1、Designation: D2674 72 (Reapproved 2012)Standard Methods ofAnalysis of Sulfochromate Etch Solution Used in SurfacePreparation of Aluminum1This standard is issued under the fixed designation D2674; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、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 These methods offer a means for controlling the effec-tiveness of the etchant which is normal
3、ly used for preparing thesurface of aluminum alloys for subsequent adhesive bonding.As the etchant reacts with the aluminum, hexavalent chromiumis converted to trivalent chromium; a measure of the two andthe difference can be used to determine the amount of dichro-mate used.1.2 The sulfochromate sol
4、ution can be replenished by re-storing the sodium dichromate and the sulfuric acid to theoriginal formulation levels. The lower limit of usefulness willvary depending upon solution storage, adhesives used, criticalnature of bond capability, variety of metals processed, etc. andshould be determined.
5、Replenishment will be limited to thenumber of times the chemical ingredients can be restored andmaintained to the required levels and should be determined bythe user. Sludge collecting in the bottom of a tank should beminimized by periodic removal of sludge. For some applica-tions, the hexavalent ch
6、romium should not fall below thetrivalent chromium content.1.3 A typical aqueous sulfochromate acid etch solutionformulation is as follows:Sodium dichromate (Na2Cr2O7) 4.5 oz/gal (33.7 g/litre)Sulfuric acid (sp gr 1.84) 45 oz/gal (337.1 g/litre)1.4 Maintenance of the aqueous concentrations is sugges
7、tedas follows by appropriate additions of sodium dichromate orsulfuric acids.Sodium dichromate 3.0 to 6.0 oz/gal (22.5 to 44.9 g/litre)Sulfuric acid 40 to 50 oz/gal (299.6 to 374.5 g/litre)1.5 Method A is intended for measuring the sulfuric acidcontent of a sulfochromate solution. Method B is intend
8、ed formeasuring the hexavalent and trivalent Chromium content of asulfochromate solution. Method C is intended as an alternativemethod for measuring the hexavalent and trivalent Chromiumcontent of a sulfochromate solution.1.6 This standard does not purport to address all of thesafety concerns, if an
9、y, 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 WaterE50 Practices
10、 for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated Materials3. Purity of Reagents and Water3.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the spe
11、cifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination
12、.3.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193.METHOD A4. Apparatus4.1 pH Meter.5. Reagents5.1 Methyl Orange Indicator SolutionPrepare in accor-dance with Practices E50.1These methods are under the jurisdi
13、ction of ASTM Committee D14 onAdhesives and are the direct responsibility of Subcommittee D14.80 on MetalBonding Adhesives.Current edition approved May 1, 2012. Published May 2012. Originallyapproved in 1967. Last previous edition approved in 2004 as D2674 72 (2004)1.DOI: 10.1520/D2674-72R12.2For re
14、ferenced 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 standards Document Summary page onthe ASTM website.3Reagent Chemicals, American Chemical Society Specifications, Americ
15、anChemical Society, Washington, D.C. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc., (USP
16、C), Rockville,MD.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 Sodium Hydroxide, Standard Solution (1.0 N)Dissolve 40 g of sodium hydroxide (NaOH) in 1 liter of waterand standardize.6. Procedure6.1 Pipet a 5-mL sample of sulfoc
17、hromate etch solution intoa 250-mL beaker.Add 100 mL of water. Titrate the sample withthe NaOH solution to a pH of 3.5, using a pH meter.6.2 An alternative method may be used whereby, instead ofthe pH meter, 1 drop of methyl orange indicator solution isadded and, the titration continued until the co
18、lor of the solutionloses all trace of orange.7. Calculation7.1 Calculate the sulfuric acid content of the sulfochromatesolution, A in oz/gal, B in g/litre, as follows:A 5 1.3 VN (1)B 5 9.81 VN (2)where:V = milliliters of sodium hydroxide solution, andN = normality of sodium hydroxide solution.7.2 Re
19、plenish the sulfuric acid content of the solution asfollows:W15 A12 A!V1(3)W25 B12 B!V2(4)where:W1= weight of sulfuric acid (H2SO4, sp gr 1.84) to beadded to solution, oz,W2= weight of sulfuric acid to be added to solution, g,A1= original concentration of solution, oz/gal,B1= original concentration
20、of solution, g/litre,V1= volume of solution in tank, gal, andV2= volume of solution in tank, litres.METHOD B8. Reagents8.1 Ammonium Persulfate Solution (NH4)2SSO8, 15weight %).8.2 Ferrous Ammonium Sulfate Solution (0.05 N)Dissolve 39.2 g of ferrous ammonium sulfate(Fe(NH4)2(SO4)26H2O) in 1 litre of
21、cold H2SO4(5 + 95) anddilute to 2 litres with H2SO4(5 + 95). Standardize this materialeach time as follows:8.2.1 Pipet 10 mL into a 400-mL beaker. Add 150 mL ofwater plus 5 mL of H2SO4(sp gr 1.84) and 1 drop of thephenanthroline ferrous complex. Titrate with the KMnO4solution just to disappearance o
22、f the indicator color. If thenormality does not fall within 0.051 to 0.049, discard the 0.05N solution.8.3 Hydrochloric Acid (1 + 1)Mix 1 volume of concen-trated hydrochloric acid (HCl) with 1 volume of water.8.4 Ortho-Phenanthroline Ferrous Complex IndicatorSolutionPrepare in accordance with Practi
