Capillary Condensation Of Nitrogen Research Articles

Simple Universal Kelvin Equation Valid in the Critical Point Vicinity, External-Internal State Correction, and their Application to Nitrogen Capillary Condensation in Mesoporous Silica SBA-15

A new simple universal form of the Kelvin equation, which can be used near the gas-liquid critical point and the correction of the pressure for vapor outside the porous medium are used for the N2 meniscus effective curvature radius calculation at the phase equilibrium in mesoporous silica SBA-15, on the basis of the capillary condensation experimental data.

Усть-ишимская кость: минералогогеохимические свойства как источник палеонтологической, палеоантропологической и палеоэкологической информации

Ust-Ishim man was the representative of one of the ancestral groups of the Homo sapiens, Neanderthals and Denisovans. The first results of a comprehensive mineralogical and geochemical study of fossil bones using a wide range of physical, chemical and physico-chemical methods: thermal analysis, optical microscopy, scanning electron microscopy, atomic-force microscopy, nitrogen capillary condensation method, X-ray fluorescence analysis, ISP-MS, gas chromatography method, amino acid chromatography analysis’s, X-ray microprobe method, X-ray diffraction method, Raman and infrared spectroscopy, isotope spectrometry are presented in this article. The studied fragment of the skeleton is of higher preservation rate than the common bone detritus of this age and even the fossils of younger Pleistocene animals that allowed determining almost all its primary properties. The unique preservation presumably was provided by the favorable environment and a special way the Ust-Ishim man originally was buried. Results of study of the chemical and mineral composition of the bone fossils allowed a reconstruction of the Ust-Ishim man life history.

Influence of the doping type and level on the morphology of porous Si formed by galvanic etching

The formation of porous silicon (por-Si) layers by the galvanic etching of single-crystal Si samples (doped with boron or phosphorus) in an HF/C2H5OH/H2O2 solution is investigated. The por-Si layers are analyzed by the capillary condensation of nitrogen and scanning electron microscopy (SEM). The dependences of the morphological characteristics of por-Si (pore diameter, specific surface area, pore volume, and thickness of the pore walls), which determine the por-Si combustion kinetics, on the dopant type and initial wafer resistivity are established.

Tantalum powders with a mesoporous structure

In this work we investigate influence of the composition and specific surface of a precursor on the porous structure of tantalum powders obtained via magnesium vapor reduction of the Та2О5, MgТа2O6 and Mg4Та2O9. Sorption and nitrogen capillary condensation have allowed an increase in the specific powder surface to be established due to the increasing amount and specific surface of mesopores with a size below 10 nm.

Stimulated emission from aluminium anode oxide films doped with rhodamine 6G

The spectral and luminescent properties of the rhodamine 6G dye in a porous matrix of aluminium anode oxide are studied. The films with a highly-ordered porous structure are produced using the method of two-stage anodic oxidation. By means of raster electron microscopy it is found that the diameter of the pores amounts to nearly and the separation between the adjacent channels is almost . The thickness of the films is equal to , and the specific surface area measured using the method of nitrogen capillary condensation is . Fluorescence and absorption spectra of rhodamine 6G molecules injected into the pores of the aluminium anode oxide are measured. It is found that under the excitation of samples with the surface dye concentration by the second harmonic of the Nd : YAG laser in the longitudinal scheme with the pumping intensity , a narrow band of stimulated emission with the intensity maximum at the wavelength appears against the background of the laser-induced fluorescence spectrum. A further increase in the pumping radiation intensity leads to the narrowing of the stimulated emission band and an increase in its intensity. The obtained results demonstrate the potential possibility of using the porous films of aluminium anode oxide, doped with laser dyes, in developing active elements for quantum electronics.

Effects of Carbon Coating and Pore Corrugation on Capillary Condensation of Nitrogen in SBA-15 Mesoporous Silica

