Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Phase relations in the systems ZrO2Y2O3Nd2O3 and ZrO2Y2O3CeO2

The phase relations of ZrO₂Y₂O₃Nd₂O₃ and ZrO₂Y₂O₃CeO₂ systems have been studied at 1100–1600°C. The single region of the fluorite phase was intensively examined using the relation between lattice parameter and composition. In the ZrO₂Y₂O₃Nd₂O₃ system, 37 mol% Nd₂O₃ is soluble in Y₂O₃-stabilized zirconia (fluorite phase) at 1100°C and 42 mol% Nd₂O₃ at 1600°C. In the ZrO₂Y₂O₃CeO₂ system, 40 mol% CeO₂ dissolves into the stabilized zirconia at 1600°C.     

Zeolite synthesis in the system pyrrolidine-Na2OAl2O3SiO2H2O

Crystallization of zeolites from the system pyrrolidine-Na₂OAl₂O₃SiO₂H₂O was investigated. Five zeolites, ZSM—5, ZSM—35, ZSM—39, ZSM—48 and KZ—1, were synthesized as single phases, whose crystallinity was very high. In this work zeolite ZSM—48 was prepared from the pyrrolidine system for the first time. It was suggested that pyrrolidine might stabilize certain aluminosilicate polyanions which have building units of oxygen five-membered rings. It was also presumed that all zeolites, except ZSM—39, have a pore opening of oxygen ten-membered rings.     

Phase Relations in the NiFe2O4–NiCr2O4–CuCr2O4System

The phase relations in the NiFe₂O₄–NiCr₂O₄–CuCr₂O₄system were investigated experimentally and theoretically. X-ray diffraction data were used to construct the phase diagram of the system and elucidate the structural mechanisms of the transitions from the cubic spinel structure to the tetragonal (I42d, c/a< 1 and I4₁/amd, c/a> 1) and orthorhombic (Fdd2) structures.     

Structure of Mechanochemical Reaction Products in the Systems PbO–Sb2O5and PbO–Sb2O3

Mechanochemical reactions in 2PbO + Sb₂O₅and 2PbO + Sb₂O₃oxide mixtures treated in a high-energy planetary mill were studied by x-ray diffraction. The reactions were found to lead to rapid formation of crystalline products with the pyrochlore and fluorite structures, in line with the reaction-zone model. The temperature ranges of the structural and chemical transformations involved were established, and the compositions of the resulting phases were accurately determined. Heating in air leads to the reduction of the sample containing the pyrochlore phase, with the formation of one crystalline product having a variable lattice parameter because of the chemical inhomogeneity of the material. Under the same conditions, the sample containing the fluorite phase oxidizes in air, yielding four phases with different Pb : Sb ratios: PbSb₂O₆, pyrochlore, a new compound Pb_1/3Sb_2/3O₂with the fluorite structure, and Pb₃Sb₂O₈. The Pb : Sb ratio is found to vary over a wide range, from 0.5 to 1.5. The morphology of the powders produced by mechanical processing at above-threshold rates is considered in terms of nonequilibrium thermodynamics: Since the powder is a dissipative structure, its inhomogeneity cannot be fully eliminated, which correlates with the formation of an intermediate, dynamic state during mechanochemical reactions.     

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.     

Phase Relations in the Systems LiOH–GeO2–H2O and LiOH–SiO2–H2O at 500°C and 0.1 GPa

Crystallization in the LiOH–GeO₂–H₂O and LiOH–SiO₂–H₂O hydrothermal systems was studied at 500°C and 0.1 GPa. The systems were shown to contain both the isostructural compounds Li₂SiO₃ and Li₂GeO₃ and phases differing in crystal chemistry: Li₂Si₂O₅, Li₂Ge₃O₆(OH)₂, and Li₃HGe₇O₁₆ · 4H₂O (containing Ge in different oxygen coordinations). The crystallization fields revealed in the germanate system are (in order of increasing LiOH concentration) GeO₂ GeO₂+ Li₂Ge₃O₆(OH)₂ Li₂Ge₃O₆(OH)₂ + Li₂GeO₃ Li₃HGe₇O₁₆ · 4H₂O + Li₂GeO₃; those in the silicate system are -SiO₂ -SiO₂+ Li₂Si₂O₅ Li₂Si₂O₆ + Li₂SiO₃ Li₂SiO₃. Increasing the LiOH concentration increases the number of Li atoms per tetrahedrally coordinated Si or Ge atom in the crystallizing compounds. The high stability of Li₂Ge₃O₆(OH)₂ is interpreted in terms of the matrix assembly of the structure from cyclic invariant subpolyhedral structural units.     