23、ces E50.8.5 Potassium Permanganate, Standard Solution (0.05 N)Dissolve 1.6 g of potassium permanganate (KMnO4) in 1 litreof water and standardize.8.6 Silver Nitrate Solution (1 weight %).8.7 Sulfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).Determination of Hexavalent Chromium as SodiumDic
24、hromate9. Procedure9.1 Pipet 1 mL of the sample into a 400-mL beaker.Add 150mL of water, followed by 5 mL of H2SO4(sp gr 1.84). Titratewith the standard ferrous ammonium sulfate solution (using 1drop of the ferrous complex indicator) (Note 1) until theindicator turns pink and then add about 5 ml of
25、the standardferrous ammonium sulfate solution in excess. Record the totalvolume of the standard ferrous solution added. Back titratewith the potassium permanganate solution until the color of thesolution becomes very slightly green.NOTE 1Barium diphenylamine sulfonate indicator may be used ifpreferr
26、ed. This indicator gives a purple to green end point. If performedwith care, back titration is not necessary.NOTE 2Upon reaching the end point, the solution will be colorless,then it will carry over by itself to a slightly green color. Any violet colorwill indicate the back titration has gone over t
27、he end point.9.2 Record the amount of potassium permanganate used toreach this end point. Use an average of three determinations inthe calculation.10. Calculation10.1 Calculate the hexavalent chromium as sodium dichro-mate (Na2Cr2O72H2O), C in oz/gal, and D in g/L, as follows:C 5 V1N12 V2N2!6.63 (5)
28、D 5 V1N12 V2N2!49.7 (6)where:V1= millilitres of ferrous ammonium sulfate solution,N1= normality of ferrous ammonium sulfate solution,V2= millilitres of potassium permanganate solution, andN2= normality of potassium permanganate solution.Determination of Trivalent Chromium as Sodium Dichromate11. Pro
29、cedure11.1 Pipet 1 mL of the sample into a 400-mL beaker. Add150 mL of water followed by 10 mL of H2SO4(sp gr 1.84).Heat to boiling. While hot, add 5 mL of the 1.0 % AgNO3solution and 20 mL of the ammonium persulfate solution. Boilfor 20 min and then cool to room temperature. Add 1 drop ofHCl and 1
30、drop of the phenanthroline ferrous complex indica-tor (Note 1). Titrate with the standard ferrous ammoniumsulfate solution until the color of the solution turns pink. Addan excess of 5 mL of titrating solution and record the totalvolume added. Back titrate with the potassium permanganatesolution unt
31、il the color of the solution becomes apple green.Record the amount of the potassium permanganate used toreach this end point. Use an average of three determinations inthe calculations.12. Calculations12.1 Calculate the total chromium as sodium dichromate(Na2Cr2O72H2O), X in oz/gal, Y in g/L, as foll
32、ows:D2674 72 (2012)2X 5 3.4 V1N12 V2N2! (7)Y 5 25.1 V1N22 V1N2! (8)where:V1= millilitres of ferrous ammonium sulfate solution,V2= millilitres of potassium permanganate solution,N1= normality of ferrous ammonium sulfate solution, andN2= normality of potassium permanganate solution.12.2 Calculate the
33、trivalent chromium, E in oz/gal, F in g/L,as follows:E 5 X 2 C (9)F 5 Y 2 D (10)12.3 Replenishment of the Sodium Dichromate ContentCalculate the weight, W1in oz, W2in g, of Na2Cr2O72H2Otobe added to the solution as follows:W15 C12 C!V1(11)W25 D12 D!V2(12)where:W1= weight of sodium dichromate to be a
34、dded to solution,oz,W2= weight of sodium dichromate to be added to solution,g,C1= original concentration of solution, oz/gal,D1= original concentration of solution, g/L,V1= volume of solution in tank, gal,V2= volume of solution in tank, L.METHOD C13. Reagents13.1 Ammonium Bifluoride (NH4HF2)13.2 Hyd
35、rochloride Acid (1 + 1)Mix 1 volume of concen-trated hydrochloric acid (HCl) with 1 volume of water.13.3 Potassium Iodide (KI), or 10 % potassium iodide so-lution.13.4 Sodium Thiosulfate, Standard Solution (0.1 N)Dissolve 24.8 g of sodium thiosulfate (Na2S2O35H2O) in 1 Lof water and standardize.13.5
36、 Starch Indicator Solution (1 weight %).Determination of Hexavalent Chromium as SodiumDichromate14. Procedure14.1 Pipet a 25-mL sample into a 250-mL volumetric flask,dilute to the mark, and mix thoroughly. Pipet a 20-mL aliquotfrom the flask into a 300-mL Erlenmeyer flask. Add 120 mL ofwater. Add 2.
37、0 g of ammonium bifluoride. Add 15 mL of HCl.Add2gofKIcrystals or 10 mL of a 10 % KI solution. Titratewith the standard sodium thiosulfate solution until the color ofthe solution just changes to a light straw color. Add 3 mL ofstarch solution. Continue the titration until the blue color justdisappea
38、rs. Use an average of three determinations in thecalculations.15. Calculation15.1 Calculate the hexavalent chromium as sodium dichro-mate (Na2Cr2O72H2O), G in oz/gal, H in g/L, as follows:G 5 6.63 VN (13)H 5 49.7 VN (14)where:V = millilitres of sodium thiosulfate solution, andN = normality of sodium
39、 thiosulfate solution.16. Report16.1 The report shall include the following:16.1.1 Date solution was prepared,16.1.2 Date tested,16.1.3 Amount of sulfuric acid present,16.1.4 Amount of sulfuric acid added,16.1.5 Amount of hexavalent and trivalent chromium pres-ent,16.1.6 Amount of sodium dichromate
40、added,16.1.7 Test method used, and16.1.8 Number of tests made.17. Keywords17.1 acid etch; aluminum; chromate; sodium dichromateASTM 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
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42、vised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you
43、may attend. If you 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 S
44、tates. 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D2674 72 (2012)3
