The Al 2 O 3 -ZrO 2 -Y 2 O 3 system was studied in the range of necessary condition is satisfaction of Van-Rein's rule: the lowest figurative point for the liquid composition in such a section temperatures 1600-2800؇C by methods of X-ray analysis at must be a saddle point on the liquidus surface of the ternary 20؇C, petrography, DTA in He at temperatures to 2500؇C, system, or a maximum point on the solidus surface. 24 thermal analysis in air using a solar furnace at tempera-Since the regions of two-phase equilibria YA ϩ F and tures to 3000؇C, and electron microprobe X-ray analysis.
Y 2 A ϩ F are narrow (the composition of F varies within the The stable and metastable phase diagrams were conlimits 4-5 mol%), it may be assumed that partially quasi-binary structed. The liquidus and solidus projections, crystallizasections pass through their centers. The two-phase region tion paths for the alloys, and polythermal sections are Y 3 A 5 ϩ F, as mentioned above, is quite broad (the F composipresented in the article. The structure of the restricting tion lies in the range 18.5-37.0 mol% Y 2 O 3 ). Hence the location systems defines the phase equilibria in the ternary system.
of the partially quasi-binary section Y 3 A 5 -F requires a more No ternary compounds were found. The metastable phase precise definition. relations were caused by the ambivalent behavior of Y 3 Al 5 O 12 during crystallization.
II. Methods of Investigation I. Introduction
Powders of alumina (99.9%; Donetskij zawod khimreaktiviv, Donetsk), zirconia (99.99%; Donetskij zawod khimreaktiviv,