High pressure and emission spectra of Eu3+ in L-EuBO3

Effects of the high pressure on the emission spectra of Eu³⁺-activated L-EuBO₃ were considered at room temperature up to 100 kbar. The position of five 0–2 lines in the ⁵D₀→⁷F₂ transition region was determined. The pressure does not have the same effect on all these lines. In four of them, high pressure induced a red shift with different shift rates:+0.0022,+0.0035,+0.0034 and+0.0027 nm kbar^?1, respectively, whereas in the last one, high pressure induced a blue shift with shift rate?0.0034 nm kbar^?1. Possible reasons for the mentioned pressure effects on the line positions were considered.     

Compressibility determination by electrical resistance measurement: a universal method for both crystalline and amorphous solids

A new method is introduced for investigating the compressibility of solids under high pressure by in situ electrical resistance measurement of a manganin wire, which is wrapped around the sample. This method does not rely on the lattice parameters measurement, and the continuous volume change of the sample versus pressure can be obtained. Therefore, it is convenient to look at the compressibility of solids, especially for the X-ray diffraction amorphous materials. The I–II and II–III phase transition of Bi accompanying with volume change of 4.5% and 3.5% has been detected using the method, respectively, while the volume change for the phase transition of Tl occurring at 3.67 GPa is determined as 0.5%. The fit of the third-order Birch–Murnaghan equation of state to our data yields a zero-pressure bulk modulus K ₀=28.98±0.03 GPa for NaCl and 6.97±0.02 GPa for amorphous red phosphorus.     

Preparation and characterization of zirconium sulfophenyl phosphate-doped sulfonated poly(phthalazinone ether sulfone) composite proton exchange membrane

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and zirconium sulfophenyl phosphate (ZrSPP) were prepared. Three ZrSPP concentrations were used: 10, 20, and 30 wt%. The membranes were characterized by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, and scanning electron microscopy (SEM). The IR results indicated the formation of intense hydrogen bonds between ZrSPP and SPPES molecules. The SEM micrographs showed that ZrSPP well dispersed with SPPES and form a lattice structure. The proton conductivity of the SPPES (degree of sulfonation (DS) 64 %)/ZrSPP (10 wt%) composite membrane reached 0.39 S/cm at 120 °C 100 % relative humidity and that of the 30 wt% of SPPES (DS 16.1 %)/ZrSPP composite membrane reached 0.18 S/cm at 150 °C. The methanol permeabilities of the SPPES/ZrSPP composite membranes were in the range of 2.1?×?10^?8 to 0.13?×?10^?8?cm²/s, much lower than that of Nafion®117 (10^?6?cm²/s). The composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance properties.     

Enhancing the performance of thin film CdS/PbS photovoltaic solar cells

This work investigates dependence of the short-circuit current density, open-circuit voltage, fill factor and efficiency of a thin film CdS/PbS solar cell on thickness of transparent conductive oxide (TCO) layer, thickness of window layer (CdS), concentration of uncompensated acceptors (width of space-charge region), carrier lifetime in PbS and the reflectivity from metallic back contact. The effect of optical losses, front and rear recombination losses as well as the recombination losses on space-charge region are also considered in this study. As a result, by thinning the front contact layer indium tin oxide from 400 to 100 nm and window layer (CdS) from 200 to 100 nm it is possible to reduce the optical losses from 32 to 20%. The effect of electron lifetime on the internal and external quantum efficiency can be neglected at high width of the space-charge region. The maximum current density of 18.4 mA/cm² is achieved at wide space-charge region (concentration of uncompensated acceptors = 10¹⁵ cm^?3) and the longest lifetime (τ_n = 10^?6 s) where the optical and recombination losses are about 55%. The maximum efficiency of 5.17%, maximum open-circuit voltage of 417 mV and approximately fixed fill factor of 74% are yielded at optimum conditions such as: electron lifetime = 10^?6 s; concentration of uncompensated acceptors = 10¹⁶ cm^?3; thickness of TCO = 100 nm; thickness of CdS = 100 nm; velocity of surface and rear recombination = 10⁷ cm/s and thickness of absorber layer = 3 μm. When the reflectance from the back contact is 100%, the cell parameters improve and the cell efficiency records a value of 6.1% under the above conditions.     

