| HS Code | 605017 |
| Chemical Formula | Na2SiO3 |
| Molar Mass | 122.06 g/mol |
| Cas Number | 6834-92-0 |
| Ec Number | 229-912-9 |
| Appearance | White crystalline powder |
| Odor | Odorless |
| Density | 2.61 g/cm3 at 20°C |
| Melting Point | 1088°C |
| Boiling Point | 1250°C |
| Crystal Structure | Orthorhombic |
| Solubility In Water | Soluble (exothermic) |
| Ph 1 Aqueous Solution | 12.4 |
| Vapor Pressure | Negligible at room temperature |
| Hygroscopicity | Hygroscopic |
As an accredited Sodium Metasilicate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium metasilicate granules supplied in 25 kg moisture-resistant laminated bags, with hazard labeling for safe handling and storage. |
| Container Loading (20′ FCL) | Load 20′ FCL with Sodium Metasilicate in sealed, dry bags/pails, secure pallets, avoid moisture, no incompatible cargo. |
| Shipping | Sodium metasilicate should ship in sealed, moisture-proof packaging (bags, drums, or IBCs) to prevent caking. Avoid contact with acids and incompatible materials. Ensure containers are secured and upright, with clear hazard labeling indicating irritant properties. Follow all applicable transport regulations for chemical shipments. |
| Storage | Store sodium metasilicate in a cool, dry, well-ventilated area inside tightly sealed original containers. Protect from moisture and humidity, as it is hygroscopic. Keep away from acids, reactive metals like aluminum, and food materials. Ensure containers are clearly labeled and stored on spill containment trays to prevent accidental contact. |
| Shelf Life | Sodium metasilicate has a shelf life of 2–5 years when stored in a sealed, dry container away from moisture and air. |
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Sodium metasilicate, Na2SiO3, is a crystalline alkali silicate with a silicon dioxide to sodium oxide molar ratio fixed at 1.00. The anhydrous form, CAS 6834-92-0, and the hydrated grades—sodium metasilicate pentahydrate, Na2SiO3·5H2O, CAS 10213-79-3, and sodium metasilicate nonahydrate, Na2SiO3·9H2O, CAS 13517-24-3—are the principal commercial forms. A 1 wt% aqueous solution of any grade produces a strongly alkaline liquid with pH typically in the range 12.5–13.0 when measured by ISO 4316. The material supplies both reactive alkalinity and soluble silica in a single dry product, which differentiates it from caustic soda, sodium carbonate, and sodium silicates with higher silica ratios.
Industrial manufacture proceeds by high-temperature fusion of silica sand with sodium carbonate, followed by dissolution, filtration, and controlled crystallization for hydrated grades. The resulting product class is used where consistent alkalinity, silica film formation, and low-foam builder performance are required in alkaline cleaning, metal pretreatment, textile processing, and cementitious formulations.
The grade selection is determined primarily by water of crystallization, active Na2O content, dissolution behaviour, and handling characteristics. Anhydrous sodium metasilicate contains the highest active alkali concentration and is specified where low water content is required or where melt-processed formulations cannot tolerate hydrate water. Its dissolution in cold water is slower; standard make-down systems use feedwater at 60–70 °C and agitated stainless steel tanks to avoid lump formation. Pentahydrate is the most common detergent and cleaning grade because it combines moderate water content with rapid dissolution at 40–50 °C. Nonahydrate has lower active alkali per unit mass and is used where reduced dusting and less heat of solution are required in manual dosing areas.
| Property | Anhydrous Na2SiO3 | Pentahydrate Na2SiO3·5H2O | Nonahydrate Na2SiO3·9H2O |
|---|---|---|---|
| Na2O content, wt% | 50.5–51.0 | 28.5–29.5 | 21.5–22.0 |
| SiO2 content, wt% | 49.0–49.5 | 27.5–28.5 | 20.5–21.5 |
| Water of crystallization, wt% | <1.0 | 42.0–43.5 | 56.5–58.0 |
| Solution pH, 1 wt%, 25 °C, ISO 4316 | 12.5–13.0 | 12.5–12.8 | 12.5–12.8 |
Compositional ranges above are drawn from typical commercial certificates of analysis; individual suppliers may apply narrower or modified internal specification bands. The Na2O and SiO2 values should be confirmed by the producer’s test method because minor deviations alter dosing in continuous make-down equipment.
