Thermal evaporation furnace with improved configuration for growing nanostructured inorganic materials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)A tubular furnace specifically designed for growing nanostructured materials is presented in this work. The configuration allows an accurate control of evaporation temperature, substrate temperature, total pressure, oxygen partial pressure, volumetric flow and source-substrate distance, with the possibility of performing both downstream and upstream depositions. In order to illustrate the versatility of the equipment, the furnace was used for growing semiconducting oxide nanostructures under different deposition conditions. Highly crystalline indium oxide nanowires with different morphologies were synthesized by evaporating mixtures of indium oxide and graphite powders with different mass ratios at temperatures between 900 degrees C and 1050 degrees C. The nanostructured layers were deposited onto oxidized silicon substrates with patterned gold catalyst in the temperature range from 600 degrees C to 900 degrees C. Gas sensors based on these nanowires exhibited enhanced sensitivity towards oxygen, with good response and recovery times. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597577]826Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [DD05/59270-0

Now you see me, now you don't : a case study of the effect of the sampling method on the perceived struture of Ichthyological communities

Fauna and Flora of the Atlantic Islands : Proceedings of the 3rd Symposium, Ponta Delgada, 21-25-September 1998.The fish community of a small rocky area near Ponta Delgada, Azores, was assessed using two methods: visual census and rotenone collections. The results obtained with each method are analysed and compared. A total of 46 species was recorded for this site. The visual census recorded more species than did the rotenone collections, but each method detected species that escaped the other. The total fish diversity was found to be similar to that reported in other localized studies of littoral rocky areas of the eastern Atlantic and the Mediterranean. Each method used revealed a different spatial structure and different trophic relationships of the ichthyological community. The visual census put in evidence the pelagic/demersal component, while the rotenone collections emphasized the benthic one. Both methods agree on the importance of the benthic primary production in the trophic food web. Visual census data further suggest that the relevance of the direct consumption of algal material by omnivores and herbivores is greater than could be guessed by the species diversity in this group. Strategies are discussed for combining visual and destructive sampling methods in order to achieve a more accurate representation of a given fish community

In situ growth of Ag nanoparticles on alpha-Ag2WO4 under electron irradiation: probing the physical principles

Exploiting the plasmonic behavior of Ag nanoparticles grown on α-Ag2WO4 is a widely employed strategy to produce efficient photocatalysts, ozone sensors, and bactericides. However, a description of the atomic and electronic structure of the semiconductor sites irradiated by electrons is still not available. Such a description is of great importance to understand the mechanisms underlying these physical processes and to improve the design of silver nanoparticles to enhance their activities. Motivated by this, we studied the growth of silver nanoparticles to investigate this novel class of phenomena using both transmission electron microscopy and field emission scanning electron microscopy. A theoretical framework based on density functional theory calculations (DFT), together with experimental analysis and measurements, were developed to examine the changes in the local geometrical and electronic structure of the materials. The physical principles for the formation of Ag nanoparticles on α-Ag2WO4 by electron beam irradiation are described. Quantum mechanical calculations based on DFT show that the (001) of α-Ag2WO4 displays Ag atoms with different coordination numbers. Some of them are able to diffuse out of the surface with a very low energy barrier (less than 0.1 eV), thus, initiating the growth of metallic Ag nanostructures and leaving Ag vacancies in the bulk material. These processes increase the structural disorder of α-Ag2WO4 as well as its electrical resistance as observed in the experimental measurements.The authors are grateful to Generalitat Valenciana (Spain) for PrometeoII/2014/022 and ACOMP/2014/270 projects, Ministerio de Economia y Competitividad (Spain), CTQ2012-36253-C03-02, and to the Spanish Brazilian Program (PHB2009-0065-PC), CAPES (203038 009607/2013- 56 088/2013), INCTMN (2008/57872-1), FAPESP (2013/ 07296-2; 2012/14468-1; 2010/16970-0) and CNPq (147001/2013-7; 573636/2008-7) for financially supporting this research. Most of the calculations were performed using IFGW-UNICAMP computer facilities and the National Center for High Performance Computing in São Paulo (CENAPAD- SP)

Study of k and LiNbO3 addition on the final properties of the relaxor pmn processed by powder blend

[ES] El relaxor cerámico PMN ha sido investigado por un gran número de investigadores en el transcurso del tiempo y muchos aspectos de este material, como la morfología de los polvos, descomposición de fases, pérdida de peso en el proceso de sinterización, densificación, entre otras, siguen siendo objetos de investigación. La preparación de polvos de PMN se ha mostrado más efectiva cuando son sintetizados por la ruta de la columbita, pero la etapa de adición de plomo para la síntesis de polvos de PMN todavía sigue problemática. Por lo tanto, este trabajo propone una nueva asociación de metodologías, utilizando la ruta de la columbita y el método de precipitación por hidróxidos. Mediante la utilización de una técnica de mezcla de polvos, la cual permitió lograr buenas densidades en verde y sinterizadas, fue posible observar que los dopantes K+ y Li+ reducen las pérdidas de peso en el proceso de sinterización y cambian significativamente las propiedades dieléctricas. La adición de semillas de LiNbO3 en la etapa de conformación, las cuales reaccionan de modo distinto dependiendo del tamaño de las partículas, promueve la formación de granos de diferente tamaño en el cuerpo cerámico. Como consecuencia de esto, propiedades dieléctricas muy diferentes que en la cerámica PMN convencional son obtenidas.[EN] PMN ceramic relaxor has been investigated by several researchers and many aspects of this material, like powder morphology, phase decomposition, weight loss during sintering process, densification, between others, still are investigated. PMN powder preparation has been shown more efficient when synthesized by columbite route, however lead addition stage for the PMN powder synthesis remains problematic. Therefore, this work proposes a new association of methodologies, using columbite route and the hydroxide precipitation method. Through use of the powder mixture technique, which permitted to obtain good green and sintered densities, was possible to observe K+ y Li+ dopants reduce weight loss in sintering process and change significantly the dielectric properties. Addition of LiNbO3 seeds in conformation stage, which react in a distinct way as a function of the particle size, promotes the formation of differenced grains in the ceramic bulk. Consequently, very different dielectrics properties from conventional PMN ceramic were obtained.Peer reviewe

