Glass Analysis M. Phillips

Composition Silicon dioxide mixed with various metal oxides Hard Brittle Amorphous solid When sand is mixed with other metal oxides, heated to a high temperature, and then cooled to a temperature without crystallization, glass is produced. Amorphous solid – no crystals.

Standard Glass Soda lime glass Bottles Picture frames Window panes Na2CO3 + sand + CaO (quicklime) Bottles Picture frames Window panes Breaks into sharp shards when it falls.

Tempered Glass 4-5x stronger than standard glass Made by extreme heating and rapid cooling Shatters into small oval pebbles (“safety glass”) Coffee makers, oven windows, computer and phone screens, car headlights, Pyrex

Laminated Glass Sandwiches a sheet of plastic between two panels of glass When the glass breaks, it sticks to the plastic film Cracks only at point of impact Windshields in cars

Acrylic/Plexiglass Thermoplastic 20x stronger than glass ½ weight of glass Flammable Dents on impact rather than cracking or shattering Aquariums, helmets, airplane windows

Radial Fracture Cracks in glass extending outward Similar to spokes of a wheel at point of impact Can feel the ridge on the REVERSE side of impact FIRST fracture type formed

Concentric Fracture Cracks in glass forming a rough circle around point of impact Can feel the ride on the SAME side as impact Forms SECOND Require more force than radial

Crack Formation

Direct Impact From an object being used to smash the glass while held Solid center

Projectile Impact From an object being thrown at the glass Crater/hollow center

Direction of Travel Exit hole is larger than entrance hole Can be used along with feeling fracture lines to determine side/angle of impact

Sequence of Fractures A radial fracture ALWAYS terminates at an existing line of fracture. This allows us to tell what sequence they occurred in.

Impact radial fracture lines end abruptly at those produced by a previous impact. In this case, fracture B followed fracture A.

Density

Refractive Index Physical property Ratio of speed of light in a vacuum to the speed of light through a medium Different liquids have a different RI If a glass sample has the same RI as the liquid, it will not be visible If the glass sample has a different RI, there will be a Becke line – a dark edge or boundary

Becke Line