Particle Characterization/Sampling

Question 1

Explain the basic principles of x-ray diffraction.

Answer 1

X-rays are sent through a sample where high energy electrons interact with the sample material. The crystalline structure of the solid reflects the electron beam in a specific interference pattern based on the crystal lattice allowing for identification of the structure.

Question 2

Explain why you obtain peaks of intensity in an x-ray diffraction pattern.

Answer 2

The electron beam reflects off the crystalline structure at slightly different angles depending on the incident angle of the beam and the reflected beams then constructively interfere with one another causing peaks of intensity.

Question 3

Which equation can you use to calculate the crystallite size from a powder XRD pattern?

Answer 3

L = K*λ/(β*cos(Θ))
K = constant
λ = wavelength of beam
β = breadth of the diffraction profile
Θ = indicent angle

Question 4

What are the assumptions in a Langmuir isotherm?

Answer 4

1. Only monolayer coverage
2. All surface sites are equivalent and surface is uniform
3. No influence by occupation of neighbouring sites

Question 5

What are the types of adsorption isotherms?

Answer 5

I. no multi-layer adsorption or microporous (<2nm) solids with small external surfaces. (activated carbon)
II. Non-porous or macroporous (>50nm). Monolayer complete at point “B”
III. Strong adsorbate-adsorbate interaction, no monolayer formation.
IV. Meso-porous material (2nm < dpore < 50nm)
V. Similar to III but with meso-pores
VI. Ideal multi-layer adsorption where step-height represents the monolayer capacity. Uniform, non-porous surface.

Question 6

Which sampling techniques result in the smallest to largest sampling error?

Answer 6

1. Spinning riffler
2. Chute splitter
3. Disk riffler
4. Cone and quarting
5. Scoop sampling

Question 7

What happens if you have sub- or super-isokinetic sampling conditions?

Answer 7

Subisokinetic where U < U0 (U = gas velocity in probe, U0 = free stream velocity) oversamples large particles
Superisokinetic where U > U0 oversamples small particles.
Large particles do not follow the streamline