Mean Valence Research Articles

The influence of cation properties on the shape of silicate chains

AbstractThe shape of silicate single chains is described by their periodicity (number of tetrahedra in the repeat unit of the chain) and the degree of shrinkage compared with a maximum stretched chain.From a regression analysis of 54 single chain silicates it is concluded that such silicates can be divided into two groups: (1) Silicates with odd-periodic chains (pyroxenoids and pyroxenes) and (2) silicates with even-periodic chains.Although the results of the analysis are not accurate enough to make reliable quantitative predictions about the shape of a silicate chain merely from the chemical composition of the silicate, some general relations could be found. So it turned out that even-periodic chains become less stretched with higher mean electronegativity and higher mean valence of their cations. In contrast, for odd-periodic chain silicates the degree of chain shrinkage is strongly correlated with the mean electronegativity and less so with the mean radius of the cations. On the other hand, the periodicity of the silicate chains is directly correlated with their degree of shrinkage. These results of the regression analysis are explained in terms of simple crystal chemical considerations.

Influence of pressure on the inhomogeneous mixed-valent state in Eu 3S 4

The 21.7-keV nuclear gamma resonance of 151Eu was used for studying the inhomogeneous mixed-valent compound Eu 3S 4 in the presence range 0 to 15 kbar. At room temperature the activation energy for electron hopping between the crystallographically equivalent divalent and trivalent Eu sites was found to decrease with pressure by dE a / dP = -1.8 ± 0.3 meV/ kbar. No change of the mean valence of Eu with pressure was observed.

Mean valence of sites in non-percolating clusters

The authors present Monte Carlo and series results for the mean valence ( nu )F of non-percolating clusters on the square lattice and corresponding series results for the simple cubic lattice. Mimic functions have been constructed from the series which, for the square lattice, agree well with the Monte Carlo data, for a wide range of densities. They have shown that if the percolation probability is continuous at rho c then ( nu )F is continuous at rho c, and have presented a heuristic argument which indicates that ( nu )1, the mean valence of a site in a percolating cluster, is greater than ( nu )F, at rho c. This allows one to infer the asymptotic behaviour of ( nu )F in the region of rho c.

ChemInform Abstract: THE MOLECULAR STRUCTURE AND CONFORMATIONS OF OXEPANE AS DETERMINED BY GAS ELECTRON DIFFRACTION

Abstract The electron-diffraction data for gaseous oxepane, collected at 310 K, can be explained in terms of a 53:47% mixture of two twist-chair conformations. Using the nomenclature of Crerner and Pople [1], the conformations are characterised by q 2 = 0.579 a, q 3 = 0.685 A, φ 2 = 13.3°, φ 3 , = 63.0° and q 2 = 0.511 A. q 3 = 0.588 A, o 2 = 116.1°, o 3 = 217.6°. The other structural parameters ( r a -structure) are r CO = 1.419 A, r cc = 1.531 A, r CH = 1.105 A, ∠H-C-H = 106.0°, with a mean ring valency angle of 112-0° for the former conformation, and of 116.2° for the latter. There is a good agreement between the experimental geometries and the results from molecular mechanics calculations.

The molecular structure and conformations of oxepane as determined by gas electron diffraction

The electron-diffraction data for gaseous oxepane, collected at 310 K, can be explained in terms of a 53:47% mixture of two twist-chair conformations. Using the nomenclature of Crerner and Pople [1], the conformations are characterised by q 2 = 0.579 å, q 3 = 0.685 Å, φ 2 = 13.3°, φ 3, = 63.0° and q 2 = 0.511 Å. q 3 = 0.588 Å, ø 2 = 116.1°, ø 3 = 217.6°. The other structural parameters ( r a-structure) are r CO = 1.419 Å, r cc = 1.531 Å, r CH = 1.105 Å, ∠H-C-H = 106.0°, with a mean ring valency angle of 112-0° for the former conformation, and of 116.2° for the latter. There is a good agreement between the experimental geometries and the results from molecular mechanics calculations.

