The Fulde–Ferrell–Larkin–Ovchinnikov State in Pnictides

We present experimental results on crosstalk of non-electrical origin between high frequency quartz tuning forks immersed in the same volume of helium gas, liquid or superfluid. We compare these results with various observations of other groups and propose an explanation of this puzzling phenomenon. To the best of our knowledge, notable crosstalk has only been observed in superfluid helium both in the two-fluid regime and at very low temperatures, but was rarely seen to behave in a systematic way. We demonstrate some of its most significant properties—amplitude dependence within a short time span, long-term temporal instability, effects of the geometry of the setup and of obstacles placed between the tuning forks. Although the results are not fully understood, as the most likely explanation, we ascribe the observations to the coupling of tuning forks to standing acoustic modes inside the experimental volume, emphasizing the importance of second sound for understanding the observations at temperatures within the two-fluid regime (1 K<T<2.17 K). Finally, we suggest simple precautions leading to suppression of excessive acoustic crosstalk between oscillating objects in He II.     

Heterogeneous Phase Equilibria in Rare Earth–Mn–O Systems in Air

The phase relations in rare earth–Mn–O systems in air are considered. Most of the phase diagrams of these systems fall into two distinct groups: R"–Mn–O (R" = Y, Ho–Lu) and R"–Mn–O (R" = Pr, Nd, Sm–Dy). In addition, the Sc–Mn–O, La–Mn–O, and Ce–Mn–O systems have phase-diagram features of their own. The Ce–Mn–O system contains no ternary oxides or solid solutions: there are only mixtures of cerium and manganese oxides. The Sc–Mn–O system has phase-diagram features in common with both the R"–Mn–O and M–Mn–O (M = Mg, Al, 3d transition metal) systems. The La–Mn–O phase diagram can be thought of as a degenerate diagram of the R"–Mn–O group, since LaMn₂O₅ exists at oxygen pressures higher than atmospheric pressure. The R"–Mn–O and R"–Mn–O systems contain two chemical compounds, RMnO₃ and RMn₂O₅, but differ in the crystal structure of RMnO₃: hexagonal in the R" group and orthorhombic perovskite-like in the R" group. A key role in determining the structure of RMnO₃ is played by the size factor. In both groups, the RMn₂O₅ compounds dissociate in air by the reaction \({\text{RMn}}_{\text{2}} {\text{O}}_{\text{5}} {\text{ = RMnO}}_{\text{3}} + \frac{1}{3}{\text{RMn}}_{\text{3}} {\text{O}}_{\text{4}} + \frac{1}{3}{\text{O}}_{\text{2}} \). The dissociation temperature of RMn₂O₅ is shown to correlate with the atomic number of R, the total number of 4f electrons, the number of unpaired 4f electrons, and the ionic radius of R³⁺.     

New trends in V–P–O solids

On the basis of the industrial interest of the oxovanadium phosphate catalysts, current research effort in this field is focused mainly on the development of synthetic strategies directed towards obtaining open-framework materials. There is a growing body of work describing preparations using hydrothermal procedures under a diversity of conditions. A great number of new solids, whose nets range from lamellar arrays to micro- and mesostructured organizations, has been prepared in last years. In this context, the applicability of concepts and procedures from the zeolites chemistry to systems involving transition elements is critically analyzed.     

Joule–Thomson Inversion in Vapor–Liquid–Solid Solution Systems

Solid phase precipitation can greatly affect thermal effects in isenthalpic expansions; wax precipitation may occur in natural hydrocarbon systems in the range of operating conditions, the wax appearance temperature being significantly higher (as high as 350 K) for hyperbaric fluids. Recently, methods for calculating the Joule–Thomson inversion curve (JTIC) for two-phase mixtures, and for three-phase vapor–liquid–multisolid systems have been proposed. In this study, an approach for calculating the JTIC for the vapor–liquid–solid solution systems is presented. The JTIC is located by tracking extrema and angular points of enthalpy departure variations versus pressure at isothermal conditions. The proposed method is applied to several complex synthetic and naturally occurring hydrocarbon systems. The JTIC can exhibit several distinct branches (which may lie within two- or three-phase regions or follow phase boundaries), multiple inversion temperatures at fixed pressure, as well as multiple inversion pressures at given temperature.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

p–T–x Phase Equilibria in the Cd–Zn–Te System

The p–T–x–y phase equilibria in the Cd–Zn–Te system are analyzed. The p–T and T–x–yprojections of the p–T–x–y phase diagram and a T–x–y isobar (for pressures at which Cd_1–x Zn _x Te_{1 ±} solid solutions sublime congruently in terms of Te) are mapped out. The key features of the sublimation behavior of the solid solution are examined. The p–T projection is studied by static vapor pressure measurements at temperatures from 700 to 1300 K and pressures of up to 101.3 kPa. The p–T sections of the phase diagram are constructed for x = 0.05, 0.10, 0.15, 0.25, 0.50, 0.75, 0.90, and 1. The solid solution containing 35 mol % ZnTe is found to phase-separate at 473 K.     

