Fluid N2 Research Articles

Flax‐ and Graphene‐Reinforced Natural Fiber Nanocomposites under Cryogenic Environment for Constructional Applications

Mostly at the micro‐ and nanoscales, efforts were made to produce innovative thermoplastic nanocomposite materials. These composites were reinforced with natural fibres and artificial additives with improved mechanical characteristics. This research entails the creation of a novel nanocomposite material made up of unsaturated polyester resin, graphite at the nanoscale, and flax fibres at the microscale. Flax fibres make up 4, 8, and 12% of the binding matrix’s weight, respectively. A constant quantity of nanoparticles equal to 4 wt% of the binding matrix is used. In order to stick the graphene to natural fibres, an appropriate surface alteration approach is needed, and this work will focus on the plasma technique of interface adherence. Fibres were employed as a reinforcement with polyester to create a nanocomposite that improved adherence between the fillers while also retaining the matrix alkalisation. In order to assess interferential adherence and fibre distribution homogeneity in the matrix system, the composite was made up of hand lay‐up technique. The manufactured composite was engrossed into fluid N2 at ‐196°C. A SEM was utilized to undertake treated and untreated specimens for spectroscopy analyses. Mechanical possessions like tension and flexural were accomplished. In comparison to previous tested doses, the 5 percent alkali‐treated flax incorporating graphite has shown promising outcomes than other samples.

A Review on Microcellular Injection Moulding.

Microcellular injection moulding (MuCell®) is a polymer processing technology that uses a supercritical fluid inert gas, CO2 or N2, to produce light-weight products. Due to environmental pressures and the requirement of light-weight parts with good mechanical properties, this technology recently gained significant attention. However, poor surface appearance and limited mechanical properties still prevent the wide applications of this technique. This paper reviews the microcellular injection moulding process, main characteristics of the process, bubble nucleation and growth, and major recent developments in the field. Strategies to improve both the surface quality and mechanical properties are discussed in detail as well as the relationships between processing parameters, morphology, and surface and mechanical properties. Modelling approaches to simulate microcellular injection moulding and the mathematical models behind Moldex 3D and Moldflow, the two most commonly used software tools by industry and academia, are reviewed, and the main limitations are highlighted. Finally, future research perspectives to further develop this technology are also discussed.

High-pressure Raman scattering and x-ray diffraction studies of the supercritical fluid of hydrogen

The high-pressure properties of the supercritical fluid H2 have been investigated in the Raman scattering and synchrotron radiation x-ray diffraction experiments at room temperature. The pressure dependence of four vibrational modes, i.e., Q1(0), Q1(1), Q1(2), and Q1(3), and four rotational modes, i.e., S0(0), S0(1), S0(2), and S0(3), were precisely obtained, and three rotational constants under pressure, i.e., B0, D0, and H0, were estimated from theoretical formulas. A peculiar change in the pressure dependence of the Raman spectra was observed at 1–2 GPa. Through x-ray experiments, halo patterns were collected within a wide pressure range of 0.1–5 GPa, and the molar volume at each pressure was estimated from the d-value of the halo peak. The obtained pressure–volume relation suggested that the fluid H2 showed a change in compressibility at around 1 GPa and became incompressible above this pressure because the repulsive term of the intermolecular potential became dominant. The dependence followed the relational expression of P ∼ Vm−3.11 above 1 GPa, whereas fluid O2 and N2 of the same homonuclear diatomic molecule followed the relational expression of P ∼ Vm−4.32 above 0.2 GPa. It was found that the fluid H2 behaves differently from fluid O2 and N2 and is more easily compressed than those. The behavior of Vm was significantly correlated with the pressure dependence of the Raman spectra, and the peculiar change of the Raman spectra has been attributed to the enhancement of the intermolecular interaction due to the transfer to the solid-like pressure–volume relation.

