XRD Flashcards
What is XRD and what is it used for?
The diffraction of short wavelengths, 0.1 nm, used to investigate single crystals and fine grain crystalline powers (Powder XRD).
How is XRD used to identify chemical composition of a sample?
A unique diffraction pattern is produced from a specific arrangement of atoms, thus acting as a fingerprint for a particular compound.
Powder XRD is a quick analytical method for….
Identifying crystalline compounds.
XRD penetrates solid material to provide info about….
The materials atomic structure and chemical composition.
X-rays are generated by an electron beam being…
Accelerated towards a metal target.
Unlike in SEM, the positive electrode plays a major part. It is usually made from….
Copper or tungsten.
The X-rays in the X-ray source consist of a continuous range and wavelengths. This is….
Background radiation.
X-rays originate from the collisions between the electrons in the electron beam and the….
Metal atoms In the positive electrode.
The interaction between the metal atoms in the positive electrode and the electrons in the electron beam results in deceleration of the electrons and as a result….
X-rays are emitted over a continuous range of wavelengths in all directions.
Super imposed on background are intense peaks of X-ray radiation at specific wavelengths. These are dependent on the….
Metal used for the positive electrode.
The radiation of X-rays of specific wavelengths generated from falling electrons is used to…
Obtain diffraction patterns from the sample.
XRD can be used on paintings to….
Determine chemical composition of inorganic pigments.
XRD was used to determine DNA structure by….
Revealing a clear structure of tissue, enabling DNA to recognised as a double helix structure.
The generated X-rays pass out of the xray source through a thin window, the window…..
Acts as a filter to remove unwanted radiation.
After passing through the window from the source, the x-rays are then further filtered to give a ….l
Single wavelength (monochromatic) using a metal filter.
The x-rays are focused using a series of curved mirrors before they hit the….
Sample to be analysed.
The output from and XRD is a series of peaks representing…..
Xray intensity as a function of the angle 2sin0
Info obtained from Braggs law is converted electronically into a series of peaks which represent….
Xray intensity, angle of incidence and reflection (2sin0)
Atoms with more electrons scatter more strongly, resulting in…..
A higher intensity of peaks.
Braggs law equation….
d = n(wavelength) / 2 sin (0)
Sample prep for powder XRD….
Powder is 10 micrometer in size.
An inorganic solid.
A few 100ml of sample is used.
Surface must be flat to prevent uneven interaction of X-rays.
Incident X-rays can interact either by….
Reflection or transmission.
After interaction, the X-rays are scattered and measured by a detector. The scattering from atoms arranged in….
Planes ins measured.
