Recristalización de bandas de aluminio procedentes de colada continua, laminadas en frío

Este artículo revisa la bibliografía existente sobre los problemas que la banda de colada continua, laminada en frío, presenta en su recristalización. Se examinan los impedimentos que presenta la precipitación de elementos de aleación o impurezas, previa o simultánea a la recristalización, para la nucleación de la recristalización y por tanto para ésta. Se explica el uso de las curvas TTT (Temperatura, Tiempo, Transformación) para la determinación de temperatura y velocidad de calentamiento críticas para llegar a la recristalización sin pasar por la zona de precipitación. Se explica también la obtención de curvas CTT (Concentración, Tiempo, Transformación) y "diagramas de tamaño de grano" para aleaciones Al-Mn en función de la velocidad de calentamiento y contenido de manganeso en solución sólida.

Obtaining data to validate a model of an induction skull melting furnace

A casting route is often the most cost-effective means of producing engineering components. However, certain materials, particularly those based on Ti, TiAl and Zr alloy systems, are very reactive in the molten condition and must be melted in special furnaces. Induction Skull Melting (ISM) is the most widely-used process for melting these alloys prior to casting components such as turbine blades, engine valves, turbocharger rotors and medical prostheses. A major research project is underway with the specific target of developing robust techniques for casting TiAl components. The aims include increasing the superheat in the molten metal to allow thin section components to be cast, improving the quality of the cast components and increasing the energy efficiency of the process. As part of this, the University of Greenwich (UK) is developing a computer model of the ISM process in close collaboration with the University of Birmingham (UK) where extensive melting trials are being undertaken. This paper describes the experimental measurements to obtain data to feed into and to validate the model. These include measurements of the true RMS current applied to the induction coil, the heat transfer from the molten metal to the crucible cooling water, and the shape of the column of semi-levitated molten metal. Data are presented for Al, Ni and TiAl.

The use of biological indicators of heavy metal contamination in estuaries. Occasional Publication of the Marine Biological Association 1

The use of the deposit-feeding molluscs Scrobicularia plana and Macoma balthica and the burrowing polychaete Nereis diversicolor as indicators of the biological availability of heavy metals in sediments has been evaluated. Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sn and Zn have been measured in organisms and sediments from more than 30 estuaries in south west England and South Wales and indicate that the biological availability of most metals varies by order of magnitude between uncontaminated and contaminated sites. The results have been compared with those obtained with the use of other species of indicator organisms in estuaries.

Mechanochemical interconversion between discrete complexes and coordination networks - formal hydration/dehydration by LAG

Using a small planetary ball mill, liquid-assisted grinding (LAG) of metal salts or oxides (ZnO, CdO, CdCO3, Cu(OAc)(2)center dot H2O, Co(OAc)(2)center dot 4H(2)O, Mn(OAc)(2)center dot 4H(2)O, Ni(OAc)(2)center dot 4H(2)O, FeSO4 center dot 7H(2)O) with two equivalents of isonicotinic acid (HINA) and small amounts of water ( up to 5.6 molar equivalents) gave discrete aquo complexes trans-[M(INA)(2)(OH2)(4)] (M = Zn, Cd, Cu, Fe, Co, Ni, Mn) efficiently within 30 min. For M = Zn, Cd and Cu these complexes readily undergo reversible formal dehydration to the extended network structures [M(INA)(2)] (M = Zn, Cu) or [Cd(INA)(2)(OH2)]center dot DMF by further LAG with non-aqueous liquids such as methanol or DMF. Overall, the mechanochemical dehydrations are more effective than heating or immersion in bulk solvents. The work demonstrates a two-step mechanochemical synthesis of coordination networks via discrete aquo complexes which may be preferable to single step reactions or grinding-annealing procedures in some cases. For example, the two step method was the only way to prepare [Cd(INA)(2)(OH2)]center dot DMF mechanochemically and the porous network Cu(INA)(2) could not be obtained from the aquo complex by heating.