High Temperature Reduced Granulite-Facies Nature of Garnetites in the Khabarny Mafic–Ultramafic Massif, Southern Urals: Evidence from Fluid and Mineral Analyses

Abstract High-grade metamorphic rocks underlying the intrusive layered dunite–pyroxenite–gabbronorite East-Khabarny Complex (EKC) are integrated in the complex Khabarny mafic–ultramafic Massif in the Sakmara Allochthon zone in the Southern Urals. These rocks are associated with high-temperature shear zones. Garnetites from the upper part of the metamorphic unit close to the contact with EKC gabbronorite are chemically and texturally analysed to estimate their formation conditions and fluid regime. Fluids provide crucial information of formation conditions and evolution of these garnetites during high-grade metamorphism, and are preserved in channel positions within Si6O1812- rings of cordierite, and in fluid inclusions in quartz and garnet. Minerals and fluid inclusions of the garnetites are studied with X-ray fluorescence spectrometry, electron microprobe analyses, Raman spectroscopy, and microthermometry. The garnetites mainly consist of garnet (up to 80 vol. %), cordierite and quartz. Accessory minerals are rutile, ilmenite, graphite, magnetite and cristobalite. Granulite-facies metamorphic conditions of the garnetites are estimated with the garnet–cordierite–sillimanite–quartz geothermobarometer: temperatures of 740 to 830 ˚C and pressures of 770–845 MPa. The average garnet composition in end-member concentrations is 48·5 mole % almandine (±3·9), 34·7 mole % pyrope (±3·3), 10·3 mole % spessartine (±1·1), 1·8 mole % grossular (±1·5), and 1·5 mole % andradite (±1·5). The cordierite electron microprobe analyses reveal an average Mg2+ fraction of 0·79 ± 0·01 in the octahedral site. Relicts of a strong positive temperature anomaly (up to 1000 ˚C) are evidenced by the preservation of cristobalite crystals in garnet and the high titanium content of quartz (0·031 ± 0·008 mass % TiO2) and garnet (0·31 ± 0·16 mole % end-member Schorlomite-Al). The fluid components H2O, CO2, N2 and H2S are detected in cordierite, which correspond to a relatively oxidized fluid environment that is common in granulites. In contrast, a highly reduced fluid environment is preserved in fluid inclusions in quartz nodules, which are mono-fluid phase at room temperature and composed of CH4 (>96 mole %) with locally minor amounts of C2H6, N2, H2S and graphite. The fluid inclusions occur in homogeneous assemblages with a density of 0·349 to 0·367 g·cm-3. The CH4-rich fluid may represent peak-temperature metamorphic conditions, and is consistent with temperature estimation (∼1000 ˚C) from Ti-in-garnet and Ti-in-quartz geothermometry. Tiny CH4-rich fluid inclusions (diameter 0·5 to 2 µm) are also detected by careful optical analyses in garnet and at the surface of quartz crystals that are included in garnet grains. Graphite in fluid inclusions precipitated at retrograde metamorphic conditions around 300–310 ± 27 ˚C. Aragonite was trapped simultaneously with CH4-rich fluids and is assumed to have crystallized at metastable conditions. The initial granulite facies conditions that led to the formation of a cordierite and garnet mineral assemblage must have occurred in a relative oxidized environment (QFM-buffered) with H2O–CO2-rich fluids. Abundant intrusions or tectonic emplacement of mafic to ultramafic melts from the upper mantle that were internally buffered at a WI-buffered (wüstite–iron) level must have released abundant hot CH4-rich fluids that flooded and subsequently dominated the system. The origin of the granulite-facies conditions is similar to peak-metamorphic conditions in the Salda complex (Central Urals) and the Ivrea–Verbano zone (Italian Alps) as a result of magmatic underplating that provided an appearance of a positive thermal anomaly, and further joint emplacement (magmatic and metamorphic rocks together) into upper crustal level as a high temperature plastic body (diapir).

Sulfide melts in ore deposits from low-grade metamorphic settings: Insights from fluid and Tl-rich sulfosalt microinclusions from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy)

