Oxide melts specific conductivity

The proposed model of the structure of oxyfluoride melts corresponds with the conductivity results shown in Fig. 69. The specific conductivity of the melt drops abruptly and asymptotically approaches a constant value with the increase in tantalum oxide concentration. This can be regarded as an additional indication of the formation of oxyfluorotantale-associated polyanions, which leads to a decrease in the volume in which light ions, such as potassium and fluorine, can move. The formation of the polyanions can be presented as follows ... 

A large number of oxides which are commonly solid insulators at room temperature (e.g., A1203) yield highly conducting (specific conductance > 10 ohm-1 cm-1) melts on fusion. Some of these melts are undoubtedly ionic conductors whereas others are electronic conductors. It is, however, not always possible to differentiate between these two general types since both mechanisms may be operative to comparable extents at a particular temperature. Relatively few experiments have been reported in which reliable estimates of the transport numbers of either ions or electrons could be made. The subdivision in this section into the two general types of conductors is thus not to be interpreted as rigid. 

A summary of most of the early work on conducting oxide melts has been prepared by Van Arkel et al. (57). These results were based primarily on the fusibility of an oxide in an electric arc furnace. Values of the specific conductance of some of these melts at the fusion temperature, with an uncertainty of 50%, estimated by these authors are shown in Table IV. 

Specific Conductivity- of Some Oxides at Tiieik Melting Tempekatohe (57)... 

The specific conductivity of a large number of oxide melts is in excess of 1 ohm-1 cm-1 and the temperature coefficient of conductance is positive. Two types of experiments from which conclusions are drawn regarding the mechanism of conduction are to be found in the literature. In one, the applicability of Faraday s laws is directly tested. In the second case, the conductivity of both the crystalline solid up to the melting point and that of the melt is measured if the change in specific conductivity on fusion is negligible, and if the so-called activation energy EK defined by... 

Besides PbO which shows a large change in conductivity in the vicinity of the melting point (Fig. 1), liquid Li20 is probably an ionic melt. The specific conductivity of the solid near the melting temperature of 1570°C is about 105 ohm-1 cm-1 but that of the melt is 7 ohm-1 cm-1 (57). The latter value is comparable to that of molten LiCl, but the increase on fusion is even greater than the halides. By analogy, other molten alkali oxides are probably also ionic conductors. 

A detailed review of these studies has already been made elsewhere (28) and hence only a summary of the more important findings are presented here. With no known exceptions, the addition of metal oxides to Si02 increases the specific conductance of the melt. When the concentration of... 

This is prepared on an enormous scale by the lead chamber and contact processes. In the former, S02 oxidation is catalyzed by oxides of nitrogen (by intermediate formation of nitrosylsulfuric acid, H0S020N0) in the latter, heterogeneous catalysts such as Pt are used for the oxidation. Pure H2S04 is a colorless liquid that is obtained from the commercial 98% acid by addition first of S03 or oleum and then titration with water until the correct specific conductance or melting point is achieved. 

Nickel was first isolated in 1751, and a relatively pure metal was prepared in 1804. In nature, nickel is found primarily as oxide and sulfide ores (USPHS 1977). It has high electrical and thermal conductivities and is resistant to corrosion at environmental temperatures between -20°C and +30°C (Chau and Kulikovsky-Cordeiro 1995). Nickel, also known as carbonyl nickel powder or C.I. No. 77775, has a CAS number of 7440-02-0. Metallic nickel is a hard, lustrous, silvery white metal with a specific gravity of 8.9, a melting point of about 1455°C, and a boiling point at about 2732°C. It is insoluble in water and ammonium hydroxide, soluble in dilute nitric acid or aqua regia, and slightly soluble in hydrochloric and sulfuric acid. Nickel has an atomic weight of 58.71. Nickel is... 

Refractory oxides are an important class of materials that enable processes to exploit extreme environments. A wide variety of unary, binary, and ternary oxides can be considered refractory, based on their melting temperatures. Refractory oxides are generally prepared from powdered precursors using standard ceramic forming techniques such as casting, pressing, or extrusion, and subsequently sintered to achieve final density. In addition to chemical compatibility, the physical properties of refractory oxides such as thermal expansion coefficient, thermal conductivity, modulus of elasticity, and heat capacity must be considered when selecting an oxide for a specific application. 

One of the earliest separations in gas liquid chromatography was that of James et al. who used a mixture of hendecanol and liquid paraffin on celite using ammonia and the methyl amines as eluents in the order of their melting points. Other stationary phases used for this and for other similar separations include triethanolamine, a mixture of w-octadecane and n-hendecanol, and polyethylene oxide. Titration cell, the first detector designed specifically for gas chromatography, was used in these early studies of the separation of ammonia and ethylamines. More recently thermal conductivity cells have been used for the detection of these compounds. 

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