Mössbauer study of the tin chemistry occurring during the hydroliquefaction of tin-treated Victorian brown coal

Mössbauer spectroscopy was used to determine the chemical changes occurring to introduced tin during the hydroliquefaction of Victorian Morwell brown coal. Tin is present in the coal as the hydrated tin oxide (SnO₂.xH₂O) which is thermally dehydrated and also reduced by molecular hydrogen to SnO and β-Sn. The presence of tin metal in the reaction at 350 °C and above, together with its previously demonstrated ability to slow the degradation of coal related phenyl alkyl ethers, is evidence that the Sn⁰ oxidation state is active during the liquefaction reaction.     

Mössbauer spectroscopy study of the chemical state of iron in Danish Mesozoic sediments

The chemical state of iron in sediments from six wells in the Danish North Sea and the Danish land area has been studied by use of Mössbauer spectroscopy. It was found that iron was mainly present in pyrite, clay minerals and the carbonates siderite and ankerite. The relative amounts of iron in different minerals have been determined as a function of depth in the wells. A comparison of the results with available data for source rock maturity suggests that there may be a correlation between the presence of ankerite and the formation of oil and gas in the sediments.     

Origin of the uniaxial magnetic anisotropy in cobalt ferrite induced by spark plasma sintering

Cobalt ferrite (CFO) is a promising candidate for magnetostrictive applications like actuators or sensors. We have recently shown that uniaxial magnetic anisotropy can be induced in CFO by reactive sintering using spark plasma sintering (SPS), which leads to an improvement of its magnetostrictive properties. However, the origin of the anisotropy and the formation mechanism remain unexplained so far. In this study, different SPS processes have been conducted to determine which parameter is responsible for the induced uniaxial anisotropy. We demonstrate that the magnetic anisotropy arises during the cooling step when done under SPS’s uniaxial compression. In addition, we also investigate the fundamental origin of the magnetic anisotropy induced during the SPS process. We show that the polycrystalline anisotropic cobalt ferrite obtained after SPS exhibits no texture. However, the SPS samples turn isotropic after being annealed in air at 400 °C/2 h, as shown by magnetic and magnetostrictive measurements. A change in ionic distribution after the annealing is also observed by Mössbauer spectroscopy. Our findings suggest that the induced magnetic anisotropy results from the ionic distribution of the Co²⁺ in the CFO’s spinel lattice, a mechanism previously observed in magnetic annealed CFO. This study advances the in-depth understanding of the relationship between SPS processing and magnetic properties of cobalt ferrite.     

Electrochemical behavior and anticorrosion properties of modified polyaniline dispersed in polyvinylacetate coating on carbon steel

Conducting polyaniline (Pani) was prepared in the presence of methane sulfonic acid (MeSA) as dopant by chemical oxidative polymerization. The Pani-MeSA polymer was characterized by FT-IR, UV-vis, X-ray diffraction (XRD) and impedance spectroscopy. The polymer was dispersed in polyvinylacetate and coated on carbon steel samples by a dipping method. The electrochemical behavior and anticorrosion properties of the coating on carbon steel in 3% NaCl were investigated using open-circuit potential (OCP) versus time of exposure, and electrochemical techniques including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic voltammetry (CV). During initial exposure, the OCP dropped about 0.35 V and the interfacial resistance increased several times, indicating a certain reduction of the polymer and oxidation of the steel surface. Later the OCP shifted to the noble direction and remained at a stable value during the exposure up to 60 days. The EIS monitoring also revealed the initial change and later stabilization of the coating. The stable high OCP and low coating impedance suggest that the conducting polymer maintains its oxidative state and provides corrosion protection for carbon steel throughout the investigated period. The polarization curves and CV show that the conducting polymer coating induces a passive-like behavior and greatly reduces the corrosion of carbon steel.     

Mössbauer study of the black-glazed Jian bowl in the Song dynasty

Jian ware, also known as “Tenmoku,” is one of the famous black-glazed porcelains in China. It was highly coveted in the Song dynasty (960–1279 AD) and was also a tribute to the royal family. The black-glazed Jian wares are mainly made from iron-rich clay. In this study, black-glazed Jian bowl sherds excavated from the Song strata of Jian kiln sites were adopted as test samples. The iron phase and firing techniques of the black-glazed Jian bowl from the Song dynasty were analyzed and discussed through Mössbauer spectroscopy on the both of body and glaze, together with X-ray diffraction and scanning electron microscopy. According to the different iron content and the unique iron oxide phase reflected in the Mössbauer spectra, we analyzed the firing atmosphere, temperature, and other conditions of the ancient Jian bowl, as well as the difference of iron phase between the body and the glaze layer due to the collapse of the silicate framework. It provides new ideas for deciphering the firing technology and improving the synthesis of ancient black-glazed Jian wares.     

