Study of trifluoromethane dissociation within wide pressure and temperature ranges by molecular resonance absorption spectroscopy

The concentration of CF₂ produced via trifluoromethane, CF₃H, dissociation behind reflected shock waves is measured by molecular resonance absorption spectroscopy method within wide ranges of CF₃H concentrations, temperatures, and pressures (38 ≤ n[CF₃H] ≤ 27000 ppm, 1180 ≤ T ≤ 2780 K, and P = 1.5–18 bar). The heat release of CF₂ radical formation in trifluoromethane pyrolysis is experimentally determined. We analyze the experimental data obtained at low and high pressures and find the normalization factor for the best coincidence of those data. We determine the activation energy E _a at low and high pressures and obtain the generalized activation energy E _a for all the experimental data.     

Intrinsic stress of magnetron-sputtered niobium films

The stresses in niobium films were studied and the following preliminary results were obtained. (1) Niobium films can be prepared in any stress state (tensile, stress free or compressive) by varying the argon sputtering pressure. (2) As the bias voltage increases, more argon is incorporated into the film; both T_c and R/R₀ decrease; and the stress becomes more compressive and seems to saturate at about 1.5 × 10¹⁰ dyn cm^?2 at higher bias voltages (at an argon sputtering pressure of 1.9 Pa). (3) The lattice parameters show a close relation to the film stresses. (4) Lowering the sputtering rate results in a higher argon content in the bias-sputtered films. (5) The as-deposited film surface is smoother when deposited at lower pressures; the film has a columnar structure and intercolumnar gaps at higher pressures. (6) The film prepared at a higher bias voltage has a smoother as-deposited surface and a much smaller column size.From this study of the behavior of the stresses in niobium films, it appears that the stress is determined mainly by the microstructure and the energetic particle bombardment. Energetic particle bombardment may promote compressive stress by the incorporation of argon, by the formation of a more dense microstructure and by a “shot-peening” action.     

Special Equations of State for Methane,Argon, and Nitrogen for the Temperature Range from 270 to 350 K at Pressures up to 30 MPa

In order to describe the thermodynamic behavior of methane, argon, and nitrogen in the so-called “natural-gas region,” namely, from 270 to 350 K at pressures up to 30 MPa as accurate as possible with equations of a very simple form, new equations of state for these three substances have been developed. These equations are in the form of a fundamental equation in the dimensionless Helmholtz energy; for calculating the pressure or the density, the corresponding equations explicit in pressure are also given. The residual parts of the Helmholtz function representing the behavior of the real gas contain 12 fitted coefficients for methane, 8 for argon, and 7 for nitrogen. The thermodynamic relations between the Helmholtz energy and the most important thermodynamic properties and the needed derivatives of the equations are explicitly given; to assist the user there is also a table with values for computer-program verification. The uncertainties when calculating the density ρ, the speed of sound w, the isobaric specific heat capacity c _p, and the isochoric specific heat capacity c _v are estimated as follows. For all three substances it is Δρ/ρ≤±0.02 % for p≤ 12 MPa and Δρ/ρ ≤ ±0.05% for higher pressures. For methane it is Δw/w≤±0.02% for p≤10 MPa and Δw/w≤+-0.1% for higher pressures; for argon it is Δw/w?-0.1 % for p≤ 7 MPa, Δw/w≤±0.3 % for 7 <p≤30 MPa; and for nitrogen it is Δw/w≤±0.1% for p≤1.5 MPa and Δw/w±0.5% for higher pressures. For all three substances it is Δc _p/c _p≤±1 % and ΔC _v/C _v≤±1 % in the entire range.     

Experimental study of pressure behind reflected shock waves in argon at mach numbers of 10–35

The results are presented for a study of the pressure behind reflected shock waves for pressures of (1–10)·1.33 · 10² N/m² ahead of the incident shock wave. It is found that during the first 1.0–2.0 · 10^?5 sec after the reflection of the shock wave the pressure of an argon plasma behind it corresponds to that calculated from the conservation laws with allowance for ionization on the assumption that the plasma is ideal.     

