Lecture 13: Metals, Paints and Soil

Question 1

What role do trace elements play in materials?

Answer 1

Trace elements act as invisible markers to identify the material source or aid in comparisons.

Question 2

What is the significance of comparing emission spectra in chemistry?

Answer 2

Comparing emission spectra allows for element identification by matching line by line between samples.

Question 3

How does an Emission Spectrograph work?

Answer 3

Samples are vaporized, atoms emit light, and the line spectrum identifies elements by characteristic frequencies.

Question 4

Describe the structure of atoms in the context of the origin of spectra.

Answer 4

Atoms have a nucleus with protons and neutrons and electrons in specific energy level electron orbitals.

Question 5

How are electron orbitals related to energy levels in the context of spectra?

Answer 5

Electron orbitals are associated with specific energy levels and contribute to the origin of spectral lines.

Question 6

What happens when an atom absorbs a definite amount of energy?

Answer 6

Electrons move into higher energy levels, creating an excited state.

Question 7

How does an atom release energy that it absorbed?

Answer 7

Electrons return to their original energy levels, emitting energy in the form of light.

Question 8

What does emission spectroscopy measure in atoms?

Answer 8

It measures the light energies emitted by atoms.

Question 9

How is the specific frequency of absorbed or emitted light determined?

Answer 9

It is determined using the relationship E = hf, where E is the energy difference between orbitals, h is Planck’s constant, and f is frequency.

Question 10

How does Inductively Coupled Plasma Emission Spectrometry (ICP) work?

Answer 10

It introduces an aerosolized sample into a hot plasma to create charged particles emitting light of characteristic wavelengths.

Question 11

What are the key components applied by automobile manufacturers to car bodies?

Answer 11

Electrocoat primer, primer surfacer, basecoat, and clearcoat.

Question 12

Why is binder significant in automotive paint?

Answer 12

Binder hardens to trap pigments, create a protective barrier, and enhance paint functionality beyond color.

Question 13

What role do pigments play in paint, and how are they distributed?

Answer 13

Pigments provide color and are suspended (not dissolved) in the paint, requiring stirring before use.

Question 14

What is the function of drying agents in paint?

Answer 14

Drying agents facilitate quick and even drying of paint.

Question 15

How are questioned and known paint specimens compared in forensic investigations?

Answer 15

They are compared under a stereoscopic microscope for color, surface texture, and layer sequence to individualize paints based on their complex layer structures.

Question 16

How do paint samples reveal the composition of compounds in the sample?

Answer 16

Paint samples are analyzed using Gas Chromatograph/Mass Spectrometer to show unique combinations of binders, delusterants, and pigments.

Question 17

What technique is used to distinguish paint binder formulations?

Answer 17

Pyrolysis Gas Chromatography and Infrared Spectrophotometry utilize high temperatures to decompose paint into gaseous products for analysis.

Question 18

How are elements in paint pigments identified?

Answer 18

Emission spectroscopy or X-ray spectroscopy methods are employed to identify the elements present in paint pigments.

Question 19

What is a crucial aspect of forensic analysis related to paint?

Answer 19

Crime labs can identify car make and model from tiny paint samples using color charts or the PDQ database.

Question 20

Why are objects typically covered in multiple layers of paint?

Answer 20

Objects have primer coats for protection and adhesion, and top coats for color, serving as evidence through the color layer sequence.

Question 21

Why is collecting uncontaminated reference paint important in hit-and-run cases?

Answer 21

Uncontaminated reference paint offers a baseline for comparison in forensic analysis to identify the source of paint chips found in hit-and-run incidents.

Question 22

How should paint samples be stored for analysis in forensic investigations?

Answer 22

Paint samples should be stored in paper druggist folds or glass/plastic vials to prevent contamination and preserve the integrity of the evidence.

Question 23

Why should garments or objects with smeared or embedded paint be sent entirely to the laboratory for analysis?

Answer 23

ending garments or objects entirely ensures that all relevant paint traces are preserved for thorough forensic analysis, aiding in identifying the source

Question 24

How can different soils be distinguished in forensic analysis based on visual examination?

Answer 24

Soils can be differentiated by color, texture, and other gross appearance features that help forensic experts classify and compare soil samples from various origins.

Question 25

What characteristics do forensic geologists analyze to compare soil samples?

Answer 25

Forensic geologists focus on mineral content, color, texture, shapes, and the presence of foreign objects to characterize and differentiate soil samples.

Question 26

What should be noted in terms of material when conducting forensic soil analysis under UV light?

Answer 26

Note the shape, size, number, and identity of any material that fluoresces under UV light.

Question 27

How should foreign objects found during soil analysis be handled?

Answer 27

Foreign objects found should be investigated separately to determine their origin and significance.

Question 28

How do similarities in previous comparisons between two soil samples guide forensic analysts?

Answer 28

Similarities in previous comparisons suggest that the samples likely originate from the same area.

Question 29

What are density gradient columns used for in forensic soil analysis?

Answer 29

Density gradient columns are used for a final comparison between soil samples to determine similarities in origin.

Question 30

Describe the process of using density gradient tubes in soil analysis.

Answer 30

Assemble two identical density columns, drop soil samples in them, allow dispersion, and compare; nearly identical tubes suggest same origins.