New Cubic Phases in the Li–Na–Sb–Bi System

New compounds with the general formula A _x A"_3-x B _y B"_1-y (A, A" = Li, Na; B, B" = Sb, Bi) were prepared in the system Li–Na–Sb–Bi. Na₃Sb_0.5Bi_0.5has a hexagonal structure (Na₃As type, a= 5.415 Å, c= 9.595 Å), and Li₃Sb_0.5Bi_0.5and Li₂NaSb_0.5Bi_0.5have a cubic structure (BiF₃type, a= 6.645 and 6.772 Å, respectively). The phase transitions of alkali-metal pnictides were studied by in situ x-ray diffraction at room temperature and pressures from 10⁵Pa to 9.0 GPa. Li₃Sb and Na₃Sb were each shown to exist in two polymorphs with hexagonal (Na₃As type) and cubic (BiF₃type) structures. At atmospheric pressure, Li₃Sb undergoes an irreversible – phase transition at 650°C, while Na₃Sb undergoes a reversible transformation into a cubic phase at 2.3 GPa and room temperature.     

Precipitation in Cu–Ni–Si–Zn alloy for lead frame

The aging of Cu–Ni–Si–Zn alloy for lead frame is investigated. The results showed that the peak of hardening effect occurs after aging for about 1 h and the electrical conductivity increases continuously with aging times. The hardness of the alloy reached a peak at 430–460 °C for 2 h and electrical conductivity reached a peak at 500–550 °C and continuously decreased afterwards. The cold rolling prior to the aging treatment was used to increase the precipitation rate. The precipitates responsible for the age-hardening effect are disc-shaped δ-Ni₂Si, which has an orthorhombic structure.     

Phase Relations in the Bi–(Pb)–Sr–Ca–Cu–Sc–O System

The phase relations in the Bi–(Pb)–Sr–Ca–Cu–Sc–O system were studied near Bi₂Sr₂CaCu₂O_{8 +} (Bi-2212) and (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 +} (Bi-2223) between 850 and 930°C. The introduction of Sc led to the formation of a new compound Sr₂ScBiO₆, which coexisted with Bi-2212 and Bi-2223. Using crystallization from a peritectic melt at different cooling rates, we obtained Bi-2212 matrix composites containing finely dispersed Sr_1.9Ca_0.1ScBiO₆inclusions, with T _cattaining 89 K. The T _cof the Bi-2223–Sr_1.9Ca_0.1ScBiO₆superconducting ceramic prepared by solid-state sintering of a Bi–(Pb)–Sr–Ca–Cu–Sc–O precursor was 108.5 K.     

Phase Relations in the Cu–Sb–O System

The Cu–Sb–O system was studied by x-ray diffraction and thermal analysis between 700 and 1000°C. The compositions of copper antimonates were refined. Sb₂O₄ was found to exist in two polymorphs above 800°C: -Sb₂O₄ (dominant phase) and -Sb₂O₄. The evolution of phase equilibria with increasing temperature was examined. The isothermal sections of the Cu–Sb–O phase diagram were mapped out using new and earlier reported results.     

Role of nickel in the oxidation of Fe–Cr–Ni alloys in air–water vapour atmospheres

Abstract

A series of experimental austenitic alloys has been produced in which the nickel content ranges from 14 to 43%, with constant levels of 20%Cr, 1%Mn and 0.5%Si. A combination of isothermal, discontinuous and cyclic oxidation testing has been used to elucidate the performance in dry air and in air with 10%, 45% or 62% water vapour at 700°C and 1000°C. Evaluation was by means of thermogravimetry, surface analysis with glow discharge optical emission spectroscopy and scanning electron microscopy.

