Synergistic use of thermogravimetric and electrochemical techniques for thermodynamic study of TiOx (1.67 <= x <= 2.0) at 1573 K

A thermodynamic study of the Ti-O system at 1573 K has been conducted using a combination of thermogravimetric and emf techniques. The results indicate that the variation of oxygen potential with the nonstoichiometric parameter delta in stability domain of TiO2-delta with rutile structure can be represented by the relation, Delta mu o(2) = -6RT In delta - 711970(+/-1600) J/mol. The corresponding relation between non-stoichiometric parameter delta and partial pressure of oxygen across the whole stability range of TiO2-delta at 1573 K is delta proportional to P-O2(-1/6). It is therefore evident that the oxygen deficient behavior of nonstoichiometric TiO2-delta is dominated by the presence of doubly charged oxygen vacancies and free electrons. The high-precision measurements enabled the resolution of oxygen potential steps corresponding to the different Magneli phases (Ti-n O2n-1) up to n = 15. Beyond this value of n, the oxygen potential steps were too small to be resolved. Based on composition of the Magneli phase in equilibrium with TiO2-delta, the maximum value of n is estimated to be 28. The chemical potential of titanium was derived as a function of composition using the Gibbs-Duhem relation. Gibbs energies of formation of the Magneli phases were derived from the chemical potentials of oxygen and titanium. The values of -2441.8(+/-5.8) kJ/mol for Ti4O7 and -1775.4(+/-4.3) kJ/mol for Ti3O5 Obtained in this study refine values of -2436.2(+/-26.1) kJ/mol and-1771.3(+/-6.9) kJ/mol, respectively, given in the JANAF thermochemical tables.

Investigation of AISI 1040 steel corrosion H(2)S solution containing chloride ions by digital image processing coupled with in electrochemical techniques

This paper presents a study of AISI 1040 steel corrosion in aqueous electrolyte of acetic acid buffer containing 3.1 and 31 x 10(-3) mol dm(-3) of Na(2)S in both the presence and absence of 3.5 wt.% NaCl. This investigation of steel corrosion was carried out using potential polarization, and open-circuit and in situ optical microscopy. The morphological analysis and classification of types of surface corrosion damage by digital image processing reveals grain boundary corrosion and shows a non-uniform sulfide film growth, which occurs preferentially over pearlitic grains through successive formation and dissolution of the film. (C) 2011 Elsevier Ltd. All rights reserved.

Decolourisation of real textile waste using electrochemical techniques: Effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSAO type material. The effect of using different anode materials (Ti/Ru0.3Ti0.7O2; Ti/Ir0.3Ti0.7O2; Ti/RuxSn1-xO2, where X = 0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm(-2)) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO2 is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L-1) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order (E-EO/kWhm(-3) order(-1)) and energy consumption (E-C/kW h kg(-1) TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature. (C) 2008 Elsevier B.V. All rights reserved.

Evaluation of corrosion behaviour of biodegradable base oils using electrochemical techniques

© 2015 Institute of Materials, Minerals and Mining. Published by Maney on behalf of the Institute. This paper describes an interesting attempt to quantitatively evaluate the corrosion behaviour of base oils using a novel approach based on electrochemical techniques. The present study evaluates the corrosion behaviour of biodegradable base oils with and without additives in an aqueous chloride solution using electrochemical measurements. Potentiodynamic polarisation and electrochemical impedance spectroscopy techniques were used to quantitatively determine the corrosion behaviour of these oils, and the results were compared to the conventional immersion tests. Both these electrochemical measurements were carried out in a three-electrode system where AS1020 mild steel alloy was used as a working electrode in a purpose made pipette cell. The results obtained from the electrochemical measurements help to evaluate the best biodegradable base oil for formulating eco-friendly industrial lubricants.

Determination of the phthalocyanine textile dye, reactive turquoise blue, by electrochemical techniques

Turquoise blue 15 (AT15) is a reactive dye widely used in the textile industry to color natural fibers. The presence of these dyes in effluent and industrial wastewater is of considerable interest due ecotoxicological and environmental problems. The electrochemical reduction of this dye has been investigated in aqueous solution using cyclic voltammetry, controlled potential electrolysis and cathodic stripping voltammetry. Optimum conditions for dye discoloration by controlled potential electrolysis use an alkaline medium. Using cathodic stripping voltammetry a linear calibration graph was obtained from 5.00×10-8 mol L-1 to 1.00×10 -6 mol L-1 of AT15 at pH 4.0, using accumulation times of 180 and 240 s and an accumulation potential of 0.0 V. The proposed method was applied in direct determination of the dye in tap water and in textile industry effluent.

