1、Designation: D 6208 07Standard Test Method forRepassivation Potential of Aluminum and Its Alloys byGalvanostatic Measurement1This standard is issued under the fixed designation D 6208; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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 A procedure to determine the repassivation potential ofaluminum alloy 3003-H14 (UNS A93003) (1)2as a me
3、asure ofrelative susceptibility to pitting corrosion by conducting agalvanostatic polarization is described.Aprocedure that can beused to check experimental technique and instrumentation isdescribed, as well.1.2 The test method serves as a guide for similar measure-ment on other aluminum alloys and
4、metals (2-5).1.3 The values stated in SI units are to be regarded as thestandard. Values given in parentheses are for information only.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 est
5、ablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 1193 Specification for Reagent WaterD 3585 Specification for ASTM Reference Fluid for Cool-ant TestsG3 Practice for ConventionsApplicab
6、le to ElectrochemicalMeasurements in Corrosion TestingG15 Terminology Relating to Corrosion and CorrosionTestingG46 Guide for Examination and Evaluation of PittingCorrosionG 107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized DatabaseInput3. Terminology3
7、.1 Definitions: Terms used in this test method can be foundin Practice G3and Terminology G15.3.2 Symbols:3.2.1 EBbreak potential, potential at which the passivealuminum oxide layer breaks down.3.2.2 EGprotection potential as measured in this galvano-static method, potential at which oxide layer repa
8、ssivates.3.2.3 Jcurrent density, in A/m24. Summary of Test Method4.1 The test method described is an adaptation of themethod described in FORD Motor Company standards (6).4.2 An aluminum alloy specimen is polarized at fixedcurrent density for 20 min. in a solution of coolant andcorrosive water conta
9、ining chloride. The potential as a functionof time is recorded.4.3 The maximum potential, EBreached upon polarizationis determined, as is the minimum potential following themaximum potential, EG.4.4 Visual examination of the specimen may be made usingGuide G46as a guide after disassembly and rinsing
10、.5. Significance and Use5.1 This test method is designed to measure the relativeeffectiveness of inhibitors to mitigate pitting corrosion ofaluminum and its alloys, in particular AA3003-H14, rapidlyand reproducibly. The measurements are not intended tocorrelate quantitatively with other test method
11、values or withsusceptibility to localized corrosion of aluminum observed inservice. Qualitative correlation of the measurements and sus-ceptibility in service has been established (1).5.2 The maximum potential reached upon initial polariza-tion, EB,is a measure of the resistance to breakdown of thea
12、luminum oxide film. Lower susceptibility to initiation of1This test method is under the jurisdiction of ASTM CommitteeD15 on EngineCoolants and is the direct responsibility of SubcommitteeD15.06 on GlasswarePerformance Tests.Current edition approved April 1, 2007. Published April 2007. Originallyapp
13、roved in 1997. Last previous edition approved in 2002 as D 6208 - 97(2002).2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Ann
14、ual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.pitting corrosion is indicated by a more noble potential (SeePractice G3and
15、 Terminology G 15.) This potential, as mea-sured in this test method, is not very sensitive to the inhibitorspresent.5.3 The minimum potential, EG,following the maximumpotential is a measure of the protection against continuedpitting corrosion by the inhibitors. Again, a more noblepotential indicate
16、s better protection. This potential is sensitiveto the inhibitors present.5.4 Visual examination of the specimens can provide infor-mation about subleties of the pitting and inhibition mecha-nisms. Number of pits, pit depth, amount of deposit, andsurface discoloration are some examples of recordable
17、 obser-vations, which can assist evaluation of inhibitor effectiveness.5.5 The presence of chloride in the test solution is critical toobservation of pitting corrosion. Also, a coolant/corrosivewater solution in which gas bubbles evolve spontaneously onthe aluminum (indicating general corrosion) is
18、unlikely to havea significant amount of observable pitting corrosion.6. Apparatus6.1 General DescriptionThe apparatus for the electro-chemical test consists of a cell, current supply, recorder, andthree electrodes. Fig. 1 is a generalized schematic of thearrangement. More specific requirements for e
