ASTM B629-77(2008)
(Practice)Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating
Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating
SIGNIFICANCE AND USE
Molybdenum is used in engineering applications where strength and rigidity of component parts are needed, especially at high temperatures. Its good strength at high temperatures, low vapor pressure, and good impact and creep resistance make it attractive for load-bearing items such as turbine blades, mechanical seals, rocket motor parts, heating elements, and electronic devices. Molybdenum, however, is easily oxidized, and the oxides are not protective. The volatility of the oxides above 800°C can lead, in the case of unprotected parts, to catastrophic oxidation and to losses in dimensions. Electroplated coatings are applied to molybdenum to prevent oxidation, to prevent seizing and galling, and to assist joining by soldering, brazing, and diffusion bonding.
SCOPE
1.1 This practice covers a procedure for preparing molybdenum and its alloys for electroplating. The procedure utilizes techniques, equipment, and chemicals that are common to electroplating. Specialized procedures such as hydrogen heat treatment and fused salt pickling are not included. These and other procedures can be found in the references listed at the end of this practice.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B629 − 77(Reapproved 2008)
Standard Practice for
Preparation of Molybdenum and Molybdenum Alloys for
Electroplating
This standard is issued under the fixed designation B629; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope surface contaminants. If a molybdenum specimen is subjected
to severe forming operations and retains a carbonaceous
1.1 This practice covers a procedure for preparing molyb-
surface layer, descale the part by immersion in a 110 g/L
denum and its alloys for electroplating. The procedure utilizes
solution of sodium hydroxide at or near boiling, or by
techniques, equipment, and chemicals that are common to
mechanical finishing. Glass bead blasting can be used to
electroplating. Specialized procedures such as hydrogen heat
remove uneven coatings of scale without disturbing the finish
treatment and fused salt pickling are not included. These and
of the metal.
otherprocedurescanbefoundinthereferenceslistedattheend
3.1.2 Cathodic alkaline cleaning is preferred for the final
of this practice.
precleaning so as to avoid anodic oxidation. Proprietary
1.2 This standard does not purport to address all of the
formulations used for cathodic alkaline cleaning of other
safety concerns, if any, associated with its use. It is the
metals are suitable. Cathodic treatment at about 6 V for 30 to
responsibility of the user of this standard to establish appro-
60 s is usually adequate, using a cleaner concentration of 60 to
priate safety and health practices and determine the applica-
75g/L and a solution temperature of 60 to 75°C.
bility of regulatory limitations prior to use.
3.2 Rinse—Here, and throughout the procedure, the water
2. Significance and Use
rinses should be warm (approximately 50°C).
2.1 Molybdenum is used in engineering applications where
3.3 Electropolishing—Either of the following electropol-
strength and rigidity of component parts are needed, especially
ishes may be used. The choice of electropolish and time
at high temperatures. Its good strength at high temperatures,
depends on the amount of material that can be removed and the
low vapor pressure, and good impact and creep resistance
degree of surface improvement desired. The cathodes may be
makeitattractiveforload-bearingitemssuchasturbineblades,
lead or carbon. The sulfuric acid bath produces a blue film that
mechanical seals, rocket motor parts, heating elements, and
is partly removed in the rinse and completely removed in the
electronic devices. Molybdenum, however, is easily oxidized,
alkaline dip.
and the oxides are not protective. The volatility of the oxides
3.3.1 Sulfuric Acid:
above 800°C can lead, in the case of unprotected parts, to
H SO (sp gr 1.83) 80 mass % (755 mL of acid/L)
2 4
catastrophic oxidation and to losses in dimensions. Electro-
Temperature 20 to 30°C
Current density 1100 to 2200 A/m anodic
plated coatings are applied to molybdenum to prevent
Time 30 s
oxidation, to prevent seizing and galling, and to assist joining
3.3.2 Sulfuric-Phosphoric Acid:
by soldering, brazing, and diffusion bonding.
H SO (sp gr 1.83) 50 % vol (500 mL/L)
2 4
H PO (85 %) 50 % vol (500 mL/L)
3. Procedure
3 4
Temperature 50 to 55°C
3.1 Precleaning: Current density 2500 A/m anodic
Time 180 s
3.1.1 The principles of electroplating on molybdenum are
similar to those of other metals. The surfaces must be free of
3.4 Rinse.
dirt, grease, and other foreign matter. Solvent, emulsion, and
3.5 AlkalineDip—
...
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