Decrease In Average Pore Diameter Research Articles

Mechanical activation of coal gasification fine slag and mechanical and thermal properties of coal gasification fine slag–poly(vinyl chloride) composites

To facilitate the high-value utilization of activate coal gasification fine slag (CGFS), a wet mechanical activation process was used. As a result of this treatment, CGFS samples with different particle size distributions were obtained. The effects of mechanical activation on various physical and chemical properties of CGFS were investigated, including its particle size distribution, mineral composition, specific surface area, pore size, crystallinity, particle morphology, chemical bonding, and binding energy. Poly(vinyl chloride) (PVC)/CGFS composites were prepared via a melt blending process, and their mechanical and thermal properties were evaluated. It was found that with increasing levels of mechanical activation, the CGFS particle size distribution became more concentrated and the particle spacing became more uniform. With the increasing mechanical activation, the crystallinity was found to decrease and the content of amorphous mineral matter (such as SiO2 and Al2O3) increased. The observed increase in specific surface area and decrease in average pore diameter due to the mechanical activation was seen to lead to an increase in the number of active sites. The produced PVC/CGFS composite materials were found to exhibit good mechanical properties and dynamic thermal stability. The thermal stability of the PVC composites was also found to improve relative to the composites produced without the use of mechanical activation.

Analysis of the effect of particle-wall collision process in DPF on the spatial structure of smoke cake layer.

Based on the rebound model of particle-wall collision, the influence of adhesion force on the deposition process of particles on the smoke cake wall was studied by using atomic force microscopy (AFM) and automatic specific surface area (BET) and pore size distribution analyzer. The interaction between the deposition process and the spatial structure of smoke cake was analyzed. The results show that with the increase of diesel engine speed, Young's modulus of particles decreases and the average particle size increases; the kinetic energy of particles impacting on the surface of smoke cake layer in diesel particle filter (DPF) increases; when the velocity of particles with the same particle size entering the wall increases, the maximum compression distance between particles and the surface of the smoke cake layer increases; and the adhesion force and adhesion energy increase. With the increase of diesel engine speed, the box counting dimension of smoke cake layer in DPF increases from 1.9478 to 1.996, the characteristic radius of pores decreases from 15.32 nm to 7.53 nm, the average pore diameter decreases, and the average pore volume increases. When the fractal dimension increases from 2.633 to 2.732, the deformation degree of particles increases, the smoke cake layer becomes more compact and dense, the internal structure of pores becomes more complex, the surface of pores is rougher, and particle adhesion requires overcoming larger adhesion barriers when particles adhere.

Static Liquefaction Capacity of Saturated Undisturbed Loess in South Jingyang Platform

According to a previous geological investigation, high-speed and long-distance loess landslides in the South Jingyang platform in Shaanxi Province are closely related to the static liquefaction of loess. Considering the typical loess landslides in this area, isotropic consolidated undrained (ICU) triaxial tests and scanning electron microscopy analyses were conducted in this study. The main conclusions are as follows: (1) The stress-strain curves indicate strong strain softening under different confining pressures. The pore water pressure increases significantly and then remains at a high level; (2) The liquefaction potential index (LPI) shows an increasing trend followed by stabilization; the larger the LPI is, the smaller the state parameter (Ψ) is. The steady-state points of the loess are in the instability region; however, the steady-state strength is not zero; (3) Based on the ICU test results, the average pore diameter decreases; the shape ratio remains essentially unchanged; and the fractal dimension and roundness show different trends. The proportions of the macropore and mesopore decrease; that of the small pore increases slightly; and that of the micropore increases significantly; (4) The compression deformation of the highly spaced pores causes rapid strain hardening. A rapid strain softening results from the pore throat blockage at the beginning of particle rearrangement and reorganization. A stable strain softening is related to the agglomeration blocking of the reconstructed pore throat in the gradually stable stage of particle rearrangement and reorganization.

