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Send EmailSodium Metasilicate, Disodium Metasilicate, Sodium Metasilicate Anhydrate, Sodium Metasilicate Pentahydrate, 6834-92-0, 10213-79-3
SODIUM METASILICATE (ANHYDROUS AND PENTAHYDRATE)
1. Chemical Identity and Material Classification
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Chemical Name: Sodium Metasilicate, Disodium Metasilicate, Silicic Acid Disodium Salt
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Synonyms: Metasilicate, Sodium Silicate (metasilicate form), Sodium Metasilicate Pentahydrate (hydrated form)
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CAS Numbers:
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Anhydrous: 6834-92-0
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Pentahydrate: 10213-79-3
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Molecular Formula:
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Anhydrous: Na₂SiO₃
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Pentahydrate: Na₂SiO₃·5H₂O (H₁₀Na₂O₈Si)
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Molecular Weight:
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Anhydrous: 122.06 g/mol
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Pentahydrate: 212.14 g/mol
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EC Number: 229-912-9
2. Physical Properties (Comparative)
| Property | Anhydrous | Pentahydrate |
|---|---|---|
| Appearance | White to off-white powder or granules | White crystalline powder or granules |
| Odor | Odorless | Odorless |
| Physical state | Solid (hygroscopic) | Solid (crystalline) |
| Density (20°C) | 2.61 g/cm³ | 1.80–1.90 g/cm³ |
| Bulk density | 0.8–1.2 g/cm³ | 0.7–1.0 g/cm³ |
| Melting point | 1089°C (decomposes) | ~72°C (loses water) |
| Freezing point | Below 0°C | Below 0°C |
| pH (1% solution, 20°C) | 12.5–13.5 (strongly alkaline) | 12.0–13.0 (strongly alkaline) |
| Solubility in water (20°C) | ~200 g/L | ~500 g/L (very soluble) |
| Stability | Hygroscopic (absorbs moisture) | Less hygroscopic than anhydrous |
3. Chemical Properties
3.1 Aqueous Solution Chemistry
| Parameter | Value |
|---|---|
| pH (1% solution) | 12.5–13.5 (strongly basic) |
| pH (5% solution) | 13.0–13.8 |
| Hydrolysis | Na₂SiO₃ + 2H₂O ⇌ H₂SiO₃ + 2NaOH (strongly alkaline) |
| SiO₂/Na₂O ratio | 1.0 ± 0.05 (metasilicate ratio) |
3.2 Thermal Properties
| Parameter | Anhydrous | Pentahydrate |
|---|---|---|
| Dehydration temperature | Not applicable | 100–150°C (loss of 5H₂O) |
| Water of crystallization | None | ~42.4% by weight |
| Enthalpy of solution (water) | Exothermic | Endothermic (cooling effect) |
3.3 Chemical Reactivity
| Reaction | Description |
|---|---|
| With acids | Na₂SiO₃ + 2H⁺ → H₂SiO₃ (silicic acid) + 2Na⁺ (forms gelatinous precipitate) |
| With metal ions | Forms insoluble metal silicates (water softening mechanism) |
| With CO₂ | Na₂SiO₃ + CO₂ + H₂O → H₂SiO₃ + Na₂CO₃ (surface carbonation) |
4. Quality Specifications
4.1 Anhydrous Sodium Metasilicate (Technical Grade)
| Parameter | Specification |
|---|---|
| Purity (Na₂SiO₃, w/w) | ≥ 98.0% |
| Na₂O content | 50–52% |
| SiO₂ content | 46–48% |
| SiO₂/Na₂O ratio | 0.95–1.05 |
| Moisture (105°C, 2 hours) | ≤ 1.0% |
| Water insolubles | ≤ 0.5% |
| Iron (Fe) | ≤ 0.02% |
| Heavy metals (as Pb) | ≤ 50 ppm |
| pH (1% solution) | 12.5–13.5 |
4.2 Sodium Metasilicate Pentahydrate (Technical Grade)
| Parameter | Specification |
|---|---|
| Purity (Na₂SiO₃·5H₂O, w/w) | ≥ 98.0% |
| Na₂O content | 28–30% |
| SiO₂ content | 26–28% |
| SiO₂/Na₂O ratio | 0.95–1.05 |
| Loss on ignition (1000°C) | 40–45% |
| Water insolubles | ≤ 0.5% |
| Iron (Fe) | ≤ 0.02% |
| Heavy metals (as Pb) | ≤ 50 ppm |
| pH (1% solution) | 12.0–13.0 |
5. Comparison: Anhydrous vs. Pentahydrate
| Feature | Anhydrous | Pentahydrate |