19、ach componentare given below.6.2 CellThe cell consists of a No.25 O-ring borosilicateglass joint held vertically using standard laboratory clamps andring stand. The working electrode will be clamped to thebottom using the matching O-ring clamp and viton or siliconerubber gasket.6.3 Current Supply an
20、d RecorderA constant current sup-ply capable of generating 872 Acontinuously is required. Therecorder must have a high input impedance ( 1012Ohms), becapable of recording potentials of 62 V with mV accuracy, andhave a low gain. These capabilities are typical of commercialpotentiostat/galvanostat ins
21、truments connected to either a stripchart recorder or computer, for experimental control and dataacquisition. The schematic in Fig. 1 shows connections using acurrent supply and mV strip chart recorder, and Fig. X2.1shows a schematic for using a computer and potentiostat/galvanostat.6.4 Electrodes:6
22、.4.1 Working Electrode (WE)The working electrode,aluminum test coupon, is cut as 51 3 51 mm (2 in. 3 2 in. )squares from aluminum sheet 2 to 6 mm (1/16 in. to 1/4 in.)thick. The standard material is AA3003-H14 (UNS A93003),used to develop the precision and bias statements. The couponis rinsed thorou
23、ghly (both sides) with methanol and placed ina low temperature drying oven. No additional surface prepa-ration is desirable. Prior to testing, a coupon is allowed to coolto room temperature. Then it is clamped to the bottom of theO-ring joint using the matching O-ring (viton or siliconerubber) and c
24、lamp. The clamping screw may be tightened tofinger tightness, if desired. Excessive tightening must beavoided. This gives an area of 8.72 cm2aluminum exposed tothe solution.6.4.2 Auxiliary Electrode (AE)Ultrafine grade graphiterod, 6-8 mm (1/4 in.) in diameter and at least 20 cm (8 in.)long. Avoid c
25、oarse grades as they can adsorb inhibitors.6.4.3 Reference Electrode (RE)The reference electrodecan be of any convenient type, for example saturated calomel(Hg/HgCl) or silver chloride (Ag/AgCl). The electrode must bein good working order and stable in the solution to bemeasured. The reference elect
26、rode is placed in Luggin probe toavoid solution impedance bias. Appendix X2 contains twosuggestions for easily constructed Luggin probes.6.5 TimerTimer with 1 s resolution out to 30 min.7. Preparation of Apparatus7.1 AssemblyPrior to running tests, assemble the cell andelectrodes, using an unprepare
27、d Al specimen as the “working”electrode using appropriate clamping. The auxiliary electrodeis positioned so that the tip is from 5 to 10 mm from theworking electrode surface. The Luggin probe is positioned sothat the tip is from 1 to 3 mm from the working electrodesurface. It is most convenient if t
28、he clamping arrangement issuch that this electrode configuration is maintained easily. Thecell is then removed and Al specimen unclamped.8. Procedure8.1 A corrosive water containing chloride, sulfate, andbicarbonate is prepared by dissolving the following amounts ofanhydrous salts in distilled or de
29、ionized water, ASTM Type II(see Specification D 1193):Sodium sulfate 592 mgSodium chloride 660 mgSodium bicarbonate 552 mgThe solution is made up to a total weight of 1 kg withdistilled or deionized water at 20C. A 4-kg batch size isconvenient if many tests are to be run, multiply amounts aboveby fo
30、ur. This will give a solution, which is 400 ppm in chloride,sulfate, and bicarbonate.8.2 Rinse cell, O-ring, Luggin probe (inside and out),auxilliary electrode, and reference electrode thoroughly withType II water.8.3 Prepare the aluminum specimen as the working elec-trode (see 5.4.2). Clamp to cell
31、, using O-ring, and set to oneside.8.4 Prepare the test solution as 25 vol % of the coolant to betested, 25 vol % of the corrosive water from 6.1, and theFIG. 1 Generalized Experimental Set-upD6208072remainder deionized or distilled water. The amount to be madedepends on ones exact cell configuratio
32、n. Sufficient testsolution is required to fill the cell (about 50 mLs) and theLuggin probe assembly. For the configurations of Luggin probegiven in Appendix X2, 160 mLs is more than sufficient.8.5 Fill the Luggin probe with test solution sufficient tocover the tip of reference electrode when inserte
33、d. Insertreference electrode. Gently tap Luggin to remove any bubblesbetween the tip and reference electrode. If a vertical Luggin isused, as in Fig. X2.2, then bubbles can be removed by allowingsolution to drain slowly into a waste container.8.6 Set up current generator to output 872 A (J = 100A/cm
34、2) continuously, set recorder to a range of 62 V (othersettings may be used if found to be necessary to achieveaccurate and representative potentials, chart speed as desired (5mm/min is reasonable). If acquiring data by computer, set dataacquisition rate to 1 point/s. Do not turn either generator or
