Resumo em Inglês:

Graft polymerization of N-vinyl-2-pyrrolidone with chitin was studied using hydrogen peroxide for initiation. The capacity of the obtained VP-g-Ch graft copolymer for adsorption of nickel was examined. The effect of temperature, pH and solute concentration on the chelating properties of the grafted and ungrafted chitin were determined. The thermal profiles obtained showed higher thermal resistance for the VP-g-Ch than chitin. The results indicate that the obtained graft copolymer under investigation is a potentially powerful ion exchanger that can be employed for heavy metals removal from wastewater effluents.

Resumo em Inglês:

The sintering of hardmetal in the solid state is studied. The influence of the WC particle size on the sintering kinetics, the role of the binder phase in the densification process and how sintering depends on the heating conditions are investigated. It is observed that alloys with different WC particle size show quite different structural evolution during sintering, although the densification mechanisms are the same. This is explained by the formation of agglomerates of WC and Co. Hardmetal alloys can sinter very rapidly when high heating rates are used, since rapid heating accelerates the binder spreading and the formation of WC-Co agglomerates. The binder phase (Co) spreads on the WC particles initially as a thin layer. Subsequently, more Co spreads on this layer and WC-Co agglomerates are formed.

Resumo em Inglês:

The present work aimed to study the transformation from as-cast structure of the Ti4Al-4V alloy, as a result of the Ti-6Al-4V recycling, after some rapid heat treatments based on martensitic reactions. The effects on mechanical properties were evaluated by Vickers hardness measurements, Charpy and monotonic tensile tests. The corrosion strength was tested by immersion during 4 months in artificial physiological solutions, to evaluate its possible use as a biomaterial. The data pointed to: a) a reduction on corrosion strength for quenching above beta transus; b) significant increasing on hardness and mechanical strength; c) a maintenance of impact toughness; d) the corrosion strength for immersion in a NaCl 1%+ NaF 0,1% (m/m) was lower in all conditions, specially for those including heating to 900 °C.

Resumo em Inglês:

The fundamental parameters approach is used to simulate the instrument contribution to the X-Ray diffraction profile. This procedure eliminates the need to experimentally prepare a reference sample of the studied crystalline material when using the Warren-Averbach method to investigate microstrutural parameters. The Warren-Averbach method is also compared to the Balzar and Enzo methods, two other popular methods of size-strain analysis. The analysis was carried out using bohmite powder having two different nominal average crystallite sizes, 80 Å and 200 Å. A 50%-50% mixture of these materials was used as a third sample. The proposed simulation procedure provides good results and is much faster to implement than the usual procedure that includes the preparation of a reference. For larger crystallite sizes, the results calculated from the Warren-Averbach method for the volume-weighted average crystallite size differs significantly from the ones obtained from the Balzar and Enzo methods. The limitations of the Balzar and Enzo methods are also discussed.

Resumo em Inglês:

Amylopectin-rich starch samples (Amidex 4001 Corn Products Brasil Ingredientes Industriais Ltda.) were grafted with polyethers with the purpose of obtaining new materials for application as solid polymeric electrolytes. Grafting reaction was performed by the addition of starch dissolved in DMSO to toluene poly(propylene oxide) diisocyanate (Resibras) dissolved in the same solvent. This reaction produced a film with good mechanical properties. The film samples were characterized by 13C-NMR, FTIR, DSC, X-Ray and SEM. The FTIR spectrum shows a sharp NH band and a very small urethane band. The 13C-NMR spectrum revealed a peak at 20 ppm, that can be attributed to the CH3 of the polyether chain, and two small peaks at 117 and 140 ppm, attributed to the aromatic ring. The X-ray diffractograms also indicated that after the grafting reaction, the samples of amylopectin-rich starch are more amorphous. Moreover, the glass transition temperature (Tg) dropped from 50 °C to -11 °C. These results indicate formation of grafted products and the low Tg of the samples suggests that polyether-grafted starch is a good candidate to obtain solid polymeric electrolytes.

Resumo em Inglês:

Melt undercooling opens new solidification pathways for non-equilibrium phases and non-conventional microstructures. Several techniques, including the fluxing technique, have been developed in order to reduce nucleation sites and to produce high undercoolings for metals and alloys. In this work the fluxing technique was applied to Pb-25wt%Sn (hypoeutectic), Pb-61.9wt%Sn (eutectic) and Pb-90wt%Sn (hypereutectic) alloys to investigate the influence of the undercooling on the microstructure of these alloys. For the hypoeutectic alloy, an increasing of the undercooling (deltaTe) from 7 to 13 K resulted in interdendritic eutectic refinement. For the hypereutectic alloy, an increasing of undercooling from 8 to 16 K resulted in a reduction of the beta-Sn primary dendrites arm spacing from 50 m to 30 m. For the both hypoeutectic and eutectic alloys, an increasing of the undercooling resulted in an interdendritic eutectic with anomalous morphology. The results indicated that the critical eutectic undercooling, deltaTe*, that causes a transition from lamellar eutectic to anomalous eutectic in the Pb-Sn alloys, is around 6 K.

