Transcript Quantitative XRD

X-ray diffraction
A tool for material characterization and
mineral quantification
Claylab Applied Geology & Mineralogy
Rieko Adriaens [email protected]
23/01/2013
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X-ray diffraction on mineral powders
Antiscatterslit
Divergence slit
Monochromator
Detectorslit
Tube
Sample
Diffraction pattern
Detector
Tube
θ
focusingcircle
Sample
measurement circle
2θ
Unique fingerprint for anorganic substances
a=b=c
 =  =  = 90 o
c
a



b
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crystalline
Amorphous
Errors in XRD – analysis: Vendor competition
Sample preparation
Measurement
Identification
Quantification
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Sample preparation: Classical approach
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Manual grinding using mortar & pestle
Back/top loading of holder applying pressure
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Classical approach: disadvantages
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Presence of coarse particles and bad loading cause several
negative effects:
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Extreme preferred orientation
Pattern shifts
Very poor reproducibility
 Complex identification & wrong quantification
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Classical approach: disadvantages
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Preferred orientation & pattern shifts
XRD pattern: Ideal case
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Classical approach: disadvantages
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Preferred orientation:
Cleavage planes & prominent crystal faces
Halite
Quartz
Gypsum
Mica
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Classical approach: disadvantages
–
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Preferred orientation & pattern shifts
Very poor reproducibility !!!
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Bulk XRD – analysis
• Disadvantages impede accurate Q-XRD
 Neccessity of standardized preparation procedures
We need a procedure which makes sure that:
- Particles should be finer than <50µm
- Wet grinding instead of dry grinding
- Particles are randomly oriented in the measurement holder
- Sample surface should be smooth and perfectly flat
- Reproducible & representative measurements
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Standardized procedure after Srodon, 2001
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Powder mixed with internal standard (ZnO, Al2O3, TiO2 )
Grinding media (Al2O3, Yttria stabilized Zr)
Grinding agent: methanol/ ethanol
McCrone micronizing mill (5min.)
Side load filling / no pressure top load
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Standardized procedure after Srodon, 2001
 Good random orientation of crystallites obtained
BUT can be improved by the making of spherical granules: use of
Vertrel XF treatment, spray drying equipment, elvacite
treatment,…
Kaolinite
Portland cement
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Standardized procedure: Validation
Classic
methodology
Renewed
methodology
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Standardized procedure: Validation
Much less preferred orientation
Classic methodology
methodology
Renewed
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Standardized procedure after Srodon, 2001
 Allows accurate Q-XRD analysis
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Other possibilities
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[The Rietveld Method]
• Most powerful method for combined quantification
and structure analysis
• Relies on the refinement of basic theoretical structures
• Minimize difference between calculated XRD pattern and
measured XRD pattern
Rietveld refinement: procedure
1.
Measure the diffraction
pattern of the sample
2.
3.
Compare both patterns
4.
Refine parameters and
recalculate pattern
5.
Draw info from the refined
data (crystallite sizes /
quantitative phase
information / …)
Introduce reasonable starting
models / values to calculate a
diffraction pattern
Quartz
Calcite
Magnesite
Kaolinite
What can be evaluated with a Rietveld
refinement ?
• Example: Cement
Fully amorphous blast furnace slag
ZnO as internal standard
What can be evaluated with a Rietveld
refinement ?
2. Crystallite Sizes / Strain
–
<10nm
crystallites
Absolute Crystallite sizes
Useful for:
– Process optimisation
– Product characterisation
– Product quality assesment
Finer crystallites are prone to react faster (or to react better as catalysts,
etc.)
– Assessment of crystallite shape (in case of anisotropic peak size
broadening)
What can be evaluated with a Rietveld
refinement ?
3. Solid Solution
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Example: Fe-rich Dolomite (CaMg(CO3)2) – Ankerite (CaFe(CO3)2)
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Change in lattice parameters as a function of the Fe-content
With a Rietveld refinement;
Lattice parameters and hence Fe-contents can be accurately determined
Example:
Fe-rich Dolomite/Ankerite in
Sedimentary rock:
Exact average formula:
Ca(Fe0,46Mg0,54)(CO3)2
Fe-Dolomite
Practical information
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Practical information
1st floor
XRD rooms
1st floor
Software
computers
Ground floor
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Practical information
Reservations
https://ees.kuleuven.be/reservations/xrd/calendar/index.html
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Practical information
Measurements
overview list
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Practical information
Technical support: Dirk Steeno
[email protected]
200C – 00.89
General support: Rieko Adriaens
[email protected]
200E – 03.217
Responsible professor: Jan
Elsen
[email protected]
200E – 02.207
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Questions / more information
Contact [email protected]
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