Crystal-Chemical Nature of Mg–M–Fe–O (M = Cr, Al) Spinel Ferrites

The composition dependences of the lattice parameter and saturation magnetization for solid solutions with bulk compositions of (MgCr₂O₄) _c (Fe₃O₄)_{1 – c} and (MgAl₂O₄) _c (Fe₃O₄)_{1 – c} (0 c 1.0) indicate that these solid solutions consist of three spinel components. This finding accounts for the observed deviations from additivity in experimental data.     

Subsolidus Phase Relations in the Systems M2 +O–M2+O–V2O5(M+ = Li, Na, K, Rb, Cs; M2+ = Mg, Ca)

Subsolidus phase relations in the M₂O(M₂CO₃)–MgO–V₂O₅ and M₂O(M₂CO₃)–CaO–V₂O₅ (M = Li, Na, K, Rb, Cs) systems are studied. Twenty mixed vanadates are obtained, of which Rb₂CaV₂O₇, Cs₂CaV₂O₇, LiMg₄(VO₄)₃, RbCaVO₄, and CsCaVO₄ are identified for the first time. Structural data are summarized for all of the mixed vanadates: the space group and lattice parameters are indicated for 14 compounds (for 6 compounds, such data are obtained for the first time), and I and d data are presented for 8 compounds. Partial series of Ca₃(VO₄)₂-based solid solutions with the general formula Ca_{3 – x} M_2x (VO₄)₂ (M = Na, K, Rb, Cs) are identified in the range 0 < x 0.14. Six phase diagrams (M⁺ = Li, Rb, Cs; M²⁺ = Mg, Ca) are investigated and are compared with the phase diagrams of the other ternary systems in question. The key features of the ternary phase diagrams and, hence, the reactivity of the constituent oxides are shown to vary systematically in going from Li₂O to Cs₂O and from MgO to SrO, which is interpreted in terms of the variation in the ionic radius of the alkali and alkaline-earth metals.     

Phase Formation in the Systems α(δ)-FeOOH–M(OH)2–H2O (M = Mn, Co, Zn)

The sequence of chemical transformations induced in the systems ()-FeOOH–M(OH)₂–H₂O (M = Mn, Co, Zn) by heat treatment in the range 125–200°C is studied. The results demonstrate that the kinetics of M(II) ferrite formation, the chemical and phase compositions of the product, and its particle size distribution depend on the heat-treatment temperature, the pH of the suspension (or NaOH concentration), the FeOOH polymorph used as a starting reagent, and the starting-mixture composition.     

Effect of synthesis pressure on hydride phases in Mg–M systems (M = Mn,Y)

High-pressure synthesis of the hydrides in Mg–M (M = Mn, Y) systems and the influence of applied pressures during synthesis on present phases and their crystal structures have been studied. In Mg–Mn system, it was found that the crystal structure of Mg₃MnH_y changed from hexagonal structure (a = 0:47107(4) nm and c = 1:0297(1) nm) to monoclinic structure (a = 0:8819(8) nm, b = 0:4658(4) nm, c = 0:4678(5) nm and b= 105:6(1)8) in a pressure range of 3–3.5 GPa. This crystal structural change was reversible with respect to pressure. The Mg₃MnH_y synthesized under 5 GPa was stable up to around 620 K. From thermogravimetric and fusion extraction analyses, the hydrogen content was determined as Mg₃MnH_5.0–5.6. In Mg–Y system, the high-pressure hydride (MgY₂H_y) with yellowish color was synthesized at 1073 K for 2 h under 3 GPa or higher. This phase exhibited an FCC-type structure with a cell parameter of a = 0:516 nm. Its hydrogen content was determined to be about 3.7 mass%, corresponding to a chemical formula of MgY₂H_7.8. The hydride was partially dehydrogenated at around 600 K, and the amount of hydrogen partially desorbed was 1.4 mass%. The FCC-type structure was stable even after the partial dehydrogenation.     

Effect of synthesis pressure on hydride phases in Mg–M systems (M=Mn,Y)

High-pressure synthesis of the hydrides in Mg–M (M=Mn, Y) systems and the influence of applied pressures during synthesis on present phases and their crystal structures have been studied. In Mg–Mn system, it was found that the crystal structure of Mg₃MnH_y changed from hexagonal structure (a=0.47107(4) nm and c=1.0297(1) nm) to monoclinic structure (a=0.8819(8) nm, b=0.4658(4) nm, c=0.4678(5) nm and β=105.6(1)°) in a pressure range of 3–3.5 GPa. This crystal structural change was reversible with respect to pressure. The Mg₃MnH_y synthesized under 5 GPa was stable up to around 620 K. From thermogravimetric and fusion extraction analyses, the hydrogen content was determined as Mg₃MnH_5.0–5.6. In Mg–Y system, the high-pressure hydride (MgY₂H_y) with yellowish color was synthesized at 1073 K for 2 h under 3 GPa or higher. This phase exhibited an FCC-type structure with a cell parameter of a=0.516 nm. Its hydrogen content was determined to be about 3.7 mass%, corresponding to a chemical formula of MgY₂H_7.8. The hydride was partially dehydrogenated at around 600 K, and the amount of hydrogen partially desorbed was 1.4 mass%. The FCC-type structure was stable even after the partial dehydrogenation.     

