What is x-ray diffraction
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Transcript of What is x-ray diffraction
EBS 325 – Analytical Chemistry LaboratoryEBS 325 – Analytical Chemistry Laboratory
Introduction To X-Ray AnalysisIntroduction To X-Ray Analysis
By
Mr. Samayamutthirian PalaniandyMr. Samayamutthirian Palaniandy
School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia.
SAMPLING&
SAMPLE PREPARATION
XRFXRD
SAMPLINGSAMPLE
PREPARATION
or
Papers
Plastics
Glass
X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
SAMPLESAMPLE
A means by which units are taken from a population in such a way as to represent the characteristics of interest in that population.
A means by which units are taken from a population in such a way as to represent the characteristics of interest in that population.
homogeneous.Well-mixed
random
accurate representative
The equipment does what we want.
Our sampling frequency is fine.
FAQ about samples and sampling
Reasons for poor procedures, equipment,
and practices of SAMPLING.
Lack of knowledge of the consequences of poorsampling.
Lack of knowledge of the sampling theory.
Trying to save money.
Questions to be answer before sampling
WHAT is being sampled?
WHY is the sample being taken?
WHO is taking the sample?
WHERE is the sample taken?
WHEN and with what frequency is the sample taken?
HOW is the sample taken?
HOW MUCH material is in the sample•?
EXAMPLES OF SAMPLING METHODS
Coning & quartering
Riffle splitter
Paper cone riffle splitter
Grab sampling
Fractional shoveling
CONING AND QUATERING
RIFFLE SPLLITING
PAPER CONE RIFFLE SPLITTER
Fractional Shoveling
Grab Sampling
Consist of taking a sample using scoop or spatula by simply inserting the sampling device into the sample
container and removing an aliquot
Sample Mixing Flowing Liquids or Gases
A static mixer can reduce the Groupingand Segregation Error.A correct cross stream
sample may beimpossible to obtain.
Precision of Sub-sampling MethodsPrecision of Sub-sampling Methods
Gerlach, Dobb, Raab, and Nocerino, 2002 Journal of Chemometrics “Gy Sampling in experimental studies. 1. Assessing soil splitting protocols” 16, 321-328
Your decisions are only as good as your samples.
Your samples are only as good as yoursampling systems.
Your sampling systems are only as good as your audit and assessment.
Summary
X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
Analytical errors – sampling
- Sample must be representative of the process
- Sampling must be reproducible (i.e. should be able to take identical duplicate samples)
Sample preparation methods
must
Simple
Low cost
Rapid
Reproducible
The quality of sample preparation is at least as important as the quality of the subsequent measurements.
Quality of sample preparation
Quality of sample preparation
An ideal sample would be:
- Representative of the material
- Homogenous
- Of infinite thickness
- Without surface irregularities
- With small enough particles for the wavelengths being measured
SAMPLES
METAL POWDER LIQUID
XRF onlyXRD and XRF
Why???
XRD Working ConceptXRD Working Concept
When a monochromatic x-ray beam with wavelength is incident on the lattice planes in a crystal planes in a crystal at an angle , diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths. By varying the angle , the Bragg’s Law conditions are satisfied by different d-spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffraction peaks produces a pattern which is characterised of the sample. Where a mixture of different phases is present, the diffractogram is formed by addition of the individual patterns.
XRF Working ConceptXRF Working Concept
In X-ray fluorescence spectroscopy, the process begins by exposing the sample to a source of x-rays. As these high energy photons strike the sample, they tend to knock electrons out of their orbits around the nuclei of the atoms that make up the sample. When this occurs, an electron from an outer orbit, or “shell”, of the atom will fall into the shell of the missing electron. Since outer shell electrons are more energetic than inner shell electrons, the relocated electron has an excess of energy that is expended as an x-ray fluorescence photon. This fluorescence is unique to the composition of the sample. The detector collects this spectrum and converts them to electrical impulses that are proportional to the energies of the various x-rays in the sample’s spectrum.