Response of aluminium-infiltrated boron carbide cermets to shock wave loading

Shock-recovery and shock-spallation experiments were performed on two compositions of aluminium-infiltrated B₄C cermets as a function of shock pressure. Sixty-five per cent volume B₄C-Al cermets were recovered largely intact after shock loading up to pressures of ca. 12 GPa which permitted a critical study of the microstructural changes produced by the shock. Significantly, shock loading to between 12 and 13 GPa produced a combination of dislocation debris, stacking faults and deformation twins in a small fraction of the B₄C grains. Fragmentation of shock-loaded 80% B₄C-Al samples prevented meaningful microstructural investigation. Spall-strength testing also provided indirect evidence for the Hugoniot elastic limits (HEL) of these composites. Spall-strength calculations based on an elastic equation of state for 65% B₄C-Al indicated that the elastic regime extended up to shock pressures of ca. 10 GPa, or approximately 65% of the HEL of polycrystalline B₄C. A complete loss of spall strength was then observed at the transition to a plastic equation of state at a pressure of 12 GPa which coincided with observations of plasticity within the B₄C-substructure. This study demonstrated that composites containing a highly ductile phase combined with a high compressive strength ceramic phase could support high dynamic tensile stresses by resisting the propagation of catastrophic cracks through the brittle ceramic substructure.     

Study on Isochoric Specific Heat Capacity of Liquid R-410A and HFE-347pcf2

The isochoric heat capacity (c _v ) of R-410A [a mixture of 49.81 mass% difluoromethane (HFC-32) + 50.19 mass% pentafluoroethane (HFC-125)] and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethylether (HFE-347pcf2) was measured at temperatures from 277 K to 400 K and at pressures up to 30 MPa. The reported density measurements for R-410A and HFE-347pcf2 are in the single-phase region and cover a density range above 0.92 g·cm^?3 and 1.33 g·cm^?3, respectively. The measured data of R-410A are compared with data reported by other researchers. Also, the measured data of R-410A are examined with an available equation of state. As a result, it is found that the present c _v data for R-410A agree well with those by other researchers and the calculated values with the equation of state in the measurement range except near the critical isochore.     

Solubility of R22, R23, R32, R134a,R152a,R125 and R744 refrigerants in water by using equations of state

This paper tries to demonstrate the ability of VPT and CPA equations of state and modified mixing rules for predicting of solubility CHC1F₂ (R22), CHF₃ (R23), CH₂F₂ (R32), C₂H₂F₄ (R134a), C₂H₄F₂ (R152a), C₂HF₅ (R125) and CO₂ (R744) refrigerants in water at different temperatures and pressures. For this purpose, the fugacity of each component in gas and liquid phases is calculated by using VPT and CPA equations of state. Also in this work, the interaction parameters for mixing rules in each mixture are optimized by using two-phase equilibrium data (VL_W). Results of the two-phase flash calculation show good agreement between obtained solubility and the experimental data. The predicted solubility of the selected refrigerants in water agrees with the experimental data with accuracy of about 1.5% and 3.5% by VPT equation of state – modified mixing rule and CPA equation of state – Van der Waals classic mixing rule respectively.     

Premelting of iron at high pressures under conditions of contact with amorphous argon

Experiments involving shock-wave loading systematically produce higher melting temperatures than those obtained in experiments involving the use of diamond anvils (DAC). The melting temperature in DAC experiments is determined by structural changes on the surface of a solid in contact with another substance (for example, with argon). We use the method of molecular dynamics to investigate the process of iron melting from the surface in single-component and two-component (in the presence of argon as medium) cases at pressures of ～100 GPa. In the argon-iron two-component model aimed at reproducing the conditions of static DAC measurements, premelting is observed at a temperature below T _m . The layer of iron adjacent to argon may make a transition to disordered state under certain conditions. The temperature interval at constant pressure, in which this effect is observed, is comparable in magnitude with the difference between the melting temperatures obtained as a result of dynamic and static measurements. Therefore, this effect may be one of the reasons for discrepancy between the experimental results for the melting curve of iron and other metals.     

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.     

Equation of State for Normal Liquid Helium-3 from 0.1 to 3.3157 K

An equation of state for normal liquid ³He has been constructed in the form of Helmholtz free energy as a function of independent parameters—temperature, and density. The equation was fitted simultaneously to the collected experimental p-ρ-T, specific heat, sound velocity, isobaric expansion coefficient and isothermal compressibility coefficient from the world’s literature to accuracies comparable with reasonable experimental errors in the measured quantities. Extensive comparisons between the equation of state and experimental data have been made by a set of deviation plots. The state equation is valid in the region for temperatures from 0.1 K to T _c = 3.3157 K, and for pressures from vapor pressures to melting pressures.     