Zur Erzeugung amorpher Zinn-Schichten durch abschreckende Kondensation mit Fremdzusätzen

Thin films of Sn with additives are prepared by quench condensation. The annealing behaviour of the electrical resistivity and the transition to the superconducting state of these films are investigated in relation to the dependence of composition and film thickness. The data indicate, whether the films are in an amorphous state or not. It appears that the films become amorphous, if the addition has an atomic radius less than Sn and if the mean valence electron concentration is less than 3.7. With further reduction of the valence electron concentration the amorphous films become more stable and the temperature of transformation from the amorphous state to the crystalline state rises. The thickness dependence of the transformation temperature can be explained with a simple further assumption.

ChemInform Abstract: ANODIC OXIDE ON SILVER IN ALKALINE SOLUTION

AbstractDurch potentiostatische Oxidation von Ag in KOH gebildetes AgQO und AgO wurden chemisch analysiert, um die mittlere Wertigkeit der Ag‐Ionen festzustellen.

Anodic oxide on silver in alkaline solution

Ag 2O and AgO formed by potentiostatic oxidation of silver in 0·1N KOH have been chemically analysed for the mean valency of silver ion. The anodic oxide formation proceeds in two stages and the silver ion in the oxide changes from Ag + to Ag 2+ at a transition potential. The reduction of AgO at constant cathodic current occurs via two potential arrests. The transition from the first to the second potential arrest, however, does not correspond to the complete reduction of AgO to Ag 2O.

起電力法による非化学量論的UO2-ThO2固溶体の熱力学的性質の測定

The thermodynamic properties of UO2-ThO2 solid solution of compositions (UyTh1−y)O2+x with y values of 0.295 to 0.048 and x values below 0.029 were determined by emf measurements. The oxygen concentration cells were of the type(This article is not displayable. Please see full text pdf.) and operated in the temperature range 900 to 1050°C.From the emf values and these temperature dependence, partial molar free energies, enthalpies and entropies of solution of oxygen in the solid solutions were calculated.Between these partial molar quantities and the mean valence of U ion in the solid solutions, there exist correlations which are nearly independent of the values of y. These results suggest that the non-stoichiometry of UO2-ThO2 solid solution is similar to that of UO2+x.

Das system UO 2UO 3LaO 1.5

At 1250°C, the following five single-phase regions were found in the UO 2UO 3LaO 1.5 region of the ternary uranium-lanthanum-oxygen system: 1. (a) β-U 3O 8: no solubility for LaO 1.5 could be observed. 2. (b) Fluorite phase: concerning the oxygen:metal ratio this phase may exist superstoichiometrically as (U, La)O 2+ x(ss) (0 ⩽ x ⩽ 0.25), substoichiometrically as (U,La)O 2− x(ss) (0 ⩽ x ⩽ 0.40) and stoichiometrically as (U 1− y ,La y )O 2(ss) (0 ⩽ y ⩽ 0.67). 3. (c) Rhombohedral phase I: as concerns the U:La ratio this ordered phase occurs stoichiometrically at the limiting compositions UO 2·6LaO 1.5 (Me 7O 11) with tetravalent uranium and UO 3.6LaO 1.5 (Me 7O 12) with hexavalent uranium, showing a maximum of phase width with the limiting compositions UO 2.5·5LaO 1.5 and UO 2.5·7LaO 1.5. 4. (d) Rhombohedral phase II: this phase extends from 71.5 to 76.5 mole-% LaO 1.5 for U(VI) and shows only little phase widths concerning the O:Me ratio. Above 1310°C this ordered phase transforms reversibly to a disordered phase having fluorite structure. 5. (e) LaO 1.5: no solubility for UO 2+ x could be observed. In the pseudo-binary system UO 2+ x -LaO 1.5 (p(O 2) = 1 atm) a third rhombohedral phase R III (Me 8O 16) occurs between 55 and 66.7 mole-% LaO 1.5 (T ⩽ 1220°C). The limiting composition of this phase regarding the highest content of lanthanum as well as that of oxygen is ( U 1 3 , La 2 3 ) O 2 . Below 1550°C, the mean valency of uranium in UO 2+ x -LaO 1.5 mixed oxides at p(O 2) = 1 atm is rather independent of the annealing temperature but markedly increases with rising content of lanthanum in the samples. A valency of exact 6.00 is observed for mixed oxides containing 66.7 mole-% LaO 1.5 or more.

