Influence Of Precursor Dispersity And Agglomeration Of Mechanical Characteristics Of 92Zro2-8Y2O3 Ceramics

Ceramics based on the systems of Y2O3- ZrO2 are widely used as constructional materials, catalist carriers, high-temperature oxygen sensors, materials of fuel cell and so on. In this connection, such properties of these materials as mechanical strength and cracking resistance are of exceptional importance. Phase transitions, producing changes in the chemical composition, crystal structure, and thermodynamic properties of ceramic materials, may be a cause of their destruction. The subject of the present investigation is powder zirconium hydroxide, both pure and Y-stabilized. Phase transformations have been studied well enough in these powders with micron size of particles. However up to now, there have been no systematic attempts to determine an interconnection between powder dispersity and phase transitions (and associated mechanical characteristics). In present work powder precursors of various dispersity were synthesized by sol-gel method allowing to obtain particles with sizes ranging from 40 nm to 5-10 μm. The main purpose of the work was to obtain powders with narrow particle size distribution, that is, essentially monodispersed powders. To characterize the powders obtained, we used the following methods: electron microscopy, laser scattering particle size distribution analysis, and adsorption methods. Experimental results have shown that dispersity of powders under investigation has a profound effect not only on their phase transition temperatures, but also on composition of precursor crystallohydrates. Three points bending measured at 1000 °C for the ceramics fabricated from these precursors also depends on the precursor dispersity. © 2006 Advanced Study Center Co. Ltd

Influence Of Precursor Dispersity And Agglomeration On Mechanical Characteristics Of Zro2-Ce2O3 And Zro2-Y2O3-Ce2O3 Ceramics

Powder precursors of ZrO2 - Ce2O3 and ZrO2- Y2O3 - Ce2P3 systems were synthesized by sol-gel method. Dispersity of the powders depended on concentrations of starting reagents and synthesis conditions. To characterize the powder dispersity and aggregated state, electron microscopy and laser scattering particle size distribution analysis were used. Ceramic samples were prepared from these powder precursors; their mechanical characteristics were studied by three points bending method at 1000°C. It was revealed that bending strength - particle size curve for ZrO2- Ce2O3 system has a pronounced maximum. This phenomenon is explained by a change in cerium valence depending on powder precursor agglomerate size. © 2007 Advanced Study Center Co. Ltd

Electrochemical Characterization of Novel Polyantimonic-Acid-Based Proton Conductors for Low- and Intermediate-Temperature Fuel Cells

The development of novel proton-conducting membrane materials for electrochemical power units, i.e., low temperature fuel cells (FCs), efficiently working up to 300 C, is a critical problem related to the rapid shift to hydrogen energy. Polyantimonic acid (PAA) is characterized by high conductivity, sufficient thermal stability and can be regarded as a prospective proton-conducting material. However, the fabrication of bulk PAA-based membranes with high proton conductivity remains a challenging task. In the present work, for the first time, the authors report the investigation on proton conductivity of bulk PAA-based membranes in the temperature range 25–250 C, both in dry air and in moisturized air. Using PAA powder and fluoroplastic as a binder, fully dense cylindrical membranes were formed by cold uniaxial pressing. The structures of the PAA-based membranes were investigated by SEM, EDX, XRD and Raman techniques. STA coupled with in situ thermo-XRD analysis revealed that the obtained membranes corresponded with Sb2O5 3H2O with pyrochlore structure, and that no phase transitions took place up to 330 C. PAA-based membranes possess a high-grain component of conductivity, 5 10 2 S/cm. Grain boundary conductivities of 90PAA and 80PAA membranes increase with relative humidity content and their values change non-linearly in the range 25–250 C