Molecular simulation for adsorption of chlorinated hydrocarbon in zeolites

Equilibrium and isosteric heat of adsorption for the system of chloroform and USY-type zeolite were studied. The USY-type zeolite (PQ Co., SiO₂/Al₂O₃=70) was used both as a pure crystalline powder and as granulated particles with binder. Chloroform was reagent grade. The adsorption equilibria were measured using a gravimetric method and were expressed as isotherms. A chromatographic method (i.e. pulse response of chloroform through the USY column with helium carrier) was used to get the initial slope of the isotherms. In the simulation, the GCMC method was used to calculate amounts adsorbed for various conditions. FF parameters were confidently applied. And modified structure model was effective for simulation. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

Facile Synthesis of Manganese‐Loaded Mesoporous Silica Materials by Direct Reaction Between KMnO4 and an In‐Situ Surfactant Template

A series of manganese oxide‐loaded SBA‐15 (MnSBA‐xh, x = 1, 2, 3, 4, 5, 6; h: hour(s)) mesoporous materials are synthesized via a facile, in‐situ reduction method with a surfactant template. The composite materials are characterized using Fourier‐transform infrared spectroscopy, X‐ray diffraction, N₂ sorption isotherms, X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy, energy‐dispersive spectroscopy, and CO oxidation catalysis. The results show that a high content of manganese (an atomic ratio of Mn/Si from 0.12 up to approximately 1) could be loaded into the channels of SBA‐15 when treated with an aqueous solution of potassium permanganate, while retaining the ordered mesostructure and large surface area of SBA‐15. Increasing the manganese oxide content results in a gradual decrease in the specific surface area, pore size, and pore volume. XPS spectra are employed to confirm the redox reaction between KMnO₄ and the surfactant. CO‐conversion tests on the calcined MnSBA‐2h sample (MnSBA‐2h‐cal) shows that it has a repeatable, and relatively high, catalytic activity.     

Preparation of Silica Nanostructured Spheres by Sol Spray Drying

Silica nanostructured spheres were obtained by spray drying of silica sol prepared in situ. Their morphologies were significantly affected by the aggregation of the primary particles in the sol. They had the mode of the pore sizes which was about the same order as Laser Particle Size Analyzer (LPA) diameter. Increasing the mixing ratio of the larger particles (20 nm) to smaller ones (7 nm) decreased the Brunauer, Emmett and Teller (BET) specific surface area, as expected. Pore volume decreased with the pore size distribution broadened and the mean pore diameter was not affected by the increase, due to the decrease in aggregation of the primary particles. Either the increase in the drying temperature and use of ethanol as a cosolvent made the agglomerates hollower, the larger of which with thinner shell transformed to doughnut type agglomerates, due to the structural and hydrodynamic instabilities.     

Routine instrumental procedures to characterise the mineralogy of modern and ancient silica sinters

Tightly constrained determinative methods can be used to characterise the silica minerals (opal-A, opal-CT, opal-C, quartz, moganite) and physical properties of silica sinters. Optimal X-ray powder diffraction operating parameters indicate silica lattice order/disorder using untreated, dry, <106 μm powders scanned at 0.6° 2θ/min with a step size of 0.01° from 10–40° 2θ and an internal Si standard. Simultaneous differential thermal and thermogravimetric analysis of 15.0±0.1 mg sinter samples of <106 μm grain size, at a heating rate of 20°C/min in dry air, identify thermal events associated with dehydration, organic combustion, and changes of state. Where abundant organic matter is present, nitrogen is the preferred atmosphere for thermal analysis. Thermogravimetric-determined water contents of sinters differ from Penfield determinations reflecting the differing nature of the two techniques. Laser Raman microprobe techniques can be used to explore the mineralogy of particular sinter morphologies and habits down to 10 μm diameter. The nature of the silica species present can assist in characterising individual sinter deposits and, combined with textural, density and/or porosity determinations, can lead to a better understanding of the hydrology and paleohydrology of a geothermal prospect.     