Hydroprocessing of Maya vacuum residue using a NiMo catalyst supported on Cr-doped alumina

Mesoporous alumina was doped with Cr using a co-precipitation method to prepare a support for hydrocracking catalysts. Ni and Mo were then impregnated on Cr-doped mesoporous alumina (NiMo/Al2O3-Cr). Catalytic activity was tested in hydrodeasphaltenisation (HDA), hydrodesulfurisation (HDS) and hydrodemetallisation (HDM) of Maya vacuum residue in a batch reactor and compared with NiMo supported on mesoporous alumina not doped with Cr (NiMo/Al2O3). Following activation and initial carbon deposition, experiments involving contact of the catalysts with fresh feed were performed. Greater HDA extent and maltene to asphaltene ratios were obtained with NiMo/Al2O3-Cr than NiMo/Al2O3 despite a larger amount of coke deposits. Significant activity of both NiMo/Al2O3-Cr and NiMo/Al2O3 towards HDS and HDM were also observed. Alumina textural properties remained relatively unaffected by the co-precipitation of Cr. X-ray photoelectron spectroscopy (XPS) showed that the catalysts contained Cr3+ and after reduction all Ni was present in metallic state at least in the near-surface region, while Mo6+ was reduced to Mo4+ and Moδ+ (0 ≤ δ ≤ 3) to a larger extent in NiMo/Al2O3-Cr. Lower reduction temperatures in the presence of Cr were determined, suggesting a larger number of metal sites available in reduced form at operating conditions. It was found that Cr aided metal dispersion in catalyst synthesis and coke dispersion during reaction. Spent catalysts showed reductions in surface area and pore volume. However, while spent NiMo/Al2O3 catalysts had a decrease in average pore diameter (APD), NiMo/Al2O3-Cr maintained the fresh material APD, which may explain the sustained catalytic activity.

Fabrication, characterization and drug loading efficiency of citric acid crosslinked NaCMC-HPMC hydrogel films for wound healing drug delivery applications

In this study, hydrogel films were prepared from sodium carboxymethylcellulose (NaCMC) and hydroxypropylmethylcellulose (HPMC) using citric acid (CA) as crosslinker. The chemical crosslinking (ester bond) between NaCMC and HPMC was confirmed by FTIR analysis. It was found that swelling degree, crystallinity and water contact angle of hydrogel films based on NaCMC-HPMC (2wt%) decrease with increase in CA from 5% to 20% (by weight). The increase in Tg and decrease in initial decomposition temperature were observed for increasing CA in NaCMC-HPMC films and were confirmed by DSC and TGA analysis, respectively. Tensile strength of hydrogel films decreases while elongation at break (%) increases with increase in CA. Highly interconnected nanoporous network and decrease in average pore diameter from micron to nanosize in cryofixed hydrogel films were found by FESEM and mercury intrusion porosimetry, respectively. The drug loading efficiency of hydrogel films was significantly higher for methylene blue compared to tetracycline. It was observed that hydrogel films release the drugs in sustained manner for 72h. The hydrogel films showed significant antibacterial activity after three days of release at 37°C in PBS (pH7.4). These findings strongly recommend that the prepared hydrogel films can be used as potential wound healing materials.

Influence of reservoir properties on the adsorption capacity and fractal features of shales from Qinshui coalfield

