Used to Analyze Nuclear Fuel Cycle Mate-rialsC 1168 P
8、ractice for Preparation and Dissolution of Pluto-nium Materials for AnalysisC 1210 Guide for Establishing a Measurement SystemQuality Control Program for Analytical Chemistry Labo-ratories Within the Nuclear IndustryC 1297 Guide for Qualification of Laboratory Analysts forthe Analysis of Nuclear Fue
9、l Cycle MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Summary of Test Method3.1 In a controlled-potential coulometric measurement, thesubstance being determined reacts at an electrode, the potentialof which is maintained at such a value
10、that unwanted electrodereactions are precluded under the prevailing experimentalconditions. Those substances which have reduction-oxidation(redox) potentials near that of the ion being determinedconstitute interferences. Electrolysis current decreases expo-nentially as the reaction proceeds, until c
11、onstant backgroundcurrent is obtained. Detailed discussions of the theory andapplications of this technique have been published (1, 2, 3, 4,5, 6).3The control-potential adjustment technique (7) can beused to terminate the electrolysis of the specimen at constantbackground current without exhaustive
12、electrolysis with con-siderable reduction in operating time. Use of the control-potential adjustment technique requires that the coulometerintegrator be capable of operations in a bipolar mode and thatthe plutonium-containing solution be of high purity, that is,nuclear grade.3.2 Plutonium(IV) is red
13、uced to Pu(III) at a working elec-trode maintained at a potential more negative than the formalredox potential. Plutonium(III) is oxidized to Pu(IV) at apotential more positive than the formal redox potential. Thequantity of plutonium electrolyzed is calculated from the netnumber of coulombs require
14、d for the electrolysis, according toFaradays law. Corrections for incomplete reaction, derivedfrom the Nernst equation, must be applied for electrolysis ofthe sample aliquot (7, 8).W 5Qs2 Qb! MnFf(1)1This test method is under the jurisdiction ofASTM Committee C-26 on NuclearFuel Cycle and is the dir
15、ect responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved July 1, 2006. Published October 2006. Originallyapproved in 1988. Last previous edition approved in 1999 as C 1108 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Ser
16、vice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo
17、x C700, West Conshohocken, PA 19428-2959, United States.where:W = grams of plutonium,Qs= coulombs required by the electrolysis,Qb= coulombs of background current,M = gram-atomic weight of plutonium (must be adjustedfor isotopic composition),n = number of electrons involved in the electrode reaction(
18、for Pu(III) Pu(IV), n = 1),F = Faraday constant, coulombs/equivalent, andf = fraction of plutonium electrolyzed.4. Significance and Use4.1 Factors governing selection of a method for the deter-mination of plutonium include available quantity of sample,sample purity, desired level of reliability, and
19、 equipment.4.1.1 This test method determines 5 to 10 mg of plutoniumwith prior dissolution using Practice C 1168.4.1.2 This test method calculates plutonium assay usingphysical constants as reference standards.4.1.3 Chemical standards are used for quality control whenprior chemical separation of plu
20、tonium is necessary to removeinterferences (9).4.2 Committee C-26 Safeguards Statement4:4.2.1 The materials (plutonium metal, plutonium oxide ormixed oxide (U, Pu) O2 powders and pellets) to which thistest method applies are subject to nuclear safeguards regula-tions governing their possession and u
21、se. Materials for use bythe commercial nuclear community must also meet composi-tional specifications.4.2.2 The analytical method in this test method both meetsU. S. Department of Energy guidelines for acceptability of ameasurement method for generation of safeguards accountabil-ity measurement data
22、 and also provides data that may be usedto demonstrate specification compliance in buyer-seller inter-actions.5. Interferences5.1 Interference is caused by ions that are electrochemicallyactive in the range of redox potentials used or by species thatprevent attainment of 100 % current efficiency (fo