To examine the origin of an ink-bottle-like structure in SBA-15 formed by carbon coating and the effects of pore corrugation on capillary condensation and evaporation of a vapor in the cylindrical pores, we measured the adsorption isotherms of nitrogen at 77 K on 10 kinds of SBA-15 samples before and after a carbon coating process by the exposure to acetylene at 1073 K, as well as desorption scanning curves and subloops on the untreated samples. These SBA-15 samples were synthesized under the different conditions of initial SiO2/P123 ratio and hydrothermal treatment. SBA-15 with relatively large microporosity tends to form easily constrictions inside the main channels by the carbon coating. This strongly suggests that the rough pore walls of SBA-15 may induce the incomplete wetting of carbon layers on the pore walls to form the constrictions inside the cylindrical pores. A comparison of two subloops implies that the pores of SBA-15 synthesized with a SiO2/P123 ratio of 75 consist of an assembly of connecting domains of different diameters; that is, the pores are highly corrugated. For SBA-15 synthesized with a SiO2/P123 ratio of 60, the amplitude of the pore corrugation is significantly decreased by the prolonged hydrothermal treatment at 373 K. On the other hand, for SBA-15 synthesized with a SiO2/P123 ratio of 45, the amplitude of the corrugation is negligibly small, although the cylindrical pores are interconnected through narrow necks with each other. It is found that the smaller the amplitude of the pore corrugation, the smaller the width of the hysteresis loop.

Catalytic activity of NASICON-type phosphates for ethanol dehydration and dehydrogenation

A1 ± x Zr2 − x M x (PO4)3 (A = H3O+, Li+; M = In, Nb; x = 0, 0.1, 0.2) NASICON-type materials have been prepared and characterized by X-ray diffraction, specific surface measurements (capillary condensation of nitrogen), and impedance spectroscopy. We have assessed their catalytic performance for ethanol dehydration and dehydrogenation. The results demonstrate that, when prepared with a large specific surface area, these materials are active catalysts for ethanol conversion to hydrocarbons.

The formation and properties of one-dimensional FeHal2 (Hal = Cl, Br, I) nanocrystals in channels of single-walled carbon nanotubes

FeCl2@OCHT, FeBr2@OCHT, and FeI2@OCHT nanocomposites were obtained by capillary filling of the channels of carbon single-walled nanotubes (SWNTs) with melts of iron halogenides. The composites were studied by high resolution transmission electron microscopy (HRTEM), the capillary condensation of nitrogen at 77K, Raman spectroscopy, optical absorption spectroscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and Moessbauer spectroscopy. Substantial distinctions in the combination scattering spectra of SWNTs and nanocomposites in the region of radial modes and in the region of longitudinal and tangential oscillations were revealed. The presence of electron transfer between the nanocrystal and the SWNT wall was established in the nanocomposites. For the FeCl2@OCHT nanocomposite, two states of Fe+2 were found: the first is characterized by electron transfer from the nanotube to the nanocrystal, which leads to the electron structure of the SWNT and FeCl2 changing; the second corresponds to the strained intercalated state resulting from the mechanical effect of the small SWNT diameter on the FeCl2 nanocrystal.

Capillary Condensation of Nitrogen in Ordered Mesoporous Silica with Bicontinuous Gyroid Structure

To know the accurate relationship between pore size and the pressure of capillary condensation or evaporation and also to elucidate the pore-connectivity effects on adsorption hysteresis and pore criticality for the ordered mesoporous silicas (MCM-48 and KIT-6) with bicontinuous gyroid structure, we carried out X-ray structural study of MCM-48 and KIT-6 and measurements of the adsorption−desorption isotherms of nitrogen in comparison with MCM-41 and SBA-15 with unconnected cylindrical pores. The results clearly show that the hydraulic diameter describes incorrectly the mean pore size of these materials expressing the strength of confinement under the assumption of cylindrical pores with no networking effects. In addition, the average pore diameter at the middle point of pore intersections still underestimates the strength of confinement compared to the unconnected cylindrical pores of MCM-41 and SBA-15. Despite a large difference in porous structure, the shape and thermal behavior of the adsorption hysteresis for KIT-6, as well as the sorption scanning behavior, were indistinguishable from those for SBA-15, indicating that interconnections among pores of almost the same size do not have a significant effect on the adsorption hysteresis and pore criticality.

Catalytic properties of zirconium phosphate and double phosphates of zirconium and alkali metals with a NaZr2(PO4)3 structure

Zirconium orthophosphate Zr3(PO4)4 and double phosphates of zirconium and alkali metals AZr2(PO4)3 (A = Na, K, Rb, Cs) with a NaZr2(PO4)3 structure were synthesized and characterized by X-ray diffraction and electron microprobe analyses and capillary condensation of nitrogen. The catalytic properties of the phosphates in the dehydration of methanol were studied.

