Thereby showing a unique diffraction phenomenon corresponding to the crystal structure. Diffraction X-ray satisfies Bragg equation: 2dsinθ=nλ where λ is the wavelength of X-ray; θ is the diffraction angle; D is the crystal plane spacing; N is an integer. The wavelength λ can be measured by the known X-ray diffraction angle, and then the plane spacing, that is, the regular arrangement of atoms or ions in the crystal can be obtained.
By comparing the calculated diffraction X-ray intensity and surface spacing with the known table, the material structure of the sample crystal can be determined, which is qualitative analysis. From the comparison of diffraction X-ray intensity, quantitative analysis can be made.
The characteristic of this method is that it can obtain the compound state of elements and the way of atoms combining with each other, so it can be used for valence state analysis and phase identification of environmental solid pollutants, such as aeolian sand and soil components in atmospheric particles, metals and their compounds (dust) emitted by industry, lead halide components in automobile exhaust, and the state of metals in water sediments or suspended solids.
Extended data:
First, the development direction
With the new development of X-ray analysis and the popularization of equipment and technology, metal X-ray analysis has gradually become a routine method for metal research and testing of organic materials and nanomaterials. It can also be used for dynamic measurement. Photography is often used in the early days, which takes a long time and has low accuracy of force measurement.
The inverse diffractometer method, which came out in the early 1950s, has been widely used because of its advantages of fast and accurate strength measurement and computer control. However, the photographic method using monochromator still has its own characteristics in trace sample analysis and exploring unknown new phases.
Since 1970s, with the appearance of high-intensity X-ray sources (including ultra-high-intensity rotating anode X-ray generator, electron synchrotron radiation and high-voltage pulsed X-ray source) and the application of computer analysis, metal X-rays have gained new impetus. The combination of these new technologies can not only greatly accelerate the analysis speed and improve the accuracy, but also make instantaneous dynamic observation and study weak or fine effects.
Second, the scope of application
The X-ray diffraction image of crystal is essentially a fine and complex transformation of crystal microstructure. The structure of each crystal corresponds to its X-ray diffraction pattern one by one, and its characteristic X-ray diffraction pattern will not change because other substances are mixed together, which is the basis of X-ray diffraction phase analysis method.
It has become the basic method of phase qualitative analysis to prepare and standardize the diffraction patterns of various standard single-phase substances and compare the diffraction patterns of the substances to be analyzed, so as to determine the constituent phases of the substances.
After identifying each phase, various components can be quantitatively analyzed according to the fact that the intensity of each phase diagram is proportional to the amount of recombinant components (except those that need absorption correction). At present, the diffraction pattern is usually obtained by diffractometer, and the phase is analyzed by powder diffraction card (PDF card) edited and published by JCPDS.
Baidu Encyclopedia -X-ray diffraction analysis