Revised thermochemistry of gaseous ammonium nitrate, NH₄NO₃(g)

In an earlier paper (Hildenbrand, D. L., Lau, K. H., and Chandra, D. J. Phys. Chem. B 2010, 114, 330.), we detected the presence of NH?NO?(g) in the vapor over the solid nitrate and evaluated its partial pressure along with those of HNO? and NH?. The molecular constants of the gaseous nitrate were estimated in the absence of experimental values in an attempt to derive its enthalpies of sublimation and formation. After publication, we became aware of the sought molecular data, evaluated primarily from high-level theoretical calculations, and revised the analysis to yield Δ(f)H???°(NH?NO?(g)) = ?61.8 ± 5 kcal mol?1.     

Composition and thermochemistry of silver bromide vapor

The mole fractions of AgBr and Ag3Br3 in the saturated vapor at 840 K have been evaluated from the vapor mass spectrum, by comparison with the corresponding spectrum of AgCl vapor, where the monomer/trimer ratio is known accurately from vapor molecular weight measurements. Combination of these results with new measurements of the vapor pressure of molten AgBr by the torsion-effusion method in the range 805-936 K yielded the third law enthalpies of vaporization and the standard enthalpies of formation DeltafH degrees 298(AgBr, g) = 27.8 +/- 0.3 kcal mol(-1) and DeltafH degrees 298(Ag3Br3, g) = -19.0 +/- 1 kcal mol(-1). The dissociation energy, D degrees 0(AgBr), is found to be 66.4 +/- 0.3 kcal mol(-1), or 2.88 +/- 0.01 eV, some 3.5-5 kcal mol(-1) lower than previous literature values. Approximate thermochemical stabilities of the dimer species Ag2Cl2 and Ag2Br2 have also been evaluated.     

Improved cathode/electrolyte interface of SOFC

The electrochemical performance of porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ (LSCF) cathodes is improved by inserting a dense LSCF layer. A 200 nm thin layer is deposited on the electrolyte substrate by pulsed laser deposition, prior to the screen printing process. This procedure enhances the adherence of the porous cathode layer to the electrolyte and allows a lower sintering temperature, which reduces grain growth during sintering. In air a decrease in polarization resistance with a factor of 3 is observed for electrodes sintered at 1100 °C. The apparent electrolyte resistance is also reduced with the dense PLD layer. A remarkable change in Po₂ dependence is observed for the Gerischer parameters that describe part of the electrode impedance, indicating a possible change in the oxygen transfer mechanism.     

Results on two-, three-, and four-body events from the100Mo+100Mo and120Sn+120Sn collisions aroundE/A=20 MeV

Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions¹⁰⁰Mo+¹⁰⁰Mo atE/A =18.7, 23.7 MeV and¹²⁰Sn+¹²⁰Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP ₃ andP ₄ of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP ₃ andP ₄ curves at high energy losses. Small deviations of theP ₃ andP ₄ curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.     

On the influence of shell structure in dissipative collisions

A kinematically complete study of the symmetric systems ¹⁴⁴Sm+¹⁴⁴Sm and ¹⁵⁴Sn+¹⁵⁴Sm has been performed at energies 30% in excess of the interaction barrier. They have been chosen because of their different internal structure: ¹⁴⁴Sm has a closed N = 82 neutron shell and a spherical ground-state configuration; ¹⁵⁴Sm with ten neutrons outside this shell is strongly deformed. The observed gross features of both reactions like energy, angular and total mass or element distributions are very similar; the ratio of the mass variances as function of the total kinetic energy loss indicates the number of exchanged nucleons to be comparable in all stages of the reactions. At small energy losses, however, the element distributions of the ¹⁴⁴Sm + ¹⁴⁴Sm reaction are considerably broader, pointing at an enhanced proton transfer at the cost of the number of exchanged neutrons in this system. This observation is attributed to the influence of the closed shell which seems to block the transfer of neutrons at low excitation energies. These results can be explained quantitatively by the different gradients of the shell-corrected potential energy surfaces of the two systems.