Effect of Heat Treatment of Molten Bi2O3 Containing 22 mol % SiO2 on the State of the Metastable δ*-Phase Forming during Solidification

Inorganic Materials - We have studied the effect of isothermal holding of a melt containing 78 mol % Bi2O3 and 22 mol % SiO2 and various melt cooling schedules on the morphology, microstructure,...     

Programming high-performance parallel computations: formal models and graphics processing units

This article presents a line of development of formal design methods that is based on the concepts of algebraic programming and algebraic dynamic program models using rewriting rules for the automated design of efficient programs for graphics processing units. The developed formal methods are illustrated by examples that show high efficiency of transformations.     

Effect of shock-wave loading on bismuth oxide-containing piezo- and ferroelectrics

The effect of shock-wave loading on bismuth and germanium oxides, their mechanical mixtures, and the compounds Bi₁₂GeO₂₀, Bi₄Ge₃O₁₂, and Bi₂GeO₅ in the form of single- and polycrystals was studied by methods of physicochemical analysis. It was established that the distribution of the elements Bi, Ge, and Fe is nonuniform because of displacement of layers from the surface into the bulk. In bismuth and germanium oxides after loading, the effect of admixtures (iron oxide and oxygen) and distortion of the crystal lattices were revealed. Under shock-wave loading, the starting components in a mixture with composition of 61 react to form the metastable Bi₂GeO₅ phase. A comparison of differential thermal analysis data of specimens on heating and cooling with metastable state diagrams makes it possible to distinguish between the effects of stuctural distortions and of admixtures on the properties of the materials after loading.Scientific-Research Physico-Technical Institute, Krasnoyarsk 660036. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 84–88, July–August, 1995.     

Stable and metastable phase equilibria in the liquid-state and solid-state PbO-GeO<Subscript>2</Subscript> system

A literature review on phase equilibria in the PbO-GeO₂ system is reported and the main sources of discrepancies in the results of different authors are considered. Uncontrolled metastable phase formation is shown to be the most probable cause for disagreements about composition and structures of phases formed in the system. The authors’ results of investigations of physicochemical properties for stable and metastable phases obtained by various routes, including mechanochemical and thermal (crystallization of a metastable melt) activation, are presented. Similar phenomena are shown to take place in the binary PbO-SiO₂ system and under partial substitution Ge → Si in the ternary oxide system PbO-GeO₂-SiO₂. The particular role played by the 6s² electron pair a Pb²⁺ ion in stabilization of intermediate energy-saturated states and meta-stable phase formation is discussed.     

High-temperature heat capacity of Pb2SnO4

The heat capacity of Pb₂SnO₄ was measured from 500 to 1000 K, and the results were used to evaluate the thermodynamic functions of solid Pb₂SnO₄.     

Stable and Metastable Phase Equilibria in the Bi2O3–BiPO4 System

The stable and metastable phase equilibria in the Bi₂O₃–P₂O₅ system were studied in the range 0–50 mol % P₂O₅ by differential thermal analysis and x-ray diffraction. The results were used to construct the corresponding phase diagrams. In the equilibrium state, the system contains one sillenite phase with Bi₂O₃ : P₂O₅ = 12 : 1 and four other bismuth phosphates (2 : 1, 3 : 1, 5 : 1, and 1 : 1). In a metastable state, resulting from solidification of metastable melts, there exist * solid solutions (0–25 mol % P₂O₅) based on the high-temperature form of Bi₂O₃. At lower temperatures, the * phase transforms eutectoidally into the metastable phase, which has the same structural basis as the high-temperature solid solutions. At room temperature, the phase exists in a narrow composition range around 15 mol % P₂O₅. At lower P₂O₅ contents, the * phase decomposes at 868 K by a monotectoid reaction to form a mixture of the metastable and phases. The phases 3Bi₂O₃ · P₂O₅ () and 2Bi₂O₃ · P₂O₅ (), melting incongruently at 1193 and 1223 K, respectively, appear in both the equilibrium and metastable phase diagrams.     

Effect of Heat Treatment on the Structure and Mechanical Properties of Eutectic Silumin Alloyed with Magnesium

Metal Science and Heat Treatment - The article investigates the possibility of replacing the AlSi7Mg0.3 alloy used for manufacturing automotive wheel disks with eutectic silumin alloyed with...     

Metastable States in Bismuth-Containing Oxide Systems

The temperature dependences of viscosity, density, and surface tension for Bi₂O₃–AO₂ (A = Si, Ge, Ti) melts are found to exhibit anomalies. The temperatures of these anomalies depend on the AO₂ content, which allows the liquidus fields in the phase diagrams of such systems to be divided into regions corresponding to different mesomorphic states of the melt. As shown by analyzing the processes occurring during melt heating, the mesomorphism is due to the polymerization of AO₄ tetrahedra and Bi₂O₂ groups, which leads to an anisotropic melt structure and the development of a mesomorphic state similar to the liquid-crystalline state. For this reason, such melts retain their high-temperature structure on cooling and pass into a metastable state. Metastable phases crystallize from metastable melts. A procedure is devised for establishing the conditions of metastable equilibria by differential thermal analysis. This approach is used to carry out physicochemical analysis and construct metastable phase diagrams of the systems Bi₂O₃–AO with A = Mg, Ca, Sr, and Ba; Bi₂O₃–A₂O₃ with A = B, Al, and Ga; Bi₂O₃–AO₂ with A = Si, Ge, and Ti; Bi₂O₃–P₂O₅; and Bi₂O₃–A₂O₃–P₂O₅ with A = B, Al, and Ga. Crystals of metastable phases are grown, and their thermal decomposition is studied isothermally and during heating. The effect of shock compression on metastable phases is investigated, and the sequence of transformations experienced by metastable phases under various external influences is analyzed. It is shown that the transition of metastable phases to the stable state is a two-step process: the first step involves precipitation of metastable binary oxides, which react in the second step to form thermodynamically stable phases. Investigation of growth defects in crystals of stable compounds demonstrates that such crystals may contain inclusions of the solidified metastable melt. The potential application fields of metastable phases are discussed.     

Change of the thermal behavior of 55Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 45B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass at annealing close to the vitrification temperature

The characteristic properties of relaxation processes for 55Bi₂O₃ ? 45B₂O₃ glass were described. The pattern of changes of the vitrification temperature (T _g ) is found to be quasi-periodic; the value of the endothermic effect near T _g (ΔC’ _p ) and the difference between the softening point and the vitrification temperature (T _m –T _g ) were determined. The temperature-time parameters of the transition from quasi-periodic to the continuous change of the properties were determined and an explanation of such behavior of the system was offered.     

Structure and Properties of an Amorphous Nickel–Titanium Alloy after Explosive Compaction

Xray phase, differentialthermal, and thermogravimetric analyses are employed to study the action of shockwave loading on the state of Ni₅₀$Ti₅₀ amorphous alloy produced by synthesis using mechanical activation. It is shown that, on the one hand, shockwave loading leads to additional disordering of the amorphous matrix, and, on the other hand, it improves the structure of microcrystals of the crystalline constituent of the Ni₅₀$Ti₅₀ amorphous alloy.