The chemical effects of composition changes in irradiated oxide fuel materials

When uranium or plutonium undergoes fission, the mean valency of the resulting fission product mixture may differ from that of the starting material. This paper describes the use of a computer programme to derive the composition of irradiated fuel, and how a combination of thermodynamic assessment and direct experiment is used to predict and confirm some of the consequences of the valency change in irradiated oxide fuels. The experiments consist of an X-ray study of the lattice dilation of uranium dioxide, a direct measurement of the oxygen/metal ratio in plutonium and mixed uranium-plutonium oxides, and electron probe microanalysis of inclusions formed in plutonium oxides. These demonstrate that the lanthanide fission products enter the oxide lattice so that irradiated uranium oxide does not become more oxidising with burn-up, but that plutonium oxide becomes significantly oxygen-rich during fission owing to the shift in the fission yield spectrum.

PETROLOGICAL CHARACTER OF THE LUNA 16 SAMPLE FROM MARE FECUNDITATIS

We have classified 1858 lithic and vitreous fragments from the Luna 16 core‐tube sample. They were taken from the soil fractions ranging in size from 150 to 425 μ, at levels A and G (γ). No important differences are observed between the proportions of particle types in levels A and G, nor between the soils of Luna 16 and those from the Apollo 11 landing site in the nearby Mare Tranquillitatis. Luna 16 basalts are texturally and mineralogically similar to Apollo 11 basalts, though the former are characterized by more Fe‐rich olivines and pyroxenes and by lower ilmenite contents than are Apollo 11 basalts. The atomic ratio Al/Ti in Luna 16 basalt pyroxenes in about 1.5; Apollo 11 basalt pyroxenes have Al/Ti = 2.0, indicating the possibility of a lower mean valence for Ti in the Luna 16 material than in the Apollo 11 material. Most light‐colored lithic fragments are anorthositic rather than noritic in character and are comparable to Apollo 11 anorthosites in mineral chemistry. We believe they are samples of terra regions to the north of the Luna 16 landing site. Triangular diagrams plotting normative plagioclase, normative mafics plus oxides, and normative orthoclase plus apatite neatly separate the three major types of lunar materials — mare basalts, anorthosites, and noritic rocks — and reveal that the Luna 16 regolith is composed of mare basalt and anorthosite, with very little norite component. Colorless‐to‐greenish glass occurs in the Luna 16 sample, which has high Fe and low Ti; it may represent gabbroic rock related to the anorthosites

The transpassive dissolution of chromium

Summary The transpassive dissolution of chromium has been studied in both acid and alkaline solutions, using potentiostatic pulses, a.c. impedance and ring-disc techniques. It is shown that in the transpassive region chromium has a thin layer of oxide on its surface, the mean valency of which is a function of electrode potential.

Positron lifetime enhancements at vacancy sites in metals

The lifetime enhancement observed for positrons at vacancy sites suggests an electron density depletion of about the mean valence value. Positron pseudoatoms are thus suggested and existing data are analysed from this viewpoint.

Conformation of non-aromatic ring compounds—LI : The crystal structure of trans-1,4-dichlorocyclooctane at −180°

Crystals of trans-1,4-dichloro-cyclooctane are monoclinic with space group P2 1/c and Z = 4. The unit cell dimensions at −180° are a = 14·10, b = 5·53, c = 12.18Å and β = 113·1°. The structure was solved by calculation of a minimum function M 4 and refined by the least-squares method. The ring has the boat-chair conformation, its symmetry being approximately C s. The one chlorine atom at the top of the chair moiety points to the axial direction, the other one to a (pseudo-) equatorial direction. The mean ring valency angle is 116·4°. Due to steric interaction the carbon chlorine bonds are large, their mean value being 1·83Å.

