V. Zelizko

Characterisation, conductivity and mechanical properties of theoxygen-ion conductor La0.9Sr0.1Ga0.8Mg0.2O3-x

The new oxygen-ion conductor La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-x has been prepared by conventional solid-state reaction at high temperatures and characterised by X-ray diffraction, scanning and transmission electron microscopy, and conductivity (four-probe dc and impedance) measurements. The room-temperature structure is orthorhombic, space groupPnma (no. 62), with a=5.5391(7) A, b=7.8236(12) A, c=5.5224(7) A. The material undergoes a phase transition at 445 K to a rhombohedral structure. Mechanical property measurements at room temperature and at 1173 K give average strength measurements of 162±14 MPa and 55±11 MPa respectively. Conductivity and ionic transport number measurements confirm predominantly ionic conduction. The contribution from the grain boundary conductivity is extremely small at temperatures below 673 K. At 1073 K, an ionic conductivity value of 0.12 S cm -1 was recorded in air.

Tubular zirconia–yttria electrolyte membrane technology for oxygen separation

Abstract Oxygen separation technology has applications in health care, defence, on-site generation of gases with known oxygen concentration, food packaging (oxygen removal), aquaculture and a number of others. The market potential for this technology is of the order of several billion dollars globally. Ceramic membranes based on O 2− or O 2− /electronic conducting materials have the potential to service this market. Pure O 2− conducting ceramic membrane technology can be used not only for production of oxygen but also for oxygen removal in gas streams and enclosures as well as for oxygen level control to produce calibration gases. In this paper, the operation of several oxygen separation devices of tubular design constructed from zirconia–yttria electrolyte has been discussed for oxygen generation, oxygen removal and control. Life time tests performed for periods up to 8000 h have been described.

A versatile polymer electrolyte membrane fuel cell (3 kWe) facility

Abstract The polymer electrolyte membrane (PEM) fuel cell technology offers many advantages over other types of fuel cells in terms of high power density, low operating temperature and fast start, stop and load following capability. However, the stringent fuel quality requirements still remain a critical barrier for its commercialization. In this context, gaining knowledge on the effect of fuel compositions on the performance of the PEM fuel cells is essential to determine the fuel cleaning requirements for reformates from different fuel sources. In this paper, a test facility is described which has been established to study fuel quality issues, start, stop, thermal cycling and load following capabilities of PEM fuel cell stacks up to 3 kW e capacity. Important features of the test facility are described along with results of testing commercial and in-house built stacks up 1 kW e capacity.

Influence of surface preparation on the rotating flexural fatigue of Mg-PSZ

Specimens of Mg-PSZ were given three different surface preparations prior to testing in rotating flexural fatigue. The preparation consisted of precise grinding with relatively coarse (55 to 80 μm) diamond-impregnated wheels along axial and radial directions as well as by polishing. Only minor differences were noted in the strength-number of cycles to failure (S-N) data, with radial grinding being more deleterious. The data showed considerable scatter; however, from the results the stress corrosion exponents were typically between 65 and 92. Failure origins were often associated with the presence of flaws or pores near the surface.

The effect of alumina addition on the conductivity, microstructure and mechanical strength of zirconia — yttria electrolytes

The effect of alumina additions on the ionic conductivity and mechanical properties of 3 and 8 mol% Y2O3 - ZrO2 compositions has been investigated. Such materials are of interest for use in fuel cells and other similar applications. Sintered specimens were characterised by XRD, SEM, impedance spectroscopy, four — probe DC conductivity and mechanical strength measurements. Alumina additions had no affect on the conductivity degradation behaviour at 1000 °C and the activation energy but resulted in an increase in the strength of 8 mol% Y2O3 - ZrO2 composition by about 25%. However, a significant drop in the ionic conductivity well above what could be accounted for by the decrease in the volume fraction of the conducting phase, was observed.

Oxygen removal and level control with zirconia — Yttria membrane cells

Oxygen-ion conducting ceramic membrane materials (pure ionic or mixed ionic / electronic conductors) allow selective transport of oxygen in the form of ionic flux at high temperatures and can be used for the production of high purity oxygen. Such materials are also more appropriate for gas purification (residual oxygen removal) and control of oxygen levels in a gas stream to produce gases with known oxygen partial pressure. In this paper, operation and limitations of laboratory scale prototypes constructed from tubular zirconia — yttria membranes have been described for the removal of oxygen from air and low oxygen containing gases to produce oxygen-free gas streams and generation of calibration gases with pre-defined levels of oxygen.