Chemicals for aerospace and defense

Aerospace and defense surface preparation follows a familiar sequence: degrease, passivate or pickle, anodize or convert, then wipe clean immediately before bonding, sealing or painting. Manufacturing, MRO and depot maintenance shops use A-A-59601E Type III high-flash petroleum cleaning solvent for general parts cleaning, nitric or citric acid to passivate stainless steel, sulfuric acid to anodize aluminum, phosphoric acid anodize ahead of adhesive bonding, and MEK, acetone or isopropyl alcohol as wipe solvents. Trichloroethylene vapor degreasing is now limited to narrow EPA exemptions, while perchloroethylene degreasing continues under EPA workplace controls.

What separates this work from general industry is the paperwork. Drawings call out ASTM A967, AMS 2700, MIL-PRF-8625 or MIL-DTL-5541, and each part has to trace back to the chemical lots used on it. Government buyers need the supplier's CAGE code and UEI for an award. Alliance Chemical holds CAGE 1LT50 and supplies about 227 NSNs in three supply classes, listed on our government buying page.

Grade questions in aerospace are mostly about residue and impurities. ACS reagent isopropyl alcohol 99.9% suits optics, sensors and electronics because it evaporates with very little non-volatile residue; a lower-grade solvent may leave a film that shows up as glare or a failed bond. Passivation specifications such as ASTM A967 and AMS 2700 set bath concentration, temperature, time and verification tests rather than naming a reagent grade, so a low-particle or ACS grade nitric acid is a choice some shops make for precision parts, not a standing requirement. In sulfuric acid anodizing to MIL-PRF-8625, iron and other impurities in the acid build up in the bath and can produce an uneven or discolored coating that struggles in salt spray testing. Match the grade to the step and the drawing.

Stainless steel passivation is usually specified to ASTM A967 or AMS 2700, sulfuric acid anodizing to MIL-PRF-8625, and chromate conversion coatings to MIL-DTL-5541. Hexavalent chromium from sodium dichromate brings the OSHA chromium (VI) standard, with exposure monitoring and medical surveillance. OSHA exposure limits govern ventilation for solvent wiping and acid tanks. EPA rules finalized in December 2024 prohibit most uses of trichloroethylene, with time-limited exemptions that include batch vapor degreasing of essential aerospace parts. Perchloroethylene vapor degreasing can continue under EPA workplace exposure controls. Both rules are under legal challenge and EPA review, so confirm the current status before you order. Shops working to AS9100 or under DCMA oversight need lot traceability on purchased chemicals. To sell to the government, a supplier needs an active SAM registration with a CAGE code and UEI; ours are 1LT50 and DCTCZDY3BLD3.

• Wiping with a solvent that leaves residue. A ketone carrying trace oil or high non-volatile residue, used immediately before bonding, can cause adhesive or coating failure. Check NVR on the COA.
• Making up a dichromate seal without the lot assay. An off-strength seal bath gives uneven color and weaker corrosion resistance on anodized aluminum. An off-strength bath gives a powdery, poorly adherent coating on aluminum.
• Finding the paperwork gap at receiving. If the COA does not report the tests your quality plan requires, the lot is quarantined and the line waits. Ask for a current COA and compare it with your requirements before you order.
• Ordering TCE or PCE for a use the EPA rules no longer allow. Confirm that the use qualifies before the drum ships.