Melting points of alkali metals

The disposition of the molten alkali metal halides to the pyrohydrolysis (2.5.13) has been shown in Ref. [258] to decrease together with the increase of radius of both alkali metal cation and halide ion. Apart from the above-said constants, the authors of Ref. [258] estimated the activity coefficients of the solutions of OH- ions in molten alkali metal halides to approach unity (1), i.e. the properties of these solutions are close to ideal ones. Qualitatively the conclusions concerning the activity coefficients agree with the data of Hanf and Sole [255]. Nevertheless, the activity coefficients of hydroxides at the melting points of alkali metal halides are close to unity (1) and then they are reduced by a factor of two or three. 

Tb, is relevant as the upper limit of this range. The melting points of alkali metal salts, and when known also their boiling points, are shown in Table 3.1, mainly taken from several compilations [1-3], converted from °C to the K-scale. Differences between the values reported in the literature may exceed 10 °C in some cases, although better agreement is seen in most cases. 

Figure 4.3 Melting point and boiling point of alkali metal halides.

A Compare the melting points of the alkali metals (Group 1 A) with the melting points of other metals. Compare the melting points of the alkali metals with each other and relate them to the locations of the elements on the periodic table. 

In contrast to transition-metal molecular clusters, the alkali-metal suboxides are stable only in the solid state. As described in Table 4.4, these clusters decompose at temperatures rather below the melting point of the metals. The stability of these species appears to be relatively precarious. It is very probable that the stabilization of this class of extreme electron-deficient compounds is possible only at relatively low temperature and in strong reducting media such as the alkali-metals rubidium or cesium. 

Group IIA metals inelude Be, Mg, Ca, Sr, Ba and Ra whieh are grey, moderately-hard, high melting-point substanees. Like the alkali metals they attaek water to liberate hydrogen but with less vigour. The salts of the alkaline earths are generally less stable towards heat and water than those of alkali metals, and less water soluble. 

The ionic conductivity of alkali-metal chloroaluminates was also investigated by Weppner and Huggins [37] but also only in the temperature range between room temperature and just above the melting point. At room temperature the ionic conductivity... 

FIGURE 14.12 The melting points of the alkali metals decrease down the group. The numerical values shown here are degrees Celsius. 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

Projected economics were also highly promising [41] capital and operating costs would be a fraction of those required by standard methods, e.g. scrubbing. Furthermore, no chemical reagents would be required and no waste stream produced. However, the high melting points of the alkali-metal sulfates (T > 512 °C) offered severe limitations to application, especially for use in power plants, where the flue gas typically is unavailable for treatment at temperatures below 400 °C. 

Although our initial entry into this area of study was by accident when we happened to mix MgC with potassium biphenylide(61), our early work concentrated on reductions without the use of electron carriers. In this basic approach, reductions are conveniently carried out using an alkali metal and a solvent whose boiling point exceeds the melting point of the alkali metal. The metal salt to be reduced must also be partially... 

As one examines the periodic table, one discovers that the melting points of the alkali metals increase as one moves from cesium to lithium, whereas the melting points of the halogens increase from fluorine to iodine. 

The high melting points of the compounds of the noble metals may be noticed. With elements of the groups from Ag to Te, alkali metal compounds are formed... 

Table 5.5. Highest melting points in the alloys of alkali metals (A) with compound-forming elements of the 5th row of the Periodic Table. See the introduction for the meaning of the symbols.

Electrowinning Generally this method is limited to La, Ce, Pr and Nd because of their low-melting points. The rare earth salt (fluoride, chloride, etc.) mixed with an alkali or alkaline-earth salt is heated to 700-1100°C and then an electric dc current passed through the cell. If the bath temperature is above the melting point of the R, drops of the molten metal drip off of the cathode and are collected at the bottom of the cell. Generally, the electrowon metal is not as pure as that obtained by metallothermic reduction. 

When we examine the melting points of all the elements, we find that they fall into different families, such as noble gases, alkali metals, and halogens. The noble gases of group 18 have very low melting points, which increases with the period in the... 

While normal molybdates of alkali metals are aU water-soluble, those of other metals are only shghtly soluble in water. All these salts have high melting points. Physical properties of some orthomolybdates and their CAS numbers are presented below ... 

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