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?