Zur anodischen auflösung von reineisen im bereich zwischen aktivem und passivem verhalten

The kinetics of anodic iron dissolution in sulphate ions containing solutions, which are free of oxygen, are investigated in a over potential range between active and passive states of the metal. The measurements were carried out on a rotating disk electrode in the pH-range between 3·5 and 5·5 using the potentiostatic triangular voltage sweep method under quasi-steady-state conditions. The measured current density-potential curves show two current maxima. At relatively low anodic overvoltages, i.e. before the maxima I is reached, the used recrystallized iron dissolves in the active state corresponding to the consecutive (Bockris-) mechanism. At high anodic overvoltages the passive state arises after passing the maxima II. In the transition range, i.e. in the potential range of the maximum I, a second mechanism of iron dissolution is discussed. This mechanism takes place parallel to the consecutive one. An intermediate [Fe (OH)₂]_ads will be formed, which dissolves in a following rate-determining chemical step or is changed in an oxide phase respectively.     

Mössbauer spectroscopy of interfaces in metals

Publications on the studies of interfaces in metals by the methods of Mössbauer (nuclear gammaresonance) spectroscopy are reviewed. Physical principles of the Mössbauer effect, various methods of nuclear gamma-resonance (NGR) spectroscopy and the Mössbauer spectra parameters are considered. The available results on grain boundary studies in coarse-grained and nanostructured materials and on interlayer interfaces in multilayers are analyzed. Capabilities of application of absorption and emission Mössbauer spectroscopy as well as of conversion electrons Mössbauer spectroscopy (CEMS) are discussed.     

Time-resolved Förster energy transfer in polymer blends

Sub-picosecond spectroscopy and pump–probe experiments show Förster energy transfer in blends from larger gap (blue or green-emitting) host polymers poly(2,3-diphenyl-5-hexyl-1,4-phenylenevinylene) (DP6-PPV) or poly[2-(meta-2′-ethylhexoxyphenyl)-1,4-phenylenevinylene) (m-EHOP-PPV) to the smaller gap, red-emitting guest polymer poly(2,5-bis(2′-ethylhexoxy)-1,4-phenylenevinylene) (BEH-PPV). The dynamics of the stimulated emission (SE) and photoinduced absorption (PA) of the blends indicate that 10–20 ps are required for complete energy transfer. Quantitative measurements of energy transfer rates give a Förster interaction range of 3–4 nm, 1.4 times longer than the theoretical values as calculated from the spectral overlap. We attribute this difference to delocalization of the excited state. Insufficient spectral overlap between the emission of the host and absorption of the guest is shown to be the cause for the absence of energy transfer in a blend with poly(2,5-bis(cholestanoxy)-1,4-phenylenevinylene) (BCHA-PPV) as the guest polymer.     

Mechanismus Der Lochfrasskorrosion Von Eisen In Perchloratlösungen

It has been shown by means of measurements of iron pitting in water and alcohol solutions that the pit bottom potential is higher than that corresponding to the active part of the polarization curve and that the solution mechanism of the metal in the active zone varies considerably from that at points in the pitting.     

凸形多面体个体晶粒的三维von Neumann准确方程

由晶粒长大过程的曲率驱动本质出发,以不同于MacPherson和Srolovitz的方法,推导出凸型多面体晶粒的三维vonNeumann关系式,无任何其他形状假设及晶粒尺寸分布或拓扑分布要求.在应用于凸型多面体晶粒时,本文结果与MacPherson和Srolovitz给出的结果完全一致.对于凸型多面体晶粒,三维个体晶粒长大速率是品粒平均切直径和晶粒棱总长度的函数,符合Kinderlehrer指出的n维体积的变化速率仅与胞的(n-2)维特征量有关的规律.     