Sodium metasilicate pentahydrate is incorporated into heavy-duty alkaline cleaning compounds at concentrations commonly between 15 wt% and 35 wt% of the dry formulation. In hot-spray degreasing lines operating at 50–80 °C and nozzle pressures of 0.2–0.5 MPa, the silicate component maintains bath pH above 11.5 while the colloidal silica film reduces corrosion of aluminium and zinc surfaces. Field experience on single-stage immersion degreasers indicates that silicate-based builders are less aggressive to non-ferrous substrates than equivalent alkalinity supplied by sodium hydroxide. Make-up dosing is often controlled by conductivity and pH, with batch-to-batch moisture variation in pentahydrate held below 1 wt% to prevent drift in feed rate.
In cotton preparation, metasilicate serves as an alkaline buffer and hydrogen peroxide stabilizer in bleaching systems. Dosing at 0.5–2.0 g/L in a bath held at pH 10.5–11.5 is used where a controlled silicate reserve is required. Published data for metasilicate-specific peroxide stabilization kinetics is limited compared with higher-ratio sodium silicate solutions; therefore, bath stability is normally verified by residual peroxide titration rather than assumed from alkalinity alone.
Cementitious and geopolymer systems use sodium metasilicate as an alkali activator because its SiO2:Na2O ratio of 1.0 provides a defined modulus for reaction with blast-furnace slag or fly ash. Compressive strength development is tested according to ASTM C109/C109M, but performance varies with activator dose, water-to-binder ratio, and curing temperature. The material is therefore specified as part of a binder formulation rather than as a standalone additive.
Substitution of sodium hydroxide by sodium metasilicate reduces the free hydroxyl attack on non-ferrous metals because the metasilicate generates a protective silica film while supplying buffered alkalinity. Sodium hydroxide has no silica reserve, and its 1 wt% solution pH is higher, typically 13.2–13.7, with a steeper pH response to acid contamination. Sodium metasilicate therefore maintains a more stable operating pH in immersed parts washers where acidic drag-in occurs.
Compared with sodium orthosilicate, which has an SiO2:Na2O molar ratio of 0.5, metasilicate provides less total alkalinity per unit mass and is less aggressive to aluminium. Compared with water glass or sodium silicate solutions having SiO2:Na2O ratios of 2.0–3.3, metasilicate has higher pH and lower silicate polymer content, producing lower-viscosity solutions and stronger cleaning action with less adhesive residue. Sodium carbonate has a 1 wt% solution pH near 11.3–11.5 and does not form a silica film; it is less effective where aluminium corrosion inhibition is required. Where phosphate content in consumer detergents is restricted under Regulation (EU) No 259/2012, metasilicate can replace trisodium phosphate as an alkaline builder, although the absence of phosphate changes the hardness control mechanism.
| Parameter | Sodium hydroxide | Sodium metasilicate pentahydrate | Sodium orthosilicate | Sodium silicate, SiO2:Na2O 2.0 | Sodium carbonate |
|---|---|---|---|---|---|
| SiO2:Na2O molar ratio | No silica | 1.0 | 0.5 | 2.0 | No silica |
| 1 wt% solution pH, 25 °C, ISO 4316 | 13.2–13.7 | 12.5–12.8 | 12.8–13.2 | 11.3–11.6 | 11.3–11.5 |
| Silica film formation | Absent | Present | Present | Present | Absent |
| Aluminium corrosion inhibition in alkaline cleaners | Low | Significant | Moderate | Moderate | Low |
Sodium metasilicate is not a universal replacement for sodium hydroxide where maximum caustic concentration is required for heavy scale removal or where formulation stability demands a liquid alkali. It is also not a direct industrial substitute for high-ratio water glass when high silica deposition, high solution viscosity, or low alkalinity is the controlling requirement.
Concentrated solutions attack aluminium, zinc, galvanized steel, and glass at elevated temperature. Storage and dosing tanks should use 316L stainless steel or polypropylene with sealed covers. Hydrated grades cake under humid ambient conditions and may lose water of crystallization in hot, dry environments; closed containers maintained at 10–30 °C are therefore recommended. Direct addition of acid to concentrated metasilicate solution produces a strongly exothermic reaction and is not permitted. Safety data sheets prepared under Regulation (EU) 2020/878 should be reviewed before bulk handling, and exposure controls must reflect the corrosive classification of the solid and concentrated solution. Dilute cleaning baths remain alkaline and require pH monitoring rather than visual inspection for exhaustion.
