ASTM B629-77(1997)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation:B629–77 (Reapproved 1997)
Standard Practice for
Preparation of Molybdenum and Molybdenum Alloys for
Electroplating
This standard is issued under the fixed designation B 629; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope surface layer, descale the part by immersion in a 110 g/L
solution of sodium hydroxide at or near boiling, or by
1.1 This practice covers a procedure for preparing molyb-
mechanical finishing. Glass bead blasting can be used to
denum and its alloys for electroplating. The procedure utilizes
remove uneven coatings of scale without disturbing the finish
techniques, equipment, and chemicals that are common to
of the metal.
electroplating. Specialized procedures such as hydrogen heat
3.1.2 Cathodic alkaline cleaning is preferred for the final
treatment and fused salt pickling are not included. These and
precleaning so as to avoid anodic oxidation. Proprietary
otherprocedurescanbefoundinthereferenceslistedattheend
formulations used for cathodic alkaline cleaning of other
of this practice.
metals are suitable. Cathodic treatment at about 6 V for 30 to
1.2 This standard does not purport to address all of the
60 s is usually adequate, using a cleaner concentration of 60 to
safety concerns, if any, associated with its use. It is the
75g/L and a solution temperature of 60 to 75°C.
responsibility of the user of this standard to establish appro-
3.2 Rinse—Here, and throughout the procedure, the water
priate safety and health practices and determine the applica-
rinses should be warm (approximately 50°C).
bility of regulatory limitations prior to use.
3.3 Electropolishing—Either of the following electropol-
2. Significance and Use
ishes may be used. The choice of electropolish and time
dependsontheamountofmaterialthatcanberemovedandthe
2.1 Molybdenum is used in engineering applications where
degree of surface improvement desired. The cathodes may be
strength and rigidity of component parts are needed, especially
lead or carbon. The sulfuric acid bath produces a blue film that
at high temperatures. Its good strength at high temperatures,
is partly removed in the rinse and completely removed in the
low vapor pressure, and good impact and creep resistance
alkaline dip.
makeitattractiveforload-bearingitemssuchasturbineblades,
3.3.1 Sulfuric Acid:
mechanical seals, rocket motor parts, heating elements, and
H SO (sp gr 1.83) 80 mass % (755 mL of acid/L)
electronic devices. Molybdenum, however, is easily oxidized, 2 4
Temperature 20 to 30°C
and the oxides are not protective. The volatility of the oxides
Current density 1100 to 2200 A/m anodic
above 800°C can lead, in the case of unprotected parts, to
Time 30 s
catastrophic oxidation and to losses in dimensions. Electro-
3.3.2 Sulfuric-Phosphoric Acid:
plated coatings are applied to molybdenum to prevent oxida-
H SO (sp gr 1.83) 50 % vol (500 mL/L)
2 4
tion, to prevent seizing and galling, and to assist joining by
H PO (85 %) 50 % vol (500 mL/L)
3 4
soldering, brazing, and diffusion bonding.
Temperature 50 to 55°C
Current density 2500 A/m anodic
Time 180 s
3. Procedure
3.1 Precleaning: 3.4 Rinse.
3.5 Alkaline Dip—Briefly immerse the specimen in a 45-
3.1.1 The principles of electroplating on molybdenum are
sim
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