Na₂SiO₃ — Sodium Silicate

Sodium silicate (Na₂SiO₃), commonly known as water glass or liquid glass, is a group of compounds composed of sodium oxide (Na₂O) and silica (SiO₂). The general formula is often represented as \(Na_2O \cdot nSiO_2\), where n varies depending on the ratio of silica to sodium oxide. It appears as a colorless, glassy, or syrupy liquid when hydrated and as a crystalline solid when anhydrous.

Sodium silicate is valued for its adhesive, binding, and waterproofing properties. It is widely used in detergents, paper manufacturing, cement, water treatment, and as a fire-resistant material. Because of its alkalinity and ability to form a gel with acids, sodium silicate is an essential compound in both industrial and household applications.

Sodium silicate consists of sodium cations (Na⁺) and silicate anions (SiO₃²⁻). The structure can vary depending on the ratio of silica to sodium oxide, forming linear, cyclic, or three-dimensional silicate networks. Each silicon atom is surrounded by four oxygen atoms in a tetrahedral arrangement, creating a polymeric silicate framework.

The general chemical representation can be given as:

In aqueous solutions, sodium silicate undergoes partial hydrolysis, producing silicate ions of varying complexity:

This property makes it useful in forming silica gels and coatings when exposed to acids or carbon dioxide.

Sodium silicate can be prepared through several industrial and laboratory methods. The most common methods are:

1. Fusion of Silica and Sodium Carbonate

In this high-temperature process, sand (SiO₂) reacts with sodium carbonate (Na₂CO₃) at around 1100–1200°C:

The product, sodium silicate glass, can then be dissolved in water to obtain liquid sodium silicate.

2. Reaction of Silica Gel with Sodium Hydroxide

This method is often used in laboratory preparation and results in an aqueous solution of sodium silicate.

3. Hydrothermal Process

Under hydrothermal conditions, silica reacts with sodium hydroxide solution at elevated temperature and pressure to form highly pure sodium silicate.

• Appearance: Colorless glassy solid or viscous liquid depending on water content.
• Solubility: Highly soluble in water, forming strongly alkaline solutions.
• Melting Point: 1088°C for anhydrous sodium silicate.
• Boiling Point: Decomposes before boiling due to polymer breakdown.
• pH: Highly basic (11–13), capable of neutralizing acids.
• Chemical Stability: Stable at room temperature but reacts with acids to produce silica gel and corresponding sodium salts.

\(Na_2SiO_3 + 2HCl \rightarrow 2NaCl + H_2SiO_3\downarrow\)

• Thermal Behavior: Resistant to fire and used as a refractory and adhesive at high temperatures.
• Corrosivity: Can corrode metals and glass under prolonged exposure due to alkalinity.

• 1. Detergent Industry: Sodium silicate is an important ingredient in detergents and soaps. It acts as a builder, improving cleaning efficiency by softening water and emulsifying oils and grease.
• 2. Adhesive and Binder: Used as a binder in cardboard, paper products, and cement. It provides excellent adhesive strength and water resistance.
• 3. Water Treatment: Added to water systems to prevent corrosion and scaling in pipes by forming a protective silicate layer.
• 4. Construction Industry: Used in concrete and masonry as a hardening and waterproofing agent. It also improves the strength and durability of cement structures.
• 5. Refractory Materials: Employed in the production of acid-resistant cements, fireproof coatings, and foundry molds due to its thermal stability.
• 6. Textile Industry: Acts as a stabilizer for bleaching agents like hydrogen peroxide during fabric processing.
• 7. Automotive Industry: Used as an anti-freeze additive, rust inhibitor, and exhaust repair compound.
• 8. Food and Agriculture: Used as a soil conditioner and a preservative coating for fruits to extend shelf life.

Sodium silicate is generally considered non-toxic and environmentally safe when used properly. However, its strong alkalinity can be harmful to aquatic organisms if released in large quantities without neutralization.

In biological systems, sodium silicate is not absorbed or metabolized and is used in controlled amounts in certain industrial food processes. Proper handling and waste management are essential to minimize environmental impact.

Sodium silicate, especially in concentrated solutions, can cause severe skin and eye irritation due to its alkalinity. It should be handled with appropriate protective gear.

• Wear gloves, goggles, and protective clothing while handling.
• Avoid inhaling dust or mist; use in a well-ventilated area.
• In case of skin contact, wash thoroughly with water.
• Store in tightly sealed containers away from acids and organic materials.

Accidental ingestion can lead to burns in the gastrointestinal tract, so it should be handled only in industrial or laboratory environments by trained personnel.