Luiz Rogério Pinho de Andrade Lima

Stabilization of electric-arc furnace dust in concrete

Electric-arc furnace dust (EAFD) is a by-product of steel production and recycling. This fine-grained material contains high amounts of zinc and iron as well as significant amounts of potentially toxic elements such as lead, cadmium and chromium. Therefore, the treatment and stabilization of this industrial residue is necessary. Concrete is a well-known suitable environment for stabilization/solidification of materials which have leachable elements in need of fixation. The effect of the EAFD content on the mechanical and chemical performance of Portland cement concrete is investigated in this paper. The effect of the EAFD content on the setting time of cement slurry was also analyzed. The axial compressive strength of the concrete samples increases with the EAFD addition in the range of 10 to 20 wt. (%) EAFD; also the tensile strength increases with the EAFD addition. An increase in EAFD content significantly increases the setting time of the concrete. The acetic acid leaching and water solubilization tests indicate low mobility of the potentially toxic elements from the EAFD concrete composite. The results of the immersion tests show that the addition of EAFD to the concrete seems to reduce chloride penetration, which may help prevent pitting corrosion in reinforced concrete.

Computational modeling of ring textures in mesophase carbon fibers

Carbon fibers are widely used in many industrial applications due the fact of their excellent properties. Carbonaceous mesophases are liquid crystalline precursor materials that can be spun into high performance carbon fibers using the melt spinning process, which is a flow cascade consisting of pressure driven flow-converging die flow-free surface extensional spinline flow that modifies the precursor molecular orientation structure. Carbon fiber property optimization requires a better understanding of the principles that control the structure development during the fiber formation processes and the rheological processing properties. This paper presents the elastic and continuum theory of liquid crystalsand computer simulations of structure formation for pressure-driven flow of carbonaceous liquid crystalline precursors used in the industrial carbon fiber spinning process. The simulations results capture the formation of characteristic fiber macro-textures and provide new knowledge on the role of viscous and elastic effects in the spinning process.

Linear viscoelasticity of textured carbonaceous mesophases

Fibras de carbono de alto desempenho podem ser produzidas a partir de piche de petroleo anisotropico usando o processo de extrusao-fiacao. O piche mesomorfico e um cristal liquido discotico nematico termotropico, que possui ordem na orientacao das moleculas. Cristais liquidos sao materiais que possuem textura, anisotropia e visco-elasticidade. Um fenomeno importante que e encontrado em cristais liquidos e a interacao entre a textura devido a orientacao das moleculas e o comportamento reologico, no qual a textura ocorre devido a presenca de defeitos na orientacao das moleculas. O processo de extrusao-fiacao usado na fabricacao de fibras de carbono a partir de precursores nematicos usa uma cascata de escoamentos que incluem fluxo capilar convergente e extensional, os quais promovem a formacao de uma variedade de estruturas, incluindo radial, concentrica, randomica e bipolar, que darao propriedades especificas para as fibras de carbono resultantes. Portanto, a compreensao fenomenologica da interacao entre a textura e a reologia do precursor nematico e necessaria para o controle do processo e para a otimizacao do produto. Neste artigo, a interacao entre a reologia e a textura de cristais liquidos discoticos nematicos sera enfocada e um modelo anisotropico sera desenvolvido para descrever o regime linear visco-elastico de piches mesofasico com textura. O modelo e capaz de prever todas as caracteristicas observadas experimentalmente, incluindo a dependencia dos modulos de armazenamento e de perda com a frequencia de oscilacao e a sua dependencia com a temperatura, assim como promover uma melhor compreensao do papel dos defeitos e da anisotropia no comportamento visco-elastico do piche anisotropico.

Corrosion resistance and glass forming ability of Fe47Co7Cr15M9Si5B15Y2 (M=Mo, Nb) amorphous alloys

In the present work the effect of substituting Mo with Nb on the glass forming ability and corrosion resistance of Fe-Co-Cr-M-Si-B-Y (M=Mo, Nb) ribbons with high corrosion resistance is investigated. The X-ray powder diffraction pattern indicates that the alloy containing both Nb and Mo presented greater glass forming ability than the alloy containing either of these elements separately. The results obtained indicate that Mo is more effective in enhancing corrosion resistance than the Nb in 4.0 M HCl solution. The alloy containing both Nb and Mo presented greater overall corrosion resistance than the alloy containing only one of these elements.

Micellar Solutions to Recover Diesel in Sand

Abstract In this chapter, the removal of diesel fuel by a washing process using micellar solution is addressed. Micellar solubilization is an important step for removal of organic contaminants from the soil matrix, especially for low aqueous solubility organic contaminants such as diesel. In addition to fundamental studies, laboratory and field studies on removal of diesel from contaminated soil and mathematical models applied are also reviewed to show the applicability of this technology. In particular this chapter presents numerical simulations of laboratory experiments where diesel, initially present at residual saturation in a sand column, was recovered by injecting a micellar solution containing a ionic surfactant and two alcohols. The micellar solution was developed and optimized for diesel recovery using phase diagrams and soil column experiments. Numerical simulations with the compositional simulator UTCHEM are also discussed. The combination of micellar solutions with other remediation techniques such as biodegradation applied to diesel recovery is presented.

Desenvolvimento e avaliação de um porta-amostra de baixo custo para caracterização elétrica de materiais cerâmicos

Conventional sample holder cells used to the electric characterization of ceramics at high temperature consists of an alumina tube and platinum wires and plates using a complex design. The high cost materials used in the conventional sampler holder cell were replaced by stainless steel and conventional ceramics. The sample holder was validated by characterizing yttria-stabilized-zirconia in a temperature range of 25 to 700 oC. The results do not present variations, discontinuity or unusual noise in the electric signals. Several samples were characterized without maintenance, which demonstrates that the sample holder is electric and mechanic adequate to be used to electrical characterization of ceramics up to 700 oC.