Abstract To investigate the adsorption capacity and fractal features of coal-measure shales and understand the influence of shale properties on the adsorption capacity and fractal features, a series of experiments were conducted on fifteen shale samples from Shanxi-Taiyuan Formations in the Yushe-Wuxiang Block, South-Central Qinshui Basin. The results indicate that organic and clay minerals are the two adsorption carriers for coal-measure shales, Langmuir volume (VL) of shales increases as the total organic matter (TOC) content or clay minerals content increases. Additionally, there is a negative correlation between VL and quartz content. As vitrinite reflectance (Ro%) increases, VL has an evolutionary path of first increasing and then decreasing, the maximum value is reached at near Ro = 2.1%. Furthermore, VL increases as specific surface area (SSA) increases or average pore diameter (APD) decreases. The coal-measure shales exhibit double fractal features. The fractal dimension of pore surface (D1) and fractal dimension of pore structure (D2) vary from 2.4899 to 2.6272 and 2.7318–2.840, respectively. The fractal dimensions show an increasing trend as SSA increases. As pore volume increases, D1 presents a slight increasing trend while D2 shows a decreasing trend. And fractal dimensions increase as APD decreases. The relationships of TOC with D1 and D2 are opposite. Clay minerals are the determining factor of the fractal dimensions as the fractal dimensions (D1 and D2) show an increasing trend as clay minerals content increases. An increase in quartz content or organic matter maturity will greatly reduce the heterogeneity of shales. As for non-clay minerals, the fractal dimensions (D1 and D2) show an increasing trend as pyrite content increases, while D1 increases and D2 decreases as carbonate mineral content increases. Regarding the composition of clay minerals, D1 increases as the mixed layers of illite/smectite (I/S) and illite contents increase or kaolinite and chlorite contents increase, while D2 is opposite. Shales with higher fractal dimensions develop stronger adsorption capacity while shales with higher D1 and lower D2 develop lower Langmuir pressure (PL).

FRACTAL NATURE OF POROSITY IN VOLCANIC TIGHT RESERVOIRS OF THE SANTANGHU BASIN AND ITS RELATIONSHIP TO PORE FORMATION PROCESSES

In this paper, in a case study of Santanghu Basin in China, the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation were investigated using the results of low temperature nitrogen adsorption experiments. This research showed that within the target layer, a large number of nanoscale, eroded pores showed an “ink bottle” morphology with narrow pore mouths and wide bodies. The fractal dimension of pores increases gradually with increasing depth. Moreover, as fractal dimension increases, BET-specific surface area gradually increases, average pore diameter decreases and total pore volume gradually increases. The deeper burial of the Haerjiawu volcanic rocks in the Santanghu Basin leads to more intense erosion by organic acids derived from the basin’s source rocks. Furthermore, the internal surface roughness of these corrosion pores results in poor connectivity. As stated above, the corrosion process is directly related to the organic acids generated by the source rock of the interbedded volcanic rocks. The deeper the reservoir, the more the organic acids being released from the source rock. However, due to the fact that the Haerjiawu volcanic rocks are tight reservoirs and have complicated pore-throat systems, while organic acids dissolve unstable minerals such as feldspars which improve the effective reservoir space; the dissolution of feldspars results in the formation of new minerals, which cannot be expelled from the tight reservoirs. They are instead precipitated in the fine pore throats, thereby reducing pore connectivity, while enhancing reservoir micro-preservation conditions.

Preparation and modulation of a novel thin-walled carbon foam

By foaming and carbonization processes under atmospheric pressure, a novel thin-walled carbon foam with developed foam structure was successfully prepared from loose medium component (LMC) separated from raw coal by extraction and back-extraction method. The influences of foaming time, carbonization time, and micromolecule content on foam structure were investigated by scanning electron microscope and mercury injection data. Moreover, foaming mechanism of LMC was analyzed and expounded. The results showed that spherical pores and uniform ultrathin pore walls constitute three-dimensional foam structure of carbon foam and foam structure is developed with well connectivity. The effects of foaming time, carbonization time, and micromolecule content on foam structure are significant. Especially, average pore diameters of carbon foams prepared from the extracts of LMC are much smaller. With the rise of extraction rate, average pore diameter decreases and pore size distribution is more concentrated on the aperture section of 0–10 μm.

