Ferrite Solid Solution Research Articles

Improved methodologies for the determination of high temperature phase equilibria

Improved methodologies for the investigation of the phase equilibria and thermodynamic properties have been developed based on the interactive combination of experimental investigation and thermodynamic modelling. The experimental technique involves high temperature equilibration, quenching and electron probe microanalysis. The computer thermodynamic modelling of oxide systems has been carried out using the computer system FACT. The general aspects of the quenching experimental technique with electron probe microanalysis are discussed and the advantages of using the electron probe X-ray microanalysis (EPMA) over conventional quenching techniques are highlighted. The effectiveness of the research approach is illustrated with experimental results on lead silicate glasses, zinc ferrite solid solutions and the complex oxide system PbO-ZnO-FeO-Fe2O3-CaO-SiO2.

An atom-probe investigation of some correlated phase transformations in Cr, Ni, Mo containing supersaturated ferrites

At 300–400°C aged ferrite of duplex stainless steels may undergo complex demixing processes which depend on the alloying element nature and content. In addition to the spinodal decomposition of the δ ferrite solid-solution into α (Fe-rich) and α′ (Cr-rich) domains, which characterizes the unmixing process, variations in the alloying element content lead to a more or less important precipitation of an intermetallic G-phase. For a given Cr-content, at least four elements (C, Si, Ni and Mo) induce a particular sensitivity to G-phase precipitation. Two duplex stainless steels, the ferrite of which exhibits almost the same C, Si and Cr but different Ni and Mo contents have been carefully studied by atom probe. Because of its high spatial resolution, the atom probe is an attractive tool for the investigation of the fine-scale spinodal decomposition and precipitation process. In order to get both reliable chemical and spatial information, technical improvements as well as refinements in the statistical analysis of the experimental data were implemented. Characterization of both the spinodal decomposition and G-phase precipitation was carried out. Pertinent microstructural aging parameters were defined in such a way as to follow both kinetics. The investigations we conducted, demonstrate that G-phase precipitation is induced by the spinodal decomposition of the ferrite phase. The influence of Ni and Mo contents on G-phase precipitation is discussed.

Aging at 400–600°C of submerged arc welds of 22Cr–3Mo–8Ni duplex stainless steel and its effect on toughness and microstructure

AbstractSubmerged arc welds of a 22Cr–3Mo–8Ni (wt-%) duplex stainless steel were aged in the temperature range 400–600°C to simulate stress relieving conditions of mild steel. Particular attention was paid to the relationship between toughness and microstructure. It was concluded that sufficient toughness could be obtained on aging in the range 500–550°C provided that the aging time did not exceed 10 h. At temperatures >550°C, rather rapid embrittlement occurred as a result of the precipitation of essentially R phase and to some extent π phase. At ~≤500°C, spinodal decomposition of ferrite caused embrittlement, albeit more slowly than the precipitate induced embrittlement. Precipitation of the Mo rich phases Rand π was found to cause depletion of Mo in solid solution in ferrite. This offers a possible explanation for the decrease in pitting corrosion resistance observed in previous work.MST/1426

Quantitative X-ray diffraction analysis of high alumina cements

The knowledge of the exact phase composition of high alumina cements is very important for both the cement production process and the development of new cement types. The most suitable method for its determination seemed to be the X-ray powder diffraction. For more wide ranging and reliable applicability, synthetic sintered clinker minerals were used. Silicon served as the internal standard. Calibration curves were fitted for several reference peaks of a large number of phases: CA 2, CA, C 12A 7, α-corundum, C 2AS and four members of the ferrite solid solution. With the aid of the elaborated method, control tests were carried out for a number of industrial clinkers. Based on these results, and taking into consideration the chemical composition, the procedure was slightly corrected.

Reply to the discussion by S. Chatterji of the paper “hydration of mixtures of C 12A 7 and granulated blastfornace slag”

The knowledge of the exact phase composition of high alumina cements is very important for both the cement production process and the development of new cement types. The most suitable method for its determination seemed to be the X-ray powder diffraction. For more wide ranging and reliable applicability, synthetic sintered clinker minerals were used. Silicon served as the internal standard. Calibration curves were fitted for several reference peaks of a large number of phases: CA2, CA, C12A7, α-corundum, C2AS and four members of the ferrite solid solution. With the aid of the elaborated method, control tests were carried out for a number of industrial clinkers. Based on these results, and taking into consideration the chemical composition, the procedure was slightly corrected.

