Post on 01-May-2018
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.