Influence of differential stress on the galvanic interaction of pyrite–chalcopyrite

The effect of stress action on pyrite–chalcopyrite galvanic corrosion was investigated using polarization curves and electrochemical impedance spectroscopy (EIS) measurements. When stress increased from 0 to 4?×?10⁵ Pa, the corrosion current density of pyrite–chalcopyrite increased from 5.678 to 6.719 μA cm^?2, and the corrosion potential decreased from 281.634 to 270.187 mV, accompanied by a decrease in polarization resistance from 25.09 to 23.79 Ω·cm². EIS results show there have three time constants in the Nyquist diagrams, which indicated the presence of different steps during the corrosion process. Stress dramatically enhanced pyrite–chalcopyrite galvanic corrosion by affecting the Cu_1???x Fe_1???y S₂ film and the double layer, whereas had little impact on the adsorption species. When the stress changed from 0 to 4?×?10⁵ Pa, the pore resistance and capacitance of the Cu_1???x Fe_1???y S₂ film, R _p and Q _p, changed by 25.72 and 72.28 %, respectively. The adsorption species resistance, R _sl, and capacitance, Q _sl, only changed by 9.77 and 2.31 %, respectively.     

Effect of Gd2O3 on the hydrogen evolution property of nickel–cobalt coatings electrodeposited on titanium substrate

The effect of rare earth compound, Gd₂O₃, on the microstructure and the hydrogen evolution property of Ni–Co alloy electrode was studied. The morphology and microstructure were characterized by SEM and XRD, respectively, and the electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from steady-state polarization curves, Tafel curves and electrochemical impedance spectroscopy measurements carried out in 0.50 M Na₂SO₄+0.10 M H₂SO₄ solution. It was found that the embedded Gd₂O₃ particles largely enhanced the electrocatalytic activity of Ni–Co alloy electrode to hydrogen evolution reaction.     

Mössbauer Spectroscopic Study on Vertical Distribution of Iron Species in Sediments from Qinghai Lake,China

In this study, ⁵⁷Fe Mössbauer spectroscopy has been applied to sediments collected from Qinghai Lake in Qinghai Province, China, to investigate the vertical distribution of iron species. Their Mössbauer spectra consisted of four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite suggested climatic changes during the past nine thousand years. It was demonstrated that the iron speciation in the salt lake sediments by Mössbauer spectroscopy can be used to reconstruct the past environment.

     

Study on the mechanisms of photoinduced carriers separation and recombination for Fe-TiO2 photocatalysts

The iron(III)-ion doped TiO₂ (Fe³⁺-TiO₂) with different doping Fe³⁺ content were prepared via a sol-gel method. The as-prepared Fe³⁺-TiO₂ nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe³⁺-TiO₂ catalysts with different Fe³⁺ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe³⁺-TiO₂ was revealed: that is, the Fe³⁺ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti ≤ 0.03 mol%); while Fe³⁺ dopant content exceeds 0.03 mol%, Fe₂O₃ became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe₂O₃ with TiO₂ leads to that the photoinduced electrons and holes of TiO₂ transfer to Fe₂O₃ and recombine quickly, which is unfavorable to the photocatalytic reaction.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

Iron speciation of sediments from Kuhai Lake in China by Mössbauer spectroscopy

The vertical distribution of iron species in the sediments collected from Kuhai Lake was investigated in this study. Their Mössbauer spectra were composed of one sextet and four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite was considered to reflect the climatic change during the past 2,000 years. Mössbauer spectroscopy was successfully applied to the analysis of the Kuhai Lake sediments so as to reconstruct the history of the past climate.     

Mechanism of charging of the pyrite/aqueous interface as deduced from the surface potential measurements

Surface potential of pyrite in an aqueous environment was measured by means of a single crystal pyrite electrode. The effect of the activity of S²⁻ and Fe²⁺ ions as well as of pH, was examined. The results show that S²⁻ and Fe²⁺ ions are the dominant potential determining ions. These ions are bound to surface sites with the extent depending on their activity in the bulk of the solution. Adsorption affinity of S²⁻ ions is significantly higher than that of Fe²⁺ ions so that in most cases the pyrite surface is negatively charged. The results were explained on the basis of the surface complexation model. It was found that the surface potential depends also on pH.     

