ASTM B629-2019 pdf free download
ASTM B629-2019 pdf free download.Standard Practice for Preparation of Molybdenum and Molybdenum Alloys for Electroplating
1. Scope
1.1 This practice covers a procedure for preparing molyb- denum 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.3 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. 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. Electro- plated coatings are applied to molybdenum to prevent oxidation, to prevent seizing and galling, and to assist joining by soldering, brazing, and diffusion bonding.
3. Procedure
3.1 Precleaning: 3.1.1 The principles of electroplating on molybdenum are similar to those of other metals. The surfaces must be free of dirt, grease, and other foreign matter. Solvent, emulsion, and soak cleaners are suitable for precleaning to remove gross surface contaminants. If a molybdenum specimen is subjected to severe forming operations and retains a carbonaceous surface layer, descale the part by immersion in a 110 g/L solution of sodium hydroxide at or near boiling, or by mechanical finishing. Glass bead blasting can be used to remove uneven coatings of scale without disturbing the finish of the metal. 3.1.2 Cathodic alkaline cleaning is preferred for the final precleaning so as to avoid anodic oxidation. Proprietary formulations used for cathodic alkaline cleaning of other metals are suitable. Cathodic treatment at about 6 V for 30 to 60 s is usually adequate, using a cleaner concentration of 60 to 75g/L and a solution temperature of 60 to 75 °C. 3.2 Rinse—Here, and throughout the procedure, the water rinses should be warm (approximately 50 °C). 3.3 Electropolishing—Either of the following electropol- ishes may be used. The choice of electropolish and time depends on the amount ofmaterial that can be removed and the degree of surface improvement desired. The cathodes may be lead or carbon. The sulfuric acid bath produces a blue film that is partly removed in the rinse and completely removed in the alkaline dip.3.6 Rinse. 3.7 Acid Dip—Briefly 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. 3.9 Chromium Striking—Electroplate the specimen in a conventional chromium electroplating solution for 1 to 5 min at 1500 to 2500 A/m 2 at a temperature of 50 °C minimum. In some cases, it may be necessary to first make the part anodic in the chromium solution for 1 min at 2200A/m 2 in order to attain good adhesion.
