Neide Aparecida Mariano

Effect of Cooling Rate on the Corrosion Behavior of As-Cast SAF 2205 Duplex Stainless Steel After Solution Annealing Treatment

The formation of intermetallic phases alters the properties of duplex stainless steel and is therefore a crucial factor in its performance. For example, the formation of sigma phase in duplex steel increases its brittleness and decreases its corrosion resistance because this phase consumes chromium and molybdenum in solid solution, thus leading to the depletion of these elements in the matrix. This study investigated the corrosion resistance of as-cast SAF 2205 duplex stainless steel after solution annealing treatment at 1100 °C for 240 minutes, under varying cooling rates. The objective was to evaluate the correlation between cooling condition, microstructural changes and corrosion resistance based on cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation (DL-EPR) measurements. The results revealed a significant reduction in the corrosion resistance of a slowly cooled sample, which presented an increase in the degree of Cr (Qr / Qa) depletion resulting from the formation of sigma phase.

Study of Cooling Rate Influence on SAF 2205 Duplex Stainless Steel Solution Annealed

In this work was investigated the microstructural evolution process of the duplex stainless steel SAF 2205 as-cast after solution annealing treatment. The aim was to detect the effects on the material microstructure by the cooling rate variation. The studied material were submitted to solution anneal at 1100 °C for 240 min, followed by cooling in water, air and furnace. The results evaluation was based on micrographic analysis, energy dispersive spectrometry measurements (EDS), X-ray diffraction and hardness tests. The ferrite volume fraction obtained in the microstructure increased with the cooling rate, because it causes diffusion inhibition of the steel constituent elements, promoting retention of the ferrite. The volume fraction of austenite phase increased with a lower cooling rate. The cooling rate is an important factor in defining the steel microstructure, particularly about intermetallic phases precipitation, which occurred by the slow cooling rate. Additionally, it was observed the precipitation of sigma phase.

Processing of Pet-Silver Nanocomposite Filaments

Nanoparticles play a fundamental role on nanocomposite properties, as they significantly increase the contact area and allow a homogeneous distribution in comparison to microparticles. Silver nanoparticles (AgNP) have been extensively used in biomedical and engineering applications due to their interesting properties, such as antibacterial activity. Polyethylene terephthalate (PET) is a semi-crystalline polymer and has excellent chemical resistance and thermal stability. Because of its remarkable properties, PET has been used in several industrial applications, such as packaging, electrical, automotive, construction and textile. The aim of this study was to prepare potential antimicrobial PET-AgNP nanocomposite filaments for textile applications. Therefore, AgNP were incorporated in the PET matrix at different concentrations (0.05; 0.10; 0.15; 0.20; 0.25; 0.30; 0.35 and 0.40%) by extruding the PET resin with specific amounts of a 10% (w/w) AgNP/PET master batch. Then, rheological characterization was carried out and filaments were produced for mechanical, optical and thermal analyses. The incorporation of up to 0.20% (w/w) of AgNP in the polymeric matrix has not significantly altered overall properties of PET nanocomposites. Moreover, the nanocomposite incorporated with 0.05% of AgNP demonstrated suitable intrinsic viscosity for fiber processing and PET-like mechanical, thermal and optical properties.

A Comparative Study of Biomimetic Coatings on Titanium and Stainless Steel

Titanium and stainless steel are examples of biomaterials widely used in dental and orthopedic implants owing to their properties of good corrosion resistance and excellent biocompatibility. This paper reports on a study of the biomimetic method applied to titanium (cp-Ti) and 316L stainless steel. The method consists in immersing the metal substrate in a synthetic solution of SBF (simulated body fluid) whose composition, pH and temperature resemble those of human blood plasma. The coating on the two metals was effective for obtaining hydroxyapatite, which was confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR).

Contaminants Recovery from Acid Mine Drainage

In some mines where sulfide minerals can occur in form of pyrite acid mine drainage (AMD) may occur, and it constitutes one of the main environmental impact. In order to prevent that AMD compromises aquifers layers and reaches mine surroundings, a treatment that consists in its neutralization with the use of a hydrated lime suspension is usually conducted. Contaminants that are soluble in AMD are precipitated, remaining in the solid phase. The work here presented aims recover uranium and rare earths found in one of these precipitates, which consists of calcium diuranate and metal hydroxides in a calcium sulfate matrix. This material contains approximately 0.25% of triuranium octoxide (U3O8) and 2.5% of rare earth oxides (TR2O3). The recovery of uranium and rare earths contained in the precipitate was performed through a hydrometallurgical process. The test resulted in a leaching with sulfuric acid presented solubilization of 96% for uranium and 90% for rare earths. A percentage yield of 99.7% and 99.9% was obtained in the steps of uranium extraction and re-extraction from the leachate, respectively.

