Zum Chemischen Transport im System Mg/Mo/O ‐ Experimente und Modellrechnungen

On the Chemical Vapour Transport in the Mg/Mo/O System ‐ Experiments and Model Calculations Single crystals of MgMoO₄ and Mg₂Mo₃O₈ have been obtained via chemical vapour transport in a temperature gradient 1273 to 1173 K using Cl₂ and Br₂ as transport agents. Pure powders of the ternary compounds have been used as starting materials as well as mixtures of three coexisting phases. The observed transport behaviour is compared with results of thermodynamical model calculations. The influence of source composition, transport agent and the moisture contents is described in detail.     

Chemischer Transport ternärer Cadmiummolybdate

Chemical Vapor Transport of Ternary Cadmium Molybdates The ternary phase diagram Cd/Mo/O at 923 K have been investigated. Single crystals of CdMoO₄ and Cd₂Mo₃O₈ have been obtained via chemical vapor transport using X₂ and NH₄X (X = Cl, Br, I) as transport agent. Deposition rates are very different: up to 10 mg/h for CdMoO₄, maximum 10^–3 mg/h for Cd₂Mo₃O₈. The observed transport behaviour is compared with results of thermodynamical model calculations. The influence of source composition, transport agent and temperature gradient is described in detail.     

Zum Chemischer Transport ternärer Übergangsmetall‐ und Erdalkaliwolframate MWO4 mit Chlor

On the Chemical Vapor Transport of Ternary Transition Metal‐ and Earth Alkaline Tungstates MWO₄ with Chlorine The chemical vapor transport of transition metal tungstates MWO₄ (M=Mn, Co, Ni, Cu, Zn, Cd) was investigated in dependence on mean transport temperature (923 K to 1223 K) and amount of transport agent Cl₂. All tungstates migrate in a temperature gradient ΔT = 100 K from the region of higher temperature to the lower temperature with migration rates of 0.5 to 8 mg/h depending on experimental conditions. The transport behaviour was determined by continuous measurement of mass change during the transport experiments. The results were compared to thermo chemical calculations and the influence of moisture content discussed in detail. MgWO₄ migrates under the influence of Cl₂ in a temperature gradient 1273 K to 1173 K (migration rate 0.7 mg/h), CaWO₄ and SrWO₄ in a temperature gradient 1423 K to 1323 K (migration rate <0.1 mg/h).     

Zum Chemischen Transport im System Mn/Mo/O

Chemical Transport Reactions in the System Mn/Mo/O For the ternary system Mn/Mo/O the phasepure preparation of the compounds MnMoO₄ and Mn₂Mo₃O₈ by chemical transport is reported. The deposition from a source of coexisting threephase mixtures give the possibility to prepare single crystals under defined oxygen partial pressure. The influence of different startmixtures and the agents Cl₂, HCl, I₂, HI, TeCl₄ and SeCl₄ on the transport behaviour are described. Results hitherto existing for the single crystals give hints of only very small homogeneity ranges for both phases.     

Zum chemischen Transport von Molybdän mit HgBr2 — Experimente und Modellrechnungen

On the Chemical Transport of Molybdenum using HgBr₂ ? Experiments and Thermochemical Calculations . Mo migrates under the influence of HgBr₂ in a temperature gradient (e.g. 1 000→900°C). Besides elementary Mo we observed in some experiments the occurence of MoBr₂ and MoO₂ (from oxygen containing impurities) respectively. The transport behaviour (deposition sequence; deposition rates of various phases) has been enlightened by continous measurement of the mass change during the transport experiments using a special “transport balance”. Thus obtained deposition rates m(Mo) for molybdenum reached in the temperature region 800 ≤ T ≤ 1 040°C a maximum at T = 980°C independend from the starting material (Mo or Mo/MoO₂ mixtures). For variable densities D of transport agent at a constant temperature (T = 950°C) increasing values for m(Mo) were observed (m(Mo) = 23 mg/h, D_max = 8.61 mg HgBr₂/cm³). Thermochemical calculation give strong evidence for the migration of Mo via the endothermal reaction . The experimental deposition rates are about half as large than the calculated values. Good agreement between calculations and experiments were obtained only assuming the presense of oxygen in the starting materials.     

