| HS Code | 354668 |
| Chemical Formula | Na2SiO3 |
| Molecular Weight | 122.06 g/mol |
| Cas Number | 6834-92-0 |
| Appearance | White crystalline powder |
| Odor | Odorless |
| Ph 1 Aqueous Solution | 12.4 |
| Melting Point | 1088°C |
| Boiling Point | 1255°C |
| Density | 2.61 g/cm³ |
| Solubility In Water | Soluble, forming alkaline solution |
| Hygroscopicity | Hygroscopic |
| Refractive Index | 1.52 |
As an accredited Sodium Metasilicate Anhydrous Powder factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in 25 kg net multi-wall paper bags with a polyethylene inner liner, sealed for moisture protection. |
| Container Loading (20′ FCL) | 20′ FCL: sodium metasilicate anhydrous powder in moisture-proof bags/drums on pallets, securely stowed and weight-optimized. |
| Shipping | Ship as UN 3253, Sodium Metasilicate (anhydrous), Class 8, Packing Group III. Use sealed, moisture-proof containers to prevent caking or hydration. Keep dry, avoid contact with aluminum or zinc, and separate from acids. Standard corrosive solid handling applies. |
| Storage | Store in a cool, dry, well-ventilated area in a tightly sealed, clearly labeled container. Keep away from moisture, humidity, and water, as the anhydrous powder is hygroscopic. Avoid contact with acids and strong oxidizers. Protect containers from physical damage and store separately from incompatible materials. |
| Shelf Life | Stable for several years if stored tightly sealed in a cool, dry place; moisture exposure reduces shelf life. |
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Product: sodium metasilicate anhydrous powder, technical grade, CAS 6834-92-0, EINECS 229-912-9, molecular mass 122.06 g/mol. The material is specified as 98.0 wt% minimum Na₂SiO₃, with the oxide balance expressed as 50.5–51.5 wt% Na₂O and 49.0–50.0 wt% SiO₂; this corresponds to a silicate molar ratio SiO₂:Na₂O of 1.00 ± 0.02. The dry powder is white, free-flowing, and supplied with a loose bulk density of 0.90–1.20 g/cm³ per ASTM D7481 and a residual coarse fraction of ≤5.0 wt% retained on 150 µm per ASTM E11. The pH of a 1% w/w aqueous solution at 25 °C is 12.5–13.0 per ASTM E70. Because the anhydrous grade contains no water of crystallization, freight and storage mass are lower than for sodium metasilicate pentahydrate, but the powder is hygroscopic and requires sealed packaging at storage humidity below 60% RH to prevent surface hydration and silo-bridging.
| Parameter | Specification | Method or reference |
|---|---|---|
| Total Na₂SiO₃ | ≥98.0 wt% | Calculation from oxide determination; manufacturer certificate of analysis |
| Na₂O | 50.5–51.5 wt% | ISO 1691 |
| SiO₂ | 49.0–50.0 wt% | ISO 1690 |
| Molar ratio SiO₂:Na₂O | 1.00 ± 0.02 | Calculated from oxide concentrations |
| Loose bulk density | 0.90–1.20 g/cm³ | ASTM D7481 |
| Residue on 150 µm | ≤5.0 wt% | ASTM E11 |
| pH, 1% w/w at 25 °C | 12.5–13.0 | ASTM E70 |
Anhydrous sodium metasilicate functions as an alkaline builder and soluble silicate source in industrial cleaning formulations. In ferrous-metal immersion washers, working baths are commonly maintained at 10–30 g/L metasilicate with 1–3 g/L of nonionic surfactant and 5–15 g/L of sodium carbonate or tetrasodium EDTA. The silicate species precipitates water hardness as insoluble mixed silicates and buffers free hydroxide concentration; this is distinct from sodium hydroxide, which raises pH rapidly but contributes no residual silicate film. The cleaning window narrows when bath temperature exceeds 80 °C or when metasilicate concentration exceeds 30 g/L, because calcium and magnesium silicate sludge can deposit on immersion-heater shrouds and recirculation pipes. Field experience in agitated production washers indicates that descaling intervals shorten when hardness exceeds 300 mg/L CaCO₃, although published data for specific steel geometries is limited.
