xray laboratory

7/29/2019 XRay Laboratory

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EBS 325Analytical Chemistry Laboratory

Introduction To X-Ray Analysis

By

Mr. Samayamutthirian Palaniandy

School of Materials & Mineral Resources Engineering,

Engineering Campus, Universiti Sains Malaysia.


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SAMPLING

&SAMPLE

PREPARATION

XRFXRD


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SAMPLING

SAMPLE

PREPARATION


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Papers

Plastics

Glass


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X-RAY analytical errors

Sampling

Sample preparation

Instrumental

Standards

Statistical


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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.


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homogeneous.Well-mixed

random

accuraterepresentative

The equipment does

what we want.Our sampling

frequency is fine.

FAQ about samples and sampling


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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.


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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?


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EXAMPLES OF SAMPLING METHODS

Coning &

quartering

Riffle

splitter

Paper coneriffle splitter

Grab

sampling

Fractionalshoveling


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CONING AND QUATERING


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RIFFLE SPLLITING


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PAPER CONE RIFFLE SPLITTER


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Fractional Shoveling


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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


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Sample Mixing Flowing Liquids or Gases

A static mixer can reduce the Groupingand Segregation Error.A correct cross stream

sample may be

impossible to obtain.


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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


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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


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X-RAY analytical errors

Sampling

Sample preparation

Instrumental

Standards

Statistical


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Analytical errorssampling

- Sample must be representative of theprocess

- Sampling must be reproducible (i.e.should be able to take identical duplicatesamples)


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Sample preparation methods

must

Simple

Low cost

Rapid

Reproducible


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The quality of sample preparation is at least asimportant as the quality of the subsequentmeasurements.

Quality of sample preparation


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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


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SAMPLES

METAL POWDER LIQUID

XRF onlyXRD and XRF

Why???


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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.


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XRF Working Concept

In X-ray fluorescence spectroscopy, the process begins by exposingthe 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, orshell, 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 ofenergy 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.


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METAL

CHIPS POLISHING SOLUTION

REMELT

CAST

BELT GRINDER/LATHE

INGOT

LIQUID

X-RAY ANALYSIS


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POWDER

GRINDING FUSION SOLUTION

PELLET

GLASS BEAD LIQUID

X-RAY ANALYSIS

PRESS


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LIQUID

LIQUID HOLDERDROP METHOD

SPOT ANALYSISDDTC METHOD

FILTER

X-RAY ANALYSIS


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Solids

Pressed powdersFused beads

Liquids

Sample types


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- 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 elementsif good accuracy is required.

Solids


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- 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 m

- 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 samplestrength 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

Pressed powders


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- 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

- Disadvantagereduced 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 & mouldbetween samples

Fused beads


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- Typical samples include environmental (waters, mud) &oils

- Easiest to prepare

- Should have a constant volume that exceeds maximumpenetration depth

- Sample is poured into a liquid cell fitted with a thin plasticwindow

- Range of window materials to suit different liquids

- Fill to a constant height (e.g. 20 mm) to avoid errors fromvariable depth

- Choose the correct thickness and material to suit thechemistry of the sample being measured

- Na is lightest element that can be detected in liquids.

Liquids


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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


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Factor of errors in Sample Preparation

Grain size and surface roughness

Uniformity of sample

Contamination through the sample preparation


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Grain size and surface roughness


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Metallic Sample

Casting condition of the sample in the molding.

Sand 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


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Contamination during polishing

Contamination effect when carbon steel and Ni-Cr alloy polish afterpolishing stainless steel.

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.

Ni Cr Fe

% Conc 0.55 0.21 2.10

% Contamination 0.05 0.03 0.38

Powder Sample


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Powder SampleGrinding Condition

Different grinding condition cause variation in particle size distribution which

leads to variation in X-Ray intensity.

Powder Sample


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Powder SampleBrequetting

Usual forming pressure 20 tons with 40mm diameter.

X-Ray intensities varies with variation of forming pressure (especiallywhen pressure is low).

Contamination

Contamination from the grinding mill and media


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CaO,CaCO3,CaMg(CO3)2Ca(OH)2 etc.

If you are givenwith four bottles of

white powder.

What will you doto identify them?

Identification


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What is X-ray diffraction?

non-destructive analytical technique for

identification and quantitative determination

of the various crystalline forms, known asphases.

Identification is achieved by comparing theX-ray diffraction pattern


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Diffractograms and ICDD Card


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What is X-ray diffraction?

XRD able to determine :

Which phases are present?

At what concentration levels?

What are the amorphous content of thesample?


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How does XRD Works???

Every crystalline substanceproduce its own XRD pattern,which because it is dependenton the internal structure, is

characteristic of that substance.

The XRD pattern is oftenspoken as theFINGERPRINT of a mineralor a crystalline substance,

because it differs from patternof every other mineral orcrystalline substances.


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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


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Fourteen (14) Bravais Lattice


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How does it work?

Diffraction

Braggs Law

n=2dsin

When a monochromatic x-ray beamwith wavelength is incident onthe lattice planes in a crystal planesin a crystal at an angle ,diffraction occurs only when thedistance traveled by the raysreflected from successive planes

differs by a complete number n ofwavelengths.


