Reference no: EM133311670

Show all reasoning behind your answers.

Question 1: Excel spreadsheets are provided with experimental XRD data

i) Plot the diffraction pattern for the powder analyzed in the laboratory (intensity vs 2-theta). Label the peaks with their Miller indices, hkl, determined, below.

ii) Show that the powder is polycrystalline sodium chloride (NaCl), a = 5.620 Å, space group Fm- 3m. You should make a table showing the experimental 2-theta values, together with the calculated d-spacings and 2-theta values. Explain why there are systematic absences in the diffraction pattern. (Show all equations and working)

iii) Explain why the peaks at high 2-theta angle appear as doublets in the raw data.

iv) If the crystals in the powder were long, thin needles how could this affect the diffraction peaks?

v) The XRD data from the aluminium oxide nano powder is provided. Using the Scherrer equation, estimate the crystallite size. Use the peak at ~60o 2-theta (assume a single peak). Use 0.11o for the instrumental line broadening.

Question 2: (a) Explain, using Abbe's theory of image formation, the importance of the objective lens.

(b) Below, is an expensive ‘apochromatic' objective lens which corrects almost completely for all aberrations (left) and a cheaper lens (right).
i) With suitable sketches, explain two aberrations corrected in the apochromatic objective lens.
ii) Estimate the lateral resolution of both lenses.
iii) Estimate the depth of field of both lenses.
iv) What is the meaning of the 0.17, 160 and ∞ symbols written on the lens?

 

(c) (i) Describe the theory behind the contrast technique of dark field microscopy.
(ii) How is this technique achieved for transmitted light microscopy?

(d) (i) How may a microscope be modified to achieve polarized light contrast?
(ii) Which materials, with examples, are suitable for examination with polarized light microscopy?

Question 3: (a) Describe, with the aid of a diagram, the design of the Scanning Electron Microscope (SEM).

(b) Give an estimate of the best lateral resolution for a modern transmission electron microscope, explaining why this is significantly better than a visible light microscope.

(c) Explain the technique of back-scattered electron imaging within the SEM. Describe and explain in detail the information these images can provide including any necessary specimen preparation.

(d) How can quantitative elemental information be obtained using an electron microscope using EDX?

(e) A ceramic material needs to be prepared for examination with the TEM.
(i) What is final diameter of the specimen?
(ii) What is a suitable final specimen thickness?
(iii) Explain a suitable method for preparing the thin specimen.

Question 4: (a) What information can be gained from the DSC thermal analysis technique?

(b) Referring to the three TGA lab videos on Minerva (Learning Resources/ Thermal analysis):
i) Describe the preparation of specimens prior to running the TGA.
iii) Explain the set up of the TGA instrument.
iii)Describe the presentation and interpretation of the output data.

(c) With reference to the TGA trace, below, what information does it give about the transitions occurring in the specimen during heating?

 

Question 5: (a) What information can be gained about a material using Fourier transform infra-red spectroscopy?

(b) Describe the principles behind this technique i.e. what causes absorbances in the infra-red spectrum?

(c) Explain, in general, how to interpret an infra-red spectrum. Interpret the infra-red spectrum from ethanoic acid (acetic acid), below.

Attachment:- Thermal analysis technique.rar