Resumo em Inglês:

The amount, distribution, size and chemical composition of non-metallic inclusions have a direct influence on steel properties. By controlling size and chemical composition of these inclusions, it is possible to get a product with good quality. The identification of the nature and the control of inclusion formation are very important for steel cleanness. The behavior of these inclusions is predictable, in some extent, by the determination of the chemical composition of non-metallic phases that form such inclusions. With the objective of studying the chemical composition, the size and the distribution of such inclusions, samples of aluminum and silicon killed low carbon steels were collected in a national steel industry in the secondary refining and continuous casting stages. These samples were analyzed in the scanning electron microscope (SEM) coupled to an energy dispersive analysis system (EDS). From the results, it was possible to evaluate the nature of inclusions and to analyze the effectiveness of the refining process in the reduction of the number and area fraction of the inclusions. It was also possible to verify that the inclusions that remained after treatment, are less damage both to the steel properties as to the continuous casting process (clogging of the submerged valve).

Resumo em Inglês:

The constant heating rate method employed in sintering studies offers several advantages over the isothermal method, particularly the fact that all the parameters that describe the sintering phenomena can be obtained from a single sample. The purpose of this work is to determine the parameters of sintering kinetics of nanosized Ni-Zn ferrite powders synthesized by combustion reaction. The nonisothermal sintering method was studied using a constant heating rate (CHR). The Ni-Zn ferrite powders, with average particle size varying from 18 nm to 29 nm, were uniaxially pressed and sintered in an horizontal dilatometer at a constant heating rate of 5.0 °C/min from 600 °C up to complete densification, which was reached at 1200 °C. The compacts were characterized by scanning electron microscopy (SEM). Experimental results revealed three different sintering stages, which were identified through the Bannister Theory. The shrinkage and the shrinkage rate analyzed showed a viscous contribution in the initial sintering stage, which was attributed to the mechanism of structural nanoparticle rearrangement.

Resumo em Inglês:

A styrene-butadiene-styrene modified asphalt cement was characterized by infrared, differential scanning calorimetry, thermogravimetric analysis and empirical tests such as ring and ball softening point, penetration and elastic recovery. After aging in the rolling thin-film oven, the polymer-modified asphalt presented structural changes relating to oxidation of the material. The infrared spectra showed an increase in hydroxyl groups and the formation of carbonyl compounds and sulphoxides. The percentage of crystallized fraction calculated from differential scanning calorimetry was 0.41%. Thermogravimetric analyses in inert and oxidative atmospheres revealed distinct events during thermal decomposition; the initial activation energies were similar, but changed as the process evolved.

Resumo em Inglês:

Gd5(Ge1-xSi x), x < 4 based alloys are potential candidates for magnetic refrigeration in the range ~20 - ~290 K. However, one of the greatest obstacles for the use of that technology in large scale is the utilization of high pure Gd metal (99.99 wt. (%)) to produce the GdGeSi alloys, since the impurity elements decrease the intensity of the magnetocaloric effect (EMC)¹. In this work, we prove that annealing of the Gd5Ge2Si2 can promote remarkable values for the EMC in comparison to those obtained for the alloy with high pure Gd. Also, the as cast alloy and the annealed alloy are not monophasic, but have at least two crystalline phases in their microstructure. Results for X-ray analysis, optical and electronic microscopy and magnetization measurements are reported.

Resumo em Inglês:

In this work was employed a 2³ factorial experiment design to evaluate the castor oil polyurethane-poly(methyl methacrylate) semi-IPN synthesis. The reaction parameters used as independent variables were NCO/OH molar ratio, polyurethane polymerization time and methyl methacrylate (MMA) content. The semi-IPNs were cured over 28 h using two thermal treatments. The polymers were characterized by infrared and Raman spectroscopy, thermal analysis and swelling profiles in n-hexane. The glass transition temperature (Tg) and the swelling were more affect by the NCO/OH molar ratio variation. The semi-IPNs showed Tg from - 27 to - 6 °C and the swelling range was from 3 to 22%, according to the crosslink density. The IPN mechanical properties were dependent on the cure temperature and MMA content in it. Lower elastic modulus values were observed in IPNs cured at room temperature.

