MRTL 486 Chemical Analysis

Chemical Analysis (Module 10) OES/LECO/XRF/LIBS/XRD/FTIR

Is chemical analysis destructive?

Yes, but only the benchtop coupon to compare the rest of the results

Why perform chemical analysis?

1. Reverse engineer

2. QA/QC

3. Material identification

4. Recycling

5. Failure analysis

6. Selecting NDT methods

7. Planning for welding and joining

Why might we require the bench top technique for welding?

The portable techniques are great for light elements

What is OES in principle?

Optical Emission Spectroscopy

Observes light from the ionized atoms produced when a samples is vapourized into plasma via arc (as plasma produces distinct photons with distinct energies)

Why do you need an OES system in a vacuum to measure carbon and sulfur content?

Carbon plasma light waves can easily be absorbed into the oxygen and atmosphere before reaching the photographic plate

What type of information do we get from OES?

elemental (qualitative) and relative elemental content (quantative) in ppm

What the primary chemical analysis for standard for alloy identification?

OES, less expensive, more precise, very fast, as compared to other more informative or accurate tests that are labour intensive and expensive

What material can OES not analyze?

N, O, H, halogens, and noble gases

What is the analysis size and surface requirements?

Size of a quarter (abotu 5mm diameter)
Cannot be thin

smooth, clean, flat, and accessible

Is OES really portable?

It has wheels…but also a whole argon tank and is huge

What is LECO?

Combustion and Inert Gas Fusion Analysis
Combust sample in inert gas to trap and put into a liquid to then count the number of each thing

Why use LECO over OES?

Can detect dissolved gasses like C, N,S, O, H missed by OES

What are some limitations?

Highly stable nitrides and carbides require additional treatment

Is LECO portable and ND

No, it is benchtop and destructive (whole chunk removed)

Why is the induction heat for LECO is specific for the desired component?

You heat it to just before it melts or just enough to liberate the desired element without melting the entire thing

What type of information cna you get from LECO

Qualitative and quantitative (50-1 ppm)

What is XRF

X-Ray Fluorescence Spectroscopy
A sorting technique that uses the principle of exciting electrons by x-ray beam and release element specific photons (fluorescence)

Is XRF portable?

XRF is the most common portable of the chemical analysis options

XRF limitations

does not perform for light elements like C, N, and O

What time of information does XRF provide?

qualitative and semi-quantitative but not really

Is XRF portable?

Yes it’s like a handheld temp taker

What are the two ways to sort XRF data?

1. Wavelength dispersive where sort by wavelength and crystal used to analyze by diffraction
   changes range of angles to product plot of intensity vs wavelength or can count the number xray at each angle at a given wavelength

2. Energy Dispersive and sort by signature energy and analyzed electronically with semiconductor
   Measures number of holes electrons and collects all energy emitted from the sample

Why use WDS over EDS?

EDS is faster but more general and good for surveying, but WDS is better for characterization

What does SEM stand for ?

Scanning Electron Microscope

What does EPMA-EDS stand for?

Electron beam probe microanalysis Energy Dispersive Spectroscopy
(XRF on an SEM with electrons instead of a xray)

What is LIBS?

Laser Induced Breakdown Spectroscopy

Pulsed laser to produce a plasma where inert gas is blowing and plasma emits element-specific light as it cools. Compare the light to known samples.

Is LIBS portable?

Yes

What information can you get from LIBs

Qualitative and quantitative (30ppm, 10% accurate, 5% precise)

What are LIBS limitations?

Reproducibility can be poor

What process is LIBS comparable to?

It is supposed to be able to rival portable OES and XRF (not often in reality tho)

What type of information will XRD give?

Sees what crystal structure is there from electron bombarding and diffraction of incident ray based on braggs law. Give compound crystalline information
Good for determining what is present in the corrosion product

What is FTIR?

Fourier-Transform Infrared Spectroscopy

For polymers and ceramics

apply beam of many frequencies of light and measure how much of each is absorbed?