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EBS 325 Analytical Chemistry Laboratory Introduction To XRay Analysis

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Title: EBS 325 Analytical Chemistry Laboratory Introduction To XRay Analysis


1
EBS 325 Analytical Chemistry LaboratoryIntrodu
ction To X-Ray Analysis
School of Materials Mineral Resources
Engineering, Engineering Campus, Universiti
Sains Malaysia.
  • By
  • Mr. Samayamutthirian Palaniandy

2
OUTLINE
SAMPLING SAMPLE PREPARATION
XRF
XRD
3
SAMPLING SAMPLE PREPARATION
FOR X-RAY ANALYSIS
4
SAMPLING SAMPLE PREPARATION
FOR X-RAY ANALYSIS
SAMPLE PREPARATION
SAMPLING
5
or
6
GARBAGE IN.......GARBAGE OUT
7
PROPER PREPARATION FOR BEST RESULT
Glass
Plastics
Papers
8
X-RAY analytical errors
  • Sampling
  • Sample preparation
  • Instrumental
  • Standards
  • Statistical

9
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.
10
FAQ about samples and sampling
accurate
representative
Well-mixed
homogeneous.
The equipment does what we want.
random
Our sampling frequency is fine.
11
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.
12
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?
13
EXAMPLES OF SAMPLING METHODS
Coning quartering
Grab sampling
Riffle splitter
Fractional shoveling
Paper cone riffle splitter
14
CONING AND QUATERING
15
RIFFLE SPLLITING
16
PAPER CONE RIFFLE SPLITTER
17
Fractional Shoveling
18
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
19
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.
20
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
21
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.
Summary
22
X-RAY analytical errors
  • Sampling
  • Sample preparation
  • Instrumental
  • Standards
  • Statistical

23
Analytical errors sampling
  • Sample must be representative of the process
  • Sampling must be reproducible (i.e. should be
    able to take identical duplicate samples)

24
Sample preparation methods
must
Simple
Rapid
Reproducible
Low cost
25
Quality of sample preparation
  • The quality of sample preparation is at least as
    important as the quality of the subsequent
    measurements.

26
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

27
SAMPLES
METAL
POWDER
LIQUID
XRD and XRF
XRF only
Why???
28
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 Braggs 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.
29
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 samples
spectrum.
30
METAL
CHIPS
POLISHING
SOLUTION
LIQUID
REMELT
BELT GRINDER/ LATHE
CAST
INGOT
X-RAY ANALYSIS
31
POWDER
SOLUTION
GRINDING
FUSION
PRESS
LIQUID
GLASS BEAD
PELLET
X-RAY ANALYSIS
32
LIQUID
LIQUID HOLDER
DROP METHOD SPOT ANALYSIS
DDTC METHOD
FILTER
X-RAY ANALYSIS
33
Sample types
  • Solids
  • Pressed powders
  • Fused beads
  • Liquids

34
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.

35
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 lt 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

36
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

37
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.

38
Influence of sample preparation
39
Factor of errors in Sample Preparation
Grain size and surface roughness
Uniformity of sample
Contamination through the sample preparation
40
Grain size and surface roughness
41
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
42
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.
43
Powder Sample
Grinding Condition
Different grinding condition cause variation in
particle size distribution which leads to
variation in X-Ray intensity.
44
Powder Sample
45
XRD XRF ANALYSIS
46
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.

47
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

48
Diffractograms and ICDD Card
49
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?

50
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.

51
Crystal lattice
  • 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

52
Fourteen (14) Bravais Lattice
53
How does it work?
  • Diffraction
  • Braggs 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.

54
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
  • ? is kept constant by using filtered X- radiation
    that is approximately monochromatic. (See Table
    1).
  • d may have value consistent with the crystal
    structure (See Figure 5).
  • ? is the variable parameters, in terms of which
    the diffraction peaks are measured.

55
Table 1 Monochromatic X-ray filters
56
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 Braggs 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
57
Table 1 Typical experimental XRD data
58
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.

