X-RAY Powder Diffraction (XRD)
X-ray
powder diffraction (XRD) is rapid analytical technique primarily used for phase
identification of the crystalline material and can provide information on unit
cell dimension and atomic spacing. The X-ray are generated by cathode ray tube,
filtered to produce monochromatic radiation, collimated to concentrate, and
directed towards the sample. The interaction of the incident monochromatic rays
with the sample produces constructive interference (and diffracted ray) when
condition satisfys Braggs Law nλ = 2d sinθ ,
this relates the wave length of electro-magnetic radiation to the diffraction
angle and the lattice spacing in a crystalline sample by scanning the sample
through arrange of 2 angles, all possible diffraction direction of the lattice
should be attained due to the random orientation of the powdered materials.
X-ray has wavelength comparable to the crystalline, thus it can be used for the
accurate measurement of lattice parameter, crystallite size, lattice strain
etc. X-ray diffraction patterns were recorded from 50 to 600 with analytical system diffractometer
supplied by Bruker AXS Model No.D8 Advanced System as shown in figure4-1, using
CuK radiation (λ=1.5418 A0) with
accelerating voltage of 40 KV. Data were collected with a counting rate of 10/min.
The crystallite size is given by the Debye-Scherrer’s Formulae
Where D Average size of the particle
θ-
Diffraction angle
Thermo
Gravimetric/ Differential thermal Analysis (TGA)
Thermo
gravimetric analysis (TGA) records theweight changes in a sample with respect
to the temperature.Changes refer either to desorption ofvolatile components
from the sample (negativeweight change) or to absorption of gaseous
componentsfrom the atmosphere surrounding the sample(positive weight change).In
a typical TGA experiment a sample within a crucible is placed on top of a
thermocoupleresting on a balance. The system is sealed into achamber and heated
with a constant heating rate.Differential thermal analysis (DTA) records
thetemperature of a sample as compared to a referencematerial. Positive and
negative peaks on the otherwisesmooth DTA curve qualitatively reveal
thethermodynamic nature (exo-/endothermic) of thechanges occurring in the
sample.In a typical DTA experiment a sample within a crucible and an empty
crucible areplaced on top of two thermocouples. The system issealed into a
chamber and heated with a constantheating rate.
Fourier
Transform Infrared Spectroscopy (FTIR)
FT-IR spectrometer Bruker ALPHA
FTIR has been used to analyze
the samples to investigate the presence of functional groups, in Particular
oxidized groups
To make it easier to write
out every bond that is discussed some abbreviations has been used.
· For a single bond both types of atoms that are included in the
bond are written out and the bond is represented with a dash; for example C-O
for a carbon-oxygen single bond.
· For a double bond both types of atoms that are included in the
bond are written out and the bond is represented with an equal sign; for
example C=O for a carbon-oxygen double bond.
· Atoms that may be represented are C (Carbon), O (Oxygen), H
(Hydrogen), Si (silicon) and N (Nitrogen).
Because there needs to be a relative scale for the absorption intensity,
a background spectrum must also be measured. This is normally a measurement
with no sample in the beam. This can be compared to the the measurement with
the sample in the beam to determine the “percenttransmittance”. This technique
results in a spectrum which has all of the instrumental characteristics
removed. Thus, all spectral features which are present are strictly due to
thesample. A single background measurement can be used for many sample
measurement becausethis spectrum is characteristic of the instrument itself.
The Fourier Transform Infrared (FTIR)technique has brought significant
practical advantages to infrared spectroscopy. It has madepossible the
development of many new sampling techniques which were designed to
tacklechallenging problems which were impossible by older technology. It has
made the use ofinfrared analysis virtually limitless.Characteristics removed.
Thus, all spectral features which are present are strictly due to the sample. A
single background measurement can be used for many sample measurement because
this spectrum is characteristic of the instrument itself. The Fourier Transform
Infrared (FTIR) technique has brought significant practical advantages to
infrared spectroscopy. It has made possible the development of many new
sampling techniques which were designed to tackle challenging problems which
were impossible by older technology. It has made the use of infrared analysis
virtually limitless.
Features:
§ Identification of inorganic compounds and organic compounds
§ Identification of components of an unknown mixture
§ Analysis of solids, liquids, and gasses
§ In remote sensing
§ In measurement and analysis of Atmospheric Spectra
§ Solar irradiance at any point on earth
§ Long wave/terrestrial radiation spectra
§ Can also be used on satellites to probe the space
Sample preparation
for FTIR
FTIR spectrum was conducted with model Bruker ALPHA and our sample
ismixed thoroughly in 400 mg of KBr for about 15 minutes. The mixture of Sample
and KBr isplaced in a die of capacity 8 tons very carefully. Later load is
applied and the pellet is removed.Care should be taken for uniform mixing in
order to make transparent. The sample wasanalyzed. It confirmed the presence of
hydroxyl, carbonyl and carboxylic group.
