The principle of X-ray diffraction measurement

Overview of X-ray diffraction test:

The material structure can be measured by neutron diffraction, electron diffraction, infrared spectroscopy, Mossbauer spectroscopy and other methods. But X-ray diffraction is an effective and widely used method for material testing, and X-ray diffraction is a method used by humans to study the microstructure of materials. X-ray diffraction has been widely used in physics, chemistry, geosciences, materials science and various engineering technology sciences. It has become an important experimental method and structural analysis means, and has the advantages of non-destructive samples. Now let's specifically understand the relevant principles of X-ray diffraction testing.

Principle of X-ray diffraction test:

X-ray is the use of diffraction principle to accurately determine the crystal structure, texture and stress of materials. Carry out phase analysis, qualitative analysis and quantitative analysis for substances. It is widely used in metallurgy, petroleum, chemical industry, scientific research, aerospace, teaching, material production and other fields.

Characteristic X-ray is an electromagnetic wave with a very short wavelength (about 20~0.06nm), which can penetrate a certain thickness of material, and can make fluorescent materials emit light, photographic emulsion sensitize, and gas ionize. The X-ray produced by bombarding the metal "target" with an electron beam contains the X-ray with a specific wavelength corresponding to various elements in the target, which is called identification X-ray. Considering that the wavelength of X-ray is close to the distance between atoms inside the crystal, the German physicist M. von Laue put forward an important scientific prediction in 1912: crystal can be used as the space diffraction light of X-ray, that is, when a beam of X-ray passes through the crystal, it will be diffracted. The superposition of diffracted waves makes the intensity of the ray strengthen in some directions and weaken in other directions. The crystal structure can be determined by analyzing the diffraction patterns obtained on the photographic negative. This prediction was immediately verified by experiments. In 1913, British physicists Bragg and his son, on the basis of Laue's discovery, not only successfully measured the crystal structures of NaCl, KCl, etc., but also proposed a formula as the basis of crystal diffraction Bragg's law: 2dsin θ= n λ

Where λ Is the wavelength of X-ray, and n is any positive integer. When the X-ray is at a sweep angle θ (The residual angle of the incidence angle, also known as the Bragg angle) When incident on a crystal plane with a lattice spacing of d, under the condition of conforming to the above formula, the diffracted rays strengthened by superposition will be obtained in the reflection direction.

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