José Adilson de Castro

Study of the Interaction of Copper Nanoparticles with Titanium in Landfill Soils Layers

The nanotechnology has spread out for every field of the sciences and engineering with applications covering the variety of human and life activities. The TiO2 nanoparticles are of special interest due to the wide range of applications from cosmetics to paint and new applications have continuously been searched. However, the effect of these particles into the environment need detailed investigation since some deleterious effects on the ecosystems have been observed. Among the nanoparticles found in natural soils the copper plays important role due to their strong interactions with the other materials. In this paper, the influence of nanoparticles of copper (NPCu) in the behavior of NPTiO2 were investigated. A normalized experimental procedure on the soil column was carried out with soil impregnated by copper nanoparticles and compared with the natural soil. Stable solutions of water and NPTiO2 were prepared and used to carried out the column percolation experiments with the concentrations of NPTiO2 measured at the inlet and outlet of the solutions. The results indicated that the TiO2 nanoparticles can mediate transport of Cu in some soil environments. Suggested that decreases in Cu transport were mainly due to increased desorption.

Modelagem e simulação computacional da injeção de carvão pulverizado no canal adutor da “raceway” de altos-fornos

O alto-forno e um reator de fluxo contra corrente e tem como principal objetivo a producao de gusa. A injecao de materiais particulados e feita via ventaneiras objetivando diminuir a quantidade de coque carregado via topo do alto-forno. Esta tecnica abriu as opcoes de utilizacao de materias-primas de menor valor agregado que o coque, insumo que no Brasil e produzido com misturas de carvoes importados. Este trabalho propoe a simulacao da injecao de carvao pulverizado utilizando um modelo matematico 3D, multifasico. Como fases consideramse uma fase gasosa e duas fases solidas correspondendo a dois tipos de carvoes pulverizados, com alto e baixo teor de volateis respectivamente. Desta forma, as fases solidas, quando consideradas simultaneamente na injecao, sao representadas por diferentes campos de velocidade e temperatura, alem de sua propria composicao quimica. As taxas de cinetica quimica das reacoes foram consideradas atraves de modelos classicos da literatura e eventualmente tiveram suas constantes ajustadas para melhor representarem os carvoes individualmente no processo industrial. A solucao numerica foi obtida atraves de um codigo desenvolvido em Fortran 90/95, com base no metodo de volumes finitos utilizado na discretizacao do sistema de equacoes diferenciais nao lineares. A malha utilizada e nao ortogonal para melhor representar a geometria do equipamento experimental descrito na literatura e utilizado para validar o modelo e, posteriormente, a geometria das ventaneiras com diferentes pontos de injecao. Os resultados obtidos de temperatura e composicao do gas apresentam uma boa concordância com os resultados experimentais. O modelo tambem se mostra eficiente para a previsao do efeito de diferentes tipos de carvao injetados via ventaneiras. Palavras-chave: Alto-forno, reducao, ventaneiras, injecao de carvao, modelagem matematica, simulacao computacional.

Numerical and experimental study of the microstructural evolution and the properties of joints welded on rebars using the GMAW process

Abstract This paper is a study of CA-50 rebars from SAE steel grade 1026. This study was carried out in order to improve the control of the mechanical properties of welded joints. Knowing certain variables are very important when it comes to finding the ideal welding parameters and the respective microstructural results, and consequently for the mechanical properties of welded joints. In order to carry out this study, a study of the material as received was carried out in order to establish a solid basis for comparison. The material was welded using argon as the shielding gas with 20% carbon dioxide. The wire used was copper-covered ER70S-6, and the welded joints were lap joints. The temperature was monitored using thermocouples for two different heat inputs. A numerical computer code was developed to simulate the phenomena that occur during the process (temperature gradient, phase transformations and heat transfer). The welded joints did not introduce martensite as a brittle phase, the weld metal had a dendritic structure, the heat-affected zone (HAZ) had two different zones with different grain sizes. All of this was due to the temperature gradient, which also led to different characteristics in the weld bead, HAZ, phases formed and different grain sizes.

Kinetic Study on Martensite Formation in Steels 1045 and 4340 under Variable Cooling Rates

The experiments were carried with two steels with different chemical compositions, aiming at understanding and comparison with the available literature. The microstructures of steels 1045 and 4340 were characterized and quantified using scanning electron microscopy (SEM) and optic microscopy (OM) with quantitative methods. Based on the experimental results, the amount of martensite, the hardness and the microhardness were determined, as a function of the distance from the quenching end, under different cooling conditions. For predicting the evolution of martensitic fraction along the sample, Koistinen-Marburger’s (K-M) model was adopted. It was found that the parameters recommended in the literature for the traditional K-M model do not represent accurately the results obtained for the steel samples under investigation. According to indications found in recent literature, parameter corrections were proposed, leading to a modified K-M model which better represents the transformations observed in the different examined steels.

Simulação transiente de um reator de leito fluidizado em 3D

Fluidized bed reactors reached became popular in the 80-90s. Since then, this equipment has become important for thermo electrical generation, because it permits fuel options for a high degree of conversion but with lower costs than those used in industrial processes. This technique does not play am important role in Brazil yet, where the use of optional electric generation technologies are now being considered. Thermal generation is one option in which that fluidized bed reactors can be used to burn materials like coal and biomasses. The mathematical models have been efficient in investigating the virtual conditions of the processes. In this work, a mathematical model aiming to simulate the fluidized bed reactor is proposed. The model uses the concept of a multiphase-multicomponent system to simulate the transient inner flowing conditions in 3D. The transport equations of mass, momentum and energy are solved by the finite volumes method. The phases are modeled using continuum mechanics principles, where a collection of identical particles is considered. The simulation results of the fluidized bed reactor showed good agreement with the experimental data.

