Metal-rich Side Research Articles

MUSE spectroscopic observations of the young massive cluster NGC 1850

Context. The double cluster NGC 1850 in the Large Magellanic Cloud is the nearest young massive cluster of the Local Group with a mass similar to those of Galactic globular clusters. Recent studies have revealed an extended morphology of its main-sequence turn-off (MSTO), which can be interpreted as a spread in either age or internal rotation. In spite of its proximity, an accurate spectroscopic determination of its chemical properties is still missing. Aims. We aim to investigate the general chemistry and the kinematics of this stellar system to test whether possible signs of multiple populations are observable in this cluster. Methods. We analysed the spectra obtained with MUSE in adaptive optics mode of 1167 stars in both components of this cluster (NGC 1850A and NGC 1850B). Thanks to this data set, we were able to measure accurate global metallicities, Ba abundances, and radial velocities for a sample of 38 red supergiants and a guess of the oxygen abundance in the brightest turn-off stars belonging to NGC 1850A. Results. We find an average metallicity of ⟨[M/H]⟩ = −0.31 ± 0.01, a mean Ba abundance of ⟨[Ba/Fe]⟩ = +0.40 ± 0.02, and a systemic radial velocity of ⟨vLOS⟩ = 251.1 ± 0.3 km s−1. The dispersion of the radial velocities suggests a dynamical mass of log(M/M⊙) = 4.84 ± 0.1, while no significant systemic rotation is detected. We detect a significant bimodality in O I line strength among the turn-off stars of NGC 1850A with ∼66% of stars with [O/Fe]∼ − 0.16 and the rest with no detectable line. The majority of O-weak stars preferentially populate the red side of the MSTO and show H lines in emission, suggesting that they are Be stars rotating close to their critical velocity. Among normal MSTO stars, red stars have broader line profiles than blue ones, on average, suggesting a correlation between colour and rotational velocity. Conclusions. The mean metallicity of this cluster lies at the metal-rich side of the metallicity distribution of the Large Magellanic Cloud following its age-metallicity relation. The Ba and O abundances agree with those measured in the bar of this galaxy. The correlation between line broadening and colour suggests that the observed colour spread among turn-off stars can be due to a wide range in rotational velocity covered by these stars.

Experimental investigation of the low-velocity impact response of sandwich plates with functionally graded core

In this study, the mechanical behavior of sandwich plates with functionally graded core under low-velocity impact loads was investigated experimentally. Sandwich plate with functionally graded core has two different structures (metal–ceramic), and the upper and lower surfaces are pure metal (Al) and the internal layers of the plate are manufactured with gradually varying material composition through the plate thickness. The low-velocity impact tests were conducted on both upper and lower surfaces of specimens using CEAST low-velocity impact device, and the contact force–time and the energy–time graphs were plotted. Metallographic and micromechanical examinations were carried out on the specimens after impact tests. As a result of the metallographic and micromechanical examinations, the material composition variation through the specimen thickness was obtained in accordance with the rule of the theoretical mixture. As a result of impact tests (v = 4 m/s) on upper surface (ceramic-rich side), crack damages occurs on the plates with n = 10.0 material composition, whereas the specimens with n = 1.0 and n = 10.0 material compositions have crack damages after impact tests on its lower surfaces (metal-rich side). Impact force on the ceramic-rich upper surface provides to meet the transferred load waves through the plate thickness by metal-rich bottom surface. This situation makes the structure more resistant against damage. Moreover, the upper and lower surfaces of the functionally graded structure reinforced by ductile pure metal layers provide an important contribution to protection of functional integrity of the structure against damage.

Phase equilibria and multi-element interaction study in the metal-rich side of the Nb–Ti–Si–Al quaternary system

The knowledge of phase diagram is theoretical principle for compositional design. Since Ti and Al are important alloying elements for Nb–Si alloys, and Nb and Si are important alloying elements for Ti–Al alloys, Nb–Ti–Si–Al phase equilibria is prerequisite for optimal microstructural design of both Nb–Si and Ti–Al systems. In this work, key alloys were selected firstly according to calculated isothermal section based on extrapolated thermodynamic description, then key alloy ingots were prepared by arc-melting and heat treated to reach equilibrium state. Currently obtained phase equilibria data coupled with critically reviewed literature data were employed to study the element interaction of relative phases (α-Nb5Si3, β-Nb5Si3, Ti5Si3, Nb3Al and TiAl et al.) in the Nb–Ti–Si–Al system. Thermodynamic parameters of these phases were modified accordingly to reproduce the determined phase relationships. Finally, the important phase equilibria features of the Nb–Ti–Si–Al system were described with several isothermal sections. The phase equilibria extending from ternary systems and new phase equilibria appearing in the quaternary space were demonstrated in this work.