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How does it work?In powder XRD method, a sample is ground to a

powder (10m) in order to expose all possibleorientations to the X-ray beam of the crystalvalues of, dand for diffraction are achievedas follows:

1. is kept constant by using filtered X- radiationthat is approximately monochromatic. (SeeTable 1).

2. d may have value consistent with the crystalstructure (See Figure 5).

3. is the variable parameters, in terms of whichthe diffraction peaks are measured.

T bl 1 M h ti X filt


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Table 1: Monochromatic X-ray filters

Basic Component Of XRD Machine


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Basic Component Of XRD Machine

Therefore any XRD machine will

consist of three basiccomponent.

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


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Angle

(2)

d-value()

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


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Design and Use of the Indexes for

Manual Searching of the PDF

Three search methods are used in the

indexesi.e.

The alphabetical index;

The Hanawalt index

The Finkindex.

The Alphabetical Index


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p



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Figure 3: Schematic search procedure when

chemical information is known

Hanawalt Method


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Hanawalt Method

The Fink Method


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The Fink Method


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XRF

X-Ray Fluorescence

is used to identify and measure the

concentration of

elements in a sample


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XRF instrumental parameters

x-ray tube kv

x-ray tube mA

primary beam filters

collimator masks

collimator

crystal

detector

path


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user benefits of wavelength

dispersive XRF versatile

accurate

reproducible

fast

non destructive

XRF i til


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XRF is versatile

element range is Be to U

atomic numbers (Z) of 4 to 92

concentration range covers0.1 ppm to 100 %

samples can be in the form of

solids, liquids, powders or fragments

XRF i t


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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


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XRF is reproducible

generally within 0.1% relative

good reproducibility requires high

quality mechanics, stable electronics

and careful construction techniques


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XRF is fast

counting times generally between 1

& 50 seconds for each element

semi-quant analysis ofall matrix

elements in 10 to 20 minutes

overnight un-attended operation


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XRF is non-destructive

standards are permanent

measured samples can be stored and

re-analysed at a later date

precious samples are not damaged


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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


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XRF analytical envelope

the following section describes the

five major areas that define theanalytical possibilities available with

wavelength dispersive XRF

spectrometers


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XRF analytical envelope

elemental range

detection limitsanalysis times

accuracyreproducibility


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elemental range

beryllium (4) to uranium (92)

in solids

fluorine (9) to uranium (92)

in liquids

range of elements in solid samples


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range of elements in solid samples

are shown in green (Be to U)

range of elements in liquid samples


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range of elements in liquid samples

are shown in green (Na to U)

detection limits (LLD)


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detection limits (LLD)

function of atomic number (Z) & themix 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


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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 andthe sample matrix)


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XRF errors

the following section describes

major source of errors in XRFanalysis, and investigates how

these errors can be minimized to

achieve maximize accuracy

overview of XRF methodology


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good accuracy requires careful sample preparation

fused beads for light elements

accurate standards selection of optimum instrument

parameters

collection of enough counts to avoidstatistical errors


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Methods of Analysis

the following presentation

describes the requirements for

quantitative and semi-quantitative

analysis


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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 anappropriate algorithm


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each specific application needs to

be looked at in detail to

determine which method will be

the most appropriate

XRF analytical methods


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the atomic number (Z) of each of theelements to be determined will have

an influence on the type of samplepreparation to be used, and the

quantitative or semi-quantitativemethod that will be the most suitable


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the quantitative method is the

most accurate, but requires calibration

standards

semi-quantitative method is less

accurate, but does not requirestandards


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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


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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 verylight elements (Be to N)


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concentration ranges

as the concentration range for each

element increased, accuracy

generally decreases

large concentration ranges willrequire more standards


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good accuracy requires

careful sample preparation

fusion of powder samples for Z 13

longer analysis time

accurate calibration standards

careful selection of each variableinstrument parameter


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calibration standards

require the same sample preparation

as unknown samples accurate chemical analysis

need to cover concentration ranges mechanically stable


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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

i t ( t d dl l i )


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semi-quant (standardless analysis)

accuracy is limited by

particle size

inhomogeneity

non-measured elements (H to N)

i t ( t d dl l i )


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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


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q y

calibration graph (x-ray intensity v/s %

element) is established for each

element that is to be measured

measure unknowns using the

established calibrations


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quantitative analysis - calibration

for a single element (a), the

concentration C is a function f of the

intensity I

Ca = fa x Ia


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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)

i i l i lib i


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the object is to obtain the best fit ofexperimental data to a given algorithm

e.g. method ofleast squares fitting(CchemCcalculated)

2 = minimum

where = sum from all standardsand C = concentration

i i l i lib i


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XRF software typically includes several

quantitative methods. The most

simplistic method is a straight line

calibration where matrix (orinter-

element) effects are absent

Soalan Pramakmal


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1. 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 fusebeads.

9. Nyatakan faktor kesilapan dalam penyediaan sampel yang

mempegaruhi analisis X-Ray.

10. Apakah maklumat yang boleh diperolehi daripada keputusanXRD.

11. Tuliskan persamaan Bragg.

12. Nyatakan komponen asas dalam mesin XRD.

S l P k l


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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?

xray laboratory

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