Equilibrium oxygen fugacity for the synthesis of zinc ferrite solid solutions

AbstractThermodynamic information is utilized to study the width of the zinc ferritemagnetite phase field, and to establish the oxygen fugacity in equilibrium with this solid solution. Information is provided for the specification of the phase boundaries and for the particular oxygen fugacity that corresponds to the 4/3 oxygen/ cation ratio in the strictly stoichiometric solid solution.

Kinetics of the dissolution of zinc-magnesium ferrites in sulphuric acid solutions related to zinc leach processes

The presence of sparingly soluble zinc and magnesium ferrites in roasted zinc concentrates can cause problems during leaching. This study aimed at the determination of the dissolution kinetics of zinc ferrite-magnesium ferrite solid solutions. The investigations have been performed for the (Zn 1− x Mg x )Fe 2O 4 powder specimens ( x = 0, 0.25, 0.50, 0.75 and 1) in solutions of 100–200 g/l H 2SO 4 at 323–363 K. Dissolution of all specimens has been found to be chemically controlled and homothetic, being described by the “unreacted-core shrinking” model. The dissolution rate constant of zinc ferrite was about seven times higher than that of magnesium ferrite (e.g. 3.83·10 −6 against 0.53·10 −6 mol/m 2s in 100 g/l H 2SO 4 at 363 K). The relation between rate constant and the x value was not linear. The activation energy was not dependent on the x value and amounted to ca. 75 kJ/mol. The results have important relevance to the “magnesium problem” often experienced in roach-leach processes in hydrometallurgy.

Microstructures, mechanical properties, and electrical resistivity of rapidly quenched Fe-Cr-Al alloys

By the rapid quenching technique, ductile supersaturated ferrite solid solution with high hardness and strength as well as unusual electrical properties has been found in Fe-Cr-Al ternary system. This formation range is limited to less than about 35 at. pct Cr and 23 at. pct Al. The ferrite phase has fine grains of about 10 μm in diameter. Their hardness, yield strength, and tensile fracture strength increase with increase in the amounts of chromium and aluminum, and the highest values reach about 290 DPN, 720 MPa, and 740 MPa. These alloys are so ductile that no cracks are observed even after closely contacted bending test. The good strength and ductility remain almost unchanged on tempering for one hour until heated to about 923 K where a large amount of Cr2Al compound begins to precipitate preferentially along the grain boundaries of the ferrite phase. The room-temperature resistivity increases with increasing chromium and aluminum contents and reaches as high as 1.86 μ Ώ m for Fe50Cr30Al20 alloy. Also, the temperature coefficient of resistivity in the temperature range between room temperature and 773 K decreases with increasing chromium and aluminum contents and becomes zero in the vicinity of 20 to 30 at. pct Cr and 15 at. pct Al. Thus, the present alloys may be attractive as fine gauge high-resistance and/or standard-resistance wires and plates because of the unusual electrical properties combined with high strength and good ductility.

Magnetic and electrical properties in the defect perovskite system La 1− xNa xFeO 3−δ

Magnetic and electrical properties were studied for the defect perovskite system La 1− x Na x FeO 3−δ. X-Ray diffraction showed that the materials with a composition range x = 0.0–0.25 were monophasic perovskite-like compounds with orthorhombic symmetry. The present ferrite solid solution showed a parasitic-ferromagnetic property, accompanying the antiferromagnetism. Values of both ferromagnetic moment and magnetic susceptibility increased with increase in Na content. Furthermore, the magnetization was strongly affected by oxygen partial pressure. These experimental facts seem to have a close relation with the oxygen vacancies. Electrical conductivity measurements suggested the presence of mixed valencies of Fe 3+ and Fe 4+ on a basis of the compositional dependence of the conductivity and its activation energy.

Thermal expansion of beta-alumina-type phases and variation of lattice parameters with potassium content

When polycrystalline potassium beta-alumina or potassium gallate were bonded to potassium ferrite by a hot pressing technique cracks appeared at the interface. This did not happen when they were bonded to equimolar potassium beta-alumina-potassium ferrite or potassium gallate-potassium ferrite solid solutions respectively. The suspected thermal expansion mismatch was confirmed by thermal expansion measurements which yielded values for potassium ferrite that were twice those for potassium beta-alumina or potassium gallate. Solid solutions gave intermediate expansion coefficients. When the potassium concentration in potassium ferrite was altered by coulometric titration the a hexagonal lattice parameter increased slightly with increase of potassium concentration while the c lattice parameter decreased. The implication of these factors on the preparation of stable solid solution electrode-solid electrolyte interfaces is discussed.