Photoluminescence and Raman spectroscopy studies of Eu3+-doped rutile TiO2 nanocrystals at high pressures

Nanocrystal samples (particle size about 90 nm) of Eu³⁺-doped rutile titanium dioxide (TiO₂) nanocrystals (rutile Eu³⁺/TiO₂ nanocrystals) were synthesized by the sol–gel method with hydrothermal treatment. The pressure effect on photoluminescence (PL) and Raman spectra of the rutile Eu³⁺/TiO₂ nanocrystals was investigated with a diamond anvil cell under hydrostatic pressure condition. Raman spectra of the samples at high pressures indicated that the critical pressure for the transition from the rutile phase to a new baddeleyite-type phase was between 10 and 14.2 GPa. The position of Raman bands shifted to high wavenumbers and the PL intensity of ⁵D ₀→⁷F ₂ transition of Eu³⁺ decreased down to zero with the increase of pressure before the phase transition occurred. After releasing the pressure, the rutile phase was not recovered and a α-PbO₂-type phase was observed at ambient pressure.     

The hydrogen‐bond effect on the high pressure behavior of hydrazinium monochloride

The first high pressure study of solid hydrazinium monochloride has been performed by in situ Raman spectroscopy and synchrotron X‐ray diffraction (XRD) experiments in diamond anvil cell (DAC) up to 39.5 and 24.6 GPa, respectively. The structure of phase I at room temperature is confirmed to be space group C2/c by the Raman spectral analysis and Rietveld refinement of the XRD pattern. A structural transition from phase I to II is observed at 7.3 GPa. Pressure‐induced position variation of hydrogen atoms in NH₃⁺ unit during the phase transition is attributed to the formation of N―H…Cl hydrogen‐bonds, which play a vital role in the stability and subsequent structural changes of this high energetic material under pressure. This inference is proved from the abnormal pressure shifts and obvious Fermi resonance in NH stretching mode of N₂H₅⁺ ion in the Raman experiment. Finally, a further transition from phase II to III accompanied with a slight internal distortion in the N₂H₅⁺ ions occurs above 19.8 GPa, and phase III persists up to 39.5 GPa. Copyright © 2015 John Wiley & Sons, Ltd.     

Low-cost set-up for Fourier-transform infrared spectroscopy in diamond anvil cell from 4000 to 400 cm−1

An experimental set-up for Fourier-transform infrared (FTIR) studies at high pressure in the mid-IR region (400–4000 cm^?1) is constructed using a compact TEO-400 FTIR interferometer module and an external microscopic optical bench with cassegrain focusing objectives. Cassegrain-type reflective objectives act as an excellent beam condenser that facilitates the interfacing between FTIR spectrometer and diamond anvil cell. This set-up is capable of recording transmission and reflection infrared spectra at high pressure. Preliminary results are reported both in the reflection (pressure dependence of polar phonons in CuWO₄) and transmission configuration (polarized light absorption of polar phonons across the wurtzite-to-rocksalt transition in ZnO).     

Infrared study of hydrogen up to 310 GPa at room temperature

We observed a strong difference of the pressure dependence of the infrared (IR) active molecular vibron of hydrogen in phase IV in the 200–310 GPa pressure range in comparison with the Raman vibrons. While the Raman vibron strongly splits (～250 cm^?1) at the transition from phases III to IV at 220 GPa, the IR vibron nearly does not change. This small spitting of IR vibron is not described by the graphene-like structure proposed for phase IV. The combined pressure dependence of Raman and IR vibrons provides a sensitive test for further theoretical models of phase IV.     

