Raman scattering spectroscopic study of n-pentane under high pressure

The Raman spectroscopy of n-pentane was investigated in a Moissanite anvil cell from 0.07 GPa to 4.77 GPa at ambient temperature. The result shows that the CH3 symmetric stretching vibration (2877 cm(-1)) and asymmetric stretching vibration (2964 cm(-1)), the CH2 symmetric stretching vibration (2856 cm(-1)) and asymmetric stretching vibration (2935 cm(-1)), and -(CH2)n- in-phase twist mode (1303 cm(-1)) shifted to higher wavenumbers almost linearly with increasing pressure. Around 2.4 GPa an abrupt visible change took place, indicating a sort of phenomenon of freezing due to over-pressurization. In the pressure range of 2.84 to 4.77 GPa a high-pressure phase transition may occur in the crystallized n-pentane. By determining pressure with the method of solid-liquid coexistence, we concluded that the equilibrium freezing pressure of n-pentane is 1.90 +/- 0.05 GPa at 27 degrees C.     

Solid-liquid phase equilibria of benzene + 2-methyl-2-propanol system under high pressures

Solid-liquid phase equilibria of the benzene + 2-methyl-2-propanol system have been investigated at temperatures from 278 to 323 K and pressures up to 300 MPa using a high-pressure optical vessel. The uncertainties of the measurements of temperature, pressure and composition are within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. The freezing pressure at a constant composition increases monotonously with pressure. The eutectic point shifts to a higher temperature and benzene-rich composition with increasing pressure. In order to describe the pressure-temperature-composition relation of high-pressure solid-liquid phase equilibria, a new simple equation has been proposed as follows:

Growth and structure of TiCxNy coatings chemically vapour deposited on graphite substrates

TiCxNy coatings were grown on graphite substrates in a computer-controlled, hot-wall chemical vapour deposition (CVD) reactor, using gas mixtures of TiCl4–CH4–N2–H2 at a total pressure of 10.7 kPa (80 torr) and at a temperature of 1400 K. Growth rate, composition, morphology and crystallographic texture of the TiCxNy coatings were investigated as a function of the CH4/CH4+N2 ratio in the range 0–1 at a constant CH4+N2 flow rate of 370 standard cubic centimeters per minute (sccm). The C/C+N ratio and growth rate of the TiCxNy coatings increased with increasing CH4/CH4+N2 ratio in the gas phase. The compositions of the coatings with C/C+N ratios in the range 0–1 were found to be between the thermodynamic and the kinetic predictions. Morphology and preferred orientation of the coatings were observed to be strongly affected by the CH4/CH4+N2 ratio in the gas phase.     

Phase Behavior of Three PBX Elastomers in High-Pressure Chlorodifluoromethane

The phase equilibrium behavior data are presented for three kinds of commercial polymer-bonded explosive (PBX) elastomers in chlorodifluoromethane (HCFC22). \(\hbox {Levapren}^{{\textregistered }}\) ethylene-co-vinyl acetate (LP-EVA), \(\hbox {HyTemp}^{{\textregistered }}\) alkyl acrylate copolymer (HT-ACM), and \(\hbox {Viton}^{{\textregistered }}\) fluoroelastomer (VT-FE) were used as the PBX elastomers. For each elastomer + HCFC22 system, the cloud point (CP) and/or bubble point (BP) pressures were measured while varying the temperature and elastomer composition using a phase equilibrium apparatus fitted with a variable-volume view cell. The elastomers examined in this study indicated a lower critical solution temperature phase behavior in the HCFC22 solvent. LP-EVA showed the CPs at temperatures of 323 K to 343 K and at pressures of 3 MPa to 10 MPa, whereas HT-ACM showed the CPs at conditions between 338 K and 363 K and between 4 MPa and 12 MPa. For the LP-EVA and HT-ACM elastomers, the BP behavior was observed at temperatures below about 323 K. For the VT-FE + HCFC22 system, only the CP behavior was observed at temperatures between 323 K and 353 K and at pressures between 6 MPa and 21 MPa. As the elastomer composition increased, the CP pressure increased, reached a maximum value at a specific elastomer composition, and then remained almost constant.     