The thermal conductivity and heat capacity of gaseous argon

This paper presents new absolute measurements of the thermal conductivity and of the thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. We measured seven isotherms in the supercritical dense gas at temperatures between 157 and 324 K with pressures up to 70 MPa and densities up to 32 mol · L^–1 and five isotherms in the vapor at temperatures between 103 and 142 K with pressures up to the saturation vapor pressure. The instrument is capable of measuring the thermal conductivity with an accuracy better than 1% and thermal diffusivity with an accuracy better than 5%. Heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity and from the density calculated from measured values of pressure and temperature from an equation of state. The heat capacities presented in this paper, with a nominal accuracy of 5%, prove that heat capacity data can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be invaluable when applied to fluids which lack specific heat data or an adequate equation of state.     

Combined equation of state for liquids and gases, which includes the classical and scaling parts

A new equation of state is suggested, which describes the P-ρ-T data for ⁴He and SF₆ in the ranges of reduced densities ?1 < (ρ?ρ _c )/ρ _c < 1 and of reduced temperatures ?0.3 < (T-T _c )/T _c < 0.3 (ρ _c and T _c are the critical values). This equation includes the regular equation of state approximating the P-ρ-T data outside of the critical region and the nonparametric scaling equation of state adequately describing the P-ρ-T data in the vicinity of the critical points, which are combined by the crossover function. The classical function of damping of fluctuations of density and temperature when moving away from the critical point is suggested as the crossover function. Two equations of state are used for the regular part of combined equation, namely, the new cubic equation of state suggested by us and the equation of state of Kaplun and Meshalkin. The nonparametric scaling equation of state with three system-dependent constants is used as the scaling part of the combined equation. The conditions (?P/?v) _T = 0 and (?² P/?v ² ) _T = 0 are valid for the combined equation at the critical point; binodal and spinodal are present, as is the case in classical equations of state. The approximation of the most exact data on ⁴He and SF₆ using the new equation reveals that the latter equation correctly describes the P-ρ-T data with mean-square error with respect to pressure of ±0.5%.     

The formation of hydrogenated yttrium nanoparticles

Nanoparticles of yttrium (Y) and YH_3?x (with the composition varying from x<1 to x?1) and the chemical reactions of these particles with hydrogen (YH₂?YH₃) were studied. Yttrium nanoparticles with an average size of ～25 nm were synthesized by method of laser ablation in an argon atmosphere. The particles deposited onto quartz substrates were exposed to H₂ at room temperature and various pressures. The phase composition of the hydrogenated nanoparticles was determined by optical density measurements in situ. In the initial stage (low H₂ pressures), the interaction of yttrium with hydrogen leads to the formation of stable metal-like YH₂ dihydride nanoparticles. As the hydrogen pressure increases, the YH₂ particles transform into dielectric nanoparticles with the composition YH_3?x . The reaction YH₂?YH₃, corresponding to the metal-dielectric phase transition in the nanoparticles, is reversible with respect to the H₂ pressure in the gas phase.     

Equations of state for helium, hydrogen, deuterium, nitrogen, oxygen, carbon monoxide, carbon dioxide, and methane at high temperatures and pressures

Equations of state are constructed for He, Ar, H₂, D₂, N₂,O₂, CO, CO₂, and CH₄ in the temperature range of (1–20) × 10³ K and at pressures up to 40 GPa on the basis of the model of canonical equation of state previously proposed by us.     

Peculiarities of reflected shock wave bifurcation on a needle

The axisymmetric bifurcation of a reflected shock wave interacting with the boundary layer on a 79-mm-long needle with a diameter of 1.1 mm has been studied. The needle, oriented in counterflow direction, was mounted at the axis on the end wall of a shock tube with 98 × 98-mm section. Experimental data on the parameters of reflected shock wave bifurcation are presented for CO₂ at an initial pressure of 4 kPa and Mach number M = 2.5 of the incident shock wave. The obtained data are compared to experimental parameters of the reflected shock wave bifurcation on side walls of the shock tube. Experimental data were obtained by schlieren imaging of flow patterns and high-speed photography with a DICAM-Pro camera in the double-frame recording mode.     

