Synthesis of NASICON with New Compositions for Electrochemical Carbon Dioxide Sensors*

Powders and pellets of new NASICON compositions have been synthesized using a mixed inorganic-organic sol-gel synthesis, by the preliminary formation of a pre-hydrolized TEOS xerogel. The investigated compositions can be described by the general formula Na₃Zr_2-(x/4)Si_2-xP_1+xO₁₂, obtained by keeping the Na concentration constant (= 3) at the optimum value reported for ionic conductivity, with x = 0 (the usual NASICON composition), 0.667, and 1.333. The xerogels were calcined at various temperatures in the range 400–1200°C. The powder samples were analyzed by TG/DTA, BET measurements, XRD, and SEM. The powders calcined at 500°C were sintered into pellets at 1100°C for 6 h. The sintering behavior of the pellets was investigated by dilatometric measurements and SEM observations. The sinterability increased with increasing x value. Dense samples of the new compositions were obtained by sintering at only 1100°C. This is attributed to the occurrence of liquid phase sintering. The electrical conductivity of the NASICON sintered bodies was measured by ac impedance spectroscopy. The conductivity decreased with decreasing c₀ lattice parameter of the hexagonal structure or increasing x value. The CO₂ gas sensors, using as electrolyte the dense samples of the new NASICON compositions, showed good EMF response that was very close to the theoretical value, even for the sample with x = 1.333 that showed much lower conductivity.     

A simple mathematical model for determining the equivalent permeability of fractured porous media

A simple mathematical model has been proposed so as to determine the equivalent permeability of fractured porous media. The model consists of square blocks placed in an array with vertical and horizontal fractures between the blocks. An analytical expression valid for all macroscopic flow directions has been derived for the equivalent permeability of the fractured porous media, assuming a horizontal flow through the blocks placed in a porous medium. The analytical expression agrees well with the existing equations and also with the microscopic numerical results carried out using a unit structure with periodic boundary conditions. The foregoing two-dimensional model has been extended to a three dimensional case in which the cubic rocks are arranged in a cubic array. The resulting three-dimensional analytical expression for the equivalent permeability is found to agree very well with both existing formula and microscopic numerical simulation.     

A new leaky NRD guide based on a grating structure

Analysis and experiment of a new leaky nrd guide based on a grating structure is described. Analysis employs a mode coupling procedure which yields highly accurate results while presenting the advantage of simplicity and ease of manipulation. Numerical values for the phase and leakage constants are presented and the role of each grating parameter is assessed. Theoretical results are compared with experimental data for different geometric and constitutive parameters and reasonable agreement between them is obtained.     

Network management in a local computer network

The functions and structure of the network management subsystem of the GAMMA-NET, a local computer network at the University of Tsukuba, are presented. The network management subsystem is an integrated subsystem that offers a convenient man-machine interface for the network users during the execution of required jobs, and levels the workload throughout the system, as well as managing the network operations.     

A New Catalyst for Selective Oxidation of CO in H2: Part 1, Activation by Depositing a Large Amount of FeO x on Pt/Al2O3 and Pt/CeO2 Catalysts

1% Pt/Al₂O₃ and 1% Pt/CeO₂ are markedly activated by the deposition of a large quantity of FeO _x , about 100 wt% in Fe with respect to the supports. In contrast, the activity of a Ru/Al₂O₃ catalyst was completely suppressed by the deposition of FeO _x , but a Ru-Pt/Al₂O₃ was markedly activated by the FeO _x . The activation depends on the sequence of the deposition, that is, no pronounced activation was observed on the Pt supported on a FeO _x /Al₂O₃ as well as on the Pt codeposited with a small amount of Fe on Al₂O₃, that is, the activity was almost equal to that of the Pt/Al₂O₃. The XPS analysis of the Pt/CeO₂ and FeO _x /Pt/CeO₂ proved that the Pt is effectively covered with the FeO _x . Selectivity for the oxidation of CO in H₂ was also improved on the FeO _x /Pt/Al₂O₃ and FeO _x /Pt/CeO₂ catalysts and it is rather independent of the conversion. In conformity with the feature of the FeO _x /Pt/Al₂O₃ and FeO _x /Pt/CeO₂ catalysts, we deduced that the deposited FeO _x is activated by the Pt and the FeO _x is responsible for the selective oxidation of CO.     

A CHEMICAL ROUTE FOR THE PREPARATION OF NANOSIZED RARE EARTH PEROVSKITE-TYPE OXIDES FOR ELECTROCERAMIC APPLICATIONS

This paper reviews the work performed by the authors on the preparation of LnTO₃ (Ln = rare earth elements, and T = transition metals) perovskite-type oxides by the thermal decomposition at low temperatures of the corresponding heteronuclear complexes. Bimetallic complexes in the series Ln[Fe(CN₆)]·nH₂O and Ln[Co(CN₆)] nH₂O, with Ln = from La through Yb, and trimetallic complexes in the series Ln¹_xLnnl-x[Co(CN₆)] nH₂O and Ln[FeyCo1-_y(CN₆)] nH₂O were prepared. The formation of the perovskite-type oxides by the thermal decomposition of the complexes has been studied by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), x-ray fluorescence (XRF), Fourier transform infrared (FTTR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The composition and temperature limits of stability for the dimetallic and trimetallic perovskite-type oxides have been clarified. The major role played by the ionic radii of the Ln3⁺ and T3⁺ ions on the formation of the perovskite-type oxides has been identified. Homogeneous perovskite-type oxide powders with nanosized particles, which possess promising characteristics for their applications as functional ceramics, are easily synthesized with this method.     

A rapid solution for the maximum loading point of a power system

This paper presents a new solution method for computing the maximum loading point of a bulk power system under the condition where the loads of the nodes can be parameterized by a scalar which is the loading level of the system. A special loading model, in which the loading level of the system depends on the voltage magnitude of a loading node, is adopted for the purpose of releasing the load-flow computation from the ill-condition near and at the maximum loading point. The loading level of the system is unknown in the aforementioned loading model. The maximum loading point is obtained by adjusting the operating parameter so as to achieve the maximum loading. The operating parameter is adjusted in the converging process of the Newton-Raphson iterative computation. The adjustment is computed based on the least squares estimation using the data set which is obtained from its own iteration process. It is shown in numerical examples that the proposed method is satisfactorily rapid, stable, and accurate.