ASTM B629-77(2019)

Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating

SIGNIFICANCE AND USE
2.1 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2019
• ICS: 77.120.99 - Other non-ferrous metals and their alloys
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.02 - Pre Treatment

Relations

• Replaces: ASTM B629-77(2013) - Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating
• Effective Date: 01-Apr-2019
• Referred By: ASTM B905-00(2021) - Standard Test Methods for Assessing the Adhesion of Metallic and Inorganic Coatings by the Mechanized Tape Test
• Effective Date: 01-Apr-2019

Overview

ASTM B629-77(2019) - Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating, published by ASTM International, establishes standardized procedures for preparing molybdenum and its alloys prior to electroplating. This practice focuses on methods using commonly available techniques, equipment, and chemicals in the electroplating industry, making it valuable for a wide range of engineering and manufacturing applications where reliable and protective coatings are required.

Molybdenum’s unique properties-such as high strength at elevated temperatures, low vapor pressure, and significant resistance to creep and impact-make it a preferred material for load-bearing parts in demanding environments. However, molybdenum is prone to oxidation, and its oxides are non-protective. Application of electroplated coatings is essential to maintain dimensional stability and extend service life in critical engineering components.

Key Topics

• Precleaning Procedures: Emphasizes thorough removal of dirt, grease, and other contaminants using solvent, emulsion, or soak cleaners. Specialized steps for parts with heavy carbonaceous layers include sodium hydroxide descale or mechanical finishing.
• Cathodic Alkaline Cleaning: Prefers cathodic cleaning to avoid anodic oxidation, offering guidance on cleaner concentrations, temperature, voltage, and duration.
• Electropolishing: Details both sulfuric acid and sulfuric-phosphoric acid processes, enabling the removal of material and improvement of surface finish. Provides basic parameters for solution composition, temperature, and current density.
• Sequential Treatment: Specifies cycles of rinsing, alkaline dipping, and acid dipping, ensuring progressive surface preparation for optimal electroplating adhesion.
• Nickel and Chromium Strike: Recommends preliminary electroplating-nickel or chromium strike-prior to final desired metal coating, enhancing bond strength and uniformity.
• Safety and Compliance: Mandates user responsibility for adhering to appropriate workplace safety, health, and environmental regulations, as specific hazards are not exhaustively covered within the standard.

Applications

• Aerospace Components: Preparation of turbine blades, rocket motor parts, and mechanical seals for reliable plating and protection against high-temperature oxidation and wear.
• Electronics Manufacturing: Ensures proper substrate conditioning for electroplating heating elements and electronic devices where precision and performance are critical.
• Industrial Equipment: Used in the treatment of molybdenum parts designed for harsh operational environments, such as heating elements and load-bearing assemblies.
• Joining Processes: Facilitates effective joining techniques-such as soldering, brazing, or diffusion bonding-by providing surfaces amenable to strong metallic bonds after electroplating.
• Dimensional Stability: Protects exposed molybdenum surfaces from catastrophic oxidation above 800 °C, preventing dimensional losses during service.

Related Standards

For comprehensive application and compliance, users may refer to the following:

• ASTM B700: Standard Specification for Electrodeposited Coatings on Various Substrates
• ASTM B814: Standard Guide for Electroplating with Precious Metals
• ISO 4527: Metallic and Other Inorganic Coatings
• References cited in the standard offer further details on advanced preparation techniques, such as hydrogen heat treatment and fused salt pickling.

ASTM B629-77(2019) enables consistent, high-quality preparation of molybdenum for electroplating, resulting in improved corrosion resistance, dimensional integrity, and component longevity across critical engineering sectors. For organizations seeking robust solutions to protect molybdenum components, adherence to this standard ensures proven preparation practices and compatibility with international trade requirements.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B629 − 77 (Reapproved 2019)
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 3. Procedure
3.1 Precleaning:
1.1 This practice covers a procedure for preparing molyb-
3.1.1 The principles of electroplating on molybdenum are
denum and its alloys for electroplating. The procedure utilizes
techniques, equipment, and chemicals that are common to similar to those of other metals. The surfaces must be free of
dirt, grease, and other foreign matter. Solvent, emulsion, and
electroplating. Specialized procedures such as hydrogen heat
treatment and fused salt pickling are not included. These and soak cleaners are suitable for precleaning to remove gross
surface contaminants. If a molybdenum specimen is subjected
otherprocedurescanbefoundinthereferenceslistedattheend
of this practice. to severe forming operations and retains a carbonaceous
surface layer, descale the part by immersion in a 110 g/L
1.2 This standard does not purport to address all of the
solution of sodium hydroxide at or near boiling, or by
safety concerns, if any, associated with its use. It is the
mechanical finishing. Glass bead blasting can be used to
responsibility of the user of this standard to establish appro-
remove uneven coatings of scale without disturbing the finish
priate safety, health, and environmental practices and deter-
of the metal.
mine the applicability of regulatory limitations prior to use.
3.1.2 Cathodic alkaline cleaning is preferred for the final
1.3 This international standard was developed in accor-
precleaning so as to avoid anodic oxidation. Proprietary
dance with internationally recognized principles on standard-
formulations used for cathodic alkaline cleaning of other
ization established in the Decision on Principles for the
metals are suitable. Cathodic treatment at about 6 V for 30 to
Development of International Standards, Guides and Recom-
60 s is usually adequate, using a cleaner concentration of 60 to
mendations issued by the World Trade Organization Technical
75g/L and a solution temperature of 60 to 75 °C.
Barriers to Trade (TBT) Committee.
3.2 Rinse—Here, and throughout the procedure, the water
rinses should be warm (approximately 50 °C).
2. Significance and Use
3.3 Electropolishing—Either of the following electropol-
2.1 Molybdenum is used in engineering applications where
ishes may be used. The choice of electropolish and time
strength and rigidity of component parts are needed, especially
depends on the amount of material that can be removed and the
at high temperatures. Its good strength at high temperatures,
degree of surface improvement desired. The cathodes may be
low vapor pressure, and good impact and creep resistance
lead or carbon. The sulfuric acid bath produces a blue film that
makeitattractiveforload-bearingitemssuchasturbineblades,
is partly removed in the rinse and completely removed in the
mechanical seals, rocket motor parts, heating elements, and
alkaline dip.
electronic devices. Molybdenum, however, is easily oxidized,
3.3.1 Sulfuric Acid:
and the oxides are not protective. The volatility of the oxides
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
Temperature 20 to 30 °C
catastrophic oxidation and to losses in dimensions. Electro-
Current density 1100 to 2200 A/m anodic
plated coatings are applied to molybdenum to prevent
Time 30 s
oxidation, to prevent seizing and ga
...