Experimental study ofPVT properties of HFC-125 (CHF2CF3)

Pressure-volume-temperature (PVT) properties and vapor pressures of HFC125 (pentafuoroethane; CHF₂CF₃) have been experimentally obtained. Vapor pressures of HFC-125 have been measured in the range of temperatures from 223 to 338 K and pressures up to 3.54 M Pa with uncertainties of 5 mK and 2.5 kPa, respectively. The vapor pressure equation for this substance was correlated based on the present data. PVT properties of HFC-125 have been determined with a constant-volume apparatus in the range of temperatures from 280 to 473 K, pressures up to 17 M Pa, and densities up to 1145 kg · m^–3 with uncertainties of 5 mK, 2.5 kPa, and 0.01%, respectively. All of the available experimentalPVT property data were compared with the equation of state correlated by Wilson et al.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Vapor pressures and gas-phase PVT data for 1,1,1,2-tetrafluoroethane

We present new data for the vapor pressure and PVT surface of 1,1,1,2-tetrafluoroethane (Refrigerant 134a) in the temperature range 40° C (313 K) to 150° C (423 K). The PVT data are for the gas phase at densities up to one-half critical. Densities of the saturated vapor are derived at five temperatures from the intersections of the experimental isochores with the vapor pressure curve. The data are represented analytically in order to demonstrate experimental precision and to facilitate calculation of thermodynamic properties.Formerly National Bureau of Standards     

The PVT behavior of liquid 1,1,1- and 1,1,2-trichloroethane

The PVT behavior of liquid 1,1,1- and 1,1,2-C₂H₃Cl₃ has been determined at 298.15, 323.15, 348.15, 373.15, and 398.15 K and at different pressures to about 100 MPa. The experimental results are shown in tabulated form. Specific volumes at high pressures are represented by the Tait equation. These results are also compared with the results obtained by a generalized Tait equation and other correlation methods. The generalized Tait equation is found to be more suitable to explain this study than the other correlations tested.     

The virial coefficients of five binary mixtures of fluorinated methanes and ethanes

We have made new measurements of the gas-phasePVT surface of five binary mixtures of hydrofluorocarbons (HFCs) in a Burnett/isochoric apparatus. The components chosen all have moderate to large reduced dipole moments. We presentPVT data, derived mixture virial coefficients, cross second virial coefficients, and binary interaction parameters for these systems, and we compare the results with a recently published model for calculating second and third viral coefficients of polar gases and their mixtures. That model accounts for the polar nature of the molecules with a term containing the reduced dipole moment, _R, and it contains mixing rules for the substance-specific parameters needed to calculate the second and third cross virial coefficients. The model and data are in satisfactory agreement. and the model can be used to greatly extend the useful range of the limited set of data.     

Microscopic Experimental Investigation on Shear Failure of Solder Joints

A microscopic investigation has been made on the shearing of one leaded and two lead-free solders by using an in situ SEM method. A shear lap joint specimen is designed and fabricated to accommodate a thin layer of solder alloy between copper strips. A non-contact method that measures strains in a very narrow area in the solder was applied. A laser grid was also used on the copper strip for measuring the back-face strain. Simultaneously micrographs at various stages were also taken. Where in situ measurements and micrographs are recorded they can reveal the continual development of damage and fracture mechanisms consistent with observations generated by low-cycle fatigue loading. This means that the shear test can be used as an alternative test to fatigue loading tests. By comparison, two lead-free solder specimens showed much smaller elongation to failure than the leaded solder, although all specimens showed similar sequence of events leading to final failure, including the boundary layer fracture phenomenon. The back-face strain indicator for the formation of a macro crack is due to the shifting of high stress concentration area from the joint-edge region to outside the joint region as revealed by a damage-coupled finite element procedure. The procedure also provides an estimate on the critical back-face strain.     

Thermophysical properties of 1,1,1,2-tetrafluoroethane (R-134a)

