Some studies on the thermal solid state stability of zircon

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

“…[9]. Wu [10], for instance, presented a thermodynamic data set obtained by fitted the liquidus line to Toropov's & Galakhov's experimental results which, therefore, resembles the miscibility gap between 58 and 82 mol-% SiO 2 at 2241 • C. For simulation of nuclear core melting and high-temperature reactions with refractory castables Ball et al [11] presented, among others, a calculated version of the ZrO 2 -SiO 2 phase diagram and provided experimental evidence for the immiscibility based on publications by Lang et al [12], Butterman & Foster [9], Anseau et al [13], Schuiling et al [14] and Evans et al [15] for proof. These sources, however, do not contain any measurements around the miscibility gap but deal with the thermal stability of zircon and its relationship to zirconia while Butterman & Foster [9] made use of the results by Toropov & Galakhov.…”

Thermal stability of zircon (ZrSiO4)

“…Our experiments yield also evidence that the decomposition is rather slow at temperatures below 1650 • C and faster at higher temperatures. Thus, both literature results 11,12 can be re-interpreted quantitatively. First of all, both figures give kinetic rather than equilibrium information for the decomposition.…”

“…First of all, both figures give kinetic rather than equilibrium information for the decomposition. The original diagram of Anseau et al 11 shows one continuous curve of increasing slope. Another interpretation is possible, however, which is that there are two reaction mechanisms, each being represented by one straight line.…”

“…Thus the impurities of the raw materials given in literature for example by Anseau et al 11 can be considered in thermochemical calculations. Therefore, a composition of 99.28 wt.% ZrSiO 4 , 0.32 wt.% Al 2 O 3 , 0.25 wt.% TiO 2 , and 0.15 wt.% Fe 2 O 3 was calculated yielding evidence for the first formation of a liquid phase at 1227 • C. The existence of a liquid phase allows the dissolution of silica as soon as it is released from the zircon crystal as a solid (crystalline or amorphous) phase.…”

“…11 The purity was given as 99.13%, the major impurities being 0.32 wt.% Al 2 O 3 , 0.25 wt.% TiO 2 , and 0.15 wt.% Fe 2 O 3 . They measured the degree of decomposition by chemical analysis of the amount of free SiO 2 as well as by the ZrO 2 /ZrSiO 4 ratio as recorded by XRD.…”