Experimental Pressure Conditions Research Articles

Controlling the foam morphology of supercritical CO2‐processed poly(methyl methacrylate) with CO2‐philic hybrid nanoparticles

AbstractHighly CO2‐philic nanoparticles, octatrimethylsiloxy polyhedral oligomeric silsesquioxanes (POSS) are used to increase the affinity of poly(methyl methacrylate) (PMMA) to CO2 in supercritical carbon dioxide (scCO2) foaming, thus to improve its foaming performance and the foam morphology. PMMA and PMMA‐POSS composite foams were produced based on the two‐factorial design, at the upper and lower experimental conditions of pressure, temperature, processing time, and venting rate. The foams of PMMA‐5% POSS composites exhibited smaller average pore sizes and higher pore densities than neat PMMA and PMMA‐0.5% POSS composites. The smallest average pore diameter (0.3 μm) and the highest pore density (6.33 × 1012 cm−3) were obtained with this composite processed at 35°C, 32 MPa, for 24 h and depressurized with fast‐venting rate (0.4 MPa/s). ScCO2 processing decreased the density of the polymer by more than 50%.

Experimental investigation of formation and decomposition of roaldite in ammonia atmosphere at 300–700 °C and associated nitrogen isotope fractionations

Roaldite (Fe4N) is one of the few nitride minerals found in meteorites. Their nitrogen (N) isotopic signatures carry important information for understanding the early N cycle in the proto-solar nebula. However, the lack of knowledge on the N isotopic effects from nitride formation to its survival from frictional heating during landing impedes the interpretation and application of N isotope compositions of nitride minerals in meteorites. Here, we carried out laboratory experiments under a recently proposed roaldite forming condition, i.e., NH3 (as starting N source) reacting with metallic Fe at medium temperatures. We observed Fe4N formation over a large range of temperatures from 300 °C to 700 °C. The formation of Fe4N was associated with equilibrium N isotope fractionations with αFe4N-NH3 values of 0.9907 (±0.0004) at 300 °C and 0.9936 (±0.0004) at 500 °C, respectively. In the experimental pressure conditions (initial PNH3 = 3.9–6.4 bar, PTotal < 8.3 bar), the formed Fe4N remained stable at 300 °C, but was unstable and quickly decomposed to Fe and N2 at 500 °C and 700 °C. The decomposition of Fe4N was associated with large kinetic isotope fractionations with αN2-Fe4N values of 0.9811 (±0.0009) at 500 °C and 0.9839 (±0.0011) at 700 °C, respectively. Our experimental results suggest that roaldite formed from NH3 can carry an isotopic signature very close to that of its source, but partial decomposition (if there is any) can easily shift its N isotope composition for several tens of per mil, and in extreme cases, to >300‰. Thus, great caution is needed when using N isotope composition of roaldite (and probably other nitride minerals as well) to trace source information.

Thermodynamic and kinetic analysis of gas hydrates for desalination of saturated salinity water

The shortage of fresh water is among the most serious issues in the world. A representative technology to overcome the problem is desalination, but most conventional methods (RO membrane or thermal distillation) have been focused on the treatment of relatively low salinity water, such as seawater or brackish water. To strengthen water security, in this study, we introduce a possibly economic technology for desalination of high salinity water (over-saturated concentration, in this study, a 30 wt% NaCl system) via gas hydrate formation by coupling LNG waste cold energy. First, the thermodynamic effects of NaCl on CH4 (methane), SF6 (sulfur hexafluoride), and HFC-134a hydrates were investigated. Based on the phase equilibrium of each hydrate, experimental pressures for kinetic experiments were selected under vapor pressure boundaries as follows: 4.5 MPa for CH4, 0.75 MPa for SF6, and 0.16 MPa for HFC-134a at 258.15 K (assuming the use of LNG waste cold energy). The results of the formation kinetics on the basis of gas moles consumed for hydrates showed the order CH4 > HFC-134a > SF6; however, after considering the hydration numbers and structures for each hydrate, surprisingly, the conversion rate of water to gas hydrates showed the order HFC-134a > CH4 > SF6, even though the experimental pressure condition for HFC-134a was very mild (0.16 MPa) compared to CH4 (4.5 MPa). For this interesting phenomenon, we suggest a possible mechanism through visual observations during hydrate formation. We believe these thermodynamic, kinetic, and morphological results show potential as an alternative desalination technology, especially for saturated salinity water, with lower energy consumption.