Zum chemischen Transport von Molybdän mit SbBr3 – Experimente und Modellrechnungen

On the Chemical Transport of Molybdenum using SbBr₃ – Experiments and Thermochemical Calculations Mo migrates in a temperature gradient from the region of higher temperature to the lower temperature using SbBr₃ as transport agent. For various mean transport temperatures (750 ? T ? 1000°C; T = 0,5 (T₁ + T₂); T₂ ? T₁ = 100°C) we observed small transport rates (? ? 0,6 mg/h) which rise up to 16 mg/h for higher transport agent concentrations. Small amounts of MoO₂ and Sb were detected beside Mo in the sink. The observed solid phases in the sink are in agreement with thermodynamical calculations by CVTrans which also demonstrate that the formation of MoO₂ and Sb as well as the transport effect of SbBr₃ are caused by traces of H₂O from the quartz glass wall. The sequence of deposition of Mo, MoO₂ and Sb in the examined temperature range can be calculated (CVTrans) and measured with the transport balance.     

Koexistenzbeziehungen,Darstellung und Eigenschaften ternärer Phasen im System Cu/Mo/O

Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO₄, Cu₃Mo₂O₉, Cu₄Mo₅O₁₇, Cu₆Mo₅O₁₈, Cu_4–xMo₃O₁₂, and Cu_xMoO₃ are found to be thermodynamical stable. The homogeneity range of Cu_4–xMo₃O₁₂ runs to x = 0.1–0.2. Single crystals of CuMoO₄ and Cu₃Mo₂O₉ were grown by chemical transport reactions with TeCl₄, Cl₂, HCl, and Br₂ as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO₄ and Cu₃Mo₂O₉ was investigated with thermal analysis and decompositon pressure measurements.     

Zum System Zn/Mo/O. II. Chemischer Transport ternärer Zinkmolybdate

On the System Zn/Mo/O. II. Chemical Transport of Ternary Zinc Molybdates The Chemical Transport is a method for preparation of phasepure multinary compounds with defined composition. We report about the possibilities to transport ternary compounds of the Zn/Mo/O system using Cl₂, HCl, Br₂, HBr, and I₂ as an agent. The influence of the solid-gas equilibria on the compositions of solids, the transport direction, and the rate is showed.     

Untersuchungen zum chemischen Transport im System V2O3/VO2

Investigation of Chemical Transport in the V₂O₃/VO₂ System The suitability of the transport agent HgCl₂ for chemical transport experiments (temperature gradient 1 173/1 113 K) in the system V₂O₃/VO₂ has been investigated. For a constant admixture of transport agent it could be observed that the transport rate, starting with V₃O₅, increases with increasing ratio O/V for the Magnéli-phases V_nO_2n–1 of this system (n′(V₃O₅) = 6 mg/d to n′(V₉O₁₇) = 20 mg/d), while the values for n′ = 12 mg/d are even for V₂O₃ and VO₂.     

Chemischer Transport ternärer Indiummolybdate

Chemical Vapor Transport of Ternary Indium Molybdates An isothermal section of the phase diagram of the system In/Mo/O at 1273 K was established by isothermal equilibration and XRD analyses of quenched samples. The chemical vapor transport of In₂Mo₃O₁₂ was investigated in dependence on mean transport temperature (823 K to 1123 K) and amount of transport agent (Cl₂ or Br₂). The observed transport behaviour is compared with results of thermodynamical calculations and the influence of mean temperature, transport agent and moisture contents is described in detail. Single crystals of the metal rich compound InMo₄O₆ were grown by chemical vapor transport in a temperature gradient 1273 K to 1173 K using H₂O as transport agent. The gaseous compound In₂MoO₄(g) accounts for the chemical vapor transport of molybdenium compounds in the metal rich part of the ternary phase diagram In/Mo/O.     

