All About Glass


Physically, glass may be defined as a hard rigid, undercooled, brittle,  non-crystalline substance having no definite melting point and sufficiently high viscosity to prevent crystallization.

Physical properties of glass :

  1. Glass is non-crystalline,transparent,amorphous solid. 
  2. Glass is hard, rigid and brittle
  3. Glass has no fixed melting point
  4. Glass is super cooled liquid having high viscosity
  5. It is an insulator of heat and electricity. 

Why glass is called super cooled liquid

Super cooled liquid  is a fluid whose temperature is below its freezing point. In order for a liquid to crystallize, it must overcome an activation energy.

  Super cooled liquid graph

Glass is sometimes called a supercooled liquid because it does not form a crystalline structure, but instead forms an amorphous solid that allows molecules in the material to continue to move. 

However, Scientific American indicates that amorphous solids are neither supercooled liquids nor solids.

True solids form crystalline structures that lock molecules into place. They retain their shape unless the temperature increases to above their melting point. However, glass, amber and plastic do not form such solids when their liquid form acools. While glass is more rigid than liquid, it is not as ordered as crystalline solids.

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