Diffraction of an X-ray beam by a crystalline solid is analogous to diffraction of light by droplets of water, producing the familiar rainbow. When a focused X-ray beam interacts with these planes of atoms, part of the beam is transmitted, part is absorbed by the sample, part is refracted and scattered, and part is diffracted. The three-dimensional structure of nonamorphous materials, such as minerals, is defined by regular, repeating planes of atoms that form a crystal lattice. In this configuration, the X-ray tube and the detector both move through the angle theta ( ), and the sample remains stationary. Simplified sketch of one possible configuration of the X-ray source (X-ray tube), the X-ray detector, and the sample during an X-ray scan. XRD does not, however, provide the quantitative compositional data obtained by the electron microprobe or the textural and qualitative compositional data obtained by the scanning electron microscope.įigure 1. Some mineralogical samples analyzed by XRD are too fine grained to be identified by optical light microscopy. Other information obtained can include the degree of crystallinity of the mineral(s) present, possible deviations of the minerals from their ideal compositions (presence of element substitutions and solid solutions), the structural state of the minerals (which can be used to deduce temperatures and (or) pressures of formation), and the degree of hydration for minerals that contain water in their structure. If the sample is a mixture, XRD data can be analyzed to determine the proportion of the different minerals present. XRD can provide additional information beyond basic identification. XRD is particularly useful for identifying fine-grained minerals and mixtures or intergrowths of minerals, which may not lend themselves to analysis by other techniques. XRD provides the researcher with a fast and reliable tool for routine mineral identification. In many geologic investigations, XRD complements other mineralogical methods, including optical light microscopy, electron microprobe microscopy, and scanning electron microscopy. One of these methods, X-ray powder diffraction (XRD), is an instrumental technique that is used to identify minerals, as well as other crystalline materials. Numerous analytical techniques are used to characterize these materials. Rocks, sediments, and precipitates are examples of geologic materials that are composed of minerals. Examples of applications of this method to geologic studies are provided. This handout provides background on the use and theory of X-ray powder diffraction. USGS Information Handout: X-Ray Powder Diffraction X-Ray Powder Diffraction
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |