Gas Adsorption Method Research Articles

Investigation on the relationship between the surface texture index and the surface free energy of aggregate

The surface free energy (SFE) of aggregate and asphalt binder can be utilized to quantify the adhesion between the aggregate and binder. The SFE value varies with the changing surface characteristics. This study investigated the effect of surface texture on the aggregate’s SFE when applying the contact angle measurement. A surface treatment protocol for granite, diabase, basalt, and limestone was designed. A dicing saw, grinder and abrasive paper were utilized and were combined into three groups to treat the aggregates’ surface — Groups A, B, and C. The group in which aggregate was not treated was labeled Group D. The aggregate image measurement system (AIMS) was employed to quantify the surface characteristic. After surface treating, four levels of surface texture index were obtained. The surface texture indexes of the treated aggregates followed an increasing rank: A < B < C < D. A higher surface texture index indicated higher surface roughness. Subsequently, the sessile drop method was utilized to measure the contact angle and obtain the SFE of the aggregates that been treated through Groups A, B, and C. The gas adsorption method was applied to determine the SFE of aggregates in Group D. With the increasing surface texture index, the contact angle also increased and resulted in an increasing SFE value. An exponential-type model was established to describe the relationship between surface texture index and SFE. The model was first employed to fit the SFE data of aggregates in the A, B, C, and D groups, which showed good satisfaction of model fitting. The model was also applied to fit the SFE data of aggregates in the A, B, and C groups and to predict the SFE values based on the surface texture index obtained in Group D, which indicated good predictability. The fitting parameters showed a variable coefficient within 20% in the two fitting methods, which confirmed the model was reliable.

A Comprehensive Review of Characterization Methods for Metallurgical Coke Structures.

The structure of coke affects its reactivity and strength, which directly influences its performance in the blast furnace. This review divides coke structures into chemical structure, physical structure, and optical texture according to their relevant characteristics. The focuses of this review are the current characterization methods and research status of the coke structures. The chemical structures (element composition and functional group) can be characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance imaging technology (13C NMR). The physical structures (pore structure and micro-crystallite structure) can be characterized by image method, X-ray CT imaging technique, mercury intrusion method, nitrogen gas adsorption method, X-ray diffraction method (XRD), and high-resolution transmission electron microscopy (HRTEM). The optical textures are usually divided and counted by a polarizing microscope. In the end, this review provides an idea of the construction of a coke molecular structural model, based on the above characterization. With the coke model, the evolution principles of the coke can be calculated and simulated. Hence, the coke performance can be predicted and optimized.

Enhancing permeability and porosity of ceramic shells for investment casting through pre-wetting

In this study, a method known as pre-wetting is applied between the multilayer ceramic investment casting shells to enhance porosity and permeability while sustaining flexural strength. Pre-wetting consists predominately of an aqueous silica binder that improves inter-coat bonding in complex areas. Porosity is developed where the pre-wetting is applied due to the evaporation of the aqueous phase. Results indicate that as porosity increases, both green and fired flexural strength reduce on average by 8.7 - 15.6 % and 18.7 - 28.5 %, respectively, whereas hot strength is increased by 20 - 25 %. Permeability increased by a factor of two when pre-wetting was applied between intermediate coatings and displayed a stepwise increase in intrusion volume in the high-pressure regime through mercury intrusion porosimetry. X-ray microtomography coupled with pore network modelling provided a validation of the increase in the permeability constant. Gas adsorption methods revealed the presence of micropores through the alpha-s method when bilayers of pre-wetting solution were applied.

Real-space modeling for complex structures based on small-angle X-ray scattering.

A three-dimensional real-space model has been created for hierarchical materials by matching observed and simulated small-angle X-ray scattering patterns. The simulation is performed by arranging the positions of small primary particles and constructing an aggregate structure in a finite-sized cell. In order to avoid the effect of the finite size of the cell, the cell size is extended to infinity by introducing an asymptotic form of the long-range correlations among the primary particles. As a result, simulations for small-angle X-ray scattering patterns can be performed correctly in the low-wavenumber regime (<0.1 nm-1), allowing the model to handle hundred-nanometre-scale structures composed of primary particles of a few nanometres in size. An aerogel structure was determined using this model, resulting in an excellent match with the experimental scattering pattern. The resultant three-dimensional model can generate cross-sectional images similar to those obtained by transmission electron microscopy, and the calculated pore-size distribution is in accord with that derived from the gas adsorption method.

