Forensics

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Author:
jane4991
ID:
50997
Filename:
Forensics
Updated:
2010-11-21 20:59:54
Tags:
Glass Soil
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  1. Physical Properties
    Describe a substance without reference to any other substance
  2. Chemical Property
    Describes behavior of a substance when it reacts or combines with another substance
  3. 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
  4. 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
  5. What's in Glass?
    • Network Components-Formers
    • Fluxes- Softeners (lowers melting point)
    • Stabalizers-Chemical/Cossosion Resistance
  6. 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
  7. How is forensic glass individualized?
    Tempered..
    • Tempered: Rapid cooling
    • Adds strenghth
    • Dices when broken
    • automotive windows & security windows
    • Float glass floresces
  8. Coated Surface modification
    Mirrors
  9. Laminated: sandwiched around plastic
    Automotive windshields
  10. Headlights
    Often borosilicate
  11. Light Bulbs
    Soda Limeglass
  12. Heat absorbing/UV filtering
    Tinting
  13. Eyeglasses:prescription
    lenses/photosensitive
  14. Container Glass
    • Lower magnesium, higher sodium
    • Clear vs. greenish(window)
  15. Glass Fibers
    • Fiberglass insulation
    • Alumino-borosilicate
    • Binfer(red or yellow) to hold fibers in bundles
  16. 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
  17. Physical Properties
    • Density: Mass/Volume
    • Sink-float method
    • Density Range: 2.465-2.540g/cm^3

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