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Anhydrous Sodium Metasilicate vs Sodium Metasilicate Pentahydrate: Structure, Properties and Production Differences

July 26, 2026 · Technical Article

Sodium metasilicate is an important inorganic silicate compound widely used in detergents, ceramics, paper processing, metal cleaning, and construction industries. According to different crystal water contents, sodium metasilicate is mainly available in two forms: anhydrous sodium metasilicate and sodium metasilicate pentahydrate.

We produce both grades at the same plant. They differ in chemical structure, physical properties, thermal behavior, storage requirements and, above all, in how they are made and tested. This note sets out those differences from the production side.

In This Article

  • Chemical structure and molecular composition comparison
  • Physical property differences (density, solubility, hygroscopicity)
  • Thermal behavior and stability guidance
  • Industrial applications by grade
  • Storage and safety; how each grade is produced and tested
  • FAQ: frequently asked questions

1. Chemical Structure and Molecular Composition

Anhydrous Sodium Metasilicate

Chemical FormulaNa2SiO3
CAS No.6834-92-0
Molecular Weight122.06 g/mol

Anhydrous sodium metasilicate contains no crystal water. It generally exists in an amorphous glassy form or as fine crystalline particles. Due to its high active content, it provides a higher concentration of sodium silicate per unit weight.

Sodium Metasilicate Pentahydrate

Chemical FormulaNa2SiO3 · 5H2O
CAS No.10213-79-3
Molecular Weight212.14 g/mol

Sodium metasilicate pentahydrate contains five molecules of crystallization water. The water molecules are incorporated into a stable monoclinic crystalline lattice structure and are not simply physically absorbed moisture.

Sodium Metasilicate Products in Warehouse

Sodium metasilicate products stored in warehouse — anhydrous and pentahydrate grades

2. Physical Property Comparison

Property Anhydrous Na2SiO3 Na2SiO3 · 5H2O
AppearanceWhite powder or fine granular solidWhite crystalline granules or powder
Density (25°C)≈ 2.33 g/cm³≈ 2.61 g/cm³
Melting / Dehydration≈ 1088°C (melting)≈ 72°C (dehydration begins)
Solution pH≈ 12.7≈ 12.4 – 12.6
HygroscopicityHighly moisture sensitive; requires sealed storageMoisture sensitive; may cake under humid conditions
Thermal StabilityExcellent; maintains properties under normal heatingDehydrates above ~100°C; converts to anhydrous form

Active Content Comparison (Na2O) — the specification parameter checked on every COA

Anhydrous Na2SiO3Approx. 51% Na2O
Na2SiO3 · 5H2OApprox. 28.7–30% Na2O

Higher Na2O content means more active alkalinity per unit weight.

3. Thermal Behavior and Stability

Anhydrous Sodium Metasilicate

Anhydrous sodium metasilicate demonstrates excellent thermal stability. It shows excellent thermal stability and maintains its chemical properties under normal industrial processing conditions, making it suitable for applications requiring elevated processing temperatures, such as high-temperature industrial cleaning, metal surface treatment, boiler cleaning systems, and glass melting processes.

Due to its absence of crystal water, it provides higher active ingredient content and better stability in temperature-sensitive formulations.

Sodium Metasilicate Pentahydrate

Sodium metasilicate pentahydrate has relatively lower thermal stability due to the presence of crystallization water. When heated, it begins losing crystallization water at approximately 70–72°C (dehydration transition, not conventional melting), undergoes gradual dehydration above 100°C, and at higher temperatures converts into an anhydrous phase.

Practical Guidance

Pentahydrate is generally not preferred for high-temperature applications due to dehydration behavior. However, at ambient temperatures, it offers excellent solubility, convenient handling, and good process compatibility — making it the preferred choice for most conventional industrial formulations.

4. Industrial Applications

Applications of Anhydrous Sodium Metasilicate

Specialty Silicate Applications

Used as an alkaline silicate source in specialty formulations where controlled alkalinity and silica content are required.

Construction Materials

Used as an alkaline activator and binder component in cement and construction material formulations, contributing to improved setting characteristics and durability.

High-Temperature Cleaning

Suitable for heavy-duty metal degreasing, industrial equipment cleaning, and boiler cleaning systems.

Concentrated Formulations

Used in concentrated detergent formulations where higher active content per unit weight is required.

Applications of Sodium Metasilicate Pentahydrate

Detergent Industry

One of the key alkaline builders in phosphate-free detergent formulations. Main functions: oil and grease removal, emulsification, soil suspension, prevention of redeposition, and pH buffering. Widely used as a phosphate-free alternative to sodium tripolyphosphate (STPP).