35、recorder on at this time.8.7 Fill cell with approximately 50 mL of test solution,about 25 mm from the top of the cell. Start timer. Do not startgenerator at this time. Recorder may be turned on at this time.Assemble cell over Luggin probe and auxiliary electrode.Attach wires to reference electrode,
36、auxiliary electrode, andworking electrode. Check for bubbles in Luggin, tap gently toremove.8.8 At 5 min on the timer, turn on current generator, andrecorder, if not already on. Record potential versus timeresponse for 20 min. Turn off current generator and recorder(see Note 1).NOTE 1A computer cont
37、rolled system can be used in place of acurrent generator and recorder. In this case the current generator consistsof a potentiostat/galvanostate operated in galvanostatic mode. The re-corder is the computer. Software is used to control all aspects of the testprotocol, including controlling the galva
38、nostate, acquiring the data,plotting, and analysis.8.9 Run the test in duplicate, steps 8.2-8.89. Interpretation of Results9.1 Break Potential, EBThe graph in Fig. 2 illustrates twoof the three possible forms of curve obtained in the experiment.In Fig. 2 there is an initial rapid rise in potential f
39、ollowed by adecrease. Record the maximum potential reached in this periodas EB. The third possibility is that the potential rises continu-ously, though perhaps oscillating. Record the maximum poten-tial reached throughout the run. Express potential as V v SHEcorrecting for type of reference electrod
40、e used (see AppendixX1).9.2 Protection Potential EGFor curves similar to curve Ain Fig. 2, asymptotic decrease in potential after break, recordthe minimum potential reached, typically at the end of the run.For curves similar to curve B in Fig. 2, there is a decrease afterthe “break” followed by a se
41、ries of rises and falls, record thelowest potential reached on the first fall. Typically, subsequentrises and falls are small and appear as oscillations. For curveswhere the potential rises continuously, EGwill be equal to EB.Express potential as V v SHE, correcting for type of referenceelectrode us
42、ed (see Appendix X1).9.3 Curve TypeRecord whether curve is asymptotic (TypeA), rising and falling (Type B), or rising only (Type C).9.4 Observations (optional)The following are optionalobservations that can be recorded as: evolution of gas bubblesduring the test, description of surface after test, l
43、ocation of pits(for example, along scratch lines, etc. number of pits, depth ofpits, area of pits, color of deposits, location of deposits inrelation to pits, and other pitting evaluations as described inGuide G 46).10. Report10.1 Report the following information:10.1.1 Report aluminum alloy tested.
44、10.1.2 Report the average EBand EGof all experimentalruns, at least two, for the formula.10.1.3 Report type of curves obtained, A, B, or C. Reportmultiple types if obtained.10.1.4 Report any visual observation made.10.1.5 Many other relevant test parameters are given inGuide G 107. These parameters
45、should be recorded properly inlaboratory notebooks for future reference.11. Precision and Bias11.1 PrecisionThe precision of this test method has notbeen determined. Round-robin testing will commence oncefinal details of the method are determined. It is expected thatthe precision associated with the
46、 “break” potential will be lessthan the precision associated with the “protection” potential. Itis also expected that precision will be constant over the rangeof measurement as opposite to being relative to the value of themeasurement and insignificantly affected by the choice ofaluminum alloy teste
47、d.11.2 Bias:11.2.1 Statement on BiasThis procedure has no biasbecause the values for the “break” and “protection” potentialsare defined only in terms of this test method. An apparent biaswill exist if the user does not correct the potentials for thespecific reference electrode used. Potential always
48、 must beexpressed as relative to a standard hydrogen electrode (SHE) atthe pH of use (see Appendix X1).NOTE 1Break potential, EB, and protection potential, EG, is indicatedfor each type of transient.FIG. 2 Two Common Potential/Time Transient Profiles AfterPolarizationD620807311.2.2 Procedure to Dete
49、rmine Bias Due to Technique orInstrumentationThe following procedure uses specific, pub-lished coolant specifications as controls to determine biasesintroduced due to ones experimental technique or instrumen-tation. Results can be corrected for this bias. The two controlformulas are Specification D 3585 with 0.2 wt % sodiumnitrate and AL39, a coolant consisting of sodium sebacate andbenzotriazole (see Table 1). Each formula is run at least fivetimes. The mean and standard deviation are compared to thevalues determined in round robin testing (see 11.1). The bia
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