Geochemical analysis of sediments from a polluted waterway in the vicinity of a metallurgical plant, Minas Gerais, Brazil

Mining and metallurgical industries are the most responsible for heavy metal contamination. These contaminants are often associated to poor management strategies and the lack of suitable containment areas. This is the case of one of the largest metal alloy producers in the São Francisco river basin, in Minas Gerais state, Brazil. During operation, the tailings of this activity have been accumulated in the surrounding area, leading to heavy metal contamination (Mn, Cu, Zn, Ni, Pb, Cd, Cr and As), much above the critical levels, which accumulate in the sediments of the nearby waterways, in the soils of the drainage area, and in the water column. In this work we are going to discuss both the contamination level and its extent in the Consciência river, a small tributary of the São Francisco river, the longest river entirely Brazilian, by analyzing the geochemistry and mineralogy of the accumulated sediments. It will be also discuss the reclamation strategies of this site and the impact on the environment.

Biogeoquímica do manganês, ferro, cobre e cádmio em sedimentos da Ria Formosa

A Ria Formosa é uma laguna costeira de características mesotidais, situada na costa Sul de Portugal, que apresenta pronunciadas variações sazonais de temperatura e radiação luminosa. As extensas zonas intertidais desta laguna são inundadas pela maré duas vezes por dia ficando, por isso, também sujeitas a flutuações semidiurnas de temperatura, pressão e radiação luminosa. Estas condições podem afectar os equilíbrios físico-químicos existentes no sedimento. Foi elaborado um esquema de amostragem de sedimentos em suspensão e de fundo em diversos locais da zona intertidal da Ria Formosa em duas escalas de tempo distintas: (a) uma escala sazonal, com o objectivo de estudar a influência das variações anuais de temperatura e os mecanismos por si desenvolvidos na composição elementar dos sedimentos; (b) ao longo de alguns minutos durante a inundação dos sedimentos pela água da maré, com objectivo de estudar o efeito da maré nos equilíbrios físico-químicos existentes no interior do sedimento. Nos sedimentos recolhidos sazonalmente foi medida a temperatura, o pH e o potencial redox, determinado o conteúdo em matéria orgânica e os teores de Al, Si, Mn, Fe, Cu e Cd na fracção sólida. Na água intersticial foram determinadas as concentrações de Mn(II), Fe, Cu e Cd totais dissolvidos. Nas amostras de água intersticial colhidas durante a inundação dos sedimentos foram determinadas as concentrações de Cl-, Mn(II), Fe(II), Fe(III), Cu e Cd totais dissolvidos. A variação do teor de cloretos na água intersticial indicou que a inundação dos sedimentos intertidais pela maré causa infiltração da água através da superfície do sedimento e movimentos de água intersticial no seu interior. Estes movimentos de fluídos ocorreram preferencialmente nas camadas de maior permeabilidade. As alterações ao equilíbrio dinâmico da água intersticial foram mais intensas nos primeiros 28 minutos de inundação, diminuindo ao longo do tempo. Os processos físicos acima referidos provocaram a exportação de Mn(II), Fe(III), Cu e Cd totais dissolvidos da água intersticial para a coluna de água e simultaneamente induziram a oxidação das espécies reduzidas de manganês e de ferro. O Mn(II) foi oxidado a Mn(IV) na camada superficial dos sedimentos e, também, exportado para a coluna de água. A oxidação do Fe(II) a Fe(III) ocorreu, por sua vez, no interior do sedimento numa curta escala de tempo (<7 min.), saindo para a coluna de água uma pequena porção de Fe(III). Estas alterações, provocadas pela inundação dos sedimentos intertidais, mascararam eventuais variações sazonais das concentrações de Mn e Fe na fracção intersticial dos sedimentos. Os perfis de Cu e Cd totais dissolvidos na água intersticial mostraram a existência de várias zonas de mobilização nos primeiros 4 cm de sedimento. A mobilização de Cu não apresentou uma variação sazonal enquanto que as concentrações de Cd mostraram um incremento no Verão. Neste período, o cálculo de fluxos difusivos indicou uma intensificação dos processos de transferência destes metais através da interface sedimento-água relativamente aos existentes no interior do sedimento. Os fluxos difusivos de Cu foram uma ordem de grandeza inferiores ao transporte advectivo associado à inundação pela maré, enquanto que para o Cd as estimativas dos fluxos difusivos e do transporte advectivo foram comparáveis. Em suma, os resultados obtidos mostraram que a distribuição destes elementos na água intersticial é reflexo do regime de transporte-reacção induzido pela inundação dos sedimentos intertidais, sendo para o Fe mais importantes os processos de reacção, enquanto que para o Mn, Cu e Cd os transportes advectivos são mais rápidos do que as reacções. Com base nestes resultados é proposto um modelo para os ciclos de Mn, Fe, Cu e Cd nas zonas intertidais de lagunas costeiras.