Quantitative determination of phases in high alumina cement clinkers by X-ray diffraction

The phase composition of high alumina cement clinkers may affect the strength development behaviour of concrete made from them and so a method of quantitatively determining these phases is needed. Quantitative X-ray diffraction using the adiabatic principle with auto flushing as proposed by Chung has proved to be a suitable method. For eleven cements produced in the UK during the period 1945 to 1975 the minerals identified were pleochroite, CA, C 12A 7, C 2AS, C 2S, CT, ferrite solid solution, FeO and CA 2. The proportions of these minerals were determined and tha major differences were in the amounts of CA and pleochroite present.

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.

The process of formation of magnesium-aluminum ferrite base solid solutions

The process of formation of magnesium-aluminum ferrite base solid solutions

Plastic anisotropy of low-carbon, low-manganese steels containing niobium

The effect of niobium additions (up to 0.23 pct) on the plastic anisotropy of cold-rolled and annealed low-carbon, low-manganese steels has been studied. When hot-rolling conditions involving coiling temperatures below 1150°F were used, increased concentrations of niobium were deleterious to the development of high plastic anisotropy. Isothermal transformation studies and special hot-rolling studies showed that when transformation from austenite to ferrite and precipitation of carbonitrides occurred at high temperatures (\s>1350°F), excellent plastic anisotropy (•gn about 2) was obtained after cold rolling and annealing. The results are interpreted on the basis of an effect of critical particle sizes or dispersions on the selection of preferred orientations during recrystallization. From electron microscope studies, the critical carbonitride size and interparticle spacing, necessary for the development of high plastic anisotropy, was estimated to be 40 to 500A and 0.04 to 0.5 μm, respectively. However, the presence of a large amount of niobium in solid solution in ferrite is apparently deleterious to the development of high plastic anistropy, even though carbonitrides having the critical size and spacing are present. On the basis of these observations and other published work, it is suggested that second-phase particles influence the development of plastic anisotropy in rimmed and aluminum-killed steels as well as in niobium-and titanium-containing steels. Thus, the degree of plastic anisotropy produced in these steels is influenced by textures developed during annealing, which in turn is dependent on the dispersion characteristics of the particular second-phase particles present.

Phase equilibria and X-ray diffraction investigation of the system Cu−Fe−O

An equilibria investigation for the system Cu−Fe−O determined nine regions of stability which were investigated in the oxygen pressure range of 1×10−4 to 5×10−1 atm (P total=1 atm) and at temperatures of 1173° to 1250°K. Oxygen dissociation pressures were determined for three univariant, four bivariant, and two trivariant equilibria. X-ray examination of selected equilibrated samples established conclusively that 1) cuprous ferrite (delafossite) is a stoichiometric compound, 2) cupric ferrite is a solid solution, and 3) solubility of delafossite in cuprous oxide is negligible. A relationship of lattice parameters with compositional variations was determined for the solid solution. Tetragonal-to-cubic spinel crystal transformation of cupric ferrite solid solution occurs with ac/a ratio at or slightly greater than 1.028. A volume discontinuity accompanies the tetragonal-to-cubic spinel transformation, which is a first-order type of thermodynamic transition.

Electric Conduction of Ferrites containing Fe2+-ions

The D.C. electric conductivity was measured between 100°K and 300°K for the ferrite solid solution (MeFe 2 O 4 ) 1- y Fe 3 O 4 ) y , where Me=Mn, Ni, Mn-Ni or Zn. Above 120°K the specific conductivity of each specimen depends on temperature as σ= A ·exp (- e / k T )/ T . The activation energy e is (5∼8)×10 -2 eV. A depends on the concentration, y , of Fe 3 O 4 as A =(6.5±2.5)×10 4 ( y /1- y ) degree/Ωcm. The analysis of these experimental expressions shows that the dependence of the mobility on temperature for each specimen can be fitted by the expression, µ=µ 0 ·exp (- e / k T )/ T and the dependence on the Fe 2+ -ion concentration, y , by µ 0 =(3.0±1.2)×10 1 (1/1- y ) degree (cm 2 /volt sec). µ 0 is independent of the kind and distribution of Me 2+ -ions.