A Mössbauer spectroscopy study of Fe based cemented carbides

Mössbauer spectroscopy has been used as a novel characterization technique to investigate Fe charge states, Fe complexes and hyperfine interaction parameters of different phases in WC-10Fe and WC-10(FeNi) materials sintered at three different temperatures (1350, 1430 and 1510 °C). The materials were characterized using standard cemented carbide quality control, and spectroscopic techniques to evaluate the structural changes and magnetic effects of the binder. The WC-10Fe grade had the highest Vickers hardness ranging from 1282 to 1320 HV₃₀, for the different sintering temperatures. X-ray diffraction data showed the presence of WC and the metal binder phase, α-Fe and γ-FeNi. Transmission Mӧssbauer spectroscopy spectra obtained for the milled powders revealed only the α-Fe phase with a hyperfine magnetic field, B_hf ~33 T. Conversion electron Mössbauer spectroscopy on the sintered compacts revealed the presence of multiple fields, suggesting the possibility of minor phases present in the binder which were not detected using X-ray diffraction. The corresponding spectra for the sintered WC-Fe grades exhibited two magnetic fields with hyperfine parameters of ~33 T and ~17 T, respectively. These fields were assigned to α-Fe with some W atoms in solution and a W-rich Fe phase, respectively. The Mӧssbauer spectrum for the FeNi binder sample at the lowest sintering temperature of 1340 °C showed a paramagnetic doublet with an isomer shift, δ = −0.08 mm/s and electric quadrupole splitting, ∆E_Q = 0.00 mm/s and a weak hyperfine magnetic field, B_hf = 15.7 T. The doublet has been assigned to γ-FeNi and the magnetic component to a W-rich γ-FeNi phase. For the higher sintering temperature, a distribution of magnetic fields (~33 T, 25 T and 9 T) was evident in the Mössbauer spectrum. These magnetic fields were tentatively assigned to multiple W-rich γ-FeNi phases.     

Mössbauer studies of the thermal stability of layered metallic systems

Methods of Mössbauer spectroscopy at ⁵⁷Fe nuclei and X-ray diffraction analysis have been used to investigate layered systems Fe (5 μm)-Zr (2 μm) and Fe_0.966Ti_0.034(13 μm)-Ti (1 μ)-⁵⁷Fe(0.8 μm) obtained by the method of ion-plasma deposition and subjected to sequential isothermal annealings at T = 900 and 650°C, respectively. The relative content of phases that are formed in the systems at each stage of annealing has been established and the sequence of transformations and their kinetics have been determined. For both systems, thermal stabilization of the structural and phase state, which is inhomogeneous in depth, has been observed.     

Copper smelting in Boliden’s Rönnskär works described

As much of the production as possible in Ronnskar works is handled during the day shift. This requires three times as large furnaces and casting machines as three shifts and involves a considerable outlay of capital, but the labor force is reduced approximately two thirds with production costs decreased to a corresponding degree.     

Mössbauer probe spectroscopy studies of initial stage of Al-Fe mechanical alloying

The initial stage of mechanical alloying (MA) in a binary mixture of powdered Al and ⁵⁷Fe in an atomic ratio of 99: 1 has been studied using X-ray diffraction and ⁵⁷Fe Mössbauer probe spectroscopy. The proposed microscopic model of MA includes the formation of a nanostructured state (～15 nm) in FCC Al, the penetration of Fe atoms across Al grain boundaries, and the formation of isolated Fe atoms and Fe-Al clusters in boundary distorted zones of Al matrix interface similar to the local atomic environment in deformed Al₆Fe and Al₉Fe₂ phases. Based on the published data, it is assumed that with increasing Fe concentration in the initial mixture, and, correspondingly, increasing amount of clusters, distorted FCC interface regions are transformed into amorphous phase.     

TbRhSn and DyRhSn – Detailed magnetic and 119Sn Mössbauer spectroscopic studies

The results of magnetic studies and Mössbauer spectroscopic investigations are reported for the stannides TbRhSn and DyRhSn crystallizing in the hexagonal ZrNiAl-type structure. The polycrystalline samples of these ternary intermetallics were synthesized by arc melting from metallic precursors. Detailed ¹¹⁹Sn Mössbauer spectroscopic studies are used to investigate the hyperfine interactions and their temperature evolutions at places occupied by the diamagnetic tin nuclei. Magnetic properties of DyRhSn and TbRhSn were studied by AC/DC magnetometry in a wide temperature range. The results show that both compounds are magnetically ordered at low temperatures. DyRhSn is a non-collinear antiferromagnet with the Néel temperature T_N = 7.5 K, whereas TbRhSn undergoes a transition from a paramagnetic to an antiferromagnetic state at T_N = 20.2 K. An additional transition at T_SR = 10.3 K is detected for TbRhSn which corresponds to some changes in the magnetic moments ordering. The role of the magnetostriction effect in the evolution of the hyperfine parameters and its influence on the observed TbRhSn Mössbauer spectra is discussed. Triangular-like antiferromagnetic arrangements with rare-earth magnetic moments lying in the hexagonal plane are proposed for both compounds at very low temperatures.     

