1. Forensic Determination of Metals
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2. Encounters with metals
Bomb investigations
Counterfeit detection
Structural analysis
Motor oils
Trace evidence

3. Identifying a metal Various methods Magnetism- iron based
Instrumentation - ICP: Induction Coupled Plasma
X-ray backscatter
Chemical reactivity
ReDox analysis
Hardness, malleability
Density
Specific heat capacity

4. Magnetic metals Most alloys of iron - especially Fe + Ni or Fe + Co
Non magnetic - aluminum, brass, copper, zinc.

5. Induction couple plasma
High frequency electromagnetic plasma
torch excites metal electrons. Allows atomic
emission spectrum to be generated.
Spectrum analysed and compared to known
standards.
Very sensitive and quantitating

6. X-ray backscatter
Part of a scanning electron microscope. Measures energies
of X-rays derived from reflected electrons. Metals have
characteristic energies of electrons they can absorb. The
reflected ones will bounce off and can be detected by the x-rays
They emit when they hit a heavy metal target.

7. Backscatter electron detector

8. SEM Electron/Specimen Interactions Incident Beam - composition info
When the electron beam strikes a sample,
both photon and electron signals are emitted.
Incident Beam
Backscattered electrons
X-rays
- composition info
- Atomic number and topographical
Cathodoluminescence
- Electrical
Secondary electrons
Auger electrons
- Surface sensitive compositional
- Topographical
Specimen
Specimen Current
Electrical

9. Chemical Reactivity Metals like to lose electrons
Aluminum is the only metal that will react with base (NaOH)
All other metals will react with acid
-Copper turns blue with nitric acid (HNO3)
-Magnesium and zinc turn nitric acid hot and yellow
-Lead will make an orange gel if mixed with equal parts nitric
and acetic acid.
-The rates of reaction can be used to distinguish metals.
-In HCL, Mg is very reactive, but nickel is less so, and Fe even
less

10. Hardness + Malleability
Pb is soft and malleable
arranged from high to low malleability are silver, lead,
copper, aluminium, tin, platinum, zinc, iron and nickel
Hardness (sclerometer)
Pb (1), Tin (2.5) , Zn (6) , Cu (8) Fe (15) Steel (21)
Cast iron (36), Ni (31) , Vn steel (35)

11. Density D = Mass/volume Al 2712 kg/m3 Brass 8430 Fe 7850 Pb 11340Zn Ni Mg Sn

12. Specific Heat Capacity
The ability to hold heat without increasing in temperature
Metal (kJ/kg K) Al Fe Pb Mg Sn Ti Zn Ag

13. Calculating SH
Q = mCDT Q = heat energy
m = mass
C = specific heat
DT = change in temp
Heat metal to a known temperature, drop into water of
known temperature, measure change. Set equations equal to
each other - solve
SH water kj/kg K

14. redox Zn + 2HCl -> Zn2+ + H2 +2Cl- Lose electrons = oxidation
Gain electrons = Reduction
Tendency to gain or lose electrons related to
Electronegativity, but can also be predicted by
Known reduction potentials

15. Making a battery to test reduction potential
Cathode (Reduction) Half-Reaction
Standard Potential E° (volts)
Li+(aq) + e- -> Li(s)
-3.04
K+(aq) + e- -> K(s)
-2.92
Ca2+(aq) + 2e- -> Ca(s)
-2.76
Na+(aq) + e- -> Na(s)
-2.71
Zn2+(aq) + 2e- -> Zn(s)
-0.76
Cu2+(aq) + 2e- -> Cu(s)
0.34
O3(g) + 2H+(aq) + 2e- -> O2(g) + H2O(l)
2.07
F2(g) + 2e- -> 2F-(aq)
2.87
Zn + CuCl2  Cu + ZnCl2
= 1.1 volts
Use a known metal electrode, and acid to generate metal salt,
Measure potential.

16. On the cathode, reduction takes place.
Oxidant + n e- ® Reductant Example: Cu e ® Cu Cu2+ is the oxidizing agent and Cu the reducing agent.
On the anode, oxidation takes place.
Reductant ® n e- + Oxidant Example: Zn ® Zn e-. Zn is the reducing agent, and Zn2+ the oxidizing agent.

17. Ni(s) + 2 Fe3+  Ni2+ + 2 Fe2+ .77 + .25 = 1.02 volts
Oxidation takes place at the anode, and the electrode must be Ni | Ni2+,
Ni(s)  Ni2+(aq) + 2 e
and the reduction occurs at the cathode: Fe3+, Fe2+:
2 Fe e  2 Fe
= volts

18. Analysis of Metal Particles A Qualitative Analysis Approach18