Sample preparation and heavy metal determination by atomic spectrometry /

Microwave digestions of mercury in Standards Reference Material (SRM) coal samples with nitric acid and hydrogen peroxide in quartz vessels were compared with Teflon® vessel digestion by using flow injection cold vapor atomic absorption spectrometry. Teflon® vessels gave poor reproducibiUty and tended to deliver high values, while the digestion results from quartz vessel show good agreement with certificate values and better standard deviations. Trace level elements (Ag, Ba, Cd, Cr, Co, Cu, Fe, Mg, Mn, Mo, Pb, Sn, Ti, V and Zn) in used oil and residual oil samples were determined by inductively coupled plasma-optical emission spectrometry. Different microwave digestion programs were developed for each sample and most of the results are in good agreement with certified values. The disagreement with values for Ag was due to the precipitation of Ag in sample; while Sn, V and Zn values had good recoveries from the spike test, which suggests that these certified values might need to be reconsidered. Gold, silver, copper, cadmium, cobalt, nickel and zinc were determined by continuous hydride generation inductively coupled plasma-optical emission spectrometry. The performance of two sample introduction systems: MSIS™ and gas-liquid separator were compared. Under the respective optimum conditions, MSIS^"^ showed better sensitivity and lower detection limits for Ag, Cd, Cu, Co and similar values for Au, Ni and Zn to those for the gas-liquid separator.

Metal complexes involving pyridoxine and pyridoxamine

Solid complexes of pyridoxine with Mn(II) , Cd(II) and Zn(II) have been isolated, as well as compounds containing Cu(II), Ni(II), Co(III), Cd(II) and Zn(II), and pyridoxamine in various protonated forms. Infrared spectra provide evidence for protonation at the pyridine nitrogen site in the complexes, but not in the neutral vitamins and the complexes of anionic pyridoxamine. Thus the complexed vitamins are in zwitterionic forms, with chelation probably occurring through the phenolate oxygen and either the amino or the hydroxy group at the 4' position.

Ligand design for molecule-based magnetic and/or conducting materials

Work in the area of molecule-based magnetic and/or conducting materials is presented in two projects. The first project describes the use of 4,4’-bipyridine as a scaffold for the preparation of a new family of tetracarboxamide ligands. Four new ligands I-III have been prepared and characterized and the coordination chemistry of these ligands is presented. This project was then extended to exploit 4,4’-bipyridine as a covalent linker between two N3O2 macrocyles. In this respect, three dimeric macrocycles have been prepared IV-VI. Substitution of the labile axial ligands of the Co(II) complex IV by [Fe(CN)6]4- afforded the self-assembly of the 1-D polymeric chain {[Co(N3O2)H2O]2Fe(CN)6}n•3H2O that has been structurally and magnetically characterized. Magnetic studies on the Fe(II) complexes V and VI indicate that they undergo incomplete spin crossover transitions in the solid state. Strategies for the preparation of chiral spin crossover N3O2 macrocycles are discussed and the synthesis of the novel chiral Fe(II) macrocyclic complex VII is reported. Magnetic susceptibility and Mössbauer studies reveal that this complex undergoes a gradual spin crossover in the solid state with no thermal hysteresis. Variable temperature X-ray diffraction studies on single crystals of VII reveal interesting structural changes in the coordination geometry of the macrocycle accompanying its SCO transition. The second project reports the synthesis and characterization of a new family of tetrathiafulvalene derivatives VIII – XII, where a heterocyclic chelating ligand is appended to a TTF donor via an imine linker. The coordination chemistries of these ligands with M(hfac)2.H2O (M( = Co, Ni, Mn, Cu) have been explored and the structural and magnetic properties of these complexes are described.