METAL
CHIPS POLISHING SOLUTION
REMELT
CAST
BELT GRINDER/LATHE
INGOT
LIQUID
X-RAY ANALYSIS
POWDER
GRINDING FUSION SOLUTION
PELLET
GLASS BEAD LIQUID
X-RAY ANALYSIS
PRESS
LIQUID
LIQUID HOLDERDROP METHOD SPOT ANALYSIS
DDTC METHOD
FILTER
X-RAY ANALYSIS
Solids
Pressed powders
Fused beads
Liquids
Sample types
- metal alloys, plastics & glass- relatively easy to prepare by cutting, machining,
milling % fine polishing- Avoid smearing of soft metals (e.g. Pb) - Polishing may introduce contamination from the
polishing material- do not have particle size problems- Surface needs to be flat- Surface needs to be homogeneous- Surface defects are more critical for light elements
if good accuracy is required.
Solids
- Typical samples types that are prepared as pressed powders include rocks, soil, slag, cements, alumina, fly ash, etc.
- Particle size of powder needs to be controlled for light element analysis- If necessary, powders are ground to achieve a particle size of < 50 µm- Grinding can be introduce contamination (e.g. Fe from a chrome steel mill)- Binding agents (e.g. wax or cellulose) can be used to increase sample
strength to avoid breakage in the spectrometer- Ground powders are pressed into a solid tablet under pressure using a
hydraulic press & 40 mm die- Relatively slow method (≈5 minutes per sample) but relatively low cost- Pressed powders suffer from particle size problems for light elementsPreparation equipment needed includes:- Grinding mill and vessel (chrome steel, zirconia, tungsten carbide, etc.)- Hydraulic press and die (usually 40 mm)- Binding agents
Pressed powders
- Typical samples that are prepared as fused beads include rocks, cements, iron ores, etc. when higher accuracy is required.
- Weighed sample is mixed with flux- Sample and flux are melted at ≈ 1000 oC- Melt is poured into a 40 mm mold- Bead surface needs to be homogenous (constant color without cracks)- Slow (10-15 minutes/sample)- High cost- Important benefit is that particle size problems disappear (fusion process
results in a homogeneous glass)- An additional benefit is that the melting flux (usually Na or Li borate)
dilutes the sample, reducing matrix variations, resulting in higher accuracy- Disadvantage –reduced sensitivity for trace elementsPreparation equipment includes:- Fusion device (manual or automatic)- Pt/Au crucible(s) & mould(s)- Fusion (melting) flux- A non wetting agent (e.g. KI or LiBr) is sometimes used to help produce a
better quality bead and to assist with cleaning the Pt/Au crucible & mould between samples
Fused beads
- Typical samples include environmental (waters, mud) & oils- Easiest to prepare- Should have a constant volume that exceeds maximum
penetration depth- Sample is poured into a liquid cell fitted with a thin plastic
window - Range of window materials to suit different liquids- Fill to a constant height (e.g. 20 mm) to avoid errors from
variable depth- Choose the correct thickness and material to suit the
chemistry of the sample being measured- Na is lightest element that can be detected in liquids.
Liquids
element Chemical % XRF % XRF % Powder Fused bead Na (Z=11) 0.43 0.36 0.46 Si (Z=14) 63.63 62.90 63.80 Ca (Z=20) 0.68 0.68 0.67 Ba (Z=56) 0.27 0.28 0.28
Influence of sample preparation
Factor of errors in Sample Preparation
Grain size and surface roughness
Uniformity of sample
Contamination through the sample preparation
Grain size and surface roughness
Uniformity of sample
Metallic Sample
Casting condition of the sample in the molding.
Sand molding
Metal molding
X-ray intensities differ according to the molding method which comesIn the measurement of light elements.
Quenching casting which makes the metallic composition fine produces good results
Sample polishing
NiK intensity CrK intensity
50# emery paper 0.686 0.974
100# emery paper 0.699 0.983
240# emery paper 0.704 0.989
Mirror polishing 0.709 0.993
Uniformity of sample
Contamination during polishing
Contamination effect when carbon steel and Ni-Cr alloy polish after polishing stainless steel.