Influence of temperature on adsorption selectivity: Coal-based activated carbon for CH4 enrichment from coal mine methane

In order to study the effect of temperature on the adsorption separation characteristics of CH4/N2 mixtures, activated carbons (AC) were prepared from low-rank bituminous coal by KOH activation method, marked as DF-AC and SM-AC. The adsorption isotherms of pure CH4 and N2 on AC were described by Langmuir-Freundlich model based on the high-pressure adsorption experiments. The adsorption selectivity calculated by ideal adsorption solution theory (IAST) method was used to evaluate the adsorption and separation characteristics of CH4/N2 binary mixtures. The influence of temperature on adsorption selectivity from 273 K to 373 K (20 K interval) were systematically analyzed. Results show that the adsorption equilibrium states of pure CH4 and N2 on activated carbons are significantly different, and the CH4 is more sensitive to the variation of temperatures. The isosteric heat of adsorption of CH4 is always larger than that of N2 under experimental pressure condition. This indicates that the interaction between the CH4 molecules with activated carbons is stronger than that of N2 molecules. With the temperature increasing from 273 K to 373 K, the separation factors first increase rapidly and then decrease slowly after arriving at the maximum value, while the adsorption selectivity decrease sharply at low pressure and subsequently tended to slowly decrease. When the experimental temperature is higher than 313 K, the adsorption selectivity is increasing monotonically with the increase of adsorption pressure. Under present experimental condition, for CH4:N2 = 50:50 mixture, the maximum adsorption selectivity of DF-AC (S = 7.06) can be obtained at 273 K and low pressure, while the minimum adsorption selectivity of DF-AC (S = 2.82) is obtained at 373 K and low pressure. The influences of temperature on adsorption selectivity of CH4/N2 binary mixture on coal-based activated carbons indicate that the lower adsorption temperature is contributed to the CH4 enrichment from low-concentration coal mine methane. And the effect of temperature on adsorption selectivity is greater than that of pressure, which provides a certain guiding significance for the efficient separation of low concentration gas combined with PSA and TSA technologies.

Kinetics of the Toluene Reaction with OH Radical.

We calculated the kinetics of chemical activation reactions of toluene with hydroxyl radical in the temperature range from 213 K to 2500 K and the pressure range from 10 Torr to the high-pressure limit by using multistructural variational transition state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and using the system-specific quantum Rice-Ramsperger-Kassel method. The reactions of OH with toluene are important elementary steps in both combustion and atmospheric chemistry, and thus it is valuable to understand the rate constants both in the high-pressure, high-temperature regime and in the low-pressure, low-temperature regime. Under the experimental pressure conditions, the theoretically calculated total reaction rate constants agree well with the limited experimental data, including the negative temperature dependence at low temperature. We find that the effect of multistructural anharmonicity on the partition functions usually increases with temperature, and it can change the calculated reaction rates by factors as small as 0.2 and as large as 4.2. We also find a large effect of anharmonicity on the zero-point energies of the transition states for the abstraction reactions. We report that abstraction of H from methyl should not be neglected in atmospheric chemistry, even though the low-temperature results are dominated by addition. We calculated the product distribution, which is usually not accessible to experiments, as a function of temperature and pressure.

