Powder x-ray diffraction Oddný Þorbergsdóttir, Oddný Ragnarsdóttir, and Linda Hancock A

Introduction Brief History of X-ray diffraction Theory of X-ray Diffraction Bragg’s Equation Instrumentation How it works Samples Preparation Analysis Spectra A Image: http://www.rcurtis.com/diffraction.jpg

History 1895: Wilhelm Conrad Röntgen discovered X-rays 1912: Max von Laue discovered that crystals behaved as diffraction gratings for X-ray wavelengths similar to the spacing of planes in a crystal lattice Max von Laue was awarded the Nobel Prize for this discovery 1915: William Lawrence Bragg and his father, Sir William Henry Bragg, were awarded the Nobel Prize in physics for their work in determining crystal structures. NaCl, ZnS, and diamond They derived Bragg’s Law A Information/Image: http://electrons.wikidot.com/x-ray-diffraction-and-bragg-s-law

Theory: Bragg’s Law A Image: http://www-outreach.phy.cam.ac.uk/camphy/xraydiffraction/xraydiffraction7_1.htm

Theory: Bragg’s Law When an X-ray beam interacts with a crystal surface at an angle (theta), part of the beam is scattered by the first plane layer of atoms at the surface The unscattered part of the beam penetrates the first plane layer and is scattered by the second layer of atoms, and so on For this diffraction to occur, there are two requirements: 1. The spacing of the planes must be on the same order as the wavelength of the incident radiation 2. The atoms, or scattering centers, must be highly ordered B Information: Skoog, Holler, and Crouch Principles of Instrumental Analysis 6th Ed. Chapter 12A

Instrumentation X-ray Tube Electrons bombard a target metal to induce X-rays The target metal at ISOR is copper Collimators focus the beam by absorbing all but the parallel beams of radiation This reduces noise and ensures the incident beam is coherent Goniometer A rotatable table that allows precise and accurate determination of the angle (theta) between the collimated incident beam and the crystal face B Image: Skoog, Holler, and Crouch Principles of Instrumental Analysis 6th Ed. Chapter 12A

Instrumentation Instrument is housed in a lead glass cabinet Protects the analyst from harmful ionizing radiation Powder samples are not highly ordered, so we do not obtain crystalline structure information, only molecular structure information Spectra from powder x-ray are compared to those in the International Centre for Diffraction Data This is especially useful with geological samples because field samples are not perfect crystals C: Protects women of reproductive age especially. Image: https://s3.amazonaws.com/Bruker/ProductPhotos/736.D8Focus.png

Samples Samples are ground into a powder and wet deposited onto an acrylic sample holder They are then placed onto the sample stage on the instrument Analysis time can take minutes or hours depending on resolution specifications C

Samples C: Peaks represent characteristic x-rays of the sample Calcite deposits

Thank you all for listening C Image: https://image.slidesharecdn.com/xrayproduction2-131113064953-phpapp02/95/xray-production-2-3-638.jpg?cb=1384325470