Sodium Silicate
Properties
| State | Solid (glassy white powder when anhydrous; viscous liquid in solution) |
| Color | White (powder) to colorless or pale yellow (solution) |
| Solubility | Soluble in water (forms strongly alkaline solution, pH 12-13); insoluble in ethanol |
| Melting Point | 1088 °C (anhydrous) |
| Boiling Point | Decomposes |
About Sodium Silicate
Sodium silicate is the family of glassy, water-soluble sodium-silicon-oxygen compounds you buy by the drum as 'water glass' — a thick, viscous, alkaline solution that pours like cold honey and sets like concrete on contact with CO2 or any acidic surface. The pure metasilicate Na2SiO3 (122.063 g/mol) is the textbook formula, but commercial products are sold by their SiO2:Na2O weight ratio (typical grades range from 1.6 to 3.85), with the higher-ratio products being less alkaline and more film-forming. Sodium silicate is made by fusing silica sand with sodium carbonate at 1300 to 1500 °C, then dissolving the resulting glass in water under steam pressure. The chemistry is dominated by the equilibrium between monomeric SiO4 4-, dimeric Si2O7 6-, and a continuum of polymeric silicate anions — ratio and pH together determine which species predominates, which in turn determines whether the product behaves as an adhesive, a binder, a sealer, or a deflocculant. It is the binder in foundry sand cores (the CO2 process: blow CO2 through a sand-silicate mix and it sets in seconds), the desiccant precursor (acidify a silicate solution to make silica gel, calcine, package in those packets that come in shoeboxes), and the historical egg preservative (a 10% solution coats the shell and seals the pores against bacteria — how grandparents stored eggs through winter before refrigeration).
Where you'll encounter it
If you have ever helped a kid drop crystals of copper sulfate, cobalt chloride, and ferric chloride into a beaker of water glass and watched colored 'plants' grow upward over the next hour, that was sodium silicate doing membrane chemistry — each metal ion forms an insoluble metal silicate skin around the falling crystal, and osmotic pressure pushes water inward through the semipermeable skin until it bursts at the top and the cycle repeats, building the characteristic chemical garden tube. In a cement-and-concrete lab, sodium silicate solution painted onto cured concrete penetrates the capillary pores and reacts with residual Ca(OH)2 from cement hydration to form calcium silicate hydrate (C-S-H), the same binding phase that makes the cement strong in the first place. The result is a denser, harder, less permeable surface — used industrially as a 'silicate hardener' on warehouse floors. Foundry workers know it as the binder in the CO2-cured sand-core process for casting iron engine blocks.
Common Uses
- Sand-core binder in iron and steel foundries via the CO2 gas-cured silicate process
- Concrete sealer and surface hardener that reacts with Ca(OH)2 to form C-S-H gel
- Precursor for silica gel desiccant production by acidification and calcination
- Builder and corrosion inhibitor in industrial and institutional detergent formulations
- Ore-flotation depressant for gangue silicates in copper and lead-zinc concentrators
- Adhesive for corrugated cardboard, paper tubes, and abrasive grinding wheels
- Drilling-mud additive for shale stabilization in oil and gas well construction
- Demonstration reagent for chemical-garden experiments in chemistry teaching labs
Safety Information
GHS: H314 (causes severe skin burns and eye damage), H335 (may cause respiratory irritation from dust). No OSHA PEL for sodium silicate as such; the OSHA particulates not otherwise regulated PEL of 15 mg/m3 total dust applies. Strongly alkaline solutions (pH 12 to 13) cause chemical burns on prolonged skin contact and serious corneal damage on splash exposure — splash goggles are non-negotiable when handling concentrated water glass. Avoid mixing with strong acids without ventilation: the resulting silicic acid gel evolves heat and can boil out of a beaker. Spills can be neutralized with dilute acetic acid before flushing. Dried sodium silicate residue is hard, glassy, and difficult to remove without strong base.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.