Oxidative alkali halides

The ionic bond is the most obvious sort of electrostatic attraction between positive and negative charges. It is typified by cohesion in sodium chloride. Other alkali halides (such as lithium fluoride), oxides (magnesia, alumina) and components of cement (hydrated carbonates and oxides) are wholly or partly held together by ionic bonds. 

The sodium chloride structure is adopted by a large number of compounds, from the ionic alkali halides NaCl and KC1, to covalent sulfides such as PbS, or metallic oxides such as titanium oxide, TiO. Slip and dislocation structures in these materials will vary according to the type chemical bonding that prevails. Thus, slip on 100 may be preferred when ionic character is suppressed, as it is in the more metallic materials. 

The M-M bond can be formed by oxidizing alkali metal derivatives, R2MM with 1,2-dihaloethane, or reducing diorganometal halides with Mg.48 Another method is the elimination of H2 from the hydrides R2MH. Tetrabenzoyldiarsane was obtained by the reaction shown in Scheme 6.49... 

Table 4.7 Migration enthalpy in alkali halides and simple oxides. Values in eV. Data from Barr and Liliard (1971) (1) and Greenwood (1970) (2).

With ionic crystals, there are some rather interesting possibilities. A large part of the perturbation which a free surface introduces is associated with the change in the electrostatic environment of an ion in going from the interior to the surface. If the normally filled valence band is associated with the anions (as is the case with the alkali halides and with certain n-type semiconducting oxides), the surface perturbation acts in the direction of producing a band of surface states with its center lying above the center of the normal anion band. This anion surface band will normally be completely filled. Conversely, for the normally empty cation band (the... 

Theoretical calculations of the surface free energy of solids date back to 1928 with the work of Lennard-Jones and Dent 10). Displacements of the positive and negative ions when a given interior layer becomes a surface layer were allowed for by Verwey 11). Calculations by Shuttleworth 12) showed that van der Waals terms make a significant contribution to surface energy. Benson and his co-workers have made an extensive study of alkali-halides 13-16) and of magnesium oxide 17). 

As well as for the preparation of alkali phosphides, the reaction of phosphine with the elements, their oxides or halides, at higher temperatures in quartz tubes have been much used recently for the preparation of other phosphides, in particular those which play important roles in semi-conductor technology. The preparations of the following phosphides using these methods have been described for example, NdP 3s> 36) 3p 137,138) Q p 139.140) SmP, LaP 136,141) TiP, Ti2P (possibly TisP) and InP See also Section IV.9. 

Rocket propulsion oxidizers, 18 384-385 Rocks, weathering of, radiation and, 3 299 Rocksalt, crystal structure of, 2 6, 29 Rock-salt-type alkali halide crystals, dissolution process, 39 411 19 alkali chlorides, 39 413, 416 alkali fluorides, 39 413-415... 

According to Hachenberg and Brauer , the maximum yield for metals, 5, is usually between 0.6 and 1.7. The maximum yield for insulators and semiconductors cover a much wider range 1 < 5 < 20. At the lower limit of this range we have the well-known semiconductive elements Ge, Si, Se and also compound semiconductors such as CujO and PbS. Substances with high yields include intermetallic compounds, alkali halides, alkali oxides, and alkali earth oxides. 

In this section we compare the theory of the preceding two sections with experimental measurements of infrared extinction by small particles. Comparisons between experiment and theory for spheres of various solids, most notably alkali halides and magnesium oxide, have been published in the scientific literature many of these papers are cited in this chapter. In most of this work, however, there is an arbitrary normalization of theory and experiment, which tends to hide discrepancies. For this reason, most theoretical calculations in this section are compared with mass-normalized extinction measurements. The new measurements presented here were made in the Department of Physics at the University of Arizona. A group of solids was selected to illustrate different aspects of surface modes. Results on amorphous quartz (Si02) particles, for example, illustrate the agreement between experi-... 

