Nitrogen Gas Adsorption Techniques Research Articles

Mechanism of compacted biochar-amended expansive clay subjected to drying–wetting cycles: simultaneous investigation of hydraulic and mechanical properties

Biochar has been extensively studied in the aspect of amendment of compacted sandy/clayed soils, whereas its application as amendment in expansive soil is rare. Hydraulic and mechanical properties of biochar-amended expansive soil especially impacts of drying–wetting cycles have been rarely investigated. Aiming at construction of sponge city, straw biochar-amended expansive soil and the control soil (i.e., without biochar) are subjected to drying–wetting cycles in this study. During drying–wetting cycles, energy-dispersive spectrometer and Fourier transform infrared (FTIR) spectroscopy analyses were conducted to investigate microchemical composition including. Pore size distribution and microstructure were measured using nitrogen gas-adsorption technique and scanning electron microscope, respectively. Further, changes in soil water retention curve, void ratio, crack intensity factor (CIF, i.e., ratio of cracked section area to the total soil area) and shear strength were also determined. It is found that there is no difference in water retention capacity between various soils for near-saturated samples. Under high suction, however, more water could be retained within mesopores of biochar-amended soil. FTIR analysis indicates that biochar-amended expansive soil shows stronger chemical bonding, irrespective of them being subjected to drying–wetting cycles. The weak alkalinity of straw biochar results from its main chemical composition (i.e., calcium carbonate). It is noteworthy that straw biochar improves soil water retention capacity, which further restrains desiccation cracks. Cohesion of biochar–soil composite is also improved due to chemical bonding. Aiming at green roofs, straw biochar could be promising option for expansive soil amendment technically and economically.

Synthesis and characterization of kaolinite coated with copper oxide and its effect on the removal of aqueous Lead(II) ions

The removal of Lead (Pb2+) ions from waste water in the aquatic environment by copper oxide–kaolinite composite forms an important step involved in the reduction of Lead ions in the environment. The study investigated the synthesis, characterization, and application of copper oxide–kaolinite composite in the removal of Lead ions from aqueous systems. The synthesis of the composite involved a trimetric process to produce the copper oxide (CuO)–kaolinite composite. The characterization involved the determination of cation exchange capacity, specific surface area, and spectral analysis by sodium saturation method, nitrogen gas adsorption techniques, and scanning electron spectroscopy, respectively. The determination of parameters affecting the reaction mechanism and reaction kinetics involved the use of batch mode techniques. The findings indicated a reaction mechanism that was less than one proton coefficient, higher mass transfer rates when compared with uncoated kaolinite. Here, the intraparticle diffusion was higher than the value for the uncoated kaolinite. The reactions based on Pb2+ initial concentration indicated that the coated kaolinite gradually became saturated as the concentration was increased. The reactions based on solid concentration (Cp) demonstrated a complex change in the capacity of adsorption over different Pb2+ concentrations (10–40 mgL−1) and solid concentrations (2–10 gL−1). Here, the reduction in specific surface area, particle size increase, mineral aggregation, and concentration gradient effect controlled the complex changes in adsorption. In conclusion, the copper oxide–kaolinite composite significantly enhanced the adsorption of Pb2+ ions.

Experimental study on microscopic formation damage of low permeability reservoir caused by HPG fracturing fluid

Hydraulic fracturing has become an important stimulation technique for low/ultra-low permeability reservoirs. Research on formation damage caused by fracturing fluid has mainly focused on permeability, sensitivity, fracturing fluid and clay minerals. However, little attention has been devoted to the microscopic changes in pore structure and properties. In this paper, nitrogen gas-adsorption techniques were introduced to characterize the microscopic changes in pore structure. Meanwhile, contact angle testing and Scanning Electron Microscope (SEM) observations were also used to show the changes in wettability and surface morphology of cores, respectively. The results showed that the pore size distributions (PSDs) of low permeability cores were wide, with approximately 75% macropore volume. The obvious changes in PSDs of damaged samples occurred in the range of 2–5 nm and 30–80 nm. The specific surface area decreased, and the adsorbability of damaged samples declined, as well. Concentrated gel and solid residues were confirmed to be the main damage mechanisms for gel breaking liquids, which resulted in changes in composition and roughness, making the cores more hydrophilic. Based on the results of the analysis, the N2 adsorption technique is deemed appropriate for the study of reservoir formation damage when a certain amount of mesopores are present. Additionally, a new method of determining contact angles for porous media is also recommended.