Phase transformation in the Al2O3–ZrO2 system

Co-precipitation methods have been used to produce 20 mol% Al2O3–80 mol% ZrO2 mixed oxides, from aqueous solutions of zirconium oxychloride and aluminium chloride, followed by precipitation with ammonia. The resulting gel was calcined at increasing temperatures, and X-ray diffraction confirmed that the structure remained amorphous up to 750°C and then crystallized as a single-phase cubic zirconia solid solution, but with a reduced unit-cell dimension. At higher temperatures, the unit-cell dimension increased and, above 950°C, this phase started to transform to a tetragonal zirconia (t-ZrO2) phase, again of reduced cell dimensions compared with t-ZrO2, with simultaneous appearance of small amounts of -Al2O3. Above 1100°C, the tetragonal phase transformed to monoclinic zirconia on cooling, and the amount of -Al2O3 increased. Above 1200°C, the -Al2O3 transformed to the stable -Al2O3. These results confirm that aluminium acts as a stabilizing cation for zirconia up to temperatures of about 1100°C. © 1998 Chapman & Hall     

Effect of O2, H2O2, and HNO2 on the stability of Np(III–VII) in aqueous solutions

Published data on reactions of Np ions with O₂, H₂O₂, HNO₂, and HNO₃ in solutions of various compositions in a wide pH range are considered. O₂ oxidizes Np(III) in acid solution and Np(IV) and Np(V) in alkaline solutions. H₂O₂ exhibits dual behavior. In weakly acidic solutions, it converts Np(III) and (IV) to Np(V), in 0.75?C1 M NaHCO₃ it oxidizes Np(V) to Np(VI), whereas in dilute HClO₄ and HNO₃ and in carbonate and alkali solutions it reduces Np(VI), and in alkali solutions it reduces Np(VII). The first step of reduction in most cases is the formation of the Np(VI) peroxide complex, and the next step is the intramolecular charge transfer. In concentrated HNO₃ solutions, H₂O₂ converts Np(V) to Np(IV) and Np(VI) and then reduces Np(VI). Some radiation-, photo-, and sonochemical reactions occur via formation of excimers, i.e., of dimers arising from excited and unexcited Np ions. The excimer decomposes into two ions with higher and lower oxidation states. In reduction reactions, the excimer eliminates H₂O₂ (in addition to the H₂O₂ arising as primary product of water radiolysis). In HNO₃ solutions, oxidation of Np ions occurs only in the presence of HNO₂ arising as reaction product or upon radiolysis, photolysis, or sonolysis. The active species are NO ₂ ^? , NO₂, and NO⁺ present in equilibrium with HNO₂.     

Interface interaction and wetting in the Er2O3/(Cu–Al) and Er2O3/(Cu–Ti) systems

The wetting behavior and metal-oxide interface interactions in the Er₂O₃/(Cu–Al) and Er₂O₃/(Cu–Ti) systems were investigated at 1,423 K in order to evaluate the compatibility of ceramic crucibles with liquid metals, containing active elements. Pure Cu does not wet Er₂O₃ (Θ ≈ 140°) but the wettability is significantly improved by the addition of Al or Ti. It was established that Er₂O₃ reacts with Ti and Al dissolved in liquid Cu and the wettable spinel ErAlO₃ and ErTiO₃ is formed at the interface. The amount of the released Er from the substrate as a result of the reaction and the depth of the reaction zone beneath the drop are controlled by the thermodynamic properties of liquid solutions.     