On the Prediction of Water Contents in Na-Saturated Dioctahedral Smectites

Properties of swellable clay minerals in technical and geotechnical applications as well as in geological systems are determined by their water content. Thereby, the water content depends on the structure and morphology of the smectites and available water while smectites are the most heterogeneous clay minerals. Here, first-principles calculations are combined with ab initio thermodynamics to systematically study the hydration states of Na-saturated dioctahedral smectites. Total energy calculations based on density functional theory are carried out for a series of montmorillonites and beidellites with varying layer charge (0.125 ≤ ξ ≤ 0.5) and increasing number of water molecules per unit cell. The thermodynamic ground state was then defined with the help of the grand canonical potential as a function of chemical potential of water, which is directly related to the experimental conditions of pressure and temperature. For the first time, p,T-phase diagrams of stable hydration states together with relative...

High-Pressure Phase Behavior for Poly(ethylene glycol) and 1,1,1,2-Tetrafluorethane Systems

The development of polymeric systems for drug delivery has received attention with the aim of producing new systems as an alternative to conventional drug therapy. The design of new systems for this purpose in a compressed medium requires a knowledge of the phase behavior for the polymeric matrix in the high-pressure fluids. This work reports the phase equilibrium experimental data of binary systems involving poly(ethylene glycol) (PEG) with molecular weights of 1000 and 2000 g·mol–1 and 1,1,1,2-tetrafluoroethane (HFA-134a). The experimental data were obtained in a high-pressure variable-volume viewing cell based on the static synthetic method at temperatures from 287.4 to 334.2 K, pressures of up to 29.81 MPa, and a PEG concentration in the range of 1 to 7 wt %. Liquid–liquid equilibrium, liquid–liquid–vapor equilibrium, and, in some cases, solid–liquid equilibrium were observed under the experimental conditions of pressure, temperature, and compositions investigated. The experimental results show that t...

Pressure-broadening of water transitions near 7180 cm−1 by helium isotopes

In this study, pressure-broadening parameters for several H2O transitions near 7180cm−1 are obtained which describe collisions with 3He and 4He. The sensitivity of those parameters to choice of theoretical line profile (Galatry vs. Voigt) is investigated. H2O is an important species in atmospheric chemistry and astronomy. Because of this, basic fundamental research, which explores the nature of the H2O spectrum in the presence of different gases of varying physical properties, can provide useful reference data which can be applied in the fields of atmospheric and planetary remote sensing. Measurements were made using an intensity-modulated laser photoacoustic spectrometer. Results from the present work show that Galatry line profiles, with a constrained narrowing parameter, more accurately describe experimental spectra than Voigt profiles over a wide range of experimental pressure conditions. Average pressure-broadening parameters were found to be 0.0216cm−1/atm and 0.0209cm−1/atm for H2O in 3He and 4He, respectively, and were compared to a literature model for the mass-dependence of line broadening. Specific values were obtained for each transition with nominal combined uncertainties of 2–6%.

An experimental study of phase transformations in olivine under pressure and temperature conditions corresponding to the mantle transition zone

