Gas Sorption Porosimetry Research Articles

Microstructural Investigations of Ultra-High Performance Concrete Obtained by Pressure Application within the First 24 Hours of Hardening

In this study, the effect of pressure application (0–50 MPa) to fresh concrete right after casting and during the first 24 hours of hardening has been examined. Supplementary cementitious materials in a form of silica fume, nanosilica and ground quartz sand were used. The aim of pressure application was to reduce porosity, thus improving concrete mechanical properties. Considerable reduction in porosity and a subsequent increase in compressive strength reaching the level of Ultra-High Performance Concrete (UHPC) were achieved. Mechanical and physical properties were tested and gas sorption porosimetry, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) were used for material characterization.

Computer-aided structure elucidation for arylene-bridged polysilsesquioxanes

Phenylene- and terphenylene-bridged polysilsesquioxane networks are modeled using computer-aided structure elucidation and molecular-dynamics (MD) simulations. The models are matched with analytical results such as elemental analysis, solid-state 29Si NMR, and gas-sorption porosimetry. Models which are cross-linked in every direction in three-dimensional space do not contain pore volume and are rejected. Models which are cross-linked in only two dimensions fit well with all analytical data. In conclusion, the bridged polysilsesquioxane networks seem to be formed by an aggregation of two-dimensional structures covalently or hydrogen bonded together.

Arylene- and alkylene-bridged polysilsesquioxanes

Bis(triethoxysilyl)arylene monomers 1–5 and the 1,6-bis(trimethoxysilyl)hexylene monomer 6 were hydrolytically condensed under sol-gel conditions using both acid and base catalysts to produce their respective arylene- and alkylene-bridged polysilsesquioxane materials (X-1 through X-6). Polymerization reactions yielded gels within 24 h. One notable exception was the acid-catalyzed polymerization of 2,5-bis(triethoxysilyl)thiophene (X-5-S1) which required approximately 1 month to gel. The gels were processed by extracting with low dielectric solvents or by aqueous extraction. Solid state 13C and 29Si CP MAS-NMR, infrared spectroscopy, and gas sorption porosimetry were measured on the xerogels. The materials were transparent, glass-like xerogels with surface areas as high as 1100 m 2/g and porosity primarily confined to a micropore region ( < 20 A ̊ diameters ). Xerogels prepared using the aqueous extraction had surface areas between 500 and 956 m 2/g.