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SAMPLE PREPARATION: HOW PARTICLE SIZE AFFECTS DATA QUALITY AND ELEMENTAL ANALYSIS

Calvin Wong – Application Specialist

[email protected]


XRF

INTRODUCTION


XRF BRIEFS

X-Ray Fluorescence (XRF) is an analytical method to determine the chemical composition of all kinds

of materials

The materials can be analysed are e.g.

• Solids

• Liquids

• Powders

• Filters

• Fusion beads

• Thin films

What is XRF


BENEFITS OF XRF

• XRF is fast, accurate, non-destructive and usually requires minimum sample preparation

• Broad application range: metal, cement, oil, polymer, plastic and food industries, mining, pharma,

environmental and waste materials

• Easy characterization of any unknown sample using standardless analysis methods

• High accuracy analysis using dedicated calibrations

• Excellent precision, typically better than 1% relative RMS

• Attractive for process control: operator proof, automation possible


THE X-RAY FLUORESCENCE SPECTROMETER

• The spectrometer measures fluorescent X-ray intensity and converts this to the concentration of

elements in the sample.

• System calibration is required to convert counts into concentration

Source Sample Optics Detector Electronics Software


WHAT ARE X-RAYS

• X-rays can be seen as electromagnetic waves with their associated wavelengths, or

as beams of photons with associated energies.

• The wavelengths of X-rays are in the range from 0.01 to 10 nm, which corresponds to

energies in the range from 0.125 to 125 keV.


X-RAY SOURCES IN XRFSPECTROPHOTOMETRY

In an X-ray spectrophotometer there are 2 places where X-rays are generated

• The X-ray tube

In the X-ray tube the excitation is provided by electrons from the tube filament

• The sample

In the sample the analyte elements are excited by the photons originating from the X-ray tube


INTERACTION OF X-RAYS WITH MATTER

▪ There are 3 main interactions when X-rays contact matter: Fluorescence, Compton scatter and Rayleigh

scatter.

▪ If a beam of X-ray photon is directed towards a slab of material, a fraction will be transmitted through, a

fraction is absorbed (producing fluorescent radiation) and a fraction is scattered back

▪ The fluorescence and the scatter depend on the thickness, density and composition of the material and on

the energy of the X-rays


XRF ANALYSIS

• A good analysis starts with a well-prepared sample and a good measurement.

• After a sample is measured, it is analysed. This is done in two steps: Qualitative analysis followed

by quantitative analysis.

• Qualitative analysis determines which elements are present and their net intensities from the

measured spectra.

• In many routine situations, the elements in the sample are known and only the net intensities need

to be determined. The net intensities are used in the quantitative analysis to calculate the

concentrations of the elements present


SAMPLE PREPARATION

• Often only a small sample of material is analysed, for instance in a steel plant a small disk

represents the full furnace contents.

• The sample must be representative of the entire material and so must be taken very carefully.

• Once taken, it must also be handled carefully.

• Another basic requirement is that a sample must be homogeneous. Spectrometers only analyse the

sample’s surface layer, so it must be representative of the whole sample


SAMPLE PREPARATIONXRF – many samples can be measured


SAMPLE PREPARATION


PARTICLE SIZE AND XRF RESULTS

• The samples at five different grain sizes (2mm-300um,

300-250um, 250-150um, 150-75um and <75um)

• It was found that the grain size of the samples influenced

major and minor elements concentrations

• The elemental concentrations of all samples increased

significantly with decreasing size of the grain for almost all

elements.

• There are several factors such as particle size, uniformity,

heterogeneity and surface condition that can determine the

accuracy and reliability of the XRF result

• The XRF efficiency decreased for the larger grain sizes of

sample because the surface area and density of soils in

the XRF cup was decreased


PARTICLE SIZE AND XRF RESULTS

• Key aspects of preparing pressed pellets is to ensure that

the sample is ground to a particle size of <75um but 50um

is ideal

• Small particle size is an important factor in producing

pellets that provide the best analytical results because it

affects how the sample will compress and bind together

when pressed

• Samples with larger or variable particle sizes can lead to

heterogeneities in the sample

• Presence of larger particle sizes at the analysis surface of

the sample can lead to analysis errors through the

“shadow effect”.


PARTICLE SIZE

ANALYSIS (LASER

DIFFRACTION)


UNDERSTANDING PARTICLE SIZE

• Product performance requirements could include:• Ability to stay in suspension

• Dissolution rate

• Reaction Rate

• Texture / Mouth feel

• Content uniformity

• Stability

• Flowability (of a powder)

• Viscosity (of a suspension)

• Packing density

• Color / Appearance

• Inhalation properties

Performance of many products can be understood and controlled


LASER DIFFRACTIONThe light scattering pattern from a group of particles


LASER DIFFRACTIONLaser diffraction – how does it work

• Angle of diffraction depends upon particle size• Large particles scatter at smaller angles and with high intensity

• Small particles scatter light at wider angles but with a lower intensity

Images: Dr Kevin Powers, PERC, University of Florida

5 microns 800 nanometres


LASER DIFFRACTION


Particle Size Analyzer

MASTERSIZER 3000

A SHORT SUMMARY

PARTICLE CHARACTERIZATION AT A GLANCE

• Wide dynamic range (10nm to 3500um)

• Rapid measurements – results reported in less

than a minute

• Repeatability – Large number of particles sampled

• High sample throughput – 100s of measurements

can be made in day

• No calibration required – 1st principles/universal

principles

• Well established technique – general principles

described by ISO13320:2009


A RANGE OF LIQUID ACCESSORIES ARE AVAILABLE TO CONTROL THE SAMPLE DISPERSION AND SAMPLING

› In-line sonication

› Full SOP control

› Automated dispersant supply

› Can be used with an external pump to deliver dispersant

› Chemically compatible

HYDRO MV

120ml

HYDRO LV

600ml

HYDRO EV

600 – 1000ml

› In-line sonication

› SOP control

› Manual dispersant supply

› Lab beaker used as sample tank

› Chemically compatible

› Precise pressure control

› SOP control

› Modular venturi dispenser

› Modular sample try design


Measurement cell Focal plane

detectors

Side scatter

detectors

Back scatter

detectors

633nm red

laser

Precision

folded optics

MASTERSIZER 3000 OPTICS: RED LIGHT MEASUREMENTS


MASTERSIZER 3000 OPTICS: BLUE LIGHT MEASUREMENTS

470nm blue

light source

Side scatter

detectors

Measurement cell

Back scatter

detectors


PARTICLE SIZE ANALYSIS OF CERAMICS

Green Body

Sintered Ceramic


CEMENT: RAW MIX CEMENT MEASUREMENTS

Size / m

0.1 1 10 100 1000

Vo

lum

e f

req

ue

nc

y/

%

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Raw Mix


CEMENT: PARTICLE SIZE OF DIFFERENT PRODUCT GRADES

Size / m

0.1 1 10 100 1000

Vo

lum

e f

req

uen

cy /

%

0

1

2

3

4

5

CEM I

CEM II


PARTICLE SIZING: CHOCOLATE


Particle Size Analyzer

MASTERSIZER 3000

A SHORT SUMMARY

PARTICLE CHARACTERIZATION AT A GLANCE

Particle Size Analyser / Zeta

Potential

ZETASIZER ULTRA/PROParticle Imaging

MORPHOLOGI 4


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