Alodine 1200 Conversion Coating Bath Storage & Tank Compatibility

Storing Alodine 1200 Conversion Coating Bath? Start Here

Alodine 1200 is a proprietary chromate conversion coating chemistry used to passivate aluminum alloys, most often to the MIL-DTL-5541 Type I specification. Supplied as a dry concentrate, it is dissolved in water (on the order of 9 g/L) to make an acidic working bath at roughly pH 1.5. The formulation is built around chromic anhydride (chromium trioxide) as the hexavalent-chromium source, with fluoride and fluorozirconate activators and a ferricyanide accelerator. In the bath, acid etches the aluminum surface while hexavalent chromium is reduced to trivalent chromium that precipitates as a thin, corrosion-resistant gel film. Because the working bath is simultaneously a strong oxidizer, a low-pH acid, and a fluoride-bearing solution, materials of construction are the deciding factor: the wrong tank or lining is attacked, embrittled, or — with a powerful oxidizer present — becomes a reactivity hazard. Composition figures here are representative of published Alodine 1200/1200S chemistry and are SDS-dependent.

Is Polyethylene (HDPE / XLPE) Safe for Alodine 1200?

No — for the working bath, treat polyethylene as Unsuitable (U). Standard chemical-resistance data rate HDPE against chromic acid as only “C — Limited use only” at 20°C and “Not Recommended” at 50°C. Alodine 1200 is more aggressive than plain dilute chromic acid: it combines that hexavalent-chromium oxidizer with active fluorides and a ferricyanide accelerator. Strong oxidizers progressively attack the polyethylene backbone, and the oxidizer-plus-organic combination is itself a reactivity concern, so polyethylene is not an appropriate choice for storing or running the live bath. For chromate conversion service the industry uses FRP/vinyl-ester, PVDF, PTFE, or properly specified CPVC, generally as a lining inside a steel vessel or as a solid engineered-thermoplastic tank. Highly dilute rinse or dragout streams are a different, milder duty — confirm the specific stream with the chemical supplier and a current resistance chart before selecting poly.

Material compatibility at a glance

Alodine 1200 working baths are acidic hexavalent-chromium oxidizers carrying fluorides and a ferricyanide accelerator. Materials of construction must resist strong oxidation, low pH, and fluoride attack: FRP/vinyl ester, PVDF, PTFE, and properly specified CPVC are the workhorse choices, typically as linings inside steel or as solid thermoplastic tanks. Bare carbon steel and standard polyethylene are not suitable for the working bath.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Carcinogen / mutagen: contains hexavalent chromium — may cause cancer and genetic defects (H350, H340); minimize all exposure.
• Strong oxidizer: may intensify fire or cause explosion in contact with combustibles, fuels, or reducing agents (H271/H272); store away from organics.
• Severely corrosive: low-pH bath causes severe skin burns and eye damage (H314); full chemical PPE, face shield, and acid-resistant gloves required.
• Acute inhalation hazard: chromic-acid mist is fatal if inhaled (H330) and damages organs on repeated exposure (H372); use local exhaust ventilation.
• Fluoride / cyanide constituents: never mix with acids that could liberate HF or HCN conditions, and never combine spent bath with incompatible wastes.
• Aquatic toxicity: very toxic to aquatic life with long-lasting effects (H410); spent bath is a regulated hazardous waste — no drain disposal.

Common questions

Can I store an Alodine 1200 working bath in a polyethylene tank?

Not recommended. The live bath is a strong hexavalent-chromium oxidizer with fluorides at about pH 1.5; chromic acid alone rates only “limited use” on HDPE at ambient and “not recommended” when warm. Use FRP/vinyl ester, PVDF, PTFE, or properly specified CPVC, typically as a lining in steel.

Why is bare steel also a poor choice?

Bare carbon steel is rapidly attacked by the acidic oxidizing bath, and even 316L stainless is unreliable because chlorides and fluorides at low pH break down its passive film. That is why chromate baths are usually run in lined steel or solid corrosion-resistant thermoplastic/FRP vessels.

Is Alodine 1200 the same hazard as plain chromic acid?

It is at least as hazardous. Its hexavalent-chromium content drives the same carcinogen, oxidizer, and corrosive classifications as chromic acid, and the added fluoride and ferricyanide constituents raise extra incompatibility concerns. Always work from the specific product SDS.

What about dilute rinse water from the line?

Dilute rinse and dragout are a milder duty and may tolerate some plastics, but they still carry hexavalent chromium and are regulated waste. Confirm the actual concentration and chemistry with your supplier and a current resistance chart before selecting any storage material.