Hydrogenation properties and crystal structures of Ti−Mn-V BCC solid solution alloys

We have proposed new hydrogen absorbing alloys of the ‘Laves phase related BCC solid solution alloy’, the hydrogen capacity of which reaches almost double that of conventional rare-earth based AB₅ alloys. We have reported the hydrogen absorbing properties of Ti−V−Mn, Ti−V−Cr and T−V−Mn−Cr alloys. It has been accepted that the crystal structural change of BCC hydrogen absorbing alloys is the same as that of V metal. The mono-hydride (H/M=1) of V metal has a BCT structure and the di-hydride (H/M=2) has an FCC structure. However, we recently found that the Ti−V−Mn alloy shows different behaviors in phase transformation with hydrogenation to V metal. We found three hydride phases with a BCC, a deformed FCC and an FCC structure in the Ti−V−Mn solid solution alloy-H₂ system. The deformed FCC hydride phase has not yet to our knowledge been reported. The lattice constant of the deformed FCC was 0.407 nm, one axis of which is reduced by about 4%. Its single-phase region appeared at a hydrogen content between 0.8 H/M and 1.0 H/M in absorption at 298 K. The lower plateau observed due to formation of the deformed FCC hydride phase gives an increase of effective hydrogen capacity by decreasing hydrogen remaining in the alloy in the desorption process. This article based on a presentation made in the symposium “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28, 2000 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Thermodynamic properties of CexTh1−xO2 solid solution from first-principles calculations

A systematic study based on first-principles calculations along with a quasi-harmonic approximation has been conducted to calculate the thermodynamic properties of the Ce_xTh_1?xO₂ solid solution. The predicted density, thermal expansion coefficients, heat capacity and thermal conductivity for the Ce_xTh_1?xO₂ solid solution all agree well with the available experimental data. The thermal expansion coefficient for ThO₂ increases with CeO₂ substitution, and complete substitution shows the highest expansion coefficient. On the other hand, the mixed Ce_xTh_1?xO₂ (0 < x < 1) solid solution generally exhibits lower heat capacity and thermal conductivity than the ThO₂ and CeO₂ end members. Our calculations indicate a strong effect of Ce concentration on the thermodynamic properties of the Ce_xTh_1?xO₂ solid solution.     

Decomposition mechanism of Al1−xSixNy solid solution and possible mechanism of the formation of covalent nanocrystalline AlN/Si3N4 nanocomposites

Using a combined ab initio density functional theory (DFT) and thermodynamic modeling, we study the stability of a variety of phases and the possible mechanism of the decomposition of the Al_1?xSi_xN_y solid solution and formation of nanocrystalline AlN/Si₃N₄ nanocomposites, which have been experimentally investigated in a number of recent publications. It is shown that the linear and exponential dependence of the interaction parameter on temperature yields reliable results. The hexagonal close-packed (hcp)(ZnS) to hcp(β) phase transition points occur at x ～ 0.36. The calculated temperature–composition diagrams show that spinodal decomposition mechanism is unlikely in this system because of too small de-mixing energy, which is comparable with the interfacial energy of semi-coherent interfaces. Thus, the decomposition should occur by nucleation and growth, accompanied by a phase transformation from the unstable hcp(ZnS)-SiN to stable hcp(β) or amorphous Si₃N₄, which probably limits the achievable hardness enhancement of the nanocomposites as compared with the nanocrystalline TiN/a-Si₃N₄ ones (where a indicates X-ray amorphous, and the stoichiometry Si₃N₄ symbolizes the fact that Si is fourfold coordinated to nitrogen, as in stoichiometric silicon nitride).     

The influence of Gd/Ce substitution on the magnetic properties,electronic structure and the valence of cerium in the solid solution CexGd1−xNi3

The polycrystalline compounds Ce_xGd_1−xNi₃ with a rhombohedral PuNi₃ (x ≤ 0.2) and hexagonal CeNi₃ (x ≥ 0.8) – type of crystal structures have been obtained. The change of the lattice parameters may suggest an unstable valence of cerium in the studied system. The effect of partial substitution of Gd by Ce is reflected in a change of the cell volume V(x), the Curie temperature T_C(x) and in the temperature dependence of the magnetic susceptibility and electrical resistivity. Thus, T_C(x) decreases from 115 K (x = 0) to ∼6.8 K (x = 0.8). The XPS spectra have been measured at room temperature. The valence band spectra (VB) as well as the core level lines have been analysed as influence of the Gd/Ce substitution on the electronic structure. The VB near the Fermi level (E_F) is dominated by Ni3d states. In the VB region some slight effects of hybridization and changes of intensity of states on E_F have been noticed. The analysis of Ce core level lines reveals the occurrence of possible intermediate valence. The values of the Ce4f - state occupation parameter (n_f) and the hybridization energy (Δ) have been estimated. The gradual filling of the Ni3d band is revealed by a reduction of the 6 eV satellite intensities in the Ni2p core level spectrum. All these effects can modify the magnetic properties of the investigated compounds.     