Replacement of NdFeB by Ferrite Magnets

The replacement of NdFeB magnets by ferrite magnets is discussed. For motors, remanence is relevant, implying in a volume three times that of NdFeB, when the relevant index of merit is remanence. However, if the relevant issue is the BHmax (maximum energy product), the volume for replacement should be ten times larger. The high resistivity of ferrites is a big advantage for motors. The temperature of operation is also relevant, because NdFeB magnets loss coercivity even with small increase of temperature. Different applications are discussed, as for instance, motors for electric cars and wind turbines. The choice of the proper volume depends on the evaluation of demagnetizing field in the condition of operation.

Hysteresis Modeling of Bonded Anisotropic Ferrite Magnets

The modeling of hysteresis curves of bonded ferrite magnets is discussed. Hysteresis of anisotropic magnets were calculated according to the Stoner-Wohlfarth Model, for the cosn (theta) distribution. The crystallographic texture has significant effect on the hysteresis curve. Two different samples were examined, one isotropic and another anisotropic. The anisotropy field of strontium ferrite magnets was determined to be 19.5 kOe. The Mr/Ms ratio of the anisotropic bonded magnet was estimated as 0.8.

Ellipsometric Characterization of AZ31 Magnesium Alloy

Ellipsometry is a non-destructive and indirect technique able to characterize both optical and dielectric properties of thin films and bulks, besides determining the thickness of thin films. This characterization is performed by evaluating the change in the polarization state of the incident light when it interacts with the material of interest. In this work, the ellipsometry technique was used to characterize optical properties of AZ31 magnesium alloy samples. This alloy has several interesting properties such as low density, high thermal conductivity, good machinability, among others, which makes it suitable for use in automotive and aerospace components. However, when this alloy is exposed to ambient atmosphere, it undergoes natural oxidation, developing a surface film of oxides and/or hydroxides. This study aimed to establish an efficient methodology for accessing the optical and dielectric characteristics of the substrate (AZ31 alloy) as well as those for the surface film of oxide/hydroxides, and to obtain the thickness of this film. Four samples mechanically grinded and polished were investigated: One sample, namely P sample, was subjected to the ellipsometric measurements immediately after grinding and polishing and three samples, namely A10, A50 and A60, were exposed to the air at 150°C during 10, 50 e 60 minutes, respectively. From the results of the ellipsometric measurements for P sample, it was possible to determine the refractive index (n) and extinction coefficient (k) curves as a function of the wavelength (λ) for the substrate (AZ31 alloy). Besides, through appropriate modeling, it was possible to determine the thicknesses of the oxides/hydroxides films presented in A10, A50 and A60 samples. The thicknesses values obtained seem to be quite coherent when we analyze the surface roughness of these samples using the confocal microscope, validating the optical model constructed to represent the A10, A50 and A60 samples. The results achieved in this study can contribute to the study of both of oxides/hydroxides layers growth and protective coating films growth for AZ31 magnesium alloy.

Effects of the silica nanoparticles (NPSiO2) on the stabilization and transport of hazardous nanoparticle suspensions into landfill soil columns

This study evaluates the stability and transport behaviors of hazardous nanoparticles into soil landfills using experimental procedures to simulate the effects of natural silica nanoparticle suspensions during their percolation into the soil layers of municipal waste landfills. For this, we prepared stabilized suspensions of nanoparticle oxides containing silicon (NPSiO2), titanium (NPTiO2), copper (NPCuO) and zinc (NPZnO), which are recognized as hazardous to the environment, and we conducted leaching experiments within the soil column by simulating landfills layers and simulating the capture and attenuation of nanomaterials into municipal waste landfills. The results demonstrated that the presence of NPSiO2 in suspensions increases the stable concentrations of copper, zinc and titanium oxides and strongly decreases soil layer effectiveness. In contrast, NPZnO improves effectiveness due to its ability to promote agglomeration and setting conditions, allowing further complexation.

Study of the Effects of SiO2 Nanoparticles Concentration on the TiO2 Nanoparticles Suspensions Stabilization

TiO2 nanoparticles (NPTiO2) suspensions are in several ecosystems and residue treatment processes or disposal systems due to their large industrial use and handling. The interactions of the NPTiO2 with NPSiO2 have special interest due to their strong ability to maintain high TiO2 nanoparticles concentration in suspension and promote nanoparticles clustering. These characteristics are used either in cleaning systems or in production of nanoparticles solution for several applications in the food industry or medicine. In this study, suspensions of NPTiO2 and NPSiO2 are synthetized and their stabilizations are discussed. A base TiO2 nanoparticles suspension was synthetized and the initial concentrations of SiO2 nanoparticles (NPSiO2) were changed in order to determine the effects of presence of SiO2 nanoparticles on the stabilization and clustering size. Zeta potential and concentrations measurements were carried out throughout the time and correlated with the initial concentrations of the base suspensions. In this study, the concentrations, zeta potential and pH are measured to estimate the stability of the suspensions. The clustering size, obtained by nanoparticle tracking analysis (NTA), are also monitored and discussed. Results of column soil experiments are discussed and compared under similar conditions with literature data.