School of Materials & Mineral Resources Engineering,
Engineering Campus, Universiti Sains Malaysia.
EBS 325 – Analytical Chemistry Laboratory
Introduction To X-Ray Analysis
By
Mr. Samayamutthirian Palaniandy
SAMPLING
&
SAMPLE
PREPARATION
XRD
XRF
SAMPLING
SAMPLE
PREPARATION
Glass
Plastics
Papers
X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
SAMPLE
A means by which units are taken from a
population in such a way as to represent the
characteristics of interest in that population.
FAQ about samples and sampling
accurate
representative
Well-mixed
homogeneous.
The equipment does
what we want.
Our sampling
frequency is fine.
random
Reasons for poor procedures,
equipment, and practices of
SAMPLING.
Lack of knowledge of the consequences of poor
sampling.
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
Paper cone
riffle splitter
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 correct cross stream
sample may be
impossible to obtain.
A static mixer can reduce the Grouping
and Segregation Error.
Precision 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
Summary
Your decisions are only as good as your
samples.
Your samples are only as good as your
sampling systems.
Your sampling systems are only as
good as your audit and assessment.
X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
Analytical errors – sampling
- Sample must be representative of the
process
reproducible
- Sampling must be
(i.e.
should be able to take identical duplicate
samples)
Sample preparation methods
must
Simple
Reproducible
Rapid
Low cost
Quality of sample preparation
The quality of sample preparation is
important as
measurements.
at least as
the quality of the subsequent
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
XRD and XRF
LIQUID
XRF only
Why???
XRD 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 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
BELT GRINDER/
LATHE
LIQUID
CAST
INGOT
X-RAY ANALYSIS
POWDER
PRESS
GRINDING
FUSION
GLASS BEAD
PELLET
X-RAY ANALYSIS
SOLUTION
LIQUID
LIQUID
LIQUID HOLDER
DROP METHOD
SPOT ANALYSIS
DDTC METHOD
FILTER
X-RAY ANALYSIS
Sample types
Solids
Pressed powders
Fused beads
Liquids
Solids
- 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.
Pressed powders
-
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 elements
Preparation equipment needed includes:
- Grinding mill and vessel (chrome steel, zirconia, tungsten carbide, etc.)
- Hydraulic press and die (usually 40 mm)
- Binding agents
Fused beads
-
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 elements
Preparation 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
Liquids
- 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.
Influence of sample preparation
element
Na (Z=11)
Si (Z=14)
Ca (Z=20)
Ba (Z=56)
Chemical % XRF %
Powder
0.43
0.36
63.63
62.90
0.68
0.68
0.27
0.28
XRF %
Fused bead
0.46
63.80
0.67
0.28
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
Sand molding
Metallic Sample
Casting condition of the sample in the molding.
Metal molding
X-ray intensities differ according to the molding method which comes
In 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
As the contamination form the polishing belt to the sample, the re contamination from
The material of the polishing belt and from the remaining trace elements of polished
Sample.
Contamination effect when carbon steel and Ni-Cr alloy polish after
polishing stainless steel.
Ni
Cr
Fe
% Conc
0.55
0.21
2.10
% Contamination
0.05
0.03
0.38
Powder Sample
Grinding Condition
Different grinding condition cause variation in particle size distribution which
leads to variation in X-Ray intensity.
Powder Sample
Brequetting
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
Identification
If you are given
with four bottles of
white powder.
What will you do
to identify them?
CaO,CaCO3,CaMg(CO3)2
Ca(OH)2 etc.
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?
XRD able to determine :
•
Which phases are present?
•
At what concentration levels?
•
What are the amorphous content of the
sample?
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
“FINGERPRINT” of a mineral
or a crystalline substance,
because it differs from pattern
of every other mineral or
crystalline substances.
Crystal lattice
A crystal lattice is a regular threedimension 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
Fourteen (14) Bravais Lattice
How does it work?
•Diffraction
Bragg’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 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 dspacing in polycrystalline materials.
Plotting the angular positions and
intensities of the resultant diffraction
peaks produces a pattern which is
characterised of the sample
Table 1: Typical experimental XRD data
Angle
(2)
27.47
27.82
28.45
44.87
46.68
47.11
55.88
68.89
76.12
83.19
87.74
92.49
94.68
94.99
106.44
106.78
113.81
114.26
127.24
127.82
d-value
(Å)
3.244
3.204
3.135
2.018
1.944
1.928
1.644
1.362
1.250
1.160
1.112
1.067
1.048
1.045
0.962
0.960
0.920
0.917
0.860
0.858
Rel. Int.
(I)
26
49
100
2
30
64
41
6
10
1
10
1
13
6
2
1
5
2
4
2
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
XRF
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
• collimator
• crystal
• detector
• path
user benefits of wavelength
dispersive XRF
• versatile
• accurate
• reproducible
• fast
• non destructive
XRF 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
XRF 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
XRF is reproducible
generally within  0.1% relative
good reproducibility requires high
quality mechanics, stable electronics
and careful construction techniques
XRF 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
XRF is non-destructive
• 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 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 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 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
overview of XRF methodology
first 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 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 methodology
good 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 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 interelement) effects are absent
Soalan Pramakmal
1.
2.
3.
4.
Nyatakan 5 punca kesalahan analitikal analisis X-Ray.
Takrifkan sampel.
Apakah punca prosedur pensampelan yang lemah?
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 Pramakmal
13. 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?