Diffusion Coefficients Of Mn Research Articles

Transition from Internal to External Oxidation of Mn Steel Alloys

The transition from internal to external oxidation of Mn-steels depends on temperature, oxygen partial pressure or dew point and alloy composition. A description for this transition includes, besides the diffusion coefficients of Mn and oxygen, also on the critical volume fraction oxide precipitates. This volume fraction for Mn-steel alloys has been determined experimentally and equals 0.2, whereas usually a value of 0.3 is adopted. A low critical volume fraction oxide implies that the alloy is more prone to external oxidation. Oxidation experiments with 1.7, 3.5 and 7.0 wt% Mn-steel alloys at 950 °C, i.e. in the austenitic region, at different oxygen partial pressure or dew points in the range of −45 to +10 °C showed excellent agreement with the oxidation mode predicted using the data obtained for the diffusivities and critical volume fraction oxide.

Simulation of Intercritical Austenization of a C-Mn Cold Rolled Dual Phase Steel

Formation of austenite strongly influences the microstructures and mechanical properties of dual phase steels. In present work, austenization process during intercritical annealing was studied in a Fe-C-Mn steel using Gleeble-1500 thermal simulator and quantitative microscopy. The experimental results show that austenite formation is separated into three different stages: (i) growth of high carbon austenite into pearlite rapidly until pearlite dissolution is completed; (ii) slower growth of austenite into ferrite; (iii) very slow equilibration between ferrite and austenite. The thermodynamic and kinetic analyses show that growth of austenite into ferrite is controlled by carbon diffusion in austenite in the primary stage and manganese diffusion in ferrite in the subsequent stage because diffusion coefficient of Mn in ferrite is several orders of magnitude smaller than that of C in austenite. The slow final equilibration between ferrite and austenite is obtained by manganese diffusion through the austenite. Based on the analysis, one dimensional diffusion model of intercritical austenization was developed and solved using finite volume method on the assumption that solute flux was local balance at interface, and the kinetics calculated was compared with experimental results. Simulated results indicate that growth of austenite reaches paraequilibrium in about one second, but remains thousands of seconds to reach final equilibrium. Simulated concentration profiles show that manganese atoms transferred from ferrite congregate in austenite near phase interface, which is consistent with the experimental phenomenon.

Electrochemical preparation of Fe–Mn alloy film in organic bath

Fe–Mn alloy films have been prepared by electrodeposition in an organic bath containing FeCl 2 + MnCl 2 in dimethyl formamide. The electroreduction of Mn(II) was irreversible and the diffusion coefficient of Mn(II) was calculated to be 8.0 × 10 − 11 m 2 s − 1 at 298 K. An amorphous film of Fe–Mn was obtained by potentiostatic electrolysis. The Mn content varied from 4.8 at.% to 72.3 at.% with increase in the applied cathodic potential. Scanning electron microscope investigation showed that the deposited film was homogeneous and consisted of spherical particles. Nano-sized pores were observed in the surface of these particles. After heat treatment at 773 K, large crystal grains formed and X-ray diffraction patterns indicate that solid solution of Mn in γ-Fe occurred. The alloying temperature of the Fe–Mn film was determined to be 1013 K using differential thermal analysis.

In-situ observation of the precipitation of manganese sulfide in low-carbon magnesium-killed steel

The in-situ observation of MnS precipitation was made on cooling using a confocal laser microscope. It was found that two types of precipitates appeared at the different temperatures. The first type precipitated at the nucleation sites of MgO or MnO-TiOx inclusions in γ-Fe in the temperature range between 1500 and 1200 K. The shape was triangular or rodlike, and the size was between 1 and 5 µm. The second type of MnS drastically precipitated in α-Fe at 1100 K just after the Ar3 transformation. The shape was triangular or polygonal, and the size was between 0.1 and 0.5 µm, much smaller than that of the first type. No significant precipitation was observed in the intermediate temperature range between 1200 and 1100 K. The reasons why MnS precipitation took place twice at the different temperature ranges and why no precipitation occurred between the two temperature ranges were discussed from the thermodynamic and kinetic viewpoints. The diffusion coefficients of Mn in γ-and α-Fe and the supercooling are the key factors which explain the reason.

