1. Powder X-ray Crystallography

2. X-ray diffraction
A rapid analytical technique primarily used for phase ID of a crystalline material and can provide information on unit cell dimensions The interaction of the x-ray with the sample produces a constructive interference and a diffracted ray

3. Characteristic States of Matter
S.O.M
Order
(pattern repetition)
Properties
Notes
Solid (crystalline)
Long Range
Anisotropic
Doesn’t repeat in all directions
Solid (amorphic)
Short Range
Isotropic
Pattern repeats in all directions
Liquid
Gas
None
Diffraction = the various phenomena (bending) that are associated when the wave passes by an object that disrupts the wave
Diffraction effects are MOST noticeable when the
wavelength of waves is similar to the size of the
diffracting objects or apertures

4. Principles of XRD Why crystals? Why X-rays?
Challenge in focus enough x- rays into a small enough volume to “see” a single molecule
Crystals have a repeating pattern on a lattice (not a single atom, but a single macromolecule)
Parallel planes of atoms
Spacing of atoms = 0.1 nm, x-ray wv = 0.1nm
Why X-rays?
To see features on the order of the distance between atoms (10-10m)
X-ray wavelength = size of space between atoms
X-rays are diffracted by crystals

5. Crystallography
Divided into 7 lattice systems  all crystalline materials fit into one of these categories
Determined by lengths of edges and angles
Crystalline parallel rows of atoms are separated by a “unique” distance (d-spacing)
Diffraction occurs when radiation enters a substance and is scattered

6. Bragg’s Law
Angle of incident ray = angle of diffracted ray
nƛ = 2dsinθ
2θ = angle between incident and reflected beams
d = spacing between planes
ƛ = wavelength
n = order of diffraction
nλ = 2d sinθ

7. Applications ID of unknown crystalline material Geology
Environmental Science
FORENSICS!!!
Material science
Biology
Specific applications in:
Characteristics of crystalline material
ID of fine grained minerals (clays)
Measurement of sample purity

8. More on xrd applications
Forensic geology
Environmental Science
Mineral ID
1-Silicates
Most common, Si-O tetrahedron group
5 configurations
2-Non-silicates
CO3, SO4, S-2, O-2, OH-, Halides
Wastewater precipitates Testing for: Alum, chlorides, phosphates Determine unknown substances by evaporation

9. How does the pxrd work? University of Washington Tutorial
When X-rays hit a powdery sample during irradiation, they get diffracted by mineral crystals contained in it, and strong scattering is observed at certain incident angles to crystals, which are specific to individual minerals. Using this phenomenon, the X-ray diffractometer identifies minerals contained in samples and examines their atomic arrangements.

10. Safety precautions Effect of exposure Threshold Dose
This machine has an x-ray; ALWAYS pay attention to SOUNDS & SMELLS
*If something is funny – STOP IMMEDIATELY!
GENERAL PRECAUSTIONS:
Be familiar with procedure to be carried out
Never expose any body part to primary x-ray beam
(primary beam = 2.4 x 107 rem/hr, diffracted beam = 80rem/hr)
Turn x-ray beam OFF before attempting to make any
changes to experimental set up
Examine system carefully for any system modifications or irregularities
NEVER leave energized system unattended in an area where access is not controlled
Effect of exposure
Threshold Dose
Erythema (skin reddening)
rem
Temporary hair loss
Permanent hair loss
700 rem
Transepidermal injury (skin burns)
1000 rem
Dermal radionecrosis (skin death
rem