23、r example,reductants, oxidants, and organic matter).5.2 PolymerPolymerized plutonium is not electrochemi-cally active (10) and thus is neither reduced nor oxidized. Thepresence of polymerized plutonium will give low results. Thepolymer may be converted to electrochemically active speciesby HF treatm
24、ent (10).5.3 Pu(VI)Plutonium(VI) is only partially reduced toPu(III) in 1 M HNO3, HCl, or HClO4supporting electrolytesolutions; therefore, the presence of Pu(VI) can lead toinaccurate results when present even as a small fraction of thetotal plutonium. Plutonium(VI) is completely reduced in 0.5 MH2S
25、O4(10) or 5.5 M HCl (11) supporting electrolyte.5.4 IronIn 0.5 M H2SO4supporting electrolyte, iron isreduced and oxidized at essentially the same formal redoxpotentials as the Pu(III)-Pu(IV) couple and thus constitutes adirect interference. Iron must be removed by prior separation,or the effect of i
26、ts presence must be corrected by a separatemeasurement of the iron concentration in the sample solution.In 1 M HCl, 1 M HNO3,or1M HClO4, iron interferes to amuch lesser extent. The effect of iron in these supportingelectrolytes may be minimized by the choice of redox poten-tials, by a secondary titr
27、ation (10), or by electrochemicalcorrection (12, 13).5.5 NitritesNitrites are electrochemically active; there-fore, saturated sulfamic acid solution should be added to theelectrolyte in the cell to destroy any interfering nitrites.5.6 SulfateBecause of the complexing action of sulfate onPu(IV) and t
28、he resultant shift in the redox potential of thePu(III)-Pu(IV) couple, only small amounts of sulfate aretolerable in HNO3, HCl, and HClO4electrolytes. When usingthese supporting electrolytes, specimens should be fumed todryness to assure adequate removal of excess sulfate (see10.1.3).NOTE 1Interfere
29、nce from a sulfate concentration of 0.004 M in 1 MHClO4has been reported (10).5.7 FluorideFree fluoride cannot be tolerated and must beremoved from the specimen. Evaporation of the specimen inHNO3to a low volume and fuming with H2SO4are effective inremoving fluoride.5.8 OxygenIn HNO3, HCl, and HClO4
30、supporting elec-trolytes, oxygen may be an interference. In H2SO4, oxygendoes interfere and must be removed. Purging the specimenwith high-purity argon prior to and during the coulometricdetermination is recommended for all electrolytes.6. Apparatus6.1 Controlled-Potential CoulometerA coulometer wit
31、hthe following specifications is recommended to achieve highlyprecise and accurate results. (Room temperature stability of61C is recommended to ensure optimum instrument perfor-mance. Instruments with smaller output current or smallervoltage span may be satisfactory.)Potentiostat (6)Output voltage 2
32、5 VOutput current 200 mAOpen-loop response d-c gain 105Unity-gain bandwidth 300 kHzFull-power response 10 kHz (slewing rate 0.5 V/s)Voltage zero offset stability 1-mV long termInput d-c resistance 50 MVInput d-c current 10 CAccuracy 1010V.54Based upon Committee C-26 Safeguards Matrix (C 1009, C 1068
33、, C 1128,C 1156, C 1210, and C 1297).5AHewlett-Packard 3455ADVM has been found to exceed these specifications.C 1108 99 (2006)26.3 Cell AssemblyThe success of controlled-potentialcoulometric methods is strongly dependent on the design of thecell. The cell dimensions, electrode area, spacing, and sti
34、rringrate are important parameters in a design that will minimize thetime required for titration. The following components arerequired for the recommended cell assembly (Fig. 1).6.3.1 CellThe coulometry cell is fabricated from a cut-off50-mL borosilicate glass beaker with an inside diameter of 38mm
35、and a height of 42 mm; the cut edges are rounded andpolished smooth. Other cells conforming to these dimensionsare satisfactory.6.3.2 Counter Electrode and Salt Bridge TubeThe counterelectrode is a coiled length of 0.51-mm (0.020-in.) diameterplatinum wire. The salt bridge tube is unfired high-silic
36、a glass6filled with the supporting electrolyte solution.6.3.3 Reference Electrode and Salt Bridge TubeThe ref-erence electrode is a miniature saturated-calomel electrode(SCE).7The salt bridge is identical to the salt bridge describedin 6.3.2 and is also filled with supporting electrolyte solution.6.