Resumo em Inglês:

The goal of this work was to study the viability of burnt biomass residue from a pulp and paper plant applied as a raw material for mortar used in the construction industry. The waste - bottom ash - was incorporated into the mortar as a mineral addition to the Portland cement. The effect of the waste's grain size on the properties of mortars containing 10% in volume of waste was investigated, as well as the effect of the concentration of waste with grain size under 0.15 mm. The samples were evaluated after 28 days of aging by uniaxial compression, leaching test and scanning electron microscopy. These characterization techniques indicated that the properties of the mortars depend on the concentration, granulation and size distribution of the waste in the mortar's structure. Furthermore, some chemical elements may be present in stabilized and/or encapsulated form in the cement matrix.

Resumo em Inglês:

Knowledge of the porous structure of amorphous materials is of fundamental importance in calculating geometrical parameters such as total porosity, pore size distribution and physical parameters relating to fluid flow inside void space. The present work deals with the measurement of the microstructural parameters of porous ceramic filters. Microtomographic measurements of samples were taken using an X-ray tube. Bremsstrahlung radiation was filtered in transmission mode with a Sn filter at 58.5 and 28.3 keV and the images analyzed in two ways. The first method consisted in analyzing transepts of the images in order to calculate total porosity based on the average particle size and media linear attenuation coefficients. The second method involved a study of the images using an image analysis software, called Imago, which allows one to calculate total porosity and pore size distribution. The total measured porosity of the filter C90 was 73.8%, 71.1%, 74.4% and 71.5% by, respectively, the Arquimedes method, simple gamma ray transmission, transept analysis and analysis of the microtomographic images at 28.3 keV.

Resumo em Inglês:

This paper describes a complementary method for determining dielectric properties of granular materials using the Transmission/Reflection Method in order to estimate their moisture content. The Newton's Complex Interactive Method is used here as a numerical tool to calculate the complex permittivity of the plaster glue material. Results for samples with moisture contents of 35%, 40% and 45% in the range of 100 MHz to 3 GHz are presented.

Resumo em Inglês:

The present work is aimed to simulate the Friction Stir Welding process as a three-dimensional thermally coupled viscoplastic flow. A Finite Element technique is employed, within the context of a general purpose FEM framework, to provide the temperature distributions and the patterns of plastic flow for the material involved in the welded joints. The computational tool presented here may be of great relevance for technologist seeking to set the process control variables, as they are intended to obtain suitable material properties that yield the adequate on service response of the structural components.

Resumo em Inglês:

Purpose: To evaluate the microtensile bond strength (µTBS) to dentin of 4 adhesive systems, the micromorphology of the adhesive/dentin interface and to compare the results to the µTS (cohesive strength) of sound dentin and resin composite. Occlusal surfaces of 24 extracted caries-free human molars were cut flat to expose the dentin surface. They were randomly assigned to 4 groups (n = 6): Adper Scotchbond Multi Purpose Plus (MP), Adper Single Bond (SB), Clearfil Protect Bond (CP) and Adper Prompt (AP). Adhesive systems were applied and "crowns" were built using Z100. Other 5 human molars were sectioned to obtain square-shaped dentin blocks and 5 resin blocks were built using a composite resin, Z100. After storage in distilled water at 37 °C for 24 h, stick-shaped specimens were obtained for all groups (n = 5) with 0.8 mm² and subjected to µTBS or µTS test. Results were analyzed using One-Way ANOVA and Tukey's test at p < 0.05. The remaining bonded teeth were cut in two halves perpendicularly to the bonded interface and prepared for SEM analyses. No significant differences were found among CP (45.6 + 7.4 MPa), SB (43.3 + 6.5 MPa) and MP (35.1 + 5.9 MPa) (p > 0.05). The lowest result was found for AP (27.4 + 4.7 MPa), although not statistically different from MP. Most specimens (89.4%) showed predominant adhesive failure. None of the systems tested reached the µTS values of dentin (108.5 + 9.4 MPa) and Z100 (86.5 + 3.6 MPa). Bonded interfaces showed lower µTBS than those µTS of dentin and resin composite blocks. The all-in-one self-etching adhesive had the lowest µTBS.

