Mechanochemical synthesis and thermal stability of phases in the Y2O3–Yb2O3 system

Substitutional, continuous solid solution of the general formula Y_2–xYb_xO₃ was obtained from the mixture of Y₂O₃ and Yb₂O₃ oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y₂O₃ and Yb₂O₃. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb³⁺ ions replacing Y³⁺ ions in the crystal lattice of Y₂O₃. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator.

     

Ionic liquid-based hydrothermal synthesis of Lu2O3 and Lu2O3:Eu3+ microcrysals

Uniform and well-defined Lu₂O₃ and Lu₂O₃:Eu³⁺ microarchitectures have been successfully synthesized via a green and facile ionic liquid-based hydrothermal method followed by a subsequent calcination process. Novel 3D micro-rodbundles and 1D microrods of Lu₂O₃ and Lu₂O₃:Eu³⁺ were controllably obtained through this method. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectra were used to characterize the micromaterials. The proposed formation mechanisms have been investigated on the basis of a series of SEM studies of the products obtained at different hydrothermal durations. The results indicated that hydrothermal temperature and the ionic liquid-tetrabutylammonium hydroxide were two key factors for the formation as well as the morphology control of the Lu₂O₃ and Lu₂O₃:Eu³⁺ microarchitectures.     

Phase equilibria in the BaO-Bi2O3-B2O3 system

Phase equilibria in the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. Quasi-binary sections have been determined, and an isothermal section of the system in the subsolidus region has been constructed. The BaO-Bi₂O₃-B₂O₃ ternary system has been divided into 22 triangles of coexisting phases. It has been found that four bismuth barium borates exist, namely, Ba₃BiB₃O₉, BaBi₂B₄O₁₀, BaBiB₁₁O₁₉, and BaBiBO₄. Ba₃BiB₃O₉ undergoes a phase transition at 850°C and exists up to 885°C, where it decomposes in the solid state. BaBiB₁₁O₁₉ and BaBi₂B₄O₁₀ melt congruently at 807 and 730°C, respectively. BaBiBO₄ melts incongruently at 780°C. X-ray powder diffraction data for the low-temperature polymorph of Ba₃BiB₃O₉ are presented.     

Subsolidus phase equilibria in the SrO-Bi2O3-B2O3 system

Phase equilibria in the SrO-Bi₂O₃-B₂O₃ system were studied using powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Quasi-binary sections were determined, and an isothermal section of the system in the subsolidus region at 600°C was constructed using the crossing spections method. A new ternary compound was found: SrBi₂B₄O₁₀. The existence of SrBi₂B₂O₇ was verified. Bi₂O₃-SrB₂O₄ and Bi₄B₂O₉-2SrO: 3B₂O₃ polytherms were constructed.     

Solid-state reactions in Y2O3:3Al2O3:4B2O3 system studied by FTIR spectroscopy and X-ray diffraction

In the Y₂O₃:3Al₂O₃:4B₂O₃ system infrared absorption spectroscopy and X-ray diffraction have been used to study the solid-state reactions in the 600–1300°C temperature range. The expected YAl₃(BO₃)₄ formation (whose optimum temperature is at about 1150°C) was proceeded and accompanied by the appearance of YBO₃ and Al₄B₂O₉ intermediate phases. At higher temperatures the Al₁₈B₄O₃₃ phase was also identified with both methods. Based on these results, some chemical reactions were suggested.     

