Navegando por Autor "Cava, Sérgio"
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Artigo Foundry sand recycling in the troughs of blast furnaces: a technical note(Elsevier, 2005-01-10) Andrade, Ricardo Magnani; Cava, Sérgio; Silva, Sidiney Nascimento; Soledade, Luiz Edmundo Bastos; Rossi, Cláudia C.; Leite, Edson Roberto; Paskocimas, Carlos Alberto; Varela, José A.; Silva, Elson Longo daThe foundry sand agglomerated with alkaline phenolic resin, used for the manufacture of molds, was found to be a residue which is able to be recycled, minimizing the costs of disposal and the environmental impact. This paper analyzes the thermomechanical regeneration and leaching processes and also assesses the influence of additives on the improvement of the mechanical properties of the sands. Besides, the industrial experiments carried out at CSN aiming at the foundry sand recycling in the covering of the blast furnace troughs are presentedThe foundry sand agglomerated with alkaline phenolic resin, used for the manufacture of molds, was found to be a residue which is able to be recycled, minimizing the costs of disposal and the environmental impact. This paper analyzes the thermomechanical regeneration and leaching processes and also assesses the influence of additives on the improvement of the mechanical properties of the sands. Besides, the industrial experiments carried out at CSN aiming at the foundry sand recycling in the covering of the blast furnace troughs are presentedArtigo Síntese e caracterização do sistema ZrO2-SiO2 com adição de cobalto para uso como pigmentos cerâmicos(ABCERAM, 2005-07) Cava, Sérgio; Tebcherani, Sérgio Mazurek; Pianaro, Sidnei Antônio; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Pós de ZrSiO4 dopado com cobalto foram sintetizados por meio do método dos precursores poliméricos para obtenção de pigmentos cerâmicos. O efeito de diferentes concentrações de Co2+ na transição de fase t-ZrO2 para ZrSiO4 foi estudado por meio de difração de raios X e análise térmica diferencial. Resultados de espectroscopia na região do UV-visível permitiram comparar o deslocamento de bandas em função da transição de fase. Além disso, foi realizado um estudo de estabilidade térmica e intensidade da alteração de cor do azul ao vermelho dos pós sintetizados em função da presença de cobalto e temperatura de calcinação, sendo estes parâmetros comparados com a transição de fase. Os resultados obtidos permitem identificar a transição de fase t-ZrO2 para ZrSiO4Artigo Structural and spectroscopic analysis of y-Al2O3 to α-Al2O3-CoAl2O4 phase transition(Elsevier, 2005-07-25) Cava, Sérgio; Tebcherania, Sérgio Mazurek; Pianaroa, Sidnei Antônio; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Co-doped alumina powders were synthesized by means of the polymeric precursor method to obtain ceramic pigments. The effect of different contents of Co2+ on phase transition to -Al2O3 and appearing of CoAl2O4 spinel were studied by means of X-ray diffraction. A partial phase diagram of the system CoAl2O3 was proposed from these data by means of determination of the percentages of these phases according to the calcining temperature. Critical particle size to phase transition was determined by means of calculations of crystallite size and determination of superficial area through the BET method. UV–vis spectroscopy of the samples allow to compare the band shift with the phase transition. Besides, a study of thermal stability and intensity of the blue coloration of the synthesized powders with the presence of cobalt in relation to the calcining temperature was accomplished and compared to the phase transition. The results show that the higher blue color intensity was obtained for the powders with Co-doped -Al2O3 closest of phase transition to -Al2O3 + CoAl2O4Artigo Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method(Springer, 2007-03-21) Cava, Sérgio; Benincá, Renata; Tebcherani, Sérgio Mazurek; Souza, Iedo A.; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Al2O3 and Al2−xCrxO3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL∗a∗b∗ color data). The obtained results allow to identify the γ -Al2O3 to α-Al2O3 phase transition. The single-phase α-Al2O3 powder was obtained after heat treatment at 1050 ◦C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al2−xCrxO3 are related to the γ to α-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium contentArtigo Structural characterization of phase transition of Al2O3 nanopowders obtained by polymeric precursor method(Elsevier, 2007-06-15) Cava, Sérgio; Tebcherani, Sérgio Mazurek; Souza, Iedo A.; Pianaro, Sidnei Antônio; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Nanocrystalline Al2O3powders have been synthesized by the polymeric precursor method. A study of the evolution of crystalline phases of obtained powders was accomplished through X-ray diffraction, micro-Raman spectroscopy and refinement of the structures through the Rietveld method. The results obtained allow the identification of three steps on the -Al2O3 to -Al2O3 phase transition. The single-phase -Al2O3 powder was obtained after heat-treatment at 1050 ◦ C for 2 h. A study of the morphology of the particles was accomplished through measures of crystallite size, specific surface area and transmission electronic microscopy. The particle size is closely related to -Al2O3 to -Al2O3 phase transition