Resumo em Inglês:

The work hardening of metals subjected to complex processing paths is different from that in monotonic deformation. Changes in the deformation mode can promote transients in the strain-hardening rate, leading to anomalous softening or hardening of the material. This paper investigates the influence of strain path changes on the tensile behavior of drawn 0.12% steel rods. Annealed or predrawn specimens were submitted to cyclic twisting and then tested in tension. The results show that the cyclic deformation causes changes in the mechanical behavior of the metal, and the effect will depend on the previous "history" of the material. Cyclic twisting causes hardening in annealed samples, but leads to softening of the drawn bars. These phenomena are in line with the corresponding substructural aspects.

Resumo em Inglês:

Several techniques can be used to improve surface properties. These can involve changes on the surface chemical composition (such as alloying and surface welding processes) or on the surface microstructure, such as hardening and melting. In the present work surface melting with a 3kW CO2 cw laser was done to alter surface features of an AISI 304 stainless steel. Microstructure characterisation was done by optical and scanning electron microscopy. Vickers and Knoop microhardness tests evaluated mechanical features after surface melting. Phase transformation during rapid solidification is analysed and discussed.

Resumo em Inglês:

This paper discusses the electrochemical behavior of copper, nickel and a copper/nickel alloy in aerated aqueous 0.10 and 1.0 mol L-1 sodium acetate. The data obtained from different electrochemical techniques were analyzed to determine the influence of Ni and Cu on the electrochemical processes of the alloy electrode. The shapes of the potentiodynamic I(E) curves of the alloy were found to be quite similar to those of the Ni voltamograms. Although the anodic current densities of Ni and the alloy increased with greater concentrations of acetate, the opposite effect occurred in Cu. The impedance measurements taken at the open circuit potential revealed that the polarization resistance (R P) of the electrodes decreased in the following order: Ni > Alloy > Cu. With increasing concentrations of acetate, the R P of the alloy and the Cu increased while that of the Ni electrode decreased.

Resumo em Inglês:

We evaluate the orientation of microstructural elements of isotatic polypropylene (i-PP) before and after deformation using computerized "Quantikov" software analysis of Scanning Electron Microscopy (SEM) images. We observed that before deformation through uniaxial compression, the polymeric material doesn’t exhibit any significant orientation. After deformation at 1349 MPa the material clearly showed preferential orientation that was attested by the orientation axis seen between two petals of the rose of the number of intercepts. This effect was more pronounced after deformation at 2699 MPa.

Resumo em Inglês:

Zirconium compounds are of great interest for ceramic application due to their excellent thermal and mechanical properties. Zirconium phases of the system Zr-O-C-N were obtained using carbonitriding reactions of zircon mineral (ZrO2.SiO2), under different reaction conditions. The reaction products were studied by X-ray diffraction (XRD) using the Rietveld method. Silicon was employed as internal standard. Zirconium compounds formed were m-ZrO2 (monoclinic), beta"-zirconium oxynitride and a cubic Zr(C,N,O) phase whose lattice parameter a o depends on the composition. The crystallite sizes of the three zirconium phases were determined also by XRD. The minority phases present are the ones of the Si-O-N-C system. The reaction conditions employed allows to obtain reaction products with low or without silicon content.

Resumo em Inglês:

Strontium barium niobate (SBN) thin films of good quality were deposited on Pt/Ti/SiO2/Si substrate using a polymeric resin containing metallic ions. Films were crystallized at different temperatures and for different duration of time. The structure of these films was studied using X-ray diffraction. The coexistence of SrNb2O6 (SN) and SBN was observed in films crystallized at 700 °C. The amount of SN decreases when the crystallization time increases. Ferroelectric properties were determined for films crystallized at 700 °C for 1 and 5 h. For SBN film crystallized at 700 °C for 1 h, the remanent polarization (Pr) and the coercive field (Ec) were 2.6 muC/cm² and 71.9 kV/cm, respectively. For the film crystallized at 700 °C for 5 h these parameters were Pr = 1.1 muC/cm² and Ec = 50.5 kV/cm.

