Viktor P. Red'ko

Triangulation and Liquidus Surface in the Al2O3 ― ZrO2 ― La2O3 Phase Diagram

A projection has been constructed for the liquidus surface in the phase diagram for the Al2O3 ― ZrO2 ― La2O3 system on to the plane of the concentration triangle. There are found to be two partially quasibinary sections LaAlO3 ― (98.5 mole% ZrO2 ― 1.5 mole% La2O3) and La2O3·11Al2O3 ― (98.5 mole% ZrO2 ― 1.5 mole% La2O3) together with one quasibinary LaAlO3 ― La2Zr2O7 section, which triangulate the ternary system, and the phase diagrams have been constructed for them. There are nine fields of primary crystallization for phases based on the T and F forms of ZrO2, the X, H, and A forms of La2O3, and also the phases La2Zr2O7, LaAlO3, La2O3·11Al2O3, and Al2O3, together with two quasibinary eutectics and three ternary ones. It is not found that there are any ternary phases and solid-solution regions based on the components and the binary compounds. The minimum temperature in the system is 1665°C. The interactions are basically of eutectic type.

Change in the Physicochemical Properties of Nanocrystalline Powder Based on ZrO2 in the Presence of a Mineralizing Agent

The change in physicochemical properties of nanocrystalline powder of the composition ZrO2 ― 3 mole% Y2O3 in the presence of aluminum fluoride is studied. The starting powder is prepared by a complex method including elements of hydrothermal synthesis and sol-gel technology. It is established that these conditions expand the temperature limits for the existence of ZrO2 monoclinic solid solution. Transformation is connected with adsorption of fluorine at the ZrO2 surface, diffusion in the solid phase, and a reduction in anion vacancy concentration.

Thermal Barrier Coatings: Current Status, Search, and Analysis

The principles for selecting materials to be used as thermal barrier coatings (TBCs) are presented. The advantages and disadvantages of new methods for TBC deposition are briefly described. After measurement of the thermal conductivity and thermal expansion coefficient, it is required to ascertain that such materials do not interact with the thermally grown aluminum oxide and then to determine their strength, fracture toughness, hardness, and Young’s modulus. The thermal conductivity of TBC can be reduced by increasing its porosity and suppressing its sintering. The need for and drawbacks of multilayer coatings are shown. If TBC meets all the requirements, then TBC corrosion resistance to Na2SO4, V2O5, P2O5, sand, and volcanic ash in operation and ways to protect TBC against damage need to be determined. The prospects and areas for development of these techniques are outlined.

Solidus Surface and Phase Equilibria in Al2O3 ― ZrO2 ― La2O3 Alloy Crystallization

The projection of the solidus surface in the phase diagram for the Al2O3 ― ZrO2 ― La2O3 system on the plane of a concentration triangle has been constructed, which consists of seven isothermal three-phase fields corresponding to three nonvariant equilibria of eutectic type and four nonvariant equilibria of peritectic type, as well as four lineated surfaces for the end of crystallization in the binary eutectics. The highest temperature on the solidus surface is 2710°C, and the lowest is 1665°C. No ternary phases and appreciable areas of solid solution are observed. Data on the bounding binary systems, liquidus and solidus surfaces have been used to construct the phase-equilibrium diagram together with a scheme for the reactions in equilibrium crystallization in the Al2O3 ― ZrO2 ― La2O3 system.

Effect of Mineralizing Agent on the Phase Composition of Nanocrystalline Powder in the System ZrO2 ― Y2O3 ― CeO2

The effect of mineralizing agent (AlF3) on microstructural rebuilding and phase transformation that occurs during heat treatment in the range 600-1000°C for powder of the composition ZrO2 ― 7 mole% CeO2 ― 1 mole% Y2O3 is studied. The original nanocrystalline powder is prepared by high-temperature hydrolysis and sol-gel technology. It is established that during heat treatment there is decomposition of the solid solution based on T-ZrO2 by a eutectoid reaction with formation of M-ZrO2 and Ce2Zr3O10. The compound Ce2Zr3O10 is retained under these conditions at 1000°C. Anisotropic crystals of different chemical composition (M-ZrO2, Ce2Zr3O10, α-Al2O3) form within the sintered matrix of a solid solution based on T-ZrO2.

Interactions in the Ca2SiO4-CaZrO3 system

X-ray analysis at 20–1200°C and differential thermal analysis have been used to refine the transformation temperatures and unit-cell parameters for crystalline modifications of dicalcium silicate. Phase equilibria have been identified in the Ca2SiO4-CaZrO3 system at 1100–2500°C. The phase diagram for this system has been derived. The characteristic features are the eutectic form for the liquidus and the formation of narrow solid-solution regions based on various crystalline modifications of Ca2SiO4.