As the contamination form the polishing belt to the sample, the re contamination fromThe material of the polishing belt and from the remaining trace elements of polishedSample.
Ni Cr Fe
% Conc 0.55 0.21 2.10
% Contamination 0.05 0.03 0.38
Powder SampleGrinding ConditionDifferent grinding condition cause variation in particle size distribution whichleads to variation in X-Ray intensity.
Powder SampleBrequetting
Usual forming pressure – 20 tons with 40mm diameter.
X-Ray intensities varies with variation of forming pressure (especially when pressure is low).
Contamination
Contamination from the grinding mill and media
CaO,CaCO3,CaMg(CO3)2
Ca(OH)2 etc.
If you are given with four bottles of white powder. What will you do to identify them?
Identification
What is X-ray diffraction?What is X-ray diffraction?
• non-destructive analytical technique for identification and quantitative determination of the various crystalline forms, known as ‘phases’.
• Identification is achieved by comparing the X-ray diffraction pattern
Diffractograms and ICDD Card
What is X-ray diffraction?What is X-ray diffraction?
XRD able to determine :
• Which phases are present?
• At what concentration levels?
• What are the amorphous content of the sample?
How does XRD Works???How does XRD Works???
• Every crystalline substance produce its own XRD pattern, which because it is dependent on the internal structure, is characteristic of that substance.
• The XRD pattern is often spoken as the “FINGERPRINTFINGERPRINT” of a mineral or a crystalline substance, because it differs from pattern of every other mineral or crystalline substances.
A crystal lattice is a regular three-dimension distribution (cubic, tetragonal, etc.) of atoms in space. These are arrange so that they form a series of parallel planes separated from one another by a distance d, which varies according to the nature of the material. For any crystal planes exist in a number of different orientations- each with its own specific d-spacing
Crystal lattice
Fourteen (14) Bravais Lattice
How does it work?
•DiffractionBragg’s Law
n=2dsin
When a monochromatic x-ray beam with wavelength is incident on the lattice planes in a crystal planes in a crystal at an angle , diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths.
How does it work?In powder XRD method, a sample is ground to a powder (±10µm) in order to expose all possible orientations to the X-ray beam of the crystal values of , d and for diffraction are achieved as follows:
1. is kept constant by using filtered X- radiation that is approximately monochromatic. (See Table 1).
2. d may have value consistent with the crystal structure (See Figure 5).
3. is the variable parameters, in terms of which the diffraction peaks are measured.
Table 1: Monochromatic X-ray filters
Basic Component Of XRD MachineBasic Component Of XRD Machine
Therefore any XRD machine will consist of three basic
component.
• Monochromatic X-ray source ()
• Sample-finely powdered or polished surface-may be rotated against the center – (goniometer).
• Data collector- such as film, strip chart or magnetic medium/storage.
By varying the angle , the Bragg’s Law conditions are satisfied by different d-spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffraction peaks produces a pattern which is characterised of the sample
Angle (2)
d-value (Å)
Rel. Int. (I)
27.47 3.244 26 27.82 3.204 49 28.45 3.135 100 44.87 2.018 2 46.68 1.944 30 47.11 1.928 64 55.88 1.644 41 68.89 1.362 6 76.12 1.250 10 83.19 1.160 1 87.74 1.112 10 92.49 1.067 1 94.68 1.048 13 94.99 1.045 6 106.44 0.962 2 106.78 0.960 1 113.81 0.920 5 114.26 0.917 2 127.24 0.860 4 127.82 0.858 2
Table 1: Typical experimental XRD data
Design and Use of the Indexes for Manual Searching of the PDF
• Three search methods are used in the indexes – i.e. – The alphabetical index;– The Hanawalt index– The Fink index.
