X-Ray powder diffraction: X-Ray powder diffraction A.Solairajan, 1 st year, M.pharm(analysis). Outline of XRD:-: O utline of XRD:- Introduction What is X-Ray? Basic principle Instrumentation X Ray diffraction methods Applications. Introduction:-: Introduction:- X-Rays are electromagnetic radiation with wavelengths in the range 0.1 - 100 Å (0.01-10nm) X Rays used in diffraction experiments have typical wavelengths of 0.5 - 1.8 Å X-rays were discovered by Wilhelm Roentgen who called them X-rays and it also called as Roentgen rays . X-ray diffraction was discovered by Max von Laue in 1912. X-Ray region:-: X-Ray region:- Basic principle:-: Basic principle:- In an atom, the electrons are arranged in layers or shells, like K-shell L-shell M-shell N-shell Contd…: C ontd … When the atom is bombarded with an electron, eject one of the electron from the inner shell. The electrons migrate from the outer shell to the inner shell to fill the gap with higher energy. A quantum of radiation (X-rays)is emitted corresponding to this transition , time scale is approximately 10 -12 -10 -4 sec. Emitted radiation is called X-rays. Theory of X-rays:-: T heory of X-rays:- Inner orbit Outer orbit Emitted radiation as X-rays Theory of X-Rays:-: Theory of X-Rays:- Generation of X-rays:-: Generation of X-rays:- X-rays are obtained in three ways. By bombardment of metal target with a beam of high energy electrons. By exposure of a substance to a primary beam of X-rays in order to generate a secondary beam of X-ray fluorescence . By use of radioactive source decay process results in X-ray emission . Generation of X-Rays:-: Generation of X-Rays:- X-Ray techniques:-: X-Ray techniques:- There are four methods available. X-ray absorption methods X-ray Emission methods X-ray fluorescence methods X-ray diffraction methods. PowerPoint Presentation: X-Ray absorption methods:- A beam of X-rays is allowed to pass through the sample and fraction of X-ray photons absorbed is considered to be a measure of the concentration of the absorbing substance. X-Ray emission methods:- X-ray are obtained by employment of radioactive source whose decay process results in emission. PowerPoint Presentation: X-ray fluorescence:- In these methods, X-rays are generated within the sample and by measuring the wavelength and intensity of the generated X-rays, one can perform qualitative and quantitative analysis. X-ray diffraction:- These methods are based on the scattering of x-ray by crystals. This method is used to identify the crystal structures of various solid compounds. X-ray absorption method:-: X-ray absorption method:- A beam of X-ray is passed to the sample X-ray photons absorbed by the substance. Measuring the concentration of absorbing substance. Applications:- Elemental analysis such as barium and iodine in the body X-ray fluorescence:-: X-ray fluorescence:- Beam of X-ray fall on sample Emits secondary X-ray Fluorescent X-ray Intensity of X-ray provides how much is present Applications:- Elemental analysis. Instrumentation:-: Instrumentation:- X-ray tube Collimator Monochromator Filter Crystal monochromator Detectors Instrumentation:-: Instrumentation:- X-ray tube:- High velocity of electrons bombarded on metal target, X-rays are produced. Collimator:- Close metal plates separated by small gap. Use is to produce narrow beam. Monochromator :- Absorbs the undesirable radiations and allows required wavelength to pass. Filter -E.g. Zirconium Crystal -E.g. Sodium chloride, Lithium fluoride PowerPoint Presentation: Detectors:- Photographic methods Counter methods Types:- Geiger- muller counter proportional counter Scintillation counter Solid state semiconductor counter Semiconductor X-ray diffraction:- : X-ray diffraction:- When X-rays interact with a solid material, the scattered beams can add together in a few directions and yield diffraction. X-ray diffraction principle:-: X-ray diffraction principle:- X-ray diffraction is based on constructive interference of monochromatic x-rays and a crystalline sample. These x-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation ,collimated to concentrate and directed towards the sample. The interaction of incident rays with the sample produces constructive interference when conditions satisfy Bragg’s law. Bragg's law and Diffraction:-: Bragg's law and Diffraction:- The relationship describing the angle at which a beam of X-rays of a particular wavelength diffracts from a crystalline surface was discovered by William Bragg and Lawrence Bragg and is known as Bragg’s law . X-ray diffraction methods:-: X-ray diffraction methods:- X-ray diffraction method is generally used for investigation on the internal structure. Laue photographic method Bragg X-ray spectrometer method Rotating crystal method Powder method Laue photographic method:-: Laue photographic method:- This method is divided into two types. Transmission method Back Reflection method. PowerPoint Presentation: Transmission method :- A beam of X-ray is passed through the crystal, after passing through the crystal, X-rays are diffracted and recorded on a photographic plate. PowerPoint Presentation: Back reflection method:- This method provides similar information as the transmission method . Bragg's X-ray spectrometer:-: Bragg's X-ray spectrometer:- Using the Laue's photograph, Bragg analysed the structures of crystals of sodium chloride, Kcl . Bragg devised a spectrometer to measure the intensity of X-ray beam. The spectra obtained in this way can be employed for crystallographic analyses. This is based on the Bragg’s equation: n λ = 2dsin ϴ Rotating crystal method:-: Rotating crystal method:- Powder method:-: Powder method:- PowerPoint Presentation: A beam of X-ray beam is fall on to the powedered specimen through slits. The sharp lines to be obtained on the photographic film which is surrounding the powder crystal in the form of circular arc. Powder diffraction patterns are typically plotted as the intensity of the diffracted X-rays vs. the angle 2 θ . Peaks will appear in the diffraction pattern at 2 θ values when constructive interference is at a maximum, when Bragg’s Law is satisfied. n λ = 2 d sin θ Application of X-ray diffraction:-: Application of X-ray diffraction:- Identification of single phase materials-Minerals, chemical compounds,ceramics . Identification of multiple phases in microcrystalline mixtures(rocks). Determination of crystallite size and shape. Crystallographic structural analysis and unit cell calculation for crystalline materials. Particle size determination-Spot counting methods, -Broadening of diffraction lines References:-: References:- Instrumental methods of chemical analysis by Gurudeep R. Chatwal . Wikipedia.org.