Sievert constant

Sieverts constant as a function of temperature and Pb concentration in Li-Pb liquids... 

Solubility (Sieverts ) constant for dissociative adsorption of a diatomic gas, followed by absorption (Pa )... 

Defining the isothermal permeability constant of a membrane material by half of the product of the membrane diffusivity and the Sieverts constant, and substituting into the Richardson Eq. 10.5 yields Eq. 10.6, which is the governing equation for the diffusion limited, atomic transport membrane process. 

In Sieverts law, nn is the hydrogen mole fraction in the solution, Ph the partial pressure of hydrogen on this solution and Ks the Sieverts constant. The value of this constant is dependent on the temperature as expressed in Eq. (21). 

By means of this equation one can estimate hydrogen concentrations in the liquid metals, if Sieverts constants are known and the partial pressure are measured. 

Ks, expressed in mol m Pa, is Sieverts constant and in Pa is the partial pressure of hydrogen in the gas phase. Equation [18.5] is an ideal limiting case that pertains to diluted solid solutions formed at low pressures with defect-free metallic hosts. As the hydrogen content increases, H-H interactions come into play that may introduce deviations. 

DSC tests show a substantial reduction of the hydrogen desorption onset (red circles) (T J and peak (T ) temperatures due to the catalytic effects of n-Ni as compared to the hydrogen desorption from pure MgH also milled for 15 min. (Fig. 2.57). It is interesting to note that there is no measurable difference between spherical (Fig. 2.57a) and fdamentary (Fig. 2.57b) n-Ni, although there seems to be some effect of SSA. We also conducted desorption tests in a Sieverts apparatus for each SSA and obtained kinetic curves (Fig. 2.58), from which the rate constant, k, in the JMAK equation was calculated. The enhancement of desorption rate by n-Ni is clearly seen. At the temperature of 275°C, which is close to the equilibrium at atmospheric pressure (0.1 MPa), all samples desorb from 4 to 5.5 wt.% within 2,000 s. 

Solubility of Gases in Platinum.—The solubility of hydrogen in platinum has been studied by Sieverts,1 who has shown that the gas is less soluble in. compact platinum than in the same weight of iron or nickel. At constant pressure the solubility rises with the temperature, whilst at constant temperature the amount of hydrogen absorbed is directly proportional to the square root of the pressure. On cooling, all the hydrogen absorbed at higher temperatures by the metal is evolved. 

Apparatus. The hydrogen-absorption system, a modified Sievert s apparatus, consisted of three self-contained units. The first unit provided a source of, and storage facilities for, pure hydrogen, which was obtained by the thermal decomposition of uranium hydride. The second unit provided precise metering of hydrogen at a known temperature, for delivery to the reaction system. The third unit was a constant-volume section in which the reaction of hydrogen with the zirconium-uranium alloy occurred at a controlled temperature ( 3° C.). The equilibrium pressures of hydrogen were measured in this section also. 

The hydrogen-in-lead data were converted to deuterium-in-lead data by assuming that the ratio of Sievert s constants for hydrogen and deuterium is constant (independent of the Pb-Li composition) and by using the Argonne data for hydrogen and deuterium in pure lithium. The adjustment was relatively small, with a 9% increase at 767 C and a 20% increase at 477°C. 

For unsaturated solutions the amount of hydrogen in solution is governed by the pressure. Over this region the Sievert s constant, K, is slightly affected by temperature and is given by the equation 32... 

Sieverts Law c = Ks4p, where c is the subsurface concentration (solubility) of the dissolved atom in the solid metal, P is the partial pressure of the diatomic gas (sometimes replaced by the fugacity, j), and Ks is the solubility constant (temperature dependent), which is the chemical equilibrium constant between the molecular species in the gas phase and the atomic species within the metal lattice. This empirical relation was first demonstrated by Sieverts in 1929 for the solubility of hydrogen in iron. Departures from this law occur at high gas pressures and/or high concentrations of dissolved atoms. 

Sieverts hydrogenator modified from the standard configuration (Fig. 7.4) for isobaric operation by the addition of a needle valve (NV) and a second pressure transducer. The needle valve feeds gas to or from the sample under feedback control such that Pceii is constant. In addition to providing the feedback signal, the second pressure transducer allows the hydrogen content of the sample to be calculated at all times. 

The hydrogen concentration in the a-phase (C ) is pressure dependent and frequently follows Sieverts law, i.e. CH=kP 2 where k is a temperature-dependent constant and P is the dihydrogen pressure. As the dihydrogen pressure is increased, saturation occurs and the metal hydride starts to form. Conversion of the saturated solution phase to hydride continues as hydrogen is added. The pressure remains constant while this conversion takes place in accordance with the Phase Rule ... 

---