Potassium self-diffusivity

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

Lin T. H. and Yund R. A. (1972). Potassium and sodium self-diffusion in alkali feldspar. Contrib. Mineral Petrol, 34 177-184. 

It should be noted that the results for the formic acid decomposition donor reaction have no bearing for ammonia synthesis. On the contrary, if that synthesis is indeed governed by nitrogen chemisorption forming a nitride anion, it should behave like an acceptor reaction. Consistent with this view, the apparent activation energy is increased from 10 kcal/mole for the simply promoted catalyst (iron on alumina) to 13-15 kcal/mole by addition of K20. Despite the fact that it retards the reaction, potassium is added to stabilize industrial synthesis catalysts. It has been shown that potassium addition stabilizes the disorder equilibrium of alumina and thus retards its self-diffusion. This, in turn, increases the resistance of the iron/alumina catalyst system to sintering and loss of active surface during use. 

Examinations of other physical properties of pyridazine include the ESR spectrum of pyridazine radical anion (obtained with pyridazine and sodium or potassium in dimethoxyethane or tetra-hydrofuran, the self-diffusion coefficient and activation energy, the half-wave potential (-2.16V), and magnetic susceptibility. Pyridazine was reported not to fluoresce and no luminiscence could be observed even under very long exposures. More recently, room-temperature fluorescence in solution is reported to be at 23,800 cm (max.), with a life time of 2.6 x 10 . ... 

Figure 6.14. Variation of self-diffusion coefficient of LF (x) and (o) ions with mole fraction of potassium. Inset variation of electrical conductivity with mole fraction of potassium. Lines are only indicative of trends. Note the occurrence of the mixed alkali effect in a. (After Balasubramanian and Rao, 1993).

For analysis, let us assume that the concentration profile migrates inward as shown in Figure 16.1b with an error-function profile whose width increases in proportion to (time), and let us assume for a start that the stress state has no effect on the migration of potassium. Let us assume that the compressive stress at any point tends to rise because of this potassium concentration effect but tends to fall because of creep or relaxation of the glassy host. And let us assume that at small distances (less than 1 pm) from the surface, stress is relieved also by self-diffusion of the glass, so that right... 

Sharma and Laskar [129] measured the self-diffusion of potassium in melt-grown potassium azide using a radioactive tracer sectioning technique. The diffusion coefficient in the range 85-254°C was found to be (0.19 0.03) exp [(- 0.80 0.06) eV/kT] cm sec. They concluded that the cation is the predominantly mobile species, with diffusion occurring by a vacancy mechanism. The value of 0.80 0.06 eV (77 kJ/mole) for the enthalpy of migration agrees well with the results of Maycock and Pai Verneker [127]. 

Diffusion of an ion which is a primary component of a glass, as discussed above, is termed self-diffusion. We can also measure diffusion of an ion which is not present in the glass, e.g., potassium diffusion in a sodium silicate glass. The results of such measurements for a set of R20-3Si02 glasses, where R is Na, K, Rb, or Cs, reveals that the diffusion coefficient is always greatest for the ion which is the component of the glass. The diffusivity of the impurity ions decreases as the difference... 

The self-diffusion of potassium in a molten LiF-NaF-KF (46.5 11.5 42.0mol%) eutectic mixture was measured by using the capillary reservoir technique and the tracer, 42k. The self-diffusion at 491 to 613C was described by ... 

On the other hand, for measurements done at constant temperature (850 °C), Dp and Dpi continually decrease monotonously with the addition of CaF2. These results clearly show the effects of the composition and of the temperature on the self-diffusion. Such observations have been already described for fluorine self-diffusion coefficients in other fluoride systems [14,15]. Nevertheless, the fact that lithium is significantly affected by the composition was not seen in LiF-KF melts. Potassium and lithium cations have close ionic radii and have the same valence. Their ionic potentials corresponding to the polarizing strength of the ions... 

The calculated viscosity, thermal conductivity and self-diffusion coefficients (the latter at 0.10 MPa) of nonionized monatomic lithium, sodium, potassium, rubidium and cesium vapors can be consulted for temperatures between 700 and 2000 K in Tables VIII to XII of the work of Fialho et al. (1993). 

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