Estimation of magneto-crystalline uniaxial anisotropy constant of β-FeOOH by Mössbauer spectroscopy

The magneto-crystalline uniaxial anisotropy constant, K_u, of β-FeOOH was estimated by analyzing temperature dependence of Mössbauer absorption spectra taking into account the thermal relaxation of the internal magnetic fields. It was deduced to be 2.1 × 10³ J/m³, using a typical volume (9 × 10^?24 m³) of synthesized β-FeOOH particles observed by TEM. The value, K_u of β-FeOOH is in the same order but twice as large as that of α-FeOOH, 1 × 10³ J/m³.     

Mössbauer study and thermodynamic modeling of Fe–C–N alloy

Mössbauer spectroscopy and Monte Carlo computer simulation have been combined to understand the reason for the solid-solution stability of Fe–0.93 C–0.91 N alloy (mass%). Interstitial concentrations in austenite and ferrite were determined on the basis of X-ray diffraction measurements of the lattice dilatation. The hyperfine structure of Mössbauer spectra was analyzed to identify different atomic configurations in solid solutions and determine their fractions. Thereafter Monte Carlo simulation of the interstitial distribution in ferritic and austenitic solid solutions was performed, and values of the interstitial–interstitial interaction energies were obtained for the first and second coordination spheres in austenite and the first to the fourth coordination spheres in ferrite. Simulation shows that in both austenitic and ferritic phases the interaction of interstitial atoms is characterized by a strong repulsion within the first two coordination spheres. Experimental data and simulated interstitial distributions are consistent and complementary. It is concluded that the absence of interstitial clusters prevents carbide and nitride precipitates and causes the higher thermodynamic stability of Fe–C–N solid solutions as compared with Fe–C and Fe–N ones.     

Emission Mössbauer spectroscopy of nanocrystalline gold produced by the method of gas condensation

Grain boundaries in nanocrystalline gold produced by the method of gas condensation and subsequent compacting have been investigated on ⁵⁷Co(⁵⁷Fe) nuclei using emission Mössbauer spectroscopy. It has been found that, in the structure there are present two types of boundaries whose properties differ appreciably, i.e., nanograin boundaries and agglomerate boundaries.     

Mössbauer investigation of Sn diffusion and segregation in grain boundaries of polycrystalline Nb

The parameters of nuclear γ resonance (Mössbauer) spectra on ^119mSn nuclei inserted into grain boundaries of polycrystalline Nb have been determined at the annealing temperatures of 680 to 994 K [0.25–0.36 melting temperature (T _m)]. Two components are observed in the nuclear emission γ resonance spectra at all of the annealing temperatures considered. One of them (component 1) is suggested to result from the ^119mSn atomic probes localized in grain boundary cores, while the other one (component 2) corresponds to that located in the near-boundary areas. Diffusion annealing temperature dependences of both components parameters have been analyzed. The coefficients and enthalpy of Sn grain-boundary segregation are determined based on this analysis, as well as the ratio of the diffusion pumping zone extension to the grain boundary width and the enthalpy of the atomic probes “pumping” from grain boundaries into the bulk.     

Enhancement of light harvesting in dye-sensitized solar cells by using Först-type resonance energy transfer

The improvement of solar energy-to-electricity conversion efficiency has continued to be an important research area for various solar cell devices. The fluorescence material was adsorbed on the TiO₂ photo-electrode with sensitizers in dye-sensitized solar cell (DSSC) to enhance the photon-to-current efficiency. The improved light harvesting efficiency which was achieved by the judicious choice/design of fluorescence material and sensitizing dyes enhances the photovoltaic performance of the DSSCs with the Först-type resonance energy transfer (FRET). The energy acceptor (N719) should absorb the fluorescence emitted from the energy acceptor on the photo-electrode surface which could enhance the light harvesting property of sensitizer in DSSC. We achieved the significant enhancement of short circuit current density (J _sc ) in DSSC by the FRET system on the photo-electrode surface. The photovoltaic performance of DSSCs containing FRET system was observed with I-V curve and incident photon-to-current efficiency. The electrical property and electron life time of DSSC was measured by using the impedance measurement method.