Mean Pore Size Distribution Research Articles

The relationship between pore structure and strength of aeolian sand concrete under low temperature

To examine the relationship between microscopic parameters and compressive strength of aeolian sand concrete (ASC) at low temperatures, the compressive strength of ASC at different temperatures is predicted by factors such as the pore structure parameters and the ambient temperature. The experiments used 100 % replacement of river sand (RS) with aeolian sand (AS) to prepare fully ASC, and regular concrete with the same water-cement ratio as the control group. The experiment used nuclear magnetic resonance (NMR) technology and grey correlation analysis method to analyze the microscopic parameters and compressive strength of concrete specimens with three curing ages of 7d, 28d, and 60d at temperatures of 20 °C, 0 °C, −5 °C, −10 °C, −15 °C, and −20 °C. It was shown that the agglomeration between the fine particles during the mixing process results in a large number of pores in the interior of the ASC, resulting in a larger porosity compared to ordinary concrete. As a result, its compressive strength was lower than that of ordinary concrete, and the loose and porous internal structure provides room for the filling of more ice crystals. Therefore, the increase in compressive strength of ASC at different curing ages in an environment of −20 °C was greater than that of ordinary concrete. Among them, at-20 °C, the compressive strength of ASC with curing ages of 7d, 28d and 60d increased by 6.31 %, 3.59 % and 3.97 % respectively compared with ordinary concrete. Finally, a predictive model between parameters such as temperature, porosity, mean pore size distribution and gel content and compressive strength was developed, which was highly accurate.

Insight into On-Wafer Crystallization of Pure-Silica-Zeolite Films through Nutrient Replenishment

Tetraethylorthosilicate (TEOS) is added to a pure-silica-zeolite MEL nanoparticle suspension and the mixture is subsequently used for preparing spin-on low-dielectric constant (low-k) films. The films are then characterized by ellipsometric porosimetry, transmission electron microscopy (TEM), and nanoindentation. Investigation into the film microstructure indicates that the addition of TEOS significantly increases the fraction of the crystalline domains, decreases the inter-crystal mesopore size, and narrows the pore size distribution. Films with 12% TEOS loading have a mean pore size distribution centered at 3.5 nm (diameter) with a full width at half maximum (fwhm) of 0.8 nm, while those with no TEOS have a distribution at 11.1 nm and fwhm of 7.9 nm. At 12% TEOS loading, the reduced modulus and hardness are 11.0 and 1.12 GPa, respectively; without TEOS, the values are 6.4 and 0.57 GPa.

Sulfonated polystyrene-modified mesoporous organosilicas for acid-catalyzed processes

Organically modified mesoporous silica materials have been prepared by direct co-condensation of styrylethyl-trimethoxysilane (STETMOS) and tetraethyl-orthosilicate (TEOS) in one-pot synthesis. The polymerizable nature of the styryl-containing precursor induces the formation of anchored polystyrene blocks on the silica surface, which are amenable to be functionalized with acid groups via sulfonation. The resultant organosulfonic-modified mesostructured silica materials exhibit hexagonal long-range mesoscopic arrangement with extended surface areas and narrow mean pore size distributions. Upon sulfonation a high number of sulfonic-acid sites have been introduced on the silica-anchored polystyrene-type organic moieties, thus providing strong acid sites embedded in a hydrophobic microenvironment. The catalytic performance of these strongly acidic hydrophobic materials has been assessed and compared with commercial catalysts in three different acid-catalyzed reactions. Two of them are acid strength-demanding reactions such as acylation of anisole with acetic anhydride and Fries rearrangement of phenyl acetate. The third one, based on the esterification of oleic acid with n-butanol, is a catalytic test wherein the hydrophobic nature of the catalyst surface plays an essential role. As result of these catalytic tests, the sulfonated polystyrene-modified hybrid materials have been shown as versatile and highly active acid heterogeneous catalysts, especially in hydrophobicity-demanding systems.

Influence of lithium chloride, lithium bromide and lithium fluoride additives on performance of polyethersulfone membranes and its application in the treatment of palm oil mill effluent

In this study three different types of lithium halides; lithium bromide (LiBr), lithium chloride (LiCl) and lithium fluoride (LiF) were used as additives in the making of polyethersulfone (PES) membranes. The concentration of PES is kept constant at 20 wt.% throughout the study, and the lithium halide concentration is varied in the range of 1–5 wt %. The solvent used is N, N-dimethylformamide and the PES asymmetric membrane was prepared by the dry/wet phase inversion process. Membrane performance was characterized in terms of pure water permeation (PWP), permeation rate (PR) and solute separation of polyethylene glycol (PEG) solution of various molecular weights ranging from 600 to 35,000 Da. The molecular weight cut off (MWCO) and mean pore size distribution were subsequently determined. Results revealed that the 3 wt.% LiBr exhibits the best performance with MWCO at 90% rejection in the range of 2.83 kDa and high flux range of 117.69 L m − 2 h − 1 . Hollow fibers spun from the dope solutions containing LiBr revealed that they are capable of treating palm oil mill effluent (POME) with reduction in turbidity, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of 96.7%, 53.12% and 76.7% respectively.

