ASTM_B_629_-_77_2013.pdf

Designation:B62977(Reapproved 2013)Standard Practice forPreparation of Molybdenum and Molybdenum Alloys forElectroplating1This standard is issued under the fixed designation B629;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 practice covers a procedure for preparing molyb-denum and its alloys for electroplating.The procedure utilizestechniques,equipment,and chemicals that are common toelectroplating.Specialized procedures such as hydrogen heattreatment and fused salt pickling are not included.These andother procedures can be found in the references listed at the endof this practice.1.2 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.Significance and Use2.1 Molybdenum is used in engineering applications wherestrength and rigidity of component parts are needed,especiallyat high temperatures.Its good strength at high temperatures,low vapor pressure,and good impact and creep resistancemake it attractive for load-bearing items such as turbine blades,mechanical seals,rocket motor parts,heating elements,andelectronic devices.Molybdenum,however,is easily oxidized,and the oxides are not protective.The volatility of the oxidesabove 800C can lead,in the case of unprotected parts,tocatastrophic oxidation and to losses in dimensions.Electro-plated coatings are applied to molybdenum to preventoxidation,to prevent seizing and galling,and to assist joiningby soldering,brazing,and diffusion bonding.3.Procedure3.1 Precleaning:3.1.1 The principles of electroplating on molybdenum aresimilar to those of other metals.The surfaces must be free ofdirt,grease,and other foreign matter.Solvent,emulsion,andsoak cleaners are suitable for precleaning to remove grosssurface contaminants.If a molybdenum specimen is subjectedto severe forming operations and retains a carbonaceoussurface layer,descale the part by immersion in a 110 g/Lsolution of sodium hydroxide at or near boiling,or bymechanical finishing.Glass bead blasting can be used toremove uneven coatings of scale without disturbing the finishof the metal.3.1.2 Cathodic alkaline cleaning is preferred for the finalprecleaning so as to avoid anodic oxidation.Proprietaryformulations used for cathodic alkaline cleaning of othermetals are suitable.Cathodic treatment at about 6 V for 30 to60 s is usually adequate,using a cleaner concentration of 60 to75g/L and a solution temperature of 60 to 75C.3.2 RinseHere,and throughout the procedure,the waterrinses should be warm(approximately 50C).3.3 ElectropolishingEither of the following electropol-ishes may be used.The choice of electropolish and timedepends on the amount of material that can be removed and thedegree of surface improvement desired.The cathodes may belead or carbon.The sulfuric acid bath produces a blue film thatis partly removed in the rinse and completely removed in thealkaline dip.3.3.1 Sulfuric Acid:H2SO4(sp gr 1.83)80 mass%(755 mL of acid/L)Temperature20 to 30CCurrent density1100 to 2200 A/m2anodicTime30 s3.3.2 Sulfuric-Phosphoric Acid:H2SO4(sp gr 1.83)50%vol(500 mL/L)H3PO4(85%)50%vol(500 mL/L)Temperature50 to 55CCurrent density2500 A/m2anodicTime180 s3.4 Rinse.3.5 Alkaline DipBriefly immerse the specimen in a 45-g/Lsolution of sodium hydroxide at room temperature.3.6 Rinse.3.7 Acid DipBriefly immerse the specimen in a 10-mass%solution of sulfuric acid(58 mL of 1.83 sp gr acid/L)at room temperature.3.8 Rinse.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatingsand is the direct responsibility of Subcommittee B08.02 onPre Treatment.Current edition approved Dec.1,2013.Published December 2013.Originallyapproved in 1977.Last previous edition approved in 2008 as B629 77(2008).DOI:10.1520/B0629-77R13.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.9 Chromium StrikingElectroplate the specimen in aconventional chromium electroplating solution for 1 to 5 min at1500 to 2500 A/m2at a temperature of 50C minimum.Insome cases,it may be necessary to first make the part anodic inthe chromium solution for 1 min at 2200A/m2in order to attaingood adhesion.3.10 Rinse.3.11 Nickel StrikingElectroplate the specimen in the fol-lowing solution at 800 A/m2for 120 s.NiCl2 6H2O240 g/LHCl(sp gr 1.18)10 vol%(100 mL/L)Temperature20 to 30CAnodenickel or carbon3.12 Rinse.3.13 Electroplate the specimen with the desired metal.REFERENCES(1)Beach,J.G.,et al.U.S.Patent 2,928,169(March 15,1960).(2)Brenner,A.,Plating,Vol 43,1956,p.1143.(3)Domnikov,L.,Metal Finishing,Vol 61,