Investigation of Microstructural Changes after Solution Annealing Treatment in a Duplex Stainless Steel

This work investigates the microstructural changes developed during the solution annealing treatment under different conditions for the steel UNS S31803. The studied material was submitted to solution anneal at 1100°C for 30, 120 and 240 min, followed by cooling in water, air and furnace. The results evaluation was based on micrographic analysis and the results showed the influence of treatment period and cooling rates in distribution and morphology of austenitic phase. It was observed the same morphology of austenitic phase in all treatment conditions, however, the volume fraction of this phase increased with the treatment period increase, and further refinement with lower cooling rates. It was found that the solution treatment by longer period with the lower cooling rate significantly enhanced the intermetallic phases transformation. The intermetallic phases precipitation could be detected when the samples were solution-treated for 120 and 240 min and cooled at furnace.

Study of the Tempering Effect in Phase Transformations of 13Cr1Ni0.15C and 13Cr2Ni0.1C Steels

The martensitic stainless steels are applied in specific conditions due to theirs corrosion and mechanical resistance. The study of these steels after heat treatment is relevant because it may involve the production and development of new steels with better properties for several applications. This study investigates the effect of heat treatment of quenching and tempering in two martensitic steels - 13Cr2Ni0.1C and 13Cr1Ni0.15C (% weight). Dilatometric tests were performed in the samples after melting process in order to obtain the initial and final temperatures of formation of austenite and martensite. The results showed that the quenched samples have the highest hardness and a martensitic microstructure with delta ferrite presence. On the other hand, the samples after tempering showed different matrix suggesting that the martensite decomposition with no change of the delta ferrite.

Estudo de caracterização de argilas não plásticas da região de Poços de Caldas, MG

Pocos de Caldas e um importante centro hidrotermomineral do Brasil, o qual apresenta depositos de argilas nao plasticas para as quais nao ha registros significativos a respeito da caracterizacao direcionada destes materiais, o que prejudica estudos de aplicacao industrial. Estas argilas nao plasticas, nao aproveitadas, vem sendo armazenadas em galpoes ou a ceu aberto, o que gera um elevado custo para a industria, alem de transformar-se em um passivo ambiental. No presente trabalho realizou-se o estudo quimico-mineralogico de seis amostras de argilas de baixa plasticidade, alem da caracterizacao preliminar destas amostras quanto a granulometria, plasticidade e propriedades cerâmicas basicas, visando ampliar os horizontes das investigacoes destes materiais. Este estudo preliminar mostrou que, de maneira geral, as amostras sao compostas por minerais refratarios como caulinita e gibbsita, apresentando teores menos significativos de outras fases, como quartzo, vermiculita e illita. Juntamente as analises quimicas, estes dados permitiram o agrupamento das materias-primas em dois grupos em funcao de sua refratariedade, norteando assim, a caracterizacao posterior. Dentre as amostras, ha material com potencial uso na formulacao de massas de porcelanato, alem de uma amostra turfosa, cuja aplicacao esta relacionada a correcao de solos.

Gelatinization Technique Applied to the Processing of Porous Clay Bodies

Conventional processes for manufacturing porous ceramic sometimes provide bodies with low mechanical strength in addition to the high complexity or cost. This work proposes a new porous ceramic processing route: gelatinization, using as raw material clay with low plasticity, water and gelatin. The characterization of the clay was carried out and specimens of various compositions were produced by varying clay content (40, 50, 55 and 60% of solids) and keeping the water and gelatin content constant in the formulation. After cold forming the samples were fired under various conditions: initial temperature of 300 or 600 °C; maximum firing temperature of 800, 900, 1000, 1100 or 1350 °C. After firing, it was obtained the values of the water absorption, bulk density, apparent porosity, linear shrinkage and mechanical resistance. The best results were for samples fired in temperatures lower than 1100 °C and 50% and 55 % of solid content.

Study on the Influence of Water-Reducing Additives in Concretes for Civil Construction

Water-reducing additives for concretes are high efficiency dispersants that promote reduction of viscosity in suspensions, minimizing the amount of water used to hydrate the cement, thus enabling the fabrication of concrete with excellent properties. However, different forms of interaction between cement and additives are observed. In this work the properties of concrete formulated with three dosages of a polycarboxylate-based water-reducing additive and cement type CPII E-32 from two distinct manufacturers were investigated. In the experimental part, we verified the importance to use this technology justified by excellent results obtained for mechanical resistance and plasticity properties of the concretes. Through statistical analysis it was possible to point a discrete superiority in compositions using Holcim cement in function of its physical and chemical characteristics, in which the interaction process showed to be more efficient.