X-Ray diffraction Spec methods for analysis
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X-rays were discovered in 1895 by Wilhelm Röntgen. X-rays are produced when high velocity electrons hit a metal target, knocking electrons out of inner shells of atoms within the target. As outer electrons fall into these vacancies, characteristic X-rays are emitted with energies specific to the element. X-ray diffraction methods like Bragg's law are used to analyze crystal structures of materials by detecting the angles and intensities of diffracted X-ray beams. Common applications include determining structures of polymers, particle sizes, and states of materials.
X-Ray diffraction Spec methods for analysis
- 1. INTRODUCTION X –RAYS: The X-ray region of electromagnetic spectrum consists of shortest wavelength in the region of about 0.1 to 100AO For analytical purposes ,the range of 0.7 to 2.0AOis mostly used. 2
- 2. Radiotherapy X-ray fluorescence method X-ray diffraction (or) crystallography X-ray absorption (or) radiography CLASSIFICATION OF X-RAY METHODS 3
- 3. DISCOVERY X-rays were discovered by W.C.Rontgen is a german physicist in 1895. For his work Rontgen awarded the first ever Nobel prize for physics in 1901 4
- 4. ORIGIN OF X-RAYS X-rays are generated when high velocity electrons impinge on a metal target . The process of producing X-rays may be visualized in terms of Bohr’s theory of atomic structure. 5
- 5. Whenever a fast moving electron impinges on an atom, it may knock out an electron completely from one of the inner shells of that atom. Following the loss of inner-shell electron one of the outer electrons will fall in to the vacated orbital ,by the emission of x-rays. 6
- 6. The energy of the emitted X-ray photon is equal to the difference in energy between two levels involved. E = E2-E1 E2 and E1 are the final and initial energies which are emitted from L and K shells respectively If the vacancy produced in the K-shell is filled by the electron from L-shell, the radiation is called Kὰ . Electron from M-shell it is called Kβ. 7
- 7. The frequency of emitted radiation is given by ϑ= Z² (2∏2me/h3)(1/N1 2 –1/N2 2 ) Z = Atomic number of an atom m = mass of the electron e = charge of the electron h = plank's constant N1 , N2 =1 & 2 for K&L shell 8
- 8. TYPES OF RADIATION 1) BREHMSSTRAHLUNG (OR) BRAKING RADIATION: 9
- 10. X-RAY DIFFRACTION INTRODUCTION THEORY INSTRUMENTATION METHODS OF X –RAY DIFFRACTION APPLICATIONS 11
- 11. In 1912 von Laue placed a crystal of copper sulphate between a white x-ray source and photographic plate The resulting photograph observed here: 12
- 13. DIFFRACTION 14
- 14. BRAGG’S LAW Bragg’s equation is n=2dsinө Constructive interference occurs only when n=AB+BC AB=BC n=2AB Sinө=AB/d n=2dsinө =2dhklsinөhkl 15
- 15. IN PHASE OUT OF PHASE 16
- 17. GENERATION OF X-RAYS X-rays are generated when high velocity of electrons impinge on a metal target. Approximately 1% of total energy of electron beam is converted in to x –radiation. Two type of devices are used for generating x-rays 1) X-ray tube 2) Synchrotron radiation 18
- 18. X-ray tubes: Side window tube End window tube 19
- 19. Synchrotron radiation Synchrotron radiation is emitted by electron and positrons travelling at near light speed in circular storage ring. Powerful sources which are thousands to millions of times more intense than x-ray tubes. 20
- 20. COLLIMATOR The x-rays produced by the target material are randomly directed. In order to get a narrow beam of x-rays ,they are allowed to pass through a collimator which consist of two sets of closely packed metal plates separated by a small gap. The collimator absorbs all the x-rays except the narrow that passes between the gap. 21
- 21. MONOCHROMATORS Mainly two types: a)FILTERS: It is a window of material that absorbs undesirable radiation but allows the radiation of wave to pass. e.g. :Zirconium filter which is used for molybdenum radiation. 22