| Alkali source | CAS | Water of crystallization (wt%) | Approx. Na₂SiO₃ or alkali equivalent | pH, 1% solution | Operational difference |
|---|---|---|---|---|---|
| Sodium metasilicate anhydrous | 6834-92-0 | 0 | ≥98.0 wt% Na₂SiO₃ | 12.5–13.0 | High hygroscopicity; dry blending with acids must be avoided |
| Sodium metasilicate pentahydrate | 10213-79-3 | 42.5 | 57.5 wt% Na₂SiO₃ | 12.5–13.0 | Lower hygroscopicity; higher shipping mass per active oxide |
| Sodium metasilicate nonahydrate | 13517-24-3 | 57.0 | 43.0 wt% Na₂SiO₃ | 12.5–13.0 | Seldom used where dry feed is required |
| Sodium hydroxide pellet | 1310-73-2 | 0 | 77.5 wt% Na₂O equivalent | 13.2–13.6 | Higher pH; no silicate corrosion inhibition; aggressive to aluminium, zinc, tin |
| Sodium carbonate dense | 497-19-8 | 0 | 58.5 wt% Na₂O equivalent | 11.3–11.5 | Weaker builder; limited alkalinity reserve |
| Sodium tripolyphosphate | 7758-29-4 | 0 | Phosphate ≥56.0 wt% P₂O₅ | 9.0–10.0 | Effective sequestrant but restricted by EU 259/2012 for consumer laundry and dishwasher detergents |
For aluminium alloys in alkaline immersion washers, the silicate dosage becomes a corrosion-control variable. Aluminium dissolution in NaOH-only baths proceeds rapidly at pH values above 11.0; the addition of 2–10 g/L anhydrous sodium metasilicate can suppress metal loss by forming a silicon-rich surface film. Mass-loss measurement per ASTM G31 on AA6061 and AA5052 coupons is used to establish the minimum silicate concentration for a given bath temperature and agitation regime. The protective effect is not unlimited; above 15 g/L metasilicate at bath temperatures above 70 °C, accelerated dissolution can reappear in some deformed aluminium grades, and silicate deposits may interfere with downstream painting or conversion coating. Bath pH is therefore held at 11.5–12.2 rather than the higher pH range used for ferrous metals.
In ceramic body preparation, anhydrous sodium metasilicate is added as a deflocculant and pH adjuster in slips containing kaolin, ball clay, quartz, and feldspar. A typical dry dose of 0.1–0.5 wt% based on dry solids reduces slip viscosity at a fixed density of 1.60–1.75 g/cm³ when measured on a rotational viscometer per ASTM D2196. The mechanism involves exchange of adsorbed calcium and magnesium ions with sodium, followed by electrostatic stabilization of clay platelets. The viscosity minimum is narrow; doses above 0.7 wt% raise ionic strength and cause re-flocculation, while doses below 0.05 wt% fail to sufficiently displace divalent cations. Production slips are typically milled in high-speed blungers and screened through 125 µm sieves before storage in agitated day tanks. Published data for specific clay bodies is limited, so dose-response trials are required for each raw-material blend.
In high-yield peroxide bleaching of thermomechanical pulp, sodium metasilicate is used as a hydrogen peroxide stabilizer and alkalinity buffer. The anhydrous powder is dissolved and metered into the bleach liquor before addition to medium-consistency pulp at 10–12% consistency. Typical sodium silicate addition is 2–4% on oven-dry pulp as 41°Bé sodium silicate equivalent; the anhydrous form can substitute on an equivalent SiO₂/Na₂O basis if pre-dissolved completely. Excessive silicate causes calcium oxalate and silicate scale on tower rings and extraction screens; insufficient silicate permits transition-metal catalysis of peroxide decomposition. Published data for specific furnish blends is limited, but mills operating pressurized peroxide stages monitor residual peroxide and brightness per ISO 2470 and adjust silicate between 1.5% and 3.5% on oven-dry pulp.
Sodium metasilicate anhydrous is classified under CLP as Skin Corr. 1A H314 and Eye Dam. 1 H318; alkaline dust may cause respiratory irritation. Handling systems with local exhaust ventilation, EN 374 chemical-resistant gloves, and sealed transfer are required. Contact with strong mineral acids below pH 10 causes precipitation of amorphous silica gel and exothermic neutralization; dry blending with acid phosphates, sulfamic acid, or aluminium sulphate is incompatible. The powder must be stored in closed bags or silos at ≤60% RH and below 40 °C; partially used bags should be resealed immediately to prevent surface hydration and caking. REACH registration obligations apply under EC 1907/2006.
