Alkoxide-based precursors for direct drawing of metal oxide micro- and nanofibres

12 páginas, 13 figuras, 3 tablas.-- et al.The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol–gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.The work was supported by the Estonian Science Foundation (grant nos. 7603, 8377, 7612, JD69, JD120, SF0180073s07 and SF0180058s07) and ESF FANAS program NANOPARMA.Peer reviewe

Residual stress measurements of alumina-zirconia ceramics by time-of-flight neutron diffraction

Neutron strain scanning and Rietveld analysis were used to study the residual stresses in Al2O3/Y-TZP ceramic composites fabricated by different green processing techniques (a novel tape casting and conventional slip casting) and with different zirconia content. The results show that the residual stresses in zirconia particulates are tensile and the ones in alumina matrix are compressive, with almost flat through-thickness residual stress profiles in all bulk samples. The residual stresses for both phases were mainly dependent on the zirconia content, irrespective of the measurement direction and the fabrication process

Residual strain scanning of alumina-based ceramic composites by neutron diffraction

The objective of this work is to non-destructively determine the residual stress profile in the bulk of two characteristic types of alumina-based composites, with the aim of improving their durability and structural integrity

Effect of iron oxide content and microstructural porosity on the performance of ceramic membranes as microbial fuel cell separators

Ceramic materials based on naturally occurring clays are a low cost and environmentally friendly alternative to commercial polymer-based membranes in bioelectrochemical systems. In this work, ceramic membranes containing different amounts of iron oxide (1.06, 2.76 and 5.75 vol.%) and sintered at different temperatures (1100, 1200 and 1300 °C) have been elaborated and tested as separators in urine-fed microbial fuel cells (MFCs). The results reveal that the presence of iron oxide in the ceramic membrane composition increases the structural porosity and reduces the pore size for the three temperatures investigated. On the other hand, it was also observed that the iron content mitigates the negative effect of the high sintering temperature on the power performance of the MFCs. In the case of the ceramic membranes sintered at 1300 °C, power output improved ca. 10-fold when the iron oxide content in the membrane increased from 1.06 up to 5.75 vol.% (30.9 and 286.6 µW, respectively). Amongst the different combinations of iron phase content and sintering temperatures, the maximum power output was obtained by MFCs working with separators containing 5.75 vol. % of iron oxide and sintered at 1100 °C (1.045 mW). Finally, the system was stable for 65 days, which supports the long-term functionality of the different materials assessed

Deposition via dip coating technique of dense yttrium stabilized zirconia layers

A deposition of yttrium stabilized zirconia layer for its use as an electrolyte in solid oxide fuel cell was performed using dip coating technique. Two commercially available surfactant systems were evaluated; nonionic surfactant which stabilizes only by steric repulsion and anionic surfactant which provides both steric and electrostatic repulsion. Dip coating process was optimized to two step deposition process. Uniform 10-15 οm thick yttria stabilized zirconia (YSZ) electrolyte layer is obtained after the final sintering step at 1400°C. Impedance spectroscopy measurements showed that selected phosphate ester based surfactant has negligible effect on the performance of the YSZ material as electrolyte. © 2012 The American Ceramic Society.The results were obtained under projects financed by the Spanish Government: MAT2006-13005-C03-01, CENIT-DEIMOS: CEN20071018, MEC PROFIT: CIT-120000-2007-50, and PSE: CIT-1200000-2008-6 (SOFCMETAL).Peer Reviewe

Laser-assisted, crack-free surface melting of large eutectic ceramic bodies

6 páginas, 5 figuras, 1 tabla.-- El pdf del artículo es la versión post-print.The modification of ceramic surfaces by directional laser melting is interesting because it can eliminate surface defects and thus improve the ceramics mechanical performance, as long as one prevents the formation of cracks. The feasibility of surface modification by laser assisted melting on large t-ZrO2-Al2O3 eutectic ceramic pieces was evaluated in this work. 0.4 mm thick, defect free, resolidified layers were obtained on plates of 40 mm width by preheating at 1200 ºC and processing at 1000 mm/h with a line-shaped CO2 laser beam and 580 W/cm2 irradiance. The surface finish was smooth, free from overlapping-track roughness. The resolidified layer had eutectic microstructure with lamellae-type Al2O3 and tetragonal ZrO2(t-ZrO2) colonies. The fracture tests of the samples confirmed the absence of crack type resolidification defects and the removal of surface defects. Although no increase in average flexural strength was observed for surface resolidified samples, they showed significantly lower standard deviation.Spanish Government; European Community FEDER program; CSIC; DGA MAT2006-13005-C03-01; MAT2009-13979-C03-03; CEN2007-2014Peer reviewe