This document discusses x-ray diffraction (XRD), including how x-rays are produced, x-ray spectroscopy, diffraction, Bragg's law, and various XRD methods. It then discusses an application of XRD - analyzing the crystalline morphology of clays, oxidized wax, LLDPE polymer, and their composites using XRD. Key results include observing how the organic modifier of different clays affects d-spacing values, and how the presence of oxidized wax leads to stronger intercalation of materials into clay layers.
3. • X-rays were discovered accidentally in 1895
by the German physicist W. Roentgen.
• X-rays mean electromagnetic waves which
has a wavelength shorter than that of
ultraviolet light.
Its wavelength varies from 0.01 to 10 nm
corresponding to frequencies in the range
3*10^16 to 3*10^19 Hz.
X-ray has photon energy , E = h v.
4. To generate x-rays, three things are needed.
A source of electrons.
A means of accelerating the electrons at high
speeds.
A target material to receive the impact of the
electrons and interact with them.
5. 5
Evacuated glass bulb
Anode
Cathode
X rays can be produced in a highly evacuated glass bulb,
called an X-ray tube, that contains essentially two
electrodes—an anode made of platinum, tungsten, or
another heavy metal of high melting point, and a
cathode.
When a high voltage is applied between the electrodes,
streams of electrons (cathode rays) are accelerated from
the cathode to the anode and produce X rays as they
strike the anode.
6. X-ray spectroscopy is a gathering name for
several spectroscopic techniques for
characterisation of materials by using x-ray
excitation.
When an electron from the inner shell of an
atom is excited by the energy of a photon , it
moves to the higher energy level.
7. When it returns to the lower energy level , the
energy which it previously gained by the
excitation is emitted as a photon which has a
wavelength that is characteristic for the
element.
Analysis of x-ray emission spectrum gives
qualitative results about the elemental
composition of the specimen.
Comparison of specimen’s spectrum with
spectra of samples of known composition
produced quantitative results.
8. Diffraction – the spreading out of waves
as they encounter a barrier.
General Characteristic of all
waves.
Modification of the behavior of
light or other waves by their
interactions with an object.
This is (obviously) a form of
scattering.
9. Crystalline solids consist of regular arrays of
atoms, ion, or molecules with inter atomic
spacing on the order of 100 pm or 1 Å.
The wavelength of the incident radiation has
to be on the same order as the spacing of the
atoms.
Monochromatic radiation is required for x-
ray diffraction.
10. When a monochromatic beam of radiation
falls on grating , the light waves emerging
from the grating interfere with one another.
Either amplify or eliminate the radiation for a
particular direction and give alternatively
white and dark bands.
11.
12.
13. Reflection of X-rays only occurs when the
conditions for constructive interference are
fulfilled.
Bragg law identifies the angles of the incident
radiation relative to the lattice planes for
which diffraction peaks occurs.
14. 14
The length DE is the same as EF, so the total
distance traveled by the bottom wave is expressed
by:
sinEF d
sinDE d
2 sinDE EF d
2 sinn d
Constructive interference of the radiation from
successive planes occurs when the path difference
is an integral number of wavelenghts. This is the
Bragg Law.
15. A diffractometer is a measuring instrument
for analyzing the structure of a material from
the scattering pattern.
16. X-ray tube: the source of x-rays.
Incident beam optics: condition the x-ray
beam before it hits the sample.
The goniometer : the platform that holds
and moves the sample,optics,detector and
tube.
The sample and the sample holder.
Receiving-side optics: condition the x-ray
beam after ihas encountered the sample.
Detector: count the number of x-rays
scattered by the sample.
20. The Laue method is mainly used to determine
the orientation of large single crystals. White
radiation is reflected from, or transmitted
through, a fixed crystal.
The diffracted beams form arrays of spots, that
lie on curves on the film. The Bragg angle is
fixed for every set of planes in the crystal.
Each set of planes picks out and diffracts the
particular wavelength from the white radiation
that satisfies the Bragg law for the values
of d and q involved.
21. Each curve therefore corresponds to a
different wavelength. The spots lying on any
one curve are reflections from planes
belonging to one zone.
Laue reflections from planes of the same
zone all lie on the surface of an imaginary
cone whose axis is the zone axis.
22. In the back-reflection method, the film is
placed between the x-ray source and the
crystal. The beams which are diffracted in a
backward direction are recorded.
One side of the cone of Laue reflections is
defined by the transmitted beam. The film
intersects the cone, with the diffraction spots
generally lying on a hyperbola.
23. In the transmission Laue method, the film is
placed behind the crystal to record beams
which are transmitted through the crystal.
One side of the cone of Laue reflections is
defined by the transmitted beam. The film
intersects the cone, with the diffraction spots
generally lying on an ellipse.
24.
25.
26. X-rays from an X-ray tube are made to pass
through two fine slits S1 and S2 which
collimate it into a fine pencil. This fine X-ray
beam is then made to fall
upon the crystal 'C' (usually sodium chloride
crystal) mounted on the spectrometer table.
This table is capable of rotation about a
vertical axis and its rotation can be read on a
circular graduated scale S.