Zum System Zn/Mo/O. I. Phasenbestand und Eigenschaften der ternären Zinkmolybdate; Struktur von Zn3Mo2O9

On the System Zn/Mo/O. I. Phases and Properties of Ternary Zinc Molybdates; Crystal Structure of Zn₃Mo₂O₉ Several ternary compounds are known in the Zn/Mo/O-system. The phases ZnMoO₄, Zn₂Mo₃O₈ and Zn₃Mo₂O₉ are stable at 900°C. The coexistence ranges are shown in the ternary phase diagram. The structure of Zn₃Mo₂O₉ has been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/m (a = 7,757(1) Å, b = 7,132(1) Å, c = 8,370(2) Å, β = 117,40(1)º, Z = 2).     

MTi(0.7)Mo(0.3)Mo(5)O(10) (M = SR, Eu), first evidence of mono- and bicapped bioctahedral Mo(11) and Mo(12) clusters: synthesis, crystal structures, and physical properties

The novel quaternary reduced molybdenum oxides MTi(0.7)Mo(0.3)Mo(5)O(10) (M = Sr, Eu) have been synthesized by solid-state reaction at 1400 degrees C for 48 h in sealed molybdenum crucibles. Their crystal structures were determined on single crystals by X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pbca with 8 formula units per cell and the following lattice parameters: a(Sr) = 9.1085 (7), b(Sr) = 11.418 (1), and c(Sr) = 15.092 (3) A; a(Eu) = 9.1069 (7), b(Eu) = 11.421 (2), and c(Eu) = 15.075 (1) A. The Mo network is dominated by bioctahedral Mo(10) clusters, which coexist randomly with Mo(11) and Mo(12) clusters (monocapped and bicapped Mo(10) clusters). The Mo-Mo distances within the clusters range from 2.62 to 2.92 A and the Mo-O distances from 1.99 to 2.17 A as usually observed in the reduced molybdenum oxides. The Sr(2+) and Eu(2+) ions occupy large cavities, which result from the fusion of two cubooctahedra and thus are surrounded by 11 oxygen atoms. The M-O distances range from 2.50 to 3.23 A for the Sr compound and from 2.49 to 3.24 A for the Eu analogue. Single-crystal resistivity measurements indicate that both materials are poor metals with transitions to semiconducting states below 50 and 40 K and room temperature resistivity values of 9 x 10(-3) and 5 x 10(-3) Omega.cm for the Sr and Eu compounds, respectively. The magnetic susceptibility data indicate paramagnetic behavior due to the Eu(2+) moment at high temperatures for the Eu compound and do not reveal the existence of localized moments on the Mo and Ti sublattice in the Sr compound. An XPS study clearly suggests that the isolated Ti ions are tetravalent. Theoretical considerations preclude the existence of heterometallic Mo-Ti clusters.     

Solid state photodecomposition of alkaline earth tris/malonato/ferrates/III/

Solid state photolysis of alkaline earth tris/malonato/ferrates/III/, i.e., M₃[Fe(CH₂C₂O₄)₃]₂.xH₂O /M=Mg, Ca, Sr, Ba/ has been investigated employing Mössbauer, infrared and reflectance spectroscopic techniques. The complexes were irradiated for 400 h using a medium pressure mercury vapour lamp of 250 Watts. Photoreduction led to the formation of M[Fe^II(CH₂C₂O₄)₂(H₂O)₂]. The extent of photoreduction showed the following order: Ca>Sr>Mg>Ba. The results have been compared with those of analogous alkaline earth tris/oxalato/ferrates/III/.     

Dependence of the Structure and Properties of (M,Cu)Sr2(Ln,Ca)Cu2O8−δ (1212) and (M,Cu)Sr2(Ln,Ce4+)2Cu2O10−δ (1222) Phases on the Cation M

The composition and structure of (M,Cu)(Sr,Ln)₂(Ln,Ca,Sr)Cu₂O_8– phases, where M = B, Al, Cr, Pb, Bi, Ru, or Mo (1212 type), and (M,Cu)(Sr,Ln(₂(Ln,Ce⁴⁺)₂Cu₂O_10– phases, where M = V, Cr, Mn, Ru, or Mo (1222 type), have been determined. The role of the M cation in the formation of the crystal structures and the superconductivity phenomenon was analyzed. The relationship between the type of M cation and structural parameters was discovered.     

