Polyvalent elements

BrF3 reacts with fluorides of polyvalent elements, e.g. SbF5 and TaF5, the structure of these compounds being BrF SbF6 and BrF TaFf, respectively. 

If, now, a polyvalent element or group is introduced into the ortho position, the tendency is for the extra valencies of the oxygen to be saturated intramolecularly, so that association with external molecules... 

The derivatives of these hydrocarbons result from the substitution of some monovalent or polyvalent element or group of elements in place of one or more hydrogen atoms. Such compounds may be illustrated by the following ... 

Zirconium is polyvalent, but only the 4- - valence state is observed in aqueous environments. In common with other polyvalent elements, it is adsorbed rapidly and relatively intensely by soils and sediments, rendering it relatively poorly available for biological absorption in the terrestrial environment. Solid-liquid distribution coefficients quoted for Zr by Sheppard and Thibault (1990) range from 600 L kg for sandy soil to 7300 L kg for organic soil. 

In this chapter we present a survey of our current understanding of interrelations between the electronic and ionic structure in late-transition-polyvalent-element metallic glasses. Evidence of a strong influence of conduction electrons on the ionic structure, and vice versa, of the ionic structure on the conduction electrons, is presented. We discuss as well the consequences to phase stability, the electronic density of states, dynamic properties, electronic transport, and magnetism. A scaling behaviour of many properties versus Z, the mean electron number per atom, is the most characteristic feature of these alloys. Crystalline alloys which are also strongly dominated by the conduction electrons are often called electron phases or Hume-Rothery phases. The amorphous alloys under consideration are consequently described as an Electron Phase or Hume-Rothery Phase with Amorphous Structure. Similar theoretical concepts as applied to crystalline Hume-Rothery alloys are used for the present amorphous samples. 

Although the composition, which depends on the valence of the polyvalent element, might be quite different, structurally similar phases exist for different alloys in similar Z-regions. In the lower part of Fig. 5.6, this is shown for some Cu10o- Mx alloys with M = Zn, Be, Al, Sn chosen for the different valencies. Such a scaling behaviour of physical properties with Z is the most characteristic feature of HR-phases. As an additional indication, effects on the DOS have often been observed experimentally and minima are well established [5.35, 47],... 

In order to show the agreement of with 5/4 AF at Z = 1.8 e/a as a characteristic feature of the alloys considered here, we show in Fig. 5.12 r, versus Z for all amorphous and liquid noble-metal-polyvalent-element alloys known to us. 

The uniform behaviour of the alloys under consideration is even reflected in their thermal stability. Figure 5.14 shows TK versus Z of different Au-alloys. The alloys at Z = 1.8 e/a crystallise all at TK = 300k + 10 K. With increasing Z, Tk becomes different with the different polyvalent elements. Influences of crystalline compounds are seen in this region. Similar behaviour exists for alloys with Ag and Cu, although TK at Z = 1.8 e/a itself is different [5.10]. 

The structural weight at 2kF obviously corresponds to depth as expected in (5.3.2). We believe this to hold valid whenever metallic polyvalent elements are involved. In the following sections we may use (1 — g) instead of S(2kF) because structure data of Ag-Sn metallic glasses are not available. 

After a rather long diseussion of electronic, structural and thermodynamics interrelationships between compounds of polyvalent elements, the author reports density measurements on various sulphates, halides, and binary and ternary oxides, and also enthalpies of reaction of such salts with solutions of different compositions. 

The simplest covalent compounds are the diatomic molecules formed from electronegative atoms. The variety and complexity of covalent structures depend essentially upon the fact that certain polyvalent elements can form stable chains of atoms, the most notable being of course those which occur among the derivatives of carbon. They are responsible for those compounds of high molecular weight which can constitute fibres and sheets and which therefore play so important a part in the structure of living tissues. Scarcely less... 

The concept of IVR comprises all reactions of electron exchange between the species of polyvalent element in every oxidation state. The disproportionation reaction, when two identical species with equal oxidation state react, is a particular case of IVR. 

According to the ideas considered in Chap. 1, when electric current passes through the electrolyte containing species of a polyvalent element in highest oxidation state A, the A - 1 low valency intermediates (LVls) are formed in aU possible oxidation states. Assuming the system is at equilibrium conditions, its properties have been determined by thermodynamic stability of the intermediates. 

As a result of the effects of a solid intermediate film at the anode, long-term continuous processes of polyvalent element electrorefining have features which cannot be predicted from data from short-term laboratory experiments. 

The general feature of such systems is that the electrochemical processes are many-electron ones since compounds of polyvalent elements are, typically, changing their oxidation states by more than one. 

Hence, the purpose of this book is to provide a unified basis for a wide range of problems relevant to the electrochemistry of many-electron processes in ionic melts and in other media as well. Equilibria in many-electron systems, non-stationary many-electron processes, electrochemical processes in mixed conductors, aspects of the electrodeposition of polyvalence elements and anode processes are considered. No arbitrary assumptions like one-step many-electron transfers or discrete discharge of complex species are involved— the consideration is based on a few very general ideas. 

I. A. Stenina, A. R. Shaykhlislamova, I. Yu. Pinus and A. B. Yaroslavtsev, Ionic Mobility in Materials Based on Lithium and Hydrogen Phosphates of Polyvalent Elements with the NASICON Structure , in Fast Proton-Ion Transport Compounds, eds. U. B. Mioc and M. Davidovic, Transworld Research Network, Trivandrum, India, 2010, p. 127. 

The damping behaviour of fibres is often critical for many applications. It is particularly affected by water and polyvalent element content. Several authors investigated the optical losses of fibres and developed fibres with reduced losses [10,11,26,150,180,219,271,379,400],... 

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