High Pressure Phase Equilibria in the Systems Ammonia+Potassium Iodide, +Sodium Iodide, +Sodium Bromide, and +Sodium Thiocyanate: Solid–Liquid–Vapor and Liquid–Liquid–Vapor Equilibria

Solid salt–liquid–vapor equilibria and liquid–liquid–vapor equilibria were determined experimentally for the binary system NH₃+KI in the temperature range 333 to 673 K and at pressures up to 80 MPa. It is found that the system NH₃+KI belongs to Type V of fluid phase behavior according to the classification of van Konynenburg and Scott. The pressure of the three-phase curve solid salt–liquid–vapor is monotonically increasing in the temperature range investigated and reaches a value of 76 MPa at 670 K. The three-phase liquid–liquid–vapor curve starts in a lower critical end point at 407.3 K and 11.59 MPa and ends in an upper critical end point at 408.8 K and 11.92 MPa. For the systems NH₃+NaI, NH₃+NaBr, and NH₃+NaSCN, Type V fluid phase behavior is also found. In the system NH₃+NaI, the lower critical end point is found at 406.8 K and 11.52 MPa and the upper critical end point at 408.5 K and 11.86 MPa. For the system NH₃+NaBr, these coordinates are 404.6 K, 11.03 MPa and 408.8 K, 11.90 MPa, respectively, and, for the system NH₃+NaSCN, 409.2 K, 11.99 MPa and 409.6 K, 12.06 MPa.     

Correlations for the viscosity of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and trans-1,3,3,3-tetrafluoropropene (R1234ze(E))

Due to concerns about global warming, there is interest in 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) as potential replacements for refrigerants with high global warming potential (GWP). In this paper we survey available data and provide viscosity correlations that cover the entire fluid range including vapor, liquid, and supercritical regions. The correlation for R1234yf is valid from the triple point (220 K) to 410 K at pressures up to 30 MPa, and the correlation for R1234ze(E) is valid from the triple point (169 K) to 420 K at pressures up to 100 MPa. The estimated uncertainty for both correlations at a 95% confidence level is 2% for the liquid phase over the temperature range 243 K to 363 K at pressures to 30 MPa, and 3% for the gas phase at atmospheric pressure.     

Characteristics of Hydrogen Storage Alloy Mg2Ni Produced by Hydriding Combustion Synthesis

A high activity and large capacity of hydrogen storage alloy Mg2Ni by hydriding combustion synthesis was investigatedby means of pressure composition isotherms, X-ray diffraction and scanning electron microscopy. The results showedthat the maximum hydrogen absorption capacity of Mg2Ni is 3.25 mass fraction at 523 K, just after synthesis withoutany activation. The relationships between the equilibrium plateau pressure and the temperature for Mg2Ni were lgp(0.1 Mpa)=3026/T 5.814 (523 K≤ T ≤623 K) for hydriding and Igp (0.1 Mpa)=-3613/T 6.715 (523 K≤T ≤623 K) for dehydriding. The kinetic equation is [-ln(1 - α)]3/2 = kt and the apparent activation energy for thenucleation and growth-controlled hydrogen absorption and desorption were determined to be 64.3±2.31 kJ/(mol.H2)and 59.9±2.99 kJ/(moI.H2) respectively.     

Shape memory characteristics and superelasticity of Ti-Ni-Cu alloy ribbons with nano Ti2Ni particles

Microstructures and deformation behaviour of Ti-45Ni-5Cu and Ti-46Ni-5Cu alloy ribbons prepared by melt spinning were investigated by transmission electron microscopy, thermal cycling tests under constant load and tensile tests. Spherical Ti2Ni particles coherent with the B2 parent phase were observed in the alloy ribbons when the melt spinning temperature was higher than 1773 K. Average size of Ti2Ni particles in the ribbons obtained at 1873 K was 8 nm, which was smaller than that (10 nm) in the ribbons obtained at 1773 K. Volume fraction of Ti2Ni phase in the ribbons obtained at 1873 K was 40%, which was larger than that (20%) in the ribbons obtained at 1773 K. The stress required at temperatures of Af + 10 K for the stress-induced martensitic transformation increased from 93 MPa to 229 MPa and apparent elastic modulus of the B2 parent phase increased from 56 GPa to 250 GPa with increasing the melt spinning temperature from 1673 K to 1873 K in Ti-45Ni-5Cu alloy ribbons. The critical stress for slip deformation of the ribbons increased by coherent Ti2Ni particles, and thus residual elongation did not occur even at 160 MPa, while considerable plastic deformation occurred at 60 MPa in the ribbons without Ti2Ni particles. Almost perfect superelastic recovery was found in the ribbons with coherent Ti2Ni particles, while only partial superelastic recovery was observed in the ribbons without coherent Ti2Ni particles.     

Influence of a dielectric medium on the phase state of carbon dioxide

The phase state of carbon dioxide gas dissolved in liquid n-heptane is determined by experimental investigations of the temperature dependences (180 < T < 250°K) of the spin-lattice relaxation time of protons, the coefficient of translational self-diffusion of n-heptane molecules and the nuclear magnetic resonance (NMR) linewidth of carbon¹³C.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 3, pp. 402–405, March, 1987.     