In situ small-angle neutron scattering study of nitrogen adsorption and condensation in mesoporous silica glass CPG-10-75

Film formation and capillary condensation of nitrogen at 78 K on the mesoporous controlled pore glass CPG-10-75 have been studied at certain relative pressures by in situ small-angle neutron scattering. On desorption ramified clusters of vapor filled voids have been observed, but not on adsorption. The kinetics of adsorption and desorption have been followed. The experimental results are discussed with respect to recent theoretical studies of fluids in complex pore systems.

Small‐angle Scattering Studies of Adsorption and of Capillary Condensation in Porous Solids

AbstractSmall‐angle scattering (SAS) studies are reviewed of adsorption and capillary condensation of water, hydrocarbons and halogenated hydrocarbons near room temperature, and of nitrogen at 78 K in some mesoporous solids, mainly silicas. The theory needed for the interpretation of SAS data is briefly covered. Calculations of the scattered intensity I(q) for a model porous medium show that I(q) depends markedly on the film thickness t. Adsorption and capillary condensation of nitrogen at 78 K in mesoporous silicas was studied by use of in situ SANS, and t as function of the relative pressure P/Ps was estimated. Adsorption of N2 in defects within the silica skeleton at P/Ps<0.1 lead to a significant increase in I(q). Isolated vapor bubbles in capillary condensed nitrogen in a Gelsil® appeared on adsorption near saturation of the pore system. The kinetics of capillary condensation and of drainage were followed. Power law scattering at low q indicated the formation of ramified clusters of voids on drainage of liquid nitrogen from the xerogel Gelsil®. Similar clusters were observed on drainage of water from Vycor® glass. Provided the clusters indicate a percolation process, the desorption branch should not be used for the estimation of a pore size distribution for materials with networked pores. The adsorptive smoothing by benzene was observed of a rough interface in a controlled pore glass.

Capillary Condensation of Nitrogen in MCM-48 and SBA-16

To examine the effects of connectivity among pores of almost the same size and of different size and geometry on adsorption hysteresis and pore criticality, we measured the temperature dependence of the adsorption−desorption isotherm of nitrogen onto MCM-48 and SBA-16 materials, respectively, with well-defined three-dimensional networks of cylindrical pores and cagelike pores, over a wide temperature range of T/Tc = 0.43 to 0.90. The results for MCM-48 strongly suggest that interconnections among pores of almost the same size and geometry do not have a significant effect on the adsorption hysteresis and pore criticality. For SBA-16 with well-defined ink-bottle pores, capillary condensation in the hysteretic isotherms takes place near the equilibrium, whereas capillary evaporation from large cavities is delayed. The classical concept of pore blocking is not supported by the experimental isotherms for SBA-16, because the delayed desorption is not concerned with emptying of the small channels. The hysteresis...

Capillary condensation of nitrogen in MCM-41 and SBA-15

We performed measurements of a series of adsorption–desorption isotherms of nitrogen into MCM-41 and SBA-15 mesoporous molecular sieves with different pore sizes in a wide temperature range between a bulk triple point (Tt) and a bulk critical point (Tc). The hysteresis loop shrinks with increasing temperature and eventually disappears at the hysteresis critical temperature (Tch), in accord with the appearance of metastable states in a single pore. We estimated the exact pore sizes of our samples from comparing the experimental equilibrium pressure at 77 K with the NLDFT isotherms, where the condensation pressures at 77 K were determined by extrapolating a plot of the equilibrium pressure versus temperature measured above Tch. The pore critical temperature (Tcp) was also determined from the inflection point in a plot of the inverse slope of the adsorption step against temperature. Tch is always lower than Tcp. Both plots of (Tc−Tch)/Tc versus d/rp and (Tc−Tcp)/Tc versus d/rp form straight lines passing through the origin, where d is the molecular diameter, although the former plot deviate from the linear relationship at large pores; Tch approaches Tcp in large pores. This strongly suggests that in large pores the energy barrier from the metastable state to the stable state is too large to be overcome within the period of observations even at the high temperatures just below Tcp.

