Magnesia (MgO) has a melting point of 2825C. Applications include refractory bricks, crucibles, cements, thermocouple protection tubes, brake linings, plasma display screens and substrates for thin-film formation.
a) Identify the cation and anion and give quantum numbers for one of the electrons donated by the cation and one of the electrons accepted by the anion.
b) MgO bonds primarily ionically and the coulombic attraction between ions, FA, is equal to 9.231x10-28 N.m2/ro2, where ro, the equilibrium spacing at Uo (the minimum in potential energy) between cation and anion, is equal to 2.107 Å. Given that U = -A/rm +B/rn and that n=9, calculate the value of Uo in kJ/mol remembering that a N. m is equal to a J.
c) Derive a relationship for Young’s modulus, E, in terms of m, n, A and ro if E = (1/ro)(dF/dr)r=ro.
d) What is the consequence of n being greater than m for thermal expansion?
f) Rank the following metals from lowest to highest binding energies: Mn, Ir, Cd, Ta, V, Na.