Investigations on the Distribution Characteristics of Heavy Metals in Squid (Loligo spp.) in Relation to Levels in Food Fishes from the West Coast of India with a Perspective on Seafood Safety

The present study entitled "Investigations on the Distribution Characteristics of Heavy Metals in Squid (Loligo spp.) in Relation to Levels in Food Fishes from the West Coast of India with a Perspective on Seafood Safety"attempts to establish the base line data on metal levels in squids along the west coast of India. The study is of great relevance in the present context when utmost importance is being given for producing wholesome seafoods especially in the export market with a perspective on seafood safety.The thesis presents a comprehensive account of the base line data on important heavy metals, viz., Hg, Cd, Pb, Cu, Zn, Fe, Mn Cr and Ni in the edible and non-edible body components of the most abundant Loligo species, viz., L. duvauceli caught along the west coast of India.

Spectral studies and crystal structures of some transition metal complexes of N4-substituted semicarbazones

The present work is concentrated on the studies of two novel semicarbazones, di-2-pyridyl ketone-N4-phenyl-3-semicarbazone (HL1) and quinoline-2-carboxaldehyde-N4-phenyl-3-semicarbazone (HL2). The compositions of these semicarbazones were determined by the CHN analyses. For the characterization of these compounds we have used IR, UV and NMR spectral studies. The molecular structure of quinoline-2-carboxaldehyde-N4-phenyl-3- semicarbazone (HL2) was obtained by single crystal X-ray diffraction studies. Also, we have synthesized Zn(II), Cd(II), Cu(II), Ni(II), Co(II) and Mn(II) complexes of these semicarbazones, HL1 and HL2. These complexes were characterized by various spectroscopic techniques, magnetic and conductivity studies. We could isolate single crystals of some Zn(II) and Cd(II) compounds suitable for X-ray diffraction studies. For other complexes we could not isolate single crystals of good quality for single crystal X-ray diffraction studies.

Una sonrisa bonita

Se presenta experiencia educativa que propone fomentar la prevenci??n para garantizar la salud bucodental entre el alumnado. Se realiza en el CPR Taxara en Venta Nueva, Granada. Los objetivos son: que el alumnado descubra y conozca las estructuras que conforman su boca; reconocer la situaci??n de los dientes en nuestra boca y saber cu??les son sus funciones; comprender la trascendencia que tiene el trato que se le de a la dentici??n definitiva; explicar al ni??o la importancia que para sus dientes tiene la dieta y que un consumo exagerado de dulces llevar?? a la aparici??n de caries; conocer algunas posibles enfermedades de nuestros dientes y enc??as; convertir la higiene oral diaria en una rutina de su higiene general, implicando a sus familias; valorar la revisi??n m??dica para prevenir posibles enfermedades de la boca.

El ni??o obeso

Analizar la obesidad infantil, y sus repercusiones en la personalidad del ni??o y en el marco escolar. La primera muestra se realiza sobre 7947 ni??os procedentes de 9 colegios valencianos, en edades comprendidas entre los 6 y 14 a??os. La segunda muestra se compone de 30 ni??os obesos y 30 no obesos para analizar el esquema corporal. La tercera muestra a 30 ni??os obesos y 30 no obesos, con edades comprendidas entre los 9 y 13 a??os para determinar la agresividad reprimida. Se hallan en la primera muestra los porcentajes totales de obesidad infantil, teniendo en cuenta el nivel socioecon??mico y cultural. En la segunda muestra se realiza un an??lisis psicol??gico del cuerpo, y en la tercera se mide la agresividad y la frustraci??n. Escala de Alexandre, completada con las matrices progresivas de Raven para la inteligencia, en los casos individuales; el test de Daurat-Hmeljak para el esquema corporal; el test de Rosezweig-Garc??a Yag??e para medir la frustraci??n-agresividad. An??lisis estad??stico: porcentajes. An??lisis comparativo de los porcentajes totales de la obesidad infantil con los de otros pa??ses. Prueba U de Mann-Whitney entre ambos grupos raz??n cr??tica, desviaci??n t??pica, varianza, niveles de significaci??n. Puede generalizarse, por la amplitud de la muestra, que el 4,65 por ciento de la poblaci??n escolar valenciana es obesa, porcentaje similar con los de otros pa??ses. El ni??o obeso puede padecer importantes trastornos de la corporeidad, encontr??ndose diferencias significativas en los niveles de colocaci??n y elecci??n. Esto es importante ya que el esquema corporal es la clave de toda la organizaci??n de la personalidad. Se confirma que el ni??o obeso tiene una agresividad reprimida, siendo la pasividad una consecuencia l??gica. Se hace necesaria la recuperaci??n del ni??o obeso mediante un tratamiento motor, diet??tico y psicopedag??gico, completado con una educaci??n psicomotriz. Este tratamiento tambi??n debe incidir en la familia. La escuela puede ayudar a la recuperaci??n mediante la educaci??n alimentaria, clases de gimnasia, asistencia al ni??o y formaci??n a los padres.