The present hypothesis of depletion of the stratospheric ozone layer by some chlorofluorocarbons has prompted a lot of research and development of new stratospherically safe fluids in various uses such as refrigerants, blowing agents in foams, aerosol propellants, solvents, and many other uses. In the areas of certain refrigeration needs 1,1,1,2-tetrafluoroethane (R-134a) has been considered as a possible alternate to the use of dichloro-difluoromethane (R-12), the most commonly used refrigerant. R-12 is estimated to have a higher potential for ozone depletion. This will require a large number of thermophysical property data to help in designing equipment and also in manufacturing R-134a. This paper is intended to fill that need. The paper details the measurement and correlation of some of the important thermophysical properties such as vapor pressure, liquid density, and pressure-volume-temperature. The measured P-V-T data have been used to generate a Martin-Hou-type equation of state for this fluid over a wide range of temperature and pressure. Correlating equations are also developed for vapor pressure, liquid density, and ideal-gas specific heat. Ideal-gas specific heat has been estimated from measured spectroscopic data. The correlating equations can be used to generate the thermodynamic tables and charts. The critical temperature of R-134a has also been measured. Critical density and pressure have been estimated from measured data. The data and the correlations presented here are expected to be very useful to the refrigeration industry in the development of R-134a as a working fluid for refrigeration applications.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The Influence of Adsorption on PVT Measurements in the Gaseous Phase

PVT measurements of 1,1,1,2-tetrafluoroethane (C₂H₂F₄, HFC-134a) and its blend with octofluoropropane (C₃F₈, FC-218) have been performed in the gas phase near the dew curve. The experimental data were obtained by variable-volume and vibrating tube methods. Discrepancies in the behavior of isotherms from their classical behavior were experimentally observed. It was found that the phase transition does not go to completion at a single point of the thermodynamic surface but extends over a limited range of conditions. Obtained results are in accordance with a concept of adsorption of the vapor sample on the surface of the experimental cell. An increase in adsorption under the conditions close to condensation is caused by capillary condensation of the sample at the walls of the cell that initiates an early phase transition. The ranges of diffuse phase transitions were determined for 1,1,1,2-tetrafluoroethane as well as for its mixture with octofluoropropane at different thermodynamic parameters. The influence of selective adsorption on the change in the conditions of phase transition of the 1,1,1,2-tetrafluoroethane/octofluoropropane mixture was also experimentally studied.     

Gas-phasePVT properties of 1,1,1,2,3,3-Hexafluoropropane

We have measured the gas-phasePVT properties of 1,1,1,2,3,3,-hexafluoro-propane (R-236ea), which is considered to be a promising candidate for the replacement of 1,2-dichlorotetrafluoroethane (R-114). The measurements have been performed with a Burnett apparatus over a temperature range of 340 390 K and at pressures of 0.10–2.11 MPa. The experimental uncertainties of the measurements were estimated to be within ±0.5 kPa in pressure. ±8 mK in temperature, and ±0.15% in density. A truncated virial equation of state was developed to represent thePVT data and the second virial coefficients were also derived. The saturated vapor densities were also calculated by extrapolating the gas-phase isotherms to the vapor pressures. The critical density estimated from the rectilinear diameter was compared with the experimental value. The purity of the R-236ea sample used in the present measurements was 99.9 mol%. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Vapor pressure and liquid and gas densities of 2,2,2-trifluoroethanol

Forty-three vapor pressures were measured for temperatures from the normal boiling point to the critical point. These data were obtained with a phase-equilibrium cell designed for precise static measurements at pressures up to 20 MPa. The cell is located within an oil-operated thermostatic bath which provides a homogeneous temperature field with variations less than ±1 mK. The vapor pressure data were fitted to a Wagner-type equation. Sixty-two liquid densities were measured on seven isotherms between 20 and 140°C for pressures up to 16 MPa. These measurements were carried out with a precision density meter operating on a vibrational technique. Sixty-nine gas-PVT triples were determined from Burnett expansion series on five isotherms between 140 and 200°C for pressures up to the saturation line. In all experiments, temperature measurements were made with platinum resistance thermometers. Precise pressure measurements were performed using a mercury column of 6-m height and a standard deadweight gauge for the higher pressures.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity andPVT measurements of pentafluoroethane (refrigerant HFC-125)

By means of the transient and steady-state coaxial cylinder methods, the thermal conductivity of pentafluoroethane was investigated at temperatures from 187 to 419 K and pressures from atmospheric to 6.0 MPa. The estimated uncertainty of the measured results is ±(2–3)%. The operation of the experimental apparatus was validated by measuring the thermal conductivity of R22 and R12. Determinations of the vapor pressure andPVT properties were carried out by a constant-volume apparatus for the temperature range 263 to 443 K, pressures up to 6 MPa, and densities from 36 to 516 kg m^–3. The uncertainties in temperature, pressure, and density are less than ±10 mK, ±0.08%, and ±0.1%, respectively.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Fabrication and biocompatibility in vitro of potassium titanate biological thin film/titanium alloy biological composite