Nickel is shown to have several roles: it accelerates the kinetics of chromia formation yet suppresses chromia spallation at 700°C. At 1000°C, it strongly decreases the breakaway oxidation and spalling associated with iron oxide formation. This effect is particularly marked in environments containing water vapour, where the material loss may be decreased 10-fold by an increase in the nickel content. Results correlate to thermodynamic and kinetic data which show nickel to increase the chromium activity and diffusivity in the alloy.     

Strengthening mechanisms in solution treated Mg–yNd–zZn–xZr alloy

A number of solution treated Mg–0.52Nd–0.08Zn–xZr (x = 0, 0.01, 0.03, 0.07, 0.12, and 0.14), Mg–yNd–0.08Zn–0.12Zr (y = 0, 0.17, 0.34, and 0.52) and Mg–0.52Nd–zZn–0.12Zr (z = 0, 0.08, 0.19, and 0.38) (at.%) cast alloys were investigated in terms of grain boundary and solid solution strengthening in this study. The hardness and yield strength of these alloys are determined by the average grain size (Zr content) and the concentration of Nd and Zn elements. The hardness can be predicted as HV₅ ≈ 23 + 3.07 d ^?0.5 (m^?0.5) + 26.5 C _Nd (at.%) + 10.5 C _Zn (at.%), with the average error of about 1.3 %. When the interactions among different solution atoms were not considered, the yield strength can be expressed as σ_0.2 (MPa) = 21 + 0.42 d ^?0.5 (m^?0.5) + (813^3/2 C _Nd (at. %) + 964^3/2 C _Zn (at. %))^2/3, with the average error of about 2.0 %. When the interactions among different solution atoms were considered, more exact yield strength prediction could be obtained with the average error of about 1.6 %.     

Violation of Mermin–Ardehali–Belinksii–Klyshko inequality in the three-Jaynes–Cummings model

In this paper, we consider the situation that three identical two-level atoms are separately trapped in the three single-mode cavities. Each atom resonantly interacts with cavity via a one-photon hopping. The dynamics of nonlocality in the system is investigated via Mermin–Ardehali–Belinksii–Klyshko inequality. The results show that when three atoms are initially in W state and three-cavity fields are in vacuum states both the quantum state of three atoms and that of three cavities all display nonlocality On the other hand, when three atoms are initially in Greenberger–Horne–Zeilinger state and three-cavity fields are in vacuum states, the quantum state of three atoms and that of three cavities all do not display nonlocality.     

Specific Features of Structural Changes in Lanthanum–Nickel–Aluminum Alloys in the Process of Heating in Hydrogen

We study interactions in LaNi_{5 – x} Al _x –H₂ (x = 0, 0.2, 0.4, 0.6, and 0.8) systems by the methods of differential thermal and X-ray phase diffraction analyses within the temperature range from the room temperature to 920°C in hydrogen whose initial pressure can be as high as 5.7 MPa. In LaNi_{5 – x} Al _x –H₂ systems with x = 0, 0.2, and 0.4, the processes of formation and decomposition of the intermetallic hydride run without changes in its symmetry. The process of heating of LaNi_{5 – x} Al _x (x = 0, 0.2, and 0.4) alloys in hydrogen results in their homogenization. Thus, the process of heating of the LaNi_4.4Al_0.6 alloy in hydrogen to 700°C for an initial pressure of about 5.7 MPa results in a partial decomposition (disproportionation) of the original phase accompanied by the formation of lanthanum hydride and Ni₃Al. As a result of heating to 575°C in hydrogen ( 5.0 MPa), the LaNi_4.2Al_0.8 compound disproportionates into Ni₃Al and an unknown phase. After heating to 840°C followed by holding for 1.5 h, we detect the original phase, lanthanum hydride, Ni₃Al, and an unknown phase. At the same time, as a result of heating to 910°C followed by holding for 2 h, we observe the formation of a hydride of the original phase with doubled spacing c, lanthanum hydride, and Ni₃Al.     

Calcite–oleate–oxalate interaction in calcite flotation system

Calcite is considered a semi-soluble mineral in flotation. Its solubility in acids plays a major role in its floatability. In this study, micro-flotation experiments are conducted to investigate the interaction of calcite particles with potassium oleate (KOl). Potassium oxalate is used as a depressant in the presence of HC1 or H₂SO₄ as pH modifiers. Flotation experiments indicated that calcite behaves differently in the presence of HCl and H₂SO₄. The calcite floatability is higher in the case of HCl. The different behavior is more obvious in the presence of oxalate. The depressing effect of oxalate is more pronounced in the case of using H₂SO₄ as a pH modifier. In addition, the sensitivity of calcite flotation to pH goes back to the amount of free Ca-ions in the solution. Ionic equilibrium of the dissolved ionic species is proved to play a crucial role in either enhancing or reducing the oleate adsorption, which in turn affects the calcite floatability.     