The reflected beam after passing through
the slits S3 and S4 enters the ionization
chamber.
27. The X-rays entering the ionization chamber
ionize the gas which causes a current to flow
between the electrodes and the current can
be measured by galvanometer G.
The ionization current is a measure of the
intensity of X-rays reflected by the crystal.
The ionization current is measured for
different values of glancing angle θ.
For certain values of glancing angle,
the ionization current increases abruptly.
The first peak corresponds to first order, the
second peak to second order and so on.
28.
29. Single crystal mounted with one axis normal
to a monochromatic x-ray beam.
Cylindrical film placed around the sample . As
sample rotates, some sets of planes
momentarily satisfy Bragg condition.
When film is laid flat, a series of horizontal
lines appears. Because crystal rotates about a
single axis, possible Bragg angles are limited
- not every plane is able to produce a
diffracted spot.
Sometimes used to determine unknown
crystal structures.
30.
31. Powder diffraction is a scientific technique
using x-ray on powder or microcrystalline
samples for structural characterization of
materials.
An x-ray instrument used to determine angles
of diffraction for a polycrystalline specimen or
a powder as a function of diffracted beam
intensities.
Each peak in the diffraction pattern correspond
to a set of crystallographic plane.
32. X-ray diffraction analysis were
carried out to investigate the
crystalline morphology of five
types of clays, oxidized wax,
LLDPE and their composites.
33.
34.
35.
36. Cloisite 15A possess highest d-spacing
values because its organic modifier contains
2 hydrogenated tallows ( tallows are naturally
occuring fats and oils).
Hydrogenated tallows contain high
percentages of long carbon chains . This will
increase the gallery space in the clay.
The modifier used in cloisite 20A is exactly
same as that in cloisite 15A , but the higher
modifier concentration leads to the high d
spacing value.
37. Cloisite 93A also contains 2 hydrogenated
tallow but its d spacing value is less than that of
cloisite 15A.Because cloisite 15A contains 2
methyl group therefore it has high sterric effect.
XRD patterns of LLDPE shows 2 diffraction
peaks,these arise from the partially crystalline
LLDPE matrix.
Oxidised paraffin wax shows the diffraction
peaks in same position indicating similar
crystalline structure.These peaks are more
intense than those for LLDPE indicating a higher
crystallinity.
38. COMPOSITE PREPARATION:
A Brabender Plastograph was used to mix
LLDPE , wax and clay at 160 deg C and 60
rpm at about 25 minutes to ensure thorough
mixing . The material was then compression
molded at 160 deg C using hydraulic press.
39.
40.
41.
42.
43. In the case of composite containing cloisite
10A , there is no change in d-spacing value
in the absence of oxidized paraffin wax ,
indicating no intercalation of LLDPE into clay
layers.
In the presence of oxidized wax, d-spacing
shift from 18 to 42 , indicating strong
intercalation of the matrix material into the
clay.
Two other small peaks are present which
indicates that these composites have a mixed
morphology.
44. Constituents in the clay may occupy new
lattice positions creating new crystalline
order.
An increase in the amount of oxidised wax
did not remarkably change the morphology of
these composites.
Similar results was observed in the composite
containing cloisite 93A clay , but smaller
increase in d-spacing. Because, d-spacing of
cloisite 93A larger than that of cloisite 10A
and therefore mostly wax chains penetrate
into the gallery space.
45. In case of cloisite 20A and 25A the polymer
chains have been intercalated between the
layers of the clays , even in the absence of
wax.
This is evident from the d-spacing values of
the diffraction peak of clay from 25 to 33 for
Cloisite 20A, and from 18 to 28 for Cloisite
25A.
In these cases more than one peak were also
observed , indicating a mixed morphology.
46. X-RAY DIFFRACTION IN POLYMER SCIENCE
1)Identification of semi crystalline polymers
and Recognition of crystalline phases
(polymorphism) of polymers
2)Polymers are never 100% crystalline. XRD is a
primary technique to determine the degree of
crystallinity in polymers.
47. 3) Microstructure: Crystallite size in polymers
is usually on the nano scale in the thickness
direction. The size of crystallites can be
determined using variants of the Scherrer
equation.
4) Orientation: Polymers, due to their long
chain structure, are highly susceptible to
orientation. XRD is a primary tool for the
determination of crystalline orientation
through the Hermans orientation function
48. “X-ray Diffraction Patterns of Polymers”, June
Turley.
“X-ray Diffraction Procedures for
Polycrystalline and Amorphous Materials”,
Harold P. Klug and L. R. Alexander.
“X-ray Diffraction Methods in Polymer
Science”, L. R. Alexander.
49. “Effect of oxidized paraffin wax on the
thermal and mechanical properties of linear
low-density polyethylene–layered silicate
nanocomposites”, A.S. Luyta, V.G.
Geethamma.
“Oxidised wax as compatibilizer in Linear
Low-Density Polyethylene-Clay
Nanocomposites:X-ray Diffraction and
Dynamic Mechanical Analysis”,
V.G.Geethamma, Adriaan S.Luyt
