Glass-ceramic material from the SiO 2-Al 2O 3-CaO system using sugar-cane bagasse ash (SCBA)

Brazil is the world's largest producer of alcohol and sugar from sugarcane. Currently, sugarcane bagasse is burned in boilers to produce steam and electrical energy, producing a huge volume of ash. The major component of the ash is SiO 2, and among the minor components there are some mineralizing agents or fluxing. Published works have shown the potential of transforming silicate-based residues into glass-ceramic products of great utility. This work reports the research results of SCBA use to produce glass-ceramics with wollastonite, rankinite and gehlenite as the major phases. These silicates have important applications as building industry materials, principally wollastonite, due to their special properties: high resistance to weathering, zero water absorption, and hardness among others. The glasses (frits) were prepared mixing ash, calcium carbonate and sodium or potassium carbonates as flux agents, in different concentrations. X-ray fluorescence was used to determine the chemical composition of the glasses and their crystallization was assessed by using thermal analysis (DTA/DSC/TGA) and X-ray diffraction. The crystallization kinetics was evaluated using the Kissinger method, giving activation energies ranging from 200 to 600 kJ/mol. © 2011 Ceramic Society of Japan.

Delocalization-localization transition of plasmons in random (GaAs)(m)(Al(0.3)Ga(0.7)As)(6) superlattices

The transition of plasmons from propagating to localized state was studied in disordered systems formed in GaAs/AlGaAs superlattices by impurities and by artificial random potential. Both the localization length and the linewidth of plasmons were measured by Raman scattering. The vanishing dependence of the plasmon linewidth on the disorder strength was shown to be a manifestation of the strong plasmon localization. The theoretical approach based on representation of the plasmon wave function in a Gaussian form well accounted for by the obtained experimental data.

Historias de al-Khwarizmi (3 entrega) : orígenes del álgebra.

Artículo centrado en el libro de al-Khwarizmi. Se discute el origen de dicha obra entre otros muchos aspectos relacionados con este libro, tan importante en la historia del álgebra.

Seqüencialització i temporalització d'alguns dels continguts d'educació plàstica al nivell 3 de la banda A : tècniques de dibuix. 'Secuenciación y temporización de algunos de los contenidos de educación plástica en el nivel 3 de la banda A : técnicas de dibujo'.

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El castellano y otras lenguas españolas. Cooficialidad lingüística y política educativa (En torno al artículo 3.õ de la Consiitución Española de 1978).

Se estudia la problemática de la existencia de varias lenguas oficiales en España. Esto se denomina Cooficialidad educativa, y se sustenta en el artículo tercero de la Constitución Española de 1978 y en el desarrollo de los Estatutos de Autonomía. El bilingüismo de algunas zonas es un hecho histórico. Lo nuevo, es el reconocimiento de tal hecho cultural y, por consiguiente, el problema de enfocarlo y resolverlo de acuerdo con loa principios de nuestra ley Suprema. De esta forma se profundiza sobre los principios que regulan el idioma castellano o español en la Constitución. El primer párrafo del artículo tercero de la Constitución de 1978 afirma: el castellano es la lengua española oficial del Estado. Todos los españoles tienen el deber de conocerla y el derecho a usarla. Tras el español, llega el turno a las autonomías políticas y las áreas lingüísticas. El párrafo segundo del artículo tercero de la Constitución de 1978 declara: Las demás lenguas españolas serán también oficiales en las respectivas comunidades autónomas de acuerdo con sus Estatutos. Por último se hace mención a los problemas de la norma y la difusión. Las lenguas vernáculas habladas en las Comunidades Autónomas presentan problemas de diversa entidad en cuanto a la fijación de sus respectivas normas de corrección idiomática. Como elemento final se reflexiona sobre la cooficialidad lingüística y la política educativa. Se trata de uno de los aspectos más conflictivos. Por ello se fijan las bases fundamentales desde las que es posible abordar con seriedad una política educativa que, respetando el marco jurídico establecido por la Constitución y los Estatutos, pretenda formar a los españoles para el ejercicio de la libertad en la solidaridad.

Characterization of aluminum hydroxide (Al(OH)(3)) for use as a porogenic agent in castable ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

En la Bastilla se baila: ¡claro que tenemos derechos : nación, ley y jaque al rey 3

Fondo Margaritainés Restrepo

Dame un pedazo de calle : mirando al Sur 3

Fondo Margaritainés Restrepo

Ceramic Crucible Corrosion by Heavy Metal Oxide Glasses, Part I: Phenomenological Study

Heavy metal oxide (HMO) glasses have received special attention due to their optical, electrical and magnetic properties. The problem with these glasses is their corrosive nature. In this work, three ceramic crucibles (Al 2O 3, SnO 2 and ZrO 2) were tested in the melting of the system 40 PbO-35 BiO 1.5-25 GaO 1.5 (cation-%). After glass melting, crucibles were transversally cut and analyzed by scanning electronic microscopy (SEM), coupled to microanalysis by energy dispersive spectroscopy (EDS). Results indicated that zirconia crucibles presented the highest corrosion, probably due to its smallest grain size. Tin oxide crucibles presented a low corrosion with small penetration of the glass into the crucible. This way, these crucibles are an interesting alternative to melt corrosive glasses in instead of gold or platinum crucibles. It is important to emphasize the lower cost of tin oxide crucibles, compared to gold or platinum ones.

Ceramic Crucible Corrosion by Heavy Metal Oxide Glasses, Part II: Diffusion Study

Due to their low cost and high resistance to corrosion, ceramic crucibles can be used for the melting of PBG glasses (PbO-BiO 1.5GaO 1.5). These glasses present good window transmission from ultra-violet to infrared, making their use as optical fibres promising. However, their disadvantage is the high reactivity, leading to the corrosion of different crucibles, including gold and platinum ones. In this work, the corrosion of Al 2O 3, SnO 2 and ZrO 2 crucibles after melting at temperatures varying from 850 to 1000°C, was evaluated by Scanning Electronic Microscopy (SEM) in conjunction with microanalysis by EDS. The lead diffusion profile in the crucible material was obtained. Diffusion coefficients were calculated according to the Fick and Fisher theories. Results indicated that the different crucibles presented similar behaviour: in the region near the interface, diffusion occurs in the volumetric way and in regions away from the interface, diffusion occurs through grain boundary.

Use of high energy ball milling on the sintering optimization of alumina ceramics

In this work, the effect of the milling time on the densification of the alumina ceramics with or without 5wt.%Y 2O 3, is evaluated, using high-energy ball milling. The milling was performed with different times of 0, 2, 5 or 10 hours. All powders, milled at different times, were characterized by X-Ray Diffraction presenting a reduction of the crystalline degree and crystallite size as function of the milling time increasing. The powders were compacted by cold uniaxial pressing and sintered at 1550°C-60min. Green density of the compacts presented an increasing as function of the milling time and sintered samples presented evolution on the densification as function of the reduction of the crystallite size of the milled powders. © (2010) Trans Tech Publications.