High-pressure polymorphs of olivine (wadsleyite and ringwoodite) are major minerals in the mantle transition zone (MTZ). Phase transformations in olivine are important for a series of geodynamic problems such as the mineralogical and evolutionary history of the mantle, mantle convection patterns, and deep focus earthquakes in subduction zones. In this study, we examine phase transformations in olivine with two compositions, namely Mg2SiO4 (Fo100) and (Mg0.9Fe0.1)2SiO4 (Fo90), at pressures between 14.1 and 20 GPa and a constant temperature of 1400°C, using the newly installed multi-anvil system at the Laboratory for Studies of the Earth’s Deep Interior (SEDI), China University of Geosciences (Wuhan). At 14.1 GPa, Fo90 transformed completely into the wadsleyite structure (β), while Fo100 remained as olivine (α). Between 14.8 and 15.6 GPa, both Fo100 and Fo90 transformed into the wadsleyite structure. Wadsleyite crystals were identified by two characteristic Raman peaks between 722 and 723 and 917 and 919 cm−1. They exhibit a bimodal grain size distribution: large-crystals with average grain sizes greater than 100 μm and microcrystals less than 10 μm. The population of microcrystals increased with pressure, apparently due to the increase in over-pressure (the difference between the experimental pressure condition and the equilibrium transformation pressure at 1400°C), which promotes nucleation and retards grain growth. All run charges contained large numbers of wadsleyite microcrystals, because of the low activation energy of the nucleation process. The experimentally observed microstructure may shed light on the morphology of wadsleyite observed in shocked meteorites. At 19.5 GPa, wadsleyite coexisted with ringwoodite (γ) in Fo100, but was absent in Fo90. At 20 GPa, both samples transformed completely into ringwoodite, which was characterized by the 798 and 840 cm−1 Raman lines. Ringwoodite crystals are euhedral grains (average grain size 10–20 μm), with well-developed triple junctions. The complex upper mantle structure in eastern China determined from seismological studies cannot be explained by the simple transformation sequence of the olivine system alone. Phase transformations in other pyroxene-normative components (including pyroxenes and garnets) and the interaction of these components with olivine may be responsible for the complex structure. High-pressure and high-temperature experimental studies on complex systems (e.g. olivine-pyroxene), combined with data from geophysical exploration, may help in establishing a more realistic geological-petrological model for eastern China and further our understanding of the possible physical mechanisms that are responsible for the complex structure. Such studies will have profound implications for understanding the dynamic processes in the deep Earth interior.

Supercritical CO2 assisted ternary-monomer grafting copolymerization of polypropylene

Free-radical grafting of ternary-monomer onto polypropylene (PP) particles in the solid state has been studied using supercritical carbon dioxide (SC CO2) as a solvent and a swelling agent. The PP particles were first swelled with the monomers and AIBN as an initiator, using SC CO2 at different experimental conditions of pressure, temperature and treatment time. After releasing CO2, monomers were grafted onto PP in different temperatures. During monomer selection, combination of soft monomer and hard monomer was used in order to tune polarity and flexibility of grafted polymer. FTIR spectra confirmed that ternary-monomer had been grafted onto PP and SEM showed that grafted molecules had been uniformly distributed in the PP substrate. TG analysis indicated that thermal stability of grafting modified PP had been improved, and DSC revealed that grafting leads to a lower degree of crystallinity of polypropylene.

Multi-Level Simulation Study of Crystal Growth and Defect Formation Processes in SiC

The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C &gt; H &gt; Si &gt; SiC2 &gt; Si2C &gt; C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.

Multi-level simulation study of crystal growth and defect formation processes in SiC

The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C > H > Si > SiC2 > Si2C > C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.

Retinal ganglion cell line apoptosis induced by hydrostatic pressure

Cellular responses to changes in pressure are implicated in numerous disease processes. In glaucoma apoptosis of retinal ganglion cells (RGCs) is associated with elevated intra-ocular pressure, however, the exact cellular mechanisms remain unclear. We have previously shown that pressure can induce apoptosis in B35 and PC12 neuronal cell lines, using an in vitro model for pressure elevation. A novel RGC line allows us to study the effects of pressure on retinal neurons. ‘RGC-5’ cultures were subjected to elevated ambient hydrostatic pressure conditions in our model. Experimental pressure conditions were 100 mm Hg and 30 mm Hg, representing acute (high) and chronic (lower-pressure) glaucoma, and 15 mm Hg for normal intra-ocular pressure, set above atmospheric pressure for 2 h. Negative controls were treated identically except for the application of pressure, while positive controls were generated by treatment with a known apoptotic stimulus. Apoptosis was determined by a combination of cell morphology and specific TUNEL and Annexin V fluorescent markers. These were assessed simultaneously by laser scanning cytometry (LSC), which also enabled quantitative marker analysis. RGC-5 neurons showed a significantly increased proportion of apoptotic cells compared with controls; maximal at 100 mm Hg, moderate at 30 mm Hg and not statistically significant at 15 mm Hg. This graded response, proportionate to the level of pressure elevation, is representative of the severity of analogous clinical settings (acute, chronic glaucoma and normal). These results complement earlier findings of pressure-induced apoptosis in other neuronal cultures. They suggest the possibility of novel mechanisms of pressure-related mechanotransduction and cell death, relevant to the pathogenesis of diseases such as glaucoma.

