Benchtop X-ray Diffraction Spectroscopy

Contact: World Agroforestry Centre (ICRAF), P.O. Box 30677-00100 Nairobi, Kenya. Tel: +254 020 722 4000. www.worldagroforestry.org

•X-Ray Diffraction (XRD) is a high-tech, non-destructive

technique for qualitative and quantitative analysis of

crystalline compounds.

•About 95% of all solid materials are crystalline.

•When X-rays interact with a crystalline substance or powder, a

diffraction pattern is produced.

•In a mixture of substances each crystalline substance

produces its pattern independently of the others and can be

quantified.

•Information obtained includes types and nature of crystalline

phases present, structural make-up of phases, degree of

crystallinity, amount of amorphous content, microstrain & size

and orientation of crystallites.

•Soil mineralogy is a key determinant of basic soil functional

properties.

•New benchtop instrumentation is enabling routine application

of XRD in soil diagnostics.

• Soil mineralogy largely dictates function:

• nutrient quantity (stock) and intensity (strength of

retention by soil)

• pH and buffering, variable charge

• anion and cation exchange capacity

• carbon saturation; protection

• aggregate stability, dispersion/flocculation

• resistance to erosion

• These properties in turn determine soil agricultural,

environmental and engineering qualities.

• Yet soil mineralogy is currently not used to predict soil

functional properties.

• High throughput, benchtop quantitative XRD could change

this.

• XRD information on mineralogy can be combined with

information from infrared spectroscopy, which characterizes

soil organic properties, to provide powerful diagnostic

capabilities.

IntroductionIntroduction

•Quantitative analysis of actual minerals in topsoils and

subsoils.

•Classification of soils in terms of weatherable minerals: soil

fertility potential.

•Use in pedotransfer functions to directly predict soil functional

properties.

ApplicationsApplications

•XRD has become an indispensable method for materials investigation, characterization and quality control.

Soil Mineralogy and FunctionSoil Mineralogy and Function

•When a sample is irradiated with a beam of monochromatic X-

rays, the sample atomic lattice acts as a 3-dimensional

diffraction grating causing the X-ray beam to be diffracted to

specific angles.

•The diffraction pattern,

angle and intensity of

diffracted beam, provide

information about a sample.

•The angles are used to

calculate the interplanar

atomic spacings (d-spacings).

•The position (d) and

intensity (I) information

is used to identify the type of material, by comparing patterns

for data entries in standard databases.

•Identification of any crystalline compounds, even in a complex

sample, can be made by this method.

•The position (d) of diffracted peaks provides information about

atoms arrangement within the crystalline compound.

•The intensity (I) information used to assess the type and

nature of atoms.

•Width of the diffracted peaks is used to determine crystallite

size and micro-strain in the sample.

•The ‘d’ and ‘I’ from a phase also used to quantitatively

estimate the amount of that phase in a multi-component

mixture.

•Non-destructive analysis

•No sample preparation

•No chemicals

•Qualitative and quantitative mineral profiles

•High throughput

•Ability to distinguish between elements and their oxides.

•Possibility to identify chemical compounds, polymorphic

forms, and mixed crystals.

XRD spectrometer with slide-up front cover for sample loading and integrated computer

Good instrument resolution resolves

overlapping diffraction peaks in

complex patterns.

Working principlesWorking principles Analysis and QuantificationAnalysis and Quantification

Key Advantages of XRDKey Advantages of XRD