Comparisons of species and coagulation effects of PFS solution and solid PFS from pyrite cinders

1　ＩＮＴＲＯＤＵＣＴＩＯＮＰｏｌｙｆｅｒｒｉｃｓｕｌｆａｔｅ (ＰＦＳ )ｗａｓｓｕｃｃｅｓｓｆｕｌｌｙ ｐｒｅ ｐａｒｅｄｉｎＪａｐａｎｉｎｔｈｅｍｉｄ 1970ｓａｎｄｗａｓｐｒｏｄｕｃｅｄａｎｄａｐｐｌｉｅｄｉｎｉｎｄｕｓｔｒｉｅｓｉｎ 1980ｓ .ＰＦＳａｓａｃ     

Diffusion formation of intermediate phases and supersaturated solid solutions in the aluminum−copper system

Studies of the processes that occur upon the interdiffusion in the aluminum?copper system in the temperature range of 320–440°C have been carried out using optical metallography, scanning electron microscopy, and electron microprobe analysis. It has been found that, in this system, at low annealing temperatures, there are no intermediate phases that correspond to the equilibrium phase diagram. Short-term high-temperature annealing leads to the formation of the equilibrium phases. The subsequent low-temperature annealing leads to the precipitation of a second phase from the solid solution in the form of particles rather than layers. It has been shown that the absence of the equilibrium phases is accompanied by the formation of a supersaturated solid solution of copper in aluminum.     

Effects of cooling rate on solidification behavior of dilute Al-Sc and Al-Sc-Zr solid solution

Six alloys with different compositions of Al-0.1%Sc, Al-0.3%Sc, Al-0.3%Zr, Al-0.1%Sc-0.1%Zr,Al-0.3%Sc-0.1%Zr and Al-0.3%Sc-0.3%Zr were prepared by casting in a wedge shaped copper mould. The hardness test, microstructure observation, and DSC thermal analysis were applied to fully investigate the solidification behavior of the wedge tip (whose cooling rate is 1000 K/s) and the top surface (cooling rate 100 K/s) of each casting. The results show that the cast structures in the hypoeutectic region of AI-Sc alloys are slightly affected by cooling rates during the solidification. In the case of hypereutectic alloy of Al-0.3%Sc-0.3%Zr, the cast grains were remarkably refined under the condition of a 100 K/s cooling rate, however, under a 1000 K/s cooling rate condition,solute atoms contribute nothing to the grain-refinement, due to the eutectic concentration becomes higher. The hardness can be improved to a greater degree by Sc single addition, compared to single Zr addition, but it can be improved even greater when Sc added together with Zr. It is sensitive to cooling rate, the higher the cooling rate, thegreater the hardness. By combining the results of TEM examination and DSC analysis, it can be seen that a supersaturated Al solid solution forms during the solidification, and the solubility of Sc in Al solution can be improved by increasing the cooling rate.     

Optical spectroscopy and crystal-field strength of Cr^3＋ in various solid matrixes

The Cr^3＋：BeAl2O4 crystal, Cr^3＋：LiNbO3 crystal, and ZnO-Al2O3-SiO2 glass-ceramic were obtained by the Czochralski technique, Bridgman method, and melting processing, respectively. The optical absorption and emission spectra of the above Cr^3＋-incorporated solid-state materials were recorded. The technical parameters for growing high-quality Cr^3＋：BeAl2O4 and Cr^3＋：LINbO3 crystals were obtained. The results indicate that the optical absorption and fluorescence spectra of Cr^3＋ show quite a few differences in various matrixes. The sharp line emissions were observed in the Cr^3＋：BeAl2O4 and Cr^3＋：LiNbO3 crystals. The crystal-field parameters （Dq） for Cr^3＋. in different matrixes were calculated from their corresponding spectra. It is indicated that Cr^3＋：BeAl2O4 and Cr^3＋：LiNbO3 belong to the high-field site crystal, while the Cr^3＋ ZnO-Al2O3-SiO2 glass and glass-ceramic belong to the weak-field site crystal.     

Effect of the sample sizes and the sampling conditions on the results of chemical analysis of castings of Cu−Sn and Cu−Sn−Pb alloys

In horizontal continuous casting of semifinished products made of alloys of the Cu−Sn and Cu−Sn−Pb systems segregation of tin and lead complicates the problem of obtaining the specified composition. The aim of this work consists in determining the size of the sample and the conditions for taking it in casting for which the specified chemical composition of the casting will be uniform over the entire volume. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 34–35, October, 1998.     

