Sylma Carvalho Maestrelli

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.

Morphological and mechanical characterization of chitosan-calcium phosphate composites for potential application as bone-graft substitutes

Bone diseases, aging and traumas can cause bone loss and lead to bone defects. Treatment of bone defects is challenging, requiring chirurgical procedures. Bone grafts are widely used for bone replacement, but they are limited and expensive. Due to bone graft limitations, natural, semi-synthetic, synthetic and composite materials have been studied as potential bone-graft substitutes. Desirable characteristics of bone-graft substitutes are high osteoinductive and angiogenic potentials, biological safety, biodegradability, bone-like mechanical properties, and reasonable cost. Herein, we prepared and characterized potential bone-graft substitutes composed of calcium phosphate (CP) - a component of natural bone, and chitosan (CS) - a biocompatible biopolymer. Methods CP-CS composites were synthetized, molded, dried and characterized. The effect of drying temperatures (38 and 60 °C) on the morphology, porosity and chemical composition of the composites was evaluated. As well, the effects of drying temperature and period of drying (3, 24, 48 and 72 hours) on the mechanical properties - compressive strength, modulus of elasticity and relative deformation-of the demolded samples were investigated. Results Scanning electron microscopy and gas adsorption-desorption analyses of the CS-CP composites showed interconnected pores, indicating that the drying temperature played an important role on pores size and distribution. In addition, drying temperature have altered the color (brownish at 60 °C due to Maillard reaction) and the chemical composition of the samples, confirmed by FTIR. Conclusion Particularly, prolonged period of drying have improved mechanical properties of the CS-CP composites dried at 38 °C, which can be designed according to the mechanical needs of the replaceable bone.

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).

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.

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.

Experimental Statistics Applied to Porous Ceramics Processing

Statistical techniques are particularly useful in the engineering, objecting the optimization of fabrication processes. This paper had the purpose of evaluating if the variables such as mechanical resistance, linear shrinkage, apparent porosity, density and water absorption are influenced by the amount of peat added to refractory clay, to ensure the porosity on the production of porous ceramics used as ceramic filters. In order to treat the data it was used the technique of variance analysis, with the regression analysis and the Scott-Knott test. According to the variance analysis, there were some differences between the treatments for all properties analyzed and, by the regression analysis, optimum peat levels were found for all properties analyzed, for some properties these levels were considered inadequate for being superior to the limit stablished.

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.

The use of nepheline as alternative source of alkalis in porcelain tiles: rheological and physical evaluation

The porcelain is a type of ceramic tile which has been contrasted for its good aesthetical, such as decorated surface, and mechanical properties, such as low water absorption and high mechanical and chemical attack resistance. The raw materials used for porcelain tiles production are mainly clay and feldspar. Feldspar is one of the raw materials responsible for the sintering during firing and it helps on the development of low porosity and high wear resistance of the ceramic piece. However, Brazil presents feldspar sources in regions distant from production centers, leading to higher cost for the porcelain tiles production. Thus, nepheline is thought as an alternative to substitute feldspar, totally or partially, since this mineral presents very similar characteristics. In order to verify the influence of this substitution to the properties of the porcelain tiles, it was necessary initially to study the influence of nepheline addition in both rheological and physical properties of the suspension. The results showed that the viscosity of the suspension increases with the addition of nepheline, as well as the apparent density of the fired piece.

Anatase-to-rutile transition in co-doped TiO2 pigments

In this paper, cobalt-doped titanium dioxide green ceramic pigments were synthesized by the polymeric precursor method. In order to investigate the obtainment of a crystalline rutile phase and particles in nanoscale, a chromophore doping was made with fixed concentrations of 1, 2, and 4 mol%, utilizing a calcination temperature of 600oC. The products were investigated by thermal analysis, X-ray diffraction, diffuse reflectance, scanning and transmission electron microscopies. The titanium dioxide:cobalt crystallite size was about 65–100 nm. A broad reflectance band around 540 nm (green region) was observed for all doped samples, indicating the appearance of a deep green pigment. Furthermore, the results have shown that cobalt-doped titanium dioxide promotes greater phase conversion of anatase to rutile. Samples submitted at a temperature of 600 °C, pure titanium dioxide contains 22% rutile, whereas titanium dioxide: 4% of cobalt contains 78% rutile. The mechanism of phase transition in presence of cobalt is attributed to the lower valences of the dopant (II or III) when compared to the titanium valence (IV). Ionic substitution leads to the generation of oxygen vacancies that promote phase transitions at lower temperatures than expected in pure titanium dioxide.Graphical Abstract

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.