Different metal chlorides unite with one another to form double lasts. Just as the acidic and basic oxides unite together to form oxy-salts, so do the halides of an electropositive element (or radicle) unite with a halide of a less positive element (heavy metal or metalloid) to form double halides. So far as is known the alkali chlorides do not unite with one another to form double salts, nor do the halides of the same natural group form compounds with one another, but compounds of the alkali chlorides with the chlorides of the more electronegative chlorides are known. A comparison of nearly 500 double halides has been made by H. L. Wells (1901).1 He calls the one component—e.g. the alkali halide—the positive halide, and the other the negative halide. A. Werner calls the halide which plays the role of the basic oxide, the basic halide, and the other, the acid halide. A great many of the simple types of the double salts predominate. Writing the number of molecules of the positive halide first, and the negative halide second, salts of the 2 1 and 1 1 ratios cover about 70 per cent, of the list of known double halides, and 4 1, 3 1, 3 2, 2 3, and 1 2 represent over 25 per cent. Two halides sometimes unite in several proportions—for instance, six caesium mercuric halides have been reported where... 

The densities and volumetric specific heats of some alkali halides and tetraalkylammonium bromides were undertaken in mixed aqueous solutions at 25°C using a flow digital densimeter and a flow microcalorimeter. The organic cosolvents used were urea, p-dioxane, piperadine, morpholine, acetone, dime thy Isulf oxide, tert-butanol, and to a lesser extent acetamide, tetrahydropyran, and piperazine. The electrolyte concentration was kept at 0.1 m in all cases, while the cosolvent concentration was varied when possible up to 40 wt %. From the corresponding data in pure water, the volumes and heat capacities of transfer of the electrolytes from water to the mixed solvents were determined. The converse transfer functions of the nonelectrolyte (cosolvent) at 0.4m from water to the aqueous NaCl solutions were also determined. These transfer functions can be interpreted in terms of pair and higher order interactions between the electrolytes and the cosolvent. 

The face-centred cubic lattice is very common. Many metallic elements crystallize in this form so also do many binary compounds such as alkali halides and the oxides of diva-lent metals. Thus the powder photo-... 

Cadmium Hydroxide. Cd(OH)2 [21041-95-2] is best prepared by addition of cadmium nitrate solution to a boiling solution of sodium or potassium hydroxide. The crystals adopt the layered structure of Cdl2 there is contact between hydroxide ions of adjacent layers. Cd(OH)2 can be dehydrated to the oxide by gende heating to 200°C it absorbs C02 from the air forming the basic carbonate. It is soluble in dilute acids and solutions of ammonium ions, ferric chloride, alkali halides, cyanides, and thiocyanates forming complex ions. 

Solubility data at 25° C. for solutions of arsenious oxide in aqueous alkali halides have been obtained.9... 

Volatile protactinium pentaehloride has been prepared in a vacuum by reaction of the oxide with phosgene at 550° C or with carbon tetrachloride at 200°C. Reduction of this at 600°C with hydrogen leads to protactinium(IV) tetrachloride, Pad. which is isostructural with uranium(IV) tetrachloride, UCI4. The pentaehloride can be converted into the bromide or iodide by heating with the corresponding hydrogen halide or alkali halide... 

At a platinum electrode, highly purified FLINAK has a voltammetric window extending from about +1.5 to -2.0 V vs. the nickel reference electrode [7]. The positive limits of the alkali halide melts discussed herein arise from the oxidation of halide ions, whereas the negative limits are due to reduction of the alkali metal ions. Because chloride ion is substantially easier to oxidize than fluoride ion, the potential window of the LiCl-KCl melt is approximately 1.5 V smaller than that for FLINAK. 

Electron donors and acceptors for reversible redox systems must invariably exhibit at least two stable oxidation states, or the net result will be an irreversible chemical reaction. The donor or acceptor components of the redox system need not be confined to independent atoms, ions, or molecules but could even be imperfections in crystal lattices capable of functioning as electron traps. The well-known color centers in alkali halides are just such acceptor systems. 

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