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Abstract A dealuminated Y-zeolite with a n Si / n Al ratio of 130 is treated in pure water and aqueous solutions of NaCl at different pH values between 3 and 7 at 100 °C for up to 3 weeks. The change of specific micropore volume, the specific external surface, and the mesopore size distribution are monitored by N 2 -adsorption (77 K). The decrease of micropore volume proceeds due to a zero order kinetics. The zeolite loses no mass, but according to an XRD analysis the loss of micropore volume is paralleled by the formation of mainly amorphous material. The amorphization is assumed to start at the outer surface of the zeolite crystals leading to a core-shell distribution of amorphous and zeolitic material. The amorphization is coupled with the formation of mesopores and an increasing external surface area. The evolution of mesopores mainly occurs at diameters near the lower boundary region of the pore size analysis by N 2 sorption (3 nm). The degradation is catalyzed by hydroxide ions present in bulk water. Both the exchange of the acidic protons with Na+-ions and the presence of NaCl in the water phase accelerate the degradation at pH 7. The zeolite is decomposed in 1 M NaCl at pH 7 and 100 °C within 40 min. However, when the pH is lowered to 3, it is stable in 1 M NaCl for more than 10 days. The protonated form in pure water is about half as stable as the Na+-form in 1 M NaCl at pH 3. Graphical abstract Image 1 Highlights • Extremely unstable in 1 M NaCl at pH 7. • Extremely stable in 1 M NaCl at pH 3. • H+-form in water somewhat less stable than in 1M NaCl at pH 3. • Decrease of micropores follows a zero order type reaction. [ABSTRACT FROM AUTHOR]

Soils containing iron oxides that are derived from chemical weathering are widespread in geotechnical systems. This work studies the effect of adsorbed iron oxides on the shear strength of laboratory-prepared iron oxide-coated sands. Goethite- and hematite-coated Ottawa sands were synthesized in the laboratory via a heterogeneous geochemical suspension-reaction method. Surface roughness parameters and fractal dimension were determined using atomic force microscopy (AFM), which showed that hematite-coated sands exhibited the roughest surfaces. N2-adsorption experiments also helped characterize the mineral surfaces. Shear strength parameters were obtained through consolidated drained (CD) triaxial compression, showing an increase in the critical state friction angle of more than 5% when the sands were coated with iron oxides. Iron oxide coatings also increased dilatancy and decreased contractiveness. The experimental results can be attributed to changes in mass-to-mass concentration and intrinsic soil fabric changes due to the presence of iron oxide coatings, as well as to increased roughness and particle-to-particle interlocking. [ABSTRACT FROM AUTHOR]

Abstract: Syntheses of NaX-coatings on highly porous stainless steel fibre substrates were carried out via direct zeolite crystallization. Both the nucleation as well as the following crystal growth took place in situ at the metal fibre bodies. The NaX-zeolite is able to adsorb nitrogen in large quantities and thus to enrich ambient air with oxygen. The advantage of the used substrates is their large pore volume of up to 90%, which was important, in order to achieve a maximum zeolite/substrate proportion. The aim was to close the cavities of the fibre bodies almost completely, that means up to an optimal degree, with zeolite in order to get a maximum N2-adsorptivity. A certain amount of free accessible pore volume is necessary in order to assure a free exchange of the gases. A better oxygen yield in a pressure swing adsorption unit for the new molecular sieves than for a comparable container volume of commercial NaX-granulates was expected. Therefore the properties of the metal fibre bodies had to be adapted and an appropriate procedure for the zeolite synthesis had to be developed. In addition the N2-adsorption behaviour of the zeolite coated fibre bodies was measured. As a result NaX-zeolite coated stainless steel fibre bodies, whose zeolite portion is almost equal to that of commercial NaX-zeolite granulates, could be manufactured. They showed a slightly better N2-adsorptivity in comparison to commercial NaX-zeolite granulates. Moreover, there are still vacancies within the highly porous metal fibre substrates so that a further increase of the zeolite portion and with this of the N2-adsorptivity seems to be achievable. The easier handling of the compact metal fibre bodies in the adsorption units compared to the commercial granulates is another advantage. [Copyright &y& Elsevier]

Abstract: The assembling mode of transition metal oxides and metallic guest phases (GP) embedded in nanotubular pores of ordered mesostructured silicas (OMS) hosts was evaluated based on N2 adsorption–desorption data. The corresponding isotherms were measured for sample sets of composite materials MoO3/Al-MCM-41, WO3/SBA-15, TiO2/SBA-15, ZrO2/SBA-15, NiO/SBA-15 and Ni°/SBA-15 with GP loadings in the range of 20–80wt%. The materials were also characterized by XRD, HRTEM and local/total EDS. It was shown that a combination of composite surface area values normalized per gram of OMS with pore size distribution (PSD) derived from the adsorption or desorption branch of the isotherm distinguishes the ensemble of small nanoparticles with a size of less than an OMS mesopore diameter and single nanoparticles of a size comparable with OMS mesopore diameter. It also discerns amorphous layer at the surface of OMS pore walls from the ensemble of amorphous nanoparticles. At high GP loadings the PSD derived from the adsorption branch of the N2-adsorption isotherm more reliably reflects the filling of OMS mesopores with crystalline or amorphous guest nanoparticles. [Copyright &y& Elsevier]

A pure, high surface area and cost-effective carbon-based material with possible application in electrochemical processes was synthesized from industrial sludge. Surface characterization included N2-adsorption isotherm data and mathematical models such as the DR equation, and BJH methods. The extent of the purity was assessed from thermogravimetric analysis (TGA). The electrochemical properties, i.e. the potential use as electrode in Li ion batteries, were evaluated using conventional electrochemical testing such as charge/discharge cycling and impedance spectroscopy. The results of the data analysis were promising and indicated that paper mill sludge can be successfully used to produce a pure carbon for potential use in electrochemical applications. [Copyright &y& Elsevier]

Silica sols have been prepared in an alcoholic solution by hydrolysis and condensation of TEOS (tetraethyl-ortho-silicate) molecules as a function of water and nitric acid concentration. The polymers are intended as precursors for ceramic, gas separation membranes. These molecules show fractal behavior as determined by SAXS (Small Angle X-ray Scattering). Microporosity of dried and calcined silica polymers is determined by N2-adsorption at 77 K. Fractal dimension and porosity increase with increasing acid concentration. Both the sol structure and the drying kinetics determine the porosity values. N2-adsorption isotherms are not very suitable for the determination of pore size distributions of microporous silica. [ABSTRACT FROM AUTHOR]