MIL-STD-1250 Corrosion Prevention And Deterioration Control In Electronic Components And Assemblies S/S By Mil-Hdbk-1250This standard establishes minimum requirements for procedures, materials and systems for protecting electronic components in DoD systems and assemblies from adverse environments. Protective measures shall be sufficient to maintain performance characteristics within specified limits both during and after exposure to moisture, high and low temperatures, corrosive gases, chemicals and microbial fungal attack.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 - 26 - 27 - 28 - 29 - 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 - 39 - 40 - 41 - 42 - 43 - 44 - 45 - 46 - 47

MIL-STD-1250A

Table IV. Prevention of dissimilar metal corrosion.

Preventive measure	Example
Select metals which form a permissible couple in table I.	Use nickel, not naval brass, in contact with silver.
Interpose a metal which reduces the potential difference between the two metals.	Tin plate brass to be used next to aluminum.
Design the metal contact so the relative area of the cathodic (more noble) metal is the smaller.	Stainless steel screws in aluminum chassis.
Apply corrosion inhibitor such as zinc chromate primer TT-P-1757 or zinc chromate paste MIL-P-8116.	Use zinc chromate inhibitor when assembling steel screws in aluminum.
Interpose an insulating barrier or nonhygroscopic gasket between the dissimilar metals.	In structural joints, interpose tape MIL-T- 23142. In components, use organic insolvents such as conformal coating MIL-I- 46058.
Apply insulating organic coating to surface of each metal.	Coatings such as MIL-P-23377 epoxy primer, MIL-C-46168 polyurethane topcoat, MIL-V-173, or MIL-I-46058.
Seal joint area with moisture-proof coating or organic sealant.	In structural joints, sealant such as MIL-S-7124 or MIL-S-81733. In components, coatings such as MIL-V-173 or MIL-I-46058

a. When reference is made to a metal, it is the metal on the surface, regardless of whether solid, plated, laminated or dipped.

b. Graphite and graphite containing composites act as a metal and shall be so considered for purposes of determining dissimilar metal contact. Solid film lubricants containing graphite shall not be used.

c. Cadmium plated, tin plated or stainless steel hardware may be mounted on aluminum chassis without further protection or insulation, except parts in contact with aluminum in exterior applications.

d. The anodic layer on aluminum is ordinarily insulating, but may lose this quality after exposure to humidity. Anodized coatings cannot be depended upon for prevention of dissimilar metal contact.