Glass

Frontline: The Real CSI https://www.youtube.com/watch?v=Kdzl1VVCvQA

Many solids are crystals A solid in which the atoms are arranged in a regular pattern Sodium chloride

Glass is an amorphous solid. A solid in which the atoms are in no order. It is also brittle Shows a conchoidal (circular) fracture pattern, Hardness, and elasticity of shape. Primarily composed of silica (SiO2) and various amounts of elemental oxides

Types of Glass a. Soda-lime glass Most common commercial glass (90% of total production) Used in plate and window glass, electric light bulbs least expensive

Composed of: Sand (silica…SiO2) Soda (Na2O) (reduces melting pt) Lime (CaO) (water insoluble) https://www.youtube.com/watch?v=k8MmEuvugG4https://www.youtube.com/watch?v=k8MmEuvugG4

Soda-lime glass is used for:

b. Borosilicate glass strong heat resistant (ex. Pyrex) contains boron oxides (B2O3) https://www.youtube.com/watch?v=PWdvQIBAzhk

c. Tempered Glass. 1. made stronger than soda-lime glass c. Tempered Glass 1. made stronger than soda-lime glass by rapid heating and cooling 2. used for side and rear windows in cars

Also used in…

Tempered glass breaks into….

d. Laminated glass For windshields

Glass Experiements https://www.youtube.com/watch?v=13B5K_lAabw

e. Soda-lead glass commonly called crystal or lead glass, expensive widely used for the finest tableware and art objects, radiation protection Lead- increases density and refractive index (sparkle)

Comparison Individualized evidence (jigsaw fit)

Physical Characteristics making up class evidence Density Refractive index (RI)—the measure of light bending due to a change in velocity when traveling from one medium to another Fractures Color Thickness Fluorescence Markings—striations, dimples, etc

Density Mass per unit of volume Density = Mass/Volume

Class characteristics 1. Flotation Used to find the density of glass by floating glass particles in liquids of known densities.

Refraction

Refractive index (RI) Formula RI = velocity of light in vacuum velocity of light in medium The RI of water at room temperature is 1.333

Refractive Index Test tube demo- water vs veg. oil

2. Immersion method – used to find the Refractive Index of glass

When the Becke line disappears MATCH POINT The point at which the Becke line disappears The RI of the glass = RI of the oil When the Becke line disappears

The Becke Line The Becke line is a “halo” that can be seen on the inside of the glass on the left, indicating that the glass has a higher refractive index than the liquid medium. The Becke line as seen on the right is outside of the glass, indicating just the opposite.

Data bank Densities Refractive indices Relative frequencies in the glass pop of US

Fragments Radial fractures- radiate out from the origin of the impact they begin on the opposite side of the force

2. Concentric fractures. a. lines are circular lines around the 2. Concentric fractures a. lines are circular lines around the point of impact b. they begin on the same side as the force

Name A and B B A

b. First Fractures Form on the side of the glass OPPOSITE the side of the penetrating object

c. Next Fracture Forms on the SAME side of the glass as the penetrating force Forms concentric fractures Puts tension on front surface causing concentric fractures A high-velocity projectile leaves a wider hole on the exit side of the glass (helps determine direction of impact)

How does Glass break?

d. Stress markings

A determination of the direction of force in breaking a window pane: -direction of the rib marks [stress marks on broken edges of glass that are perpendicular to one side of glass] 3R rule—radial cracks form a right angle on the reverse side of the force.

Fracture Termination Which bullet hole was made first?

Also know… Blowback - the backscattering of particles toward the direction of the force.