Experimentelle Bestimmung der Gleichgewichtslagen im System NaCl(l)-KCl(l)-Na(l)-K(l)

Zusammenfassung Ausgehend von nahezu äquivalenten Mengen an Na und KCl werden die Gleichgewichtszusammensetzungen der metallreichen und der salzreichen Phase des Systems NaCl–KCl–Na–K im Bereich von 1140 bis 1240° K ermittelt. Die Gleichgewichtskonzentrationen der Komponenten werden zur Berechnung der GleichgewichtskonstantenK _x in beiden Phasen herangezogen.

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The equilibrium compositions of both metal-rich and salt-rich phases of the system NaCl–KCl–Na–K are investigated in the temperature range from 1140 to 1240° K, starting from nearly equivalent amounts of Na and KCl. From the experimentally determined concentrations the equilibrium constantsK _x were calculated.

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Chemical and Transport Properties of Carbon–Oxygen–Hydrogen Plasmas in Isochoric Conditions

The composition and transport properties of CO₂, CO, CH₄, CO + Ar (50 vol%), CO + Fe (50 vol%) have been calculated at constant volume assuming local thermodynamic equilibrium (LTE). Except at low temperature (T < 3000 K), when the formation of condensed species or more complex molecules can occur, pressure increases with temperature at constant volume. For example, for 1 mol of CH₄ starting at 0.1 MPa and 298 K the pressure can reach 40 MPa at 20,000 K. The consequence is a shift to higher temperatures of dissociation and ionization. The electrical conductivity σ_e at constant volume increases drastically relative to that obtained at 0.1 MPa over 15,000 K, in spite of the decrease of the electron density n_e This is due to the increase in the neutral species density. n_i, with a much lower electron-neutral species collision cross section σ_ei (σ_e is inversely proportional to n_i,σ_ei). The viscosity always exhibits a maximum when the ionization degree increases over 1–30%, but this maximum is shifted to higher temperatures and its peak value is higher. The thermal conductivity peaks due to dissociation and ionization are shifted to higher temperatures and their values are reduced compared to those obtained at constant pressure.     

Untersuchungen in den Systemen: Mangan—{Vanadin,Rhenium, Eisen}—silicium

Zusammenfassung Die strukturchemischen Verhältnisse werden in den Dreistoffen: Mn–{V, Re, Fe}–Si für einen Zustand –1000° C homogenisiert und abgeschreckt — untersucht. Die neu aufgefundene Mn–Re--Phase ist hinsichtlich der Ordnung mit der Re–Nb--Phase vergleichbar. Mn₅Si₂ wird durch Mn/Re-Austausch bei 1000° C stabilisiert. Einer ternären Kristallart (X) mit erheblichem Homogenitätsgebiet kommt die ungefähre Formel Mn_2–3Re_2–1Si zu. Der Austausch Mn/Re in Mn₅Si₃ erfolgt nur in der 6g-Lage. MnSi und ReSi sind lückenlos mischbar.Gitterparameter für die Mn–Re–Si- und V–Mn–Si--Phasen werden bestimmt. V₃Si löst etwa 50 Mol% Mn₃Si. Die lückenlose Mischreihe Mn₃Si–Fe₃Si wird bestätigt; gegenüber Literaturbefunden besteht jedoch im ganzen Bereich ein Ordnungszustand (BiF₃-Typ).

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The ternary systems: Mn–{V, Re, Fe}–Si have been studied after anneal at 1000° C followed by a quench by means of X-ray methods. The newly found Mn–Re--phase compares with the Re–Nb--phase as far as the ordering is concerned. Mn₅Si₂ can be stabilized by Re/Mn-substitution up to higher temperatures. A ternary phase X having a large homogeneous region, can roughly be described by a formula Mn_2–3Re_2–1Si. Re substitutes Mn within the Mn₅Si₃-phase occupying the 6g positions only. Lattice parameters of the Mn–Re–Si- and V–Mn–Si--phases have been determined. V₃Si dissolves about 50 mole% Mn₃Si. The solid solutions Mn₃Si–Fe₃Si can be confirmed; however there is an ordering throughout the whole domain (BiF₃-structure type).

