Tetraethyl Orthosilicate (TEOS) Storage & Tank Compatibility

Storing Tetraethyl Orthosilicate (TEOS)? Start Here

Tetraethyl orthosilicate (TEOS), C₈H₂₀O₄Si, is a clear, water-white liquid with a mild, alcohol-like odor. It is a silicate ester widely used as a precursor for silicon dioxide in sol-gel coatings, optical and semiconductor films, refractory binders, and high-purity fumed and precipitated silica. Chemically, TEOS behaves much more like an organic solvent than like the aqueous salts and acids most polyethylene tanks are built for, and it slowly hydrolyzes on contact with water or humid air, releasing ethanol and forming silica. It is also a flammable liquid, with a flash point in the flammable-liquid range. This page summarizes its hazard profile and material compatibility so engineers can specify the correct containment. For TEOS service the proven materials are stainless steel, glass, and PTFE; polyethylene offers only conditional, limited-contact resistance.

Can You Store Tetraethyl Orthosilicate in HDPE or XLPE Tanks?

Only with caution. Tetraethyl orthosilicate is a flammable silicate ester that behaves like an organic solvent, and polyethylene tanks (HDPE and crosslinked XLPE) are rated only Conditional (C) for this service. Polyethylene gives limited resistance to organic esters, and the ethanol formed as TEOS slowly hydrolyzes can swell and stress-load the resin over time, so polyethylene is not the preferred primary store. Equally important, TEOS is a flammable liquid: storing it demands flammable-liquid handling under the applicable fire code, including bonding, grounding, proper ventilation, and code-compliant secondary containment, which a standard polyethylene tank is not designed to provide. The proven materials for TEOS are stainless steel, glass, and PTFE seals. If your process involves bulk TEOS storage, contact us about the correct containment rather than relying on a general-purpose polyethylene tank.

Material compatibility at a glance

Tetraethyl orthosilicate is a flammable, water-white silicate ester used as a precursor for silica, sol-gel coatings, and high-purity silicon dioxide. It behaves like an organic solvent rather than an aqueous chemical, and it slowly hydrolyzes in the presence of water or humid air to release ethanol and form silica. For materials of construction, stainless steel, glass, and PTFE are fully resistant and are the usual choices for storage and transfer. Polyethylene (HDPE/XLPE) and polypropylene offer only conditional resistance to the ester and the ethanol it generates on hydrolysis, so polyethylene tanks are not the preferred primary store. Because TEOS is a flammable liquid, any storage must follow flammable-liquid handling codes with bonding, grounding, and proper containment.

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

• Flammable liquid and vapor (H226); keep away from heat, sparks, and open flames, bond and ground all transfer equipment, and use spark-proof tools and explosion-proof fittings.
• Slowly reacts with water and humid air, releasing ethanol and forming silica - keep containers tightly closed and store in a dry, well-ventilated area.
• Harmful if inhaled and may cause respiratory irritation, drowsiness, or dizziness (H332, H335, H336); use local exhaust ventilation or appropriate respiratory protection.
• Causes skin and serious eye irritation (H315, H319); wear chemical goggles, face protection, and chemical-resistant gloves.
• Can cause organ damage on single or repeated exposure (H370, H372, H373); avoid prolonged contact and use closed handling where practical.
• Store away from water, strong acids and bases, and oxidizers; provide eyewash and safety shower and have flammable-liquid spill control available.

Common questions

Is tetraethyl orthosilicate compatible with polyethylene (HDPE/XLPE) tanks?

Only conditionally. TEOS is a flammable silicate ester that acts like an organic solvent, and polyethylene gives limited resistance, so it is rated Conditional (C). It is suitable only for short-term, limited-contact service with chart verification, and because TEOS is flammable, storage must follow flammable-liquid codes. Stainless steel, glass, and PTFE are the preferred materials.

What happens when tetraethyl orthosilicate contacts water?

It slowly hydrolyzes, producing ethanol and silica. This is the basis of sol-gel chemistry, but in storage it means containers must stay tightly closed and dry, and it is why NFPA 704 assigns TEOS the W special hazard for reaction with water.

Is tetraethyl orthosilicate flammable?

Yes. TEOS is a flammable liquid with a flash point in the flammable-liquid range (about 113 F / 45 C, closed cup), giving it NFPA flammability 3. Vapors can form explosive mixtures with air, so ignition sources must be controlled and equipment bonded and grounded.

What is the NFPA 704 rating for tetraethyl orthosilicate?

Health 1, Flammability 3, Instability 2, with the special hazard W for reaction with water, per the published Safety Data Sheet for CAS 78-10-4.