An examination of the shrinking-core model of sub-micron aluminum combustion

We revisit the shrinking-core model of sub-micron aluminum combustion with particular attention to the mass flux balance at the reaction front which necessarily leads to a displacement velocity of the alumina shell surrounding the liquid aluminum. For the planar problem this displacement simply leads to an equal displacement of the entire alumina layer, and therefore a straightforward mathematical framework can be constructed. In this way we are able to construct a single curve which defines the burn time for arbitrary values of the diffusion coefficient of O atoms, the reaction rate, the characteristic length of the combustion field, and the O atom mass concentration within the alumina provided that it is much smaller than the aluminum density. This demonstrates a transition between a ‘d  ²–t’ law for fast chemistry and a ‘d–t’ law for slow chemistry. For the spherical geometry, the one of physical interest, the outward displacement velocity creates not a simple displacement, but a stress field which, when examined within the framework of linear elasticity, strongly suggests the creation of internal cracking. We note that if the molten aluminum is pushed into these cracks by the high internal pressure characteristic of the stress field, its surface, where reaction occurs, could be fractal in nature and affect the fundamental nature of the burning law. Indeed, if this ingredient is added to the planar model, a single curve for the burn time can again be derived, and this describes a transition from a ‘d  ²–t’ law to a ‘d  ^ν–t’ law, where 0<ν<1.     

Probing structural stability of double-walled carbon nanotubes at high non-hydrostatic pressure by Raman spectroscopy

Theoretical calculations predict that the collapse pressure for double-walled carbon nanotubes (DWCNTs) is proportional to 1/R ³, where R is the effective or average radius of a DWCNT. In order to address the problem of CNT stability at high pressure and stress, we performed a resonance Raman study of DWCNTs dispersed in sodium cholate using 532 and 633 nm laser excitation. Raman spectra of the recovered samples show minor versus irreversible changes with increasing I _D/I _G ratio after exposure to high non-hydrostatic pressure of 23 and 35 GPa, respectively. The system exhibits nearly 70% pressure hysteresis in radial breathing vibrational mode signals recovery on pressure release which is twice that predicted by theory.     

Experimental and Numerical Investigation of the Effect of Turbulator on Heat Transfer in a Concentric-type Heat Exchanger

This article experimentally and numerically analyzes the effect of turbulators with different geometries (Type I, Type II, Type III, and Type IV) located at the inlet of the inner pipe in a concentric-type heat exchanger. Experiments were performed at parallel-flow conditions in the same and opposite directions to investigate the impact of manufactured turbulators on heat transfer and pressure drop. In the numerical study, ANSYS 12.0 Fluent code program was used, and basic protection equations were solved in the steady-state, three-dimensional, and turbulence-flow conditions. Results were obtained from numerical analysis conducted at different flow values of air (7, 8, 9, 10, 11, and 12 m³/h). The distribution of temperature, velocity, and pressure was demonstrated as a result of numerical analyses. Experimental and numerical results were compared, and it was observed that they were in conformity with each other. When the data obtained from the analyses were examined, the highest heat transfer, pressure drop, and friction factor increase were detected to be in the Type IV turbulator.     

Physical and mechanical properties of C60 under high pressures and high temperatures

The physical and mechanical properties of a C₆₀ fullerene sample have been investigated under high pressure–high temperature conditions using a designer Diamond Anvil Cell. Electrical resistance measurements show evidence of C₆₀ cage collapse at 20 GPa, which leads to the formation of an insulating phase at higher pressure. Energy dispersive X-ray diffraction (EDXD) data indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa. A C₆₀ sample was laser-heated at a pressure of 35 GPa to a temperature of 1910±100 K and, subsequently, decompressed to ambient conditions. The photoluminescence spectra and the Raman spectrum of the pressure–temperature-treated sample were measured at a low temperature of 80 K. Raman peak at 1322.3 cm^?1 with full-width half-maximum of 2.9 cm^?1 was observed from the sample, which is attributed to the hexagonal diamond phase in the sample. The room temperature photoluminescence spectra showed a symmetric emission band centered in the red spectral range with a peak at 690 nm. The structural analysis of the pressure–temperature-processed C₆₀ sample using EDXD method showed strong internal structure orientation and a phase close to hexagonal diamond. Mechanical properties such as hardness and Young’s modulus were measured by nanoindentation technique and the values were found to be 90±7 and 1215±50 GPa, respectively and these values are characteristic of sp³-bonded carbon materials.     