Synthesis and electrochemical performance of α-nickel hydroxide codoped with Al3+ and Ca2+

α-Nickel hydroxide codoped with Al³⁺ and Ca²⁺ was prepared by chemical coprecipitation method. The phase structure and surface morphology of the prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical performances of the prepared samples were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. XRD and SEM tests reveal that the Al³⁺/Ca²⁺ codoped α-nickel hydroxide has a relatively good crystallization and a very coarse surface. Electrochemical tests show that the Al³⁺/Ca²⁺ codoped α-nickel hydroxide has higher proton diffusion coefficient, lower electrochemical reaction resistance, and higher discharge capacity (395.3 mAh g^?1 at 0.2 C) than the Al³⁺ singly doped α-nickel hydroxide, which indicates its potential application as an electrode material for secondary alkaline batteries.     

The origin of copiapite from chlorite pyritic schist (Wieściszowice, Lower Silesia, Poland) in the light of Mössbauer analysis

This work presents the results of the analysis of copiapite, formed from weathering and oxidation of pyrite in pyritic schist from Wie?ciszowice, Lower Silesia (Poland). The pure phase of copiapite was found in secondary minerals after pyrite and identified by optical microscopy, XRD and Mössbauer spectroscopy. In the analyzed copiapite major cations appear to be Fe^2?+? and Fe^3?+?. Some Fe^3?+? is substituted by other cations, mainly Al^3?+?. Al^3?+? probably comes from leaching of chlorite from which hydrated sulphates of iron, mainly szomolnokite, form followed by hydrated sulphates fibroferrite, which is replaced by copiapite.     

The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La alloys in sodium chloride solution

The electrochemical behaviors of Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes in NaCl solution are investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). It is found that the Mg-8Li-3Al-1La electrode is of higher discharge activity than the Mg-5Li-3Al-1La electrode in 0.7 mol L^?1 NaCl solution, which is consistent with the results observed from SEM images. The composition of the discharging products is also analyzed by means of XRD diffraction. This result shows that the Mg-8Li-3Al-1La alloy displays better compatibility with salt than the Mg-5Li-3Al-1La alloy, and the electrolyte can easily permeate the electrode, which enlarges the reaction zone and improves the activity of the electrode. The continuous discharging utilization efficiency of the Mg-5Li-3Al-1La and Mg-8Li-3Al-1La electrodes is 47.36 and 50.46%, respectively. The utilization of the Mg-Li-Al-La electrode is increased by 3.10% with the amount of Li increased from 5 to 8%. Meanwhile, the interval discharging utilization efficiency of the two electrodes is 46.13 and 49.88%, respectively, and the increase in the amount of Li in the electrode also brings a favorable effect on the interval electrochemical properties of the electrode.     

The effect of different concentrations of Na2SnO3 on the electrochemical behaviors of the Mg-8Li electrode

In this research, the effect of the different concentrations of NaSnO₃ as the electrolyte additive in 0.7 mol L^?1 NaCl solution on the electrochemical performances of the magnesium-8lithium (Mg-8Li) electrode are investigated by methods of potentiodynamic polarization, potentiostatic current-time, electrochemical impedance technique, and scanning electron microscopy (SEM). The corrosion resistance of the Mg-8Li electrode is improved when Na₂SnO₃ is added into the electrolyte solution. The potentiostatic current-time curves show that the electrochemical behaviors of the Mg-8Li electrode in the electrolyte solution containing 0.20 mmol L^?1 Na₂SnO₃ is the best. The electrochemical impedance spectroscopy results indicate that the polarization resistance of the Mg-8Li electrode decreases in the following order with the concentrations of Na₂SnO₃: 0.05 mmol L^?1?>?0.00 mmol L^?1?>?0.30 mmol L^?1?>?0.10 mmol L^?1?>?0.20 mmol L^?1. The scanning electron microscopy studies indicate that the electrolyte additive prevents the formation of the dense oxide film on the alloy surface and facilitates the peeling off of the oxidation products.     

