坝址渗水析出物及其潜在影响研究

坝址析出物是伴随渗水而出现的，对大坝安全运行具有潜在的不利影响。采用现场调查、取样多手段测试等方法，对此进行综合分析与评价。按照出露位置，可分为坝基及坝体析出物两类。其形成机理包括溶解—沉淀作用、还原—氧化—絮凝作用、浸析作用等。坝址析出物的潜在影响反映在对岩体的渗透稳定性、对帷幕体的防渗时效性以及对坝体结构的耐久性等方面；不同成因的析出物具有不同的潜在影响程度：化学成因者多限于微观方面，而物理成因者则在一定阶段可显现在宏观方面。在实际工作中，应加强对具有物理成因或化学—物理双重成因一类析出物的监测。     

Thermosensitive Molecular,Colloidal, and Bulk Interactions Using a Simple Surfactant

Efficient use of (nano)particle self‐assembly for creating nanostructured materials requires sensitive control over the interactions between building blocks. Here, a very simple method for rendering the interactions between almost any hydrophobic nano‐ and microparticles thermoswitchable is described and this attraction is characterized using colloid probe atomic force microscopy (CP‐AFM). In a single‐step synthesis, a thermoresponsive surfactant is prepared that through physical adsorption generates a thermosensitive brush on hydrophobic surfaces. These surface layers can reversibly trigger gelation and crystallization of nano‐ and microparticles, and at the same time can be used to destabilize emulsions on demand. The method requires no chemical surface modification yet is universal, reproducible, and fully reversible.     

Gelation—A review

This paper reviews the modern ideas on the process of gelation which have arisen from the analogy between gelation and percolation. The basic features which are common to all types of gels, colloidal or polymeric systems are first recalled; then after a simplified presentation of the percolation model, a few examples illustrating these concepts are chosen (for chemical gelation, a copolymerisation reaction and for physical gelation, the gelatin sol-gel transition). In conclusion, electron micrographs of gel networks (gelatin gel and an inorganic gel of thorium phosphate) are shown, which reveal the great diversity and complexity of the structures.     

Vibrational Spectroscopic Study of Structural Evolution in the Coprecipitated Precursors to La2Sn2O7 and La2Ti2O7

Structural evolution in the X-ray amorphous precursors to La₂Sn₂O₇ and La₂Ti₂O₇ is examined using IR and Raman spectroscopy. These precursors are prepared by rapid coprecipitation from mixed aqueous solutions of the corresponding metal chlorides. Rapid coprecipitation from an SnCl²⁻₆ and La³⁺-containing aqueous solution yields microcrystalline particles of SnO₂· n H₂O and La(OH)₃, which instantaneously interconnect to form an ultimate, complex colloid particle. The Ti(OH)²⁺₂ and La³⁺ in the other solution system coprecipitate into a different, complex colloid (an unidentified phase), which is definitely not a mixed dispersion of single-component colloids. A comparative examination of the vibrational spectra of the coprecipitates heated to various temperatures indicates that the SnO₂ and anatase phases develop in the respective precursors before crystallization of the desired double oxides. Crystallization itself can be attributed to a solid-state reaction among the various microcrystallites of each single-metal oxide in a gel particle of the precursor.     

Sediment dynamics and pollutant mobility in rivers: An interdisciplinary approach

Characteristic dynamic features of sediment‐related processes in rivers include dramatic effects of stormwater events on particle transport, rapid and far‐reaching effects of sulphide oxidation during resuspension, and biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result of the stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine‐grained sediments and suspended matter as these materials exhibit large surface areas and high sorption capacities. Organic materials are highly reactive. Degradation of organic matter will induce oxygen depletion and might enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. Major questions relate to the potential reduction of sorption sites on minerals and degradation of organic carrier materials. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modelling the overall effects of pollutants on the water body and aquatic ecosystems. With respect to handling and remediation of contaminated river sediments, either in‐place or excavated, a chemical and biological characterization of the material, of the (disposal) site and of the long‐term processes is crucial. Passive techniques (e.g. in situ stabilization, subaqueous capping) provide economic advantages as there are no operation costs following their installation. However, the success of these ecological and geochemical engineering approaches is mainly based on an in‐depth knowledge of the underlying processes.     

