| HS Code | 746590 |
| Product Name | Silicon Ethoxide |
| Iupac Name | Tetraethoxysilane |
| Synonyms | Tetraethyl orthosilicate; TEOS; Ethyl silicate; Tetraethyl silicate |
| Cas Number | 78-10-4 |
| Einecs Number | 201-083-8 |
| Molecular Formula | C8H20O4Si |
| Linear Formula | Si(OC2H5)4 |
| Molecular Weight | 208.33 g/mol |
| Appearance | Colorless clear liquid |
| Odor | Mild ether-like odor |
| Density | 0.933 g/cm³ at 20 °C |
| Boiling Point | 168 °C at 760 mmHg |
| Melting Point | -77 °C |
| Flash Point | 45 °C (closed cup) |
| Autoignition Temperature | 260 °C |
| Refractive Index | 1.392 at 20 °C |
| Vapor Pressure | 1.3 mmHg at 20 °C |
| Vapor Density | 7.2 (air = 1) |
| Solubility | Soluble in ethanol, ether, benzene; hydrolyzes in water |
| Logp | 2.2 (estimated) |
| Viscosity | 0.77 mPa·s at 20 °C |
| Purity | ≥98% typical |
| Stability | Stable under normal conditions; moisture sensitive |
As an accredited Silicon Ethoxide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Silicon Ethoxide is packaged in 1 L amber glass bottles, nitrogen-blanketed, with PTFE-lined caps, labeled flammable and moisture-sensitive. |
| Container Loading (20′ FCL) | 20′ FCL loading of Silicon Ethoxide: palletized drums, secured and labeled as UN 1292 flammable liquid, with compliant shipping documentation. |
| Shipping | Silicon Ethoxide (tetraethyl orthosilicate) is transported as UN1292, Tetraethyl silicate, Class 3 flammable liquid, Packing Group III. Use approved containers, flammable-liquid labels, placards as required, and compliant shipping papers. Keep away from ignition sources, oxidizers, and moisture; follow DOT/IATA/IMDG requirements. Ensure personnel are trained and emergency response information is available. |
| Storage | Store Silicon Ethoxide (TEOS), a flammable, moisture-sensitive liquid, in a cool, dry, well-ventilated, fireproof area away from heat, sparks, flames, and oxidizers. Keep containers tightly closed, preferably under inert gas, to prevent hydrolysis from moisture. Use original labeled containers; ground and bond during transfers. Segregate from acids, bases, and water. Protect from direct sunlight. Ensure spill containment and emergency eyewash/shower nearby. |
| Shelf Life | Silicon ethoxide typically has a shelf life of about two years if stored cool, dry, sealed, and under inert gas. |
Silicon ethoxide enters anti-corrosion sol-gel coating lines as a pre-hydrolysed silica source, metered into acidified ethanol/water media at 5–30 wt% of the liquid bath, with water-to-alkoxide molar ratios held between 2.0:1 and 4.0:1 and nitric acid adjustment to pH 2.0–3.5. On production-scale dip-coating equipment with withdrawal speeds of 1–5 mm/s, the hydrolysed sol deposits a continuous film of 1–10 μm dry thickness after thermal cure at 120–180 °C for 30–90 min; thicker films on threaded fasteners have shown meniscus pooling at thread roots when sol viscosity exceeds 10–15 cSt. The specification gate for aluminium and stainless steel articles in marine and aerospace exposure is neutral salt spray resistance evaluated under ISO 9227:2022 parallel to ASTM B117-19, with crosshatch adhesion measured under ISO 2409:2020 or ASTM D3359-17, and surface finish acceptance aligned to ISO 12944-6:2018 for C3/C4 corrosivity categories. Downstream processes include ultrasonic cleaning, alkaline degrease, rinse, silane-based adhesion promotion, immersion or spray application, flash-off, and staged thermal cure; racking density and anodic edge effects are controlled because TEOS-derived silica films solidify through condensation to a cross-linked Si–O–Si network that is brittle beyond approximately 8 μm unless an organic-functional silane is copolymerized. Finished article categories span compressor inlet housings, pump casings, marine engine brackets, aerospace fasteners, and rail brake system hardware.
