Saturday, 23 August 2008

Composition of Glass


Glass can do most anything. From bottles to spacecraft windows, glass products include three types of materials:
  • Formers are the basic ingredients. Any chemical compound that can be melted and cooled into a glass is a former. (With enough heat, 100% of the earth's crust could be made into glass.)
  • Fluxes help formers to melt at lower temperatures.
  • Stabilisers combine with formers and fluxes to keep the finished glass from dissolving, crumbling, or falling apart.
Chemical composition determines what a glass can do. There are many thousands of glass compositions and new ones are being developed every day.

Formers: Most commercial glass is made with sand that contains the most common former, Silica. Other formers include:

  • Anhydrous Boric Acid
  • Anhydrous Phosphoric Acid
But melting sand by itself is too expensive because of the high temperatures required (about 1850°C, or 3360°F). So fluxes are required. Fluxes let the former melt more readily and at lower temperatures (1300°C, or 2370°F). These include:
  • Soda Ash
  • Potash
  • Lithium Carbonate
But fluxes also make the glass chemically unstable, liable to dissolve in water or form unwanted crystals. So stabilizers need to be added. Stabilisers are added to make the glass uniform and keep its special structure intact. These include:
  • Limestone
  • Litharge
  • Alumina
  • Magnesia
  • Barium Carbonate
  • Strontium Carbonate
  • Zinc Oxide
  • Zirconia

Based on an article from the Corning Museum of Glass