Sulfide melting is increasingly recognized as an efficient ore remobilization process in several ore bodies deformed and metamorphosed under amphibolite to granulite facies conditions. Actually, sulfide melts may also occur at lower metamorphic conditions, provided the abundance of the so-called Low-Melting point Chalcophile Elements (LMCE). The Monte Arsiccio ore body (Apuan Alps, northern Tuscany, Italy) is strongly enriched in several LMCE, i.e., Ag, As, Hg, Pb, Sb, and Tl, and experienced greenschist facies metamorphism (T = 350–450 °C; P = 0.3–0.4 GPa) during the Alpine orogeny. Trails of polyphase sulfosalt inclusions (up to five phases), coexisting with fluid inclusions, were observed within quartz and baryte crystals found in late-stage veins. Sulfosalt assemblages are formed by LMCE-rich phases, the main being ferdowsiite, Ag8As3Sb5S16, chabournéite, Tl2Pb(Sb,As)10S17, and intermediate members of the arsiccioite/routhierite isotypic pair, (Ag1−xCux)Hg2TlAs2S6, along with minor realgar. Sulfosalt inclusions range between 200 nm and more than 100 µm in size, whereas larger inclusions, likely formed through the coalescence of smaller melt droplets, are up to 500 µm. Sulfosalt inclusions are associated with primary two-phase liquid-rich fluid inclusions (Type 1a), containing CO2 and N2, as revealed by microthermometric investigations and micro-Raman spectroscopy. Secondary two-phase liquid-rich fluid inclusions (Type 1b) were also identified. Microthermometric measurements carried out on Type 1a fluid inclusions gave homogenization temperatures (Th) in the range 265–296 °C, whereas Type 1b fluid inclusions showed lower Th, between 222 and 246 °C. As microthermometric heating experiments on sulfosalt inclusions revealed homogenization temperatures around 270 °C, it is very likely that sulfosalt inclusions were in the liquid state during their entrapment, in agreement with many Tl-bearing systems. These results are fully consistent with the occurrence of LMCE-rich sulfide melt during the formation of the sulfosalt assemblages observed at the Monte Arsiccio mine. In addition, the polyphase nature of most of the observed sulfosalt inclusions may be related to the unquenchable nature of sulfide melts. The formation of LMCE-rich sulfosalt assemblages could be related to the release of these elements from pyrite during its metamorphic recrystallization. Consequently, pyrite ores may produce sulfide melts, with potential implications in the change of speciation of LMCE, from trace to major elements.

Spark-ignited engine NOx emissions in a low-nitrogen oxycombustion environment

This paper investigates the formation of the pollutant nitric oxides (NOx) in the low-nitrogen (N2) environment of methane oxycombustion in a spark-ignited (SI) internal combustion engine. Working fluid composition, N2 concentration, O2 concentration, compression ratio (CR) and spark-timing have been investigated to evaluate the feasibility of operating such a system below NOx regulation levels without after-treatment systems.NOx emissions in g/kWh are shown under equivalent CR, intake temperature, and indicated mean effective pressure (IMEP) at maximum brake torque spark-timing, to have an approximately linear dependence on N2 concentration from no N2 to normal air combustion. At a given N2 concentration, NOx emissions were found to be adversely correlated with power, thermal efficiency, and the coefficient of variation of IMEP. It was found that with 2–3% N2 by volume in the working fluid, it was possible to reduce NOx emissions to satisfy regulation levels, but this corresponds to non-ideal engine performance in other metrics. Satisfying regulations while operating at the maximum thermal efficiency required the N2 concentration be reduced to 1–2% by volume.The system was simulated using an AVL Boost model, with results indicating that the increasing NOx concentrations at higher O2 cases and earlier spark-timings can largely be attributed to higher burned-gas temperatures. An additional simulation utilizing CHEMKIN and the GRI 3.0 mechanism was used to estimate NOx formation, and with results indicating that air-calibrated NOx mechanisms maintain reasonable accuracy in low-N2 environments.

Processing of poly(hydroxybutyrate-co-hydroxyvalerate)-based bionanocomposite foams using supercritical fluids

Abstract

Nested Markov chain Monte Carlo sampling of a density functional theory potential: Equilibrium thermodynamics of dense fluid nitrogen

An optimized variant of the nested Markov chain Monte Carlo [n(MC)(2)] method [J. Chem. Phys. 130, 164104 (2009)] is applied to fluid N(2). In this implementation of n(MC)(2), isothermal-isobaric (NPT) ensemble sampling on the basis of a pair potential (the "reference" system) is used to enhance the efficiency of sampling based on Perdew-Burke-Ernzerhof density functional theory with a 6-31G(*) basis set (PBE6-31G(*), the "full" system). A long sequence of Monte Carlo steps taken in the reference system is converted into a trial step taken in the full system; for a good choice of reference potential, these trial steps have a high probability of acceptance. Using decorrelated samples drawn from the reference distribution, the pressure and temperature of the full system are varied such that its distribution overlaps maximally with that of the reference system. Optimized pressures and temperatures then serve as input parameters for n(MC)(2) sampling of dense fluid N(2) over a wide range of thermodynamic conditions. The simulation results are combined to construct the Hugoniot of nitrogen fluid, yielding predictions in excellent agreement with experiment.

