Abstract: This work is carried out to confirm the existence of the surface potentials in extracted tooth by electrochemical method. The surface potentials were measured between enamel crown’s buccal side and tooth root. Surface potentials examined in all the teeth in the presence of KCl. It is found that potential increased with increasing KCl concentration and after acid corroded. The results suggest that potentials can be affected by the surrounding electrolytes and establish an electrical double layer. It is also found that on passing electric current through enamel causes degradation.

Abstract: This work was focused on analyzing the effect produced by the addition of tannic acid as a crosslinking agent of chitosan matrix and the influence of the heat treatment applied. Taking into account those aspects relevant for packaging applications, thermal stability, mechanical properties, water resistance and kinetics of biodegradation of the film were monitored. The chemical crosslinking as well as the curing of the matrices have improved the mechanical properties and those related to the water affinity such as solubility, permeability and contact angle. Although both processes had an influence on the extent of the film degradation, these materials conserved their biodegradable character. Moreover, it was observed a synergistic effect of both chemical and physical treatments since the two processes in simultaneous caused further delay in the biodegradation. Consequently, in these materials the access to fungal attack and all those reactions mediated by the presence of water were restricted, which confirmed the higher stability of the matrices submitted to chemical or physical crosslinking.

Abstract: Friction Stir Welding (FSW) is a novel solid-phase welding process, which has proved to have a great potential for the realization of welded joints in materials with poor weldability such as heat-treatable aluminum alloys. However, the thermal cycles generated during FSW change the mechanical properties in heat affected zone (HAZ) due to two effects: over-age and re-dissolution of hardening precipitates. In other hand, the re-dissolved precipitates produce a evolution of both the microstructure and mechanical properties due to the natural aging phenomenon. The aim of this paper was to analyze the microstructural evolution in the HAZ of FSW joints in AA7075-T651 alloy. For this purpose samples FSW welded butt plate 4 mm in thickness. On the welded joint microstructural characterization was performed by light microscopy (LM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) and Vickers microhardness profiles (HV) after different elapsed times post welding. It was observed that the hardness increases with time after welding, due to the evolution of the phases present.

Abstract: This research studies the metallurgical transformations happening during the SMAW welding of AISI 316L austenitic stainless steel with AISI 430 ferritic stainless steel. Two different electrodes, AWS E309L austenitic and AWS E2209-16 duplex stainless steels 3.2 mm diameter, were used to perform the study. The joining was made with a single pass welding and keeping a low heat input ranging from 700 - 1000 J/mm. The influence of the type of electrode and the heat input on the microstructural evolution of the heat affected and the fusion zone was evaluated. Differences between δ ferrite morphology were found for both weld metals. The heat affected zone of the ferritic side showed grain coarsening and grain refinement with martensite at the grain boundaries. Tensile strength was similar for both welding conditions. Microhardness and δ ferrite percent were measured as well.

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