Effect of Phosphates on the Metal Ion Activated Surface Complexes at the SiO_2-H_2O Interface and in Quartz Deactivation in Flotation System

The complexation of phosphates in thequartz-metal ion-H_2O-oleate system was studied.Computer assisted calculations with the aid of theadvanced program SOLGASWATER and knownequilibrium constants were used to evaluate themechanism,The calculation results revealed that inthe presence of a certain amount of phosphates,metal ions adsorbed at the quartz-H_2O interfacewill be transferred into solution.Thus the competi-tion for metal ions between phosphates and thequartz surface leads to surface deactivation and re-duced floatability.Various distribution diagramsclearly demonstrate the change of surfacecomplexation as a function of added phosphateconcentration.The deactivation products were alsoevaluated.     

Thermal decomposition of CuCrO4·2CuO·2H2O and phase relations in the Cu-Cr-O system

The compound, CuCrO₄·2CuO·2H₂O has been synthesized by precipitating it from the aqueous solution containing chromium (VI) oxide and basic copper (II) carbonate. Thermal decomposition of CuCrO₄·2CuO·2H₂O has been studied by thermogravimetry and differential scanning calorimetry in flowing air and pure oxygen between 298 and 1373 K. The formation of different phases after each stage of decomposition were identified by X-ray diffraction analysis. The compound CuCrO₄ was found to be non-stoichiometric. Based on the results obtained in this study and those reported earlier, the isothermal section of the phase diagram of the Cu-Cr-O ternary system has been composed at 600 and 1150 K. Scanning electron microscopy studies of CuCrO₄·2CuO·2H₂O precipitate showed rectangular plate-like morphology. The decomposition of CuCrO₄·2CuO·2H₂O at 798 K in air resulted in the formation of a mixture of fine powder of CuCr₂O₄+CuO (Adkin's catalyst) having a uniform spherical geometry and a particle size less than 0.1 m.     

Formation of oxide phases in the system Fe2O3−Gd2O3

The formation of oxide phases in the system (1 -x) Fe₂O₃ +xGd₂O₃ was investigated for 0 x 1. On the basis of XRD measurements the distribution of oxide phases, -Fe₂O₃, Gd₃Fe₅O₁₂, GdFeO₃ and Gd₂O₃ was determined, as a function ofx. No solid solutions were observed with certainty even at the very ends of the concentration range. This was also confirmed by⁵⁷Fe Mössbauer spectroscopy. New accurate crystallographic data for Gd₃Fe₅O₁₂ are given. The formation of oxide phases in the system Fe₂O₃- Gd₂O₃ is compared with the data for analogous system Fe₂O₃-Eu₂O₃.     

Phase Relations in the SrO–Bi2O3–Fe2O3 System

The phase relations in the composition region SrFeO_{3 –} –Fe₂O₃–BiFeO₃ are studied in air by x-ray diffraction and electron microscopy. The 1000°C phase compatibility diagram is constructed. Sr_{1 – x} Bi _x FeO_{3 –} solid solutions are prepared in the range 0 < x 0.8. Their lattice parameter is found to vary nonlinearly with x. Two new phases were identified: (Sr,Bi)₃Fe₄O _y (tetragonal lattice, a= 3.907(2) Å, c= 27.30(2) Å) and Sr_0.6Bi_0.4FeO_{3 –} (tetragonal lattice,a = 5.555(2) Å, c= 11.848(5) Å).     

Effects of the Preparation Procedure and In2O3 Thickness on the Electrical and Photovoltaic Properties of In2O3 /CuInSe2 Heterostructures

In₂O₃/CuInSe₂ heterostructures were produced by growing indium oxide layers on bulk single-crystal and polycrystalline p-type CuInSe₂ substrates using thermal oxidation and magnetron sputtering. The substrates were prepared by cleaving or abrasive polishing and chemical etching. The resistivity of the In₂O₃ layers was measured as a function of temperature and layer thickness, and the current–voltage characteristics and spectral response of the heterostructures were analyzed. The results indicate that the structures exhibit reduced reflection losses at oxide thicknesses below 0.5 m. The reduced thickness of interfacial layers owing to the low process temperature in the case of magnetron sputtering makes it possible to extend the spectral region of photosensitivity of the heterostructures.     