Corrosion inhibition of iron in acidic solutions by alkyl quaternary ammonium halides: Correlation between inhibition efficiency and molecular structure

The corrosion inhibition of iron in 0.5 M H₂SO₄ solutions by alkyl quaternary ammonium halides (AQAH) inhibitors has been studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. The correlation between inhibition efficiency and molecular structure of the AQAH compounds is investigated. The results show that besides the concentration, the structure of alkyl groups and the type of halide ions of these AQAH inhibitors greatly influence the inhibition efficiency. Data obtained from EIS measurements are analyzed to model the corrosion inhibition process through appropriate equivalent circuit models.     

Optical characterization of the phosphate glasses containing pair transition ions

The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe–Mn and Fe–Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe²⁺/Fe³⁺), manganese (Mn²⁺/Mn³⁺) and chromium (Cr³⁺/Cr⁶⁺) in the vitreous network. Mössbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe–Mn doped glasses, the percentage of Fe²⁺ is about 40% and a doubled iron content leads to an increasing of Fe²⁺ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe²⁺ percentage up to 56%. The occurrence of the tetrahedral or octahedral symmetry of Fe²⁺ ions bonded by O^2? ions depends on the transition ion nature and Li⁺/Na⁺ ratio. Infrared absorption spectra of the pair transition ions-doped aluminophosphate glasses reveal optical phonons specific for the phosphate glass matrix.     

The In Situ Synthesis of Fe(OH)3 Film on Fe Foam as Efficient Anode of Alkaline Supercapacitor Based on a Promising Fe3+/Fe0 Energy Storage Mechanism

Herein, a simple in situ charge/discharge activation strategy is proposed to synthesize Fe(OH)3 film on Fe foam as an efficient anode of supercapacitors. The physical characteristics of electrodes are characterized and the electrochemical energy storage performances are investigated. Importantly, it is demonstrated the as‐synthesized Fe(OH)3@Fe foam electrode adopted a novel Fe³⁺/Fe⁰ redox reaction mechanism for energy storage in alkaline electrolytes. Compared with previously reported Fe³⁺/Fe²⁺ mechanisms, the Fe³⁺/Fe⁰ redox couple shows a more promising application value (e.g., higher theoretical‐specific capacitance, excellent conductivity of its reduction state). As for supercapacitor anodes, the electrode achieves high areal capacitance of 5.55–3.94 F cm⁻² at a current range of 20–200 mA cm⁻² and shows good stability for high‐rate and long‐term cycling. The assembled single supercapacitor device gives a high energy density of 11.64–7.43 Wh m⁻² at a power density of 157–1461 W m⁻². More importantly, the as‐adopted in situ activation strategy may also have potential value for synthesizing other transition metal oxide‐based products.     

Deep reduction behavior of iron oxide and its effect on direct CO oxidation

Reduction of metal oxide oxygen carrier has been attractive for direct CO oxidation and CO₂ separation. To investigate the reduction behaviors of iron oxide prepared by supporting Fe₂O₃ on γ-Al₂O₃ and its effect on CO oxidation, fluidized-bed combustion experiments, thermogravimetric analyzer (TGA) experiments, and density functional theory (DFT) calculations were carried out. Gas yield (γCO₂) increases significantly with the increase of temperature from 693 K to 1203 K, while carbon deposition decreases with the increase of temperature from 743 K to 1203 K, where temperature is a very important factor for CO oxidation by iron oxide. Further, it were quantitatively detected that the interaction between CO and Fe₂O₃, breakage of O-Fe bonds and formation of new C-O bonds, and effect of reduction degree were quantitatively detected. Based on adsorptions under different temperatures and reducing processes from Fe³⁺ into Fe²⁺, Fe⁺ and then into Fe, it was found that Fe²⁺ → Fe⁺ was the reaction-controlling step and the high oxidation state of iron is active for CO oxidation, where efficient partial reduction of Fe₂O₃ into FeO rather than complete reduction into iron may be more energy-saving for CO oxidation.     