Effects of extraction process on the dried cell wall pore structure of messmate heartwood

In order to study the effects of a messmate heartwood extraction process on its cell wall pore structure and its drying ability, its nanopore structure was explored after via gas adsorption technology. Specifically, the messmate heartwood particles were extracted with methanol, and then the cell wall pore structure of the original and extracted samples were evaluated by N2 and CO2 sorption and pycnometer methods, respectively. Overall, compared with the original samples, the cell wall porosity, micropore volume, mesopore volume, BET specific surface area, and specific surface area of the micropores of the extracted messmate heartwoods increased by 2.55%, 0.007 cm3/g, 0.0014 cm3/g, 0.24 m2·g-1, and 21.9 m2·g-1, respectively. The cell wall pore volume measured via the gas adsorption method was smaller than the measurement from the pycnometer method. The results indicated that the presence of extractives made the messmate cell wall have a decreased pore volume and porosity, which may be one of the reasons messmate wood is difficult to dry. Messmate extractives primarily were present in the micropores of the cell wall in the range of 0.4 nm to 0.7 nm. However, gas sorption technology could not detect all the pores in the cell wall of the messmate heartwood sample.

Use of Gas Adsorption and Inversion Methods for Shale Pore Structure Characterization

The analysis of porosity and pore structure of shale rocks has received special attention in the last decades as unconventional reservoir hydrocarbons have become a larger parcel of the oil and gas market. A variety of techniques are available to provide a satisfactory description of these porous media. Some techniques are based on saturating the porous rock with a fluid to probe the pore structure. In this sense, gases have played an important role in porosity and pore structure characterization, particularly for the analysis of pore size and shapes and storage or intake capacity. In this review, we discuss the use of various gases, with emphasis on N2 and CO2, for characterization of shale pore architecture. We describe the state of the art on the related inversion methods for processing the corresponding isotherms and the procedure to obtain surface area and pore-size distribution. The state of the art is based on the collation of publications in the last 10 years. Limitations of the gas adsorption technique and the associated inversion methods as well as the most suitable scenario for its application are presented in this review. Finally, we discuss the future of gas adsorption for shale characterization, which we believe will rely on hybridization with other techniques to overcome some of the limitations.

Comprehensive evaluation and interpretation of mercury intrusion porosimetry data of coals based on fractal theory, Tait equation and matrix compressibility

Accurate characterization of coal pore structure is vital for understanding the mechanism of gas storage and migration. As an effective method for pore evaluation, mercury intrusion porosimetry (MIP) remains questionable without addressing the effects of interparticle voids filling and matrix compression properly. In this study, three intact coal samples with different metamorphic grades, one tectonic coal sample and two activated carbon (AC) samples were selected. Fractal theory was applied to identify the three stages of MIP test and to simulate the interparticle voids volume quantitatively using extrapolation method. Compared with the conventional matrix compressibility (MC) method for MIP data correction, we put forward the semi-empirical Tait equation (TE) method to compensate for the deficiencies of MC method. The results indicate that the simultaneous mercury filling of interparticle voids account for 1.9–3.4% of the total intrusion volumes for coals and 8.3% for AC. However, the proportions of matrix compression could reach 46.72–80.41% for coals and 14.30% for AC. In combination with low pressure N2 gas adsorption (LPN2GA) method, total pore volume (TPV) in the range of 33–320 nm from TE method is in closer proximity to the results using Barret-Joyner-Halenda (BJH) model. Whereas, MC method is superior in correcting MIP data of smaller pore sizes (7–33 nm). Overlapped pore size distributions (PSD) indicate that peak numbers, peak positions and incremental pore volumes of MIP corrected data show good consistency with LPN2GA measurement. For samples of low strength and with abundant ink-bottle shaped pores, it is inappropriate to correct their MIP data.