The Formation of Porous Membranes by Filtration of Aerosol Nanoparticles

Flame-generated aerosol particles of Al2O3 were deposited by gas filtration on two types of porous and ceramic tubes of α-Al2O3 with mean pore diameters of 450 and 2700 nm, respectively. The particles were aggregates with average mobility diameters in the range of 30–100 nm and primary particle diameters of 4–8 nm. The particles are characterized by differential mobility analysis, transmission electron microscopy, and by their specific surface area. The deposited membranes are characterized by gas permeability measurements, scanning electron microscopy, and by their pore size distribution from nitrogen capillary condensation. The particles form a distinct, homogeneous membrane layer with a porosity of ∼90% on top of the substrate surface and only penetrate slightly into the substrate structure. The mean pore sizes of the deposited membranes determined by nitrogen condensation agree approximately with those determined by gas permeation and the specific surface area. The mean pore diameter varies in the range of 30–70 nm. The gas permeability of the deposited membranes is related to the specific surface area but influenced by the high porosity. The mean pore size and the permeability of the membranes are almost independent of the substrate structure.

Gauge cell method for simulation studies of phase transitions in confined systems

A method for Monte Carlo studies of phase equilibrium in confined systems is presented using an example of vapor-liquid equilibrium (capillary condensation and evaporation) in cylindrical pores. The method, named the gauge cell method, allows one to construct the full phase diagram of a confined fluid in the form of a van der Waals loop, which includes stable, metastable, and unstable equilibrium states. The phase coexistence is then determined by thermodynamic integration along the metastable and unstable regions of the phase diagram employing Maxwell's rule of equal areas. The simulation results agree with experimental data on the capillary condensation of nitrogen at its boiling temperature on mesoporous molecular sieves. The method can be applied to other phase transitions in confined systems such as fluid-fluid separation, layering, and freezing.

The Effect of Pressure on Pore Structure in Mercury Porosimetry

The pore volume distributions of chrysotile, Mg3(OH)4. Si2O5, ZrO2and of four samples of silica with pore volumes from 1.45 to 2.70 cm3/g have been measured by means of nitrogen capillary condensation and mercury penetration.It is shown that compaction of the porous structures can occur under the influence of the high mercury pressures applied. The degree of compaction depends on the mechanical strength of the sample, its initial porosity and the magnitude of the mercury pressure. The extremely strong ZrO2sample, with its low pore volume of 0.18 cm3/g does not show any sign of cracking up to pressures as high as 190 MPa. Hollow chrysotile needles compact in the pressure range from 100 to 400 MPa. Highly porous silicas all show severe compaction. In accordance with Brown & Lard (Brown & Lard, 1974) it is concluded that silicas with pore volumes larger than 1.2 cm3/g are not suitable for study by mercury porosimetry.

Influence of the method of preparation on the porous structure of perovskite oxides

The results of investigation of the textural properties of perovskite-type binary oxides corresponding to the formulae LaMeO 3 (Me ≡ Fe, Co, Ni, Cr) and La 0.85Me′ 0.15CoO 3 (Me′ ≡ Ca, Ba, Ce) are presented. The texture of the samples was studied by physical adsorption and capillary condensation of nitrogen, and is discussed in relation to the method of preparation of the samples.

Size exclusion chromatography of polymer molecules on microparticulate silica gels: A comparative study

Inverse size exclusion chromatographic procedures have been applied to silica gel packings with different pore size distributions and the resulting pore dimensions have been compared with those obtained by nitrogen capillary condensation. It is shown that the evaluation of pore sizes depends on the model which is assumed to describe the real pore texture. The empirical method developed by Halàsz seems to be useful in checking the adequacy of the pore model adopted. The differences in the results obtained from the chromatographic and absolute methods are discussed.

Gas phase hydroformylation of propylene with porous resin anchored rhodium complexes part I. Methods of catalyst preparation and characterization

Hydridocarbonyltris(triphenylphosphine)rhodium(I) anchored to the surface of macroreticular polystyrene—divinylbenzene is applied in the heterogeneous hydroformylation of propylene at 90 °C and 0.1 MPa total pressure. The performance of the catalyst depends on the method of preparation. We finally succeeded in preparing highly stable, active and selective catalysts. The methods of functionalization of the support with phosphine and phosphite ligands by means of chloromethylation and chlorophosphonation are studied and correlated with the performance of the catalyst. The method of coupling of the rhodium complex to the functionalized support influences the activity and selectivity of the catalyst. Laser Raman spectroscopy showed the presence of a high content of unpolymerized vinyl groups. Functionalization of the resin lowers the amount of vinyl groups substantially, which is supported by the results of a specific reaction with iodine chloride. The texture of the catalyst was studied by physical adsorption and capillary condensation of nitrogen and is discussed in relation to the preparation of the catalyst.