Theoretical Study on the Electronic Structure of Heavy Alkali-Metal Suboxides.

On the metal-rich side of the phase diagrams of the Rb-O, Cs-O, and Rb-Cs-O systems, one can find a variety of stoichiometries: for example, Rb9O2, Rb6O, Cs4O, Cs7O, Cs11O3, RbCs11O3, and Rb7Cs11O3. They may be termed heavy alkali-metal suboxides. The application of the standard electron-counting scheme to these compounds suggests the presence of surplus electrons. This motivated us to carry out a theoretical study using the first-principles density functional theory (DFT) method. The structures of these compounds are based on either a formally cationic Rb9O2 or Cs11O3 cluster. The analyses of the partial charge density just below the Fermi level and the electron localization function (ELF) have revealed that there exist surplus electrons in interstitial regions of all the investigated suboxides so that the excess positive charge of the cluster can be compensated. Density of states (DOS) calculations suggest that all of the compounds are metallic. Therefore, the suboxides listed above may be regarded as a new family of metallic electrides, where coreless electrons reside in interstitial spaces and provide a conduction channel. Except for the phases of Rb9O2 and Cs11O3, the suboxide structures include both the cationic clusters and alkali-metal matrix. Several charge analyses indicate that the interstitial surplus-electron density can be assigned to the alkali-metal atoms in the metal matrix, leading to the possibility of the presence of negatively charged alkali-metal atoms, namely Rb- (rubidide) and Cs- (caeside) ions, a.k.a. alkalides. In Rb6O, Rb-, Rb0, and Rb+ are found to coexist in the same crystal structure. Similarly, in Cs7O, one can find the three types of Cs atoms. However, in Cs4O, no Cs0 state is identified. In the Rb-Cs-O ternary suboxides, Rb takes a negatively charged anion state or neutral state, while all of the Cs atoms are found to be cationic because they get involved in the Cs11O3 cluster and all the Rb atoms exist in interstitial sites. Orbital interactions between the clusters are analyzed to understand how the condensation of the clusters into the solid happens and how the electride nature ensues. These clusters are found to have some superatomic character.

On the linear stability of eccentrically stiffened functionally graded annular spherical shell on elastic foundations

The study deals with the formulation of governing equations of eccentrically stiffened functionally graded materials annular spherical shells resting on elastic foundations and based upon the classical shell theory and the smeared stiffeners technique taking into account geometrical nonlinearity in Von Karman-Donnell sense. The annular spherical shells are reinforced by eccentrically longitudinal and transversal stiffeners made of full metal or full ceramic depending on situation of stiffeners at metal-rich side or ceramic-rich side of the shell respectively. Approximate solutions are assumed to satisfy the simply supported boundary condition and Galerkin method is applied to obtain closed-form relations of bifurcation type of buckling loads. Numerical results are given to evaluate effects of inhomogeneous, dimensional parameters, outside stiffeners and elastic foundations to the buckling of structures.

NGC 5824: a luminous outer halo globular cluster with an intrinsic abundance spread

We present a detailed study of the strengths of the calcium triplet absorption lines in the spectra of a large sample of red giant members of the luminous outer Galactic halo globular cluster NGC 5824. The spectra were obtained with the FORS2 and GMOS-S multi-object spectrographs at the VLT and the Gemini-S telescope, respectively. By comparing the line strengths of the NGC 5824 stars with those for red giants in clusters with well established abundances, we conclude that there is an intrinsic abundance dispersion in NGC 5824 characterized by an inter-quartile range in [Fe/H] of 0.10 dex and a total range of ~0.3 dex. As for omega-Cen and M22, the abundance distribution shows a steep rise on the metal-poor side and a shallower decline on the metal-rich side. There is also some indication that the distribution is not unimodal with perhaps 3 distinct abundance groupings present. NGC 5824 has a further unusual characteristic: the outer surface density profile shows no signs of a tidal cutoff. Instead the profile has a power-law distribution with cluster stars detected to a radius exceeding 400 pc. We postulate that NGC 5824 may be the remnant nuclear star cluster of a now disrupted dwarf galaxy accreted during the formation of the Galaxy's halo. We further speculate that the presence of an intrinsic [Fe/H] spread is the characteristic that distinguishes former nuclear star clusters from other globular clusters.