High CO 2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids?

Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with the gold mineralisation contain a low salinity ( CO2 and low salinity ( ± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids.

Computer simulations of the linewidth of the Raman Q-branch in fluid nitrogen

By means of molecular dynamical simulations, the width of the Raman line in fluid N2 is calculated at room temperature and pressures up to the melting line. The results are compared with experimental results for the linewidth and for the dephasing time. Detailed information is given about the relaxation mechanism of the vibrational frequency. For instance, a marked influence of the vibration-rotation coupling is seen, in particular at high pressures. Moreover, the time correlation function of the frequency reveals a long time behavior at high pressures. From a comparison of the simulated change in vibrational frequency as a function of pressure with experimental data for the line shift, an estimate is made for the contribution of the so-called ‘‘attractive part’’ to that shift.

Computer simulation study of the Rayleigh and Raman spectra of fluid N2

Computer simulations of the Rayleigh and Raman spectral time-correlation functions (TCFs) are reported for N2 at 323 K and densities ranging from 0.48 to 2.5 times the critical value. The results are compared with experiment. Particular attention is paid to the density dependence of the spectral intensity due to the correlated permanent polarizability and to the interaction-induced contributions to the polarizability. The partial cancellations that occur between various two-, three-, and four-body terms in the cross and collision induced (CI) parts of the spectral TCFs are evaluated. It is shown that these terms are significant in both the Raman and the Rayleigh spectra, but cancellation greatly reduces their net contribution at all densities studied. The weak but uncancelled TCFs that are associated with orientational correlations of the molecular polarizability anisotropies are shown to be a significant part of the high density Rayleigh TCFs. It is argued that the long-range nature of this TCF means that its simulated values are poorly known.

Raman spectroscopy and melting of nitrogen between 290 and 900 K and 2.3 and 18 GPa

Raman spectroscopy was used to study the melting of nitrogen from 290 to 900 K at pressures from 2.3 to 18 GPa. This work, which extends the melting by a factor of 9 over previously published results was made possible by new developments in high-temperature diamond-anvil cells. The β/δ phase boundary was also determined, and the β–δ–fluid triple point was found to be at 578±10 K and 9.9±0.5 GPa. The Raman frequencies of the vibron in fluid N2 and the ν2 vibron in δ-N2 were found to have the same pressure dependence and be independent of temperature to a good approximation. A temperature-independent pressure scale, useful to at least 900 K is approximated by P/GPa=0.4242 ν/cm−1 −987.8, where ν is the frequency of either the ν2 vibron in δ-N2 or the vibron in fluid-N2.

Vibrational spectroscopy of fluid N2 up to 34 GPa and 4400 K.

Single-pulse multiplex coherent anti-Stokes Raman scattering (CARS) was used to observe the vibrational spectra of liquid N/sub 2/ shock compressed to several pressures and temperatures up to 34 GPa and 4400 K. Vibrational frequencies, peak Raman susceptibilities, and Raman linewidths were determined for the fundamental and several excited-state transitions by comparing experimental spectra to synthetic spectra calculated using a semiclassical model for CARS intensities. The question of excited-state populations in the shock compressed state is addressed.

Thermodynamic character of the vibron frequencies and equation of state in dense, high-temperature, fluid N2.

The pressure-temperature dependence of the vibron stretching mode frequency, the intramolecular bond lengths, and the pressure-volume curves along various isotherms are calculated for fluid ${\mathrm{N}}_{2}$ in the ranges 2\ensuremath{\le}P\ensuremath{\le}150 kbar and 300\ensuremath{\le}T\ensuremath{\le}1500 K. A constant-pressure Monte Carlo procedure with continuously deformable, periodic boundary conditions is used. The results are in good agreement with recent high-temperature diamond cell, dynamic shock, and earlier P-V data.

