ASTM B482-85(1998)
(Practice)Standard Practice for Preparation of Tungsten and Tungsten Alloys for Electroplating
Standard Practice for Preparation of Tungsten and Tungsten Alloys for Electroplating
SCOPE
1.1 This practice makes recommendations of several reported practices for electroplating on tungsten and its alloys along with comments as a guide in the selection of a processing method for a given application. Because data on methods and results of evaluation with electroplated coatings on tungsten are limited, a recommendation of one method over another cannot be made.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B 482 – 85 (Reapproved 1998)
Standard Practice for
Preparation of Tungsten and Tungsten Alloys for
Electroplating
This standard is issued under the fixed designation B 482; 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.
INTRODUCTION
Because of the high melting point of tungsten, (3410°C) this metal and its alloys are used in
ultra-high-temperature applications. However, tungsten oxidizes readily and the oxides offer little or
no protection to the metal because they melt or sublime below 2200°C. Tungsten has a body-centered-
cubic structure as does chromium. Its coefficient of thermal expansion is 4.3 μm/m · °C; the coefficient
of chromium is 6.1 μm/m · °C, therefore, chromium-coated tungsten offers a reasonable match based
on crystal structure and coefficient of thermal expansion. The effect of hydrogen must be considered
in the design of coating systems for tungsten. Molecular hydrogen when trapped under a coating can
result in failure of the part. Although failure can occur if the adhesion of the coating to the tungsten
is inadequate, failure within the basis metal as rupture at laminations of stringers has been observed
with off-grade tungsten.
1. Scope and oil by organic solvents. Remove saponifiable and dispers-
ible surface dirt by soak cleaning in a hot alkaline cleaner.
1.1 This practice makes recommendations of several re-
2.2.2 Anodic treatment of tungsten surfaces ina5to25
ported practices for electroplating on tungsten and its alloys
mass % sodium hydroxide solution at 71 6 6°C and 16 to 25
along with comments as a guide in the selection of a processing
A/dm can be used to remove undesired surface metal. Anodic
method for a given application. Because data on methods and
etching in a 10 mass % hydrofluoric acid electrolyte at
results of evaluation with electroplated coatings on tungsten
24 6 3°C and 5.4 A/dm can be used to remove light scale and
are limited, a recommendation of one method over another
undesired surface metal before activation and electroplating of
cannot be made.
tungsten.
1.2 This standard does not purport to address the safety
2.3 Activation and Electroplating—Two alternative meth-
concerns, if any, associated with its use. It is the responsibility
ods are presented below. The selection of one process over the
of the user of this standard to establish appropriate safety and
other should be based on preliminary experimentation. Both
health practices and determine the applicability of regulatory
procedures produce as-deposited adhesion of electroplated
limitations prior to use.
metals on tungsten.
2. Processes 2.3.1 Methods 1 —Treat the precleaned tungsten in a hy-
drofluoric acid electrolyte (30 6 10 mass % HF) at 24 6 3°C,
2.1 The several processes reported for electroplating on
using 2 to 5 V, 60-Hz ac, and 2 to 5 A/dm for 1 to 2 min. Either
tungsten can be classified as either (1) providing as-deposited
divide the work between two work rods or make one electrode
adhesion of the coating or (2) depending on diffusion alloy
of platinum. After rinsing, the work is electroplated in acid
bonding to provide such adhesion. Appraisal of the relative
electrolytes.
merits of these processes depends on the application for the
2.3.2 Method 2—Electroplate the precleaned tungsten with
coating.
a chromium strike prior to subsequent electroplating with other
2.2 Precleaning:
3,4
metals using the following processing st
...
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