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Phase Equilibrium Relations in the Binary System Barium Oxide-Niobium Pentoxide.

ABSTRACT: A large portion of the phase equilibrium diagram for the binary system barium oxide-niobium pentoxide has been constructed from observations of fusion characteristics and X-ray diffraction data. In the system five binary compounds were observed with BaO: Nb2O5 ratios of 5:2, 1:1, 6:7, 3:5, and 1:3 and a 6:1 compound was postulated. The 1:1 compound was found to melt congruently at 1,455 °C and have only one stable polymorph, although a second metastable polymorph can also be prepared. The 5:2 compound melts congruently at 1,542 °C; the 6:7, 3:5, and 1:3 phases melt incongruently at 1,330, 1,290, and 1,315 °C, respectively. The phase relations of the 6:1 compound could not be determined due to the reaction between this phase and platinum metal. No 2:1 compound was observed in this system.

SUBMITTER: Roth RS

PROVIDER: S-EPMC5287139 | biostudies-literature | 1961 Jul-Aug

REPOSITORIES: biostudies-literature

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Phase Equilibrium Relations in the Binary System Barium Oxide-Niobium Pentoxide.

Roth R S RS Waring J L JL

Journal of research of the National Bureau of Standards. Section A, Physics and chemistry 19610701 4

A large portion of the phase equilibrium diagram for the binary system barium oxide-niobium pentoxide has been constructed from observations of fusion characteristics and X-ray diffraction data. In the system five binary compounds were observed with BaO: Nb<sub>2</sub>O<sub>5</sub> ratios of 5:2, 1:1, 6:7, 3:5, and 1:3 and a 6:1 compound was postulated. The 1:1 compound was found to melt congruently at 1,455 °C and have only one stable polymorph, although a second metastable polymorph can also b ...[more]

PMID: 32196182

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Project description:A general theoretical framework is developed to account for the effects of an external potential on the energetics of membrane proteins. The framework is based on the free energy relation between two (forward/backward) probability densities, which was recently generalized to non-equilibrium processes, culminating in the work-fluctuation theorem. Starting from the probability densities of the conformational states along the "voltage coupling" reaction coordinate, we investigate several interconnected free energy relations between these two conformational states, considering voltage activation of ion channels. The free energy difference between the two conformational states at zero (depolarization) membrane potential (i.e., known as the chemical component of free energy change in ion channels) is shown to be equivalent to the free energy difference between the two "equilibrium" (resting and activated) conformational states along the one-dimensional voltage couplin reaction coordinate. Furthermore, the requirement that the application of linear response approximation to the free energy functionals of voltage coupling should satisfy the general free energy relations, yields a novel closed-form expression for the gating charge in terms of other basic properties of ion channels. This connection is familiar in statistical mechanics, known as the equilibrium fluctuation-response relation. The theory is illustrated by considering the coupling of a unit charge to the external voltage in the two sites near the surface of membrane, representing the activated and resting states. This is done using a coarse-graining (CG) model of membrane proteins, which includes the membrane, the electrolytes and the electrodes. The CG model yields Marcus-type voltage dependent free energy parabolas for the response of the electrostatic environment (electrolytes etc.) to the transition from the initial to the final configuratinal states, leading to equilibrium free energy difference and free energy barrier that follow the trend of the equilibrium fluctuation relation and the Marcus theory of electron transfer. These energetics also allow for a direct estimation of the voltage dependence of channel activation (Q-V curve), offering a quantitative rationale for a correlation between the voltage dependence parabolas and the Q-V curve, upon site-directed mutagenesis or drug binding. Taken together, by introducing the voltage coupling as the energy gap reaction coordinate, our framework brings new perspectives to the thermodynamic models of voltage activation in voltage-sensitive membrane proteins, offering an a framework for a better understating of the structure-function correlations of voltage gating in ion channels as well as electrogenic phenomena in ion pumps and transporters. Significantly, this formulation also provides a powerful bridge between the CG model of voltage coupling and the conventional macroscopic treatments.

Dataset Information

Phase Equilibrium Relations in the Binary System Barium Oxide-Niobium Pentoxide.

Publications

Phase Equilibrium Relations in the Binary System Barium Oxide-Niobium Pentoxide.

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