The lean flammability limits in air of methane,hydrogen and carbon monoxide at low temperatures

The lean flammability limits in air for methane, hydrogen and carbon monoxide at atmospheric pressure were established under isothermal initial conditions at temperatures extending down to ?130°C. Simple guidelines are then suggested for predicting these limits on the basis of the calculated flame temperature of the limiting mixtures. Estimates were also made of the extent of changes in these limits due to heat transfer over a wide mixture temperature range.     

The limits of flammability of mixtures of ammonia,hydrogen and methane in mixtures of nitrogen and oxygen at elevated temperatures and pressures

As part of a program investigating the flammability characteristics of ammonia in mixtures with air, nitrogen and ammonia side-products, the flammabili The flammable regions are not as large as those found in a previous study for mixtures of ammonia and hydrogen, but are still remarkably wider than the     

Experimental determination of the equation of state of solid hydrogen and deuterium at high pressures

Isochores of solid hydrogen and deuterium have been measured for melting line pressures up to 2000 bar. These are corrected to correspond to para-H₂ and ortho-D₂. The 4.2 K isotherm of H₂ has been determined and compared to the extrapolated low-pressure isochore of Anderson and Swenson (AS). Deviations have led us to reanalyze the AS data. The 4.2 K isotherm and the isochores are used, with the aid of a Mie-Grüneisen analysis, to determine P-V-T data for these solids up to 25 kbar. An analysis is presented which enables a determination of P-V-T-C ₁ for all values of C ₁, the ortho-para concentration. Results, including the Debye temperature, Grüneisen constant, and bulk modulus, are presented both in tabulated and graphical form. We also present what we feel to be the best of the 4.2 K, zero-pressure molar volumes of disordered H₂ and D₂ as a function of C ₁. Our measurements show no indication of the premelting phase transition reported in recent Russian literature and a possible explanation is presented.Supported in part by the Stichting FOM.     

Adsorption and diffusion of nitrogen,oxygen, argon,and methane in molecular sieve carbon at elevated pressures

Diffusion and equilibrium adsorption of nitrogen, oxygen, argon, and methane on molecular sieve carbons 3A and 5A were studied at 273, 303, and 323°K. The adsorbate pressure was varied over a pressure range of 0–1.3 MPa in a gravimetric setup. On a molar basis, methane had the highest adsorption capacity among the four gases studied. Oxygen and nitrogen had approximately similar equilibrium adsorption capacity. Equilibrium adsorption data were represented by the Langmuir model and the vacancy solution model (VSM). Langmuir equation showed deviations at high pressures. The isosteric heat of adsorption was found to increase slightly with an increase in surface coverage. Kinetic data showed that oxygen had the highest diffusion rate and methane the lowest. Diffusivities were found to be generally independent of pressure.     

The thermal conductivity of pure nitrogen and of mixtures of nitrogen and carbon dioxide at elevated temperatures and pressures

The thermal conductivities of nitrogen at 470 K and six mixtures of nitrogen and carbon dioxide at various temperatures have been measured as a function of pressure up to 25 MPa. The mixtures were measured at the following temperatures: one at 302 K, three at 380 K, one at 430 K, and one at 470 K. The data were used to test three prediction methods for the thermal conductivity of gas mixtures under pressure. Surprisingly good agreement was found with predictions using the corresponding-states method of Ely and Hanley. The predictions of the more theoretically based method of Mason et al. were low throughout, due partly to its use of the Hirschfelder-Eucken equation as the low-density limit, but also because the predicted density dependence rises too slowly. The simplified version of this method proposed by Svojskij gave slightly worse predictions, particularly at higher densities. The zero- density results for nitrogen are examined by comparing the zero-and first-density coefficients with the trends shown at lower temperatures.     

A microporous aluminum-based metal-organic framework for high methane,hydrogen, and carbon dioxide storage

We report a microporous aluminum-based metal-organic framework(MOF),BUT-22 for high methane(CH₄),hydrogen(H₂),and carbon dioxide(CO2)storage.At 296 K and 80 bar,BUT-22 exhibits a high gravimetric CH4 storage capacity of 530 cm³(STP)/g(0.379 g/g).BUT-22 also has a high gravimetric H₂storage capacity of 12 wt.%at 100 bar and 77 K.In addition,the CO₂adsorption studies revealed that BUT-22 exhibits a high absolute gravimetric CO2 uptake of 1.7 g/g at 296 K and 40 bar.     

Behaviour of the equation of state of liquid methane at high pressures

The equation of state of liquid methane is analyzed at high pressures along a series of isotherms which cover a substantial part of the range of existence of the liquid phase. It is found that experimental data are well reproduced by means of an equation of state which was initially proposed for the high density hardsphere system, provided that the effective excluded volume is properly determined for each isotherm. These effective excluded volumes decrease slightly as the temperature increases.     

Theoretical study of the thermodynamic properties of nitrogen at high temperatures and pressures

A theoretical analytical equation of state is derived and used to compute new thermodynamic data for nitrogen at high tempratures and pressures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 975–983, December, 1987.     