Zum chemischen Transport von Wolfram mit HgBr2 – Experimente und Modellrechnungen

On the Chemical Transport of Tungsten using HgBr₂ – Experiments and Thermochemical Calculations Using HgBr₂ as transport agent tungsten migrates in a temperature gradient from the region of higher temperature to the lower temperature (e.g. 1 000 → 900°C). The transport rates were measured for various transport agent concentrations (0.64 ? C(HgBr₂) ? 11.74 mg/cm³; T? = 950°C) and for various mean transport temperatures (800 ? T? ? 1 040°C). Under these conditions tungsten crystals were observed in the sink region. To observe the influence of tungsten dioxide (contamination of the tungsten powder) on the transport behaviour of tungsten, experiments with W/WO₂ as starting materials were performed. According to model calculations the following endothermic reactions are important for the migration of tungsten: In the presence of H₂O or WO₂ other equilibria play a role, too. Using a special “transport balance” we observed a delay of deposition of tungsten (e.g. T? = 800°C; 15 h delay of deposition) with W and W/WO₂ as starting materials. The heterogeneous and homogeneous equilibria will be discussed and an explanation for the non equilibrium transport behaviour of tungsten will be given.     

Extraction liquide-liquide par des esters alkylphosphoriques. II. Extraction des nitrates de béryllium et des autres alcalino-terreux par le tri-n-butylphosphate

The solvent extraction systems Be(NO₃)₂? HNO₃? H₂O? TBP/kerosene and M(NO₃)₂? H₂O? TBP/kerosene (TBP = tri-n-butylphosphate, M = Be, Mg, Ca and Sr) have been studied. The alkaline earths elements are poorly extracted. Only very high acidities allow better extraction of beryllium. The sequence of extraction of the alkaline earths elements by the TBP depends on the concentration of the cations and is Ca > Be > Sr > Mg if the metal concentration is lower than 2 M.     

Die Clusterazide M2[Nb6Cl12(N3)6]·(H2O)4—x (M = Ca,Sr, Ba)

The Cluster Azides M₂[Nb₆Cl₁₂(N₃)₆]·(H₂O)_4—x (M = Ca, Sr, Ba) The isotypic cluster compounds M₂[Nb₆Cl₁₂(N₃)₆] · (H₂O)_4—x (M = Ca (1) , M = Sr (2) and M = Ba (3) ) have been synthesized by the reaction of an aequeous solution of Nb₆Cl₁₄ with M(N₃)₂. 1 , 2 and 3 crystallize in the space group Fd3¯ (No. 227) with the lattice constants a = 1990.03(23), 2015.60(12) and 2043, 64(11) pm, respectively. All compounds contain isolated 16e— clusters whose terminal positions are all occupied by orientationally disordered azide ligands.     

Thermochemische Untersuchungen zum System Mn/Mo/O

Thermodynamical Investigations to the System Mn/Mo/O The thermodynamical data of the two ternary phases Mn₂Mo₃O₈ and MnMoO₄ can determined with EMF measurements using solid zirconia ionic conductors in tablets arrangement. The thermodynamical data was found in a 3. law calculation:      

Thermal stability and surface structure of Mo/CeO<Subscript>2</Subscript> and Ce-doped Mo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

In order to explore the influence of CeO₂ on the structure and surface characteristics of molybdena, an investigation was undertaken by using N₂ adsorption (BET method), thermal analysis and in-situ diffuse reflectance infrared (DRIFT) techniques. In this work, the Mo/CeO₂ and Ce-Mo/Al₂O₃ samples were prepared by impregnation and co-precipitation methods with high Mo loadings. Combining the results one may notice that the presence of ceria led to the increase of polymerized surface Mo species so as to forming Mo-O-Ce linkages besides the formation of coupled O=Mo=O bonds indicative of polymeric MoO₃. From thermal analysis, it can be inferred that Mo/Al₂O₃ is the thermally most stable material in the temperature range used in the experiment (up to 900°C), whereas Ce-Mo/Al₂O₃ and Mo/CeO₂ samples undergo morphological modifications above 700°C resulting in lattice defects, which motivate the mobility of Mo and Ce ions and thus enhance the possibility of interaction between them. Additionally, their activity towards CO adsorption needs reduced ceria and molybdena containing coordinatively unsaturated sites (CUS), oxygen vacancies and hydroxyl groups to form various carbonate species.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。