A portable high-pressure stress cell based on the V7 Paris–Edinburgh apparatus

We describe a new device, based on a V7 Paris–Edinburgh press, for torsional testing of material at pressures up to 7 GPa (extendable to 15 GPa). Samples are deformed using a simple shear geometry between opposed anvils by rotating the lower anvil, via a rotational actuator, with respect to an upper, stationary, anvil. Use of conical anvil profiles greatly increases sample dimensions more than other high-pressure torsional apparatus did. Samples of polycrystalline Zr (2 mm thick, 3.5 mm diameter) have been sheared at strains exceeding γ ～1.5 at constant strain rate and at pressures from 1.8 to 5 GPa, and textural development has been studied by electron microscopy. Use of amorphous-boron-epoxy gaskets means that nearly simple shear of samples can be routinely achieved. This apparatus allows study of the plastic and anelastic behaviour of materials under high pressure, and is particularly suited for performing in situ investigations using synchrotron or neutron radiation.     

Optimization of Paris–Edinburgh press cell assemblies for in situ monochromatic X-ray diffraction and X-ray absorption

We describe some important improvements allowed by the development of new cell assemblies coupled to opposed conical sintered diamond anvils in the Paris–Edinburgh press. We provide X-ray absorption and diffraction experiments carried out at pressures up to 16.5 GPa. The maximum temperature reached was 1800 K for P<10 GPa and 1300 K for higher pressures. The sintered diamond anvils are X-ray transparent and give access to a much larger X-ray window than the tungsten carbide anvils, even at the highest pressure. Therefore, X-ray measurements are performed using in situ cross-calibration simultaneously. We also describe a new heating setup used to reach high temperatures, despite the low conductivity of the sintered diamond core by deviating the electrical current using copper strips. These improvements are illustrated by recent data collected using angle dispersive in situ X-ray diffraction on liquid Fe-18%wt S and using EXAFS at the barium K-edge on Ba₈Si₄₆ silicon clathrates and at the iodine K-edge on iodine-intercalated nanotubes.     

Atomic mobility in a ternary liquid Ga–In–Sn alloy of the eutectic composition

The nuclear spin–lattice relaxation and Knight shift of ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In nuclei in a ternary liquid gallium–indium–tin alloy of the eutectic composition, which was introduced into pores of an opal matrix and porous glasses with pore sizes of 18 and 7 nm, have been investigated and compared with those for the bulk melt. It has been found that longitudinal relaxation is accelerated and the Knight shift is decreased, depending on the size of pores. The correlation time of the atomic motion has been calculated for the nanostructured melt in porous matrices. It has been shown that the atomic mobility in the melt decreases with decreasing size of pores in the glasses.

     

Experimental evidence of the transformation from microheterogeneous to microhomogeneous states in Ga–Sn melts

The electrical resistivities of liquid Ga–Sn system have been carefully measured as a function of temperature for different compositions employing direct-current four-probe method. It was well known that the electrical resistivity varies linearly with temperature for typical liquid metals. However, an abnormal change on the resistivity-temperature curve in the intermediate temperature region Ts–Te$T_s\text{–}{T}_e$ (385–422 °C for Ga₂₀Sn₈₀ melt and 395–449 °C for liquid Ga₁₀Sn₉₀ melt, here Ts$T_s$ and Te$T_e$ are denoted as the start-temperature and the end-temperature of the abnormal change) is observed in the initial Ga₂₀Sn₈₀ and Ga₁₀Sn₉₀ melts during first heating, but this abnormal behavior disappears during subsequent cooling as well as reheating process. This result indicates that in the initial Ga₂₀Sn₈₀ and Ga₁₀Sn₉₀ melts there may exist the microheterogeneities, during heating in the temperature range from Ts$T_s$ to Te$T_e$ the irreversible structure transition possibly takes place from microheterogeneous melt to microhomogeneous melt. It suggests that the necessary overheating above liquidus up to Te$T_e$ is a guarantee of the molten alloy getting the microhomogeneous sate or the true solution and conserving it during cooling down to liquidus at any cooling rates.     

In situ Raman Spectroscopic Study of the Kinetics of the Chemical Dissolution of Ytterbium Oxide in YbCl3–KCl Melt

Journal of Applied Spectroscopy - Using the Yb2O3–YbCl3–KCl oxide–chloride system as an example, an approach has been proposed and tested permitting a Raman spectral study of the...     

