Primary Pore Size Research Articles

Ultrasonic synthesis of mesoporous molecular sieve

The ultrasonic irradiation synthesis of mesoporous molecular sieve (MMS) was investigated by using cationic surfactant and organic silica source in acidic condition. Mesoporous silica that is analogous to the hexagonal MCM-41 could be synthesized over a range of irradiation power from 0 to 250 W within a short synthesis time about 20 min and a quiescent time of 5 h. The material has large BET surface area over 1100 m 2/g, primary pore size in the range of 22–30 Å, pore volume around 1 cm 3/g and wall thickness from 14 to 25 Å. Ultrasonic irradiation has a particular effect on MMS structural uniformity. Generally, the BET surface area increases as the ultrasonic power, time, temperature, solution acidity and quiescent time increasing. The pore volume and primary pore size increase as the ultrasonic power, but decrease as the ultrasonic time and solution acidity increasing. Further more, the strong acidity and long quiescent time are favorable for obtaining higher yield in this research work. Experimental results indicate that this method is satisfactory for saving time and energy than the hydrothermal processing in basic condition although its structural uniformity is slight lower.

Synthesis of Bimodal Nanostructured Silicas with Independently Controlled Small and Large Mesopore Sizes

We report on the synthesis of bimodal, structured silicas by a fully chemical, templating−scaffolding route that enables independent control over small and large mesopore sizes. Mesoporous MCM-41 nanoparticles, synthesized in a first step, are cross-linked in a second step, leading to a bimodal porous material. Triblock copolymer surfactants added during the second synthesis step form assemblies, around which the nanoparticles aggregate and cross-link, considerably influencing both the average and the width of the secondary pore size distribution, without affecting the primary pore size. By changing the conditions of the second step, one can easily synthesize a broad variety of silicas with a controlled bimodal nanopore size distribution. Textural and structural properties were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, 29Si solid-state NMR spectroscopy, N2 adsorption and desorption, and thermogravimetric analysis.

Grain size, composition, porosity and permeability contrasts within cross‐bedded sandstones in Tertiary fluvial deposits, central Spain

ABSTRACTPermeability measured with a portable probe permeameter on outcrops of cross‐bedded sandstones ranges between 0·9 and 19 D. The highest permeability (2–19 D with an average of 8·5 D) occurs in the coarsest grained foreset laminae (CFL), intermediate values (2–12 D with an average of 5·3 D) occur in finer grained foreset laminae (FFL) and the lowest values (0·9–10 D with an average of 4·8 D) occur in bottomset layers (BL). In the cross‐beds the average grain size ranges from medium grained sand in the CFL to fine grained sand in the FFL and BL. In all three subfacies, the average size of the primary pores is approximately 1φ unit smaller than the average grain size. The abundance of unstable carbonate clasts correlates with increasing average grain size, micritic clasts being most abundant in the CFL. Conversely, quartz content increases with decreasing grain size and is highest in the FFL and BL. Diagenetic destruction of primary porosity by compaction and cementation, as well as generation of secondary porosity through dissolution, were controlled by the original mineralogical composition of the sand. Contrasts in grain size determine the primary pore size contrasts and differences in composition between CFL, FFL and BL. Permeability contrasts reflect variations in average primary pore size rather than differences in total porosity. Probe permeability contrasts between CFL, FFL and BL depend on contrasts in average pore size and contrasts in mineralogical composition between the subfacies.