Effects of composition changes of coal treated with hydrochloric acid on pore structure and fractal characteristics

In order to investigate the influence of coal compositions on the pore structure, low temperature gas adsorption (LTGA) method was used to analyze the pore evolution of coal samples treated with hydrochloric acid. The results demonstrate that hydrochloric acid treatment significantly reduced the content of minerals and volatile matter in coal, which could increase the porosity and the pore connectivity of coal. The removal of volatile matter has an obvious reaming effect on supermicropores, but ultramicropores remained unchanged. The role of minerals in pores of different pore widths is different, which are the fillers in macropores, the skeletons of some large mesopores and the blockage in some small mesopores. With the decrease of minerals, the macropore volume increased, and the large mesopore volume first decreased and then increased. In addition, the opening of many closed small mesopores increased the fractal dimension D2 of pore structure complexity, and provides an increase in specific surface area, but it has no significant relationship with the fractal dimension D1 of pore surface roughness.

The effect of mineral composition in the compound soil of soft rock and sand on special surface area and cation exchange capacity

The X-ray diffraction method and gas adsorption method were used to investigate the mineral composition and special surface area of different soft rocks, sands, and composed soil. The results showed that (1) Montmorillonite, kaolinite, potash feldspar, calcite, quartz, plagioclase and illite, constitute the soft rock. Quartz, potash feldspar, plagioclase, calcite, montmorillonite, illite, and kaolinite constitute the soft rock in the Mu Us sandy land. There are several types of soft rocks, and there are some differences in the mineral composition of different types. The highest primary mineral content is 94.6% and the lowest 41%; the secondary mineral content is the highest 59% and the lowest is 5.4; (2) The special surface area of different types of soft rock is quite different, and the special surface area is up to 17.14 m2g−1, the lowest is 3.12 m2g−1, and the average content is 9.98 m2g−1. The cation exchange capacity is up to 7.25 cmol(+)/kg, and the lowest is 3.36 cmol(+)/kg; (3) The fitting formula of secondary minerals and specific decomposition of arsenic sandstone, aeolian sandy soil and composite soil is y = 2.423e0.0871x, and the correlation coefficient R2 = 0.8258. The fitting formula for the exchange capacity of secondary minerals and cations is y = 3.105e0.0348x, and the correlation coefficient R2 = 0.9235.

Estimating the nuclear magnetic resonance surface relaxivity of Eocene sandstones: A comparison of different approaches

Nuclear magnetic resonance (NMR) relaxometry typically involves the analysis of a relaxation time distribution. The surface relaxivity ([Formula: see text]) is the key parameter that relates the relaxation time to the pore radius. Only a good estimate of the surface relaxivity enables a reliable determination of the pore radius distribution in a rock or sediment sample. A wide variety of approaches for the estimation of [Formula: see text] has been proposed; however, the accuracy of [Formula: see text] determination approaches has rarely been checked. We have compared different approaches of [Formula: see text] determination for a set of Eocene sandstone samples. Most approaches based on a weighted logarithmic mean of relaxation times or the peak relaxation time result in significant underestimation of [Formula: see text]. However, the correct weighting of the set of relaxation times has proven to be a crucial approach in [Formula: see text] determination. The consequent application of geometric rules suggests the application of the weighted harmonic mean ([Formula: see text]). The specific surface area per unit pore volume ([Formula: see text]), which results from the gas adsorption method, is another crucial parameter in most approaches for [Formula: see text] estimation. The quantities [Formula: see text] and [Formula: see text] depend on the resolution of the used method. Applying the fractal theory, we adopt an approach that performs an upscaling of [Formula: see text] to the resolution of the NMR relaxometry. Using equal resolution for [Formula: see text] and [Formula: see text], we obtain more reliable [Formula: see text] estimates. The resulting [Formula: see text] values are comparable with the ones determined by using the median relaxation time from NMR and the median pore-throat radius from the mercury injection capillary pressure method.