Autogenous shrinkage of high-strength concrete containing silica fume under drying at early ages

The present study investigated experimentally autogenous shrinkage of high-strength concrete containing silica fume under drying at early ages. The influence of drying on hydration of cementitious materials in the high-strength concrete with water-binder ratios of 0.25, 0.35 and 0.45 was evaluated based on bound water content (BWC), which was exposed to drying at the ages of 0.5, 1.0 and 3.0 days, respectively. By establishing the relationship between the BWC and autogenous shrinkage strain under sealed conditions, autogenous shrinkage strain under drying conditions and drying shrinkage strain were separated from total shrinkage strain, and, then, the contribution of autogenous shrinkage in total shrinkage was discussed. The results showed that the percentage of autogenous shrinkage was macroscopically 50-20% based on the present method, while that was 70-30% based on the conventional superposition principle (SP). The latter resulted in overestimating autogenous shrinkage strain under drying conditions.     

Relationship between resistivity, diffusivity and microstructural descriptors for mortars with silica fume

Mortars with a sand-to-cement ratio of 3 and water-to-cement ratio of 0.5 were made with 0% and 10% silica fume (SF). Resistivities were measured with alternating current impedance spectroscopy (ACIS). Diffusivities were determined with the propan-2-ol counterdiffusion method. Microstructure was investigated with mercury intrusion porosimetry. It was found that there is a relationship relating hydration time to the product of resistivity and diffusivity. Furthermore, the product of resistivity and diffusivity was related to porosity, mean and threshold pore diameters. The influence of silica fume in refining the pore structure was marked.     

提高焦炉硅砖质量的途径

用X射线衍射仪、偏光显微镜及扫描电子显微镜对焦炉硅砖进行了分析研究。结果表明：原料和矿化剂不同，其显微结构及制品的残余石英和鳞石英的含量不同，而这些差异与制品的物理性能有直接关系，因此要提高焦炉硅砖的物理性能就必须严格控制相组成和微观结构。建议焦炉硅砖的标准中列入残余石英的允许含量及鳞石英的最低含量。     

Low‐Temperature Formation of Well‐Aligned Nanocrystalline Si/SiOx Composite Nanowires

Well‐aligned nanocrystalline (nc)‐Si/SiO_x composite nanowires have been deposited on various substrates at 120 °C using SiCl₄/H₂ in a hot‐filament chemical vapor deposition reactor. Structural and compositional analyses reveal that silicon nanocrystals are embedded in the amorphous SiO_x nanowires. The nc‐Si/SiO_x composite nanowires are transparent in the range 500–900 nm. Photoluminescence spectra of the nc‐Si/SiO_x composite nanowires have a broad emission band, ranging from 420 to 525 nm. Water vapor from the chamber wall plays a crucial role in the formation of the well‐aligned nanowires. A possible mechanism for the formation of the composite nanowires is suggested.     

Probing the Effects of Nanoscale Architecture on the Mechanical Properties of Hexagonal Silica/Polymer Composite Thin Films

We examine the effects of controlling nanoscale architecture on the tensile properties of honeycomb‐structured silica/polymer composite films. The hexagonal films are produced using evaporation‐induced self‐assembly and uniaxially strained using a home‐built tensile testing apparatus. Significant differences in the yield strain, failure strain, and tensile moduli between the axes parallel and perpendicular to the film‐deposition direction are observed for the thinnest films examined and are attributed to anisotropy in the film nanostructure that is further characterized with transmission electron microscopy and atomic force microscopy. For properly oriented composites, these films have tensile moduli comparable to the Young's modulus of bulk silica but exhibit failure strains that are about an order of magnitude larger than those seen in typical bulk‐silica systems. The yielding and failure processes are explored using X‐ray diffraction and optical microscopy and are characterized by irreversible changes in the nanoscale architecture. We show that tuning the nanoscale architecture can provide control over the tensile properties of composites, allowing for materials with combinations of stiffness and elasticity unachievable in the analogous bulk systems.