Sergio Serna

Enzymatically synthesized polyaniline film deposition studied by simultaneous open circuit potential and electrochemical quartz crystal microbalance measurements

The chemical and enzymatic deposition of polyaniline (PANI) films by in situ polymerization was studied and the resulting films were characterized. The film formation and polymerization processes were simultaneously monitored by the evolution of the open circuit potential and quartz-crystal microbalance measurements. Different substrates, such as Indium-Tin oxide electrodes and gold-coated quartz-crystal electrodes were used as substrates for PANI deposition. Electroactive PANI films were successfully deposited by in situ enzymatic polymerization at low oxidation potential. The electrogravimetric response of the enzymatically deposited PANI film was studied by cyclic voltammetry in monomer-free acidic medium. The morphology of the films was observed by scanning electron microscopy, revealing a granular structure in enzymatically deposited PANI. The PANI films were also characterized by thermogravimetric analysis, electrochemical impedance spectroscopy, and X-ray photoelectron and Fourier-transformed infrared spectroscopy. The simultaneous use of quartz crystal microbalance and open circuit potential is presented as a very useful technique to monitor enzymatic reactions involving oxidoreductases.

Mechanical characterization of the welding of two experimental HSLA steels by microhardness and nanoindentation tests

The microhardness and nanohardness of the welding zone of two experimental HSLA steels were determined. The first steel has a microstructure of martensite and bainite, and the second one has a microstructure of quasipolygonal ferrite and acicular ferrite. In the bainitic - martensitic steel, softening of the heat affected zone was observed. This softening can be attributed to: the formation of polygonal ferrite in the recrystallization subzone, the formation of quasi-polygonal ferrite and the tempering of martensite in the intercritical subzone, and the tempering of martensite in the subcritical subzone. Besides the softening, with nanoindentation technique, hardening was observed at the position where the peak temperature reached the critical temperature Ac1, which can be attributed to a phenomenon of secondary hardening by precipitation of carbides of alloying elements. In the ferritic steel, a softening phenomenon did not appear since there was no martensite in its initial microstructure. Finally, it was noted that both polygonal ferrite and the bainite have similar behavior and nanohardness, this coincidence can be attributed to the effect of grain boundary.

Corrosion Behavior of Ψ and β Quasicrystalline Al–Cu–Fe Alloy

Two nanostructured Al–Cu–Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline (ψ) Al64Cu24Fe12 and crystalline cubic (β) Al62.5Cu25.2Fe12.3 cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain ψ icosahedral and β intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different pH values. Current density (icorr), polarization resistance (Rp), and impedance modulus (|Z|) were determined. The results showed that regardless of pH value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the ψ phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.

Experimental Fatigue Crack Propagation Simulation by ANN of a Newly Developed Controlled Rolled Microalloyed Steel Plate

In this work, fatigue crack propagation life of a new micro alloyed steel plate under the influence of constant load ratio was simulated by using artificial neural network (ANN). Numerous methodologies such as cycle by cycle prediction, prediction by correlation and finite element methods have been proposed for simulating fatigue life [1]. However, few studies relate ANNs for modeling the fatigue crack growth propagation in materials particularly for micro alloyed steels technology. The applied ANNs simulation methodology showed great potential for simulating the experimental fatigue crack growth rate complex data set. In this case especially by interpolation within the trial tested range.