23,000 h steam electrolysis with an electrolyte supported solid oxide cell

An electrolyte supported solid oxide cell of 45 cm² area was operated in the steam-electrolysis mode during more than 23,000 h before scheduled shutdown, of which 20,000 h with a current density of j = ?0.9 A cm^?2. The cell consisted of a scandia/ceria doped zirconia electrolyte (6Sc1CeSZ), CGO diffusion-barrier/adhesion layers between electrolyte and electrodes, a lanthanum strontium cobaltite ferrite (LSCF) oxygen electrode, and a nickel/gadolinia-doped ceria (Ni/GDC) steam/hydrogen electrode. Voltage degradation in the operation period with j = ?0.9 A cm^?2 was 7.4 mV/1000 h (0.57%/1000 h) and the increase in the area specific resistance 8 mΩ cm²/1000 h. The final cell voltage was 1.33 V (at 851 °C cell temperature). After dismantling, the cell showed no mechanical damage at electrolyte and H₂/H₂O electrode; a small fraction of the oxygen electrode was delaminated. Impedance spectroscopy applied at the steady state DC current density confirmed a degradation dominated by an increasing ohmic term, mainly due to ionic conductivity decay in the electrolyte. In addition, a small non-ohmic and at least partly reversible O₂ electrode contribution to degradation was identified, affected by a pollution from the (compressor) purge air.     

CRYSTAL SIZE GROWTH IN THE LIQUID PHASE METHANOL SYNTHESIS CATALYST

ABSTRACT

The phenomenon of crystal growth in the methanol synthesis catalyst has been studied. Crystallite size distributions in the cuo/ZnO/Al₂O₃ methanol synthesis catalyst have been determined. The effects of temperature, reaction environment and time under reaction conditions have been studied. It is observed that water in the reaction mixture promotes crystal growth.     

A SINGLE-STAGE,LIQUID-PHASE DIMETHYL ETHER SYNTHESIS PROCESS FROM SYNGAS III. DUAL CATALYST CRYSTAL GROWTH,DEACTIVATION, AND ACTIVITY CONSERVATION STUDIES

ABSTRACT

In the liquid phase dimethyl ether (DME) synthesis process, both the methanol synthesis catalyst )composed of CuO, ZnO, and Al₂O₃) and the methanol dehydration catalyst (composed of gamma-alumina) are slurried in the inert oil phase. Various long-term activity checks were conducted on these dual catalysts to characterize the crystal growth and the thermal aging behavior. X-ray powder diffraction, X-ray fluorescence and elemental intensity compositions, and the crystallite size distributions of the aged catalysts were examined. Based on the current investigation, it was established that the crystal growth and the catalyst deactivation problems in the methanol synthesis catalyst are less severe when it is used along with the methanol dehydration catalyst.     

Tribological properties of powder metallurgical tool steels used in powder compaction pressing dies

The tribological properties of two powder metallurgical (PM) tool steels, high and low nitrogen containing, are investigated by means of three different wear tests: ball‐on‐disc, rubber wheel and scratch test. The ball‐on‐disc tests showed two distinct friction curves corresponding to each material. In order to simulate the tribosystem existing in metal powder compaction dies, the rubber wheel and the scratch test were modified. The rubber wheel test was performed using ferrous powder instead of sand, and scratch testing was carried out by sliding a powder compact over the tool steels. The scratch tests indicated a higher steady‐state coefficient of friction for the low nitrogen containing PM steel as compared with the high nitrogen containing alloy. Additionally, the results from the rubber wheel tests were in agreement with industrial experiences, showing the low nitrogen containing tool steel to suffer from severe galling. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiple paths to nanocrystalline high silica beta zeolite

Several principles from nanozeolite synthesis lore were investigated in order to prepare discrete pure silica nanocrystalline BEA zeolite. It was discovered that lowering reaction temperature to 100 °C results in a significant reduction in nano-BEA crystal size, that lowering synthesis mixture water content to the lowest possible level for a ‘pourable’ gel provides nano-BEA crystals, that tetraethylorthosilicate (TEOS) more consistently provides smaller crystals than fumed silica as a raw material, that increasing the level of structure-directing agent resulted in more discrete and smaller crystals (25–30 nm), and that ‘surfactant’ addition could generate even smaller nano-BEA crystals or nanocrystalline domains, but mild to severe aggregation was still a problem. Nearly pure silica nanocrystalline BEA zeolites were prepared from Al-containing products by a calcination followed by acid extraction procedure. The calcination step is critical for more complete Al removal. Defects generated by acid extraction could be healed by treatment of resultant powder with a hexamethyldisilazane (HMDS). Another key finding was that Al-containing synthesis mixtures could provide nanocrystalline BEA zeolite with 4,4′-trimethylenebis(N-methyl, N-benzyl-piperidinium) dihydroxide (TMP(OH)₂) as organic structure-directing agent. Interestingly, adjusting synthesis parameters in TMP and Al-containing synthesis mixtures provided some differences to pure Si BEA products. For example, stirring or lowering reaction temperature did not decrease crystal size, but did shorten crystallization time. The smallest crystals from TMP-based, Al-containing reaction mixtures were prepared when a freeze–dried colloidal silica was utilized as silica source.     

Transient operation of a solid oxide electrolysis cell

In order to investigate the transient behaviour of a solid oxide electrolysis cell, tests were carried out on a single SOEC both under steady-state and transient conditions for 600 h. Steady-state operation was performed at the reference current of −20 A, corresponding to the thermoneutral voltage (1.28 V), whereas transient tests consisted in 1800 square waves applied over 140 cumulated hours, with a current of −1 A and −20 A as well as 0 A and −20 A. Independently from the operating conditions, the measured voltage degradation rate of 5% (70 mV)/1000 h was stable for the entire experiment. Consequently, it was concluded that an SOEC can be operated under on–off conditions with no increase of the degradation rate. This result paves the way for modular operation of a high temperature electrolyser fed with intermittent electrical energy.     

Superficial heat transfer by forced convection and radiation in a horizontal channel

This paper presents a numerical investigation of turbulent forced convective flow in a horizontal channel. An exchanger isothermal test plate is embedded in the lower wall, in the fully developed region of the flow close to the exit of the channel. Above this isothermal plate, on the upper surface, a black coated isothermally heating resistance facing downwards is installed. This absorbing surface provides a controlled radiative heat flux on the lower test plate. In this study, custom-built tangential gradient fluxmeters (TGFM) are used to provide local measurements of convective heat transfer so as to validate the numerical predictions. Then, parametric studies are carried out. The profiles for the heat flux are presented for different Reynolds numbers in the flow direction along the cold isothermal lower plate. Then, the influence of the presence of an obstacle, located on the lower surface, on the heat flux is also investigated. All numerical predictions are carried out with Fluent, previously calibrated against benchmark problems and experimental measurements. In the paper, special emphasis is given in the systematic comparison between experimental and numerical results.     

Black clients: Implications for supervision of trainees.

Presents a model to assist supervisors in training therapists with Black clients. Errors of beginning therapists (both Black and White) are described, including the trainee's language being full of slang, assuming an "us against the system mode," acting as a client controller, and acting as the self-effacing helper. It is suggested that racial identity is as much an issue for the Black helper as for the Black client and that the most difficult aspect of therapy with Black clients is establishing the relationship. (PsycINFO Database Record (c) 2010 APA, all rights reserved)