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Shattered: Forensic Glass Analysis

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Shattered: Forensic Glass Analysis

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    1. Shattered: Forensic Glass Analysis

    2. What is Glass? “An inorganic product of fusion which has cooled to a rigid condition without crystallizing” Uniform amorphous solid No specific m.p. Softens over a temperature range

    6. What’s in Glass? Network Components-Formers: SiO2, B2O3, P2O5, GeO2, V2O5, As2O3, Sb2O5 Fluxes–Softeners [lowers melting point]: Na2O, K2O, LiO, Al2O3, B2O3, Cs2O Stabilizers–Chemical/Corrosion Resistance: CaO, MgO, Al2O3, PbO, SrO, BaO, ZnO, ZrO

    7. Major Types and Uses Soda lime silicate glass SiO2 + Na2O / K2O + CaO / Al2O3 / MgO Flat glass, container glass, electric light bulbs Borosilicate glass > 5% B2O3 (replaces Na2O) Lab glassware, thermometers, cookware, sealed-beam headlights

    8. Aluminosilicate glass Higher percentage of aluminum higher temperatures than borosilicate Aluminoborosilicate – 50:50 Al/B Labware, cookware, and glass fibers Lead alkali silicate (leaded glass) Up to 80% PbO high refractive index “Crystal” tableware,

    10. Forensic Individualization of Glass Flat Glass–Soda lime silicate -Rolling or Floating Tempered: Rapid Cooling Adds Strength Dices when broken Automotive windows & security windows Float Glass floresces when excited at 254 nm.

    11. Coated: Surface modification Mirrors Laminated: Sandwiched around plastic Automotive windshields Headlights: often borosilicate Light bulbs: soda lime glass Heat absorbing/ UV filtering tinting Eyeglasses: prescription lenses/photosensitive

    12. Container Glass Lower magnesium, higher sodium Clear vs. greenish (window) Glass Fibers Fiberglass insulation Alumino-borosilicate Binder (red or yellow) to hold fibers in bundles

    13. Forensic Analysis of Glass Fundamental Question: Is it Glass? Isotropic vs. Anisotropic Glass: Isotropic dark when rotated under crossed polarizers Crystalline solids and plastics: Anisotropic Change retardation when rotated under crossed polarizers Hardness Solubility

    14. Comparison of Physical Characteristics Color Flatness Thickness Fluorescence–Float Glass 254 nm

    15. Physical Properties Density Sink-Float Method CHBr3, C2H2Br4, Sodium Polytungstate Density Range: 2.465-2.540 g/cm3

    22. Chemical Composition – Inductively Coupled Plasma (ICP) SEM/EDS Neutron Activation Analysis X-Ray Fluorescence

    24. Radial

    25. Concentric Motion of the projectile through the glass puts tension on the front surface of the glass, causing concentric fractures. -high-speed projectile [a rock] penetrates the glass, it leaves an exit hole larger than it's entrance hole. -helps to determine the direction on impact.

    27. Bullets and Glass It’s possible to determine the bullet's direction by noting the side of the cone- shaped hole left by the bullet. -small opening is on the entrance side

    28. Counting Bullet Holes

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