Effect of clay and organic matter on nitrogen adsorption specific surface area and cation exchange capacity in shales (mudrocks)

The resistivity log and its conventional application is one of the most important analysis used to find oil and gas saturated intervals. In unconventional oil and gas producing rocks, however, this tool and the consequent technique, is affected by many factors and not considered very reliable. Shale reservoir rocks usually have high total specific surface area (TSSA) due to high clay and total organic content (TOC) and nano-scale pores. Resistivity values are rather low and usually not indicative of reservoir zones in high TSSA rocks. Nitrogen adsorption and cation exchange capacity (CEC) are the common techniques to measure TSSA. Clays and organic matter (OM) affect the measured TSSA using either technique. This effect must be taken into account while calculating water saturation using conventional models. In this paper we investigate the mineralogical and geochemical associations of CEC and TSSA and their effects on resistivity in shale reservoirs.We studied samples from oil and gas producing reservoirs such as Bakken, Haynesville, European Silurian, Niobrara, and Monterey formations. CEC was measured using Co(III)-hexamine3+ with the spectrophotometric technique and the equivalent TSSA (CEC-TSSA) was calculated. We also measured the specific surface area using sub-critical Nitrogen gas adsorption technique (N2-SSA). Rock mineralogy, organic matter properties and scanning electron microscope (SEM) images were used to further analyze the data.We find that CEC values are directly correlated with the clay type and content regardless of the OM content or level of thermal maturity. Smectite and illite (when negligible smectite is present) dominate the CEC value in shales. N2-SSA correlates with clay content, especially smectite and illite, but is less sensitive to clay type as CEC. This correlation between N2-SSA and clay content was observed in Bakken (no organic matter), thermally mature (gas window) Haynesville, and low TOC (<2.67 wt%) Niobrara (oil window) samples. We also find that OM significantly affects N2-SSA in two different ways: (1) Blockage of pores and throats by bituminous kerogen, which limits the accessibility of nitrogen to clay surfaces. This effect was observed in thermally immature (oil window) Niobrara (TOC>2.6 wt%) and Monterey shales. (2) Development of nano-scale OM-hosted pores with high surface area mostly for thermally mature (gas window) shales as observed in high TOC (>1.5 wt%) Silurian shales. Correlation with N2-SSA and CEC values revealed that the average charge density for most of the shales in this study varies between 3 and 5 e/nm2 and for some high TOC Niobrara samples can be as high as 32. Relatively higher charge density is due to underestimation of the TSSA by nitrogen adsorption technique. The correlation between SSA/CEC and clay content/type are well studied in the literature. However the results of this study aid in understanding how mineralogy, geological factors, organic matter content and thermal maturity affect this correlation in mud rocks from various reservoirs.

Application of nitrogen gas-adsorption technique for characterization of pore structure of mudrocks

Subcritical N2 gas-adsorption techniques are used more frequently now for characterizing the pore structure of mudrocks. This article discusses some application challenges associated with mudrocks: sample preparation, choice of inversion techniques of the raw isotherm data, representation of pore-size distribution (PSD) data, and reproducibility of measurement data. Gas-adsorption analysis on hand-ground &lt; 40-mesh powder samples is recommended over using intact rock samples because of the slow diffusion process. Crushing the sample to &lt;40-mesh powder has no significant effect on any of the measured pore-structure attributes. The dV/d(logD) representation is recommended for graphical PSD results because log-scale pore-size abscissa are used most commonly for geologic materials. Pore-size distribution inversion using the Barett-Joyner-Halenda (BJH) method should be preferred over the density-functional-theory (DFT) method because it yields more consistent and less noisy inverted data. The Harkins-Jura thickness equation is recommended as the choice of thickness equation. The Brunauer–Emmett–Teller (BET) theory specific surface area, total pore-volume, and PSD are reproducible within a variation range of 10% to 20%.

Specific surface area and pore‐size distribution in clays and shales

ABSTRACTOne of the biggest challenges in estimating the elastic, transport and storage properties of shales has been a lack of understanding of their complete pore structure. The shale matrix is predominantly composed of micropores (pores less than 2 nm diameter) and mesopores (pores with 2–50 nm diameter). These small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore‐size distribution is critical to understand the shale pore network. Historically, mercury intrusion techniques are used for pore‐size analysis of conventional reservoirs. However, for unconventional shale reservoirs, very high pressures (&gt; 414 MPa (60 000 psi)) would be required for mercury to access the full pore structure, which has potential pitfalls. Current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales. Nitrogen gas‐adsorption techniques can be used to characterize materials dominated by micro‐ and mesopores (2–50 nm). A limitation of this technique is that it fails to measure large pores (diameter &gt;200 nm). We use a nitrogen gas‐adsorption technique to study the micro‐ and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques.Our results on pure clay minerals and natural shales show that (i) they have a multiscale pore structure at different dimensions (ii) fine mesopores, with a characteristic 3 nm pore size obtained with N2 gas‐adsorption are associated with an illite‐smectite group of clays but not with kaolinite; (iii) compaction results in a decrease of pore volume and a reduction of pore size in the ‘inter‐aggregate’ macropores of the illite‐smectite clays while the fine ‘intra‐tachoid’ mesopores are shielded from compaction; (iv) for natural shales, mineralogy controls the pore‐size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite‐smectite type of clays in the rock. Our assessment of incompressible 3 nm sized pores associated with illite‐smectite clays provides an important building block for their mineral modulus.

Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells: I. Characterization of the Catalytic Activity and Surface Structure

A new dual plasma coating process to produce platinum-free catalysts for the oxygen reduction reaction in a fuel cell is introduced. The catalysts thus produced were analyzed with various methods. Electrochemical characterisation was carried out by cyclic voltammetry, rotating ring- and rotating ring-disk electrode. The surface porosity of the different catalysts thus obtained was characterized with the nitrogen gas adsorption technique and scanning electron microscopy was used to determine the growth mechanisms of the films. It is shown that catalytically active compounds can be produced with this dual plasma process. Furthermore, the catalytic activity can be varied significantly by changing the plasma process parameters. The amount of H2O2 produced was calculated and shows that a 2 electron mechanism is predominant. The plasma coating mechanism does not significantly change the surface BET area and pore size distribution of the carbon support used. Furthermore, scanning electron microscopy pictures of the produced films are presented and show the preference of columnar growth mechanisms. By using different carbons as the support it is shown that there is a strong dependence of the catalytic activity that is probably related to the chemical properties of the carbon.

Effect of Pore-Size Distribution on Shrinkage of Concretes

The effects of pore structure of concrete made with slag-blended cement on shrinkage behavior of concrete when exposed to drying were presented in this paper. The investigated parameters were the length of curing (1-day and 7-day curing), slag and gypsum contents in mixtures. Pore structure analysis was studied by conducting mercury intrusion porosimetry and nitrogen gas adsorption technique tests. The results show that 65% slag concrete with 7-day curing exhibited the lowest shrinkage evolution compared to 0, 35, 50% slag mixes. This is attributed to the highest pore radius where meniscus forms when drying in these concretes. It was found that addition of gypsum in slag mixes tend to reduce the nanopores (within the range from 4 to 20 nm pore size) and decrease the proportion of mesopores. The higher proportion of mesopores and the lower value of meniscus pore radius could explain the increase in drying shrinkage of concrete made with 65% slag cement containing 0% added gypsum.

Facile heterogenization of homogeneous ferrocene catalyst on SBA-15 and its hydroxylation activity

Hexagonally ordered mesoporous silica SBA-15 was synthesized with amino propyl groups by direct co-condensation method using triblock co-polymer (P123) as a template, tetra ethyl orthosilicate as a silica source under conventional SBA-15 synthesis conditions. Amino propyl trimethoxy silane was utilized for introducing SBA-15 with propyl amine anchoring moiety. Ferrocene was anchored to SBA-15 post-synthetically by the condensation of amine group from propylamine SBA-15 with the carbonyl group of ferrocenecarboxaldehyde. The structural ordering and the textural properties of propyl amine functionalized SBA-15 (SBA-15-NH2) and further ferrocene tethered SBA-15 (SBA-15-N = ferrocene) were characterized by low angle XRD and nitrogen gas adsorption techniques. The attached organic moieties were identified by mid-infrared (MIR) and near-infrared (NIR) spectroscopy. The ferrocene functionalized SBA-15 is highly active towards the hydroxylation of benzene to phenol. The catalyst was reused without significant loss in activity.

Characterization and Preliminary Assessment of a Sorbent Produced by Accelerated Mineral Carbonation

This study shows that calcium silicate/aluminate-based materials can be carbonated to produce sorbents for metal removal. The material chosen for investigation, cement clinker, was accelerated carbonated, and its structural properties were investigated using X-ray diffraction (XRD), scanning electron microscopy, thermal gravimetric and differential thermal analysis, nuclear magnetic resonance spectroscopy, and nitrogen gas adsorption techniques. The principal carbonation reactions involved the transformation of dicalcium silicate, tricalcium silicate, and tricalcium aluminate into a Ca/Al-modified amorphous silica and calcium carbonate. It was found that carbonated cement had high acid buffering capacity, and maintained its structural integrity within a wide pH range. The uptake of Pb(II), Cd(II), Zn(II), Ni(II), Cr(II), Sr(II), Mo(VI), Cs(II), Co(II), and Cu(II) from concentrated (1000 mg L(-1)) single-metal solutions varied from 35 to 170 mg g(-1) of the carbonate cement. The removal of metals was hardly effected by the initial solution pH due to the buffering capability of the carbonated material. The kinetics of Pb, Cd, Cr, Sr, Cs, and Co removal followed a pseudo-second-order kinetic model, whereas the equilibrium batch data for Cu fitted the pseudo-first-order rate equation. PHREEQC simulation supported by XRD analysis suggested the formation of metal carbonates and silicates, calcium molybdate, and chromium (hydro)oxide. Cesium was likely to be adsorbed by Ca/Al-modified amorphous silica.