Optimal strength design of the outer wound part of the axisymmetrical high pressure compound vessel

Abstract

The modified ribbon winding theory was proposed, called as 'conception of the variable corrected design stress', that corresponds to the optimal constant effective stress (ev. shear stress) distribution at the wound supporting cylinder during the most dangerous working state of the compound vessel, when internal pressure is acting. The influence of the bending stress is taken into account. Internal core of the compound vessel consists of matrix and ring, made of different materials. The relations were derived in analytical form, describing the radial distribution of necessary tangential prestressing and also the stress distribution at the whole compound body in the characteristic loading states.     

Condensation heat transfer and pressure drop characteristics of R-134a inside the flattened tubes at high mass flux and different saturation temperature

In this study, heat transfer coefficients and pressure drops of R-134a inside round and flat tubes are investigated experimentally with mass flux of 450, 550, and 650 kg m^?2 s^?1 at saturation temperatures of 35°, 40°, and 45°C. The effects of mass flux and saturation temperature on heat transfer coefficient and pressure drop are examined. The maximum enhancement factor and pressure drop penalty are obtained by flat tube (FT-2) up to 2.101 at 450 kg m^?2 s^?1 and 3.01 at 650 kg m^?2 s^?1, respectively. The correlation for flat tubes is proposed to predict the heat transfer coefficient within ±20% error.     

Raman spectroscopy of melamine at high pressures up to 60 GPa

In this work, the Raman scattering of melamine was studied under high pressure up to 60 GPa. The behavior of the most intensive peaks of the Raman spectrum of melamine, 677 cm^?1 and 985 cm^?1 modes, and their line widths do not show any phase transition or indication of formation of sp ³ bonds. Comparing the behavior of the line width of the Raman peaks of graphite under pressure and that of melamine leads us to conclude that the s-triasine (C–N) ring is more rigid than the C–C graphite ring. High pressure results with melamine suggest that the direct phase transition g-C₃N₄ to dense C₃N₄ phase should occur above 60 GPa.     

Simultaneous electrical and X-ray diffraction studies on neodymium metal to 152 GPa

Using designer diamond anvils and angle dispersive X-ray diffraction technique at a synchrotron source, we have performed simultaneous electrical and structural studies on neodymium metal to 152 GPa in a diamond anvil cell. Four-probe electrical resistance measurement shows a 38% decrease in the electrical resistivity, associated with the delocalization of the 4f-shell electrons, starting at 100 GPa up to a final pressure of 152 GPa. The continuous decrease in electrical resistivity is consistent with the observation of a gradual phase transition to α-U structure in this pressure range. The (1 1 1) diffraction peak of α-U structure first appears at 100 GPa and increases in intensity with increasing pressure to 152 GPa. This increase in intensity is attributed to an increasing volume fraction of α-U phase and an increase in structural y-parameter from 0.07 at 118 GPa to 0.095 at 152 GPa. In contrast to the abrupt pressure-induced f-electron transition seen in cerium and praseodymium, the continuous evolution of α-U structure and electrical resistivity in neodymium confirms the gradual nature of 4f delocalization process in this element.     