| Test requirement | Standard designation | Method scope |
|---|---|---|
| Artificial atmosphere salt spray | ISO 9227:2022 / ASTM B117-19 | Continuous neutral salt spray for corrosion-resistance ranking |
| Cross-cut adhesion | ISO 2409:2020 / ASTM D3359-17 | Lattice scribe and tape pull on coated metal coupons |
| Dry film thickness | ISO 2808:2019 | Non-destructive or destructive coating thickness measurement |
| Coating hardness | ASTM D3363-20 | Pencil gouge hardness on cured film surface |
| Protective paint system evaluation | ISO 12944-6:2018 | Performance testing for C3/C4 environments |
Refractive index of an organically modified silica hardcoat on polycarbonate or allyl diglycol carbonate substrates is governed by the TEOS-to-functional-silane molar ratio; TEOS is charged at 20–40 wt% of total solids and co-hydrolysed with glycidoxypropyltrimethoxysilane or methacryloxypropyltrimethoxysilane at water-to-alkoxide molar ratios between 1.5:1 and 3.0:1. The resulting layer is adjusted to 1.48–1.52 at 589 nm by varying the TEOS:functional-silane copolymerization ratio, with higher TEOS fractions increasing silica density and lowering organic flexibility. In spin-coating cells running 1,500–2,500 rpm for 20–40 s, the formulation is dispensed through 0.2 μm filtration to prevent gel particle defects; thermal cure at 100–130 °C for 2–4 h drives condensation to a dense silica network with sufficient organic functionality to avoid stress cracking on flexible polycarbonate. Production-scale lens coating lines track pot life at 21–23 °C and reject batches when viscosity drift exceeds 15% from initial value; relative humidity above 60% during storage accelerates premature gelation and causes streak defects on spin-coated surfaces. Optical conformance is tested with ISO 9211-4:2022 for coating defects and environmental durability, abrasion resistance with ASTM D1044-19 Taber haze or ISO 8980-5:2022 Bayer ratio, adhesion with ISO 2409:2020, and anti-reflective-layer compatibility with ISO 9211-3:2022. Downstream processes include plasma or chemical pre-treatment, hardcoat deposition, flash-off, thermal cure, and vacuum deposition of antireflective stacks. Finished article categories are polycarbonate ophthalmic lenses, impact-resistant safety spectacles, visors, and automotive headlamp lenses.
A hydrolysed ethyl silicate binder derived from silicon ethoxide is incorporated into primary zircon or fused silica slurries at 8–20 wt% of liquid binder, corresponding to 1.5–4.0% dry silica binder on refractory weight. Slurry viscosity is maintained at 12–25 s on a Zahn #4 cup, and binder gelation is triggered by exposure to ammonia vapour after each dip, with gel times of 60–120 s recorded on automated shell lines. The drying window at 22–25 °C and 50–60% relative humidity is critical because rapid water removal collapses the sol-gel network and creates shell cracking, while insufficient drying leaves residual ethanol that lowers green strength and causes shell spalling during dewax. Shell systems for turbine blades, impellers, and medical implant castings are qualified by dimensional tolerance under ISO 8062-3:2021, radiographic soundness under ASTM E192-20, refractory modulus of rupture under ASTM C133-97, and visual surface inclusion limits under ISO 8062-1:2021. Downstream processes include pattern assembly, wetting agent application, primary slurry dipping, fluidized-bed stuccoing with zircon or fused silica, tunnel drying, secondary coats, steam autoclave dewax, and firing at 950–1,150 °C. Finished article categories include nickel-base superalloy turbine blades, titanium medical implants, pump impellers, and aerospace structural castings.
In semiconductor dielectric deposition, silicon ethoxide is delivered as a liquid precursor via vaporizer with carrier gas flows of 200–1,000 sccm for TEOS and 400–3,000 sccm for O₂, maintaining O₂:TEOS flow ratios between 4:1 and 12:1. Chamber pressure is held at 1–10 Torr, susceptor temperature between 200 °C and 400 °C, and RF power between 300 W and 800 W on 200 mm parallel-plate PECVD platforms. Film characteristics shift with the O₂:TEOS ratio: low oxygen ratios yield carbon-rich oxide with lower compressive stress but higher wet etch rates; high oxygen ratios above 10:1 reduce carbon and increase density but may induce conformality loss in via sidewalls below 0.35 μm feature diameter. Process records from production tools show that raising susceptor temperature without reducing O₂:TEOS ratio increases tensile stress and can cause film cracking above 350 MPa, while lowering temperature below 200 °C traps silanol and produces unstable dielectric constant. The specification gate for inter-metal dielectric and passivation films includes refractive index at 1.44–1.47 measured by ellipsometry, within-wafer non-uniformity below 2%, thickness matching to ±3% of target, and particle contamination limits defined by ISO 14644-1:2015 class 3 cleanroom protocols and SEMI S2-0717 equipment safety qualification. Downstream processes include wafer preclean, TEOS vaporization, plasma-enhanced chemical vapour deposition, anneal, chemical mechanical planarization, and photolithographic patterning. Finished article categories are inter-metal dielectric layers, shallow trench isolation fill, gate sidewall spacers, passivation overlayers, and microelectromechanical system sacrificial layers.