Grafting of glycidyl methacrylate onto polypropylene using supercritical carbon dioxide

Free-radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) films has been studied using supercritical carbon dioxide (SC-CO 2) as a solvent and a swelling agent. As the reaction temperature was below the melting point, PP was modified in the solid phase. The PP film was first soaked with the monomer GMA and benzoyl peroxide (BPO) as an initiator using SC-CO 2 at different experimental conditions of pressure, temperature, and thermal treatment time. After releasing CO 2, film GMA molecules were grafted onto PP in different times. Using this method, the degree of grafting and the morphology could be controlled through the combination of pressure, temperature, and soaking time. FTIR spectra confirmed that GMA had been grafted onto PP and that polypropylene-graft-glycidyl methacrylate (PP-g-GMA) presented a high surface reactivity for conductive polyaniline anchoring. DSC measurements and TG analyses showed that the thermal profiles of the graft copolymer and virgin PP are quite similar and that the graft PP does not exhibit changes in terms of thermal degradation profile and melting temperature, respectively. X-ray data showed that a high degree of grafting leads to a lower degree of crystallinity of polypropylene.

Laminar jet dispersion and jet atomization in pressurized carbon dioxide

Laminar jet dispersion and more particularly jet atomization of water, methylene chloride and ethyl alcohol into pressurized carbon dioxide are investigated under experimental conditions of pressure, temperature and liquid flow rate commonly used for supercritical anti solvent (SAS) precipitation processes. The different modes of dispersion are characterized as a function of the jet velocity. Axisymmetrical, asymmetrical and atomized jets are observed at 308 K, under a pressure ranging from 6 to 9 MPa, and for a liquid jet velocity ranging from to 0.14 to 8.02 m s −1. A new correlation is given between the jet Reynolds number and the Ohnesorge number, determining the transition to the atomization regime. Experimental values of dynamic interfacial tensions are used to elaborate the correlation.

The role of the 132–160 region in prion protein conformational transitions

The native conformation of host-encoded cellular prion protein (PrP(C)) is metastable. As a result of a post-translational event, PrP(C) can convert to the scrapie form (PrP(Sc)), which emerges as the essential constituent of infectious prions. Despite thorough research, the mechanism underlying this conformational transition remains unknown. However, several studies have highlighted the importance of the N-terminal region spanning residues 90-154 in PrP folding. In order to understand why PrP folds into two different conformational states exhibiting distinct secondary and tertiary structure, and to gain insight into the involvement of this particular region in PrP transconformation, we studied the pressure-induced unfolding/ refolding of recombinant Syrian hamster PrP expanding from residues 90-231, and compared it with heat unfolding. By using two intrinsic fluorescent variants of this protein (Y150W and F141W), conformational changes confined to the 132-160 segment were monitored. Multiple conformational states of the Trp variants, characterized by their spectroscopic properties (fluorescence and UV absorbance in the fourth derivative mode), were achieved by tuning the experimental conditions of pressure and temperature. Further insight into unexplored conformational states of the prion protein, likely to mimic the in vivo structural change, was obtained from pressure-assisted cold unfolding. Furthermore, salt-induced conformational changes suggested a structural stabilizing role of Tyr150 and Phe141 residues, slowing down the conversion to a beta-sheet form.

Induced fatigue effects on velopharyngeal closure force.