Resumo em Inglês:

Poly(L-lactic acid) (PLLA) and poly(ethylene oxide) (PEO) blends were prepared by mechanical mixture and fusion of homopolymers. Samples were submitted to in vitro degradation tests (immersion in a phosphate buffer solution with pH = 7.4 at 37 °C). Independently of the blend composition, PEO was dissolved after 14 days of immersion. As expected, after immersion, scanning electron microscopy showed that the blends were porous, contrary to the samples, which were not immersed in the buffer solution. Phase separation was not evident. Using differential scanning calorimetry, the melting points (Tm) of both PLLA and PEO crystalline fractions were observed and remained practically constant, indicating no miscibility. Thermogravimetry showed that the temperature where the main mass loss stage starts (Tonset), depended on the blend composition and period of immersion in the buffer. The blends and the PLLA homopolymer were implanted in defects produced in the tibias of rats. The blends were as biocompatible as the PLLA.

Resumo em Inglês:

Cu-Nb microcomposites are attractive in magnet pulsed field technology applications due to their anomalous mechanism of mechanical strength and high electrical conductivity. In this sense, recently it was conceived the use of Cu 15% vol. Nb wires to operate as a high tensile strength cable for a diamond cutting tool (diamond wires) for marble and granite slabbing. The multifilamentary Cu 15% vol. Nb composite was obtained using a new processing route, starting with niobium bars bundled into copper tubes, without arc melting. Cold working techniques, such as swaging and wire drawing, combined with heat treatments such as sintering and annealing, and tube restacking were employed. The tensile property of the composite was measured as a function of the niobium filaments dimensions and morphology into the copper matrix, in the several processing steps. An ultimate tensile strength (UTS) of 960 MPa was obtained for an areal reduction (R = Ao/A, with Ao-initial cross section area, and A-final cross section area) of 4x10(8) X, in which the niobium filaments reached thickness less than 20 nm. The anomalous mechanical strength increase is attributed to the fact that the niobium filaments acts as a barrier to copper dislocations.

Resumo em Inglês:

An effective positive charge carrier mobility of 4.4 x 10 -9 cm²/V.s was directly determined using analytical expressions for space-charge-limited current in poly(1,10-decanedioxy-2-methoxy-1,4-phenylene-1,2-ethenylene-3,6-dimethoxy- 1,4-phenylene-1,2-ethenylene-3-methoxy-1,4-phenylene), OPPVDBC, which is a soluble electroluminescent alternating block copolymer. Current vs. voltage measurements have been made using single carrier injection and transport in metal/OPPVDBC/metal structures. The experimental results demonstrate that the positive charge transport in these devices is space-charge-limited and temperature dependent. Additionally, there is evidence that the evaporation of the aluminum electrode induces an increase in the charge density near the Al/OPPVDBC interface.

Resumo em Inglês:

Hard thin TiN, TiCxNy and CrN films deposited by Physical Vapor Deposition (PVD) techniques onto steel substrates were immersed in an aggressive environment and evaluated by Atomic Force Microscopy (AFM) and Electrochemical Impedance Spectroscopy (EIS). The mechanical and electrochemical behavior, as well as the microstructure of TiCxNy depended directly on the contents of carbon and nitrogen in the coating. The best results were obtained with stoichiometric coatings that are presented in this work. Although a small amount of pinholes could be observed, the electrochemical performance of TiN film was poorer than the stoichiometric TiCxNy coating. However, the CrN films showed the highest initial and residual corrosion resistance values, probably due to their dense structure.

Resumo em Inglês:

Considering recent modifications on n-type highly doped silicon parameters, an emitter optimization was made based on one-dimensional models with analytical solutions. In order to get good accuracy, a fifth order approximation has been considered. Two kinds of emitters, homogeneous and non-homogeneous, with phosphorus Gaussian profile emitter solar cells were optimized. According to our results: homogeneous emitter solar cells show their maximum efficiencies (<FONT FACE="Symbol">h @ 21.60-21.74%)</FONT>with doping levelsnus = 1x10(19) - 5x10(18) (cm-3) and (1.2-2.0) mum emitter thickness range. Non-homogeneous emitter solar cells provide a slightly higher efficiency (eta = 21.82-21.92%), with Ns = 1x10(20) (cm-3) with 2.0 mum thickness under metal-contacted surface and Ns = 1x10(19) - 5x10(18) (cm-3) with (1.2-2.0) mum thickness range, (sheet resistance range 90-100 <FONT FACE="Symbol">W/ <img SRC="http:/img/fbpe/mr/v4n2/n2a17fou.gif" BORDER="0"></FONT>) under passivated surface. Although non-homogeneous emitter solar cells have a higher efficiency than homogeneous emitter ones, the required technology is more complex and their overall interest for practical applications is questionable.