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Zirconium-Containing Compositions with a Component Ratio Characteristic of the Garnet Structure: Physicochemical and Catalytic Properties

The possibility for the formation of garnet structures in the Mn–Fe–Zr–O and Ca–Sm–Zr–O systems obtained by the precipitation of the corresponding salts is studied. It is shown that, in the Mn–Fe–Zr–O system, garnet is crystallized at 860–920°C, for which probable cation distribution is estimated to be {Zr_2.5 ⁴⁺Mn_0.5 ²⁺}[Mn₂ ²⁺](Fe_2.5 ³⁺Mn_0.5 ³⁺)O₁₂. In the Ca–Sm–Zr–O system, the perovskite CaZrO₃, pyrochlore Sm₂Zr₂O₇, and CaO are formed at 900–1200°C, but compounds with garnet structures are not found. The reported systems are characterized by surface areas of 300–450 m²/g at 450°C, and they have the polydisperse distribution of pores over sizes. The introduction of surfactants at the stage of component mixing enables an increase in the overall pore volume and mechanical strength of these systems. The Mn–Fe–Zr and Ca–Sm–Zr compositions are active catalysts for the complete oxidation of hydrocarbons.     

Vapour pressure of 4-methylpyridine (MePy) over [Ni(MePy)4(NCS)2]·y(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy) clathrates during their dissociation

Strain measurement and quasiequilibrium thermogravimetry were used to study the dissociation processes of two clathrates, [Ni(MePy)₄(NCS)₂]·(MePy) and [Cu(MePy)₄(NCS)₂]·2/3(MePy), accompanied by the liberation of MePy into the gaseous phase. In the Ni clathrate dissociation process in the temperature range 298–368 K the liberated MePy was redistributed between the solid clathrate and gaseous phases; the MePy vapour pressure over the clathrate is a function of temperature and the guest contenty, which agrees with the presence in the MePy-[Ni(MePy)₄(NCS)₂] system of a wide range of -clathrate solutions, [Ni(MePy)₄(NCS)₂]·y(MePy). The same methods used to study the Cu clathrate dissociation resulted in conclusions different from those obtained for the dissociation process of the above clathrate: the process is described by the equation [Cu(MePy)₄(NCS)₂]·2/3(MePy)_solid =[Cu(MePy)₂(NCS)₂]_solid+22/3(MePy)_gas; the temperature dependence of the Mepy vapour pressure over the solid sample does not depend on its composition, which points to the absence from the system of solid solutions based on the clathrate. Standard changes of the enthalpy, entropy, and isobaric-isothermal reaction potential for the temperature range 292–325 K are equal to 178.6±1.7 kJ (mole of clathrate)^–1, 463±5.6 J (mole of clathrate)^–1 K^–1, and 40.4±2.4 kJ (mole of clathrate)^–1, respectively.     

Adsorption characteristics of chloroform on modified zeolites from gaseous phase as well as its aqueous solution

Adsorption characteristics of chloroform from its aqueous solution on Na–Y and Li–Na–Y modified by SiCl₄ were measured and compared with those on Na–ZSM-5 and Na-Mordenite.No adsorption occurred on Na–Y with high hydrophilicity, while the siliceous faujasites became capable of adsorption and its amount increased with increase in the Si/A1 ratio. Adsorption isotherms are of Langmuir type, suggesting that adsorption proceeds by pore filling. The adsorption amounts expressed in volume on Na–Y with high hydrophobicity corresponded to their pore volumes.Adsorption characteristics of chloroform from gaseous phase on Na–Y with different Si/A1 ratio were also measured. The adsorption capability decreased with increasing Si/A1 ratio.Immersional heats of zeolites into water or chloroform were measured in order to evaluate the surface affinity to both solvents. Immersional heats into water were almost constant (about 500 mJ·m^–2) for zeolites with their Si/A1 ratio below 10. The heats decreased with an increase in the Si/A1 ratio above 10, then became almost constant (about 120 mJ·m^–2) over 30 in their ratio. Heats of immersion of Na–Y series into chloroform were almost constant irrespective of their Si/A1 ratio, but decreased slightly when the ratio exceeded 20.Adsorption characteristics of chloroform could be well related to immersional heats into both solvents.     