Solid solution strengthening and damping capacity of Mg−Ga binary alloys

The mechanical behaviors and damping capacities of the binary Mg?Ga alloys with the Ga content ranging from 1 to 5 wt.% were investigated by means of optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), hardness test, tensile test and dynamic mechanical analyzer (DMA). The hardness (HV_0.5) increases with the increase of Ga content, which can be described as HV_0.5=41.61+10.35c, and the solid solution strengthening effect Δσ_s of the alloy has a linear relationship with cⁿ, where c is the molar fraction of solute atoms and n=1/2 or 2/3. Ga exhibits a stronger solid solution strengthening effect than Al, Zn or Sn due to the large atomic radius difference and the modulus mismatch between Ga and Mg atoms. The addition of Ga makes the Mg?Ga alloys have better damping capacity, and this phenomenon can be explained by the Granato?Lücke dislocation model. The lattice distortion and the modulus mismatch generated because of the addition of Ga increase the resistance to motion of the dislocation in the process of swinging or moving, and thus the better damping capacity is acquired.     

High-angle annular dark-field scanning transmission electron microscopy and electron energy-loss spectroscopy of nano-granular Co–Al–O alloys

Atomic structures of cobalt–aluminum–oxygen nano-granular films prepared by reactive rf-sputtering from CoAl alloys in oxygen gas were investigated by high-angle annular dark-field scanning transmission electron microscopy and electron energy-loss spectroscopy to clarify the atomic structures of the films and the interfacial layers in relation with their magnetic properties and tunnel magneto-resistance.     

Electrodeposition and corrosion behavior of Zn−Ni−Mn alloy coatings deposited from alkaline solution

The potentiostatic electrodeposition of Zn−Ni−Mn was carried out in an alkaline solution with the addition of Mn salt. The effects of electrolyte Mn²⁺ concentration and deposition potential on the surface morphology, phase structure and corrosion behavior of coatings were studied. The results of corrosion polarization showed that the presence of higher Mn content in Zn−Ni−Mn coatings could lead to the formation of a good passive layer with a 7-fold increase in R_p of coating and a significant decrease in the corrosion current density compared to those of Zn−Ni coating. The XRD and the XPS analyses from the surface of Zn−Ni−Mn after corrosion test showed that the passive layer was composed of zinc hydroxide chloride, zinc oxide, zinc hydroxide carbonate, and manganese oxides.     

Effect of microalloying on the structure and properties of alloys in the Al−Si−Cu system

Conclusions  

Effect of composition and heat treatment on the structure and properties of Fe−Ni−Be invar alloys

Conclusions Addition of Be (0.5–1%) to Fe–Ni invar alloys provides dispersion hardening after quenching and aging, with retention of a low (close to invar) value of LCTE. Increase of the Be concentration in alloy 36N is accompanied by an increase in LCTE in the quenched as well as the aged condition, and increase of the Ni concentration to 38–41% at a fixed concentration of Be leads to a decreased value of LCTE in the aged alloys, approaching that of the alloy 36N. The optimum composition range for Fe–Ni–Be alloys in which the best combination of properties can be obtained — low value of LCTE (3.10^–6, K^–1) and higher strength (_0.2910 N/mm², _u1100 N/mm²) — was determined to be (39–40% Ni, 0.7–0.8% Be). The alloy 40NL (40% Ni, 0.8% Be) is proposed as a high strength invar alloy.I. P. Bardin Central Scientific-Research Institute for Ferrous Metallurgy (TsNIIChERMET). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 33–36, February, 1992.     

Correlation between the oxide impedance and corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys

The correlation between the oxide impedance and corrosion behavior of two series of Zr−Nb−Sn−Fe−Cu alloys was evaluated. Corrosion tests were performed in a 70 ppm LiOH aqueous solution at 360°C for 300 days. The results of the corrosion tests revealed that the corrosion behavior of the alloys depended on the Nb and Sn content. The impedance characteristics for the pre- and post-transition oxide layers formed on the surface of the alloys were investigated in sulfuric acid at room temperature. From the results, a pertinent equivalent circuit model was preferably established, explaining the properties of double oxide layers. The impedance of the oxide layers correlated with the corrosion behavior; better corrosion resistance always showed higher electric resistance for the inner layers. It is thus concluded that a pertinent equivalent circuit model would be useful for evaluating the long-term corrosion behavior of Zr−Nb−Sn−Fe−Cu alloys.     

Dependence of the thermal conductivity of alloys of the Al−Mg system on the composition and temperature

It is a common practice to study the dependencies of the physical properties of alloys on the temperature and the composition without generalizing the results. It is more logical to study these dependences complexly, i.e., as fragments of “composition-temperature-property” diagrams (whole diagrams in the ideal case). Today’s mathematical and computer possibilities provide processing of the dependences of any property on the temperature and the composition even for multicomponent systems. Mathematical analogs replace the “composition— property” graphical diagrams. The present work generalizes data on the thermal conductivity of 11 alloys of the Al−Mg system that contain 1 to 14% Mg in the temperature range of 20–350°C. The results are obtained in the form of a single regression equation that describes the data on the thermal conductivity within the range 86–190 W/(m·K) with a standard deviation of 0.7%. The choice of the regression equation is based on the existence of an analogy between heat transfer and electric transfer in metallic systems and on dependences of the electrical resistivity on the temperature and the concentration of the alloying elements known from solid-state physics. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 13–15, June, 1998.