Molecular-dynamics simulation of fluid N2 adsorbed on a graphite surface

A sub-monolayer film of fluid nitrogen adsorbed on a graphite surface has been studied using the molecular-dynamics technique. The molecule–molecule potential consists of a two-centre Lennard-Jones interaction with additional coulombic interactions between partial charges. The surface is modelled as a static external field using a Fourier expansion in the reciprocal lattice vectors of the graphite basal plane.Simulations are performed at a variety of coverages at a temperature close to 75 K. The isosteric enthalpy of the model is in good agreement with experiment. The underlying surface lattice modifies the structure of the adsorbed liquid and there is significant out-of-plane orientational ordering at all the coverages studied.

Raman bands of fluid N2

Molecular dynamic simulations and experimental measurements on Raman bands of fluid N2 at about 150 K and two densities (1·05 and 1·8 times the critical density) are reported. Induced effects are accounted for by the dipole-induced-dipole mechanism at the first order. A satisfactory agreement between time correlation functions and spectral shapes derived from simulation and experiment is obtained. A detailed analysis of the different contributions to the total correlation function is reported, either performing or without performing the projection of the collision induced polarizability onto the orientational variables. The density dependence of static and dynamical properties is discussed together with the role played by the cross and pure collision induced contributions. The approximation of neglecting all orientational correlation is successfully used for the estimate of the pure collision induced terms.

The thermodynamics of dense fluid nitrogen by molecular dynamics

We present an extensive set of molecular dynamics results for the thermodynamics of dense fluid N2. The density and temperature regime is 1.3 g/cm3≲ρ≲2.3 g/cm3 and 500 K≲T≲12 000 K. These data are then analyzed to study the effects of internal degrees of freedom on the N2 equation of state. Most importantly, we demonstrate the existence of an effective spherical potential that models very accurately (to 1.5% or better in pressure and energy) the true equation of state for the anisotropic N2 potential. We discuss the relation of this effective potential to the median average over angles and other averaging methods, including the arithmetic mean.

Raman spectra of fluid N2

The depolarized rotovibrational band in fluid N2 has been measured in a wide temperature and density range. The behaviour of normalized second moment versus temperature and density is analysed in order to clarify the role played by the various non-rotational contributions. Practically no dependence on temperature is found while a net increase with density is present. Induced effects are carefully analysed in the dipole-induced-dipole approximation. In particular exact formulas are derived for both the intensity and second moment of induced cross contributions. Good agreement with experimental data is obtained. The cross contributions are responsible for the observed second moment increase with density. The different second moment density behaviour of rotovibrational and rotational bands has been interpreted in terms of the different permanent anisotropies and different many-body contributions involved in the scattering process.

Rayleigh spectra of N2fluid

The normalized second moments of rotational Rayleigh bands of fluid N2 are reported versus density at various temperatures (296, 202 and 150 K). The reduced second moments fit quite well a universal curve which differs significantly from the pure rotational value in the overall density range investigated (50 < ρ < 700 amagat). The discrepancies are attributed to the induced contributions. In particular, the purely collision induced contributions are responsible for the low density decay, while the cross interference between permanent and induced anisotropy increases the second moment at increasing density. A ‘theoretically’ constructed second moment is reported which reproduces quite well the experimental data up to the critical density. Experimental torques derived from M 4/M 2 and M 4/Mo have been briefly discussed. Some conclusions on the spectral shape analysis and mean square torque values have been worked out.

Rotational and collisional contributions in the Rayleigh and Raman spectra of fluid N2

Rotational and rotovibrational spectra of fluid N2 at T = 119 K and ρ = 570 and 625 amagatare reported. Substantial agreement is found with a recent molecular dynamics simulation which takes into account all dipole–induced-dipole effects including the cross interference term betwen permanent and induced anisotropy. A procedure is described to derive the nonrotational contribution from the experimental spectra using a rotational model spectrum based on a parametrized memory function.The derived lineshapes (collision induced plus cross term) are in agreement with molecular dynamics results.