59
The Alphabetical Index
60
The Alphabetical Index
Figure 3 Schematic search procedure when
chemical information is known
61
Hanawalt Method
62
The Fink Method
63
XRF
  • X-Ray Fluorescence
  • is used to identify and measure the concentration
    of
  • elements in a sample

64
XRF instrumental parameters
  • x-ray tube kv
  • x-ray tube mA
  • primary beam filters
  • collimator masks
  • collimator
  • crystal
  • detector
  • path

65
user benefits of wavelength dispersive XRF
  • versatile
  • accurate
  • reproducible
  • fast
  • non destructive

66
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

67
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

68
XRF is reproducible
  • generally within ? 0.1 relative
  • good reproducibility requires high quality
    mechanics, stable electronics and careful
    construction techniques

69
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

70
XRF is non-destructive
  • standards are permanent
  • measured samples can be stored and re-analysed
    at a later date
  • precious samples are not damaged

71
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

72
XRF analytical envelope
  • the following section describes the five major
    areas that define the analytical possibilities
    available with wavelength dispersive XRF
    spectrometers

73
XRF analytical envelope
  • elemental range
  • detection limits
  • analysis times
  • accuracy
  • reproducibility

74
elemental range
  • beryllium (4) to uranium (92) in solids
  • fluorine (9) to uranium (92) in liquids

75
range of elements in solid samples are shown in
green (Be to U)
76
range of elements in liquid samples are shown in
green (Na to U)
77
detection limits (LLD)
  • function of atomic number (Z) the mix of
    elements within the sample (sample matrix)
  • lt 1 ppm for high Z in a light matrix (e.g. Pb
    in petrol)
  • or gt 10 ppm for low Z in a heavy matrix (Na
    in slag)

78
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 lt 0.5 relative
  • typical LLD is normally 1 - 10 ppm (depends on
    element being measured and the sample matrix)

79
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

80
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

81
Methods of Analysis
  • the following presentation describes the
    requirements for quantitative and
    semi-quantitative analysis

82
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

83
overview of XRF methodology
  • each specific application needs to be looked at
    in detail to determine which method will be the
    most appropriate

84
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

85
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

86
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

87
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)

88
overview of XRF methodology
  • concentration ranges
  • as the concentration range for each element
    increased, accuracy generally decreases
  • large concentration ranges will require more
    standards

89
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

90
overview of XRF methodology
  • calibration standards
  • require the same sample preparation as unknown
    samples
  • accurate chemical analysis
  • need to cover concentration ranges
  • mechanically stable

91
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

92
semi-quant (standardless analysis)
  • accuracy is limited by
  • particle size
  • inhomogeneity
  • non-measured elements (H to N)

93
semi-quant (standardless analysis)
  • accuracy of the semi-quantitative method can
    be as good as 1 relative typically accuracy is
    between 5 and 10

94
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

95
quantitative analysis - calibration
  • for a single element (a), the concentration C
    is a function f of the intensity I
  • Ca fa x Ia

96
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)

97
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
  • S(Cchem Ccalculated)2 minimum
  • where S sum from all standards
  • and C concentration

98
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

99
Soalan Pramakmal
  • 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.
  • Terangkan prinsip kerja XRD.
  • Terangkan prinsip kerja XRF.
  • Berikan 5 contoh kaedah pensampelan.
  • Terangkan cara penyediaan fuse beads.
  • Nyatakan faktor kesilapan dalam penyediaan sampel
    yang mempegaruhi analisis X-Ray.
  • Apakah maklumat yang boleh diperolehi daripada
    keputusan XRD.
  • Tuliskan persamaan Bragg.
  • Nyatakan komponen asas dalam mesin XRD.

100
Soalan Pramakmal
  • Nyatakan 3 kaedah pencarian index unsur dengan
    manual PDF.
  • Apakah perbezaan kaedah Hanawalt dan Fink?
  • Lakarkan carta alir kaedah Fink.
  • Lakarkan carta alir kaedah Hanawalt.
  • Nyatakan julat no. atom yang boleh dikesan dengan
    kaedah XRF pada sampel pepejal dan cecair.
  • Apakah kaedah penyediaan sampel yang baik untuk
    unsur yang mempunyai no. atom yang rendah.
  • Kejituan keputusan XRF dipengaruhi oleh 3 faktor.
    Nyatakan fator-faktor itu.
  • Apakah itu LOI?
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