A vibrating-tube densimeter for fluids at high pressures and temperatures

A vibrating U-tube apparatus has been developed for determining the densities of pure fluids and fluid mixtures at 10-200 MPa and 323-773 K. Measured parameters areP,T, andr (period of vibration). Fluids are injected into the U-tube at constantP andT. Three or more reference fluids are used to calibrate the response of the instrument. Fluid mixtures are produced by pumping pure fluids into T-junctions on the upstream side of the U-tube using high accuracy syringe pumps. An automated syringe pump is used to maintainP at setpoint ±0.01 MPa.T is controlled to ±0.01 K using a closed-loop, electronic signal amplification/feedback system. For mixtures, a statistically significant number of measurements of r are obtained to account for the effects of small heterogeneities in fluid composition (generally <0.005X;). Typically, density data for 15 fluids can be obtained in a 6- to 8-h period. Considering all of the potential sources of error in the experimentation, conservative estimates of uncertainty are as follows:P, ±0.02 MPa;T, ±0.05 K;p (pure fluids), ±0.0005g.cm^–3; andp (fluid mixtures), ±0.0005-0.0010g-cm^–3.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Size and temperature dependences of the resistivity of thin alkali metal wires at liquid nitrogen,hydrogen and helium temperatures

The temperature variation of the resistivity ?, the size effect on the resistivity and the residual resistivity were investigated for thin wires of the alkali metals Na, K, Rb and Cs (which were of high purity and had a high crystalline order) from room to liquid He temperatures.The results obtained allowed us to determine the fundamental quantity ?_∞l and also the resistivity ?(T)_∞ of the bulk metal and the mean free path l(T) of the conduction electrons.The values of ?_∞l obtained near 0 K for these thin alkali metal wires of high crystalline order were found to correspond, within experimental error, to those obtained previously using highly disordered thin films of the same alkali metals at liquid nitrogen temperatures. Both sets of ?_∞l valuescorrespond to the values expected theoretically according to the fundamental equation $\text{1}\text{?}{}_{\mathrm{\infty }}\text{l}\text{=}\text{const.}\text{× N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ (where N is the density of effective conduction electrons), thus proving that ?∞l is independent of temperature and of degree of crystalline order as expected.The results on the temperature variation of the resistivity ?(T)_pho due only to electron-phonon scattering reveal a T⁵ law for Na in the temperature interval 15?T?20 K and for Rb and Cs in the range 1.6?T?3 K, and a T³ law for K in the range 14?T?20 K. Moreover, at temperatures below 4 K the resistivities of the thinnest wires of Cs and, to a lesser extent, of Rb deviate from Matthiessen's rule, thus revealing a temperature-dependent size effect.     

Raman scattering of vibrational overtones in deuterium at high pressures

We report observations of the Raman-active vibrational overtone in normal deuterium at 77K and pressures up to 36.4 GPa (1 GPa = 10⁴ bar). We observed a sharp Q₂(J) line corresponding to the v=20, J=0, k=0, k=0 transition and a broad Q₁(J)+Q'₁(J) band corresponding to v,v'=10, J=0, k-k' transitions. The selection rules for the Q₁(J)+Q'₁(J) manifold allowed us to measure the joint density of states of the manifold which we compared to a theoretical density of states for the v=1 vibrational band.     

Graphitization and preparation of diamond in an amorphous carbon material at high pressures and temperatures

Structural transformations of a carbynoid amorphous carbon material after high-temperature, high-pressure processing at different rates of isobaric heating have been studied by scanning electron microscopy and Raman spectroscopy. Using the 6 GPa data as an example, we demonstrate that slow heating leads to gradual graphitization of the material at temperatures above 600°C, in perfect agreement with previous measurements, in which graphitization was observed up to 8 GPa. At the same time, increasing the heating rate to 50°C/s at a sufficiently high pressure (8 GPa) leads to significant changes in the nature of the transformations. Whereas heating to temperatures from 1100 to 1200°C also leads to the formation of graphite-like phases, rapid heating to 1300°C ensures the formation of considerable amount of diamond in the absence of catalysts.     

FTIR spectroscopy of hydrogen, carbon monoxide, and methane adsorbed and co-adsorbed on zinc oxide

Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H₂/CO, H₂/CH₄ and CO/CH₄ on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn²⁺ ions. Adsorption lowers the CH₄ symmetry from T_d to C_3v, which is reflected in activation of the v₁ (symmetric stretching) mode and discrete frequency shifts of the v₃ (antisymmetric stretching) and ν₄ (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(O–H) band, which originally appear at 1710 and 3492 cm⁻¹, respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas.     

Thermal conductivity of nitrogen at high pressures

The results of the measurements of the thermal conductivity coefficients of nitrogen at 298.15 K from atmospheric pressure up to 1 GPa are reported. The experimental values are used to test the Modified Enskog Theory and the corresponding state principle. The experimental values are also compared with the results of computer simulation of the thermal conductivity of a Lennard Jones fluid.     

Thermal conductivity of sandstone at high pressures and temperatures

Results are given of experimental investigations of the coefficient of thermal conductivity of samples of sandstone at hydrostatic pressures of up to 400 MPa and temperatures of 275–523 K. It is demonstrated that the pressure increase causes a weaker temperature dependence of thermal conductivity. Processes are discussed which lead to additional scattering of heat waves in disordered media.     

The equation of state for magnesium at high pressures

A caloric model of the equation of state is presented, which allows the properties of substances to be described in a broad range of densities and pressures. A new method for determining the curve of cold compression at T=0 K is proposed. The thermodynamic characteristics of magnesium calculated using the proposed model are compared to the experimental data available for high energy densities.