An Experimental Study of the <Emphasis Type="Italic">pVTx</Emphasis> Properties for Binary Mixtures of HFC-32 and HFC-125 from 258 to 354 K at Pressures up to 16.9 MPa

An experimental study of the pVTx properties for binary mixtures of HFC-32 (CH₂F₂) and HFC-125 (C₂HF₅) was conducted in the range of temperatures from 258 to 354 K, pressures up to 16.9 MPa, densities from 900 to 1400 kg·m⁻³, and compositions from 0 to 1 mole fraction of HFC-32, within the uncertainties of 4.8 mK of temperatures, 1.8 kPa of pressures, 0.022% of densities, and 0.0022 mole fraction of compositions. The present results were determined with the use of a constant-volume apparatus consisting of a cylindrical vessel of approximately 173 cm³ internal volume. The available data including the present measurements are critically compared with the equation of state developed by Tillner-Roth et al., and it is found that, in the liquid region for the range of compositions from 0.1 to 0.4 mole fraction of HFC-32, this equation of state is less reliable because of the lack of experimental data. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Predictions of the Joule–Thomson inversion curves for polar and non-polar fluids from the SAFT-CP equation of state

In this work, we calculate the Joule–Thomson inversion curves of some non-polar fluids, including argon, nitrogen, oxygen, carbon dioxide, n-alkanes (C₁–C₄), ethene, acetylene, benzene and toluene and some polar fluids, including hydrogen sulfide, ammonia, acetone and ethyl ether from the SAFT-CP equation of state. Comparisons with correlated experimental data and reference equation of state indicate that this molecular based equation of state gives good prediction for non-polar fluids. For polar fluids, the predictions of the low-temperature branch are satisfied; but, unfortunately, due to lack of isenthalpic data for high-pressure–high-temperature gas condensate, the reliability of model predictions could not be completely verified. In this work, the performance of some cubic equations of state in predicting the Joule–Thomson inversion curves is also compared with SAFT-CP equation of state.     

R.F. sputtered β-tantalum and b.c.c. tantalum films

Tantalum films have been deposited on both glass and Ta₂O₅-coated substrates by r.f. sputtering. The structure, resistivity ρ and temperature coefficient of resistance TCR of films sputtered in pure argon or reactively in Ar-O₂ or Ar-N₂ have been determined. In pure argon on sufficiently preheated substrates a very pure b.c.c. Ta phase (α^∗-Ta), with ρ∼25 μΩ cm and TCR∼1500 ppm/°C, is formed. Sputtering on substrates which are only slightly preheated or are heated solely by the sputtering process yields a tetragonal Ta phase (β-Ta) with ρ∼165 μΩ cm and TCR∼-160 ppm/°C. With added oxygen the β−Ta phase is produced over the whole partial pressure range investigated. Low partial pressures of nitrogen lead to β-Ta. At higher nitrogen partial pressures b.c.c. Ta (α-Ta) with ρ∼50 μΩ cm and TCR∼650 ppm/°C is formed and finally the plateau region is observed.     

Dynamics of radiation in a CO:N<Subscript>2</Subscript> mixture behind strong shock waves

Experiments are performed in determining the spectral composition and dynamics of radiation in a CO:N₂ mixture behind the front of incident shock wave at velocities up to 6.5 km/s and initial pressures in the mixture of 1–9 torr. Absolute values of radiation intensity are obtained. It is determined that the main source of radiation under the conditions being investigated is provided by the violet system of CN. Also considered are the fourth positive system of CO and the Swan system of C₂ molecule. Comparison is made of the radiation intensity and time dynamics of the molecular systems identified above.     

Dynamic behavior of selected ceramic powders

An experimental setup has been developed on the continuous recording of the stress profiles in ceramic powders subject to shock loading with manganin gauges. A series of plate impact experiments on highly porous ceramic powders such as Al₂O₃, SiC and B₄C were conducted at the laboratory's single stage powder gun facility. The relationship between shock wave velocity and particle velocity was measured to obtain the Hugoniot data. Plate impact onto powder sample experiments were conducted at loading stresses ranging from 1.6 to 4.2 GPa. The experimental results show that the shock wave speeds in various ceramic powders vary between 1 and 2 km/s. Linear Hugoniot relations between shock velocity (D) and particle velocity (u) are observed. The loading stress–specific volume form of Hugoniot relations (P–V) was constructed using the data from quasistatic compression test results, Hopkinson bar dynamic compression test results and powder gun plate impact experiment results. The P–V diagram shows that the crush strength of ceramic powders is comparable to the loading stress level. The B₄C and SiC powders with bigger particle size more easily reach the solid state Hugoniot than the powders with smaller particle size at the same loading condition. In the case of Al₂O₃, the material shows less sensitivity to particle size difference at the same level of loading rate as compared to B₄C and SiC.