Nickel and potassium co-modified β-Mo2C catalyst for CO conversion

Nickel and potassium co-modified -Mo2C catalysts were prepared and used for CO hydrogenation reaction. The major products over -Mo2C were C1–C4 hydrocarbons, only few alcohols were obtained. Addition of potassium resulted in remarkable selectivity shift from hydrocarbons to alcohols at the expense of CO conversion over -Mo2C. Moreover, it was found that potassium enhanced the ability of chain propagation with a higher C2+OH production. Modified by nickel, -Mo2C showed a relatively high CO conversion, however, the products were similar to those of pure -Mo2C. When co-modified by nickel and potassium, -Mo2C exhibited high activity and selectivity towards mixed alcohols synthesis, and also the whole chain propagation to produce alcohols especially for the stage of C1OH to C2OH was remarkably enhanced. It was concluded that the Ni and K had, to some extent, synergistic effect on CO conversion.     

Synthesis, characterization and photophysics of bimetallic manganese(I) and ruthenium(II) complexes

A series of new manganese(I) and ruthenium(II) monometallic and bimetallic complexes made of 2,2′-bipyridine and 1,10-phenanthroline ligands, [Mn(CO)₃(NN)(4,4′-bpy)]⁺, [{(CO)₃(NN)Mn}₂(4,4′-bpy)]²⁺ and [(CO)₃(NN)Mn(4,4′-bpy)Ru(NN)₂Cl]²⁺ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized, in addition to already known ruthenium(II) complexes [Ru(NN)₂Cl(4,4′-bpy)]⁺ and [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl]²⁺. The electrochemical properties show that there is a weak interaction between two metal centers in Mn–Ru heterobimetallic complexes. The photophysical behavior of all the complexes is studied. The Mn(I) monometallic and homobimetallic complexes have no detectable emission. In Mn–Ru heterobimetallic complexes, the attachment of Mn(I) with Ru(II) provides interesting photophysical properties.     

Structural Studies on Saturated Aqueous Solutions of Manganese(II), Cobalt(II), and Nickel(II) Chlorides by X-ray Diffraction

As a part of our studies on crystallization processes of electrolytes, the structure of aqueous solutions of MCl₂ (M = Mn, Co, Ni) equilibrated with hydrate crystals, MCl₂ · mH₂O (m = 6, 4, 2), was investigated by means of X-ray diffraction at 25, 40, 55, and 70°C. The complexes formed in MnCl₂ solutions, were found to be mixed–ligand chloroaqua octahedral complexes of M²⁺ ions with the Mn—O and Mn—Cl distances of about 220 and 251 pm, respectively. The average number of Mn—Cl and Mn—O interactions increased from 1.2 to 1.9 and decreased from 4.8 to 4.1, respectively, with changing MnCl₂ solutions from Mn25 (MnCl₂ solution at 25°C) to Mn70 (MnCl₂ solution at 70°C). In the octahedral species of Co²⁺, the Co—O and Co—Cl distances were found to be about 211 and 240 pm, respectively. With an increase in the saturated concentration by changing temperature from 25 to 70°C, the average coordination number of the Co—Cl contact per Co²⁺ increased from 0.5 to 1.2, and the average number of Co—O interactions decreased from 5.5 to 4.8. The structural analysis was carried out by taking into consideration the existence of the tetrahedral species in the solutions saturated at 40, 55, and 70°C, on the assumption of the existence of [CoCl₄]^2–. The Co—Cl distance was found to be 228 pm, while the number of Co—Cl interactions in the [CoCl₄] complex was calculated to be 3.7 by the least-squares calculations. The Ni—O and Ni—Cl distances were estimated to be about 206 and 237 pm, respectively. The frequency factor n of the Ni—O and Ni—Cl interactions decreased monotonously from 5.6 to 5.0 and increased from 0.4 to 1.0, respectively, with increasing NiCl₂ concentration. The n values of the Co—Cl and Ni—Cl interactions of the octahedral complexes increased sharply with concentration at higher concentrations. Comparing structures of the complexes in the saturated solutions and the hydrate crystals of these metal ions, we discussed a role of the complexing species on crystallization of the hydrates.     

The potential/pO2− diagrams of uranium and the feasibility of a pyrochemical head-end treatment of nuclear fuels in molten chlorides

In this paper, the values of the solubility products of UO₂ and MgUO₄ in the (K–Na–Mg 1/2)Cl eutectic and the solubility products of UO₂ and (K,Na)UO₃ in the (K–Na)Cl eutectic are reported. The complete potential/pO^2– diagram of uranium is set up in these liquid melts and a method of separation UO₂/PuO₂ is discussed in the molten chlorides media.     

