Paints

Question 1

Chemical composition of glass types:

Answer 1

• Soda Lime
• Borosilicate
• Lead Silicate

Question 2

Soda Lime glass:

Answer 2

Made by melting silica from sand, soda ash, limestone, magnesium oxide, aluminum oxide, potassium oxide, barium oxide

Question 3

Borosilicate glass:

Answer 3

Contains boric oxide and silica; excellent thermal and shock resistant; made into headlamps and cookware

Question 4

Lead Silicate glass:

Answer 4

Contains lead oxide and silica; used in a range of optical, crystal and electrical glass products.

Question 5

Glass manufacture process:

Answer 5

1. Storage , weighing and mixing raw materials.
2. Melting of raw materials; refining and homogenizing
3. Forming the melt into required shape
4. Annealing of the glass
5. Warehousing and secondary processing

Question 6

Transfer and persistence of breaking glass:

Answer 6

• Minute fragments transferred to breaker
• Called backscatter or “backward fragmentation”
• Secondary transfer occur in small percentages

Question 7

Factors that effect transfer of glass fragments :

Answer 7

• Manner glass was broken
• Type and amount of glass broken
• Distance between glass and breaking glass

Question 8

Factors that effect persistence of glass transfer:

Answer 8

• Type of clothing worn
• Length of time from break and seizure of clothing
• Activity of wearer
• Whether clothing was damp

Question 9

The Becke Line:

Answer 9

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

Question 10

Quality of measurements:

Answer 10

Edge- edge tracings and edge count
Edge- Edge count ranges 1-99
“Contrast”- contrast of Becke Line depends on edge morphology of glass fragment and instrumentation & debris contamination.
“Control”- control samples usually display large edge counts and less variation then recovered fragments.

Question 11

Elemental analysis of glass serve two purposes:

Answer 11

-Classification according to end use (from window or container)
Based on composition of major elements
- Discrimination; differentiate glass with same end use, example: glass
from 2 different windows; relies on minor or trace elements

Question 12

Elemental Techniques:

Answer 12

• X ray florescence spectrometry
• Micro ZRF
• Energy dispersive X-ray spectroscopy
• Inductively coupled plasma mass spectrometry (dissolution of sample)
• Laser ablation ICP-MS (solid sample)

Question 13

Reasons why substrates are painted:

Answer 13

For protection and decoration

Question 14

Resin or Binder System (paint):

Answer 14

“Resin portion” of paint system is part of holds everything together and imparts most of the physical characteristics as well as curing mechanism and durability qualities to final coating.

Question 15

Curing mechanism (paint system):

Answer 15

Way the wet paint or powder particle becomes a solid continuous film (done by polymerization or evaporation)

Question 16

Resin Solution Coating Types:

Answer 16

Solvent borne - made fluid with use of solvent
Waterborne - some or all of solvent is water
Emulsion Coating (latex)- resin in the form of particles dispersed in immiscible liquid
Powder Coating- consist of epoxy, polyester or acrylic resin systems;
can be cured by heat, exposure to UV

Question 17

Solvents:

Answer 17

• adjust paint for environmental conditions to be used in
• referred to as thinner or reducer
• ability of paint to remain on vertical surface without dripping (evaporating)
• solubilize resin and adjust viscosity of paint
• permits ease of application to service w/no protection qualities

Question 18

Additives:

Answer 18

• Enhance performance of paint
• improve durability of dried paint
• contain chemicals to prevent mold, mildew, fungus and algae growth
• can be seen as treatment for issues encountered with wet paint or
  treatment for environmental issues encountered in dry film

Question 19

Solvents in architectural paints:

Answer 19

“Solvent thinned coatings” -based on resins soluble in organic solvents
“Water thinned coatings” - latex

Question 20

Interior paints come in:

Answer 20

Gloss, semi-gloss and flat

Question 21

Gloss finish:

Answer 21

Hard, easily cleaned and reflects light
Binder to pigment ratio is higher than in semi-gloss
Adhesion of subsequent coating minimal

Question 22

Semi Gloss:

Answer 22

Binder to pigment ratio higher than flat paint
More pigment than gloss
Silky appearance

Question 23

Flat finish:

Answer 23

No gloss

Adhesion is good between flat film and successive coating, no need for primer

Question 24

Auto paint layers:

Answer 24

“Primer”- closest to substrate
“Base coat”- layer that contain color and effect pigments
“Clear coat”- applied over wet or uncured coat

Question 25

Assume re-coating done factory when:

Answer 25

Layer system consists of series of base coats and clear coats with no additional primer

Question 26

Auto is painted aftermarket when:

Answer 26

There is “primer” over base coat or clear coat.

Question 27

Optical examination (auto paint):

Answer 27

Stereo-microscopy and microscopy - morphology of paint *surface characteristics, number of layers, size and appearance to specific type of paint; use of episcopic illumination allows observation of effect pigments and of surface defects space as striae or scratches.

Question 28

Analysis of auto paint:

Answer 28

Bright field- enhances contrast of red layers Dark field- enhances color contrast between opaque layers Crossed polarizers- allow observation of birefringent material UV- allows good observation of clear coat layers based on flourescence

Question 29

IR Spectrometry:

Answer 29

Technique of choice for organic and inorganic components of paint system; fast, repeatable, “semi- destructive”, high discriminating power and existence of databases

Question 30

FTIR:

Answer 30

Provides molecular structure information on organic and inorganic components of “coating”

Question 31

Raman Spectroscopy:

Answer 31

Disadvantage: Possible florescence of sample that will mask Raman spectrum Advantage: no sample prep, high spatial resolution

Question 32

Elementary Analysis: SEM/EDS X-ray

Answer 32

Most commonly used in forensic labs Provides indirect ID of inorganic content of paint Technique will characterize extenders and “inorganic” pigments Rapid analysis and sensitive, complimentary as it analyzes inorganic component Comparison purposes in qualitative or semi quantitative modes

Question 33

Level of Association:

Answer 33

Level 1- physical match of sample (paint came from source). Level 2- high degree of association (unusual characteristics) Level 3- conventional association (nothing unusual in population) Level 4- limited association (only certain aspects of paint could be examined and information from such a sample would be limited). Level 5- inconclusive (similarities but can not be associated) Level 6- Elimination/exclusion (fundamental difference)