Silica aerogel blanket production using ambient-pressure drying combines silicon ethoxide with ethanol and water at a molar ratio near 1:4–8:2–4, hydrolysed under hydrochloric acid at pH 2.0–3.0, and condensed with ammonium hydroxide at pH 5.5–7.0; gel times typically fall between 10 min and 60 min at 25–40 °C. The wet gel is aged for 12–48 h in ethanol/water to strengthen the silica network, then surface-modified with hexamethyldisilazane or trimethylchlorosilane at 5–20 wt% of gel mass to replace surface silanol groups and enable springback during drying. Solvent exchange with n-hexane or heptane precedes staged drying at 60–180 °C, where the hydrophobic silica retains pore structure and resists capillary collapse. Production-scale roll-to-roll lines impregnate glass-fibre or polyester needled blankets and monitor solvent vapour concentration below lower explosive limits. Thermal performance is certified under ASTM C518-23 or ISO 8302:1991, with typical thermal conductivity for silica aerogel blankets in the range 0.015–0.021 W/m·K at 25 °C; fire classification is evaluated under EN 13501-1:2018. Downstream processes include sol preparation, fibre mat saturation, gelation, ageing, silylation, solvent exchange, drying, calendering, and slit-to-width. Finished article categories include industrial pipe insulation blankets, LNG cold-chain panels, building façade insulation, battery pack thermal barriers, and silica aerogel granules for translucent daylighting elements.
On woven and nonwoven finishing lines, silicon ethoxide is diluted to 10–30 g/L in an ethanol-water bath, acidified with acetic or citric acid to pH 3.5–5.0, and co-hydrolysed with alkyltrialkoxysilanes at a molar ratio of 1:0.2–1:0.6 to create hydrophobic methyl or octyl functionality. Pad mangle pressure is set to achieve 60–80% wet pick-up, followed by drying at 100 °C and curing at 140–170 °C for 1–3 min. The finishing bath has a limited production window because TEOS oligomer growth raises viscosity and causes silica aggregation; filtration through 25 μm bag filters and controlling bath age below 6 h prevent visible white deposits on dark textiles. Water repellency is measured under AATCC TM22-2023 spray rating, laundering durability under EN ISO 6330:2021 plus AATCC TM22 after 10 wash cycles, abrasion resistance of the treated fabric under ISO 12947-2:2016, and tensile strength before and after treatment under ISO 13934-1:2013. Downstream processes include desizing, scouring, pad application, infrared predrying, hot-air cure, compressive shrinking, and laboratory lot release testing. Finished article categories include outdoor awning fabrics, protective workwear, military tentage, filtration media, and automotive interior textiles requiring reduced surface soiling.
Competitive Silicon Ethoxide prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615380400285 or mail to sales2@ascent-chem.com.
We will respond to you as soon as possible.
Tel: +8615380400285
Email: sales2@ascent-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Silicon ethoxide, also designated tetraethyl orthosilicate and identified by CAS 78-10-4 and EINECS 201-083-8, is a colourless alkoxysilane liquid with the molecular formula Si(OC₂H₅)₄ and a molecular weight of 208.33 g/mol. The substance is produced by direct esterification of silicon tetrachloride with ethanol followed by multistage rectification; high-purity grades are further refined to reduce residual chloride and trace transition metals. At 20 °C and 101.3 kPa, the liquid density is approximately 0.934 g/cm³ when measured according to ASTM D4052-18a, the refractive index nD20 is 1.382–1.384 by ASTM D1218-12(2016), and the boiling point is 168–169 °C under ASTM D1078-11(2019). The closed-cup flash point is 45–46 °C by ASTM D3278-96(2011), and the dynamic viscosity at 25 °C is 0.70–0.75 mPa·s under ASTM D445-21. The material is not a model-numbered consumer product; commercial designations are purity-grade descriptors such as technical, purified, electronic, or semiconductor grade, and each lot is released against a certificate of analysis.