Petrophysical Characterizations of Shale Gas Reservoirs of the Ranikot Formation in the Lower Indus Basin, Pakistan

The complex pore structure with nano-pores of shale gas reservoirs has an impact on the hydrocarbon storage and transport systems. We examined the pore structure of the shales of the Ranikot Formation in the Lower Indus Basin, Pakistan to investigate the full scaled pore size distributions by using a combination of techniques, mercury injection capillary pressure analysis and low pressure gas adsorption methods using N2 and CO2. Isotherm curves obtained N2 and CO2 adsorptions were interpreted using density functional theory analysis for describing the nano-scaled pore size distributions. The pore geometry of the shales was estimated to be slit-type from the isotherm hysteresis loop shape. The pore size distributions determined the density functional theory showed the dominant pore size of below around 10 nm. The Micro-scale effects such as slippage and adsorption/desorption also significantly influence the gas flow in nano-pore structure. The gas flow regimes in shales are classified into four types Darcy flow, slip flow, transition flow, Knudsen flow based on the value of the Knudsen number. Applying the specific reservoir conditions in Ranikot shale and pore size distribution to the Knudsen number, the gas flow regimes of the Ranikot shales were estimated mostly within the transition and slip flow.

In situ observation of pressure modulated reversible structural changes in the graphitic domains of carbide-derived carbons

Carbons are important in a multitude of applications, and thus, the reversible control of carbon structures is of high interest. Here we report the reversible formation of graphitic structures with three distinct interlayer distances in case of two carbide-derived carbons (CDCs) loaded under hydrogen pressure observed with in situ neutron scattering methods. The formation of these graphitic structures determined with in situ neutron diffraction is brought forth by the confinement of H2 in the porous structure when the temperature, T, is increased from T = 20 K–50 K under H2 loading from 68 mbar to 10 bar. The confinement of the desorbing H2 causes the pressure to increase inside the CDC structure and this increase of pressure is the cause for the reversible formation of graphitic domains. The confinement of H2 at T = 50 K is possible due to the presence of ultramicropores and suitable curved carbon structures. The three distinct formed graphitic domains correspond to a highly pressurized, conventional highly ordered graphitic, and disoriented graphitic domains with possible H2/H intercalation. In situ quasi-elastic neutron scattering and gas adsorption methods are used to determine the H2 transport properties and interactions with the CDCs.

The Spontaneous Combustion of Chemically Activated Carbons from South African Coal Waste

ABSTRACT A spontaneous combustion test termed the Wits-Ehac test was used to examine the spontaneous combustion liability of activated carbons prepared using KOH activation from three coal waste samples obtained in South African Coalfield. The effect of KOH addition on the activated carbon textural characteristics, physicochemical properties, and self-heating characteristics was investigated. The textural properties such as pore volume and surface area were evaluated using the nitrogen gas adsorption method. The morphological effect of the activated carbons on their liability toward spontaneous combustion was studied. The results showed that, with increased KOH weight ratio, the pore volume, and surface area of the activated carbon increased. The influence of KOH addition decreases the volatile matter, while the influence either increases/decreases the moisture, ash, or fixed carbon contents of the activated carbons. In addition, an increase in the KOH weight ratio increases the liability values of the activated carbons. The liability of activated carbon depends not only on the origin of the coal material but also on the volume of pore and surface area, which also depends on the quantity of KOH used during the preparation process. This study provides a scientific basis for a simple test to establish whether pore volume and surface area of activated carbon can promote its propensity to self-heating.

Hydrothermal Activation of Porous Nitrogen-Doped Carbon Materials for Electrochemical Capacitors and Sodium-Ion Batteries.

Highly porous nitrogen-doped carbon nanomaterials have distinct advantages in energy storage and conversion technologies. In the present work, hydrothermal treatments in water or ammonia solution were used for modification of mesoporous nitrogen-doped graphitic carbon, synthesized by deposition of acetonitrile vapors on the pyrolysis products of calcium tartrate. Morphology, composition, and textural characteristics of the original and activated materials were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared spectroscopy, and nitrogen gas adsorption method. Both treatments resulted in a slight increase in specific surface area and volume of micropores and small mesopores due to the etching of carbon surface. Compared to the solely aqueous medium, activation with ammonia led to stronger destruction of the graphitic shells, the formation of larger micropores (1.4 nm vs. 0.6 nm), a higher concentration of carbonyl groups, and the addition of nitrogen-containing groups. The tests of nitrogen-doped carbon materials as electrodes in 1M H2SO4 electrolyte and sodium-ion batteries showed improvement of electrochemical performance after hydrothermal treatments especially when ammonia was used. The activation method developed in this work is hopeful to open up a new route of designing porous nitrogen-doped carbon materials for electrochemical applications.

