QUESTION 7
As a forensic materials expert – you have been asked to identify a metallic powder found on the clothing of someone suspected of fabricating an incendiary device used in an armed robbery.
The suspect suggests that the powder is tungsten – which he uses a lot in his line of work. The police believe that the powder is part of a chromium/silver/nickel mixture often used in such devices. Armed with the following information from an X-ray powder diffraction analysis – what can you conclude?
Using Cu ka radiation of 0.1542nm, three large diffraction peaks were observed at 44.4°, 64.6° and 81.7°.

QUESTION 9 – Crystallographic transformation
On cooling from the molten state, titanium solidifies into a BCC lattice structure. However, on cooling to below 880°C, a change occurs whereby the crystal structure transforms into an HCP structure. Assuming the number of atoms remains constant and that the lattice parameters are as shown below, calculate the volume change associated with this transformation.
For the BCC lattice: a = 3.32Å
For the HCP lattice: a = 2.956 Å and c = 4.683 Å
Titanium is a commonly used metal in engineering structures. Explain why your findings above should be cause for concern if these engineering structures are to be used at high temperatures.

Posted Date: 3/25/2013 9:14:33 PM | Location : Australia

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