Lecture 13: Metals, Paints and Soil Flashcards
What role do trace elements play in materials?
Trace elements act as invisible markers to identify the material source or aid in comparisons.
What is the significance of comparing emission spectra in chemistry?
Comparing emission spectra allows for element identification by matching line by line between samples.
How does an Emission Spectrograph work?
Samples are vaporized, atoms emit light, and the line spectrum identifies elements by characteristic frequencies.
Describe the structure of atoms in the context of the origin of spectra.
Atoms have a nucleus with protons and neutrons and electrons in specific energy level electron orbitals.
How are electron orbitals related to energy levels in the context of spectra?
Electron orbitals are associated with specific energy levels and contribute to the origin of spectral lines.
What happens when an atom absorbs a definite amount of energy?
Electrons move into higher energy levels, creating an excited state.
How does an atom release energy that it absorbed?
Electrons return to their original energy levels, emitting energy in the form of light.
What does emission spectroscopy measure in atoms?
It measures the light energies emitted by atoms.
How is the specific frequency of absorbed or emitted light determined?
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.
How does Inductively Coupled Plasma Emission Spectrometry (ICP) work?
It introduces an aerosolized sample into a hot plasma to create charged particles emitting light of characteristic wavelengths.
What are the key components applied by automobile manufacturers to car bodies?
Electrocoat primer, primer surfacer, basecoat, and clearcoat.
Why is binder significant in automotive paint?
Binder hardens to trap pigments, create a protective barrier, and enhance paint functionality beyond color.
What role do pigments play in paint, and how are they distributed?
Pigments provide color and are suspended (not dissolved) in the paint, requiring stirring before use.
What is the function of drying agents in paint?
Drying agents facilitate quick and even drying of paint.
How are questioned and known paint specimens compared in forensic investigations?
They are compared under a stereoscopic microscope for color, surface texture, and layer sequence to individualize paints based on their complex layer structures.
How do paint samples reveal the composition of compounds in the sample?
Paint samples are analyzed using Gas Chromatograph/Mass Spectrometer to show unique combinations of binders, delusterants, and pigments.
What technique is used to distinguish paint binder formulations?
Pyrolysis Gas Chromatography and Infrared Spectrophotometry utilize high temperatures to decompose paint into gaseous products for analysis.
How are elements in paint pigments identified?
Emission spectroscopy or X-ray spectroscopy methods are employed to identify the elements present in paint pigments.
What is a crucial aspect of forensic analysis related to paint?
Crime labs can identify car make and model from tiny paint samples using color charts or the PDQ database.
Why are objects typically covered in multiple layers of paint?
Objects have primer coats for protection and adhesion, and top coats for color, serving as evidence through the color layer sequence.
Why is collecting uncontaminated reference paint important in hit-and-run cases?
Uncontaminated reference paint offers a baseline for comparison in forensic analysis to identify the source of paint chips found in hit-and-run incidents.
How should paint samples be stored for analysis in forensic investigations?
Paint samples should be stored in paper druggist folds or glass/plastic vials to prevent contamination and preserve the integrity of the evidence.
Why should garments or objects with smeared or embedded paint be sent entirely to the laboratory for analysis?
ending garments or objects entirely ensures that all relevant paint traces are preserved for thorough forensic analysis, aiding in identifying the source
How can different soils be distinguished in forensic analysis based on visual examination?
Soils can be differentiated by color, texture, and other gross appearance features that help forensic experts classify and compare soil samples from various origins.