Effect of mesoporous characteristics on competitive adsorption kinetics of uremic-like toxin and atorvastatin on spherical carbon adsorbents for an in vitro chronic renal failure therapeutic model

Indole-3-acetic acid (IA, urine-like toxin) coexisting with atorvastatin (AT) was adsorbed by spherical carbonaceous adsorbents (SCs). The relationship between the competitive adsorption kinetics and the mesoporous structures was investigated. The pore structures of the four SCs were analyzed using the Hg and gas adsorption methods. SC adsorption tests were performed using the dissolution test with the paddle method with an SC sample in distilled water containing IA and/or AT at 37.0 °C. The amounts of IA and AT adsorbed on SCs in single- and binary-drug administration tests were measured based on the ultraviolet-visible spectra using classical least squares analysis. Rate constants for the drug adsorption of IA and AT by SCs (kIA and kAT, respectively) were suppressed by the effect of coexisting drugs. The suppression of IA adsorption by the coexisting drug was dependent on the pore structure of the SCs. kIA and kAT against the SCs were competitively inhibited by coexisting drugs.

Surface-governed electrochemical hydrogenation in FeNi-based metallic glass

The hydrogenation and oxide formation behavior of Fe–Ni-based metallic glasses (MGs), where measurements by the conventional gas-solid reaction method are difficult, is analyzed by a two-step approach: chronoamperometry followed by cyclic voltammetry (CA + CV). We introduce a concept of effective volume by measuring the thickness of the region where the hydrogen and hydroxyl ion interactions with Fe-based MG take place, which is characterized by high-angle annular dark-field scanning transmission electron microscopy. A very constant film thickness influenced by the OH− and H+ is confirmed by TEM, where the chemical homogeneity is maintained within this region. The weight percent of hydrogen and the corresponding hydrogen-to-metal ratio are determined as 1.16% and 0.56, respectively. When compared to previous studies conducted by the electrochemical-permeation method, the H/M ratio is found to be an order of magnitude larger. Electrochemical impedance spectroscopy (EIS) and subsequent equivalent circuit modeling (ECM) of the tested ribbons resolve the surface-diffusion processes for hydride formation and oxidation kinetics. This contribution provides a different perspective for the design and study of low-cost and high-performance amorphous nanofilms for hydrogen-energy applications, particularly when the common gas-adsorption methods are problematic.

Clay in situ resource utilization with Mars global simulant slurries for additive manufacturing and traditional shaping of unfired green bodies

The wet processing of regolith simulant for clay in situ resource utilization (ISRU) on Mars is presented. The two raw materials from the Mars global simulant family, one without clay (MGS-1) and one with clay - sodium montmorillonite smectite - (MGS-1C) were milled and mixed to produce a simulant with small particle size and reduced clay content (MGS-1C/8). All three simulants and the pure clay raw material were extensively characterized using XRF, synchrotron XRD, gas adsorption and gas pycnometry methods. In a straightforward processing approach, MGS-1C/8 was mixed with water and different dispersant approaches were investigated, all of which gave stable slurries. Particle size distribution, rheology, ion concentration, pH and electrical conductivity of these slurries were characterized. The slurry systems can easily be adapted to fit all typical ceramic shaping routes and here parts of varying complexity from slip casting, throwing on a potter's wheel and additive manufacturing, including material extrusion (robocasting) and binder jetting (powder bed 3D printing) were produced. The unique properties of the sodium montmorillonite clay, which is readily accessible in conjunction with magnesium sulfate on the Martian surface, acted as a natural nanosized binder and produced high strength green bodies (unfired ceramic body) with compressive strength from 3.3 to 7.5 MPa. The most elaborate additive manufacturing technique layerwise slurry deposition (LSD) produced water-resistant green bodies with a compressive strength of 30.8 ± 2.5 MPa by employing a polymeric binder, which is similar or higher than the strength of standard concrete. The unfired green bodies show sufficient strength to be used for remote habitat building on Mars using additive manufacturing without humans being present.

