MIL-STD-1501F
or in the plating bath, per this paragraph:
Chromic Acid: 225-300 gram/liter (30-40 ounce/gallon) Temperature: 32-60°C (90-140°F).
CAUTION: Etching increases iron contamination in the plating bath; therefore, the use of the above solution is recommended.
5.2.3.1 Alternate reverse etch solutions. A sulfuric acid or a sulfuric-hydrofluoric acid mixture can be used as an alternate, reverse etch solution, to the
solution specified in paragraph 5.2.3. The conditions for the employment of either the sulfuric acid or sulfuric-hydrofluoric acid mixtures are as follows:
a. Forty (40) percent sulfuric acid:
(1) Operating range - Concentrated (93%) sulfuric acid diluted to 35 to
45% by volume.
(2) Temperature - ambient.
(3) Current density - 31.0 to 62.0 amps/decimeter squared (2 to 4A per square inch), anodic.
(4) Time - 30-120 seconds. b. Sulfuric-hydrofluoric acid.
(1) Operating range - Concentrated (93%) sulfuric acid diluted to 20 to
30% by volume and concentrated (70%) hydrofluoric acid diluted to 2 to 7% by volume. Ammonium bifluoride may be used at an equivalent total fluoride concentration in place of hydrofluoric acid.
(2) Temperature - ambient.
(3) Current density - 31.0 to 62.0 amps/decimeter squared (2 to 4A per square inch), anodic.
(4) Time - 60-90 seconds.
c. Twenty-five percent (25%) sulfuric acid.
(1) Operating range - Concentrated (93%) sulfuric acid diluted to 20 to
30% sulfuric acid by volume.
(2) Temperature - Ambient
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