Promoted ternary CuO-ZrO2-Al2O3 catalysts for methanol synthesis

Ternary CuO-ZrO₂-Al₂O₃ catalysts promoted by palladium or gold were prepared and tested in CO hydrogenation reaction at 260°C under elevated pressure (4.8 MPa). The promotion effect of palladium or gold addition on the physicochemical and catalytical properties of CuO-ZrO₂-Al₂O₃ catalysts in methanol synthesis (MS) was studied. The catalysts were characterized by BET, XRD, TPR-H₂, TPD-NH₃ methods. The BET results showed that the ternary system CuO-ZrO₂-Al₂O₃ had the largest specific surface area, cumulative pore volume and average pore size in comparison with the promoted catalysts. The yield of methanol can be given through the following sequence: 5%Pd/CuO-ZrO₂-Al₂O₃ > CuO-ZrO₂-Al₂O₃ > 2%Au/CuO-ZrO₂-Al₂O₃. We also found that the presence of gold or palladium on catalyst surface has strong influence on the reaction selectivity. The high selectivity of gold doped ternary catalyst is explained by the gold-oxide interface sites created on the catalyst surface and the acidity of those systems. The higher selectivity to methanol in the case of the palladium catalyst is explained by the spillover effect between Pd and CuO.      

Phase equilibria in the Bi2O3-BaB2O4-B2O3 system in the subsolidus region

The phase equilibria in the concentration triangle Bi₂O₃-BaB₂O₄-B₂O₃ of the BaO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction and DTA. Barium bismuth borates of the composition BaBi₂B₄O₁₀ and BaBiB₁₁O₁₉ have been found to exist. These borates melt at 730 and 807°C, respectively. The quasi-binary sections have been determined. It has been shown that the isothermal section of the Bi₂O₃-BaB₂O₄-B₂O₃ in the subsolidus region at 600°C is characterized by 13 triangles of coexisting phases.     

Hydrothermal crystal synthesis in the Ho2O3(Yb2O3)GeO2KFH2O systems

Crystallization in the Ho₂O₃(Yb₂O₃)GeO₂KFH₂O systems has been investigated under hydrothermal conditions. Crystallization fields of the crystalline phases have been determined. Single crystals of Ho₂Ge₂O₇, Yb₂Ge₂O₇ (two types), K₂HoF₅, K₂YbF₅, K_xYb_yGe_pO_q (P-type), Ho(OH)₃, Yb(OH)₃, and K₂Ge₄O₉ have been obtained. The germanates synthesized have been studied by X-ray analysis and infrared-spectroscopy. Diorthogermanate Yb₂Ge₂O₇ has been found to crystallize in two structural types; the first is characterized by the usual structure that is typical for rare-earth germanates, the second is new for germanates of rare-earth elements. High chemical resistance is typical of these crystals. The P-type germanate also has a new type of structure among rare earth germanates. Some suggestions are made as to the structure of these new germanates on the basis of X-ray and ir-spectroscopic data.     

Phase Relations in the Solidus Region of the SrO-Bi2O3-B2O3 System

Phase equilibria in the SrO-Bi₂O₃-B₂O₃ system have been investigated by X-ray powder diffraction analysis and DTA. Ternary compounds SrBiBO₄ and Sr₇Bi₈B₁₈O₄₆ congruently melting at 820 ± 5°C and 760 ± 5°C have been found. Quasi-binary sections are determined and the isothermal section of the system in the region Bi₂O₃-Sr₂Bi₂O₆-Sr₃B₂O₆-B₂O₃ at 600°C has been constructed.     

Catalytic Properties of the System Fe2O3-Ga2O3 in Ammonia Oxidation

The catalytic properties of the system Fe₂O₃-Ga₂O₃ in high-temperature oxidation of ammoniaand the influence exerted by the phase composition of the system on the physicochemical, catalytic properties of the catalysts were studied.     

Subsolidus Phase Relationships in the Er2O3-Rh2O3 System

The Er₂O₃-Rh₂O₃ system was studied by the annealing and quenching method using X-ray phase, thermal, and chemical analyses. A schematic subsolidus diagram of phase relationships was constructed.     

Subsolidus phase relations in the Gd2O3-Rh2O3 system

The Gd₂O₃-Rh₂O₃ system is studied using the anneal-and-quench technique, X-ray powder diffraction, thermal analysis, and chemical analysis. A schematic subsolidus phase diagram is designed. One double oxide of composition GdRhO₃ is found to exist. It was characterized using some physicochemical methods.     