Bloch–Siegert shift in application to the astrophysical determination of the fundamental constants variation

We have evaluated the Bloch–Siegert shift for the different values of magnetic field?s strengths defined at astrophysical conditions, i.e. when the stars with the strong surface magnetic fields are taken as a powerful pumping source of radiation. It is found that the additional shift of resonant frequency should be taken into account in the search for the time variation of the fundamental constants. The main conclusion is that the influence of the electromagnetic field should be considered carefully in each special case of the corresponding frequency determination.     

Heat distribution in Paris–Edinburgh press assemblies through finite element simulations

Knowledge on the temperature distribution in high pressure and temperature devices is important for the interpretation of data and can often not be obtained from experiments. Here, we report on the thermal characteristics of the most employed Paris–Edinburgh press assemblies for in-situ X-ray purposes using finite element calculations. The maximal horizontal T variations in the sample are found to be small and amount maximal 50?K at 2500?K. Temperature differences between the sample and the calibrant material are in the same order of magnitude only if the latter is placed well centred on the sample capsule. The present (pure thermal) calculations can only partly reproduce the discrepancies between experimentally determined input power to T relations (1000?K at 350?W) indicating that different deformation behaviours of assemblies may play a crucial role. Based on the obtained results we present an optimized assembly in terms of sample temperature and gradients.     

Experimental verification of the Stokes-Einstein relation in liquid Fe—FeS at 5 GPa

Experiments have been performed at 5 GPa on liquid Fe-FeS in order to determine Fe and S self-diffusivity as a function of temperature. The viscosity of the sample was then obtained using the Stokes-Einstein relation. The results are in excellent agreement with previous experiments where the viscosity of a material of the same composition under similar conditions was measured directly. These results support high, near-metallic, values of diffusivity and low viscosity in liquid Fe-S up to a few hundred K above the eutectic temperature, in contrast with some previous studies. Moreover, these results fully confirm the validity of the Stokes-Einstein relation between viscosity and diffusion coefficients for Fe_0.61S_0.39.     

Simple approach to approximate predictions of the vapor–liquid equilibrium curve near the critical point and its application to Lennard-Jones fluids

We propose a simple analytical form of the vapor–liquid equilibrium curve near the critical point for Lennard-Jones fluids. Coexistence densities curves and vapor pressure have been determined using the Van der Waals and Dieterici equation of state. In described method the Bernoulli differential equations, critical exponent theory and some type of Maxwell?s criterion have been used. Presented approach has not yet been used to determine analytical form of phase curves as done in this Letter. Lennard-Jones fluids have been considered for analysis. Comparison with experimental data is done. The accuracy of the method is described.     

In situ high-pressure study of LiNbO3-type FeTiO3: X-ray diffraction and Mössbauer spectroscopy

The structure of LiNbO₃-type FeTiO₃ and the oxidation state of Fe have been investigated using X-ray diffraction and Mössbauer spectroscopy in the diamond anvil cell up to 18 GPa at room temperature. A structural phase transition is observed at 15.7 GPa from LiNbO₃-type to perovskite-type, accompanied by a volume collapse of 1.5%. LiNbO₃-type FeTiO₃, which is shown to contain only ferrous iron up to this pressure, and no charge transfer is observed. In addition to the c/a axial ratio that has been used to distinguish between ilmenite and LiNbO₃-type FeTiO₃, the hyperfine parameters (isomer shift and quadrupole splitting) provide an efficient way to discriminate between these two phases.     

In situ analysis of the tensile deformation mechanisms in extruded Mg–1Mn–1Nd (wt%)

An extruded Mg–1Mn–1Nd (wt%) (MN11) alloy was tested in tension in an SEM at temperatures of 323?K (50°C), 423?K (150°C), and 523?K (250°C) to analyse the local deformation mechanisms through in situ observations. Electron backscatter diffraction was performed before and after the deformation. It was found that the tensile strength decreased with increasing temperature, and the relative activity of different twinning and slip systems was quantified. At 323?K (50°C), extension twinning, basal, prismatic ?a?, and pyramidal ?c?+?a? slip were active. Much less extension twinning was observed at 423?K (150°C), while basal slip and prismatic ?a? slip were dominant and presented similar activities. At 523?K (250°C), twinning was not observed, and basal slip controlled the deformation.     

In situ TEM characterisation of dislocation interactions in α-titanium

In situ straining in the transmission electron microscope and diffraction-contrast electron tomography has been applied to investigate dislocation interactions in α-Ti. Dislocation debris, in the form of small loops, was seen to form from sequential cross-slip events. Electron tomography provided direct three-dimensional visualisation of the dislocation structures, allowing accurate identification of slip planes, dislocation line directions and spatial relations between dislocations.     