Ceramic Industry

Used as a deflocculant to reduce slurry viscosity and improve casting efficiency through electrostatic repulsion effects.

Paper & Textile Industries

Applied in wastepaper deinking, paper surface treatment, pulp processing, and textile pretreatment to improve bleaching stability and washing performance.

Construction & Specialty Applications

Used in acid-resistant concrete, cement accelerating systems, mortar modification, egg preservation, molecular sieve production, and metal corrosion inhibition.

Sodium Metasilicate Production Line

Zhongzhi Chemical production facility, Changyi, Shandong — quality documentation available for review

5. Safety and Storage Requirements

Safety Note

  • Both products are strongly alkaline (aqueous solution pH > 12)
  • Direct contact may cause irritation or chemical burns to skin and eyes
  • Classified under GHS05 — Corrosive substances
  • May react with acids and atmospheric CO2, forming silicic acid gel which causes agglomeration and performance degradation
Storage Anhydrous Pentahydrate
EnvironmentCool and dryDry and well-ventilated
ContainerTightly sealedStrict moisture-proof packaging required
Key RiskMoisture absorption causing cakingMoisture causing lump formation or partial dissolution
Shelf Life24 months (sealed, cool & dry)24 months (sealed, cool & dry)

6. How the Two Grades Are Produced and Tested

Both grades start from the same intermediate: sodium silicate solution adjusted with alkali to a SiO2/Na2O molar ratio of 1.0. The routes then diverge.

Production step Pentahydrate Anhydrous
From the modulus-1.0 solutionCrystallised as Na2SiO3 · 5H2OWater removed completely to Na2SiO3
FinishingDried below the dehydration point, then screened into granules or powderDried at high temperature, then milled or granulated
Critical control pointCrystal water: over-drying turns part of the lot into lower hydratesMoisture pick-up after drying; the product is strongly hygroscopic
Checked on each batchNa2O, crystal water, whiteness, dissolution, particle sizeNa2O, moisture, whiteness, dissolution, particle size
PackingMoisture-proof bagsSealed, moisture-proof bags

The economic side of the choice between the two grades (active content per ton shipped, freight per unit of alkalinity, price difference) is a purchasing question rather than a production one; it is worked through in the pentahydrate vs anhydrous buyer guide on silicatechem.com.

Frequently Asked Questions

Q1: What is the main difference between anhydrous sodium metasilicate and sodium metasilicate pentahydrate?

A: The main difference is the crystal water content. Anhydrous sodium metasilicate (Na2SiO3) contains no crystal water and provides higher active content per unit weight. Sodium metasilicate pentahydrate (Na2SiO3 · 5H2O) contains five molecules of crystallization water and offers faster dissolution and better process compatibility at ambient temperatures.

Q2: Which grade is more commonly used in detergent formulations?

A: Sodium metasilicate pentahydrate is the mainstream grade in detergent manufacturing because of its solubility and balanced cleaning performance; it is widely used as a phosphate-free alkaline builder. The anhydrous grade is used in concentrated formulations where higher active content per unit weight is required.

Q3: Which grade is suitable for high-temperature industrial applications?

A: Anhydrous sodium metasilicate is more suitable for high-temperature processes (such as metal treatment, glass melting, and boiler cleaning) due to its superior thermal stability and absence of crystal water. Pentahydrate begins dehydrating above 70–100°C and is not recommended for high-temperature use.

Q4: How should sodium metasilicate be stored?

A: Both grades require sealed packaging stored in a cool, dry environment. Pentahydrate requires stricter moisture-proof packaging due to its strong hygroscopicity. Shelf life is 24 months under proper storage conditions for both grades.

Conclusion

Anhydrous sodium metasilicate and sodium metasilicate pentahydrate are the same compound at two hydration states, made from the same modulus-1.0 intermediate by two different finishing routes. That difference in route is what produces the differences in active content, thermal behavior, hygroscopicity and storage described above.

Sodium metasilicate pentahydrate remains the mainstream choice for detergents, ceramics, paper, and textile industries due to its cost efficiency and excellent solubility. Anhydrous sodium metasilicate is preferred for high-performance applications requiring higher active content, improved thermal stability, and reduced water content.

Both grades provide strong alkalinity, excellent cleaning performance, and versatile silicate chemistry for industrial applications worldwide.

Produced at Zhongzhi Chemical
Shandong Zhongzhi Chemical Technology Co., Ltd. manufactures both anhydrous sodium metasilicate and sodium metasilicate pentahydrate in Changyi, Shandong. For TDS, SDS, batch COA or technical questions about either grade, contact the factory or read about our manufacturing capability.

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