Yu.B. Petrov

Phase relations in the ZrO2-FeO system

We present the results of the investigation of the ZrO2-FeO system under an inert atmosphere. We have refined the position of the eutectic point, which lies at 1332 ± 5°C and 10.3 ± 0.6 mol % ZrO2. The iron oxide solubility boundaries in zirconium dioxide have been determined over a wide temperature range taking into account the polymorphism in ZrO2. A phase diagram for the system has been designed.

Experimental investigation and thermodynamic simulation of the uranium oxide–zirconium oxide–iron oxide system in air

The behavior of melts and the phase composition of crystallization products of six compositions in the uranium oxide-zirconium oxide-iron oxide system in air have been investigated. It has been revealed that crystallized samples containing 20–50 wt % uranium oxide and 25–80 wt % iron oxide (the rest is zirconium oxide) consist of five crystalline phases and involve two types of eutectic structures. The possible factors responsible for this phenomenon have been considered.

Phase equilibria during crystallization of melts in the uranium oxide-iron oxide system in air

The uranium oxide-iron oxide system is investigated. It is revealed that, upon both quenching and slow cooling of samples after their melting in air, the solid phase contains five crystalline phases, such as the oxide of quadruply charged uranium UO2, the mixed oxide UO2.66(U3O8), hematite FeO1.5(Fe2O3 ), magnetite Fe1.33(Fe3O4), and the binary compound Fe2+U6+O4.

Monotectic crystallization of melts in the ZrO2-Al2O3 system

The morphology of the crystalline phases prepared at different cooling rates, temperatures, and compositions of melts in the ZrO2-Al2O3 system is investigated. It is established that both the quenched and slowly crystallized samples containing 35–70 wt % ZrO2 have a submicron structure. Outside this concentration range, the ingots have a zonal structure: the peripheral region is formed by large baddeleyite crystals (at a ZrO2 content higher than 70 wt %) or corundum crystals (at a ZrO2 content lower than 30 wt %). This character of the crystallization confirms the presence of the phase separation (liquid immiscibility) region in melts of this system. A variant is proposed for the phase diagram of the system under investigation.

Ternary eutectics in the systems FeO-UO2-ZrO2 and Fe2O3-U3O8-ZrO2

The systems FeO-UO2-ZrO2 (in inert atmosphere) and Fe2O3-U3O8-ZrO2 (in air) were studied. For the FeO-UO2-ZrO2 system, the eutectic temperature was found to be 1310°C, with the following component concentrations (mol %): 91.8 FeO, 3.8 UO2, and 4.4 ZrO2. For the Fe2O3-U3O8-ZrO2 system, the eutectic temperature was found to be 1323°C, with the following component concentrations (mol %): 67.4 FeO1.5, 30.5 UO2.67, and 2.1 ZrO2. The solubility limits of iron oxides in the phases based on UO2(ZrO2,FeO) and UO2.67(ZrO2,FeO1.5) were determined.

Behavior of melts in the UO2-SiO2 system in the liquid-liquid phase separation region

The behavior of melts in the uranium oxide-silicon dioxide system is experimentally investigated in air upon induction melting in a “cold crucible.” The existence of the two-phase liquid region in this system is confirmed. It is demonstrated that the melts absorb oxygen from air, which leads to crystallization of the UO2.25 compound upon cooling. In the case of considerable internal heat release, sharp cooling of the melt surface results in the liberation of gas, which brings about bulging and, sometimes, melt ejection from the crucible.