EFFECTS OF HEAT TREATMENT ON SYNTHETIC GRAPHITES FOR CARBON NANOTUBES SYNTHESIS

Carbon materials are well known for their excellent adsorbent property towards gases. Much work has been done to improve the properties of carbon materials as to enhance their absorption capacity towards gases. Recent developments have resulted in the discovery of novel carbon materials such as carbon nanotubes. Numerous researches have shown that carbon nanotubes have excellent capacity for hydrogen storage. However, significant research has been undertaken to further improve the adsorption capacity through the advancement in synthesis methods for the fabrication of carbon nanotubes. Among the starting material widely employed for synthesis of carbon nanotubes is high purity graphite. Therefore, purpose of this work is to investigate the effect of thermal treatment on several synthetic graphites. Thermal treatment was conducted at temperatures ranging from 400–800°C at different dwelling times. The morphology and surface analysis of the graphites were examined using Scanning Electron Microscope and nitrogen gas adsorption techniques, respectively. It was found that temperature, time and conditions of treatment significantly change the surface structure of the graphites. A decrease in particle size was observed due to the release of internal surface area.

Three-Dimensional Characterization of Sand Grain Shape and Surface Texture Using a Nitrogen Gas Adsorption Technique

ABSTRACT Shape and surface texture are fundamental characteristics of sand grains, which have long been used by sedimentologists to provide information about grain provenance, transport pathways, and postdepositional weathering. Hitherto, most work on the gross aspects of grain shape (sphericity, roundness, or angularity) has been undertaken on two-dimensional digitized grain images analyzed by Fourier or fractal methods, or simple shape-factor measurements, and studies of grain surface textures have mainly involved qualitative or semiquantitative recording of the relative abundance of a number of discrete surface textural features. Here we describe a new nitrogen gas adsorption technique that can be used to provide information on three-dimensional shape and surface texture with very high precision, and to test hypotheses about sediment sources and postdepositional alteration. The method has been tested on a range of sandy sediments from around the world and found to provide a useful quantitative measure of the shape and surface texture of different sediments, provided that strict protocols are observed in sample preparation.

Effect of Some Admixtures on the Surface Properties of the Hydration Products of Silica Fume/Ca(OH)2 Mixtures

The effect of sodium naphthalene formaldehyde sulphonate polycondensate and stearic acid on the surface properties of calcium silicate hydrates, formed as a result of the hydration reaction between silica fume and calcium hydroxide, has been examined by the use of low-temperature nitrogen gas adsorption techniques. In addition, the interaction of such admixtures with the calcium silicate hydrates formed was investigated by infrared (IR) spectroscopic analysis. It was observed that both admixtures increased the specific surface area of the calcium silicate hydrates quite considerably relative to the behaviour of a blank sample (i.e. without addition of admixture), especially during the initial stages of hydration (after 24 h). IR examination demonstrated that the admixtures used did not interact chemically with the calcium silicate hydrates although physical interaction was possible.

The dielectric constant of sandstones, 60 kHz to 4 MHz

Complex impedance data were collected for eight sandstones at various levels of water saturation [Formula: see text] in the frequency range of 5 Hz to 4 MHz. The measurements were made using a two‐electrode technique with platinum electrodes sputtered onto the flat faces of disk‐ shaped samples. Presentation of the data in the complex impedance plane shows clear separation of the response due to polarization at the sample‐electrode interface from the bulk sample response. Electrode polarization effects were limited to frequencies of less than 60 kHz, allowing us to study the dielectric constant κ′ of the sandstones in the frequency range of 60 kHz to 4 MHz. κ′ of all samples at all levels of saturation shows a clear power‐law dependence upon frequency. Comparing the data from the eight sandstones at [Formula: see text], the magnitude of the frequency dependence was found to be proportional to the surface area‐to‐volume ratio of the pore space of the sandstones. The surface area‐to‐volume ratio of the pore space of each sandstone was determined using a nitrogen gas adsorption technique and helium porosimetry. κ′ also exhibits a strong dependence on [Formula: see text]. κ′ increases rapidly with [Formula: see text] at low saturations, up to some critical saturation above which κ′ increases more gradually and linearly with [Formula: see text]. Using the surface area‐to‐volume ratios of the sandstones, the critical saturation in the dielectric response was found to correspond to water coverage of approximately 2 nm on the surface of the pore space. Our interpretation of the observed dependence of κ′ on both frequency and [Formula: see text] is that it is the ratio of surface water to bulk water in the pore space of a sandstone that controls the dielectric response through a Maxwell‐Wagner type of mechanism.