The Alphabetical Index
The Alphabetical Index
Figure 3: Schematic search procedure when chemical information is known
Hanawalt Method
The Fink Method
XRFXRF
X-Ray Fluorescence
is used to identify and measure the
concentration of
elements in a sample
X-Ray Fluorescence
is used to identify and measure the
concentration of
elements in a sample
XRF instrumental parameters
• x-ray tube kv
• x-ray tube mA
• primary beam filters
• collimator masks
• x-ray tube kv
• x-ray tube mA
• primary beam filters
• collimator masks
• collimator
• crystal
• detector
• path
• collimator
• crystal
• detector
• path
user benefits of wavelength dispersive XRF
• versatile
• accurate
• reproducible
• fast
• non destructive
• versatile
• accurate
• reproducible
• fast
• non destructive
XRF is versatileXRF is versatile
element range is Be to U
atomic numbers (Z) of 4 to 92
concentration range covers 0.1 ppm to 100 %
samples can be in the form of solids, liquids, powders or fragments
element range is Be to U
atomic numbers (Z) of 4 to 92
concentration range covers 0.1 ppm to 100 %
samples can be in the form of solids, liquids, powders or fragments
XRF is accurateXRF is accurate
generally better than 1 % relative
(i.e. 10% ± 0.1%)
accuracy is limited by calibration
standards, sample preparation,
sample matrix, sampling,
instrumental errors & statistics
generally better than 1 % relative
(i.e. 10% ± 0.1%)
accuracy is limited by calibration
standards, sample preparation,
sample matrix, sampling,
instrumental errors & statistics
XRF is reproducibleXRF is reproducible
generally within 0.1% relative
good reproducibility requires high
quality mechanics, stable electronics
and careful construction techniques
generally within 0.1% relative
good reproducibility requires high
quality mechanics, stable electronics
and careful construction techniques
XRF is fastXRF is fast
counting times generally between 1 & 50 seconds for each element
semi-quant analysis of all matrix elements in 10 to 20 minutes
overnight un-attended operation
counting times generally between 1 & 50 seconds for each element
semi-quant analysis of all matrix elements in 10 to 20 minutes
overnight un-attended operation
XRF is non-destructiveXRF is non-destructive
• standards are permanent
• measured samples can be stored and
re-analysed at a later date
• precious samples are not damaged
• standards are permanent
• measured samples can be stored and
re-analysed at a later date
• precious samples are not damaged
properties of x-rays
the following four slides list some
of the more important properties
of x-rays that contribute to the
nature of XRF analysis
XRF analytical envelope
the following section describes the
five major areas that define the
analytical possibilities available with
wavelength dispersive XRF
spectrometers
XRF analytical envelope
elemental range
detection limits
analysis times
accuracy
reproducibility
elemental range
beryllium (4) to uranium (92)
in solids
fluorine (9) to uranium (92)
in liquids
range of elements in solid samples are shown in green (Be to U)
range of elements in liquid samples are shown in green (Na to U)
detection limits (LLD)
function of atomic number (Z) & the mix of elements within the sample
(sample matrix) < 1 ppm for high Z in a light matrix
(e.g. Pb in petrol) or > 10 ppm for low Z in a heavy
matrix (Na in slag)
XRF applications summary
• Na to U in all sample types
• Be to U in solid samples
• accuracy generally 0.1 to 1 % relative
• reproducibility typically < 0.5% relative
• typical LLD is normally 1 - 10 ppm (depends on element being measured and
the sample matrix)
XRF errors
the following section describes
major source of errors in XRF
analysis, and investigates how
these errors can be minimized to
achieve maximize accuracy
overview of XRF methodologyoverview of XRF methodology
good accuracy requires• careful sample preparation
• fused beads for light elements• accurate standards
• selection of optimum instrument parameters
• collection of enough counts to avoid statistical errors
Methods of Analysis
the following presentation
describes the requirements for
quantitative and semi-quantitative
analysis
overview of XRF methodologyoverview of XRF methodology
• the objective of XRF is to determine as accurately as possible the
composition of unknown samples
• measured x-ray line intensities are converted to concentrations using an