Synthesis and electrochemical performance of amorphous nickel hydroxide codoped with Fe<Superscript>3+</Superscript> and CO<Stack><Subscript>3</Subscript><Superscript>2−</Superscript></Stack>

Amorphous nickel hydroxide codoped with Fe³⁺ and CO₃²⁻ was synthesized by micro-emulsion precipitation method combined with rapid freezing technique. The microstructure and composition of the sample were characterized by X-ray diffraction and IR analysis. The electrochemical performance of the sample was analyzed by cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The results showed that the Fe³⁺ and CO₃²⁻ codoping enhances the amorphous feature of the prepared nickel hydroxide. Moreover, the Fe³⁺ and CO₃²⁻ codoping could increase the specific capacity and improve the electrochemical reversibility of the amorphous nickel hydroxide electrode.     

57Fe Mössbauer spectroscopy used to develop understanding of a diamond preservation index model

⁵⁷Fe Mössbauer spectroscopy has provided precise and accurate iron redox ratios Fe²⁺/Fe³⁺ in ilmenite, FeTiO₃, found within kimberlite samples from the Catoca and Camatxia kimberlite pipes from N.E. Angola. Ilmenite is one of the key indicator minerals for diamond survival and it is also one of the iron-bearing minerals with iron naturally occurring in one or both of the oxidation states Fe³⁺ and Fe²⁺. For this reason it is a good indicator for studying oxygen fugacities (fO₂) in mineral samples, which can then be related to iron redox ratios, Fe²⁺/Fe³⁺. In this paper we demonstrate that the oxidation state of the ilmenite mineral inclusion from sampled kimberlite rock is a key indicator of the oxidation state of the host kimberlite assemblage, which in turn determines the genesis of diamond, grade variation and diamond quality. Ilmenite samples from the two different diamondiferous kimberlite localities (Catoca and Camatxia) in the Lucapa graben, N.E. Angola, were studied using Mössbauer spectroscopy and X-Ray Diffractometry, in order to infer the oxidation state of their source regions in the mantle, oxygen partial pressure and diamond preservation conditions. The iron redox ratios, obtained using Mössbauer spectroscopy, show that the Catoca diamond kimberlite is more oxidised than kimberlite found in the Camatxia pipe, which is associated within the same geological tectonic structure. Here we demonstrate that⁵⁷Fe Mössbauer spectroscopy can assist geologists and mining engineers to effectively evaluate and determine whether kimberlite deposits are economically feasible for diamond mining.     

Fluorination of perovskite-related SrFeO3−δ

We report here on the fluorination of the perovskite-related phase SrFeO_3−δ through a low temperature (400 °C) reaction with poly(vinylidene fluoride). X-ray powder diffraction shows that fluorination leads to an expansion in the unit cell which is consistent with partial replacement of oxygen by fluorine and consequent reduction in the oxidation state of iron giving SrFeO₂F. This reduction in oxidation state is confirmed by X-ray absorption- and Mössbauer-spectroscopy. The latter show complex magnetically split hyperfine patterns for the fluorinated sample, reflecting the interactions between Fe³⁺ ions which are not possible in oxides containing Fe⁴⁺.     

Magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> surface

The magnetic properties of the magnetite Fe₃O₄(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density are presented. Problems related to magnetic moments of bivalent (Fe²⁺) and trivalent (Fe³⁺) ions on the Fe₃O₄(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms.     

Experimental, density function theory calculations and molecular dynamics simulations to investigate the adsorption of some thiourea derivatives on iron surface in nitric acid solutions

The effects of thiourea derivatives, namely N-methyl thiourea (MTU), N-propyl thiourea (PTU) and N-allyl thiourea (ATU) on the corrosion behaviour of iron in 1.0 M solution of HNO₃ have been investigated in relation to the concentration of thiourea derivatives. The experimental data obtained using the techniques of weight loss, Tafel polarization and electrochemical impedance spectroscopy, EIS. The results showed that these compounds revealed a good corrosion inhibition, (ATU) being the most efficient and (MTU) the least. Computational studies have been used to find the most stable adsorption sites for thiourea derivatives. This information help to gain further insight about corrosion system, such as the most likely point of attack for corrosion on iron (1 1 0), the most stable site for thiourea derivatives adsorption and the binding energy of the adsorbed layer. The efficiency order of the inhibitors obtained by experimental results was verified by theoretical analysis.