Materials Science and Engineering Crystalline and Non-Crystalline Systems X-Ray Diffraction: Determination of Crystal Structure

Crystalline and Non-Crystalline Single Crystals ◦ Uninterrupted repeating unit of a unit cell ◦ Often forms geometric shapes ◦ Most solids form multiple crystal orientations and breaks forming grains

Crystalline and Non-Crystalline Polycrystalline ◦ Many crystalline grains in a microstructure ◦ Is heavily influenced by cooling.  Nucleation, Growth, and Formation of Boundaries (figure 3.18) ◦

Crystalline and Non-Crystalline Anisotropy ◦ Axis/Direction determines properties  (structure – properties correlation)  Isotropy – Equal properties on all axis. ◦ Example:  Young’s Modulus, Conductivity, Index of Refraction can vary between [100] and [111]

Crystalline and Non-Crystalline Anisotropy ◦ Inversely proportional to structural symmetry  Triclinic vs Simple Cubic  Highly anisotropic (directional dependant properties) vs  Highly Isotropic (uniform shape = uniform properties) ◦ Usually see isotropy on macroscopic scale in metals due to polycarystallinity

X-Ray Diffraction Most of the information in this chapter comes from X-Ray Diffraction. What is diffraction!?

X-Ray Diffraction Diffraction ◦ Results from constructive and destructive interference

X-Ray Diffraction Diffraction ◦ Consistent overlap in 3-D space creates “diffraction pattern” ◦ Used heavily in research and higher education

X-Ray Diffraction Diffraction ◦ Regularly spaced obstacles capable of scattering a wave ◦ Are spaced comparable to wavelength

X-Ray Diffraction X-Rays ◦ Form of electromagnetic radiation ◦ High Energy, Low Wavelength ◦ Portion of X-Ray beam scatters in different directions (locations) when hitting solid object.

X-Ray Diffraction X-Rays ◦ At an angle… Bragg’s Law ◦ Relationship among x-ray wavelength, interatomic spacing, and angle of diffraction for constructive interference  (further ahead)

X-Ray Diffraction Like Orchard Rows ◦ Angle of view creates perspectives

X-Ray Diffraction Technique: ◦ Sample placed on a stationary rig ◦ Detector turns on rotating axis  Scans part along a set range of angles. XRD Demo/Visual  X-Ray Diffraction

X-Ray Diffraction ◦ Example:

X-Ray Diffraction ◦ What are we looking at?

X-Ray Diffraction ◦ What are we looking at?

X-Ray Diffraction What are we looking at? ◦ What does each variable mean?