appropriate algorithm
overview of XRF methodologyoverview of XRF methodology
each specific application needs to
be looked at in detail to
determine which method will be
the most appropriate
XRF analytical methods
the atomic number (Z) of each of the
elements to be determined will have
an influence on the type of sample
preparation to be used, and the
quantitative or semi-quantitative
method that will be the most suitable
XRF analytical methods
the quantitative method is the most accurate, but requires
calibration standards
semi-quantitative method is less accurate, but does not require
standards
the quantitative method is the most accurate, but requires
calibration standards
semi-quantitative method is less accurate, but does not require
standards
overview of XRF methodologyoverview of XRF methodologyfirst determine the following:
• which elements are to be measured• what are their concentration ranges
• what accuracy is required• how many samples are to be measured
• are suitable standards available
overview of XRF methodologyoverview of XRF methodology
elements to be measured
• low Z will require careful preparation
• low Z may have lower accuracy
• low Z may require fusion of powders
• semi-quant does not measure the very light elements (Be to N)
overview of XRF methodology
concentration ranges
as the concentration range for each element increased, accuracy
generally decreases
large concentration ranges will require more standards
overview of XRF methodologyoverview of XRF methodologygood accuracy requires
careful sample preparation fusion of powder samples for Z 13
longer analysis time accurate calibration standards
careful selection of each variable instrument parameter
overview of XRF methodology
calibration standards
• require the same sample preparation as unknown samples
• accurate chemical analysis
• need to cover concentration ranges
• mechanically stable
XRF applications summary
• Na to U in all sample types
• Be to U in solid samples
• accuracy typically 0.1 to 1 % relative
• typical LLD is between 1 - 10 ppm
semi-quant (standardless analysis)
accuracy is limited by
particle size
inhomogeneity
non-measured elements (H to N)
semi-quant (standardless analysis)
accuracy of the semi-quantitative
method can be as good as 1%
relative; typically accuracy is
between 5% and 10%
quantitative analysisquantitative analysis
calibration graph (x-ray intensity v/s %
element) is established for each
element that is to be measured
measure unknowns using the
established calibrations
quantitative analysis - calibration
for a single element (a), the
concentration C is a function f of the
intensity I
Ca = fa x Ia
quantitative analysis - calibration
for multiple elements (a & b) in a
sample matrix, the concentration is
related to both a & b:
Ca = f(Ia, Ib) or Ca = f(Ia, Cb)
quantitative analysis - calibration the object is to obtain the best fit of
experimental data to a given algorithm
e.g. method of least squares fitting
Σ(Cchem – Ccalculated)2 = minimum
where Σ = sum from all standards
and C = concentration
quantitative analysis - calibration XRF software typically includes several
quantitative methods. The most
simplistic method is a straight line
calibration where matrix (or inter-
element) effects are absent
Soalan Pramakmal1. Nyatakan 5 punca kesalahan analitikal analisis X-Ray.2. Takrifkan sampel.3. Apakah punca prosedur pensampelan yang lemah?4. Nyatakan 5 perkara yang mempengaruhi kualiti penyediaan
sampel yang ideal.5. Terangkan prinsip kerja XRD.6. Terangkan prinsip kerja XRF.7. Berikan 5 contoh kaedah pensampelan.8. Terangkan cara penyediaan “fuse beads”.9. Nyatakan faktor kesilapan dalam penyediaan sampel yang
mempegaruhi analisis X-Ray.10. Apakah maklumat yang boleh diperolehi daripada keputusan
XRD.11. Tuliskan persamaan Bragg.12. Nyatakan komponen asas dalam mesin XRD.
Soalan Pramakmal13. Nyatakan 3 kaedah pencarian index unsur dengan manual PDF.14. Apakah perbezaan kaedah Hanawalt dan Fink?15. Lakarkan carta alir kaedah Fink.16. Lakarkan carta alir kaedah Hanawalt.17. Nyatakan julat no. atom yang boleh dikesan dengan kaedah XRF
pada sampel pepejal dan cecair.18. Apakah kaedah penyediaan sampel yang baik untuk unsur yang
mempunyai no. atom yang rendah.19. Kejituan keputusan XRF dipengaruhi oleh 3 faktor. Nyatakan
fator-faktor itu.20. Apakah itu LOI?