Stone–Wales Defect in Graphene

2D graphene the most investigated structures from nanocarbon family studied in the last three decades. It is projected as an excellent material useful for quantum computing, artificial intelligence, and next generation advanced technologies. Graphene exists in several forms and its extraordinary thermal, mechanical, and electronic properties, principally depend on the kind of perfection of the hexagonal atomic lattice. Defects are always considered as undesired components but certain defects in graphene could be an asset for electrochemistry and quantum electronics due to the engineered electronclouds and quantum tunnelling. The authors carefully discuss the Stone-Wales imperfections in graphene and its derivatives comprehensively. A specific emphasis is focused on the experimental and theoretical aspects of the Stone-Wales defects in graphene with respect to structure-property relationships. The corroboration of extrinsic defects like external atomic doping, functionalization, edge distortion in the graphene consisting of Stone-Wales imperfections, which are very significant in designing graphene-based electronic devices, are summarized.     

Solid state phase transformations in Ti–Al–C and Ti–Al–Nb–C alloys

Abstract

Results are reported of an investigation of solid state transformations in a series of α₂ based alloys having an aluminium content of 26 at.-% with carbon up to 3 at.-%; two α₂ basedquaternary Ti–Al–Nb–C alloys with 5 and 12 at.-%Nb and 3 at.-%C were also studied. Ordering occurs in the ternary Ti–Al–C alloys and also in the 23Al–5Nb–3C alloy on quenchingfrom 1250°C. Additional carbide precipitation was not observed in the ternary Ti–Al–C alloys on reheating to 750°C. Additions of niobium resulted in the presence of the β phase at 1050°C in the 5%Nb alloy and at 1050 and 750°C in the 12%Nb alloy. In the quaternary Ti–Al–Nb–C alloys, (Ti, Nb)₃AlC was found to be the primary phase and was present in the microstructure over the temperature range studied. In the 21Al–12Nb–3C alloy, the ordered β phase transformed to α″₂ martensite on quenching from 1250;amp;#x00B0;C.

MST/1306     

Decomposition of supersaturated solid solutions in Al–Cu–Mg–Si alloys

The Al–Cu–Mg–Si alloying system is a base for a diverse group of commercial alloys which acquire their properties after quenching and aging. Therefore, the knowledge of the phase composition of hardening precipitates and the conditions under which they are formed is very important. ast reference data were analyzed along with experimental results and calculations of phase equilibria. Different alloys were compared based on the composition of the supersaturated solid solution. It is shown that the phase composition of aging products in alloys with Mg : Si > 1 agrees well with the equilibrium phase composition at a temperature of annealing. However, the sequence of precipitation in the alloys with Mg : Si < 1 is more complicated. The hardening in these alloys occurs with precipitation of the and phases and their precursors. The former phase may contain copper and later transforms either to and (Mg₂Si) or to Q phase depending on the amount of copper and annealing temperature.     

Structure of metastable precipitate in some Al–Cu–Mg–Ag alloys

Abstract

The high strength of some Al–Cu–Mg–Ag alloys has been attributed to very thin (~2·5 nm), but broad, hexagonal-shaped precipitates. Previous work has shown that the precipitates have a hexagonal unit cell, but different lattice parameters have been reported. In the present paper, the intensities of X-ray diffraction reflections from the precipitates have been measured on Buerger precession photographs, and it is shown that the crystal structure is monoclinic (space group P2/m) with the parameters a = b = 0·496 nm, c = 0·848 nm, γ = 120°. The special values of these parameters confer a hexagonal symmetry on the lattice. This unusual structure is a slightly distorted form of θ-CuAl₂, to which it appears to change after long aging times at 200°C.     

Pearlite growth rate in Fe–C and Fe–Mn–C steels

The kinetic theory for the growth of pearlite in binary and ternary steels is implemented to ensure local equilibrium at the transformation front with austenite, while accounting for both boundary and volume diffusion of solutes. Good agreement is on the whole observed with published experimental data, although the reported growth rate at the lowest of temperatures is much smaller than predicted. To investigate this, experiments were conducted to replicate the published data. It is found that the cooperation between cementite and ferrite breaks down at these temperatures, and surface relief experiments are reported to verify that the resulting transformation product is not bainite.