The speed of sound of <Emphasis Type="Italic">n</Emphasis>-heptane, <Emphasis Type="Italic">n</Emphasis>-octane and their binary mixtures at temperatures <Emphasis Type="Italic">T</Emphasis> = 293.15 to 523.15 K and pressures up to 60 MPa

Speeds of sound in liquid n-heptane, n-octane and their binary mixtures were measured at the temperatures T = 293.15 to 523.15 K and pressures up to 60 MPa. The pulse-echo method with a frequency of 8MHz and uncertainty of ±0.08% was used. The measured values were fitted by polinomials, as functions of temperature and pressure, and the reliability of the present results was proved by comparison with the literature data.     

镁基储氢合金氢化物Mg2NiH4的制备及性能研究

以不经压制的Mg、Ni混合粉末为原料,利用氢化燃烧合成法在合成温度850 K和1.8 MPa初始合成氢压下制备了镁基储氢合金氢化物Mg2NiH4,并利用XRD及PCT仪分析了其物相组成和储氢性能.研究表明,产物由单一物相Mg2NiH4组成,无未反应的Ni和不完全氢化的Mg2NiH0.3;相对于传统熔炼法制备的Mg2Ni,氢化燃烧合成产物具有更高的氢化活性,在没有任何活化处理的前提下,第一次吸氢就能以很快的速度达到饱和吸氢量,同时在任何吸氢温度下均具有较好的吸氢动力学性能,且随温度的降低,最大吸氢量降低幅度较小,平台压和吸放氢温度的关系为:lgP(0.1 MPa)=-3 187.6/ T 6.362 4(吸氢),lgP(0.1 MPa)=-3 468.4/T 6.694 3(放氢).     

Phase equilibrium and critical lines in n-pentane + water and n-hexane + water systems

Results are given of experimental investigation of the thermal properties of n-pentane + water and n-hexane + water binary systems in the temperature range from 300 to 680 K at pressures up to 60 MPa in a wide density range. Measurements are performed for several values of concentration. The investigations cover the region of liquid-liquid, liquid-vapor, and gas-gas phase equilibria and extend to the homogeneous region. Lines of phase equilibrium and critical lines of these systems are obtained.     

Liquid thermal conductivity of binary mixtures of difluoromethane (R32) and pentafluoroethane (R125)

The thermal conductivities of refrigerant mixtures of difluoromethane (R32) and pentafluoroethane (R125) in the liquid phase are presented. The thermal conductivities were measured with the transient hot-wire method with one bare platinum wire. The experiments were conducted in the temperature range of 233–323 K and in the pressure range of 2–20 MPa. An empirical equation to describe the thermal conductivity of a near-azeotropic mixture, R32+R125, is provided based on the measured 168 thermal conductivity data as a function of temperature and pressure. The dependence of thermal conductivity on the composition at different temperatures and pressures is also presented. The uncertainty of our measurements is estimated to be ±2%. Paper dedicated to Professor Edward A. Mason.     

Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal

The first experimental evidence for a giant, conventional barocaloric effect (BCE) associated with a pressure‐driven spin crossover transition near room temperature is provided. Magnetometry, neutron scattering, and calorimetry are used to explore the pressure dependence of the SCO phase transition in polycrystalline samples of protonated and partially deuterated [FeL₂][BF₄]₂ [L = 2,6‐di(pyrazol‐1‐yl)pyridine] at applied pressures of up to 120 MPa (1200 bar). The data indicate that, for a pressure change of only 0–300 bar (0–30 MPa), an adiabatic temperature change of 3 K is observed at 262 K or 257 K in the protonated and deuterated materials, respectively. This BCE is equivalent to the magnetocaloric effect (MCE) observed in gadolinium in a magnetic field change of 0–1 Tesla. The work confirms recent predictions that giant, conventional BCEs will be found in a wide range of SCO compounds.     

Thermal Radiation Calorimeter for Measuring the Specific Heat Capacity of Liquid Samples

A new thermal radiation calorimeter for measuring the specific heat capacity of liquid samples continuously in the temperature range from 280 to 360 K is described. The heat input to the sample cell from the heater by thermal radiation is estimated using the effective emissivity, which is the apparatus constant. The heat capacity of a sample can be calculated from the temperatures of the sample and the heater, and the temperature change rate of the sample. The present sample cell was made of Pyrex glass; therefore most liquid samples do not react with the sample cell, and blackening of the surface of the sample cell is not necessary in the present temperature range. The specific heat capacities for ethanol, ethylene glycol, n-heptane, n-valeric acid, and water+ethanol mixtures were measured to confirm the reliability of the present calorimeter.     

