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CERAMIC PHASE DIAGRAMS
Phase diagrams have been experimentally determined for a large number of ceramic systems. For binary or two-component phase diagrams, it is frequently the case that the two components are compounds that share a common element, often oxygen. These diagrams may have configurations similar to metal–metal systems, and they are interpreted in the same way.
The Al2O3-Cr2O3 System
One of the relatively simple ceramic phase diagrams is that found for the aluminum oxide–chromium oxide system, Figure 1.This diagram has the same form as the isomorphous copper–nickel phase diagram, consisting of single liquid and single solid phase regions separated by a two-phase solid–liquid region having the shape of a blade. The solid solution is a substitutional one in which substitutes for and vice versa. It exists for all compositions below the melting point of inasmuch as both aluminum and chromium ions have the same charge as well as similar radii (0.053 and 0.062 nm, respectively). Furthermore, both Al2O3 and Cr2O3 have the same crystal structure.