Los rincones de juego al aire libre

Se proponen los rincones de juego al aire libre como una actividad m??s de la escuela, en la que se ofrece al ni??o alternativas de juego fuera del aula, en este caso en el patio. Con este tipo de actividades el alumno parece encontrar mayor motivaci??n en sus tareas y en su comportamiento, al verse fuera de la 'mirada vigilante' de los adultos. De esta forma se respeta el ritmo de cada alumno y se facilita el desarrollo de su intimidad, socializaci??n y el experimentar con el medio a trav??s de los materiales que les ofrecen; estos rincones de juego son: zonas de movimiento, rinc??n de intimidad, huerto, y zona de agua y arena..

Instrucci??n y progreso escolar en ni??os con par??lisis cerebral, de Preescolar y ciclo inicial : un estudio de seguimiento

Estudiar el desarrollo y el aprendizaje de los ni??os paral??ticos cerebrales de las primeras etapas educativas y especialmente, la utilidad que para ellos pueda tener el uso del ordenador. 14 ni??os paral??ticos cerebrales, sus familias y 14 profesores. La investigaci??n tiene un car??cter descriptivo y exploratorio, pues pretende recoger el modo en el que se trabaja en el aula. Se divide en dos cap??tulos: introductorio, que expone la historia del proyecto, presenta las concepciones te??ricas y describe la metodolog??a adoptada y el dise??o utilizado; y resultados, que se estructura de acuerdo con un eje temporal. Se inicia con el desarrollo de algunos instrumentos de medida, contin??a con una descripci??n del estado inicial de las 3 instancias (alumnos, profesores y padres), as?? como con los cambios contemplados. A continuaci??n, se describen las interacciones que se producen en el aula alrededor de los procesos de instrucci??n, tanto con ordenador como sin ??l, para finalmente poner en relaci??n los cambios observados entre las diversas evaluaciones de los sujetos con los procesos de interacci??n estudiados y con los tipos de afectaci??n que sufren. Instrumentos de evaluaci??n, pruebas cl??sicas de aptitudes y conocimientos, escalas de apreciaci??n de conducta. Tablas. Las pruebas pedag??gicas graduadas y el c??digo de observaci??n cumplen sus papeles. El profesorado en ninguna de las variables tomadas en consideraci??n sufre modificaciones. Los padres constatan variaciones significativas en aspectos actitudinales: la par??lisis cerebral y los ordenadores. Los ni??os avanzan en los aspectos psicopedag??gicos y en las medidas cl??sicas de inteligencia, a pesar de que su desarrollo motriz no mejora. El tipo y cantidad de ayuda que el profesor ofrece, as?? como los mensajes motivacionales y sistemas de incentivos, no tienen en cuenta el nivel de dificultad que la tarea le supone al ni??o. El rendimiento en las tareas realizadas por ordenador es el mismo que en las tareas realizadas sin ??l. En los primeros a??os del curr??culum juegan un papel importante las actividades de rehabilitaci??n. Los resultados parciales se estructuran en 13 estudios independientes agrupados en 5 bloques diferentes organizados segun un criterio temporal y explicativo. Ofrecen implicaciones educativas.