Oxides and Other Inorganic Compounds

Another application of ND is to distinguish between atoms whose X-ray 

The principle of the null matrix is illustrated by work on Zr. Tio-esH. Since for natural zirconium and titanium are, respectively, 7.0 and —3.4 fermis, a material of the above composition, in which Zr and Ti randomly occupy equivalent cation sites, will have its metal atoms taken out so far as ND is concerned. This facilitates study of the hydrogen position, and of the phase-changes as H is progressively replaced by D. 

The same principle would theoretically hold for a material that was 37 % deuteriated, sinceis —3.8 and -1-6.5 fermis for H and D. This has not been applied in practice. Deuteriation often has an appreciable effect on the thermodynamic and kinetic properties, and hence uniform deuteriation of chemically dissimilar sites cannot be expected. A fresh example has been reported, in KDs(Se03)2, where there was a significantly different degree of deuteriation in the two hydrogen bonds. 

The room-temperature form of KCN and the high-temperature form of CaQ crystallize in the rock-salt type. The diatomic anions might be supposed rotationally disordered to simulate spherical ions. Atoji, using limited ND powder data for CaQ and Sequeira s (1962) data for KCN, has found evidence that the disordered anions lie preferentially along the cell diagonals. The same author has studied CejSs, and found it to have a deficit structure of ThgP type. 

Partial ND data have been used to improve the (1943) A -ray parameters for some scheelites, AXOi, when A = Sr, Ca, or Ba, and X = Mo or W. For a given X the X-O distances are independent of A. 

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The compositions and chemical formulae for metal oxides and other inorganic compounds are usually written with a definite ratio of cations to anions, e.g. MaOb where a and b are usually small integers determined by the valence of the constituent atoms. In crystalline compounds this also reflects that the structure contains different types of sites (e.g. close-packed sites and tetrahedral or octahedral interstices) in simple ratios and that these are selectively and systematically filled with cations or anions. When the oxide MaOb contains M and O atoms in the exact ratio a b, it is said to have a stoichiometric composition. 

As discussed in the previous chapter several different types of point defects may be formed in metal oxides and other inorganic compounds. In principle, all types of defects will be present, but in general, only a small number of different defects will predominate. 

The relative contribution of the different types of diffusion in oxides and other inorganic compounds are functions of the temperature, partial pressures or activities of the constituents of the compounds, the microstructure, grain size, porosity etc. Grain boundary and dislocation diffusion generally have smaller activation energies than lattice diffusion and as a result become increasingly important the lower the temperature in solids with a given microstructure. 

Lattice diffusion takes place through the movement of point defects. The presence of different types of defects gives rise to different mechanisms of diffusion. These are illustrated schematically for elemental solids in the following descriptions. But they also apply to metal oxides and other inorganic compounds when the diffusion is considered to take place in the sublattices of the cations or anions. 

While most of the earlier research was done on metals and alloys, more recently a good deal of emphasis has been placed on ceramics and other inorganic compounds, especially functional materials used for their electrical, magnetic or optical properties. A very recent collection of papers on oxides (Boulesteix 1998) illustrates this shift neatly. In the world of polymers, the concepts of phase transformations or phase equilibria do not play such a major role 1 return to this in Chapter 8. 

When atomic theory developed to the point where it was possible to write specific formulae for the various oxides and other binary compounds, names reflecting composition more or less accurately then became common no names reflecting the composition of the oxosalts were ever adopted, however. As the number of inorganic compounds rapidly grew, the essential pattern of nomenclature was little altered until near the end of the 19th century. As a need arose, a name was proposed and nomenclature grew by accretion rather than by systematization. 

On metal oxide surfaces and other inorganic compound catalysts, where the distance between adsorption sites are larger than on metal surfaces, diffusion barriers are often found to be larger. This means that the mobility of adsorbates on the surfaces of compounds can become important for the overall reaction rate. 

Flame and Smoke Retardants. Molybdenum compounds are used extensively as flame retardants (qv) (93,94) in the formulation of halogenated polymers such as PVC, polyolefins, and other plastics elastomers and fabrics. An incentive for the use of molybdenum oxide and other molybdenum smoke and flame retardants is the elimination of the use of arsenic trioxide. Although hydrated inorganics are often used as flame retardants, and thought to work by releasing water of crystallization, anhydrous molybdenum oxides are effective. Presumably the molybdenum oxides rapidly form... 

Other studies of the toxicity of stannous fluoride, sodium pentafluorostannite, sodium pentachlorostannite, sodium chlorostannate, stannous sulfide [1314-95-0] stannous and stannic oxides, stannous pyrophosphate [15578-26 ] stannous tartrate [815-85-0] and other inorganic tin compounds are reviewed in References (dh—12. The OSHA TLV standard for inorganic tin compounds is two milligrams of inorganic tin compounds as tin per cubic meter of air averaged over an eight-hour work shift (47). 

Other methods for indicating or implying the presence of an atom in a nonstandard valence state have been used, especially the use of the prefix hydro e.g. 108). Such methods are sometimes convenient for simple molecules, but they are difficult to apply generally. A more general method that has seen extensive use utilizes the italicized symbol for the element with a superscript Roman numeral to indicate the valence (e.g. 109). This method has been objected to, however, because of ambiguity the superscript Roman number is also used to indicate oxidation number in inorganic compounds, and italicized atomic symbols are customarily used as locants for substituents. The A convention is a modification of the principle of this method, and avoids the objection. It was made a Provisional Recommendation of lUPAC in 1981. 

Also included in Table 7.7 are the nitrogen fixation reactions. These are similar to the carbon fixation reactions in that they involve the conversion of an oxidized inorganic species (N2) 1° a reduced form, such as ammonium. The fixed forms of nitrogen can be taken up by plants. As with carbon fixation, this process requires an energy source in order to proceed. Some N2 fixers are photosynthetic and others use energy obtained from the oxidation of reduced inorganic compounds. 

A statistical report of the oxygen coordination environments about divalent metal ions in minerals and other inorganic (oxidic) compounds was published (105) in 1984. The coordinations about the Cu2+ ion (VIrCu 0.73 A) shows a pronounced square planar tendency (IV sq. pi.). Quite often, however, one or two additional oxygen atoms are located perpendicular to the square plane, yielding a distorted "V"-coordination (IV + I square pyramid) or a highly distorted octahedron, "VI"-coordination (IV + II), see Figure 20. 

However, although the oxidation process was ascribed to either direct reaction on the electrode surface, or mediated by peroxodisulphate and other inorganic reagents electrogenerated at the anode surface, the linear decrease of the Faradic yield down to zero in the investigated range of concentration was interpreted as an indication of a process under diffusive control. This leads to the conclusion that the oxidative degradation of the compounds essentially occurred at the electrode interface. 

Other Thiobacillus produce sulfate from the oxidation of elemental sulfur and other inorganic sulfur compounds ... 

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