Damage characteristics and catastrophic failure mechanism of coal rock induced by gas adsorption under compression

Abstract To reveal the damage characteristics and catastrophic failure mechanism of coal rock caused by gas adsorption, physical tests and theoretical methods are employed. The results show that adsorption swelling can damage coal rock, which can be distinguished by fractal dimension. A fitting relationship between the adsorption damage and fractal dimension is proposed by experimental testing and theoretical analysis. High gas adsorption pressure proves to be the dominant factor that leads to coal failure softening and gas outburst disasters. Three main parameters concerning adsorption damage include the change rate of released energy density, the transition difference in the post-peak acoustic emission (AE) b value and the change rate of cumulative AE energy. Results show that all the three parameters present a step-type decreasing change with the increase in fractal dimension, and the fractal dimension shows a linear relationship within the same failure mode. Finally, a method is proposed to evaluate coal rock disaster transformation, based on the aforementioned three main parameters of adsorption damage.

Experimental study of the relationship between porosity and surface area of carbonate reservoir\xa0rocks

Over the time by increasing global demand for source of energy and decreasing hydrocarbon production from reservoirs, recovery methods have become important. The surface area and porosity are central physical characteristics that highly affect the estimation of original oil and gas in place and understanding the mechanisms incorporating in production. The surface area is the internal surface area per unit of pore volume and determines the amount of space in rocks exposed to injectant during injection operation. The occurrence of fractures system in carbonated reservoirs increases the complexity and decreases the homogeneity; hence, it is difficult to determine the correct surface area of reservoir. Therefore, the existence of a local correlation which relates effective porosity to specific surface area is needed and it can help to estimate effective surface area exposed to chemicals during Enhanced Oil Recovery (EOR) process. In this study, the specific surface area in carbonate reservoir rocks was measured by gas adsorption (nitrogen) method and petro-graphical image analysis. In addition, the effective porosity was determined by a gas porosimeter, followed by plotting specific surface area measured by the Brunauer, Emmett and Teller (BET) method versus specific surface area determined from core scan and calibration curve. According to this calibration curve, a new relationship was developed (with R2 = 0.92) that could give BET data for a known data of core scan. The relationship between porosity and specific surface area was analyzed statistically and a relationship with accuracy of R2 = 0.89 was proposed. This relationship was compared with other models such as Pirson and Kotyakhov. Results show that the latter one is more accurate than other models and is more compatible with experimental data (with R2 = 0.84). The results obtained from the experiment indicate that the specific surface area shows an initial decrease upon increasing of porosity up to 0.2. After this decrease, the curve indicates an increasing trend. Moreover, a novel relationship was developed depending on the specific surface area, porosity and permeability and some constant parameters for carbonate rocks (with R2 = 0.95).

An experimental study on the effect of the acid and heavy metal treatments on the adsorption of CH4 by sepiolite.

This study investigated methane (CH4) adsorption by natural sepiolite-obtained from Eskisehir in Turkey-and its Ag-, Cu-, Fe-, and H-exchanged forms by using a volumetric gas adsorption method. Sepiolite was modified with 1 M AgNO3, 1 M Cu(NO3)2∙3H2O, 1 M Fe(NO3)3∙9H2O, and 1 M HCl solutions at 80°C for 6h, respectively. The natural and modified sepiolite samples were characterized by using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), differential thermal analysis (DTA), and the nitrogen adsorption method. Quantitative XRD analysis showed that the sample consisted primarily of sepiolite clay mineral and dolomite as an impurity in small amounts. It was found that acid and heavy metal treatments caused apparent changes in the structure and microporosity of the sepiolite samples. CH4 adsorption isotherms of clay samples were examined at temperatures of 0°C and 25°C and pressures up to 100kPa. It was determined that the CH4 adsorption capacities of sepiolite samples increased at both temperatures according to the following sequence: CuS < AgS < HS < S < FeS. CH4 adsorption values of sepiolite samples varied between 0.084mmol/g and 0.299mmol/g. It was observed that the CH4 adsorption capacities of heavy metal cation-exchange clay samples were related to the surface area.