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Journal of Material Sciences & Engineering

ISSN: 2169-0022

Open Access

Current Issue

Volume 8, Issue 6 (2019)

    Research Article Pages: 1 - 7

    Electrochemical Study of the Hydrogenation of LaZr2Cr4Ni5-Based Alloys

    Ines Sahli, Mouna Elghali, Marwa Ayari, Ouassim Ghodbane and Mohieddine Abdellaoui

    The electrochemical behavior of LaZr2Cr4Ni5-based alloys applied as negative electrode materials for Ni–metal hydride (Ni–MH) batteries was investigated by cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques. The hydrogen diffusion coefficient, determined by CV, was equal to 1.28 × 10−8 cm2s−1 reflecting an appropriate electrochemical hydrogenation kinetic of the LaZr2Cr4Ni5-based compound. The evolution of the hydrogen diffusion coefficient was also investigated by EIS first at different state of charge (10% and 100%) and second as function of charge/discharge cycling. Upon the first cycle, the diffusion coefficient increases from 31.72 × 10-8 cm2s-1 to reach a maximum value of 13.14 × 10-6 cm2s-1 at the fifth cycle. A further cycling leads to a sharp decrease of the diffusion coefficient to 82.14 × 10-8 cm2s-1 after 30 cycles. The hydrogen diffusion coefficient values determined by electrochemical impedance spectroscopy after 50 charge-discharge cycles are equal to 4.41.10-8cm2s−1 for the α phase (10% state of charge) and 1.12 × 10-8 cm2 s−1 for the β phase (100% state of charge). As compared to the mean value determined by cyclic voltammetry, these values are higher for α phase and less for the β phase.

    The exchange current densities of the electrodes were estimated as a function of the charge/discharge cycling by EIS. The charge transfer kinetic is faster at the beginning of cycling. The chronoamperometry measurements indicate that the size of the cluster of particles involved in the electrochemical reaction (the depth or the degree of the material impregnation by the electrolyte) decreases from 63 to 6.2 μm after 50 cycles.

    Research Article Pages: 1 - 7

    Spark Plasma Sintering Techniques Improve the Properties of AlN-TiB2 Ceramics with Nb2O5, Y2O3 and ZrO2 as a Sintering Precursors

    José C González, Miguel A Rodríguez, Ignacio A Figueroa, María-Elena Villafuerte-Castrejón and Gerardo C Díaz

    AlN-TiB2 composites ceramics were prepared by Spark Plasma Sintering (SPS). The effects of Nb2O5, Y2O3 and ZrO2 additives on mechanical properties and densification were investigated. X-ray diffraction was used to identify the phases in the resulting composites. Good densification results were obtained using the different sintering additives. The mechanical properties such as hardness and fracture toughness were obtained using a Vickers indentation, the maximum values of hardness and fracture toughness were 13.9 ± 0.4 GPa for A4TN (90.48% AlN-4.76% TiB2-4.76% Nb2O5. wt% of composite ceramic) and 5.8 ± 0.9 MPa.m1/2 for A23TZ (71.43%AlN-23.81%TiB2-4.76%ZrO2 wt% of composite ceramic).

    Research Article Pages: 1 - 5

    EDTA-Modified Carbon Paste Composite for Electrochemical Determination of Pb(II) Ions

    Sakina Touzara, Amina Amlil, Hind Saâdane, Charaf Laghlimi and Abdelilah Chtaini

    This paper studies the detection of Lead ions by using a Disodium ethylenediaminetetraacetate dihydrate (EDTA) modified Carbon Paste electrode. The modified electrode was used for the electrochemical analysis of trace lead ions by square wave voltammetry (SWV) technique. It was found that the EDTA-CPE electrode shows a better performance than the carbon paste electrode. Under optimal conditions such as modification method, pH, time of contact with the organic molecule and pre-concentration time of lead, the modified electrode proved the best linear response to lead (II). The proposed method has been applied to a possible electrochemical sensor for heavy metals in solution.

    Research Article Pages: 1 - 5

    Empirical Relationship between Hardness and Tensile Strength for Medium Carbon Steel Quenched in Different Media

    Njoku RE, Ocheri C, Okuu JC and Nnamchi PS

    The possibility of predicting the ultimate strength of medium carbon steel sample quenched in different media has been investigated. A 0.4%C steel was austenitized in a carbolite furnace, quenched in water, hydraulic oil and olive oil and later tempered while some samples were normalized. All experimental samples were tested in a computer controlled Testometric universal materials testing machine and Rockwell hardness tester and later viewed in an optical microscope. The results show that a linear relationship exists between the ultimate tensile strength and the hardness of the steel material and it is of the type: UTS=ao+a1HRC where the regression constant (ao) and regression coefficient (a1) have been evaluated for the steel sample to be equal to 241.4 and 10.97 respectively. Stress Vs strain curves revealed that the normalized samples showed a yield point phenomenon while the hardened samples did not. The microstructure of the normalized sample is constituted by combination of ferrite and pearlite while microstructure of the hardened samples is predominantly martensitic. The water- quenched samples showed the highest ultimate tensile strength and hardness while the sample, quenched in olive oil showed the least strength and hardness.

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