A potassium titanate biological thin film/titanium alloy biological composite was fabricated by way of bionic chemistry. The biocompatibility in vitro of Ti-15Mo-3Nb and the potassium titanate biological thin film/titanium alloy was studied using simulated body fluid cultivation, kinetic clotting of blood and osteoblast cell cultivation experiments in vitro. By comparing the biological properties of both materials, the following conclusions can be obtained: (1) The deposition of a calcium phosphate layer was not found on the surface of Ti-15Mo-3Nb, so it was bioinert. Because the network of potassium titanate biological thin film could induce the deposition of a calcium phosphate layer, this showed that it had excellent bioactivity. (2) According to the values of kinetic clotting, the blood coagulation time of the potassium titanate biological thin film was more than that of Ti-15Mo-3Nb. It was obvious that the potassium titanate biological thin film possessed good hemocompatibility. (3) The cell compatibility of both materials was very good. However, the growth trend and multiplication of osteoblast cells on the surface of potassium titanate biological thin film was better, which made for the concrescence of wounds during the earlier period. As a result, the potassium titanate biological thin film/titanium alloy showed better biocompatibility and bioactivity. Translated from Journal of Functional Materials, 2006, 37(10): 1,638–1,642 (in Chinese)     

Thermodynamic Properties of 1,1,1,2,3,3,3-Heptafluoropropane

A vapor pressure equation has been developed for 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) based on previous measurements from 202 to 375K, from which the boiling point of HFC-227ea was determined. Based on the previous pressure–volume–temperature (PVT) measurements in the gaseous phase for HFC-227ea, virial coefficients, saturated vapor densities, and the enthalpy of vaporization for HFC-227ea were also determined. The vapor pressure equation and the virial equation of state for HFC-227ea were compared with the available data. Based on the previous measurements of speed of sound in the gaseous phase for HFC-227ea, the ideal-gas heat capacity at constant pressure and the second acoustic virial coefficient of HFC-227ea were calculated. A correlation of the second virial coefficient for HFC-227ea was obtained by a semiempirical method using the square-well potential for the intermolecular force and was compared with results based on PVT measurements. A van der Waals-type surface tension correlation for HFC-227ea was proposed, based on our previous experimental data by the differential capillary rise method from 243 to 340K.     

Thermodynamic properties and excess volumes of 2,2,4-trimethylpentane + n-heptane mixtures from 298 to 338 K for pressures up to 400 MPa

(p, V, T) data for mixtures of 2,2,4-trimethylpentane (TMP) and heptane have been obtained in the form of volume ratios for four temperatures in the range 298.15 to 338.15 K for pressures up to 390 MPa. The data have been represented by the Tait equation of state for the purposes of interpolation and extrapolation. The atmospheric pressure densities of both pure components and their mixtures for three temperatures have been measured and used to determine the excess molar volumes. Isothermal compressibilities have been evaluated from the volumetric data.     

Study of viscosity and specific heat capacity characteristics of water-based Al2O3 nanofluids at low particle concentrations

In this paper, the specific heat capacity and viscosity properties of water-based nanofluids containing alumina nanoparticles of 47 nm average particle diameter at low concentrations are studied. Nanofluids were prepared with deionised water as base fluid at room temperature by adding nanoparticles at low volume concentration in the range of 0.01%–1% to measure viscosity. The effect of temperature on viscosity of the nanofluid was determined based on the experiments conducted in the temperature range of 25°C to 45°C. The results indicate a nonlinear increase of viscosity with particle concentration due to aggregation of particles. The estimated specific heat capacity of the nanofluid decreased with increase of particle concentration due to increase in thermal diffusivity. Generalised regression equations for estimating the viscosity and specific heat capacity of nanofluids for a particular range of particle concentration, particle diameter and temperature are established.     

n-hexane as a model for compressed simple liquids

Isobaric thermal expansivities, _p, ofn-hexane have been measured by pressure-controlled scanning calorimetry from just above the saturation vapor pressure to 40 MPa at temperatures from 303 to 453 K and to 300 MPa at 503 K. These new data are combined with literature data to obtain a correlation equation for _p valid from 240 to 503 K at pressures up to 700 MPa. Correlation equations are developed for the saturated vapor pressure, specific volume, and isobaric heat capacity of liquid n-hexane from 240 to 503 K. Calculated volumes, isobaric and isochoric specific heat capacities. isothermal compressibilities, and thermal coefficients of pressure are presented for the entire range of pressure and temperature. The pressure-temperature behavior of these quantities is discussed as a model behavior for simple liquids without strong intermolecular interactions.     

