Stable Eutectoid Transformation in Nodular Cast Iron: Modeling and Validation

This paper presents a new microstructural model of the stable eutectoid transformation in a spheroidal cast iron. The model takes into account the nucleation and growth of ferrite grains and the growth of graphite spheroids. Different laws are assumed for the growth of both phases during and below the intercritical stable eutectoid. At a microstructural level, the initial conditions for the phase transformations are obtained from the microstructural simulation of solidification of the material, which considers the divorced eutectic and the subsequent growth of graphite spheroids up to the initiation of the stable eutectoid transformation. The temperature field is obtained by solving the energy equation by means of finite elements. The microstructural (phase change) and macrostructural (energy balance) models are coupled by a sequential multiscale procedure. Experimental validation of the model is achieved by comparison with measured values of fractions and radius of 2D view of ferrite grains. Agreement with such experiments indicates that the present model is capable of predicting ferrite phase fraction and grain size with reasonable accuracy.     

Crystallographic Texture Evolution of a Zinc Sheet Subjected to Different Strain Paths

Metallurgical and Materials Transactions A - The use of zinc sheets has largely increased in the last years, fundamentally because of new tendencies in architecture and, at the same time, due to...     

Food Deprivation Promotes Oxidative Imbalance in Rat Brain

ABSTRACT:  The present study was aimed to evaluate the effect of food deprivation in brain oxidative status of Wistar and Goto-Kakizaki (GK) rats. For this purpose, we evaluated several oxidative stress parameters: lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) and protein oxidation markers, hydrogen peroxide (H₂O₂) levels, nonenzymatic (reduced [GSH] and oxidized glutathione [GSSG] and vitamin E) and enzymatic (glutathione peroxidase [GPx], glutathione reductase [GRed], and manganese superoxide dismutase [MnSOD]) antioxidant defenses. Four-mo-old Wistar and GK rats were divided into 2 groups. One group of each rat strain was maintained under normal diet and the other groups were maintained under 50% food deprivation during 2 mo. GK rats under normal diet presented lower levels of vitamin E and higher GRed activity and GSH/GSSG ratio when compared with Wistar control rats. In Wistar rats, food deprivation induced a significant decrease in vitamin E levels and a significant increase in GPx activity, H₂O₂ production, and TBARS formation in the presence of the prooxidant pair ADP/Fe²⁺. However, GK rats under food deprivation presented a significant decrease in vitamin E levels and GRed activity and a significant increase in H₂O₂ production when compared with GK under normal diet. In summary, our results indicate that food deprivation affects brain oxidative status, which could predispose brain cells to degeneration and death.     

Development,characterization, and photocytotoxicity assessment on human melanoma of chloroaluminum phthalocyanine nanocapsules

In this work we have developed nanocapsules containing chloroaluminum phthalocyanine (ClAlPc) and assessed their phototoxic action on WM1552C, WM278, and WM1617 human melanoma cell lines. The ClAlPc-loaded nanocapsules were prepared by the nanoprecipitation method and optimized by means of a 2³ full factorial design. The ClAlPc nanocapsules were characterized by particle size and distribution, zeta potential, morphology, encapsulation efficiency, singlet oxygen production, stability, and phototoxic action on melanoma cells. Both the development and optimization studies revealed that stable colloidal formulations could be obtained by using 1.75% (w/v) soybean lecithin, 1.25% (w/v) Poloxamer 188, 2.5% (v/v) soybean oil, and 0.75% (w/v) poly(D,L-lactide-co-glycolide). The nanocapsules had a mean diameter of 230 nm, homogeneous size distribution (polydispersity index < 0.3), and negative zeta potential (about ? 30 mV). Their morphology was spherical, with evident polymer membrane coating droplet. The encapsulation efficiency was 70%, as expected for hydrophobic drugs, and the nanoencapsulated ClAlPc was able to produce high singlet oxygen quantum yield. ClAlPc nanocapsules exhibited good physical stability over a 12-month period. WM1552C primary melanoma cells were more sensitive (p < 0.05) to the phototoxic effect elicited by ClAlPc nanocapsules (0.3 μg ml^? 1) under light irradiation at 20 mJ cm^? 2. On the other hand, the cell survival percentage for all the melanoma cell lines treated with the highest light dose (150 mJ cm^? 2) was lower than 10%. In summary, ClAlPc nanoencapsulation could enable application of this hydrophobic photosensitizer in the treatment of malignant melanoma with the use of both low sensitizer drug concentration and light dose.     