|---|---|---|
| Alkalinity | Higher (more concentrated) | Lower (diluted by water of crystallization) |
| Dissolution in water | Exothermic (heats up) | Endothermic (cools down) |
| Hygroscopicity | High (absorbs moisture readily) | Low (more stable in humid air) |
| Storage stability | Requires airtight containers | More forgiving; less caking |
| Handling | Dusty, can cause skin irritation | Less dusty, safer handling |
| Shipping weight | Lower (no water weight) | Higher (contains ~42% water) |
| Cost per unit active | Lower (more concentrated) | Higher (contains water weight) |
| Preferred applications | Industrial where high alkalinity needed | Detergents, consumer products |
6. Mechanisms of Action
6.1 Builder Function (Detergents)
| Mechanism | Description |
|---|---|
| Water softening | Precipitates Ca²⁺ and Mg²⁺ as insoluble silicates |
| Alkalinity buffer | Maintains high pH (9–11) for optimal detergency |
| Soil suspension | Prevents redeposition of soil on fabrics |
| Emulsification | Aids in emulsifying oily and greasy soils |
| Enzyme stabilization | Stabilizes proteases and amylases in detergent formulations |
6.2 Corrosion Inhibition (Metal Treatment)
| Mechanism | Description |
|---|---|
| Passivation | Forms a protective alkaline silicate film on metal surfaces |
| pH buffering | Maintains alkaline pH (10–12) that inhibits corrosion |
| Precipitation | Precipitates metal ions that could cause galvanic corrosion |
6.3 Binding Function (Ceramics & Paper)
| Mechanism | Description |
|---|---|
| Particle binding | Silicate ions bond to particle surfaces, creating strong bridges |
| Drying hardening | Dehydrates to form insoluble silica gel that binds particles |
| Thermal stability | Remains stable at high temperatures (ceramic firing) |
7. Industrial Applications – Detergents and Cleaning Products
7.1 Laundry and Dishwashing Detergents
| Parameter | Value |
|---|---|
| Function | Builder, water softener, alkalinity source, enzyme stabilizer |
| Typical concentration (powder detergents) | 5–15% by weight |
| Typical concentration (liquid detergents) | 1–5% by weight |
| Form preference | Pentahydrate (less reactive, safer handling) |
| Benefits | Prevents mineral deposits, improves cleaning efficiency, stabilizes bleaches |
7.2 Industrial and Institutional Cleaners
| Parameter | Value |
|---|---|
| Function | Heavy-duty degreaser, concrete cleaner, tank and pipe cleaner |
| Typical concentration (concentrates) | 2–10% by weight |
| Application method | Diluted in water (1:10 to 1:100) |
| Preferred form | Anhydrous (high alkalinity for tough soils) |
| Benefits | Removes grease, oil, mineral deposits, and proteinaceous soils |
7.3 CIP (Clean-in-Place) Systems
| Parameter | Value |
|---|---|
| Function | Alkaline detergent for food and beverage processing equipment |
| Typical concentration | 0.5–2% by weight |
| Temperature range | 50–80°C |
| Benefits | Effective removal of protein, fat, and carbohydrate residues |
8. Industrial Applications – Water Treatment
| Parameter | Value |
|---|---|
| Function | Corrosion inhibitor, pH adjuster, hardness stabilizer |
| Typical dosage | 10–50 mg/L (as Na₂SiO₃) |
| Application | Boiler water treatment, cooling water systems, potable water |
| Benefits | Forms protective film on metal surfaces, prevents red water corrosion |
9. Industrial Applications – Paper Industry
| Parameter | Value |
|---|---|
| Function | Strength enhancer, filler retention aid, de-inking aid |
| Typical addition | 0.5–3% by weight of pulp |
| Application method | Added to pulp during preparation or coating stage |
| Benefits | Improves paper strength (newspaper, cardboard, packaging paper) |
| Mechanism | Silicate ions bond with cellulose fibers, increasing inter-fiber bonding |