Immiscibility in liquid metal systems

A review is given of the various expressions that have been derived to predict the miscibility behaviour of alloy systems, with particular reference to the suggested modifications to the Hildebrand rule for non-polar liquids. The original Hildebrand formula was based on a solubility parameter, δ, and the atomic volume, V, and immiscibility was predicted between two liquids if 1/2(V A+V B) (δ A−δ B)2>2RT Mott introduced a correction term in this expression to allow for the difference in electronegativity (χ A−χ B) between the two component elements and defined a Mott number, $$\frac{{\tfrac{1}{2}(V_A + V_{_B } ){\text{ }}(\delta _A - \delta _B )^2 - 2{\text{R}}T}}{{23060{\text{ }}(\chi _A + \chi _{_B } )^2 }},$$ where T is the melting point, in degrees absolute, of the more refractory metal. It was postulated that if the calculated Mott number for a given binary alloy system was greater than the number of bonds that could be formed, the two metals would be immiscible in the liquid state. In an earlier paper, the Mott number was compared with the lower Pauling valency of the two elements and when this is applied to 1401 known alloy systems, the overall agreement is 85% compared with 59.9% conforming to the simple Hildebrand rule. In this paper, an alternative suggestion is made that the Mott number can be compared with the mean group valency of the two alloying elements. On this basis, of the 1401 systems analysed, 1181 conform, compared with 1191 on the earlier criterion.

Theory of charged particles in semiconductors

The dielectric response function of semiconductors is derived for an isotropic model characterized by an effective Fermi energy, EF, corresponding to a mean valence electron density, and an energy gap of width Eg. The response to the fields set up by impurity atoms and by moving charged particles is investigated. The screening of impurities changes with the energy gap: as Eg increases from zero, the potential expands in range and approaches the bare Coulomb potential, while the Friedel oscillations in the induced electron density about the impurity are suppressed. The contribution of electronic excitations from the valence band of semiconductors to their stopping power for swift heavy particles is calculated.

The Electrodeposition of Coherent Deposits of Refractory Metals: IV . The Electrode Reactions in the Deposition of Niobium

The mechanism for the electrodeposition of coherent deposits of niobium from a molten fluoride electrolyte has been studied by means of chronopotentiometry and compared with that of tantalum. The reduction of the pentavalent niobium in solution occurs in three steps: a reversible one‐electron step to the tetravalent state at −0.11v (referred to the Ni/Ni2+ electrode), a reversible three‐electron step to the monovalent state at −0.76v, and finally an irreversible one‐electron reduction to metal at −1.02v. However, the reaction interferes with coherent metal deposition from the pentavalent solutions, and consequently in order that coherent metal be produced at high efficiency the mean valence of the bath must be reduced to approximately four. In these circumstances the chronopotentiogram of a working bath shows two steps only: a three‐electron reduction, followed by the metal producing step . The diffusion coefficient of has been found to be and its activation energy for diffusion to be 8.75 kcal/mole. The diffusion coefficient of the tetravalent species is .

Etude, aux faibles tensions, de la valence initiale de dissolution du cuivre

The study of polarization curves of electrodes allows us to distinguish changes in the mechanism of charge transfer and to separate the partial currents that take part in the over-all reaction. With an electronic potentiometer we have imposed on a copper electrode a pd varying linearly with time and have measured the polarization curve. We have also measured the mean valency of the initial dissolution of copper: for each dissolution at a particular anode potential, the quantity of electricity is measured by integration of the current and the metal dissolved by weight loss or by the radioactivity of the solution caused by dissolution of electrodes labelled with 64Cu.In phosphoric acid, sulphuric acid and copper sulphate solutions the mean initial valency of dissolution is 2, even for small overpotentials; in the presence of chloride or perchlorate ions, it is between 1 and 2.

Crystal structure and mean valency of manganese ions of some compounds in the system CuOx·FeOy·MnOz

Crystal structure and mean valency of manganese ions of some compounds in the system CuOx·FeOy·MnOz