Use of conventional electrochemical techniques to produce crystalline FeRh alloys induced by Ag seed layer

By combining galvanic displacement and electrodeposition techniques, an ordered Fe20Rh80 structure deposited onto brass was investigated by X-ray diffractometry, Mössbauer spectroscopy and magnetization measurements. Mössbauer and X-ray diffraction analyses suggest that the Fe-Rh alloy directly electrodeposited onto brass displays a nanocrystalline state while a similar alloy deposited onto Ag/brass shows a faced centered cubic-like structure, with dendrites-like features. These results directly indicate that the presence of Ag seed layer is responsible for the Fe-Rh alloy crystallization process. In addition, room temperature Mössbauer data indicate firstly paramagnetic states for two Fe-species. In the dominant Fe-species (major fraction of the Mössbauer spectra), Fe atoms are situated at a cubic environment and it can be attributed to the γ-Fe20Rh80 alloy based on their hyperfine parameters. In the second species, Fe atoms are placed in a non-local symmetry, which can be related to Fe atoms at the grain boundaries or/and Fe small clusters. These Fe-clusters are in superparamagnetic state at room temperature, but they may be ordered below 45 K, as suggested by magnetization data. © 2013 Elsevier B.V. All rights reserved.

Direct electrochemical formation of alloyed AuPt nanostructured electrocatalysts for the oxidation of formic acid

The formation of highly anisotropic AuPt alloys has been achieved via a simple electrochemical approach without the need for organic surfactants to direct the growth process. The surface and bulk properties of these materials were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and electrochemically by cyclic voltammetry to confirm alloy formation. It was found that AuPt materials are highly active for both the model hydrogen evolution reaction and the fuel cell relevant formic acid oxidation reaction. In particular for the latter case the preferred dehydrogenation pathway was observed at AuPt compared to nanostructured Pt prepared under identical electrochemical conditions which demonstrated the less preferred dehydration pathway. The enhanced performance is attributed to both the ensemble effect which facilitates CO(ads) removal from the surface as well as the highly anisotropic nanostructure of AuPt.

Physicochemical, Electrochemical, and Spectroscopic Characterization of Zinc-Based Room-Temperature Molten Electrolytes and Their Application in Rechargeable Batteries

Room-temperature zinc ion-conducting molten electrolytes based on acetamide, urea, and zinc perchlorate or zinc triflate have been prepared and characterized by various physicochemical, spectroscopic, and electrochemical techniques. The ternary molten electrolytes are easy to prepare and can be handled under ambient conditions. They show excellent stability, high ionic conductivity, relatively low viscosity, and other favorable physicochemical and electrochemical properties that make them good electrolytes for rechargeable zinc batteries. Specific conductivities of 3.4 and 0.5 mS cm(-1) at 25 degrees C are obtained for zinc-perchlorate-and zinc-triflate-containing melts, respectively. Vibrational spectroscopic data reveal that the free ion concentration is high in the optimized composition. Rechargeable Zn batteries have been assembled using the molten electrolytes, with gamma-MnO2 as the positive electrode and Zn as the negative electrode. They show excellent electrochemical characteristics with high discharge capacities. This study opens up the possibility of using acetamide-based molten electrolytes as alternate electrolytes in rechargeable zinc batteries. (C) 2009 The Electrochemical Society.

Electrochemical, gravimetric and quantum chemical analysis of mild steel corrosion inhibition by colchicine in 1 M HCl medium

The inhibition effect of colchicine (CC) on mild steel (MS) corrosion in 1 M HCl solution has been investigated by electrochemical techniques such as electrochemical impedance spectroscopy, potentiodynamic polarization, chronoamperometry and also by the gravimetric method. Polarization studies showed that CC acts as mixed type corrosion inhibitor. The inhibitor adsorption process in the MS/CC/HCl system was studied at different temperatures (303-333 K). The adsorption of CC on MS surface is an exothermic process and obeys the Langmuir adsorption isotherm. Based on potential of zero charge values and quantum chemical parameters, the mechanism of adsorption has been proposed.

A novel nanometer-scale "gold electrode-molecular wires-silver" junction: An efficient test bed for electrochemical investigation of electron transportation through molecular wires in self-assembled monolayers

A novel "gold electrode-molecular wires-silver" junction was facilely fabricated for electrochemical study on the electron transportation through molecular wires. Rapid electron transportation through this sandwich-like structure was indeed observed by cyclic voltammograms and ac impedance measurements. Since rather reproducible and reliable results are easily available by electrochemical techniques, it would be an efficient and reliable test bed for electrochemical investigation of charge transportation through molecular wires in self-assembled monolayers on electrodes.