Benchtop X-ray Diffraction Spectroscopy X-ray... · Benchtop X-ray Diffraction Spectroscopy ... •...

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.

• 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.

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

• 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.