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Claylab Applied Geology & Mineralogy
X-ray diffraction
A tool for material characterization and mineral quantification
Rieko Adriaens [email protected]
23/01/2013
X-ray diffraction on mineral powders
Divergence slit
Detector-
slitTube
Antiscatter-slit
Sample
Mono-chromat
or
Diffraction pattern
Tube
measurement circle
focusing-circle
θ
θ2
Detector
Sample
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Unique fingerprint for anorganic substances
a
b
c
a = b = c
= = = 90o
crystalline
Amorphous
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Errors in XRD – analysis: Vendor competition
Sample preparationMeasurementIdentification Quantification
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Sample preparation: Classical approach
• Manual grinding using mortar & pestle• Back/top loading of holder applying pressure
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Classical approach: disadvantages
• Presence of coarse particles and bad loading cause several negative effects:
– Extreme preferred orientation – Pattern shifts– Very poor reproducibility
Þ Complex identification & wrong quantification
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XRD pattern: Ideal case
Classical approach: disadvantages
– Preferred orientation & pattern shifts
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Classical approach: disadvantages
– Preferred orientation: Cleavage planes & prominent crystal faces
Halite Gypsum Mica Quartz
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Classical approach: disadvantages
– Preferred orientation & pattern shifts– Very poor reproducibility !!!
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Bulk XRD – analysis
• Disadvantages impede accurate Q-XRDÞ 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
• 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
Þ Good random orientation of crystallites obtainedBUT can be improved by the making of spherical granules: use of
Vertrel XF treatment, spray drying equipment, elvacite treatment,…
KaolinitePortland 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 Renewed methodology
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Standardized procedure after Srodon, 2001
Þ Allows accurate Q-XRD analysis
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Other possibilities
[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: procedure1. Measure the diffraction
pattern of the sample
3. Compare both patterns
4. Refine parameters and recalculate pattern
5. Draw info from the refined data (crystallite sizes / quantitative phase information / …)
2. Introduce reasonable starting models / values to calculate a diffraction pattern
QuartzCalciteMagnesiteKaolinite
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
– 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)
<10nm crystallites
What can be evaluated with a Rietveld refinement ?3. Solid Solution
– Example: Fe-rich Dolomite (CaMg(CO3)2) – Ankerite (CaFe(CO3)2)• 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
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Practical information
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Practical information
1st floor
1st floor
Ground floor
XRD rooms
Software computers
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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 [email protected] – 00.89
General support: Rieko [email protected] – 03.217
Responsible professor: Jan Elsen [email protected] – 02.207
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