Formulation and evaluation of diclofenac potassium fast-disintegrating tablets and their clinical application in migraine patients

The aim of this study was to prepare fast-disintegrating tablets (FDTs) of diclofenac potassium with sufficient integrity as well as a pleasant taste, using two different fillers and binders: Tablettose 70® and Di-Pac^®. Tablets were made with direct compression method. Tablet properties such as porosity, hardness, and disintegration time were determined. Diclofenac potassium determinations were carried out using a validated spectrophotometric method for the analysis of drug. Furthermore, in vivo experiments were carried out to compare the analgesic effect and the time to relieve migraine headache between the commercial tablets and FDTs of diclofenac potassium against placebo. Results showed that FDTs of diclofenac potassium with durable structure and desirable taste can be prepared using both fillers and binders but tablets prepared with Di-Pac had a better taste so the tablet formulation containing Di-Pac was chosen for in vivo experiments. Placebo controlled in vivo trial demonstrated that 50 mg diclofenac potassium, administered as a single dose of FDTs or commercial tablets, was effective in relieving the pain and both of them were superior to placebo.     

Ideal Gas Thermodynamic Properties of Propyl tert-Butyl Ethers from Density Functional Theory Results Combined with Experimental Data

Ideal gas thermodynamic properties, S°(T), C _p°(, T), H°(T)–H°(0), _f H°(T), and _f G°(T), are obtained on the basis of density functional B3LYP/6-31G(d,p) and B3LYP/6-311 + G(3df,2p) calculations for two propyl tert-butyl ethers. All torsional motions about C–C and C–O bonds were treated as hindered internal rotations using the independent-rotor model. An empirical approximation was assumed to account for the effect of the coupling of rotor potentials. The correction for rotor–rotor coupling was found by fitting to entropy values determined from calorimetric measurements. Enthalpies of formation were calculated using isodesmic reactions.     

Correlation of magnetic properties to oxygen and potassium stoichiometry in single-crystal Ba1?xKxBiO3?y

Recent theoretical calculations have suggested the coupling of electrons to high-energy oxygen phonons as an explanation of superconductivity in the Ba_1–x K _x BiO_3–y system. We have synthesized high-quality single crystals of the material and have examined the behaviors of critical field and critical current parameters as a function of changes in the oxygen content and in the Ba/K ratio. We have determined, via positron lifetime spectroscopy and singlecrystal X-ray measurements, that the oxygen stoichiometry in this system can be varied without significant impact on the metal atom sublattice. These results facilitate an investigation of the dependence of critical parameters on dopant and defect levels in this system.     

Estimation and experimental study of the density and specific heat for alumina nanofluid

This study analyses the density and specific heat of alumina (Al₂O₃)/water nanofluid to determine the feasibility of relative calculations. The Al₂O₃/water nanofluid was produced by the direct-synthesis method with cationic chitosan dispersant served as the experimental sample, and was dispersed into three concentrations of 0.5, 1.0 and 1.5?wt.%. This experiment measures the density and specific heat of nanofluid with weight fractions and sample temperatures with a liquid density meter and a differential scanning calorimeter (DSC). To assess the availability of these equations, it then compares the experimental data with the calculated results according to the concepts of mixing theory and statistical mechanism. Comparing the calculated results of density and specific heat with the experimental data, the deviation of density fell within the range of ?1.50% to 0.06% and 0.25% to 2.53%, whereas the deviation of specific heat fell within the range of ?0.07% to 5.88% and ?0.35% to 4.94%, respectively. Calculated results of density and specific heat show a trend of greater deviation with an increased concentration of nanofluid. However, two kinds of density and specific heat of the calculated results fall within an acceptable deviation range in this study.     

Experimental research on residual carbon of Y211 inclusions in a melt-textured Y123/Y211 composite

The inherent doping of residual carbon during the preparation of Y₂BaCuO₅ (Y211) inclusions would degrade the physical and mechanical performance of the Y₁Ba₂Cu₃O_7-x (Y123) superconducting matrix. Y211 precursor powders were prepared by the oxalate coprecipitation process in this study. Residual carbon contents of Y211 powders under different heat treatment processes were studied by the high-frequency combustion infrared absorption method. The residual carbon content of Y211 reached the current best level ～0.012% when calcined in O₂ flow at 950°C for 20?h. Y211 powders with the lowest carbon content were used to prepare a small batch of melt-textured Y123/Y211 composites. All samples were single-domain crystals without macro defects, which were usually caused by the emission of CO₂. Among them, one sample (Ø27?mm?×?14?mm) has a maximum levitation force of 71?N (77?K, 0.5?T), with critical current density J_c of 3.2?×?10⁸ A/m² (77?K, 0?T).