The metal titanium, which is useful in making alloys to resisthigh temperatures and extremely corrosive environments, adopts twocrystal structures – close-packed hexagonal (α-phase) at roomtemperature and body-centred cubic (β-phase) above 882 °C. Underfavourable circumstances, the α phase can dissolve up to 32 atomic% (nearly 15 wt %) of oxygen whereas the β phase can dissolve verylittle oxygen at the transition temperature (882 °C) and a littlemore at higher temperatures. Oxygen atoms have a radius ofapproximately 0.7 x 10-10 m.

a) Given that the “distance of closest approach” between twotitanium atoms is approximately 2.92 x 10-10 m, calculate the radiiof the octahedral and tetrahedral interstices in both the hexagonaland cubic forms of titanium. .

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b) Use your answers to part a) to explain why the solubility ofoxygen is different in the two structures of titanium? .

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c) Can you explain how a metal that is capable of dissolving somuch oxygen below 882 °C can simultaneously have excellentoxidation resistance? .

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