Liquation in the system ZrO2-SiO2

Direct observation of the liquid miscibility gap in the zirconia–silica system

“…The equilibrium position of the miscibility gap was confirmed between 59.5 mol-% (monotectic composition L 1 = L 2 + ZrO 2 ) and 78 mol% SiO 2 (L 2 ) at 2250 • C which is very close to the data given by Toropov & Galakhov [7]. Data for the low temperature equilibria have been taken from our previous publication on the decomposition of zircon [6].…”

“…Uncertainties regarding the fusion of zirconia motivated Toropov & Galakhov [7] in 1956 to re-investigate the liquidus surface of the binary system by starting from pure oxide mixes. Cooling down samples very fast from temperatures >2500 • C obtained by sintering and melting a powder compact inside a tungsten coil yielded dendritic crystallites of a refractive index n > 2.05, identified as ZrO 2 , grown inside a brown opaque glass.…”

“…Cooling down samples very fast from temperatures >2500 • C obtained by sintering and melting a powder compact inside a tungsten coil yielded dendritic crystallites of a refractive index n > 2.05, identified as ZrO 2 , grown inside a brown opaque glass. They repeated the experiments with natural zircon crystals and observed "unexpect- [7]. Solid state part is based on the proposal by Curtis & Sowman [8].…”

“…The position of the miscibility gap was given with 59.3-76.8 mol% SiO 2 , corresponding to 41-62 mass-% SiO 2 at 2250 • C while the composition of the critical point was 69.8 mol%/53 mass-% SiO 2 at 2430 • C. Fig. 1 presents a re-drawn version of this phase diagram [7] which additionally contains the positions of the originally measured points. It should be pointed out that Toropov & Galakhov also used the unproven solid solubility of SiO 2 in ZrO 2 as proposed by Zhirnova and Curtis & Sowman. Surprisingly, all phase diagrams and thermodynamic data sets published later make use of these quite early results without any own experimental evidence regarding the liquidus surface, e.g.…”

“…Solid state part is based on the proposal by Curtis & Sowman [8]. The diagram is re-drawn and transferred to mol-%, the points are original data from the Tables in [7]. edly", as they wrote, two immiscible liquids consisting of emulsified droplets with different concentrations of ZrO 2 precipitates.…”