Characterisation techniques Flashcards
What does FTIR stand for
Fourier Transform Infa red
Give an overview of the process of FTIR
IR radiation is fired at a sample, some radiation is absorbed by the sample, and some is passed through
What is the principle of FTIR
Relies on the fact that for a molecule to IR active, there must be a change in dipole moment as a result of the vibration that occurs when IR radiation is absorbed.
The absorption corresponds to the bonds present in the molecule
The background emission spectrum of the IR source is first recorded then the spectrum with the sample in place
What can FTIR identify
Unknown material or species
Determine quality or consistency of a sample
Determine the amount of components in a mixture
What information does X-ray diffraction provide
Elemental composition
Catalyst structure
Particle size (provided by width of peaks)
What equation governs X-ray diffraction
Bragg’s law
nlambda=2d(hkl)*sin(x)
Give an overview of the X-ray diffraction process
An x-ray source is used to illuminate the sample.
The source will diffract the ray, and the diffraction is measured by a detector.
The intensity of the ray is measured.
A plot of intensity against 2*x is plotted.
What does SEM stand for and what is it used for?
Scanning electron microscope
To visualise the surface of the objects
What does TEM stand for and what is it used for?
Transmission electron microscope
Allows one to stude the inner structure of an object.
Give an overview of TEM
A mircoscopy technique where a beam if electrons is passed through an ultra thin specimen, interacting with the specimen as it goes through.
A 2D image is produced on a fluorescent screen.
The pores of the specimen are demonstrated.
Give an overview of SEM
A sample is bombarded with electrons to generate X-rays of the characteristic of the elements present.
An image is produced on a TV monitor displaying the surface of the sample.
What can the BET method be used to identify?
Pore Size
Pore shape
Specific surface area
Give an overview of the BET process
A cell will contain the specimen in liquid N2 reservoir.
The pressure of N2 will gradually be increased.
The amount of gas absorbed by the sample is calculated.
The pressure is gradually reduced.
The amount of material depletion is calculated.
A graph of volume of N2 gas absorbed and desorbed by the surface on the basis of relative pressure and constant temperature.
The graph can be used to extract the effective surface area of the material.