Scanning
Electron Microscope
The morphology and
microstructure of nanoparticles were analyzed using scanning electron
microscope. The system is coupled with energydispersivex-ray spectrometer
(EDAX).The scanning electron microscope (SEM) is a type of electron microscope
that images thesample surface by scanning it with a high-energy beam of electrons
in a raster scan pattern. Ina typical SEM, electrons are thermionic ally
emitted from a tungsten or lanthanum hexaboride(LaB6) cathode and are
accelerated towards an anode. The electrons interact with the atomsthat make up
the sample producing signals that contain information about the sample's
surfacetopography, composition and other properties such as electrical
conductivity.
Principle
A finely focused
electron beam scanned across the surface of the sample generates
secondaryelectrons, backscattered electrons, and characteristic X-rays. These
signals are collected bydetectors to form images of the sample displayed on a
cathode ray tube screen. Features seenin the SEM image may then be immediately
analyzed for elemental composition using EDS.Fig 4.4: Schematic Outline of SEM
Working
Primary electrons
generate low energy secondary electrons, which tend to emphasis thetopographic
nature of the specimen. Primary electrons can be backscattered which
producesimages with a high degree of atomic number (Z) contrast. Ionized atoms
can relax by electronshell-to-shell transitions, which lead to either X-ray
emission or Auger electron ejection. TheX-rays emitted are characteristic of
the elements in the top few micrometres (μm) of the sample.Secondary Electron Imaging
shows the topography of surface features a few nm across. Filmsand stains as
thin as 20nm produce adequate-contrast images. Materials are viewed at
usefulmagnifications up to 100,000X without the need for extensive sample
preparation and withoutdamaging the sample.
Schematic Outline
of SEM
Transmission
Electron Microscope (TEM)
This instrument is used for studying samples at very high
magnifications (>500000X)
Intransmission. The
200kV system is equipped with a LAB6 filament and has EDS andElectronEnergy
Loss Spectroscopy attachments.The transmission electron microscopes(TEMs)
aredesigned to offer a truly universal imaging and analysis solution for
lifesciences, materialssciences, nanotechnology, and the semiconductor and data
storageindustries.
A TEM consist of
four parts:electron source, electromagnetic lens system, sample holder,
andimaging System.
Electron source
The electron source consists of a cathode and an anode. The
cathode is a tungsten filamentwhich emits electrons when being heated. A
negative cap confines the electrons into a looselyfocused beam. The beam is
then accelerated towards the specimen by the positive anode.Electrons at the
rim of the beam will fall onto the anode while the others at the center will
passThrough the small hole of the anode. The electron source works like a
cathode ray tube.
Electromagnetic lens system
After leaving the electron source, the electron beam is tightly
focused using electromagneticlens and metal apertures. The system only allows
electrons within a small energy range to passthrough, so the electrons in the
electron beam will have a well-defined energy.Magnetic Lens: Circular
electro-magnets capable of generating a precise circular magneticfield. The
field acts like an optical lens to focus the electrons.Aperture: A thin disk
with a small (2-100 micrometers) circular through-hole. It is used torestrict
the electron beam and filter out unwanted electrons before hitting the specimen.
Sample holder
The sample holder is a platform equipped with a mechanical arm for
holding the specimen andcontrolling its position.
Imaging system
The imaging system consists of another electromagnetic lens system
and a screen. Theelectromagnetic lens system contains two lens systems, one for
refocusing the electrons afterthey pass through the specimen, and the other for
enlarging the image and projecting it ontothe screen. The screen has a
phosphorescent plate which glows when being hit by electrons.Image forms in a
way similar to photography
Transmission Electron Microscope
Sample preparation:
1 mg of as synthesized powders was well dispersed in 10 ml of
Tetrahydrofuran by ultra-sonication for 10 min to make the transparent
solutions. And place a drop of solution onto thecopper grid and air dried.
ENERGY DISPERSIVE
ANALYSIS OF X-RAY (EDAX)
Energy dispersive X-ray spectroscopy (EDS or EDX) is an analytical
technique used for the elemental analysis or chemical characterization of a
sample. It is one of the variants of X-ray fluorescence spectroscopy which
relies on the investigation of a sample through interactions between
electromagnetic radiation and matter, analyzing X-rays emitted by the matter in
response to being hit with charged particles. Its characterization capabilities
are due in large part to the fundamental principle that each element has a
unique atomic structure allowing Xrays that are characteristic of an element's
atomic structure to be identified uniquely from one another.
To stimulate the emission of characteristic X-rays from a specimen,
a high-energy beam of charged particles such as electrons or protons (see
PIXE), or a beam of X-rays, is focused into the sample being studied. At rest,
an atom within the sample contains ground state (or unexcited) electrons in
discrete energy levels or electron shells bound to the nucleus. Theincident
beam may excite an electron in an inner shell, ejecting it from the shell while
creatingan electron hole where the electron was. An electron from an outer,
higher-energy shell thenfills the hole, and the difference in energy between
the higher-energy shell and the lower energyshell may be released in the form
of an X-ray.As the energy of theX-rays are characteristic of the difference in
energy between the two shells, and of the atomicstructure of the element from
which they were emitted, this allows the elemental compositionof the specimen
to be measured.
1 comments:
commentsThe electrons interact with the atomsthat make up the sample producing signals that contain information about the sample's surfacetopography, composition and other properties such as electrical conductivity. Nanoparticle Characterization Techniques
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