This investigation studied the effects of induced velopharyngeal fatigue in speakers with normal mechanisms. Five adult female and 5 adult male subjects were used. A force sensing bulb was placed in the velopharynx to measure velopharyngeal closure force and intramuscular electrodes were inserted in the levator veli polatini muscle to sample muscle activation levels. The subjects' task was to repeat the syllable /si/100 times while an external load was placed on the velopharyngeal mechanism. The external load consisted of various levels of air pressure (0 as a control, 5, 15, 25, and 35 cm H2O relative to atmospheric pressure) delivered to the nasal passages via a tube and nasal mask assembly. Fatigue was defined as a declination of force across the series of syllables within a pressure condition and was depicted as the slope of a linear regression line that was fit to the data. The more negative the slope, the greater was the rate of fatigue. Within each experimental pressure condition, small cyclic variations in force were noted about each regression line that corresponded to individual breath groups. This type of declination, within breath groups, has been reported in the literature previously. Overall declination in force over an entire series of syllables and over several breath groups is a new finding. It was possible to induce such fatigue in most subjects, and greater rates of fatigue generally occurred at the higher levels of external loading, i.e., at 25 and 35 cm H2O. Two subjects, 1 male and 1 female, reached exhaustion. The female subject could not perform the syllable repetition task at 25 cm H2O, and the male subject could not complete the task at 35 cm H2O. Three subjects, 1 female and 2 males, exhibited virtually no force declination even at the highest level (35 cm H2O) of external loading. There were no discernable differences in patterns of fatigue or in initial velopharygeal closure force values between the male and female subjects.

Effective Thermal Conductivity of Graphite - Metallic Salt Complex for Chemical Heat Pumps

An experimental procedure was developed for measuring the effective thermal conductivities of graphite-CaCl 2 -nNH 3 (n = 8, 4, 2), MnCl 2 -nNH 3 (n = 6, 2), and BaCl 2 -8NH 3 complex for chemical heat pumps. Graphite-metallic salt complex was manufactured tbrougb the impregnation of metallic salt Into a porous graphite matrix. Experimental conditions of pressure and temperature were directly established by the thermodynamic equilibrium lines of salt-ammonia systems obtained by the calorimetric method. Afterward, effective thermal conductivities were measured using a transient one-dimensional heat flow technique at a fixed pressure and temperature under an ammonia atmosphere. Effective thermal conductivities of the graphite-metallic salt complex were in the range of 10-49 W/mK, which are significant higher values than powder beds of 0.1-0.5 W/mK. Results showed that the effective thermal conductivity of a graphite-metallic salt complex has a strong dependency on the bulk density, the weight fraction of graphite, and the ammoniated state of salt

The Effect of Static Air Pressure in the External Auditory Meatus on Hearing Acuity

The specific purposes of this study were to determine the effects of various static air pressures in the external auditory meatus on (1) threshold sensitivity and (2) hearing acuity at two loudness levels above threshold. To determine the effect of a pressure differential across the tympanic membrane on the threshold sensitivity, measurements were obtained by the Method of Adjustment for 10 ears at each of 41 frequencies (from 100 to 8000 cps) at each of four pressure conditions (−10, −20, +10, +20 cm H2O). For all pressures used threshold sensitivity was generally decreased for frequencies below 1500 cps. with a slight increase in sensitivity for frequencies between 1500 and 2300 cps and a general decrease in sensitivity for frequencies between 2300 and 8000 cps. To test the effect of pressure on loudness, five subjects made equal loudness balance judgments for six frequencies (200, 400, 1000, 1600, and 4000 cps) at 30 db and at 60 db above threshold under each of the four experimental pressure conditions. As in the threshold sensitivity study results indicated a general decrease in sensitivity for frequencies below 1000 cps and only slight effects on the higher frequencies. The effect of static pressure on speech intelligibility was also studied and in the range investigated was found negligible. This work was done at Ohio State University.