SpectroscopIC aNALYSIS Part 7 – X-ray Analysis Methods Chulalongkorn University, Bangkok, Thailand January 2012 Dr Ron Beckett Water Studies Centre & School of Chemistry Monash University, Melbourne, Australia Email: Ron.Beckett@monash.edu Water Studies Centre 1 X-ray Analysis Methods • Properties of X-radiation • X-ray diffraction • X-ray emission spectroscopy • Production of X-radiation in an X-ray tube • X-ray fluorscence 2 Properties of X-radiation • Frequency n 3x1016 – 3x1018 Hz • Wavelength l 10 nm – 100 pm • High energy radiation, damaging to biological cells • High penetration of materials due to low absorbance is useful in medicine (body X-rays) and material science (fracture detection) 3 4 X-ray Imaging in Medicine and Dentistry 5 X-ray Diffraction by Crystals X-rays are reflected from planes of atoms in the crystal lattice of compounds 6 X-ray Diffraction by Crystals X-rays reflected from two planes of atoms in the crystal lattice constructively interfere only when the path length difference is an integral number of wavelengths For waves 1 and 2 path lengths BC + CD = l , 2 l , 3l , ...., n7 l X-ray Diffraction by Crystals This condition results in the following law for X-ray diffraction by crystals 8 X-ray Powder Diffraction Patterns Direction of incident beam Diffracted beams Random orientation of crystals in the powder 9 X-ray Powder Diffraction Camera 10 X-ray Powder Diffraction Camera 11 X-ray Powder Diffractometer 12 X-ray Powder Diffractometer 13 X-ray Powder Diffraction Patterns are used to identify crystalline materials and to determine the amount of each phase in a mixture 14 Single Crystal X-ray Crystallography Analysis of the geometry and intensity of spots enables the crystal and molecular structure of compounds to be determined 15 X-ray Studies Lead to the Discovery of the Double Helix Structure of DNA Rosalyn Franklin 16 Single crystal X-ray pattern of DNA Single Crystal X-ray Diffraction Monochrometers 17 Single Crystal X-ray Diffraction Monochrometers 18 X-ray Emission Spectrometer Excitation Source electrons protons X-rays g-rays Monochrometer 19 X-ray Emission Excitation Source electrons protons X-rays g-rays X-ray Emission 20 X-ray Emission 21 X-ray Emission Energy Jumps Excitation Emission Emission 22 X-ray Emission Energy Jumps 3d 3p 3s 2p 2s 1s 23 X-ray Emission Spectroscopy X-ray emission spectrum of a Ni compound the exact position and intensity of the peaks can give information about the oxidation state and bonding 24 Production of X-radiation in an X-ray Tube 1. High voltage extracts electrons from the anode and accelerates them towards the metal cathode 2. These high energy collisions eject electrons from inner atomic orbitals of the metal High Voltage ~100,000 V + Metal Target e- _ X-radiation Frequency depends on target metal 25 Production of X-radiation in an X-ray Tube 26 X-ray Tube 27 Production of X-radiation in an X-ray Tube High energy electron accelerated by voltage e- .. . .. . e- High energy electron after collision with metal atom in the target e- .. . .. . Inner shell electron ejected from the metal atom in the target .. .. . 28 Production of X-radiation in an X-ray Tube EX-ray = hn = DEelectron .. .. . . . .. . 29 X-ray Fluorescence Atomic Fluorescence 1. Excitation by X-rays ejects electrons from inner orbitals of atoms 2. Electrons from higher orbitals jump back to fill vacancies 3. Emission of fluorescence X-rays occurs 4. EExcitation = hnEx eKE = 1/2mv2 e- EFluorescence = hnFl e- Results in Stokes shift to longer wavelength (lower energy since EFluorescence < EExcitation). 30 X-ray Fluorescence Instrument X-ray Excitation Source Monochrometer X-ray Tube + e- _ Detector EExcitation = hnEx X-ray Emission EFluorescence = hnFl Sample 31 X-ray Fluorescence Spectrometer 32 X-ray Fluorescence Analysis • The fluorescence frequencies can be used to identify the elements in the sample • The intensity of the fluorescent X-ray beam is used to determine the concentration of specific elements using callibration standards 33 Thank You for your Attention ! 34