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Engineering Assignment 代写 Powder X Ray Diffraction

Engineering Assignment 代写  Powder X Ray Diffraction



The discovery of X-rays in 1895 enabled scientists to probe crystalline structure at the atomic level. X-rays are electromagnetic radiation of wavelength about 1 Å (10-10 m), which is about the same size as an atom. They occur in that portion of the electromagnetic spectrum between gamma-rays and the ultraviolet.

Powders of crystalline materials diffract x-rays. A beam of x-rays passing through a sample of randomly-oriented microcrystal produces a pattern of rings on a distant screen. Powder x-ray diffraction provides less information than single-crystal diffraction, however, it is much simpler and faster. Powder x-ray diffraction is useful for confirming the identity of a solid material and determining crystallinity and phase purity.

What is X-ray Powder Diffraction (XRD)

X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely ground, homogenized, and average bulk composition is determined.

X-ray diffraction has been in use in two main areas, for the fingerprint characterization of crystalline materials and the determination of their structure.

Each crystalline solid has its unique characteristic X-ray powder pattern which may be used as a “fingerprint” for its identification. Once the material has been identified, X-ray crystallography may be used to determine its structure, i.e. how the atoms pack together in the crystalline state and what the interatomic distance and angle are etc. X-ray diffraction is one of the most important characterization tools used in solid state chemistry and materials science.

We can determine the size and the shape of the unit cell for any compound most easily using the diffraction of x-rays.

Fundamental Principles of X-ray Powder Diffraction (XRD)

X-ray diffraction is now a common technique for the study of crystal structures and atomic spacing.

X-ray diffraction is based on constructive interference of monochromatic X-rays and a crystalline sample. These X-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation, collimated to concentrate, and directed toward the sample. The interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy Bragg’s Law (nλ=2d sin θ). This law relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample. These diffracted X-rays are then detected, processed and counted. By scanning the sample through a range of 2θangles, all possible diffraction directions of the lattice should be attained due to the random orientation of the powdered material. Conversion of the diffraction peaks to d-spacing allows identification of the mineral because each mineral has a set of unique d-spacing. Typically, this is achieved by comparison of d-spacing with standard reference patterns.

All diffraction methods are based on generation of X-rays in an X-ray tube. These X-rays are directed at the sample, and the diffracted rays are collected. A key component of all diffraction is the angle between the incident and diffracted rays. Powder and single crystal diffraction vary in instrumentation beyond this.

Engineering Assignment 代写  Powder X Ray Diffraction