Kinetics and catalysis by NaY entrapped Pt carbonyl clusters in the CO+NO reaction

[Pt₁₂(CO)₂₄]^2–/NaY and [Pt₉(CO)₁₈]^2–/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al₂O₃. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.     

Electrochemical generation of a nickel–carbonyl complex, catalyst for the electroreductive coupling of organic halides and carbon monoxide into ketones

The nickel–carbonyl complex Ni(CO)bpy is involved in the nickel-catalysed electroreductive coupling of organic halides and carbon monoxide into ketones. The active species is obtained from a stoichiometric mixture of Ni⁰, 2,2′-bipyridine and CO. The electrochemical method used to generate this complex allows a good tuning of Ni⁰ production versus CO dissolution. We have shown that Ni(CO)bpy results from a CO equilibrium exchange between Ni(CO)₂bpy and Nibpy.     

Dissociative chemistry of ionic transition metal cluster fragments

The ionic fragments formed by collision-induced dissociation of Mn₂(CO) _y ⁺ ions (y=1–10) are reported. The ratio of product ions formed by metal-metal vs. metal-ligand bond cleavage are discussed in terms of the dependence of the metal-metal bond energy on the metal-to-ligand ratio. The collision-induced dissociation data indicate that the metal-metal bond energy of Mn₂(CO) ₅ ⁺ and Mn₂(CO) ₁₀ ⁺ is less than that for Mn₂(CO) _y ⁺ (y=1–4 and 6–9). The product ions arising by metal-metal and metal-ligand bond cleavage reactions for collision-induced dissociation and photodissociation are compared. On the basis of this data and the known photochemistry/photophysics of Mn₂(CO)₁₀, it is proposed that the difference in collision-induced dissociation and photodissociation product ion branching ratios is attributable to spin-orbit transitions of the activated ions.     

Chemical transformations of a SiO2-supported [Fe5RhC(CO)16]− cluster and catalysis of propylene hydroformylation

Chemical transformations of SiO₂-supported [Fe₅RhC(CO)₁₆]^– and [Fe₄RhC(CO)₁₄]^– clusters in Ar, CO, and synthesis gas are studied by IR spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy. It is shown that partial transformation of the [Fe₅RhC(CO)₁₆]^– cluster to the [Fe₄RhC(CO)₁₄]^– cluster occurs immediately after its deposition on the substrate surface with the simultaneous formation of Fe²⁺ ions. The complete conversion of the supported [Fe₅RhC(CO)₁₆]^– cluster to [Fe₄RhC(CO)₁₄]^– is observed at 323 K in the synthesis gas. At 373 to 423 K [Fe₅RhC(CO)₁₆]^– transforms into a mixture of Fe₄Rh₂C(CO)₁₆, [Fe₄RhC(CO)₁₄]^–, and [Fe₅₃Rh₃C(CO)₁₅]^– clusters. In the 523 to 623 K range, the supported [Fe₅RhC(CO)₁₆]^– cluster decarbonylates completely to form bimetallic species Å 5 Å in size. Silica-supported FeRh clusters are active in propylene hydroformylation at 423 to 473 K and form a mixture of butyl alcohols and butyraldehydes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 632–641, April, 1995.This work was financially supported by the Krasnoyarsk Region Scince Foundation (Grant No. 1F0020).     

Vibrational energy storage in high pressure mixtures of diatomic molecules

CO/N₂, CO/Ar/O₂, and CO/N₂/O₂ gas mixtures are optically pumped using a continuous wave CO laser. Carbon monoxide molecules absorb the laser radiation and transfer energy to nitrogen and oxygen by vibration–vibration energy exchange. Infrared emission and spontaneous Raman spectroscopy are used for diagnostics of optically pumped gases. The experiments demonstrate that strong vibrational disequilibrium can be sustained in diatomic gas mixtures at pressures up to 1 atm, with only a few Watts laser power available. At these conditions, measured first level vibrational temperatures of diatomic species are in the range T_V=1900–2300 K for N₂, T_V=2600–3800 K for CO, and T_V=2200–2800 K for O₂. The translational–rotational temperature of the gases does not exceed T=700 K. Line-of-sight averaged CO vibrational level populations up to v=40 are inferred from infrared emission spectra. Vibrational level populations of CO (v=0–8), N₂ (v=0–4), and O₂ (v=0–8) near the axis of the focused CO laser beam are inferred from the Raman spectra of these species. The results demonstrate a possibility of sustaining stable nonequilibrium plasmas in atmospheric pressure air seeded with a few percent of carbon monoxide. The obtained experimental data are compared with modeling calculations that incorporate both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, showing reasonably good agreement.     

