Presentation on x ray diffraction

XRD- an advanced method of determining the composition of any substance.

1. X-RAY DIFFRACTION OF CLAY MINERALS Presented By:- Shaheen Praveen M.Sc. (Ag.) Deptt . of SS&AC College of Agriculture, IGKV Raipur

2. INTRODUCTION

3. Continue… X -ray diffraction analysis is one of the principle method involved in identification of clay minerals by using specific properties of clay minerals . X-ray diffraction is a technique that provides detailed information about the atomic structure of crystalline substances. It is a powerful tool in the identification of minerals in rocks and soils

4. PRINCIPLE When a focused X-ray beam interacts with planes of atoms, part of the beam is transmitted, part is absorbed by the sample, part is refracted and scattered, and part is diffracted . Diffraction of an X-ray beam by a crystalline solid is analogous to diffraction of light by droplets of water, producing the familiar rainbow. X-rays are diffracted by each mineral differently, depending on what atoms make up the crystal lattice and how these atoms are arranged . When an X-ray beam hits a sample and is diffracted, we can measure the distances between the planes of the atoms that constitute the sample by applying Bragg's Law, named after

5. Continue… Willium Lawrence Bragg, who first proposed it in 1921. Bragg's Law is: nλ =2d sinθ ,   where the integer n is the order of the diffracted beam, is the wavelength of the incident X-ray beam, d is the distance between adjacent planes of atoms (the d- spacings ), and is the angle of incidence of the X-ray beam. The geometry of an XRD unit is designed to accommodate this measurement. The characteristic set of d- spacings generated in a typical X-ray scan provides a unique "fingerprint" of the mineral or minerals present in the sample. When properly interpreted, by comparison with standard reference patterns and measurements, this "fingerprint" allows for identification of the material.

6. PROCEDURE Generation of X-rays X- ray diffraction Detection X-ray diffraction analysis

7. Generation of X-rays In X-ray diffractometry, X-rays are generated within a sealed tube that is under vacuum . A current is applied that heats a filament within the tube; the higher the current the greater the number of electrons emitted from the filament . This generation of electrons is analogous to the production of electrons in a television picture tube . A high voltage, typically 15-60 kilovolts, is applied within the tube. This high voltage accelerates the electrons, which then hit a target, commonly made of copper . When these electrons hit the target, X-rays are produced. The wavelength of these X-rays is characteristic of that target.

8. Working Principle

9. Working Principle

10. X-RAY DIFFRACTION X-ray diffraction occurs when X-rays are scattered by atoms arranged in an orderly array in crystals. The atoms serve as scattering centers (Moore and Reynolds, 1997), re-emitting X-rays at the same wavelength as the incident radiation in all directions (coherent scattering). The orderly arrangement of atoms results in the scattered X-rays within the crystal being ( i ) in phase in specific directions dictated by symmetry and atomic spacings and (ii) out of phase in all other directions . The X-rays that are in phase constructively interfere and emerge as intense beams (diffracted beams) from the crystal, while those that are out of phase destructively interfere and hence have minimal emergence. This systematic combination of constructive and destructive interference arising from the pe­riodicity of atoms in crystals is X-ray diffraction.  

11. X-ray Diffraction

12. DETECTION A detector detects the X-ray signal; the signal is then processed either by a microprocessor or electronically, converting the signal to a count rate. Changing the angle between the X-ray source, the sample, and the detector at a controlled rate between preset limits is an X-ray scan.

13. X-RAY DIFFRACTION ANALYSIS Obtaining useful information from XRD requires the ability to control and/or measure angular relations between incident and diffracted radiation. Two types of instruments have been used to perform X-ray diffraction analysis: the XRD powder camera and the X-ray diffractometer. The powder camera approach entails recording diffraction maxima “cones” on cylindrically mounted photographic film surrounding the specimen . The diffractometer records the intensity of the diffracted beam electronically at precise angles as the specimen is scanned over an angular range . Modern diffractometers have a number of advantages over the powder camera and are the more commonly used instru­ments in soil mineralogy. Therefore , the diffractometer approach will be emphasized in this chapter, but the d-spacing and intensity data obtained from either type of instrument are interpreted the same way.

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