XRay Powder Diffraction

(Marta J.K Flour, 1997) Theory A non amorphous material consists of a three dimensional structure having atoms in a series of planes separated by a distance. When X-Rays are directed on to this structure, part of it is transmitted the specimen, some part is absorbed, a part is refracted and the rest diffracted. Diffraction of the beam brings out a fingerprint of the crystal lattice which depends on the arrangement of atoms in different planes and the type of mineral in the lattice. (Ron Jenkins, 2000) Applications 1. Apart from identifying the different minerals present it also gives an accurate data regarding the proportion of each of these minerals in the mixture. 2. It is also used in determining the degree of crystalline phase in a mineral and the divergence from its ideal state. 3. Study of secondary minerals helps in ascertaining the degree of solubility of the mineral and the kind of storage facility this would require. 4. Analysis of the under clays lying under coal beds have helped in identifying the nature of environment and climate that existed in these Middle Pennsylvanian regions. Introduction-2 The discovery of x rays by W.C Roentgen in 1895 led to its use in identifying the structure of crystalline materials. In principle a monochromatic beam of x-ray electrons will be dispersed by the atomic electrons and different diffraction patterns are obtained for each plane of crystal lattice. The diffraction pattern that is obtained by using the x ray powder diffraction method is used to identify the various phases in different materials.( James R Connelly, 2007) Theory X rays generated under vacuum conditions are made to impinge on a sample that has been ground into powder of size less than 10 microns. The arrangement of atoms in the crystal lattice causes these electrons to be diffracted by varying degrees. This can therefore be used to ascertain the distances between different planes of atoms by applying Bragg’s law. This ‘fingerprint’ allows in better identification of a material. ( Mike Meier, 2004) Applications 1. Identification of materials chemical compounds and rocks in single phase and multiphase respectively. 2. Ascertaining amorphous materials that are partly in crystalline state. 3. The amount of different phases calculated using peak-ratio calculations 4. These are used in remote sensing study of hydrothermally distorted rocks that are found on several Cascade volcanoes and its study helps in gathering information regarding landslides and mudflows. Introduction-3 X ray powder diffraction method is a non-destructive procedure used in the identification of phases and determination of crystal structure along with its imperfections. All kinds of microcrystalline structures of metals, ceramics, organics and catalysts can found out using this technique which was initially devised by Debye and Scherrer in 1916. Theory Current applied releases electrons from a filament. These electrons are then accelerated at voltages of 60kV onto a copper piece producing x rays on impingement. These x rays are then directed onto a sample that has been ground to fine powder of size less than 10 microns. The diffraction pattern that is obtained can be used to measure the actual distances between crystalline planes using the equations of Bragg’s Law. ( Stock.S.R amp. Cullity B.D, 2001) Applications 1. Ascertain crystal structure of an unknown material and phase identification of high and low temperature phases. 2. Degree of crystalline phase that is present in a material. A crystalline phase presents narrower diffraction peaks compared to amorphous phases. 3. The amount of residual stress that exists in a material after the external load has been removed. 4.