x ray diffraction

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diffraction methods

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X-RAY DIFFRACTION:

X-RAY DIFFRACTION HEMANTH.GAMPALA, M.PHARM, PHARMACEUTICAL ANALYSIS . BY

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INTRODUCTION : ORIGIN OF X-RAYS INTERACTION OF X-RAYS WITH MATTER METHODS INSTRUMENTATION X-RAY DIFFRACTION METHODS APPLICATIONS

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INTRODUCTION: X-rays are a form of light. They are in fact more energetic than the visible light. X-radiation is part of the electromagnetic spectrum, just like visible light, radio waves, microwaves, etc. Here's a schematic of the whole spectrum

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As the wavelengths of light decrease, they increase in energy. X-rays have smaller wavelengths and therefore higher energy than ultraviolet waves .

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OUT LINE ORIGIN OF X-RAYS: study about atom and its shells INTERACTION OF X-RAYS WITH MATTER Absorption 2. Diffraction 3 MAIN METHODS : x-ray absorption method x-ray diffraction method x-ray fluorescence method

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ORIGIN OF X RAYS: High velocity of electrons bombarded on metal target x rays are produced.

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INTERACTION OF X RAY WITH MATTER: In 3ways: ABSORPTION: x rays Matter Loss energy by scattering Absorption take place. Incoming X-rays Secondary emission

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Follows beers law i = i o e- µ lp i 0 = intensity of incident x ray i = intensity after absorption l = thickness of material µ = mass absorption co-efficient p = density of absorption material.

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Mass absorption co-efficient: (µ ) is a measurement of how strongly a chemical species absorbs or scatters light at a given wavelength µ = CN/A λ C =Proportional constant N= Avogadro's number A= Atomic weight λ = wavelength of x rays.

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2. Scattering and diffraction: concept: x ray beam substance Contain electrons Absorption Oscillation Emits EM radiations in form of waves Waves under go constructive interference Diffracted by crystal plane.

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Sets Electron cloud into oscillation Sets nucleus (with protons) into oscillation Small effect  neglected

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Oscillating of electrons with the incoming x-rays

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n λ = AP+PC AP = PC = l n λ = l + l =2l But triangle OPA, l = d sin θ n λ =2d sin θ  = angle of incidence d = space between plans n = integer(1,2,3…etc) Millers: n λ =2d hki sin θ BRAGGS LAW

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METHODS: 1 . X-ray absorption method : imperfection of internal structure. A beam of x rays is passed Sample X ray photons absorbed by substance Measuring concentration of absorbing substance. Use : elemental analysis, thickness measurement.

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2. X ray diffraction method: x rays fall on sample (crystal) Scattering of x rays. Use: crystal structure. 3.X ray fluorescence method: X ray fall on Sample Emits x ray beam.

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Wavelength: determine which element is present in sample. Intensity: determine how much is present. Use: qualitative and quantitative elemental analysis Above 3 methods are non destructive.

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INSTRUMENTATION: PRODUCTION OF X-RAYS COLLIMATOR MONOCHROMATOR filter crystal monochromator DETECTORS

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INSTRUMENTATION: Amplifier recorder

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Collimator: Close metal plates separated by small gap Use is to produce narrow beam(pencil rays) Monochromator : Absorbs the undesirable radiations and allows required wavelength to pass. Types: 1.filter: eg : zirconium 2.crystal: eg : sodium chloride , lithium fluoride. PRODUCTION OF X RAYS High velocity of electrons bombarded on metal target x rays are produced

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DETECTORS Photographic. Counter method: types Geiger- muller tube counter Proportional counter Scintillation counter Solid state semiconductor counter Semiconductor

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Geiger muller tube counter : :

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Scintillation detector :

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X-RAY DIFFRACTION METHODS: investigation of internal structures. Laue photographic Bragg X-ray spectrometer Rotating crystal Power metho d

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.Laue photographic: 2 types: Transmission method Back reflection method 1 Transmission method:: In this method the crystal is held stationary in a beam of x-rays , after passing through the crystal is diffracted and is recorded on a photographic plate.

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2.Back reflection method : This method provides similar information as the transmission method.

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Bragg’s X-ray spectrometer Bragg’s x-ray spectrometer method: Using the Laue’s photograph, Bragg analyzed 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: nλ =2d sin θ.

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For measurement of λ : Wave length of x rays can determine by following equation: 2dsin θ =n λ λ /d is lattice constant. Knowing d, wavelength λ can determined. Measurement of d: d = a∫ 2 /2 for simple cubic lattice. d = a/2 Fcc crystal lattice . d = a∫ 3 /2 for bcc crystal lattice . simple cubic lattice bcc crystal lattice Fcc crystal lattice

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Where (a) can calculated by m wt Х no.of atoms in unit cell 1/3 a = Avogadro no. Х density for Nacl crystal. d is calculated Belongs to fcc crystal Four atom in a unit cell Its density is 2.18g/cc Molecular wt is 58.5 Avogadro no is 6.02 Х 10 23

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58.5 Х 4 1/3 a = = 5.63 Х 10 -8 cm 6.02 Х 10 23 x 2.18 For fcc lattice: a 5.63 Х 10 -8 d = 2 = 2 = 2.815 Х 10 -8 cm d = 2.815A 0

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d100:d110:d111= 1 : 1 : 1 for simple cubic lattice ∫ 2 ∫ 3 d100:d110:d111= 1 : 1 : 1 for fcc crystal ∫ 2 ∫ 3 d100:d110:d111= 1 : 1 : 1 for bcc crystal ∫ 2 ∫ 3 Light is passed at angles 5.9 0 ,8.4 o ,5.20 0 DETERMINATION OF CRYSTAL STRUCTURE BY BRAGGS LAW: Ratio of spacing for the planes can be obtained. Space will be different for different crystals. For NACL crystal:

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d100:d110:d111 = 1 1 1 sin5.9 sin8.4 sin5.2 = 1 1 1 0.1028 0.146 0.0906 = 1: 0.704 : 1.155 = 1 : 1 : 1 ∫ 2 ∫ 3

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Rotating crystal: 2 types 1.Complete rotation method: occurs in a series of complete revolutions 2.Oscillation method: oscillated through an angle 15 to 20 o

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Powder method:

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Different cones for different reflections Cone of diffracted rays

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Compared to other methods the sample used in this method is low quantity that is 1mg. By using this formula, the crystal nature can be studied Θ = 360 x 1 / π r Where , Θ = Angle of incidence 360 = scattering angle R = film radius. Used for: Cubic crystals Determination of complex structures of alloys and metals.

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APPLICATIONS: STRUCTURE OF CRYSTALS Non-destructive method Molecular structure and size of crystal. POLYMER CHARACTERISATION Powder method determines degree of crystalinity of the polymer. Non crystalline portion scatters the x ray beam gives continuous background. Crystaline portion causes diffraction lines that are not continuous Amorphous materials: causes scattering. Crystal materials : causes diffraction

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STATE OF ANNEAL IN METALS Well annealed metals-sharp diffraction lines If subjected to hammering or bending-diffused diffraction pattern PARTICLE SIZE DETERMINATION a)Spot counting method: particles above 5microns b)Broadening of diffraction lines particles of the range 30-1000A o

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APPLICATION TO COMPLEXES a)Determination of cis -trans isomerism b)Determination of linkage isomerism MISCELLANEOUS APPLICATIONS a)Soil classification based on crystallinity b)Analysis of industrial dusts c)Assessment of weathering and degradation of natural and synthetic minerals d)Study of corrosion products e)Examination of tooth enamel and dentine f)Effects of diseases on bone structure.