Question 10.2: Ceramic Solid Solutions of MgO NiO can be added to MgO to pr......

The Science and Engineering of Materials [1006415]

Ceramic Solid Solutions of MgO
NiO can be added to MgO to produce a solid solution. What other ceramic systems are likely to exhibit 100% solid solubility with MgO?

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In this case, we must consider oxide additives that have metal cations with the same valence and ionic radius as the magnesium cations. The valence of the magnesium ion is +2, and its ionic radius is 0.66 Å. From Appendix B, some other possibilities in which the cation has a valence of +2 include the following:

The percent difference in ionic radii and the crystal structures are also shown and suggest that the FeO-MgO system will probably display unlimited solid solubility. The CoO and ZnO systems also have appropriate radius ratios and crystal structures.

	r (Å)	$[ \frac{ r_{ion} \ – \ r_{Mg^{2+}}} {r_{Mg^{2+}}}]$ × 100%	Crystal Structure
$Cd^{2+}$ in CdO	$r_{Cd^{2+}}$ = 0.97	47	NaCl
$Ca^{2+}$ in CaO	$r_{Ca^{2+}}$ = 0.99	50	NaCl
$Co^{2+}$ in CoO	$r_{Co^{2+}}$ = 0.72	9	NaCl
$Fe^{2+}$ in FeO	$r_{Fe^{2+}}$ = 0.74	12	NaCl
$Sr^{2+}$ in SrO	$r_{Sr^{2+}}$ = 1.12	70	NaCl
$Zn^{2+}$ in ZnO	$r_{Zn^{2+}}$ = 0.74	12	NaCl

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