alpha-SiAlON ceramics with elongated grain morphology using an alternative sintering additive

In this work, the use of a natural yttrium oxide and rare earth oxide solid solution (CRE2O3) as stabilizers of the alpha-Si3N4 phase to form alpha-SiAlON has been investigated. This oxide mix is produced at FAENQUIL-DEMAR, at a cost of only 20% of pure commercial Y2O3. Two alpha-SiAlONs using pure Y2O3 or CRE2O3 have been prepared, using mixes of 20% by volume of a molar fraction of 9:1 of AlN to Y2O3 or AlN to CRE2O3, respectively, with 80% alpha-Si3N4. Samples were gas pressure-sintered at 1900 degreesC, under 1.5 MPa of N-2 for 60 min. Both compositions yielded alpha-SiAlON ceramics with high relative densities (98% t.d.), hardness of 18 GPa and fracture toughness of 5 Mpa m(1/2), with homogeneous microstructures composed of elongated alpha-SiAlON grains with aspect ratios of 5. It is concluded that the mixed rare earth concentrate (CRE2O3) can be used to produce alpha-SiAlON ceramics with similar microstructures and mechanical properties of alpha-SiAlON ceramics fabricated using pure Y2O3, but with the advantage of its lower production cost. (C) 2004 Elsevier B.V All rights reserved.

Effect of different surface penetrating sealants on the roughness of a nanofiller composite resin

This study evaluated the effectiveness of different sealants applied to a nanofiller composite resin. Forty specimens of Filtek Z-350 were obtained after inserting the material in a 6x3 mm stainless steel mold followed by light activation for 20 s. The groups were divided (n=10) according to the surface treatment applied: Control group (no surface treatment), Fortify, Fortify Plus and Biscover LV. The specimens were subjected to simulated toothbrushing using a 200 g load and 250 strokes/min to simulate 1 week, 1, 3 and 6 months and 1 and 3 years in the mouth, considering 10,000 cycles equivalent to 1 year of toothbrushing. Oral-B soft-bristle-tip toothbrush heads and Colgate Total dentifrice at a 1:2 water-dilution were used. After each simulated time, surface roughness was assessed in random triplicate readings. The data were submitted to two-way ANOVA and Tukey's test at a 95% confidence level. The specimens were observed under scanning electron microscopy (SEM) after each toothbrushing cycle. The control group was not significantly different (p>0.05) from the other groups, except for Fortify Plus (p<0.05), which was rougher. No significant differences (p>0.05) were observed at the 1-month assessment between the experimental and control groups. Fortify and Fortify Plus presented a rougher surface over time, differing from the baseline (p<0.05). Biscover LV did not differ (p>0.05) from the baseline at any time. None of the experimental groups showed a significantly better performance (p>0.05) than the control group at any time. SEM confirmed the differences found during the roughness testing. Surface penetrating sealants did not improve the roughness of nanofiller composite resin.

Die Begebenheiten vom 11. bis Ende März 1848

Enth.: 1. Die Begebenheiten vom 11. bis Ende März 1848. 2. Die Begebenheiten vom 1. April bis 3. Mai 1848. 3. Die Begebenheiten vom 4. Mai bis 17. Mai 1848. 4. Die Begebenheiten vom 18. bis 31. Mai 1848. 5. Die Begebenheiten vom 1. Juni bis 12. Juni 1848, die Verhandlungen des Slavencongresses mitbegriffen

Metodologías de análisis del espacio audiovisual online: Entre la innovación y la ansiedad de la novedad

La aparición de espacios digitales que incluyen grandes bases de datos de videos online ha generado una serie de innovaciones metodológicas y prácticas emergentes que suelen venir acompañadas de discursos esperanzadores y profecías sobre el papel de los medios online en la investigación social. Este medioambiente discursivo ha alterado sensiblemente la recepción y evaluación de lo que podríamos denominar las metodologías audiovisuales. En este artículo, a partir de una serie sencilla de rasgos específicos de las plataformas de videos en Internet (principalmente Youtube) se ha intentado catalogar una serie de modelos de investigación audiovisual o de prácticas de producción e interpretación de materiales audiovisuales en el entorno de las ciencias sociales. El objetivo es identificar sus rasgos distintivos y sus potencialidades epistemológicas sacando a la luz, además, algunos de sus presupuestos tácitos. Se trata, en última instancia, de una evaluación constructiva de estos modelos de investigación que a través del análisis de sus hipótesis subyacentes aspira a contribuir al correcto aprovechamiento de las oportunidades metodológicas que ofrecen los repositorios audiovisuales online.