ASTM_D_2674_-_72_2012.pdf

Designation:D267472(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 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 normally 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 solution 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.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 chromium 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 suggestedas follows by appropriate additions of sodium dichromate orsulfuric acids.Sodium dichromate3.0 to 6.0 oz/gal(22.5 to 44.9 g/litre)Sulfuric acid40 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 intended 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 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 WaterE50 Practices 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 specifications 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.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 jurisdiction 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 referenced 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,AmericanChemical 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.,(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.2 Sodium Hydroxide,Standard Solution(1.0 N)Dissolve40 g of sodium hydroxide(NaOH)in 1 liter of water andstandardize.6.Procedure6.1 Pipet a 5-mL sample of sulfochromate etch solution intoa 250-mLbeaker.Add 100 mLof 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 t