Two distinguishable products are routinely transferred under the same CAS number: a technical-grade liquid used in ceramics, investment casting, and crosslinked silane formulations, and an electronic-grade liquid used where mobile alkali and transition-metal contamination must be minimised. The distinction is not a simple assay number; it is a trace-metal, water, and chloride boundary. Table 1 gives typical release ranges derived from supplier certificates of analysis and physical-property test methods. The liquid is Newtonian, and viscosities outside 0.70–0.75 mPa·s are an early indicator of hydrolysis or oligomer formation.
| Parameter | Test method | Technical grade range | Electronic grade range |
|---|---|---|---|
| Density at 20 °C | ASTM D4052-18a | 0.930–0.936 g/cm³ | 0.933–0.936 g/cm³ |
| Refractive index nD20 | ASTM D1218-12(2016) | 1.381–1.384 | 1.382–1.384 |
| Assay as Si(OC₂H₅)₄ by GC-FID area% | Gas chromatography with flame ionisation detection | ≥99.0% | ≥99.5% |
| Water content | ASTM E203-16 | ≤500 mg/kg | ≤50 mg/kg |
| Chloride | Ion chromatography after hydrolysis | ≤10 mg/kg | ≤1 mg/kg |
| Colour, APHA | ASTM D1209-05(2019) | ≤15 | ≤10 |
| Viscosity at 25 °C | ASTM D445-21 | 0.70–0.75 mPa·s | 0.70–0.75 mPa·s |
| Distillation range at 101.3 kPa | ASTM D1078-11(2019) | 166–170 °C | 168–169 °C |
| Flash point, closed cup | ASTM D3278-96(2011) | 45–46 °C | 45–46 °C |
Electronic-grade lots are packaged in 200 L 316L stainless steel drums with nitrogen-blanketed closures and are sampled through closed-loop valves. Technical lots may be shipped in epoxy-phenolic lined steel drums. The certificate of analysis should be reviewed for boron and phosphorus when the liquid is directed to dielectric film formation, because these elements migrate into oxide films and shift electrical flatband voltage. Compliance documentation under REACH Regulation (EC) No 1907/2006 and supplier ISO 9001:2015 batch-release records are normally provided, but the absence of a harmonised monograph means that grade definitions remain supplier-specific.
Silicon ethoxide reacts with water by hydrolysis and polycondensation, releasing ethanol and forming siloxane oligomers. The reaction is catalysed by mineral acids and bases, and proceeds measurably even at ambient temperature in humid air. In a closed drum with damaged nitrogen blanketing, water ingress above 50 mg/kg produces a gradual viscosity rise followed by turbidity and precipitation of hydrated silica. The viscosity increase is detectable by ASTM D445-21 before gelation becomes visible. At relative humidity greater than 60%, unprotected transfer operations shorten pot life significantly; the operational boundary for open handling is therefore a dry inert atmosphere with a dew point below −40 °C.
Two hydrolysis-processing regimes are used. In acid-catalysed sol-gel synthesis, a water-to-silicon ethoxide molar ratio between 1 and 4 is maintained, with pH adjusted to 2–3 using hydrochloric acid; gelation is relatively slow and produces dense, microporous networks. Under base catalysis with ammonia, gelation accelerates and the resulting network is more particulate. Bulk mixing with aqueous media must remove the hydrolysis exotherm; addition of base to undiluted silicon ethoxide should not be performed because local pH excursions cause rapid condensation, solid aggregation, and possible reactor fouling. Amine-based additives are similarly incompatible in formulations where extended working time is required because they catalyse premature crosslinking.
Failure modes observed on production-scale sol-gel lines include pressure build-up from ethanol release in closed mixing vessels and filter blinding from partially condensed oligomers. A 1000 L glass-lined reactor equipped with a condenser and pH probe is typical for acid-catalysed sol manufacture; the addition sequence is normally TEOS to solvent, then water/acid mixture under controlled agitation, because reverse addition can create high local water concentration and non-uniform molecular weight development.
The choice between silicon ethoxide and tetramethyl orthosilicate is governed by reaction rate, toxicology of the hydrolysis byproduct, and vapour handling. TMOS hydrolyses faster because the methoxy leaving group is smaller and methanol is more acidic than ethanol. The acceleration is useful for rapid gelation, but released methanol has a lower occupational exposure limit than ethanol: the ACGIH TLV-TWA for methanol is 200 ppm compared with 1000 ppm for ethanol. TMOS also exhibits a closed-cup flash point near 10 °C, which places it in flammable-liquid handling category II under the global harmonised system, whereas silicon ethoxide at 45–46 °C falls into category III. The difference reduces the need for explosion-proof cold storage when silicon ethoxide is selected.