Pressureless sintering of ZrO2–ZrSiO4/NiCr functionally graded materials with a shrinkage matching process

Shrinkage matching was applied as the basic concept for the processing of five-layered ZrO2–ZrSiO4/NiCr functionally graded materials (FGMs) by pressureless sintering. Shrinkage behavior of the constituent layers of FGM was matched based on the strategy of reducing the mismatches of shrinkage rate between the adjacent layers by a systematic adjustment of the ZrSiO4 inclusion content and the particle size of ZrO2 matrix. Before shrinkage matching, sintering defects such as warping towards the ceramic-rich side of FGM and cracking in the 100 vol% ceramic layer were generated, due to the relatively high mismatches of shrinkage rate between the ceramic- and the metal-rich sides and at the interface of 100 and 75 vol% ceramic layers, respectively. After shrinkage matching, FGMs without any sintering defects were obtained, whereas the green bodies warped towards the metal-rich side already before sintering, due to the relatively higher shrinkage of the metal-rich side during isostatic pressing.

Nonlinear postbuckling of eccentrically stiffened functionally graded plates and shallow shells

The paper deals with the formulation of governing equations of eccentrically stiffened functionally graded plates and shallow shells based upon the classical shell theory and the smeared stiffeners technique taking into account geometrical nonlinearity in Von Karman-Donnell sense. Material properties are assumed to be temperature-independent and graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of constituents. The shells are reinforced by eccentrically longitudinal and transversal stiffeners made of full metal or full ceramic depending on situation of stiffeners at metal-rich side or ceramic-rich side of the shell respectively. Obtained governing equations can be used in research on nonlinear postbuckling of mentioned above structures. By use of the Galerkin method an approximated analytical solution to the nonlinear stability problem of reinforced FGM plates and shallow shells is performed. The postbuckling load-deflection curves of the shells are investigated and analytical expressions of the upper and lower buckling loads are presented. A comparison of the effectiveness of stiffeners in enhancing the stability of FGM plates and shallow shells is given.

Ultracompact Dwarf Candidates in the Hydra Cluster

NGC 3311, the giant cD galaxy in the Hydra Cluster (A1060), has one of the largest globular cluster systems known. We describe new Gemini GMOS (g', i') photometry of the NGC 3311 field which reveals that the red, metal-rich side of its globular cluster population extends smoothly upward into the mass range associated with the new class of ultracompact dwarfs (UCDs). We identify 29 UCD candidates with estimated masses >6 × 106 M☉ and discuss their characteristics. This UCD-like sequence is the most well-defined one yet seen, and reinforces current ideas that the high-mass end of the globular cluster sequence merges continuously into the UCD sequence, which connects in turn to the E galaxy structural sequence.

Electronic properties of liquid noble metal–Si alloys

The electrical resistivity, ρ, of liquid noble metal–Si alloys (M1−cSic, M=Cu, Ag, Au) increases rapidly with the addition of Si to liquid noble metals. The composition dependence of ρ exhibits a maximum at the composition c=0.3, 0.4 and 0.4 for liquid Cu–Si, Ag–Si and Au–Si, respectively. A positive to negative transition of thermoelectric power, S, is observed at c=0.3, 0.15 and 0.1 for liquid Cu–Si, Ag–Si and Au–Si, respectively. Their composition dependence of S reaches a minimum value in the composition range c=0.6–0.8. The experimental results of ρ and S have been analyzed using the Faber–Ziman theory. The composition dependence of χ for liquid Cu–Si and Au–Si alloys exhibits a clear deviation from a straight line on the noble metal-rich side. As a result, liquid Cu–Si and Au–Si alloys have a minimum in the composition dependence of paramagnetic susceptibility.