Phase equilibria in the system NiO-V2O5-Fe2O3 in subsolidus area

Reactivity of FeVO₄ towards Ni₂V₂O₇ and Ni₃V₂O₈ in the solid state was investigated. On the base of XRD and DTA results, phase diagrams in subsolidus area of the FeVO₄-Ni₂V₂O₇ and FeVO₄-Ni₃V₂O₈ intersections of the ternary system NiO-V₂O₅-Fe₂O₃ have been worked out and the phase diagram of this ternary system in subsolidus area in the whole component concentration range has been verified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase equilibria in the P2O5-rich part of the system Y2O3−Na2O−P2O5

In the ternary system Y₂O₃?Na₂O?P₂O₅, the partial system Y(PO₃)₃?NaPO₃?P₂O₅ was examined by means of differential thermal analysis and X-ray powder diffraction; its phase diagram is given.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal analysis of the Bi2O3-Y2O3-ZrO2 pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new colour inorganic pigments. Chemical compounds of the Bi_2-xY_x/2Zr_3x/₈O₃ type were synthetised. The host lattice of these pigments is Bi₂O₃ that is doped by Y³⁺ and Zr⁴⁺ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

Thermal analysis of the Bi2O3-Er2O3-Zro2 pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new ecological inorganic pigments. Chemical compounds of the Bi_2−xEr_x/2Zr_3x/8O₃ type were synthetized. The host lattice of these pigments is Bi₂O₃ that is doped by Er³⁺ and Zr⁴⁺ ions. The incorporation of doped ions provides interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

Ba2Cu3O5+δ as an intermediate phase during the synthesis of YBa2Cu4O8

We propose a reaction model for the synthesis of YBa₂Cu₄O₈ under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide react to Ba₂Cu₃O_5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected to Ba₂Cu₃O_5+δ, which reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈ or decomposes to BaCuO₂ and CuO. In a last step parts of BaCuO₂ reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈.     

Hydrothermal synthesis followed by post heat-treatment: A novel route for the fabrication of KCa2Nb3O10 layered compound

Due to unique properties, KCa₂Nb₃O₁₀ compound has received great attention worldwide. High-temperature solid-state reaction is the common route for the synthesis of this compound. In order to propose a new low-temperature method (i.e. hydrothermal synthesis), which could improve the final properties of KCa₂Nb₃O₁₀, this study has been planned and performed. The preliminary experiments in KOH-Nb₂O₅ and Ca(OH)₂-Nb₂O₅ systems revealed that KCa₂Nb₃O₁₀ could be hydrothermally synthesized from a KOH-Ca(OH)₂-Nb₂O₅ system using an alkaline condition (i.e. 5 M < KOH <10 M). However, the experimental results showed that the product only consisted of KNbO₃ and Ca₂Nb₂O₇ phases. To initiate the reaction between KNbO₃ and Ca₂Nb₂O₇, the obtained KNbO₃-Ca₂Nb₂O₇ mixture was heat-treated in an air atmosphere. The results showed that KCa₂Nb₃O₁₀, with a high crystallinity and good purity, has been successfully obtained at 800 °C. This temperature is the lowest temperature, reported for the synthesis of KCa₂Nb₃O₁₀ compound so far. The SEM investigations revealed that the obtained KCa₂Nb₃O₁₀ powder has plate-like morphology due to its layered structure.     

Solid State Phase Formation in the Bi2O3-PbO-CaO System

Following our previous research, this work is dedicated to the study of phase formation in the subsolidus domain of the Bi₂O₃-PbO-CaO system. Former investigations performed by DTA/TGA and XRD have pointed out that under non-isothermal conditions only the formation of binary compounds occurs. Under such conditions these compounds could be non-equilibrium phases. In order to establish the conditions of formation of equilibrium phases, a study of the Bi₂O₃-PbO-CaO system, in isothermal conditions, was carried out. The results obtained in isothermal conditions have confirmed the presence of Bi₂O₃-rich solid solutions and Ca₂PbO₄ as main equilibrium phases. An attempt to represent the phase relations of the mentioned system at 700°C should be equally mentioned. This revised version was published online in July 2006 with corrections to the Cover Date.