A new route for the preparation of cyano‐containing poly(N‐isopropylacrylamide) microgel latex for specific immobilization of antibodies

A prepolymerization process was used to prepare functionalized poly(N‐isopropylacrylamide) latexes with surface cyano groups. The functionalized latexes prepared were characterized by FTIR, ¹H NMR, scanning electron microscopy and quasi‐elastic light scattering. In addition, the polymerization conversion and the water‐soluble polymer amounts were quantified. The polymerization conversions were found to be above 80% with 5–14 wt% of water soluble polymer formation. The immobilization of antibody (immunoglobulin) onto such cyano‐containing thermally sensitive particles, suggests the feasibility of specific dipole–dipole interactions between the cyano and hydroxyl functional groups from particle and antibody, respectively. Copyright © 2004 Society of Chemical Industry     

Aqueous Dispersion and Slip Casting of Boron Carbide Powder: Effect of pH and Oxygen Content

The effect of pH and oxygen content on the zeta potential, viscosity, and casting performance of fine (>3 μm) boron carbide powder is presented. X-ray photoelectron spectroscopy of the powder revealed a surface layer of adsorbed water and oxides of boron and carbon. The soluble boric acid impurity was removed by washing the powder with water or alcohols. Electrophoresis indicated that the B₄C surface was negatively charged in water above pH 1, but the presence of dissolved boric acid suppressed the zeta potential at high pH. Stable, low-viscosity dispersions of >30 vol% solids were prepared and slip cast at pH >6, but boric acid was destabilizing for dispersions prepared above pH 7. The green density of slip-cast parts was more reproducible and about 3% to 5% higher for washed powders than for high-oxygen-content powders.     

Colloidal Processing and Mechanical Properties of Whisker-Reinforced Mullite Matrix Composites

Aqueous colloidal suspensions in the two systems of CVD-processed ultrafine mullite powder (<0.1 μm), -Si₃N₄ whisker and -mullite whisker, were prepared near the isoelectric point of mullite (pH 7.0) to prevent cracking during drying of wet green compacts consolidated by filtration. The freeze-dried porous green compacts were hot-pressed with a carbon die at 1500°C for 1 h at a pressure of 39 MPa in N₂ atmosphere. The relative densities of the mullite matrix composites with whiskers of 0 to 10 vol% were in the range of 95.2% to 99.8%. Increasing the fraction of Si₃N₄ whisker increased the density, flexural strength, and fracture toughness of the hot-pressed composites. On the other hand, addition of the mullite whisker increased the fracture toughness but decreased the density and strength of the composites.     

Inverse Opal Scaffolds with an Embossed Surface Pattern Prepared from Sticky Golf‐Ball‐Shaped Microparticle Assemblies

Inverse opal scaffolds presenting an embossed‐pattern surface are prepared from colloidal crystal assemblies of uniformly sized golf‐ball‐shaped microparticles. Post‐treatments, such as thermal annealing during the bridging of the microparticles for opal preparation, are avoided to prevent deterioration of surface patterns of the sacrificial template. This presents a new approach to increase the surface‐area‐to‐volume ratio (SAV) by the alteration of morphological features in sophisticated 3D structures that remain largely unexamined owing to difficulties in their preparation. Previous results observed in 2D surfaces that show effective performance improvement through an increase in contact area, especially in biomedical applications, also appear applicable to patterned inverse opal scaffolds based on comparable results obtained from cell cultures. As the field of application of opal and inverse opal structures is expanding due to their unique structural advantages, such as 3D interconnectivity and periodic structures, our strategy opens the door for the use of patterned surfaces on highly sophisticated 3D structures, improving their performance via an increase in SAV.