Structure,Crystallization and Electrochemical Corrosion Behaviour of Amorphous Cu66Ti34 Alloy

The effect of thermally induced structural changes on electrochemical corrosion behaviour of amorphous Cu₆₆Ti₃₄ alloy is studied using electrochemical potentiodynamic polarization technique in conjunction with XRD, TEM and DTA. The heat treatment has been carried out at two temperatures: 300 °C — where the process of structural relaxation is only possible and 500 °C — where crystallization of the alloy occurs. As model corrosive media 1N H₂SO₄ and 1N HNO₃ solutions are used. The short range order of the amorphous samples is studied with the total pair correlation function. Some changes of the interatomic distances and a tendency to increasing of the density of the amorphous structure after low temperature heating are established. The crystallization leads to formation of Cu₃Ti₂, β-Cu₃Ti and Cu₂Ti crystalline phases. It has been found that structural relaxation may have a beneficial effect on the susceptibility of the amorphous alloy to passivation, while crystallization lowers considerably its corrosion resistance.     

Influence of molybdenum on the transpassivity of a Fe + 12%Cr alloy in H2SO4 solutions

The influence of Mo addition (5–10 wt.%) on the transpassive dissolution, secondary passivation and oxygen evolution on a Fe + 12%Cr alloy in 1M H₂SO₄ is studied by voltammetric and AC impedance measurements within the frame of an investigation of the impact of Mo on the stability of the passive state of ferrous alloys in acidic media. A semi-quantitative model of the processes is proposed, based on the experimental results obtained and model approaches presented in the recent literature. It was found to be consistent with the experimental data and could serve as a first approximation to a generalized model of transpassivity.     

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li₄Ti₅O₁₂, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li₄Ti₅O₁₂ oxide composite as a positive electrode, and an organic electrolyte (LiPF₆–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m² g^?1) and texture parameters, as well as three types of organic electrolytes: Et₄NBF₄–propylene carbonate (PC), LiBF₄–PC and LiPF₆–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g^?1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g^?1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.     

Mössbauer study of surface films on steels formed in phosphate environments under stress-corrosion cracking conditions

A study on the composition of the surface films and corrosion products of mild and low-alloy (2% Cr) steels in 1M NaH₂PO₄ under stress-corrosion cracking (SCC) conditions has been carried out using Mössbauer spectroscopy. At potentials in the SCC region the films formed on both steels contain Fe₃(PO₄)₂.4H₂O, Fe₃(PO₄)₂.8H₂O and FePO₄.xH₂O. The precipitates in the solution formed under these conditions consist of FePO₄.xH₂O and iron(III) hydrogen phosphate [most probably Fe(H₂PO₄)₃.2H₂O]. An attempt has been made to relate the surface film composition to SCC susceptibility.