Phase Transformation of Yttria-Stabilized Zirconia (3 mol% Y<SUB>2</SUB>O<SUB>3</SUB>) in Fuel Cell Caused by Manganese Diffusion

The diffusion coefficient of Mn in yttria-stabilized zirconia (YSZ, 3 mol%Y 2 O 3 ) and the structural change in YSZ have been investigated. The diffusion coefficients of Mn were determined to be 7 x 10 -14 m 2 /s at 1573 K and 2 x 10 -13 m 2 / at 1673 K by analyzing the concentration profiles of Mn in YSZ/Mn 3 O 4 diffusion couples. The solubilities of MnO x were 7.4 mol% and 7.6 mol% at 1573 and 1673 K, respectively. Remarkable grain growth was observed on the YSZ side near the interface. The dissolution of MnO x almost up to the solubility limit of 7.6 mol% resulted in grain growth and the phase transformation from the tetragonal phase to the fluorite-type cubic phase. These results were discussed by comparing with the previous studies on the ZrO 2 -Y 2 O 3 -MnO x ternary system and on the ZrO 2 -MnO binary system.

Electrochemical characteristics of the Mn(iii)/Mn(ii) and Co(iii)/Co(ii) systems at platinum in anhydrous acetic acid solutions

The electrochemical oxidation of Mn(ii) and Co(ii) and reduction of Mn(iii) and Co(iii) at Pt in glacial acetic acid has been investigated by the rotating disc electrode technique. The diffusion coefficients of Mn(iii), Mn(ii), Co(iii) and Co(ii) ions, formal potentials and kinetic parameters of the Mn(iii)/Mn(ii) and Co(iii)/Co(ii) electrode reactions were evaluated. It was shown that the anodic oxidation of Mn(ii) and Co(ii) occurs at the surface blocked by a layer of adsorbed acetate ions. In addition, some experiments with an electrochemical quartz crystal microbalance (EQCM) were performed to explain the acetate adsorption on the surface of the polycrystalline platinum electrode.

Homogeneity examination of a disordered magnetic alloy by means of CEMS

The depth sensitivity of the Mossbauer effect conversion electron spectroscopy (CEMS) offers a possibility to check the homogeneity of an alloy as a function of the sample thickness. We present experimental results on (Fe0.65Ni0.35)1-xMnx (x=0.026) prepared by diffusion of Mn into a Fe0.65Ni0.35 foil. On an inhomogeneous sample we determined the diffusion coefficient of Mn in Fe0.65Ni0.35 at 1300 K to be about 10−11 cm2/s.

Interdiffusion of Mn in austenitic and ferritic CrNi steels

AbstractThe interdiffusion coefficients of Mn have been obtained in different austenitic and ferritic CrNi‐steels between 1000 and 1300 °C using Boltzmann‐Matano and Grube methods. The diffusion coefficients of Mn (≦ 2 wt%) were found to be independent on its concentration. Small variations in Cr and Ni contents in both types of steels showed neglegible effect on manganese diffusion. The interdiffusion results in austenitic steels are comparable with the Mn tracer diffusion in Type 316 steel. The results of diffusion of manganese in ferritic CrNi steels reported here are first to be published.

Manganese and germanium redistribution in In0.53Ga0.47 As grown by molecular beam epitaxy

The redistribution of Mn in MBE grown In0.53Ga0.47 As layers containing different combinations of Mn and Ge doping pulses and subjected to various annealing conditions has been studied by secondary ion mass spectrometry (SIMS). The results indicate that Ge has a negligible diffusivity for temperatures up to 700 °C while the diffusion coefficient of Mn is approximately inversely proportional to the local Mn concentration. Accumulation of Mn in amounts proportional to the local Ge concentration has also been observed, suggesting the formation of donor–acceptor pairs with a certain fraction of Ge in the crystal. For those Mn atoms not immobilized by pairing, the diffusion coefficient is found to be reduced by nearly two orders of magnitude by the presence of Ge in the layer with very little dependence on the spatial distribution of Ge.

The voltammetric behaviour of the Mn 2+, Mn 3+, Mn 4+ system in 15 N H 2SO 4 on a smooth platinum microelectrode

The voltammetric behaviour of Mn 3+, Mn 4+ and mixtures of these ionic species in 15 N H 2SO 4 on a smooth platinum micro-electrode with periodical renewal of the diffusion layer shows that the reduction occurs through the electro-active couple Mn 2+, Mn 3+. The value of the electron-transfer coefficient α relative to the electrode process Mn 3+ + e ⇌ Mn 2+ has been determined together with the diffusion coefficients of Mn 2+, Mn 3+ and Mn 4+.