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8/6/2019 Sample Preparation for X-Ray Analysis
http://slidepdf.com/reader/full/sample-preparation-for-x-ray-analysis 1/2
SAMPLING & ANALYSIS
he use o X-ray analysis in the cement industry
has increased considerably in recent years. While
X-ray fuorescence (XRF) is the universally accepted
standard method or raw material control, X-ray di-
raction (XRD) is now also proving to be an essential
technology in this rapidly evolving industry. Te in-
creased use o XRD has been helped by the development
o advanced instrumentation, enabling the method to
replace traditional calibration, wet chemical or Bogue
methods or quantitative clinker and cement crystalline
phase analysis.
X-ray analysis enables optimised use o raw materi-
als, reduces the energy costs o production and controls
product quality, while also providing the necessary level
o analysis or alternative raw uels, such as hazardous
waste uels. Tese attributes are vital in today’s climate
o stringent environmental legislation and rising
energy costs.
Simple to learn, easy to use
Te key requirements o sample preparation or
both XRF and XRD are that samples are homog-
enous and representative o the source material.
Additionally, the composition o the sample should
not be altered beore or during the preparation
process.
Fortunately, X-ray analysis usually requires
only very simple, inexpensive, sample preparation
work. Methods are both easy to learn and easy to
use. Tereore, even when the need or good sample
preparation is taken into account, X-ray analysis is
a much easier and quicker process than almost all
other chemical analysis techniques.
Sample preparation or XRF
For high quality XRF analysis in ce-
ment production, reproducible samplepreparation and a good calibration o
the XRF spectrometer are essential.
However, this can be di cult as there are ew suitable
reerence materials available. Furthermore, available
standards may not have the same mineralogy as local
samples, which can lead to inaccurate data.
Preparing samples as pressed pellets is widely re-
garded as the most eective and economical way o
preparing samples or routine control in cement pro-
duction. Good sample preparation can minimise two o
the major eects that can lead to bad data—particle size
and mineralogical eects:
Particle size efects
Tese arise due to the penetration depth o X-rays. I
large, unrepresentative particles are analyzed in the top
layer o a sample, X-ray data will provide inormation
about the composition o these large particles, not the
overall sample composition.
Mineralogical efects
Tese happen when a single element is present in di-
erent phases, a sample that has silicon present as both
silica and silicate, or example. o prevent problems,
it is important that when pressed powder samples are
measured, the standards and samples have the same
mineralogical composition.
Sample preparation or XRD
XRD is a powerul tool or the analysis o the phase prop-
erties o samples. As with XRF, good sample preparationhelps minimise errors and ensures good statistical repre-
sentation. A measurement on a single sample must give
Sample preparation or X-ray analysist h e c r i t i c a l i r s t s t e p
One o the many benefts o X-ray uorescence (XRF) spectrometry and X-ray diraction (XRD) is
simple sample preparation. However, even though it is straightorward, it is still vitally important
to get it right. In this article PANalytical demonstrates that good sample preparation is the critical
frst step to consistent and reliable X-ray analysis.
globalglobalcementcementMAGAZINEMAGAZINE May 2008 17
Figure 1, right: Particle
statistics efects.
(a) Good statistics: all
difraction peaks within the
difractogram produced by a
similar number o crystallites
(true pattern).
(b) Bad statistics: difraction
peaks produced by diferent
numbers o crystallites (alse
pattern).
Figure 2, bottom: Mica
thin layer sample: dusted vs.
pressed.
Figure 3, below: Efect o
sample spinning.
Remy Denker, Nienke Oosten-Nienhuis, Roger Meier PANalytical BV
(a)
(b)
(a)
(b)
8/6/2019 Sample Preparation for X-Ray Analysis
http://slidepdf.com/reader/full/sample-preparation-for-x-ray-analysis 2/2
the same result as an average measure-
ment on a number o the same samples.
Inadequate sample preparation can
lead to signicant variation, which is
di cult to correct ollowing analysis.
Particle size
Particle size is an important aspect insample preparation or XRD. Te par-
ticle should not be too big, because o
particle statistics (also known as crys-
tal statistics) eects. Crystal statistics
cause incorrectly measured intensi-
ties. In severe cases, these eects also
infuence the shape o the peaks. In
this instance, peak shapes are not
smooth but show a jagged outline,
which aects peak intensities (see Figure 1).
Equally, the particle should not be too small.
Tis can cause damage to the crystal structure or
alteration o phases, making it di cult to identiy orquantiy the actual phases present in the sample.