- 22. some more examples of beta filters: b)Crystal monochromators 1)Flat crystal monochromator 2)Curved crystal monochromator TARGET ELEMENT ß-FILTERS THICKNESS %LOSS IN K∞ INTENSITY Co Fe 0.012 39 Cu Ni 0.015 45 Fe Mn 0.011 38 Mo Zr 0.081 57 Ni Co 0.013 42 23
- 23. CRYSTAL MONOCHROMATOR: The beam is split into component wavelength by the crystal line material such material is called as Analyzing crystal. Crystals used in monochromators are sodium chloride, lithium fluoride, quartz etc. 24
- 24. DETECTORS 1) photographic method 2)counter methods a) Geiger - Muller tube method b) proportional counter c) scintillation detector d) solid-state semiconductor detector e)semi conductor 25
- 25. PHOTOGRAPHIC METHOD PRINCIPLE : By using plane or cylindrical film Developing the film D=log Io/I D is the total energy Measured by using densitometer USES: For diffraction studies For quantitative measurement DIS ADVENTAGES: Time consuming 26
- 26. SCINTILLATION DETECTOR Its mainly contains a large crystal of sodium iodide activated with small amounts of thallium. They convert incident x-rays in to visible light which is detected by photo multiplier tube. e.g. for crystals : sodium iodide , anthracene, naphthalene ,p- terpenol in xylene. Used for short wavelengths 27
- 27. PROPORTIONAL COUNTER METHOD: It is filled with heavier gas like xenon ( or) krypton it is preferred because it is easily ionized. More efficiency and sensitive 28
- 28. GIEGER MULLER COUNTER PRINCIPLE: Ionization of argon gas which is filled in the Geiger tube by x-rays. ADVANTAGES: In expensive Trouble-free DISADVANTAGES: only for counting low rates Efficiency will be less 29
- 29. SOLID- STATE SEMI CONDUCTOR DETECTOR: Electrons produced by x-ray beams are converted in to conduction bands ,the current which flows is directly propotional to incident x-rays. SEMI CONDUCTOR DETECTOR: A pure silicon block set up with a thin film lithium metal placed on to one end. Semi conductor 30
- 30. X-RAY DIFFRACTION METHODS 1) SINGLE CRYSTAL DIFFRACTOMETER: A) LAUE METHOD a)TRANSMISSON METHOD b)BACK REFLECTION METHOD B) BRAGG’S SPECTROPHOTOMETER METHOD 2)POWDER CRYSTAL DIFFRACTOMETER 31
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- 39. 3)PARTICLE SIZE DETERMINATION: a)Spot counting method: b)Broadening of diffraction lines c)Low-angle scattering 4)APPLICATIONS OF DIFFRACTION METHODS TO COMPLEXES: a)Determination of cis-trans isomer b)Determination of linkage isomer 40
- 40. 5)STATE OF ANNEAL IN METALS : Well annealed metals are in well ordered crystal form and give sharp diffraction lines. If the metal breaking is present then the x-ray pattern more diffuse. 6)MISCELLANEOUS APPLICATIONS: Soil classification based on crystallinity Analysis of industrial dusts Weathering and degradation of naturals and synthetic minerals Corrosion products can be studied by this method Tooth enamel and dentine have been examined by X-ray diffraction. 41
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- 42. PANALITICAL XPERT INSTRUMENT Features: X-ray source: Philips high intensity ceramic sealed tube (3kW) Wavelength: Cu Ka (1.5405 Å) Incident beam optics: 2 interchangeable fixed slits and one Soller slit. Diffracted beam optics: fixed slit plus programmable receiving slit, graphite analyzer Detectors: sealed proportional counter and X'celerator PSD for high speed data collection Sample stage: powder stage, texture cradle with sample translation Software: Philips X’PERT suite: Data Collector, Graphics & Identify, Texture XPERT Powder (I) - for high-speed phase identification XPERT Thin Film (II) - for thin film, grazing-incidence XRD, texture measurement 43
- 43. REFERENCES Remington 21st edition pg.no.481 Instrumental methods of chemical analysis by Gurdeep. R. Chatwal ,12th chapter,pg.no.2.303-2.339 Analytical chemistry by Clive Whiston (x-ray methods) 44