Effect of Debonding at the Phase Interface on Young’s Modulus of Sintered PSZ/Stainless Steel Composite

A theoretical estimation has been made on the effect of debonding at the phase interface on Young's modulus in sintered PSZ/stainless steel composites with an abnormal deterioration of Young's modulus. The present analysis is based on Eshelby's equivalent inclusion method and a debonding model. A comparison is made between the theoretically predicted Young's modulus and experimental data for the composites having three different combinations of original powder size. The theoretical calculation shows that the Young's modulus decreases with increasing fraction of debonding. The fraction of debonding can be, in turn, predicted by comparing the theoretical calculation with the experimental data which have been found to depend on the composition of PSZ and original particle size. The particle size dependence on debonding has been discussed using the Weibull distribution, which shows that the coarser dispersoids have more debonded interface. The composition dependence has been explained by the variation of interface's residual stress with composition, which is generated by the mismatch of thermal expansion coefficients between the matrix and the dispersed particles, and the residual stress is compressive at the metal-rich side and tensile at the ceramic-rich side. The tensile stress at the interface enhances the debonding, however, the compressive stress defend it and improve the Young's modulus. The dependence of the abnormal deterioration of Young's modulus on the composition and particle size has been well accounted for

Interfacial segregation and the wetting transition in fluid metal-salt systems

The authors report the first systematic study of the wetting behaviour in fluid alkali metal-alkali halide systems on the metal-rich side of the phase diagram. To this end the interface of fluid sample-inert substrate (sapphire) has been probed by ellipsometry. Of particular interest is the influence of differences of the bulk phase diagram on the wetting characteristics. If the bulk fluid phase exhibits homogeneous miscibility like Cs-CsCl the optical reflectivity changes continuously with composition consistent with metallic Drude type behaviour. However, in systems with a critical and a triple point like K-KCl and Na-NaCl a wetting transition is observed. This occurs in metal-rich solutions approaching the triple point along the phase boundary. In K-KCl a salt-rich wetting film of approximately=100 nm thickness and composition corresponding to K0.1KCl0.9 has been determined. This is the film thickness in thermal equilibrium as has been found by vigorous ultrasonic stirring.

Examination of reference potentials for the molten Kx(KCl)1-xsystem by the Percus-Yevick approximation

The structure of the molten K x (KCl)1-x system at the metal rich side has been investigated by using three kinds of reference potential, which are the simplified versions of the model pair potentials proposed previously, within the framework of the Percus-Yevick (PY) approximation. It is shown that the sharp rise of the total structure factor at low momentum transfers, which is characteristic of the neutron diffraction experiment, and the very long range correlation between anions are due to the relatively weak attraction between anions. The similarity of the results for the screened and the unscreened Coulomb potentials is pointed out. The existence of the same similarity has been tested in the case of pure molten KCl. The four kinds of screened potentials, which were obtained for K0·8(KCl)0·2, have been used to mimic the pair distribution functions of the molten KCl system. The results are compared with those of the simulation calculation and of the mean spherical approximation (MSA) calculations for t...

A neutron scattering investigation of the structural order in RbBrRb solutions

Neutron scattering investigation of the RbBrRb system offers the advantage of giving directly the partial number density structure factor S NN . On the salt rich side not much deformation of the short range ionic correlations is observed except for a linear decrease with salt dilution. On the metal rich side the strong disorder introduced by the anions and already observed for KKCl is confirmed, as well as the detection of ionic short range correlations at 80% metal concentration. A tendency to segregation as noticeable from the scattering at low angles is observable over the whole concentration range. We also see that the strong shoulder K p appearing in all MCl salts at about twice the first maximum position of the S cc partial definitely belongs to S NN .

