Controlling phase distributions in macroporous composite materials through particle-stabilized foams

Aqueous foams stabilized by ceramic and thermoplastic polymeric particles provide a general method for producing novel porous materials because their extraordinary stability against disproportionation and drainage allows them to be dried and sintered into solid materials. Here, we report the different microstructures that can be obtained from liquid foams stabilized by binary mixtures of particles when the interfacial energies between the particles and the air-liquid interfaces are manipulated to promote either preferential or competitive self-assembly of the particles at the foam interface. Modification of the interfacial energies was accomplished through surface modification of the particles or by decreasing the surface tension of the aqueous phase. Materials derived from liquid foams stabilized by poly(vinylidene fluoride) (PVDF) and alumina (Al(2)O(3)) particles are investigated. However, as is shown, the method can be extended to other polymeric and ceramic particles and provides the possibility to manufacture a wide range of porous composite materials.     

Micro-solid oxide fuel cells: status, challenges, and chances

Abstract  

Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode (i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics.     

Materials design for perovskite SOFC cathodes

Abstract  

This article focuses on perovskite materials for application as cathode material in solid oxide fuel cells. In order to develop new promising materials it is helpful to classify already known perovskite materials according to their properties and to identify certain tendencies. Thereby, composition-dependent structural data and materials properties are considered. Structural data under consideration are the Goldschmidt tolerance factor, which describes the stability of perovskites with respect to other structures, and the critical radius and lattice free volume, which are used as geometrical measures of ionic conductivity. These calculations are based on the ionic radii of the constituent ions and their applicability is discussed. A potential map of perovskites as a tool to classify simple ABO₃ perovskite materials according to their electrical conduction behavior is critically reviewed as a structured approach to the search for new cathode materials based on more complex perovskites with A and/or B-site substitutions. This article also covers the approaches used to influence electronic and the ionic conductivity. The advantage of mixed ionic electronic conductors in terms of the oxygen exchange reaction is addressed and their important properties, namely the oxygen-exchange coefficient and the oxygen diffusion coefficient, and their effect on the oxygen reduction reaction are presented.     

Neutron scattering studies of Bi2Sr2Ca0.5Ho0.5Cu2O8+x

Neutron scattering has been employed to study the crystalline electric field (CEF) interaction at the Ho³⁺ site in Bi₂Sr₂Ca_0.5Ho_0.5Cu₂O_8+x. The observed energy spectra exhibit a large number of broad but well-resolved CEF transitions between 1.2 and 73 meV, so that we have been able to unambiguously determine all nine CEF parameters required for the average orthorhombic symmetry. The unusually large line widths of the CEF transitions are shown to be related to the modulated structure. The CEF potential is essentially governed by the charge distribution of the CuO₂ planes which turns out to be very similar as in HoBa₂Cu₃O_7-x.     

Observation of quantum coherence in mesoscopic molecular magnets

By applying a transverse magnetic field B( perpendicular) of sufficient strength to the uniaxial molecular magnets Fe8 and Mn12, the tunneling splitting Delta(t) of their S = +/-10 magnetic ground states can be made large compared to perturbations such as hyperfine and dipolar interactions. We present evidence for such a Delta(t) from magnetic specific heat data below 1 K that is consistent with coherent quantum mechanical tunneling in a "mesoscopic" system under such conditions.     

不同岩蔷薇浸膏挥发性致香成分的SED-GC-MS分析研究

岩蔷薇(cistusladaniferusL.)又名赖百当(labdanum),属半日花科。利用其树脂分泌物及枝叶,通过蒸馏、浸提和萃取等方法,可制得岩蔷薇精油、浸膏、净油、油树脂等各种香原料品种。岩蔷薇的香原料制品是膏香类的极重要品种,主要应用于日化和食品行业,在烟草行业也多有应用。因香料烟香味的主要来源是类赖百当化合物的降解,故被归为烟草的五大类香味物质之一:赖百当类、双萜烯及其降解产物类。这类物质在香料烟中的含量较高,对形成香料烟的特殊香味风格具有重要意义,且在烟草中赖百当仅存在于香料烟中,烤烟、自肋烟中均不存在。赖百当类化合物是香料烟中特有的香气物质,主要成分是冷杉醇、赖百当烯二醇,经调制和醇化转化为多种降赖百当类化合物,其中降龙涎香醚、龙涎香内酯、脱氢龙涎香内酯等都具有强烈的龙涎香香气,对增进卷烟香气和吃味有很好作用。     

Thermodynamic modeling of the ZrO2–YO1.5 system

In the present work, an optimized set of Gibbs energy functions is proposed for the Y–Zr–O ternary system. We focus on the ZrO₂–YO_1.5 quasi-binary system, but reoptimizations of the Zr–O and Y–O binary systems are included as well. The parameters for the Y–Zr binary system were taken from a previous assessment.

The ZrO₂–YO_1.5 system was treated as a quasi-binary section of the Y–Zr–O ternary system. The existing experimental data on the ZrO₂–YO_1.5 system were carefully reviewed. The related parameters were optimized using both thermodynamic data and phase diagram data. A calculated phase diagram of the ZrO₂–YO_1.5 system is presented. Our optimization agrees well with most experimental data. Two calculated isothermal sections of the Y–Zr–O system at 1500 and 2000 K are also included.     

Metastable Energy Strata in Weakly Nonlinear Wave Equations

We consider the problem of the long-time stability of plane waves under nonlinear perturbations of linear Klein-Gordon equations. This problem reduces to studying the distribution of the mode energies along solutions of one-dimensional semilinear Klein–Gordon equations with periodic boundary conditions when the initial data are small and concentrated in one Fourier mode. It is shown that for all except finitely many values of the mass parameter, the energy remains essentially localized in the initial Fourier mode over time scales that are much longer than predicted by standard perturbation theory. The mode energies decay geometrically with the mode number with a rate that is proportional to the total energy. The result is proved using modulated Fourier expansions in time.