Alkali metal vapors

The purpose of this overview is to provide a bridge between the various sorts of fundamental high temperature science, many of which are described earlier in this volume, and the areas of applications of much of this fundamental science involving specifically alkali metal vapors. Alkali metal vapors are chosen because of their unique combination of properties (Table I). 

Halides. Indium trichloride [10025-83-8] InCl, can be made by heating indium in excess chlorine or by chlorinating lower chlorides. It is a white crystalline soHd, deUquescent, soluble in water, and has a high vapor pressure. InCl forms chloroindates, double salts with chlorides of alkaLi metals, and organic bases. 

Fixed-Bed Vapor-Phase Oxidation of Naphthalene. A sihca gel or sihcon carbide support is used for catalyst involved in the oxidation of naphthalene. The typical naphthalene oxidation catalyst is a mixture of vanadium oxide and alkali metal sulfate on the siUca support. Some changes, such as the introduction of feed vaporizers, are needed to handle a naphthalene feed (14), but otherwise the equipment is the same. 

Metals do not generally react with vitreous siUca below 1000°C or their melting point, whichever is lower. Exceptions are alurninum, magnesium, and alkah metals. Aluminum readily reduces siUca at 700—800°C. Alkali metal vapors attack at temperatures as low as 200°C. Sodium vapor attack involves a diffusion of sodium into the glass, followed by a reduction of the siUca. 

Vaporization of solvents covering alkali metals during storage can expose the metals to moisture. 

Other possibilities are the reduction of nitro groups by applying the sample solutions to adsorbent layers containing zinc dust and then exposing to hydrochloric acid vapors [110] 3,5-Dinitrobenzoates and 2,4-dinitrophenylhydrazones can also be reduced in the same way on tin-containing silica gel phases [111] Cellulose layers are also suitable for such reactions [112] Seiler and Rothweiler have described a method of trans-salting the alkali metal sulfates to alkali metal acetates [113]... 

Vaporization, molar heat of, 66 alkali metals, 94 alkaline earths, 381 copper, 67 chlorine, 67 inert gases, 105 metals, 305 neon, 67... 

The alkali metals are the most violently reactive of all the metals. They are too easily oxidized to be found in the free state in nature and cannot be extracted from their compounds by ordinary chemical reducing agents. The pure metals are obtained by electrolysis of their molten salts, as in the electrolytic Downs process (Section 12.13) or, in the case of potassium, by exposing molten potassium chloride to sodium vapor ... 

Since the synthesis temperatures are higher than the dissociation temperatures of the phases that are formed (at a pressure of lO N m ), it is necessary to react the alkali metal with boron under metal pressure in excess of that defined by Eq. (a), in sealed vessels. The alkali metal is present as a liquid in equilibrium with the vapor phase, the pressure of which is determined by the T of the coldest point. This pressure (greater the more volatile the metal) favors the synthetic reaction relative to the reverse dissociation reaction. 

The parameters controlling the synthesis are the temperature, the vapor pressure of the alkali metal and the crystalline state of boron. The reactions are unaffected by the atomic ratio, M/B, provided it is much larger than the M/B ratios characteristic of the phases that are to be prepared values of, e.g., ca. 1 /2, 1 or 2, are satisfactory. 

The thermal stability of alkali-metal borides is relatively low, which is expected from the high vapor pressures of the corresponding metals at high T. Consequently, the alkali-metal vapor pressure is an important parameter, and synthesis of alkali-metal boride is carried out in isothermal reactors that permit maximum alkali-metal pressure and hence optimum preparation conditions. 

The B-Na system includes two phases with different thermal stabilities. Either of these two borides can be obtained by direct synthesis on adjusting the alkali-metal pressure in the vapor phase. Thus, the preparation of NaB can be carried out in isothermal reactors at < 1100°C (p a = 45 X 10 N m" ) where the equilibrium... 

The chloride is mixed on a laboratory scale with xs Ca (powder or chips) in an Fe tube in a high-T glass distillation vessel. The Fe tube protects the glass from corrosive attack by the alkali-metal vapors. The vessel is inclined and evacuated while slowly heating to 700-800°C. The liberated Rb or Cs distills onto the cooler upper walls of the vessel and runs into integral glass ampules, which are sealed under vacuum for storage. Further purification is achieved by repeated. vacuum distillation at 300°C. Yields arc theoretical. 

A vapor generator for the successive deposition of Na, K and Cs on photocathodes without emission of solid particles may be used to prepare alkali-metal-gold compounds. ... 

The high temperatures of coal char oxidation lead to a partial vaporization of the mineral or ash inclusions. Compounds of the alkali metals, the alkaline earth metals, silicon, and iron are volatilized during char combustion. The volatilization of silicon, magnesium, calcium, and iron can be greatly enhanced by reduction of their refractory oxides to more volatile forms (e.g., metal suboxides or elemental metals) in the locally reducing environment of the coal particle. The volatilized suboxides and elemental metals are then reoxidized in the boundary layer around the burning particle, where they subsequently nucleate to form a submicron aerosol. 

Since the demonstration by Schumacher et al ) of the use of alkali metal vapor inclusion into a supersonic beam to produce clusters, there have been a number of attempts to generalize the approach. It has recently been recognized that instead of high temperature ovens, with their concommitant set of complex experimental problems, an intense pulsed laser beam focused on a target could be effectively used to produce metal atoms in the throat of a supersonic expansion valve. ) If these atoms are injected into a high pressure inert gas, such as helium, nucleation to produce clusters occurs. This development has as its most important result that clusters of virtually any material now can be produced and studied with relative ease. 

The auxiliary electrolyte is generally an alkali metal or an alkaline earth metal halide or a mixture of these. Such halides have high decomposition potentials, relatively low vapor pressures at the operating bath temperatures, good electrolytic conductivities, and high solubilities for metal salts, or in other words, for the functional component of the electrolyte that acts as the source of the metal in the electrolytic process. Between the alkali metal halides and the alkaline earth metal halides, the former are preferred because the latter are difficult to obtain in a pure anhydrous state. In situations where a metal oxide is used as the functional electrolyte, fluorides are preferable as auxiliary electrolytes because they have high solubilities for oxide compounds. The physical properties of some of the salts used as electrolytes are given in Table 6.17. 

Effect of molecular diffusion and vapor-phase chemical reactions Liquid metal vapors consist of molecules and gaseous atoms. Working with alkali metals, Ewing et al. (1967) found that the molecules are principally dimers and tetramers. The... 

The properties of liquid metals can cause flow instability (oscillation) because of vapor pressure—temperature relationship. Most liquid metals, especially alkali metals, show a greater change in saturation temperature, corresponding to a given change of pressure, than does water. In a vertical system under gravitational force, the change of static pressure could appreciably alter the saturation temperature such that explosion -type flow oscillation would occur that would result in liquid... 

Bonilla, C. F., D. L. Sawhuey, and N. M. Makansi, 1962, Vapor Pressure of Alkali Metals III, Rubidium, Cesium, and Sodium-Potassium alloy up to 100 psia, Proc. 1962 High Temperature Liquid MetaI Heat Transfer Tech. Meeting, BNL-756, Brookhaven, NY. (3)... 

---