Structure of Expanded Liquid Rubidium by Neutron Diffraction

Abstract

The static structure factor, S(Q), of liquid rubidium has been studied by neutron diffraction for temperatures up to 2000 K and pressures up to 139 bar near saturation conditions, corresponding to an expansion of the liquid from 1.46 to 0.54 gcm-3. The characteristic changes of the scattering behaviour and of the microscopic structure approaching the M-NM transition region are discussed. A comparison of these results with simple hard sphere model calculations is given.

Structural studies of expanded fluid rubidium up to the supercritical regions

“…It is quite evident that our observation is different from those of the previous observations [10,11] in which microscopic structural variation is essentially similar to that of rare-gas liquids. The shortening of r 1 is seemingly consistent with the appearance of diatomic molecules as suggested by the inelastic neutron scattering measurements [20].…”

“…Several diffraction measurements have been carried out for expanded fluid alkali metals. Franz et al [10] measured the neutron diffraction for fluid Rb up to the critical region. They reported that the local structure of expanded fluid Rb changes in the way that is similar to that of simple liquids; the coordination number decreases linearly while the nearest-neighbor distance is almost unchanged or slightly increased.…”

“…Experimentally accessible range of the critical constant of fluid alkali metals [2] (rubidium (Rb): T c ¼ 2017 K, P c ¼ 12:45 MPa, r c ¼ 0:29 g cm À3 , cesium (Cs): T c ¼ 1924 K, P c ¼ 9:25 MPa, r c ¼ 0:38 g cm À3 ) allows a considerable amount of experimental work to investigate the physical properties of expanded fluid alkali metals, such as equation of state [3,4], electrical conductivity [5,6], magnetic susceptibility [7,8] and nuclear magnetic resonance (NMR) [9]. These measurements show that the physical properties of fluid alkali metals are strongly dependent on their thermodynamic state.…”

“…Molybdenum (Mo) is a material resistant to chemical corrosion with alkali metals and widely regarded as a suitable material for those experiments at extremely high temperatures up to the critical temperature of fluid alkali metals such as the equation of state [3,4], electrical conductivity [5,6], and also the neutron diffraction [10,11].…”

Analysis of neutron diffraction data in the case of high-scattering cells. II. Complex cylindrical cells

“…Special experimental high-temperature high-pressure techniques have been developed in order to deal with the problem of containing highly corrosive metals in uncontaminated form in these extreme thermodynamic conditions. In particular, a quite complex cell has been designed for neutron diffraction studies in these systems (Freyland, Hensel & Glaser, 1979) and successfully employed for measurements of the static structure factor in liquid Cs (To= 1924K, Pc=92.5x 0108-7673/92/040508-08506.00 10 SPa) and Rb (Tc=2090K, Pc=140x10 SPa) (Franz, Freyland, Glaser, Hensel & Schneider, 1980;Freyland, Hensel & Glaser, 1984;Winter & Bodensteiner, 1988;Winter, Hensel, Bodensteiner & Glaser, 1987). The manufacture of such a cell opens the possibility of studying the microscopic properties of many fluids in critical conditions, even though the neutron scattering investigation turns out to be complex.…”