| Comparison parameter | Silicon ethoxide | Tetramethyl orthosilicate | Sodium silicate | Colloidal silica |
|---|---|---|---|---|
| Hydrolysis by-product | Ethanol | Methanol | Alkali residues | None; pre-formed particles |
| Hydrolysis rate in acid sol | Moderate | Faster | Not applicable as monomer | Not applicable |
| Closed-cup flash point | 45–46 °C (ASTM D3278-96(2011)) | ≈10 °C | Non-flammable aqueous solution | Non-flammable aqueous dispersion |
| Mobile alkali contamination | Below trace-metal specification | Below trace-metal specification | Present as sodium | Low, but stabilising cations may be present |
| Film formation route | In situ hydrolysis/condensation | In situ hydrolysis/condensation | Drying and ion exchange/acidification | Particle packing and sintering |
The substitution is not kinetically neutral. Formulations optimised for TMOS cannot be transferred to silicon ethoxide on a simple weight-per-weight basis because the molecular weight difference, 208.33 g/mol versus 152.22 g/mol, changes the moles of released alcohol and the silica yield per kilogram. The silica yield per kilogram of silicon ethoxide is approximately 0.288 kg SiO₂/kg; for TMOS the value is approximately 0.394 kg SiO₂/kg. When silicon ethoxide replaces TMOS, the mass charged must be increased by a factor of approximately 1.37 to maintain the same theoretical silica content. This calculation is stoichiometric and does not account for volatilisation losses during open mixing.
Compared with sodium silicate, silicon ethoxide provides alkali-free silica after hydrolysis, which is relevant in dielectric and optical applications where sodium migration causes flatband voltage drift. Compared with colloidal silica, silicon ethoxide is a reactive monomer rather than a pre-formed particle dispersion; it penetrates smaller pores and forms a continuous gel network, but it also shrinks more during drying and requires solvent management.
Silicon ethoxide is vaporised in stainless steel source vessels and delivered to heated vacuum chambers for silicon dioxide film growth. Low-pressure chemical vapour deposition using silicon ethoxide and oxygen is performed in horizontal tube furnaces at 650–750 °C and pressures near 0.5–1.0 Torr. Plasma-enhanced deposition operates at 300–450 °C in RF-excited parallel-plate reactors. The resulting silicon dioxide film exhibits a refractive index close to 1.46 and a dielectric constant near 3.9 at 1 MHz. The dielectric constant is evaluated on metal-insulator-semiconductor structures according to ASTM D150-18 and the capacitance-voltage method.
Electronic-grade silicon ethoxide must maintain sodium, aluminium, iron, titanium, boron, and phosphorus individually below 1 mg/kg in most dielectric specifications, because these contaminants are electrically active or degrade oxide breakdown strength. Some semiconductor users specify particle contamination using liquid particle counters; current practice is to reject lots with more than 20 particles per millilitre larger than 0.2 µm. Published data for specific fabrication facilities is limited, and acceptance limits are determined by process layer and device node.
Compared with silane-based silicon dioxide chemistry, the TEOS route shows higher sidewall coverage in structures with aspect ratios above 3:1, but deposition rates can be lower at equivalent temperature. Ozone-TEOS sub-atmospheric CVD at approximately 400 °C is used for gap-fill applications; the process window for ozone concentration and substrate temperature is narrow because excessive ozone can introduce carbonaceous residues and increase film wet etch rate in buffered hydrofluoric acid. The wet etch rate in 7:1 buffered HF is used as a film quality metric; TEOS oxide typically etches faster than thermal oxide before densification.
Prehydrolysed silicon ethoxide is also used as a binder in investment casting shell deposition. The precursor is hydrolysed with acidified water to a controlled polysiloxane concentration, then blended with refractory fillers such as fused silica or zircon. Viscosity is maintained between 8 and 15 mPa·s on production slurries, and gel time is adjusted by pH and water ratio to match robot-assisted slurry dipping stations. Compared with sodium silicate binders, silicon ethoxide-derived binders avoid alkali residues that can cause shell softening at pouring temperatures; compared with colloidal silica binders, the prehydrolysed TEOS system offers lower initial viscosity and faster drying shell strength development, but it requires careful ethanol vapour extraction from enclosed dipping lines.
Optical coating formulations based on silicon ethoxide are used for antireflective silica layers on glass and for fibre preform overcladding. A single dip-coating pass from an acid-catalysed sol with water-to-precursor ratio near 2–3 and ethanol dilution deposits a film that densifies to approximately 100–150 nm after calcination. Thicker single-pass films crack because of capillary stress during solvent evaporation; the critical thickness is a function of sol pH, ageing time, and relative humidity. Coating thicknesses above 1 µm typically require multiple passes or the addition of controlled colloidal silica particles. At ambient humidity above 60%, film drying is retarded and gelation can occur in the coating bath before dip withdrawal is complete; closed solvent-recovery systems and dry nitrogen stripping are used to stabilise bath viscosity.
