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Physical Properties
Describe a substance without reference to any other substance
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Chemical Property
Describes behavior of a substance when it reacts or combines with another substance
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Why is glass so important to a crime scene?
- It can be lodged in a suspects shoe or clothing
- Headlight glass can identify a vehicle
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What is Glass?
- An inorganic product of fusion which has cooled to a rigid condition without crystallizing
- UNIFORM AMORPHUS SOLID
- Softens over a temperature
- Made up of silicon and Metal oxides
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What's in Glass?
- Network Components-Formers
- Fluxes- Softeners (lowers melting point)
- Stabalizers-Chemical/Cossosion Resistance
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Major Types and Uses
- 1) Soda lime silicate glass: Flat glass, containerglass, electric light bulbs
- 2) Borosilicate glass: Lab glassware, thermometers, cookware,sealed-beam headlights
- 3) Aluminosilicate glass:
- Higher percentage of aluminum/ higher temp than boro
- labware,cookware, glass fibers
- 4) Lead alkali silicate(leaded glass)
- Up to 80% pbO
- High refractive index
- "Crystal" tableware
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How is forensic glass individualized?
Tempered..
- Tempered: Rapid cooling
- Adds strenghth
- Dices when broken
- automotive windows & security windows
- Float glass floresces
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Coated Surface modification
Mirrors
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Laminated: sandwiched around plastic
Automotive windshields
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Headlights
Often borosilicate
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Light Bulbs
Soda Limeglass
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Heat absorbing/UV filtering
Tinting
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Eyeglasses:prescription
lenses/photosensitive
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Container Glass
- Lower magnesium, higher sodium
- Clear vs. greenish(window)
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Glass Fibers
- Fiberglass insulation
- Alumino-borosilicate
- Binfer(red or yellow) to hold fibers in bundles
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Isotropic vs.Anisotropic
- Isotropic:Glass
- dark when rotated under crossed polarizers
- Anisotropic:Crystalline solids and plastics
- Change retardation when rotated under crossed polarizers
- Hardness
- Solubility
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Physical Properties
- Density: Mass/Volume
- Sink-float method
- Density Range: 2.465-2.540g/cm^3
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