Self-accommodation in polycrystalline 10M Ni–Mn–Ga martensite

10M Ni–Mn–Ga polycrystals show a typical self-accommodated microstructure consisting of macro and micro twins. The macro twin lamellae separate micro twins creating a so-called “twins within twins” microstructure. Such a configuration allows the distribution of martensitic variants with no net change in shape of the sample. The arrangement of variants can occur on different length scales, from a few nanometers up to a few millimeters, not only depending on grain size but also on processing condition (e.g., extrusion, torsion). Small austenite grains do not completely transform to martensite giving rise to some residual austenite. Furthermore, characteristic branching of macro and micro twins is observed due to lowering of the elastic energy at grain and macro twin boundaries, respectively.     

Structure and dielectric properties of a new series of pyrochlores in the Ca–Sm–Ti–M–O (M = Nb and Ta) system

The present work investigates the dielectric properties of pyrochlore type oxides, Ca–Sm–Ti–M–O (M = Nb and Ta) in the low frequency region (100 Hz–1 MHz) over the temperature range 30–100 °C. The 1 MHz dielectric constants (K) of these oxides are in the range 23–108 and show low variation with frequency (1 kHz–1 MHz). The temperature coefficient of dielectric constant (TCK) over the temperature range varies from positive to negative values in the range 48 to −107 ppm/°C. Rietveld analysis of the X-ray diffraction data establishes a cubic pyrochlore-type phase in the space group Fd3 m (no. 227).The grain morphology observation by scanning electron microscope shows well sintered grains.     

Structure,Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo₂N, AlN–Si₃N₄, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃, M₆C and MC is important by adding elements such as Cr, W, V and Mo.The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.In this report, the solidified temperature of γ+M₂C and γ+M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidification process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ+M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.The authors have already measured the k values of other eutectic carbides, such as γ+M₃C, austenite+M₇C₃, and γ+VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃,M₆C and MC is important by adding elements such as Cr, W, V and Mo.

The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.

In this report, the solidified temperature of γ + M₂C and γ + M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidiication process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ + M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.

The authors have already measured the k values of other eutectic carbides, such as γ + M₃C, austenite + M₇C₃, and γ + VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Surface tension and density data for Fe–Cr–Mo,Fe–Cr–Ni,and Fe–Cr–Mn–Ni steels

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (?_Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.     

Thermodynamic characterization of Al–Cr,Al–Zr,and Al–Cr–Zr alloy systems

Abstract

The equilibrium phase diagrams of Al–Cr, Al–Zr, and Al–Cr-Zr, with particular reference to aluminium-rich alloys, have been critically reviewed. On the basis of these, and consistent with measured thermodynamic values, the binary systems have been thermodynamically characterized. Using these characterizations, phase equilibria have been extrapolated in the ternary, with the intention of augmenting the sparse experimental information concerning the equilibrium liquidus (0–10 at.%Cr, Zr) and solid solution range of aluminium in Al–Cr–Zr. Using the same parameters that define the equilibrium phase relationships, metastable phase relationships can also be extrapolated into the ternary.

MST/418     

Dy(Fe,M)_(12)(M=Si,Ti,V)合金的Mssbauer谱学研究

DyFe_(10)Si_2合金的~(57)Fe变温Mssbauer谱学研究,发现温度在210K处,超精细场随温度有不连续变化。此温度对应于合金的自旋重取向温度。Si,Ti和V作为形成ThMn_(12)型结构的稳定化元素,造成各相应合金的自旋重取向温度有一些差别。分析了Si,Ti和V元素造成合金磁晶各向异性差别的原因,它使得DyFe_(10)V_2,DyFe_(11)Ti和DyFe_(10)Si_2合金的自旋重取向温度不同。DyFe_(10)Si_2合金的8i晶位四极劈裂在温度210K处改变符号。     

Phase composition,structure, and mechanical properties of arc PVD Mo–Si–Al and Mo–Si–Al–N coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al coatings with a uniform distribution of equiaxed grains 8–12 nm in size and Mo–Si–Al–N coatings with a multilayer structure and a modulation period from 22 to 25 nm. The former coatings consist of MoSi₂ and Mo and the latter consist of Mo2N and amorphous Si₃N₄ and AlN. The hardness of the Mo–Si–Al–N and Mo–Si–Al coatings is 41 and 18 GPa, respectively; they are similar in resistance to elastic deformation; and the Mo–Si–Al–N coating has a considerably higher resistance to plastic deformation. The coatings have roughly identical coefficients of friction (~0.67–0.69 at 20°C and ~0.52–0.56 at 550°C), but the wear resistance of the Mo–Si–Al–N coating is higher by three and two orders of magnitude at 20 and 550°C, respectively. The coatings of the two systems exhibit good adhesion to the substrate and cohesive fracture. Partial wear of the Mo–Si–Al and Mo–Si–Al–N coatings in the course of scratch testing occurs at indentation loads of 80 and 63 N, respectively.     

The relationship between the mean dopant-ion radii and conductivity of co-doped ZnO systems, Zn1−x−y M x M′ y O (M, M′ = Al, In, Ga, Y)

The conductivities of the Zn_1–x–y M _x M _y O (M, M = Al, In, Ga, Y) and Zn_1–x M _x O (M = Al, In, Ga) systems were measured from room temperature to 1173 K in order to elucidate a dominant parameter of the conducting mechanism. The conductivity at 873 K first increased with the dopant content. However, it showed a maximum value at a given dopant content, and then gradually decreased. For the samples with the same dopant content, their conductivity at 873 K was strongly dependent on the mean dopant-ion radii, and reached a maximum value at around 0.51 Å of the mean dopant-ion radii. The results suggested that the conductivity of the system would be influenced not only by the dopant content, but also by the mean dopant-ion radii. It was found that the co-doped ZnO system of Zn_0.995Al_0.003In_0.003O had a conductivity higher than that of the other usual mono-doped system.