Ein Beitrag zur Kenntnis ternärer Phosphorlegierungen

Zusammenfassung Die Schnitte bei 25 und 33,3 At% P in den Dreistoffsystemen Cr–Mn–P, Cr–Fe–P, Cr–Ni–P, Cr–Cu–P, Mn–Fe–P, Mn–Ni–P, Mn–Cr–P, Fe–Ni–P, Fe–Cu–P und Ni–Cu–P werden röntgenographisch untersucht. Es wird das Ergebnis vonVogel und Mitarbeitern hinsichtlich der Mischbarkeit von Fe₃P–Ni₃P bzw. Cr₃P–Fe₃P bestätigt.Eine solche Mischreihe bilden auch Cr₃P und Mn₃P. Dagegen dürften Cr₃P und Ni₃P nur begrenzt mischbar sein; Fe₃P nimmt mindestens 25 Mol% Mn₃P auf. Ni₃P löst rund 50 Mol% des nicht isotypen Cu₃P, während zwischen den isotypen Phasen Mn₃P und Ni₃P sowie zwischen Cr₃P, Mn₃P, Fe₃P einerseits und Cu₃P keine merkliche Löslichkeit beobachtet wurde.Lückenlose Mischreihen bilden auch Mn₂P–Fe₂P, Fe₂P–Ni₂P sowie Ni₂P–Mn₂P. Obwohl keine isotype Cr₂P-Phase gefunden wird, besteht ein praktisch homogener Übergang zwischen Fe₂P–Cr₂P, Ni₂P–Cr₂P. Mn₂P löst rund 50 Mol% Cr₂P; Mn₂P sowie Fe₂P nehmen jeweils etwa 20 Mol% Cu₂P auf.Mit 4 Abbildungen     

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH₄–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH₄ and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C₃–C₅ hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H₂ reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H₂ reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.     

Ion-exchange selectivities of amorphous and anatase-types hydrous titanium dioxides and the possible separation of bivalent transition metal ions

Summary Amorphous and anatase-type hydrous titanium dioxides showed typical amphoteric ion-exchange properties. The ion-exchange selectivity for bivalent transition metal ions was studied as a function of both pH and metal ion concentration in ammonium nitrate media. The selectivity series was Co<Ni<Mn<Zn<Cd<Cu for the amorphous and Ni<Co<Mn<Zn<Cd<Cu for the anatase-type material. The separation factor on the anatase-type material is larger than on the amorphous material. Effective group separation of Co–Ni and Zn–Cd–Cu could be achieved on an ion-exchange column containing the anatase-type hydrous titanium dioxide.Part XXIV in a series on synthetic inorganic ion-exchange materials.     

Synthesis, Structure and Properties of Na2Zn(OEt)4(HOEt)5

The synthesis, structure and properties of Na₂Zn(OEt)₄(HOEt)₅, having the right Na:Zn ratio for sol–gel synthesis of the highly Na-ion conducting ceramic Na_1.8Zn_0.9Si_1.1O₄, is described. It was synthesised in high yield by a metathesis reaction of ZnCl₂ and 4NaOEt in ethanol or ethanol/toluene solvent. The structure was determined by single-crystal X-ray methods and consists of two symmetry related polymeric strands with the metal sequence ...–Zn–Na–Na–Zn–.... Extensive hydrogen bonding is present within each chain. Further characterization was made with IR- and Raman-spectroscopy and thermo-calorimetry, showing that the compound is stable to 65°C.     

Synthesis and electrochemical study of Li-Mn-Ni-O cathodes for lithium battery applications

Cathode powders of the Li–Mn–Ni–O system have been prepared at a Mn/(Mn+Ni) ratio varying from 0 to 1. The solid state reaction method was used to obtain the cathode materials by mixing MnO₂, LiCO₃ and NiO. A 20% excess of lithium was used in the precursors. The materials produced were examined by X-rays to identify their structure. Batteries were assembled by using these materials as cathode with a liquid electrolyte consisting of EC/DC 1:1, 1 LiPF₆ and Li anode. Their capacity, cycle fading and charge-discharge conditions were evaluated.Presented at the 3rd International Meeting "Advanced Batteries and Accumulators", June 16th–June 20th 2002, Brno, Czech Republic