Spinel ferrites NiFe2O4 NCs enhanced Mössbauer spectra,magnetization and Faraday rotation of diamagnetic tellurite glasses

Glass containing magnetic nanocrystals are attractive for obtaining high magnetic and magneto-optical properties. In this study, for the first time, 10 nm cubic NiFe₂O₄ (NFO) nanocrystals doped heavy metal oxide glasses were fabricated and the influence of NFO to glass structure, chemical bonds, Mössbauer spectra, magnetization and Faraday rotation was studied. X-ray diffraction, Raman and X-ray photoelectron spectra revealed the existence of multi-valence states of Fe/Ni ions, oxygen vacancies in cubic lattice and modifications on glass structure, which in turn adjusted the polarizability, oxygen packing density, Mössbauer spectra, magnetic property and magneto-optical behaviors. Through Mössbauer study, the increase of NFO amount enhanced the hyperfine field intensity of tetrahedral Fe³⁺ ions at the expense of octahedral ones. NFO doped glasses exhibited ferromagnetic behavior whose M_s and H_c increased with the NFO amount due to the NCs size effect. Verdet constant and Faraday rotation angle were studied as function of wavelength, magnetic field, polarizer angle and NFO amount. 3%NFO glass exhibited significant enhancement in magnetization and Verdet constant of 91 rad/T.m at 633 nm which is 5-fold of host glass and superior than literatures. In addition, due to the nanoscale NCs, the thermal stability of obtained NFO glasses remained higher than 100 °C which is promising for photonics devices fabrication.     

Investigation of cation distribution and magnetocrystalline anisotropy of NixCu0.1Zn0.9−xFe2O4 nanoferrites: Role of constant mole percent of Cu2+ dopant in place of Zn2+

Co-precipitated and 800 °C heat treated Ni-Cu-Zn nanoferrites with chemical formula Ni_xCu_0.1Zn_0.9-xFe₂O₄ (x=0.5, 0.6, 0.7) were prepared because of their potential use as multilayer chip inductors in electromagnetic applications. Their structural, magnetic properties and phase formation were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FE–SEM), vibrating sample magnetometer (VSM), Mössbauer spectrometer, thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The XRD patterns confirm the cubic spinel structure of the ferrite phase belonging to Fd3m space group. Lattice parameters and cation distributions were obtained by Rietveld refinement of the XRD patterns. The lattice parameter decreases with increase in Ni²⁺ ion concentration. Rietveld analysis indicates that Cu²⁺ ions predominantly occupy the B-sites and Ni²⁺ ions partly going into B-sites but predominantly into A-sites. An excellent agreement is observed between the experimental lattice parameters and lattice parameters theoretically calculated using this cation redistribution. The inversion parameter (λ) observed for Fe³⁺ ions by Mössbauer spectroscopy is different from that of Rietveld analysis. Magnetization and Mössbauer spectroscopic measurements indicate that the ferrite nanoparticles are mostly superparamagnetic. The cation redistribution is supposed to alter the magnetocrystalline anisotropy which in turn affects the magnetic parameters of the present ferrite samples. The reduced magnetization is attributed to core-shell interactions and possible canting of A- and B-shell magnetizations. TGA-DSC studies indicate that ferrite formation in the 800 °C heat treated samples is completed but grain growth increases as the particles are subject to the increased temperature.     

Dynamics of hydrated iron(II) cations in nafion polymer membranes

Mössbauer studies of Fe²⁺ in water-soaked nafion polymer membranes in the temperature range between 90 K and 250 K have been performed. Above a critical temperature (～ 180 K) the spectra exhibit both elastic narrow absorption lines and quasielastic broad lines. These spectra are typical of bounded diffusion phenomena observed by Mössbauer spectroscopy in macromolecular systems like haemoglobin, myoglobin and ferritin. Similar spectral shapes have been observed by quasielastic neutron scattering from water in nafion membranes. Within 50 K above the critical temperature the total Mössbauer absorption area decreases by an order of magnitude whereas the narrow absorption line decreases by two orders of magnitude. The results are interpreted in terms of bounded diffusive motion of the iron. Using a model based on overdamped harmonically bound Brownian motion, the essential parameters of the iron motion can be derived as a function of temperature. The iron motion most probably reflects the motion of a large Fe²⁺ complex, e.g. Fe(H₂O)²⁺₆, which is attached to the polymer side chains via the sulphonic group.     