Orientation efects
Additionally, preerred orientation eects,
which can be induced merely by touching a
sample, play an important role or the analysis
o, or example, gypsum and calcite samples.
Figure 2 shows comparison between dusted
(random orientation) and pressed (preerred
orientation) samples. Refections o type hk0
disappear in the pressed sample.
Instrumental parameters and samplepreparation solutions
For good crystal statistics, a large number o
crystallites should contribute to the diraction
process. Tis can be achieved by grinding sam-
ples to reduce the average particle size. A range
o grinders is available or this process, many o
which are optimised or specic powder types.
It is important to identiy the optimum level o
sample grinding, or broadening o peaks can
still occur i particles are too small or i lattice
damage occurs. Tereore, thorough investiga-
tion o dierent grinding methods is essential.
Tere are many sample preparation tech-
niques that address the problem o preerred
orientation eects, including back- or side-
loading, surace roughening, use o amorphous
ller or isostatic pressing. Additionally, modern
X-ray analysis instruments are equipped with
spinning sample holders, greatly reducing the
infuence o sample orientation (see Figure 3).
Inuences o sample preparation
parameters
A very important aspect o sample prepara-
tion, particularly or cementitious materials, isensuring that a sample’s physical properties are
not altered during preparation. Tis is achieved
by monitoring the eects o certain parameters,
such as applied pressure and milling time, prior
to actual sample measurement.
Figures 4-7 show data rom studies to de-
termine the infuence o various parameters
on sample preparation. Te data underline
the importance o monitoring and controlling
infuential parameters during the sample prepa-ration process. Tese results cannot, however,
be used to extrapolate a trend to other samples
because cements dier widely in composition.
Inuence o pressure
Te Portland cement analysed in the diracto-
gram in Figure 4 was used to study the eects
o applied pressure when samples are pressed
as part o the preparation method. Te results
on peak intensity are clearly visible in Figure
5. Te higher the applied pressure, the lower
the intensity o the peak. Tis eect is caused
by the loss o crystal water, which alters thephysical property o the cement.
Inuence o milling time
Various milling times were applied to samples
o the Portland cement. Te results are shown in
Figure 6. It can be concluded that the longer the
milling time, the lower intensity o the peak.
Measurements under vacuum
Once milling time and pressure parameters
have been optimised, the selection o the right
measurement sequence must also be considered.
With XRD technology becoming increasingly
commonplace in the cement industry, a manu-
acturer may have the option to perorm both
XRD and XRF analysis. However, with XRF
analysis, cement samples are usually measured
under a vacuum, which has an eect on subse-
quent XRD measurement.
Figure 7 shows the infuence o a vacuum on
cement samples. Here, an XRF measurement
has been conducted under vacuum, ollowed by
XRD analysis. Tis results in reduced peak inten-
sity. In this example, the reduced intensity o the
gypsum peak occurs because the gypsum phase
is partly transormed into a semi-hydrate phase.
Conclusion
For many years, XRF has been at the heart o pro-
duction control in every modern cement works.
Now, to keep pace with industry needs, advanced
XRD technologies are also becoming increas-
ingly commonplace. Both are used routinely—as
the principal means o controlling composition
o raw materials, raw eed, clinker and cement.
As reliance on X-ray analysis increases,
so too does the importance o good sample
preparation. Tis, and the correct measurementsequence, ensures the highest possible accuracy
and precision.
SAMPLING & ANALYSIS
18 globalglobalcementcement MAGAZINEMAGAZINE May 2008
Figure 4: Difractogram o an
ordinary Portland cement - theblue bars indicate the position o
gypsum related peaks.
Figure 5: The efect o
applied pressure in sample
preparation.
Figure 6: The efect o milling
time during sample preparation.
Figure 7: The inuence o
vacuum on XRD analysis.
As world leaders in X-ray analysis
systems, with over 50 years o
experience, PANalytical is at the
oreront o X-ray analysis sample
preparation methods. The com-
pany’s comprehensive range o
manual and automatic, advanced
sample preparation systems
helps users create perectly pre-
pared samples.
The range includes the compact,
bench-top MiniMill 2, which grinds
samples at low cost with a high
degree o reproducibility; and the
MiniFuse 2 and Perl’X 3 instruments
which oer, respectively, semi- and
ully-automatic high quality used
bead preparation.
Expertise rom sample preparation to analysis result
From left: Bench-top MiniMill 2, Perl’X and MiniFuse 2.