Optical pressure sensors for high-pressure–high-temperature studies in a diamond anvil cell

We review the various optical pressure sensors that are suitable for high-pressure and high-temperature studies in a diamond anvil cell. Two different kinds of sensors are considered: those based on the pressure shift of a fluorescence line (ruby, SrB₄O₇:Sm²⁺) and those based on the pressure shift of a Raman line (c-BN, diamond). The calibration of those sensors are presented in detail, and discussion is made on their useful pressure and temperature ranges.     

Theory of multinonlinear media and its application to the soliton processes in ferrite–ferroelectric structures

A theory is developed to describe the wave processes that occur in waveguide media having several types of nonlinearity, specifically, multinonlinear media. It is shown that the nonlinear Schrödinger equation can be used to describe the general wave process that occurs in such media. The competition between the electric wave nonlinearity and the magnetic wave nonlinearity in a layered multinonlinear ferrite–ferroelectric structure is found to change a total repulsive nonlinearity into a total attractive nonlinearity.     

Thermal conductivity of liquid rubidium in the interval of 312–873 K

The thermal conductivity λ and the thermal diffusivity a of liquid rubidium were measured by the laser flash method in the temperature interval from the melting point up to 873 K. The measurement error was 4–6%. The data of this paper were compared with the results of other authors. Approximation equations and the table of reference values for the temperature dependence of λ and a have been obtained. The dependence of the Lorentz number on temperature has been calculated.     

The evolution of covalent bonding structures of liquid In–Sn alloys

The short-range orders of liquid In_xSn_100−x binary alloys have been investigated along the liquidus based on the experimental results obtained using X-ray diffraction. The covalent bonding structures characterized by the shoulder on the high-Q side of the first peak of S(Q) for all the In_xSn_100−x melts are detected. With increasing Sn content, there is a rather continuous change of the local structure possibly related to the presence of nearly covalent bonds in the liquid alloy. The peculiar temperature dependence of the viscosity is assigned to the evolution of tetrahedral units. The observed correlation between liquid structures and peculiar viscosity behaviors provides new insight into nucleation phenomena from microscopic viewpoint.     

Thermophysical properties of Cu–In–Sn liquid Pb-free alloys: viscosity and surface tension

The viscosity of a few Cu–In–Sn liquid alloys has been investigated by a number of geometric (Muggianu, Kohler, Toop) and physical thermodynamic models (Kozlov–Romanov–Petrov, Budai–Benko–Kaptay, Schick et al.) and GSM for the cross section (z/y = 1/3) in Pb-free liquid alloy Cu_x–In_y–Sn_z at 1073 K. Moreover, the surface tensions of the same liquid alloys have been investigated by a number of geometric models and the Butler model for the cross section Cu_x–In_y–Sn_z (z/(y + z) = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) at the same temperature. The best agreement of the surface tensions was obtained in the Kohler model for x_Cu = 10 at % and the Butler model for x_Cu = 20 at % and x_Cu = 30 at.%, respectively. The best agreement among chosen geometric and physical models and experiment for these selected sections Cu₈₀In₁₅Sn₅, Cu₇₅In₁₅Sn₁₀, Cu₅₅In₇Sn₃₈, Cu₃₃In₅₀Sn₁₇ and Cu₂₆In₅₅Sn₁₉ at 1073 K was obtained for the Budai–Benkö–Kaptay model.     

Investigation of the Livengood–Wu integral for modelling autoignition in a high-pressure bomb

The reaction progress variable, which is widely used in premixed and diffusion combustion studies, comprises a set of pre-selected intermediate species to denote reaction progress. Progress towards autoignition can also be traced by the Livengood–Wu (LW) integral. Autoignition occurs when the LW integral attains a value of unity. This concept is further explored by applying it to an inhomogeneous mixture scenario, to determine the time and place of autoignition occurrence. A semidetailed mechanism (137 species and 633 reactions) for n-heptane/iso-octane/toluene is used in this study. Two numerical schemes based on the LW integral are proposed and incorporated into a computational fluid dynamics platform, to model autoignition in a 3D configuration, when a spray is injected into a constant volume bomb under diesel engine conditions. Tabulated chemistry, a traditional method of modelling autoignition using information from pre-calculated igniting diffusion flames, is also used for comparison purposes. The associated predicted pressure profiles are compared with experimental measurements.     

The magnetic contribution to the driving force for crystal nucleation in undercooled Co–Pd melts

To account for the dependence of the crystal nucleation temperature in Co–Pd melts over the entire range from 50 to 100?at.%?Co it is necessary to incorporate a contribution to the driving free energy that derives from the difference in magnetic free energies between liquid and melt. A simple molecular-field model provides a satisfactory fit of the earlier data.