Synthesis,thermal stability and unknown properties of Fe1–xAlxVO4 solid solution

A continuous solid solution Fe_1-xAl_xVO₄ was synthesized by conventional ceramic method and characterized by DTA, XRD, IR, UV–vis/DRS and Mössbauer spectroscopy. Fe_1-xAl_xVO₄ crystallizes in a triclinic system and is isostructural with FeVO₄ and AlVO₄. With increasing content of Al³⁺ ions substituted for Fe³⁺ in the matrix structure of FeVO₄ a contraction of crystal lattice was observed, accompanied by shifts of IR absorption bands towards higher wavenumbers and shifts of UV absorption bands towards shorter wavelength. On the basis of the results of UV–vis investigations, the band gap energies were calculated. The solid solution sample of composition Fe_0.67Al_0.33VO₄ was found to have the highest melting point from among all examined samples, which equals to 870?°C. Moreover, the solid product of incongruent melting of Fe_1-xAl_xVO₄ for 0.75?>?x?≥?0.5 is Fe_1-xAl_xVO₄ solid solution, richer in iron. On the grounds of Mössbauer investigation, the partition of iron and aluminum ions over three accessible crystallographic sites was established. Fe_0.5Al_0.5VO₄ sample was successfully used as a reactant for Fe₄Al₄V₁₀W₁₆O₈₅ preparation.     

Tuning of ferrimagnetic nature and hyperfine interaction of Ni2+ doped cobalt ferrite nanoparticles for power transformer applications

Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni²⁺ substitution effect in Co_1-xNi_xFe₂O₄ (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni²⁺ concentration. The M-H loops reveals that saturation magnetization(M_s), coercive field(H_c) remanence magnetization(M_r) and magnetron number(η_B) decreases significantly with increasing Ni²⁺ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(H_c) is found strongly dependent on the concentration of Ni²⁺ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni²⁺ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application.     

Synthesis of coral-shaped yttrium-aluminium-iron garnets by solution-combustion method

Aluminium substituted yttrium-iron garnet (Y₃Al_xFe_5?xO₁₂, x = 0, 1, 2, 3, 4 and 5) powders were synthesized by solution combustion route followed by calcination at 1000 °C for 6 h. According to the X-ray diffraction (XRD) results, the as-prepared samples were amorphous. Calcination of the samples at 1000 °C for 6 h results in the formation of phase pure (Ia$\stackrel{?}{\mathit{3}}$d) garnet structure. The morphology of the samples (for all compositions) were found to be coral-network-like. The Rietveld refinement of the XRD patterns and the Mössbauer spectroscopy confirmed that Y³⁺ ions occupy the dodecahedral site, whereas Al³⁺ and Fe³⁺ ions are distributed in the tetrahedral and octahedral sites of the bcc (Ia$\stackrel{?}{\mathit{3}}$d) structure of the garnet phase. The Al³⁺ ions have a preference to occupy the octahedral site. The lattice parameter decreases with increase in Al-content due to the small size of the Al³⁺ cations. For the yttrium-iron-garnet (YIG) sample (x = 0), a saturation magnetization (M_S) value of ~ 29 emu/g was obtained, which decreases to ~ 7 emu/g for the sample with x = 2. Further addition of Al makes the garnets paramagnetic. The coral network shape of our garnet samples renders them useful for various applications in catalysis.     

Investigation of structural,optical and magnetic properties of thermal plasma synthesized Ni-Co spinel ferrite nanoparticles

Magnetic nanoparticles of nickel substituted cobalt ferrites, Ni_xCo_1−xFe₂O₄, (x=0 to 1 in the step of 0.2) were successfully synthesized by gas phase nucleation and growth process. For the first time, we report feasibility of synthesizing such mixed ferrite system using thermal plasma route. Further, effect of change in molar ratio of Co:Ni on the structural, optical and magnetic properties has been investigated in detail. The structural and phase formation analysis of the samples under investigation have been carried out using powder X-ray diffraction and Raman spectroscopy. The surface morphology of these particles has been studied using scanning electron microscopy and the micrographs so obtained were used to find out average gain size and size distribution. The optical and magnetic properties of the as synthesized samples were finally correlated with the magnetic moment of substituted species such as Ni for Co and cation distribution, analyzed using Mössbauer spectroscopy. Special modification in Thermo Gravimetric Analyzer was used to determine magnetic transition temperature.     

Investigation of structural,magnetic and Mössbauer properties of Co2+ and Cu2+ substituted Ni–Zn nanoferrites

We investigated the effects of Co²⁺ and Cu²⁺ substitution on the super-exchange interactions in Ni–Zn nanoferrites. The cation distribution technique was taken into account to explain the results. To authenticate the cation distribution, we have estimated the cation distribution in the light of X-ray diffraction method, Mössbauer spectroscopic analysis, and magnetization study. Statistical model based on the cation distribution was used to calculate the Curie temperature. The values of magneton number n_B and Curie temperature T_C calculated by using the cation distribution is found to be in agreement with the experimentally obtained values.