Influence of Nanocrystalline MgAl2O4 Spinel Addition on the Properties of MgO-C Refractories

Nanopowders of magnesium aluminate (MgAl2O4) spinel, prepared through citrate-nitrate gel method and calcined at 800°C, were incorporated to the matrix of magnesia-carbon (MgO-C) refractory. The physical and chemical properties of the nano-MgAl2O4 spinel-added (0.5 and 1.0 wt%) MgO-C bricks were compared with those of MgO-C bricks containing no spinel and commercially available micron-sized (<45 µm) stoichiometric spinel (AR-78). It was observed that nano-spinel (NS) (1 wt%) containing MgO-C refractories effectively prevents the oxidation, slag corrosion, and penetration resistance compared to MgO-C bricks with or without micron-sized spinel added. The average pore diameter decreases, and the concentration of the fine pore increases with addition of nano-MgAl2O4 spinel in the matrix of MgO-C bricks. Due to the lower pore size and higher concentration of fine pores as well as higher amount of carbon retention, nano-MgAl2O4 spinel-added MgO-C bricks show better physical as well as chemical properties and may have potential applications in both steel and refractory industries.

Removal of water‐soluble azo dye by the magnetic material MnFe2O4

AbstractMagnetic ferrite material, MnFe2O4, as a novel adsorbent was prepared and characterized. Adsorption tests indicated that it is an excellent adsorbent for the removal of the azo dye Acid Red B (ARB) from water. After adsorbing ARB and recovery by the magnetic separation method, it can be regenerated by Fenton's reagent. The pseudo‐first‐order and second‐order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The adsorption capacity was highly affected by the pH of the solution, and pH 3.8 was optimal. After regeneration, the adsorption capacity of MnFe2O4 increased significantly, which was the result of a decrease in average pore diameter, an increase in surface area of the adsorbent and the adsorption of ferric hydroxide produced in the regeneration reaction. The adsorption can be described with the Langmuir model and the maximum adsorption capacity for ARB was 53.8 mg g−1 adsorbent. FTIR study for ARB on MnFe2O4 indicated that the adsorption of ARB occurred via the azo group and the sulfonic group of the dye through the formation of a complex with the adsorbent surface. Copyright © 2004 Society of Chemical Industry

Characterization and reactivity of molybdenum oxide catalysts supported on Nb2O5–TiO2

A series of MoO3/Nb2O5 catalysts with Mo loadings varying from 2.5 to 15 wt % were prepared and characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of ammonia, electron spin resonance (ESR), oxygen chemisorption, and pore size distribution measurements. X-ray diffraction patterns indicate the presence of a crystalline molybdenum phase at higher Mo loadings on niobia. Dispersion of molybdenum was determined by the oxygen chemisorption at 623 K by a static method on the samples prereduced at the same temperature. At low Mo loadings, i.e., <10.0%, molybdenum oxide is found to be present in a highly dispersed state. Pore size distribution studies indicate a decrease in average pore diameter and pore volume with increased Mo loading. ESR results suggest the presence of Mo5+ in the reduced catalysts. TPR results suggest that the reducibility of MoO3 increases with increased Mo loading. The reduction peaks due to niobia in TPR appeared at high...

The effect of molecular weight on the cross section and properties of polyacrylonitrile precursor and resulting carbon fiber

AbstractIn this study, we investigated the effect of molecular weight in the range 1.65−4.29 × 105 (Mw) on the cross section, surface, thermal, and mechanical properties of polyacrylonitrile (PAN) precursor and its resulting carbon fiber. From the results, it can be seen that the molecular weight, with the same solid content of polymer, changes from 1.65 × 105 to 4.29 × 105 and the cross section of PAN precursor changes from a circular shape with no notable grooves surface to a been shape with a surface containing deep and straight grooves. PAN precursor with higher molecular weight has a higher onset of exothermic temperature and a higher peak temperature, but has a higher aromatization index (AI value) due to its thin and flat cross section, which causes rapid cyclization during oxidation. An increase in molecular weight results in an increase in crystal size and preferred orientation and a decrease in average pore diameter. This decrease can improve the mechanical properties of PAN precursor and its resulting carbon fiber.