Effect of the AL2O3 and BaO Addition on the Thermal and Physical Properties of Ternary Glass System （B2O3-BaO-AL2O3）

In borate glasses, the main structural units are the [BO3] triangles and [BO4] tetradral which form different superstructural units like; boroxol rings, metaborate rings and chains, pentaborate, diborate, triborate and pyroborate. In this work, the Barium aluminoborate glasses were prepared. Some of properties were investigated by measure like density and chemical durability and the other by calculs. The dilatometric curves were determined and they revealed that the temperature of transition （Tg） and softening （Ts） and the dilatation coefficient increase by addition of Al2O3 and BaO content.     

Phase Transformations in the Y2Cu2O5–BaCuO2 System

The sequence of phase transformations in the Y₂Cu₂O₅–BaCuO₂ pseudobinary system was studied during heating and cooling in the range 1170–1310 K. The results demonstrate that the reaction zone in BaCuO₂/Y₂Cu₂O₅ diffusion couples consists of BaCuO₂/YBa₂Cu₃O_{7 –} /Y₂BaCuO₅/Y₂O₃/Y₂Cu₂O₅ layers, corresponding to the sequence of chemical changes during YBa₂Cu₃O_{7 –} crystallization between 1170 and 1220 K. In the range 1260–1310 K, BaCu₂O₂ is formed. During cooling of a Y₂Cu₂O₅ + 4.3BaCuO₂ mixture, YBa₂Cu₃O_{7 –} crystallizes in a wide temperature range, between 1240 and 1190 K. The process depends on the presence of BaCu₂O₂ on the surface of Y₂BaCuO₅ grains in the high-temperature solution and the oxygen supply from the gas phase.     

Phase Relations in the BaO · 2B2O3–La2O3 · 3B2O3 System

The BaO · 2B₂O₃–La₂O₃ · 3B₂O₃ join of the ternary system BaO–La₂O₃–B₂O₃ is studied using differential thermal analysis, x-ray diffraction, and density measurements. The join is shown to be pseudobinary, with eutectic phase relations. In the composition range 5–99.8 mol % La₂O₃ · 3B₂O₃, glassy materials are obtained, which seems to be associated with the existence of the congruently melting compound BaO · La₂O₃ · 5B₂O₃.     

Mechanochemical Synthesis and Thermal Behavior of Metastable Mixed Oxides in the CaO–Sb2O3–Bi2O3 System

The phase composition of crystalline mechanochemical synthesis products in the CaO–Sb₂O₃–Bi₂O₃ system was determined. Of the known phases in this system, only three could be prepared mechanochemically: Ca₂Sb₂O₅, CaSb₂O₄, and CaBiO_2.5 (fcc). A new metastable phase, "-Bi₂O₃, with an orthorhombic structure close to that of the high-temperature, fluorite phase -Bi₂O₃, was obtained by mechanical processing at 30°C. A number of new metastable fluorite solid solutions of binary and ternary oxides were obtained as single-phase powders by mechanochemical synthesis. The mechanochemical yield of primary crystalline products was shown to be several times higher than that of secondary products. A broad composition range was revealed in which perovskite and fluorite phases are in mechanochemical equilibrium. The composition dependence of the lattice parameter of the metastable fluorite phase Bi_{2 – x} Sb _x O₃ was found to be the opposite of the one predicted by Vegard's law. Metastable mixed oxides undergo phase transformations during heating (starting at 280°C in the case of the ternary perovskite phase). Bi_{2 – x} Ca _x O_{3 – 0.5x} fluorite solid solutions experience a transformation at 400°C, accompanied by oxygen loss. During heating in air, Sb₂O₃-containing fluorite phases partially stabilize owing to oxidation but, nevertheless, undergo structural transformations above 480°C. The transformation of Sb_{2 – x} Ca _x O_{3 – 0.5x} metastable fluorite solid solutions near 500°C in air is accompanied by the formation of needle-like Sb₂O₃ crystals. A mechanism is proposed for the extremely rapid growth of such crystals: extrusion of the Sb₂O₃ resulting from fluorite decomposition in agglomerates through triple junctions of aggregates and through cracks in the surface layer of agglomerates.