37、3.4 Working Electrode, fabricated from either 8Au8-5/0expanded annealed-gold metal or from 45-mesh platinumgauze (Fig. 2). Storage of either electrode in 8 M HNO3whennot in use and rinsing with 8 M HNO3between specimens arenormally adequate to maintain satisfactory electrode response.(Satisfactory r
38、esponse may be defined as the ability of theelectrode to oxidize and reduce the supporting electrolyte to 1to 2 A in about 3 min with the current following anexponential curve.) If such electrode response is not obtained,the following electrode reconditioning treatments, in increas-ing order of seve
39、rity, have been found to be successful inrestoring response.6.3.4.1 The gold electrode may be: (1) briefly dipped in coldconcentrated HCl and thoroughly rinsed with 8 M HNO3;(2)briefly dipped in hot HCl and thoroughly rinsed with HNO3;(3) briefly dipped in aqua regia and thoroughly rinsed withHNO3;o
40、r(4) soaked 10 min in the sulfuric acid-hydrofluoricacid mixture (7.16), the residual acid removed by fuming andthe hot electrode quenched in 8 M HNO3.After each treatment,the electrode is stored in 8 M HNO3overnight. Followingovernight storage, conditioning, that is, alternating reduction6Either a
41、test tube with unfired Vycor bottoms of Type 7930 glass obtained fromCorning Glass Works, or a 0.5 cm long, 0.5-cm diameter rod of unfired Vycor Type7930 sealed into one end of a glass tube with heat-shrinkable TFE-fluorocarbontubing, has been found satisfactory for this application.7A Fisher Calome
42、l Reference Electrode Catalog No. 13-639-79 has been foundsatisfactory.FIG. 1 Exploded View of Cell Assembly: (a) Counter Electrode,(b) Cell Head, (c) Counter Electrode Frit Tube, (d) ReferenceElectrode Frit Tube, (e) NBL-Designed S-Shaped Stirrer, (f)Working Electrode, (g) Sample Cell, (h) Stirrer
43、Motor, (i) MotorPedestal and Bearing, and (j) Stirrer Shaft FIG. 2 Working Electrode (Top View)C 1108 99 (2006)3and oxidation of the supporting electrolyte with and withoutplutonium, may be required to achieve desired electrodeperformance.6.3.4.2 The platinum electrode may be subjected to any ofthe
44、above treatments, or it may be: (1) heated to red heat in agas flame and quenched in 8 M HNO3or (2) heated in a furnaceto 900C and quenched in 8 M HNO3. Do not use these lattertreatments on gold electrodes as melting may occur.6.3.5 StirrerSeveral types of stirrers have performed sat-isfactorily. A
45、paddle-type stirrer capable of being driven at1800 r/min by a synchronous motor, or a magnetically drivenstirring bar, is adequate. Magnetic stirring slightly simplifiesthe arrangement of the cell cap. For optimum stirring efficiencywith freedom from losses due to splashing, an S-shapedpolytetrafluo
46、roethylene stirrer (Fig. 3) (15) driven by synchro-nous motor is recommended.6.3.6 Inert Gas Inlet TubeA polyvinyl chloride tube,approximately 3 mm in outside diameter (1 mm in insidediameter), is inserted so that its tip is about 10 mm above thesurface of the electrolyte solution. The gas flow is a
47、djusted sothat the surface of the solution is depressed almost 3 mm. Thegas is high-purity argon. While inert gas is not required for allelectrolytes, it is recommended for this procedure.6.4 Quartz Heating LampsOptimum heating or evaporat-ing efficiency without bumping of solutions, or both, isobta
48、ined using overhead heating with quartz heat lamps8controlled by a variable power supply. However, with propercare, other conventional means of heating may be used.6.5 Hot PlateRecommended for heating during the plu-tonium oxidation state adjustment with hydrogen peroxide.6.6 Quartz Clock Timer, acc
49、urate to 0.001 s.6.7 100-V Precision Resistor, accurate to better than0.01 %.97. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.10Other 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.7.2 Arg