Ferroelectric properties of pulsed laser deposited PZT (92/8) thin films

The effect of pulse amplitude on the ferroelectric and switching properties of pulsed laser deposited PZT (92/8) thin films has been studied. The structural analysis revealed that the films had a well crystallized perovskite phase without secondary phases. The atomic force microscopy has been employed to estimate the grain size and surface roughness of the film. A well-saturated P–E hysteresis loop was observed with average values of remnant polarization (P_r) ≈ 16.0 μC/cm², saturation polarization (P_s) ≈ 21.7 μC/cm² and coercive field ≈138 kV/cm. The P–E loops were very stable with frequency, confirming that the contribution of the leakage current and/or mobile free charges to the polarization is minimum. The polarization current exhibits the exponential dependence on the pulse amplitude and the leakage current seems to be governed by the hopping mechanism which is generally associated to structural defects.     

Biological evaluation of alginate-based hydrogels, with antimicrobial features by Ce(III) incorporation, as vehicles for a bone substitute

A novel hydrogel, based on an alginate/hyaluronate mixture and Ce(III) ions, with effective bioactive and antimicrobial ability was developed to be used as vehicle of a synthetic bone substitute producing an injectable substitute (IBS). Firstly, three different IBSs were prepared using three developed alginate-based hydrogels, the hydrogel Alg composed by alginate, the hydrogel Alg/Ch composed by an alginate/chitosan mixture and the hydrogel Alg/HA composed by an alginate/hyaluronate mixture. MG63 cells viability on the IBSs was evaluated, being observed a significantly higher cell viability on the Alg/HA_IBS at all time points, which indicates a better cell adaptation to the material, increasing their predisposition to produce extracellular matrix and thus allowing a better bone regeneration. Moreover, SEM analysis showed evident filopodia and a spreader shape of MG63 cells when seeded on Alg/HA_IBS. This way, based upon the in vitro results, the hydrogel Alg/HA was chosen to the in vivo study by subcutaneous implantation in an animal model, promoting a slight irritating tissue response and visible tissue repairing. The next step was to grant antimicrobial properties to the hydrogel that showed the best biological behavior by incorporation of Ce(III) ions into the Alg/HA, producing the hydrogel Alg/HA2. The antimicrobial activity of these hyaluronate-based hydrogels was evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Candida albicans. Results showed that Ce(III) ions can significantly enhance the hydrogel antimicrobial ability without compromising the osteoconductivity improvement promoted by the vehicle association to the synthetic bone substitute.     

Enhanced photocatalytic performance of Fe-doped SnO2 nanoarchitectures under UV irradiation: synthesis and activity

A facile, sol–gel method has afforded highly crystalline, Fe-doped SnO₂ nanoarchitectures with efficient photocatalytic degradation of rhodamine B (RhB) under ultraviolet irradiation. The effects of iron modification to tin dioxide were investigated. The structural properties were characterized by powder X-ray diffraction, gas sorption (adsorption/desorption) techniques, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). The photocatalytic activity of these materials was studied by examining the degradation of RhB with pure SnO₂ and each Fe modified sample (3 and 5 %), all annealed at 350 °C. Diffraction results reveal that the synthesized nanocrystals are ~3 nm in diameter. Gas sorption analyses detail high-specific surface areas (>330 m² g^?1). Electron microscopy studies illustrate the enhanced porosity brought on through annealing. EDS confirms the presence of Fe in the most active Fe-modified SnO₂ sample. It is found that the 5 % Fe-modified SnO₂ degrades RhB by more than half after 2 h.     

Study correlating the bubble phenomenon and electrical signals in underwater wet welding with covered electrodes

The bubble phenomenon in underwater wet welding is very important to the final quality of the weld. A good understanding of the formation and collapse of the bubbles and knowledge of the behaviour of welding parameters during the process can improve the practices used in underwater welding and, consequently, improve the final quality of the weld. This study was developed to understand and try to correlate the phenomenon of growth, detachment and frequency of bubbles with electrical signals during the welding process. Beads were made on plate metal at a depth of 0.50 m, with three types of commercial coated electrodes: E6013, E7024 and E7018. High-speed filming to visualize the process of formation, detachment and counting of the bubbles was performed, along with acquisition of their electrical signals. Thus, it was possible to try to correlate the bubble frequency with the electrical signals observed during the process. It was observed in the current data that the mean number of variations under 5% of the mean current is similar to the mean detachment rate of the bubbles. Therefore, it was concluded that there is a possible relationship between bubble detachment and a determined variation in the current.