Resumo em Inglês:

The aim of this work is to characterize physically and mineralogically six samples of natural and industrialized bentonites from Paraíba, Brazil, and to study its rheological properties to be used as a components of water based drilling fluids. Also it is intended to compare the evolution of the mineralogical composition and rheology of these clays after 40 years of exploitation. The natural bentonite clays were transformed into sodium bentonite by addition of concentrated Na2CO3 solution. The suspensions were prepared with 4.86% w/w to measure their rheological properties (apparent and plastic viscosities and water loss). The results showed that: i) the samples present typical mineralogical compositions of bentonites, but after four decades of exploitation, presents inferior quality and ii) among the clays samples, only one presented satisfactory rheological properties be used as a components of water based drilling fluids.

Resumo em Inglês:

The present work examines microstructure, tensile properties and quality (porosity level) of two thixoformed products, namely an assembly of three cylindrical rods from which tensile samples were machined out, and a cup-shaped part. The material is an A356 aluminium alloy and the microstructural conditioning was carried out by the deformation - recrystallization technique. Additionally, the microstructures of an A356 ingot produced by the magnetic stirring process was also investigated. Results showed that solid fraction and soaking time in the semi-solid state determine the thixoforming forces, that very low porosity levels can be achieved and minimized by the maintenance of high pressures during solidification, and that the material flow during injection in the mould is relatively homogeneous, except for the material conditioned by magnetic stirring. Physical simulation experiments of the thixoforming process (rods) showed a strong correlation between liquid segregation and porosity level. Finally, the tensile properties were shown to be much higher that those of permanent cast samples.

Resumo em Inglês:

The purpose of this study was to evaluate the degree of conversion (DC) of the Z250 composite, using six photo-activation methods, two storage periods and two preparation techniques of the FTIR specimens (n = 3). For the KBr pellet technique, the composite was placed into a metallic mold and photo-activated as follows: continuous light, exponential light, intermittent light, stepped light, PAC and LED. The measurements were made after 24 h and 20 days. For the resin film technique, approximately 0.07 g of the composite was pressed between two polyester strips, photo-activated as above described and analyzed. The DC was calculated by the standard technique and submitted to ANOVA and Tukey's test (alpha = 5%). Independently of the storage period and specimen preparation technique, there were no significant differences among photo-activation methods. No statistical difference was observed between the time periods used. The specimens analyzed under the KBr pellet technique presented higher DC values than those analyzed by the resin film technique.

Resumo em Inglês:

This study aimed to demonstrate the feasibility of obtaining wood-polymer composites (WPC) displaying a performance superior to that of untreated wood from reforested genera. To this end, wood samples of Pine (Pinus caribaea) and Eucalyptus (Eucalyptus grandis), whose density is compatible with this process, were impregnated with the polymeric monomers styrene and methyl methacrylate, using benzoyl peroxide to initiate the polymerization process forming free radicals. The vacuum-pressure method was used to impregnate the samples with monomer-initiator solution. The results indicated a significant improvement of all the properties investigated, including dimensional stability, for the Pine-WPC, while Eucalyptus-WPC, owing to the wood's low permeability, showed only increased values of hardness parallel and perpendicular to grain.

Resumo em Inglês:

Porous silicon layers (PSL) were produced by stain etching from a HF:HNO3 500:1 mixture with etching time varying in the range of 1 up to 10 min. The samples have presented nanometric porosity as a function of etching time, characteristic of heavily doped p type silicon. The residual stress and the correlation length of the layers were obtained through the analysis of the micro-Raman spectra using a phonon confinement model including a term to account for the amorphous phase. The residual compressive stress tends to increase as expected due to the contribution of smaller crystallites to be more representative as the etching time increases. PbTe thin films were electrodeposited on PSL from aqueous alkaline solutions of Pb(CH3COO)2, disodium salt of ethylendiaminetetraacetic acid (EDTA) and TeO2 by galvanostatic and potentiostatic method. It was also obtained nanostructured PbTe thin films with polycrystalline morphology evidenced by X-ray Diffraction (XRD) spectra. Scanning Electron Microscopy (SEM) analysis has demonstrated good films reproducibility with an average grain size of 100 nm.

