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Claylab Applied Geology & Mineralogy

X-ray diffraction

A tool for material characterization and mineral quantification

Rieko Adriaens rieko.adriaens@ees.kuleuven.be

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 Steenodirk.steeno@ees.kuleuven.be200C – 00.89

General support: Rieko Adriaensrieko.adriaens@ees.kuleuven.be200E – 03.217

Responsible professor: Jan Elsen jan.elsen@ees.kuleuven.be200E – 02.207

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Questions / more information

Contact rieko.adriaens@ees.kuleuven.be