Powder X-Ray Diffraction (1 out of 2) 

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Powder X-Ray Diffraction (XRD) allows the determination of crystallographic density and hence crystal structure of unknown crystalline solids. X-rays are diffracted by atoms in a plane and a spherical wave is radiated. If there are two or more such scattering centres, the spherical waves at specific angles reinforce one another (constructive interference) and at other angles cancel one another (destructive interference). A crystal with planes oriented at an angle θ to an incident x-ray beam of wavelength λ will diffract the rays according to Bragg's equation: 2dsinθ = nλ.

 

In video (1 out of 2), the concept of XRD will be illustrated for compound Tungsten which has a BCC structure using planes 110 and 200. 

 

In video (2 out of 2), with the Bragg’s angle θ obtained from the Powder XRD Spectrum, the unit cell length and volume and hence the experimental crystallographic density (g/cm3) is calculated. Interplanar distance is also determined.