Resumo em Inglês:

Several techniques have been utilized for the preparation of hydroxyapatite (HA) and other calcium phosphates for the development of biomaterials. It is vital to know the reaction kinetics to be able to control the material obtained by the aqueous solution route. In the present work, HA has been produced by different wet precipitation processes and different experimental conditions. Calcium hydroxide, calcium phosphate, ammonium phosphate and phosphoric acid were used as reagents. The precipitate was dried at 100 °C overnight and then some samples were treated at 900 °C for 2 h. The powder samples were characterized by scanning electron microscopy (SEM), X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses. SEM photomicrographs showed an aggregate powder, granular to dense and suggested typical columnar particles. Qualitative XRF showed that the main components of HA powders were calcium and phosphorus. Pure HA and other phases according to processing parameters were observed by XRD analysis.

Resumo em Inglês:

The focus of this work is to show the influence of surface charge on the bioactivity of modified collagen fiber surface. Because silica plays an important role on bone mineralization process, silica obtained by a sol-gel process was used as a surface modification agent. Zeta potential (xi) of silica-coated and non-coated samples was measured as a function of pH. It was observed a shift in xi vs. pH. The isoelectric point for silica-coated collagen was 6.8, while that of non-treated sample it was near 10. Pure silica has isoelectric point near 2, and the shift observed indicates that at least part of the silica was incorporated onto the surface during the treatment. The ability of samples exposed to biological simulated fluids (SBF) to form a hydroxyapatite layer has been used to recognize bioactive materials. The pH of these biological solutions is about 7.3. It means that treated samples acquire negative charge when in contact with the biological solution and attract ions like Ca2+, HPO4(2-), and OH- to form HA coatings. Micrographs of chemically treated samples corroborate this assumption. For treated samples, the formation of a coating layer is clear after 5-day immersion in SBF, while pure collagen remains practically unaltered. Fourier Transform Infrared Spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands near 1060 cm-1 and 600 cm-1 characteristic of hydroxyapatite (HA).

Resumo em Inglês:

Samples of a commercial glass fiber FM® (Fiber Max) were used to test the efficacy of a chemical sol-gel surface treatment to enhance their bioactivity. After treatment with tetraethoxysilane (TEOS), individual fiber samples were soaked into a simulated body fluid (SBF) solution, from which they were removed at intervals of 5 and 10 days. Micrographs obtained by scanning electron microscopy (SEM) analysis of samples chemically treated with TEOS revealed the formation of a hydroxyapatite (HA) coating layer after 5 days into SBF solution. Fourier transform infrared spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands characteristic of HA. The in vitro cytotoxicity was evaluated using a direct contact test, minimum essential medium elution test (ISO 10993-5) and MTT assay. Fibers immersed in SBF and their extracts exhibited lower cytotoxicity than the controls not subjected to immersion, suggesting that SBF treatment improves the biocompatibility of the fiber.

Resumo em Inglês:

New types of copolymers using monomers which form inorganic polymers network (glass-like) and organic networks have been developed, known as ormocers. The aim of this work was to study how a particular dental filling material is degraded when subjected to a caries challenge by using low pH solutions. The supernadants were studied by HPLC to detect the presence of molecules from the resin, while the changes of the material surface were evaluated by contact angle. An organic modified ceromer (ormocer) called Definite® (Degussa ) was tested. Samples were built following manufacturer's instructions. After pH cycles, solutions were injected in a HPLC. The contact angle was obtained using a goniometer after and before the cycles. HPLC results showed material degradation, only detected in acid solutions. Bis-GMA and TEGDMA were detected in Definite® residues. Means and S.D. of contact angle were (p < 0,05): baseline: 85.16° ± 3.90° and after pH cycles: 69.77° ± 7.12°. The authors concluded that an ormocer filling material degraded on a caries simulated environment.

Resumo em Inglês:

The need for new materials to substitute injured or damaged parts of the human body has led scientists of different areas to investigate bioceramics since the 70's, when other materials in use started to show rejection problems. Ceramics show some advantages like being the material that best mimics the bone tissue, although present low toughness when compared with the metallic materials. As patients have become more and more demanding regarding esthetic and biocompatibility aspects of their dental restorations, ceramic material has become a main object of scientific interest especially from the material point of view. The alumina-zirconia composites are one of the relatively good and promising candidate for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where Y-TZP zirconia content was varied from 5 to 80 wt.% These systems can achieve a flexural strength 93 % and fracture toughness 29 % superior when compared to the pure alumina ceramics. These results showed that ceramic abutments components can be prepared for prosthetic rehabilitations with dental implants.