Analysis ppt xrd

Presentation on X-Ray
Diffraction
Submitted to Submitted by
Dr. Sudipta Saha Pooja Joshi
M.Pharma Ist sem

Contents
o Introduction
o Principle
o Bragg’s law & diffraction
o Instrumentation
o X-Ray diffraction methods
o Applications
o Conclusion
o Reference

INTRODUCTION
 “ Every crystalline substance gives a pattern; the same substance
always gives the same pattern; & in a mixture of substances each
produces its pattern independently of the others”
 The X-ray diffraction pattern of a pure substance is, therefore,
like a fingerprint of the substance. It is based on the
scattering of x-rays by crystals.
 Definition :-“The atomic planes of a crystal cause an
incident beam of X-rays to interfere with one another as they
leave the crystal. The phenomenon is called X-ray diffraction”

Diffraction occurs only when Bragg’s Law is satisfied Condition for
constructive interference (X-rays 1 & 2) from planes with spacing d
X Ray 1
X Ray 2
Bragg’s Law and Diffraction

d




Ray 1
Ray 2

Deviation = 2
 The path difference between ray 1 and ray 2 = 2d Sin
 For constructive interference: n = 2d Sin
BRAGG’s
EQUATION

“Constructive interference of the reflected beams emerging
from two different planes will take place if the path lengths
of two rays is equal to whole number of wavelengths”.
for constructive interference,
nλ=2dsin
this is called as BRAGG’S LAW

INSTRUMENTATION
 Production of x-rays
 Collimator
 Monochromator
a. Filter
b. Crystal monochromator
 Detectors
a. Photographic methods
b. Counter methods

PRODUCTION OF X-RAYS:
 X-rays are generated when high velocity electrons impinge on a
metal target.
 Approximately 1% of the total energy of the electron beam is
converted into x-radiation.
 The remainder being dissipated as heat.
 Many types of x-ray tubes are available which are used for
producing x-rays.

 A . Positive voltage in the form of anode having a target.
 B . Battery to emit thermo ionic electrons.
 C . Cathode –filament of tungsten metal.
 The electrons are accelerated towards the target A
 On striking the target the electrons transfer their energy to
its metallic surface which gives off x-ray radiation
Coolidge tube
A
CB

COLLIMATOR
 In order to get a narrow beam of x-rays, the x-rays generated by
the target material are allowed to pass through a collimator which
consists of two sets of closely packed metal plates separated by a
small gap.
 The collimator absorbs all the x-rays except the narrow beam
that passes between the gap.

TYPES OF MONOCHROMATORS
 In order to do monochromatization,2 methods are available
1.Filter
2.Crystal monochromator
a)Flat crystal monochromator
b)Curved crystal monochromator
Materials used- NaCl, quartz etc,.

1.FILTER:
 X-ray beam may be partly monochromatized by insertion
of a suitable filter
 A filter is a window of material that absorbs undesirable
radiation but allows the radiation of required wavelength
to pass

2)CRYSTAL MONOCHROMATOR
 Crystal monochromators is made up of suitable crystalline
material positioned in the x-ray beam so that the angle of
reflecting planes satisfied the Bragg’s equation for the
required wavelength.
 The beam is split up into component wavelengths
crystals used in monochromators are made up of materials
like Nacl, lithium fluoride , quartz etc.

DETECTORS
 The x-ray intensities can be measured and recorded either by
1)Photographic methods
2)Counter methods
a) Geiger - Muller tube counter
b) Proportional counter
c) Scintillation detector
d) Solid state semi conductor detector
e) Semi conductor detectors
 Both these types of methods depends upon ability of x-rays to
ionize matter and differ only in the subsequent fate of electrons
produced by the ionizing process.

Photographic method: To record the position and intensity of
x-ray beam ,a plane or cylindrical film is used
 The film after exposing to x-ray is developed
 The blackening of the developed film is expressed in terms of
density units D given by
D=log I₀/I
I₀- incident intensities
I- transmitted intensities
D-Total energy that causes blackening of the film
D is measured by densitometer
 The photographic method is mainly used in diffraction studies
since it reveals the entire diffraction pattern on a single film.
 Dis advg: time consuming and uses exposure of several hours.