Study of phase transition on nanocrystalline (La, Sr)(Mn, Fe)O system using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction

Pressure-induced structural changes on nano-crystalline La_0.8Sr_0.2Mn_0.8Fe_0.2O₃ were studied using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction. Mössbauer measurements up to 10 GPa showed first order transition at 0.52 GPa indicating transformation of Fe^4?+? to high spin Fe^3?+?, followed by another subtle transition at 3.7 GPa due to the convergence of two different configurations of Fe into one. High-pressure X-ray diffraction measurements carried up to 4.3 GPa showed similar results at 0.6 GPa as well as 3.6 GPa. Attempts were made to explain the changes at 0.6 GPa by reorientation of grain/grain boundaries due to uniaxial stress generated on the application of pressure. Similarly variation at 3.6 GPa can be explained by orthorhombic to monoclinic transition.     

Characterisation of backflow events over a wing section

Rare backflow (negative wall-shear stress) events have recently been found and quantified in the near-wall region of canonical wall-bounded turbulent flows. Although their existence and correlation with large-scale events have been established beyond numerical and measurement technique uncertainties, their occurrence at numerically high Reynolds numbers is still rare (less than 1 per thousand and 1 per million at the wall and beyond the viscous sublayer, respectively). To better quantify these rare events, the turbulent boundary layer developing over the suction side of a wing section, experiencing an increasing adverse pressure gradient (APG) without separation along its chord c, is considered in the present work. We find that the backflow level of 0.06% documented in turbulent channels and zero-pressure-gradient (ZPG) turbulent boundary layers is already exceeded on the suction side for x/c > 0.3, at friction Reynolds numbers three times lower, while close to the trailing edge the backflow level reaches 30%. Conditional analysis of extreme events indicates that for increasing Clauser pressure-gradient parameters (reaching β ? 35), the flow reaches a state in which the extreme events are more likely aligned with or against the freestream, and that the otherwise strong spanwise component of the wall-shear stress reduces towards the vicinity of the trailing edge. Backflow events subjected to moderate up to strong APG conditions (0.6 < β < 4.1) exhibit an average width of Δz⁺ ? 20, and an average lifetime of Δt⁺ ? 2. This directly connects with the findings by Lenaers et al., and implies that there is a connection between high-Re ZPG and strong APG conditions.     

A new multi-anvil press employing six independently acting 8 MN hydraulic rams

A new large volume multi-anvil system which employs six independently acting hydraulic rams with independent oil pressurization systems has been developed for high pressure and temperature experiments. The six 8 MN hydraulic rams approach at right angles inside a composite steel plate frame and can each advance a square faceted anvil of either hardened steel or tungsten carbide. The position of each anvil can be measured relative to the frame of the press to a precision of 0.1 μ m. The press is designed to perform both deformation experiments using cubic ceramic pressure media and experiments employing eight inner cubic anvils to compress an octahedral pressure medium. During compression, the position of each anvil relative to the press frame can be precisely measured and controlled independently, thus ensuring a high level of symmetry in the compressive stress environment. The highly cubic compressive regime provides an optimal environment for the use of inner sintered diamond cubic anvils, which can potentially obtain pressures above 50 GPa. The large loading capacity (24 MN) allows larger cubic pressure media to be used at higher pressures than conventional systems.     

Surface influence on the behavior of stabilized zirconia nanoparticles under pressure

The surface state of partially stabilized zirconia with nanoparticles of sizes 10–30 nm after temperature and pressure treatments was investigated by Fourier transform infrared spectroscopy, X-ray diffraction and small-angle X-ray scattering. It is shown that the synthesized nanoparticles are surface fractals and the fractal dimensions non-monotonically change with nanoparticles size change. The martensite tetragonal-to-monoclinic transition of the partially stabilized zirconia nanoparticles under hydrostatic pressure (100–1000 MPa) was investigated. It was shown that the character of the martensite transition in nanoparticles’ system depends on the pressure values. Three ranges of pressures were revealed. It was shown that the stability of martensite tetragonal–monoclinic transition decreases with the increase in size of the nanoparticles only for the pressures range of 300–500 MPa. Below 200 MPa, the character of the martensite transition is extreme and has a maximum for the particle size of 17 nm. In pressure range of 600–1000 MPa, the degree of martensite transition is dependent on the fractal dimension of the surface.