Tailored mesoporous alumina prepared from different aluminum alkoxide precursors

The importance of aluminum alkoxides precursors (ethoxide, isopropoxide and sec-butoxide) in the tailoring of the structural and textural properties of γ-alumina was reported. It has been found that the specific surface areas (336–426 m2/g), as well as the mean pore size distribution are modified in function of the length and branching of the aluminium alkoxide used in the synthesis. A narrow pore size distribution was obtained with aluminum ethoxide (14.7 nm), meanwhile a broad pore size distribution was observed in samples prepared with aluminium sec-butoxide or aluminium isopropoxide precursors (18.2 and 19.4 nm). In fresh samples, Boehmite phase and AlVI octahedraly coordinated were identified by XRD and 27Al MAS-NMR spectroscopies. After annealing at 500°C, the samples showed the γ-alumina phase formation and a mixture of aluminium in tetrahedral AlIV and octahedral AlVI coordination in variable proportions. The acidity of the calcined samples, determined from the pyridine-FTIR spectra, showed Lewis and Bronsted type acidity. Activity in the 2-propanol dehydration reaction showed that the highest activity corresponds to the samples showing the highest Lewis acidity.

Assembly of Large-Pore Silica Mesophases with Wormhole Framework Structures from α,ω-Diamine Porogens

Large-pore mesoporous silicas with wormhole framework structures have been assembled through hydrogen-bonding pathways from sodium silicate or tetraethyl orthosilicate (TEOS) as the silica source and amine-terminated Jeffamine surfactants of the type H2NCH(CH3)CH2[OCH2CH(CH3)]xNH2 as the structure-directing porogen. Depending on the molecular weight of the α,ω-diamine surfactant (x ∼ 33 and 68 for Jeffamine D2000 and D4000, respectively) and the synthesis temperature (25−65 °C), the mean pore size distributions of the mesostructured silicas (denoted MSU-J) were centered between 4.9 and 14.3 nm, making these materials comparable to hexagonal SBA-15 mesostructures in average framework pore size. In addition to the BET surface areas of MSU-J silicas (408−1127 m2/g) being comparable to those of SBA-15 (630−1040 m2/g), MSU-J silicas exhibit larger pore volumes (1.37−2.29 cm3/g) than SBA-15 silicas (0.56−1.23 cm3/g) prepared in the absence of mesitylene. MSU-J wormhole mesostructures represent the largest pore sizes observed to date for a fully three-dimensional mesoporous framework assembled from a single micellar porogen. Only mesostructured micellar foam structures exhibit larger pore sizes, but the preparation of foam structures requires the use of more complex microemulsions or latex polymers as porogens.

Effect of gas hydrates melting on seafloor slope instability

We present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature, pressure, pore water chemistry, and the mean pore size distribution. The model uses a new formulation based on the enthalpy form of the law of conservation of energy. The developed model shows that due to a temperature and pressure increase, hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water. This original result confirms what has been already shown through experiments. The second part of the paper presents an application of the model through a back-analysis of the giant Storegga Slide on the Norwegian margin. Two of the most important changes during and since the last deglaciation (hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature) were considered in the calculation. Simulation results show that melting of gas hydrate due to the change of the gas solubility can be at the origin of a retrogressive failure initiated at the lower part of the Storegga slope. Once again, the developed model leads to predictions, which are supported by laboratory experiment results, but contradictory to previous interpretations and beliefs considering that hydrate dissociation occurs only at the bottom of the gas hydrate stability zone.

A reconstruction technique for three-dimensional porous media using image analysis and Fourier transforms

A truncated gaussian method based on Fourier transforms is proposed to generate periodic 3D porous structure from a 2D image of the sample. This technique improves a previous method developed by Quiblier [Quiblier, J.A., 1984. A new three-dimensional modeling technique for studying porous media. J. Colloid Interface Sci 98, 84–102] and Adler et al. [Adler, P.M., Jacquin, C.G., Quiblier, J.A., 1990. Flow in simulated porous media. Int. J. Multiphase Flow 16 (4), 691–712]. The difference between the present method and previous work [Adler, P.M., 1992. Porous Media: Geometry and Transports. Butterworth-Heinemann, New York] is that the gaussian field is directly generated from its autocorrelation function and the use of a linear filter transform is avoided. It is not required to solve a set of nonlinear equations associated with this transform. In addition, memory requirements are reduced because non-correlated gaussian field data are not needed. Porous structure is described by the porosity and autocorrelation function, which are measured from a 2D binarized image of a thin section of the sample. When the autocorrelation function is positive–definite, the corresponding gaussian field can be generated using Fourier transforms. Phase angle distribution is assumed to be random and does not affect the autocorrelation function. 3D porous media are generated by truncating the gaussian distribution. Using the fast Fourier transform makes this algorithm more efficient. Both processing time and computer memory requirements are improved. Results for a Berea sandstone sample show that the mean pore size distribution, obtained taking several serial cross-sections of the reconstructed 3D porous structure into account, is in good agreement with the original thresholded 2D image.