COUNTER METHODS:
a) Geiger - Muller tube counter
 Geiger tube is filled with inert gas like argon
 Central wire anode is maintained at a positive potential of 800
to 2500V .
 The electron is accelerated by the potential gradient and causes
the ionisation of large number of argon atoms ,resulting in the
production of avalanche of electrons that are travelling
towards central anode
X-RAY Collision with filling gas Production of
an ion pair
Electon-
central
anode
Positive
ion-moves
to outer
electrode

b)Proportional counter
 Construction is similar to Geiger tube counter.
 Proportional counter is filled with heavier gas like xenon
and krypton.
 Heavier gas is preferred because it is easily ionized.
 Operated at a voltage below the Geiger plateau.
 The dead time is very short (~0.2μs), it can be used to
count high rates without significant error.

c) Scintillation Detector
 In a scintillation detector there is large sodium iodide
crystal activated with a small amount of thallium.
 When x-ray is incident upon crystal , the pulses of visible
light are emitted which can be detected by a photo
multiplier tube.
 Useful for measuring x-ray of short wavelength.
 Crystals used in scintillation detectors include sodium
iodide , anthracene ,napthalene and p-terphenol.

d) Solid state semi-conductor detector
 In this type of detector ,the electrons produced by x-ray beam
are promoted into conduction bands and the current which
flows is directly proportional to incident x-ray energy
 Disadvantage: Semi – conductor device should be maintained
at low temperatures to minimize noise and prevent
deterioration

 When x-ray falls on silicon lithium drifted detector an electron (-e) and a
hole (+e)
 Pure silicon made up with thin film of lithium metal plated onto one end
 Under the influence of voltage electrons moves towards +ve charge and
holes towards –ve
 Voltage generated is measure of the x-ray intensity falling on crystal
 Upon arriving at lithium pulse is generated
 Voltage of pulse=q/c; q-tot charge collected on electrode, c-detector
capacity.
e)semi-conductor detectors

X-RAY DIFFRACTION METHODS
 These are generally used for investigating the internal structures
and crystal structures of various solid compounds.
 They are:-
1.Laue’s photographic method
a)Transmission method
b)Back reflection method
2.Bragg’s X-ray spectrometer method
3.Rotating crystal method
4.Powder method

X-Ray Diffraction
Method
Laue
Orientation
Single Crystal
Polychromatic Beam
Fixed Angle
Rotating Crystal
Lattice constant
Single Crystal
Monochromatic Beam
Variable Angle
Powder
Lattice Parameters
Polycrystal
(powdered)
Monochromatic Beam
Variable Angle

1) Laue photographic method
a)Transmission Laue method
 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.
 Can be used to orient crystals for solid state experiments.
 Most suitable for the investigation of preferred orientation sheet
particularly confined to lower diffraction angles.
 Also used in determination of symmetry of single crystals.

b)Back-reflection method
 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 an hyperbola.
 This method is similar to Transmission method however, black-
reflection is the only method for the study of large and thick
specimens.
 Disadvantage: Big crystals are required

 Laue-beam of x-ray-crystal-emitted x-ray obtained on
photographic plate-using photograph-brag analyzed structures
of crystals of Nacl, Kcl,and ZnS.
 Bragg devised a spectrometer to measure the intensity of X-Ray
beam.
 This method is based on Bragg’s law .
2) The Bragg’s x-ray spectrometer method

The Bragg’s x-ray spectrometer method
 Various components of Bragg’s X-ray spectrometers are as
follows:-
i) X-rays from the anticathode A are allowed to pass through two
adjustable slits B & B’ to get a thin beam of X-rays. Then ,
these rays are made to fall upon the crystal C.
ii) The position of crystal can be adjusted by the vernier V
capable of motion along the circular scale C.

iii) The reflected X-rays from the crystal after passing through
the slit F enter the ionization chamber E through a narrow
aluminium window W.
iv) One plate of ionization chamber is connected to the
positive terminal of a H.T Battery , while negative terminal is
connected to quadrant electrometer Q(measures the strength
of ionization current)

Working:
 Crystal is mounted such that ѳ=0° and ionization chamber is
adjusted to receive x-rays.
 Crystal and ionization chamber are allowed to move in small
steps, so that the angle through which the chamber is moved is
twice the angle through which the crystal is rotated.
 X-ray spectrum is obtained by plotting a graph between
ionization current and the glancing angle ѳ
 Peaks are obtained, peaks corresponds to Bragg’s reflection
corresponding to different order glancing angles ѳ1, ѳ2, ѳ3 are
obtained, with known values of d and n and from the observed
value of ѳ , λ can be measured.