Solubilities of CdTe in the liquid III metals

Recently, CdTe has been studied extensively because of its possible applications in radiation detectors, solar batteries and other opto-electronic devices [1]. Liquidus solubility data of various solutes in solvents are needed to grow crystals by a liquid-phase epitaxial growth method or to make ohmic or rectifying contact by an alloying method. For these reasons, the phase diagrams of the CdTe-Bi [2], CdTe-Sb [2], CdTe-Sn [3], CdTe-Pb [3], CdTe-In [4], CdTe-CdCI2 [5] and CdTe-CdBr2 [5] systems have been studied by the present authors. The column IIlb metals such as Ga, In and Yl may be expected to be solvent metals suitable for the liquid-phase epitaxial growth of CdTe, because they have a low melting point and do not form an intermediate compound with CdTe. The phase diagrams of CdTe-Ga [6], CdTe-In [4, 7] and CdTe-T1 [8] systems are already presented in the literatures, but precise liquidus solubilities of CdTe in the IIIb metals have not been presented. In this paper the liquidus solubilities of CdTe in Ga, In and T1 were measured by differential thermal analysis (DTA) and disolution methods, with particular attention being paid to the lowtemperature region where the solubility becomes quite small. The single crystals of CdTe were grown by the Bridgman method from Cd and Te, both of 99.999% purity. The purities of Ga and In were 99.999% and that of Tl was 99.9%. Details of the DTA apparatus have been described in a previous paper [2]. The specimen for DTA was sealed in an evacuated quartz ample. The DTA peak becomes more obscure with decreasing CdTe content in the specimen. At the same time, since supercooling phenomena are prone to occur, it becomes very difficult to determine the liquidus temperature by the DTA method. In such cases, the liquidus temperature was determined by the dissolution method. At each temperature, liquid III b metal was saturated with one or two pieces of CdTe crystal in the evacuated quartz ample for sufficient time and quenched. After equilibration, the Ga or In metal which had adhered to the CdTe crystals was amargamated with Hg and removed from the CdTe in dilute nitric acid. The solubility was calculated from the weight loss of the CdTe crystals. Identification of the phases in the systems and lattice parameter measurements were carried out using an X-ray diffractometer (Type cl-3F, from Rigaku Denki Co.,). The metal-rich side of the liquidus solubility curves of the CdTe-Ga, CdTe-In and CdTe-T1 systems are shown in Fig. 1. Solid marks and open marks indicate data points determined by the DTA method and the dissolution method, respectively. In the CdTe-Ga and CdTe-In systems, thermal effects which were assigned to liquidus and eutectic lines were detected by the DTA method, while in the CdTe-T1 system other thermal effects were detected near 653 and 498 K. The thermal effect at the 498K was assigned to the phase trans-

Phase equilibria and thermodynamics in the Fe-Mo and Fe-Mo-O systems

The Fe-Mo-O system was reinvestigated at 1173 and 1273 K on the metal-rich side of the FeO-MoO 2 boundary. Two ternary oxides, Fe 2MoO 4 and Fe 2Mo 3O 8, were observed which coexist with α-Fe(Mo) at 1173 K and with Fe 3Mo 2 at 1273 K. Electromotive force measurements were made on galvanic cells with oxygen ion conducting solid electrolytes between 1190 and 1330 K for the determination of the Gibbs energies of formation of Fe 3Mo 2, Fe 2MoO 4 and Fe 2Mo 3O 8. The results can be presented by the following relationships: f ΔG°〈Fe 3Mo 2〉 = + 46.1 −0.0533 T ± 3.1 (kJ mol −1) f ΔG°〈Fe 2Mo O 4〉 = −1081.7 + 0.2667 T ± 2.6 (kJ mol −1) f ΔG°〈Fe 2Mo 3 O 8〉 = −2267.8 + 0.6165 T ± 4.5 (kJ mol −1) The heat of formation and the standard entropy of Fe 3Mo 2 were calculated using the Gibbs energy of formation results and literature data of calorimetric measurements, which give f ΔH 298°〈Fe 3Mo 2〉 = +15.0 kJ mol −1 and S 298°〈Fe 3Mo 2〉 = 177 J K −1 mol −1 at 298 K. The Gibbs energy of formation of Fe 3Mo 2 can then be expressed by f ΔG°〈Fe 3Mo 2〉 = + 18.0 −0.0535 T + 0.0000177 T 2 (kJ mol −1) between 298 and 1500 K.

The Electrochemical and Thermodynamic Behaviour of Transition Metal Sulfides

AbstractThe sulfides of Fe, Co and Ni, as obtained by precipitation in aqueous solution at low acidity, are X‐ray amorphous. Their Me/S ratio may be altered within very large limits by electrochemical polarization of the suspended sulfide. An apparent equilibrium potential versus the metal or sulfide ions is set up, function of the Me/S ratio. On the sulfur rich side metal depletion is limited by the segregation of rhombic sulfur; on the metal rich side the normal Me/Me+ +potential is reached at compositions Fe.1.04S, Co9S8, Ni3S2 above these amorphous superactive metal is deposited.The ΔG and ΔH data, obtained from half‐cell voltage measurements and enthalpometric titrations, correspond with the literature values for the crystalline compounds indicating that the short‐range order is similar in both. Attention is drawn to the interesting difference between the bonding of the metal partner in Co—S and Ni—S in connection with hydrometallurgical developments.