10. Industrial Applications – Metal Treatment and Corrosion Protection
| Parameter | Value |
|---|---|
| Function | Corrosion inhibitor, metal surface passivation |
| Typical concentration | 1–5% by weight in solution |
| Application method | Dipping or spraying (immersion or spray) |
| Benefits | Forms alkaline film on surface, prevents rusting (automotive, metal parts) |
11. Industrial Applications – Ceramics and Refractories
| Parameter | Value |
|---|---|
| Function | Binder for ceramic bodies, refractory materials, and foundry sands |
| Typical addition | 1–3% by weight of mixture |
| Application method | Mixed into ceramic slurry or dry batch |
| Benefits | Increases green strength, reduces cracking during drying/firing |
12. Industrial Applications – Fire Fighting (Foam Stabilizer)
| Parameter | Value |
|---|---|
| Function | Stabilizer for foam-based fire extinguishing systems |
| Typical concentration | 0.5–2% in foam concentrate |
| Application | Foam concentrates (AFFF, protein foam) |
| Benefits | Increases foam durability, improves extinguishing efficiency |
13. Industrial Applications – Food Storage (Desiccant)
| Parameter | Value |
|---|---|
| Function | Moisture absorber (desiccant) for food packaging |
| Application | Small sachets or as a coating on packaging materials |
| Target products | Coffee, tea, powdered milk, spices |
| Benefits | Prevents caking, extends shelf life |
14. Comparison with Other Silicates
| Property | Sodium Metasilicate | Sodium Orthosilicate | Sodium Disilicate |
|---|---|---|---|
| Formula | Na₂SiO₃ | Na₄SiO₄ | Na₂Si₂O₅ |
| SiO₂/Na₂O ratio | 1.0 | 0.5 | 2.0 |
| Alkalinity (1% solution pH) | 12.5–13.5 | 13.5–14.0 | 11.0–12.0 |
| Water solubility | Very high | High | Moderate |
| Builder efficiency | Excellent | Excellent | Good |
| Corrosivity | Moderate | High | Low |
| Applications | Detergents, water treatment | Heavy-duty cleaners | Paper, adhesives |
15. Safety and Toxicology
| Parameter | Value |
|---|---|
| Oral LD₅₀ (rat) | 1,280–2,500 mg/kg (moderate toxicity) |
| Dermal LD₅₀ (rabbit) | >2,000 mg/kg |
| Skin irritation | Corrosive (causes burns) |
| Eye irritation | Severe damage (corrosive) |
| Inhalation | Dust may cause respiratory tract irritation |
| Skin sensitization | Non-sensitizer |
| Mutagenicity | Negative |
| Carcinogenicity | Not classified |
15.1 Occupational Exposure Limits
| Authority | Limit | Type |
|---|---|---|
| ACGIH TLV (as respirable dust) | 10 mg/m³ | TWA (8 hour) |
| OSHA PEL (as total dust) | 15 mg/m³ | TWA |
| NIOSH REL (as respirable dust) | 5 mg/m³ | TWA |
16. Safety Precautions and Personal Protective Equipment (PPE)
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Hazards:
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Corrosive – causes severe skin burns and eye damage
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Harmful if swallowed
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Dust may cause respiratory tract irritation
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PPE (mandatory):
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Chemical-resistant gloves (nitrile or neoprene, EN 374)
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Safety goggles (EN 166) or face shield
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Protective clothing (acid/alkali-resistant)
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Dust mask (FFP2/N95) – for powder handling
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Engineering controls:
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Local exhaust ventilation (LEV) for powder handling
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Eyewash stations and safety showers
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First aid:
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Inhalation: Move to fresh air
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Skin contact: Wash with copious water for 15 minutes; remove contaminated clothing
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Eye contact: Rinse with water for 15–20 minutes, lifting eyelids; seek immediate medical attention
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Ingestion: Rinse mouth; do NOT induce vomiting; drink milk or water; seek medical attention
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17. Storage and Shelf Life
| Parameter | Anhydrous | Pentahydrate |
|---|---|---|
| Storage temperature | 10–30°C | 10–30°C |
| Humidity sensitivity | High (must be kept dry) | Low (stable in normal humidity) |
| Container | Airtight HDPE or lined steel | Sealed HDPE or PP bags |
| Shelf life (sealed) | 12–24 months | 24–36 months |
| Shelf life (opened) | 3–6 months (if kept dry) | 12–18 months |
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Degradation indicators:
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Caking/hardening (moisture absorption)
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pH decrease (carbonation with CO₂)
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18. Transport Information
| Regulation | Classification |
|---|---|
| UN Number | 3253 (Disodium trioxosilicate, pentahydrate) |
| ADR/RID | Class 8 (Corrosive), Packing group III |
| IMDG | Class 8, PG III |
| IATA | Class 8, PG III |
| Proper shipping name | Disodium trioxosilicate (sodium metasilicate) |
| Hazard label | Corrosive (8) |
19. Synonyms and Common Names
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English: Sodium metasilicate, Disodium metasilicate, Silicic acid disodium salt, Sodium metasilicate pentahydrate, Water glass (metasilicate form)
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Turkish: Sodyum metasilikat, Disodyum metasilikat, Metasilikat pentahidrat
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German: Natriummetasilikat
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French: Métasilicate de sodium
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Spanish: Metasilicato de sodio
20. Sectoral Suitability Summary Table
| Sector | Application | Typical Concentration | Preferred Form | Alternatives |
|---|---|---|---|---|
| Detergents | Laundry & dishwashing builder | 5–15% (powder), 1–5% (liquid) | Pentahydrate | Sodium carbonate, zeolites, phosphates |
| Industrial Cleaning | Heavy-duty degreaser, CIP cleaner | 2–10% (concentrate) | Anhydrous | Sodium hydroxide, potassium hydroxide |
| Water Treatment | Corrosion inhibitor, pH adjuster | 10–50 mg/L | Anhydrous | Sodium phosphate, sodium carbonate |
| Paper Industry | Strength enhancer, de-inking aid | 0.5–3% of pulp | Anhydrous | Starch, polyacrylamide |
| Metal Treatment | Corrosion protection, passivation | 1–5% solution | Anhydrous | Sodium chromate (toxic), phosphates |
| Ceramics | Binder for bodies and refractories | 1–3% of mixture | Anhydrous | Bentonite, organic binders |
| Fire Fighting | Foam stabilizer | 0.5–2% in foam concentrate | Pentahydrate | Synthetic polymers |
| Food Storage | Desiccant (moisture absorber) | Small sachets | Pentahydrate | Silica gel, calcium oxide |
| Textile | Bleaching stabilizer, desizing agent | 1–5 g/L | Anhydrous | Sodium carbonate |
| Construction | Concrete densifier, waterproofing | 2–10% solution | Anhydrous | Sodium silicate (other ratios) |
This TDS is prepared in compliance with ISO 11014-1 format and is intended for detergent formulators, water treatment engineers, paper industry professionals, industrial cleaners, and procurement professionals. Certificates of Analysis (CoA), Safety Data Sheets (SDS), and sample validation reports are available upon request.
