Rubidium Systems

Nalimova, V. A., S. N. Chepurko, V. V. Avdeev, and K. N. Semenenko. 1991. Intercalation in the graphite-rubidium system under high pressure. Synth. Metals 40 267-273. 

The rubidium-containing system Rb2TaF7 - RbF displays similar behavior, but the band attributed to the TaF6 ion vibration disappears at a RbF concentration of 0.6 mol fraction and higher (Fig. 76, c). This means that in the case of rubidium-containing melts, the equilibrium in Equation (89) is more significantly shifted to the left. 

A similar activity is found in Mendeleevs first attempt at a periodic system as presented in a hand-written table. If one examines the calculations that he is carrying out one finds again an attempt to compute differences between the atomic weights of elements in the columns of his table. For example Mendeleev writes the number 27 in smaller writing below the symbols for potassium (Zn - K = 65 - 39 = 27) and again below rubidium (Cd-Rb = 112-85 = 27). 

A suitable extrathermodynamic approach is based on structural considerations. The oldest assumption of this type was based on the properties of the rubidium(I) ion, which has a large radius but low deformability. V. A. Pleskov assumed that its solvation energy is the same in all solvents, so that the Galvani potential difference for the rubidium electrode (cf. Eq. 3.1.21) is a constant independent of the solvent. A further assumption was the independence of the standard Galvani potential of the ferricinium-ferrocene redox system (H. Strehlow) or the bis-diphenyl chromium(II)-bis-diphenyl chromium(I) redox system (A. Rusina and G. Gritzner) of the medium. 

Under these conditions the rubidium is highly volatile and removed from the system. 

As shown in Table 11.1, hydrothermal emissions are a major source of soluble iron, manganese, and zinc and a minor source of aluminum, cobalt, copper, and lead. Other elements with significant hydrothermal inputs include lithium, rubidium, cesium, and potassium. Considerable uncertainty also surroimds these flux estimates because they are the result of extrapolations from measurements made at a small number of hydrothermal systems at single points in time. These fluxes appear to vary significantly over short time scales as tectonic activity abruptly opens and closes cracks in the oceanic crust. 

In 1863 R. C. Bottger of Frankfort-on-the Main found that thallium occurs in some spring waters. A certain salt mixture from Nauheim contained, in addition to the chlorides of sodium, potassium, and magnesium, those of cesium, rubidium, and thallium. Since he was able to prepare a thallium ferric alum exactly analogous to potassium ferric alum, he regarded thallium as an alkali metal (72, 73). Although it is sometimes univalent like sodium and potassium, it is now classified in Group III of the periodic system. 

In 1988, Cava and co-workers also prepared (88a) a quaternary oxide, Ba/K/Bi/O, and observed superconductivity at -28 K. This compound was the first "non-transition metal" oxide with a Tc above the legendary "alloy record" of 23 K. Further studies indicated (88a) that the optimum composition for "high temperature" superconductivity in this system was Ba0 6K0 4BiO3 x, having a Tc of 30.5 K (Figure 17). The samples were multiphase, and the superconducting fraction varied from 3 to 25%. Superconductivity for the rubidium-substituted compound was observed at -28.6 K. 

There is yet another general method to prepare random copolymer. As stated earlier, when one uses potassium, rubidium or cesium initiator, styrene polymerizes first, to give a S/B-B type of tapered block polymer. But when one mixes an alkyllithium with a potassium compound such as potassium t-butoxide, quite a different system is obtained. 

A wide variety of rock types can be dated by the 87Rb-87Sr system, provided that the samples satisfy the assumptions that the system was initially isotopically homogeneous (had a uniform 87Sr/86Sr ratio) and did not gain or lose rubidium or strontium after if formed. Both... 

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