Compositional analysis

Yancy W. Riddle, Ph.D.

June 2005

Vice President of Technology• Nickel-Boron coatings

– On metal alloys– Tribological features

• Low coefficient of friction• Increased wear resistance• Corrosion protection

Compositional Analysis• Conservators are materials scientists too

– Metallurgist– Ceramist– Paper and fiber scientists– Biologist

• The art & science of measuring things• Some methods

– Energy Dispersive Spectroscopy (EDS)– Wavelength Dispersive Spectroscopy (WDS)– X-ray Florescence (XRF)

– Inductive Coupled Plasma (ICP)– Atomic Absorption (AA)

Conservator, Material Scientist• All objects are made of something

• Do not treat something until you understand it

• Do not use an instrument until you understand it

• Surfaces vs. Bulk material

Remember !!!

• Every instrument gives you a number.

• Does that number mean anything?

Remember !!!

• Accuracy - Deviating within acceptable limits from a standard

• Precision – Exact in amount

• Resolution – Fineness in detail

The temperature today is 27°C

Accurate, but not preciseResolution = 10°C

Precise, but not accurateResolution = 2°C

Measurement Errors

The temperature today is 27°C

accurate, precise, and well resolved

What is missing ?

Measurement Errors

Micro vs. bulk analytical techniques

Microvolume techniques•Energy Dispersive Spectroscopy•Wavelength Dispersive Spectroscopy•X-ray Florescence

Bulk techniques•Neutron activation•Atomic Absorption•Spark spectrometry•Inductive Coupled Plasma

Choose an appropriate technique !

Scanning Electron Microscope& Microprobe

Scanning Electron Microscope& Microprobe

Source = Electrons

X-ray Florescence (XRF)

Source = X-rays

X-ray Florescence (XRF)

Great for field work !!!

This could be you.

Interaction Volume3 – 125 µm3

Monte Carlo simulation

Energy Dispersive Spectroscopy (EDS)& X-ray Florescence (XRF)

Possible errors:•calibration•Lacks intensity•Peak shift•Si-escape peaks•Overlapping peaks•Too much background

•Sample too far from detector

•Light elements•Wrong accelerating voltage

•Software•Background

subtraction•Wrong elementsEDS & XRF are qualitative or

semi-quantitative techniques. Precision = +/- 10%

Fast data collection

Wavelength Dispersive Spectroscopy (WDS)

WDS is a (semi)-quantitative technique. Precision = +/- 1%

Slow data collectionLittle/no backgroundWell resolved

Advanced EDS & WDS techniques

Line Scans Area Maps

Sample Preparation & Handling

•Distance from detector•Surface contamination•Effects of etching•Corrosion/oxidation of metallic surfaces•Non-electrical conductors (sputter coating)

•Cleanliness is next to Godliness•use gloves•store samples in dry, arid location•clean in alcohol (beware of residues)•dry with forced hot air

References

J. Goldstein, et al., Scanning Electron Microscopy and X-Ray Microanalysis 3rd Edition, Plenum Press, New York

S.E.M, E.D.S., W.D.S.

Metallography•George F. Vander Voort, Metallography:

Principles & Practices,1984, ISBN: 0871706725

•Gunter Petzow, Metallographic Etching, 2nd Edition, 1999, ISBN: 0871706334

•David A. Scott, Metallography & Microstructure ofAncient & Historic Metals

Discussion

My contact information

Yancy W. Riddle

yriddle@uctcoatings.com

-or-yancy_riddle@yahoo.com