The Effect Of Preparation Method And Sb Content On Sno2-cuo Sintering

The sintering behavior of SnO2-CuO system has been investigated for two preparation methods and as a function of antimony concentration. A chemical preparation (Pechini's method) resulted in powders with smaller particle sizes than for a conventional oxide mixture. This led to smaller grain sizes in Pechini's method ceramics. The microstructures were heterogeneous in both systems, showing grain coarsening. The densification was aided by liquid phase formation, due to copper, in both systems, but the temperature of maximum shrinkage rate was larger for the Pechini's method ceramic because copper had to diffuse to the grain surface. Independently of the preparation method, antimony did not aid densification, and increasing its concentration led to a higher densification temperature and lower shrinkage rate. © 2003 Kluwer Academic Publishers.381533253330McAleer, J.F., Moseley, P.T., Morris, J.O., Williams, D.E., (1987) J. Chem. Soc. Faraday Trans., 83, p. 1323Tournier, G., Pijolat, C., Lalauzeand, R., Patissier, B., (1995) Sens. Actuators B, 26-27, p. 24Pianaro, S.A., Bueno, P.R., Longo, E., Varela, J.A., (1998) Ceram. Int., 25, p. 1Castro, M.S., Aldao, C.M., (1998) J. Eur. Ceram. Soc., 18, p. 2233Gouvea, D., Smith, A., Bonnet, J.P., Varela, I.A., (1998) J. Eur. Ceram. Soc., 18, p. 345Varela, J.A., Gouvêa, D., Longo, E., Dolet, N., Onillon, M., Bonnet, J.P., (1992) Solid State Phenom., 25-26, p. 259Cerri, J.A., Leite, E.R., Gouvea, D., Longo, E., Varela, J.A., (1996) J. Amer. Ceram. Soc., 79, p. 799Perazolli, L., Giraldi, T.R., Biscaro, R.S., Varela, J.A., Longo, E., (2000) Sint. Sci. and Techn., p. 117Dolet, N., Heintz, J.M., Rabardel, L., Onillon, M., Bonnet, J.P., (1995) J. Mater. Sci., 30, p. 365Duvigneaud, P.H., Reinhard, D., (1980) Sci. Ceram., 12, p. 287Lalande, J., Ollitrault-Fichet, R., Boch, P., (2000) J. Eur. Ceram. Soc., 20, p. 2415Bonnet, J.P., Dolet, N., Heintz, J.M., (1996) J. Eur. Ceram. Soc., 16, p. 1163Gouvêa, D., Smith, A., Bonnet, J.P., (1996) Eur. J. Solid State Inorg. Chem., 33, p. 1015Cox, P.A., Egdell, R.G., Harding, C., Patterson, W.R., Tavener, P.J., (1982) Surf. Sci., 123, p. 179Egdell, R.G., Flavell, W.R., Tavener, P., (1984) J. Solid State Chem., 51, p. 345Las, W.C., Dolet, N., Dordor, P., Bonnet, J.P., (1993) J. Appl. Phys., 74, p. 6191Szczuko, D., Werner, J., Oswald, S., Behr, G., Wetzig, K., (2001) Appl. Surf. Sci., 179, p. 301Szczuko, D., Werner, J., Behr, G., Oswald, S., Wetzig, K., (2001) Surf. Interface Anal., 31, p. 484Uematsu, K., Mizutani, N., Kato, M., (1987) J. Mater. Sci., 22, p. 915Uematsu, K., Kato, Z., Uchida, N., Saito, K., (1987) J. Amer. Ceram. Soc., 70, pp. 142CZaghete, M.A., Varela, J.A., Cilense, M., Paiva-Santos, C.O., Las, W.C., Longo, E., (1999) Ceram. Inter., 25, p. 239Gouvêa, D., Varela, J.A., Longo, E., Smith, A., Bonnet, J.P., (1993) Eur. J. Solid State Inorg. Chem., 30, p. 915Mazali, I.O., Las, W.C., Cilense, M., (1999) J. Mater. Synth. Process., 7, p. 387Santilli, C.V., Pulcinelli, S.H., (1993) Cerâmica, 39, p. 11Gouvea, D., Varela, J.A., Smith, A., Bonnet, J.P., (1996) Eur. J. Solid State Inorg. Chem., 33, p. 343Sahar, M.R., Hasbullah, M., (1995) J. Mater. Sci., 30, p. 5304Chiang, Y.M., Birnie D.P. III, Kingery, W.D., (1997) Physical Ceramics: Principles for Ceramic Science and Engineering, p. 407. , John Wiley & Sons, New Yor

Austenite decomposition of C-Mn steel containing boron by continuous cooling

The austenite decomposition in C-Mn steel containing boron was studied by continuous cooling from 1100 and 845 degreesC using the Jominy test. The results indicate that the different cooling speeds and the presence of boron refine and change the percentage of ferrite microstructure, martensite, and fine pearlite. (C) 2001 Elsevier B.V. B.V. All rights reserved