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GATE Metallurgy : Xray diffraxtion covered

 X-Ray Diffraction

·         Electrons from a filament directed toward target material by applying a high electric field. This electron then strikes on target materials which result in heat X-ray radiation.

·         These X-rays then directed toward sample need to be analyze

·         X-ray diffraction used to determine crystal structure, phase identification, crystal size, crystallographic texture, defect studies, thin-film quality and residual stresses.

 

·          The wavelength of X-rays for diffraction falls in the range of 0.5-2 A0

 

·         Bragg’s law: Essential condition for diffraction results in constructive interference to occur  

                        Bragg’s law:       nλ = 2d sinθ

·        Where n = Order of diffraction, λ is wavelength of X-rays

·        d spacing between atomic planes

·        θ is the angle between the line of source and line of detector



Schematics of X-Ray Diffractometer 


Important questions related topics covering hkl, lattice parameter and theta values

·        Each peak represent a diffraction line

·        Each line  have particular hkl  ( miller indices) values

So each crystal structure will show only allowed set of diffractions lines (reflections)






·         Formula to calculating dhkl spacing for given  lattice parameter

 

For cubic crystals for lattice parameter a0 and interplanar spacing dhkl

  

           dhkl = a0/ (h2+k2+l2) ½

 

·         So if they have given d and hkl values we can calculate lattice parameter

·         If they have given wavelength, theta values we can calculate d by Bragg’s law

·         They can ask wavelength of X-ray used for given theta and d values

·         Or they can give particular peak hkl values or can say nth peak for BCC (or any other), determine d values for given wavelength and theta. 


 


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