A Small-Volume Apparatus for the Measurement of Phase Equilibria

An apparatus has been designed and constructed for the measurement of vapor-liquid equilibrium properties. The main components of the apparatus consist of an equilibrium cell and a vapor circulation pump. The cell and all of the system valves are housed inside a temperature controlled, insulated aluminum block. The temperature range of the apparatus is 260 K to 380 K to pressures of 6 MPa. The uncertainty of the temperature measurement is 0.03 K, and the uncertainty in the pressure measurement is 9.8 × 10⁻⁴ MPa. An automated data acquisition system is used to measure temperature and pressure at equilibrium. The apparatus has been performance tested by measuring the vapor pressures of propane, butane, and a standard mixture of propane + butane.     

Compressibility and sound velocity measurements on N2 up to 1 GPa

A gas expansion technique has been used to determine the pVT properties of N₂ up to 1 GPa at 298.15 K, with an accuracy of 0.08% in density, 1 mK in temperature, and 0.05%+0.2 MPa in pressure. The sound velocity has been measured by a phase-comparison pulse-echo technique between 123 and 298 K at intervals of 25 K and at pressures up to 1 GPa, with an accuracy of better than 0.02% in sound velocity, 10 mK in temperature, and 0.05%+0.2 MPa in pressure. An equation of state is presented that correlates the density data over the wide pressure range of 36–1000 MPa with maximum deviations between the calculated and the experimental densities of less than 0.05%.     

Eu-doped titania nanofibers: processing, thermal behaviour and luminescent properties

Undoped and Europium-doped titania nanofibers have been fabricated by electrospinning technique, using a single multielement Titanium/Europium source. In this communication we present the synthesis, structural and spectroscopic characterisation of Eu-doped TiO2 nanofibers starting from polyvinylpyrrolidone, titanium tetraisopropoxide (Ti(OiPr)4) and Eu(hfa)3 x diglyme (Hhfa = 1,1,1,5,5,5-hexafluoroacetyacetone, diglyme = CH3O(CH2CH2O)2CH3). The chosen system allowed to investigate a wide compositional range, i.e., from 3 to 10% mol of Eu3+. Microstructure was studied by means of scanning electron microscopy (SEM), thermal behaviour followed by thermogravimetric and differential thermal analysis (TG-DTA). Phase analysis was performed by means of X-ray diffraction (XRD) and high temperature X-ray diffraction analysis (HT-XRD) up to 1100 degrees C. Luminescence properties were investigated by means of luminescence spectroscopy, using a laser excitation source at 395 nm. All electrospun materials consisted of randomly oriented nanofibers of fairly uniform diameter. The average fiber size was 80-100 nm and 40 nm for, respectively, Eu-doped and undoped TiO2 calcinated at 500 degrees C. The presence of Europium shifted toward higher values either the crystallization temperature of anatase and the anatase to rutile phase transition, the latter being accompanied by the formation of the Eu2Ti2O7 phase. The doped samples showed a strong luminescence of Eu3+ ions. The emission spectra were dominated by the 5D0 --> 7F2 emission, suggesting a notable distortion around the Eu3+ ions. The broadening of the bands pointed to the presence of a relevant inhomogeneous disorder around the Eu3+ sites. The Eu3+ doped TiO2 nanofibers showed a higher emission intensity with respect to the PVP/TiO2 ones.     

The transport properties of ethane. I. Viscosity

A new representation of the viscosity of ethane is presented. The representative equations are based upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory in the zero-density limit, vapor phase, and critical region. The representation extends over the temperature range from 100 K to the critical temperature in the liquid phase and from 200 K to the critical temperature in the vapor phase. In the supercritical region, the temperature range extends to 1000 K for pressures up to 2 MPa and to 500 K for pressures up to 60 MPa. The ascribed accuracy of the representation varies according to the thermodynamic state from ±0.5 % for the viscosity of the dilute gas near room temperature to ±3.0% for the viscosity at high pressures and temperatures. Tables of the viscosity, generated by the relevant equations, at selected temperatures and pressures and along the saturation line, are also provided.     

Raman spectroscopic studies of the phase transitions in hexane at high pressure

Raman spectroscopic study of n-hexane was carried out in a cubic zirconia anvil cell up to approximately 2.0 GPa. Under high pressure, the C-H stretching region of the spectrum at 2850-3000 cm(-1) shows measurable changes in frequency, bandwidth, and intensity. These Raman bands shift towards higher frequencies with increasing pressure. At about 1.4 GPa, phase transition from liquid to solid was induced by compression, as was simultaneously observed with the built-in microscope.