3)ROTATING CRYSTAL METHOD
 Photographs can be taken by :
1.Complete rotation method: in this method series of complete
revolutions occur.
 Each set of a plane in a crystal diffracts four times during rotation
 Four diffracted beams are distributed into a rectangular pattern
in the central point of photograph
2.Oscillation method: the crystal is oscillated at an angle of 15° or
20°
 The photographic plate is also moved back and forth with the
crystal
 The position of the spot on the plate indicates the orientation of
the crystal at which the spot was formed

X-ray powder diffraction (XRD) is a rapid analytical technique
primarily used for phase identification of a crystalline material
and can provide information on unit cell dimensions.
The analyzed material is finely ground, homogenized, and
average bulk composition is determined.
4)POWDER CRYSTAL METHOD

 When monochromatic beam is allowed to pass different
possibilities may happen :-
1. There will be some particles out of random orientation of
small crystals in the fine powder.
2. Another fraction of grains will have another set of planes in
the correct positions for the reflections to occur.
3. Reflections are possible in different orders for each set.

 If the angle of incidence is ѳ then the angle of reflection will be 2ѳ
 If the radius is r the circumference 2πr corresponds to a scattering
angle of 360°
 From the above equation the value of ѳ can be calculated and
substituted in Bragg's equation to get the value of d
Applications
 Useful for determining the complex structures of metals and
alloys.
 characterization of crystalline materials.
 identification of fine-grained minerals such as clays and mixed
layer clays that are difficult to determine optically.
 determination of unit cell dimensions.
 measurement of sample purity.
Ѳ=360*1/πr

Applications Of XRD
1. Structure of crystals.
2. Polymer characterization.
3. State of anneal in metals.
4. Particle size determination.
a) Spot counting method.
b) Broadening of diffraction lines.
c) Low-angle scattering.
5 Applications of diffraction methods to complexes.
a) Determination of cis-trans isomerism.
b) Determination of linkage isomerism.
6.Miscellaneous applications.

1)Structure of Crystals
a-x-ray pattern of salt Nacl
b-x-ray pattern of salt Kcl
c-x-ray pattern of mixture of Nacl &Kcl
d-x-ray pattern of a powder mixed crystal of Nacl & Kcl

2) Polymer Characterization
 Determine degree of crystanillity
 Non-crystalline portion scatters x-ray beam to give a
continuous background(amorphous materials)
 Crystalline portion causes diffraction lines that are not
continuous.(crystalline materials

3)State of anneal in metals: XRD is used to test
the metals without removing the part from its position and
without weakening it.
4)Particle size determination
Spot counting method:
v=V.δθ.cosθ/2n
V=volume of individual crystallite
V=total volume irradiated
n=no. of spots in diffraction ring
δθ =divergence of x-ray beam

5)Miscellaneous Application
 Soil classification based on crystallinity
 Analysis of industrial dusts
 Assessment of weathering & degradation of minerals &
polymers
 Study of corrosion products
 Examination of tooth enamel & dentine
 Examination of bone state & tissue state
 Structure of DNA&RNA

CONCLUSIONS
 For materials including metals, minerals, plastics,
pharmaceuticals and semiconductors XRD
apparatus provide highly accurate tools for non-
destructive analysis.
 The diffraction systems are also supported by an
extensive range of application software

Refrencences
 1) Chatwal R Gurdeep, Anand k Sham, Instrumental methods of
chemical analysis, Himalayan publications. page no:2.303-2.332
 Sagar vidya G, Instrumental methods of drug analysis, Pharma
med press. Page no:- 491-510
 2) http://www.scienceiscool.org/solids/intro.html
 3) http://en.wikipedia.org/wiki/X-ray_crystallography

Analysis ppt xrd

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Analysis ppt xrd