Effect of admicellar properties on adsolubilization: column studies and solute transport

Mixtures of anionic and cationic surfactants exhibit synergistic behavior as evidenced by low critical micelle concentrations (CMC) of the mixed system, increased surface activity, and improved detergency performance. The adsorption of a single-head anionic surfactant, sodium dodecyl sulfate (SDS), in mixture with a twin-head cationic surfactant, pentamethyl-octadecyl-1,3-propane diammonium dichloride (PODD), showed synergism of adsorption onto silica when present at a mixing ratio of 1:3 (cationic-rich), and also demonstrated lower surfactant desorption with water flushing of columns packed with the surfactant-modified media. In addition, the proportion of the mixed surfactants in the admicelles moved from the initial ratio of 1:3 towards equimolar after rinsing the surfactant-modified silica absorbent. The retardation of organic solutes passing through columns packed with modified-silica adsorbent increased nominally three fold for silica modified with mixed surfactants versus single surfactants (retardation factors increase from 4.0 to 12.8 for styrene and from 32.1 to 90.2 for ethylcyclohexane for single and mixed surfactants, respectively). Thus, this study demonstrates that mixed surfactant systems more effectively modified the silica surface than single surfactant systems both in terms of enhanced retardation of organic solutes and in terms of reduced surfactant desorption.     

Effect of Multifunctional Additive on Filler Dispersion in Carbon-Black- and Silica-Filled Natural Rubber Compounds

The effect of multifunctional additive (MFA) on filler dispersion in carbon-black- (CB) and silica-filled natural rubber (NR) compounds has been studied. Silica dispersion, measured by computer-aided image analysis and scanning electron microscopy (SEM), showed a substantial improvement when MFA concentration is increased from 1 to 3 phr. After this level, there is a further but small improvement. However, for CB-filled NR compounds, CB dispersion showed a substantial improvement when the MFA used between 0 and 1 phr. As in silica-Filled NR compounds, there is only a small improvement in dispersion after 1 phr.     

石英陶瓷色斑污染原因分析及解决措施

研究了石英陶瓷在生产过程中出现的一种蓝色色斑．分析和验证了石英陶瓷内表面蓝包色斑产生的原因和机理．并提出了解决色斑问题的技术途径和措施。研究了蓝包色斑对石英陶瓷电性能的影响．准确评价了色斑对石英陶瓷性能的影响规律及影响程度．彻底解决了石英陶瓷色斑污染的问题。     

亚微米4A分子筛的合成与表征

以云南云天化国际股份有限公司的磷肥副产物硅胶湿样为基础原料,补加铝酸钙,水热法制备亚微米4A分子筛.采用XRD、SEM和FT-IR等分析手段对产品进行了表征.结果表明采用水热法制备的产品结晶度为95%,形状规则、大小均匀,分布范围较窄;粒度较小、粒度≤1μm的可达到100%;钙离子交换容量为336 mgCaCO3/g(干基)4A分子筛,白度为95%,完全满足洗涤助剂的要求.     

Investigation of MOSFET operation in bipolar mode

The work is concerned with the properties of conventional MOSFET in bipolar mode of operation. It is shown that the base current can provide useful information about interface trap density at the Si–SiO₂ interface. The new device characteristics are found promising for use in low-voltage low-power logic circuits.     

Kinetics and mechanism of low-temperature ozone decomposition by Co-ions adsorbed on silica

Kinetics and mechanism of low-temperature ozone ((5–50) × 10⁻³ mol/m³ in the gas–air mixture) decomposition by Co-catalysts supported on silica have been studied. Co-ions adsorbed on silica react with surface oxygen species, thus resulting in an active catalyst. Low concentrations of Co-ions form a monolayer on the surface. Their specific catalytic activity remained constant, but sharply decreased at higher concentrations due to a formation of polynuclear Co-complexes. Ozone decomposition may occur either as a stoichiometric or catalytic process, depending on the ozone and catalyst concentrations. The turnover number increases with ozone concentration reaching a saturation point. It also increases with Co-concentration in the beginning, but drops at a concentration >1 × 10⁻⁴ mol/g. The mechanism of the reaction is discussed.     

Behaviour of silicon released during alteration of nuclear waste glass in compacted clay

Long term integrated in situ experiments are performed in the HADES underground research facility (Mol, Belgium) in order to study the coupled reactivity between the different components of an underground repository for vitrified high level radioactive waste (HLW): glass, compacted clay, and stainless steel containers, at 90 °C and under gamma irradiation. Studies pertaining to the behaviour of silicon, a major element released during glass alteration, are presented here. Data collected from the integrated experiment, from simplified tests, and from modelling are put together, giving complementary information. The integrated experiment is used to investigate overall reactivity, whereas diffusion experiments coupled with modelling focused on the precipitation of silica in clay media. In the integrated in situ experiment, a bentonite clay (FoCa7) mixed with 5 wt.% of powdered glass frit was put in contact with U/Th-doped SON68 reference glass specimens for 1.2 years. One of the samples was thoroughly analysed by ESEM, SEM-EDS, TEM, XRD, and FTIR. The observations showed that after combined heating and γ irradiation, the glass/clay interface is still fully reactive. At this interface, the most important process occurring is silica precipitation either as spherical flaky nodules, or in the form of coatings on the clay surface, as chalcedony and amorphous silica. In parallel, numerical modelling was used to investigate the interactions between silica and clay material in a simplified experiment using diffusion cells. A fit between calculation results and silica migration measurements in diffusion cells was performed, including sensitivity tests with regard to the diffusion coefficients and the precipitation rate of amorphous silica. A satisfactory agreement is reached with the experimental results, using a set of reasonable fitting parameters for the FoCa7 clay material. Surface area values for silica precipitation are found to be very high, i.e. 2% of the total surface area of the clayey material indicating that silica precipitation occurs on surfaces other than those of pure silica minerals.     

Binding of externally supplied chlorides in micro silica concrete under field exposure conditions

Chloride binding has remarkable influence on the chloride penetration and hence, on the time to corrosion initiation in reinforced concrete structures. Previous studies have mainly looked at the chloride binding from internal sources in laboratory, which is not representative of practical situations. The current work focuses on the chloride binding characteristics of concrete samples exposed to an external source of chlorides from the sea water at Persian Gulf region. Some of the important parameters including w/c ratio, silica fume replacement and effect of chloride concentration on chloride binding were investigated in order to provide insight into the distribution of free and bound chloride ions after a long-term exposure.The results of the current study suggest that the chloride binding capacity increases with increasing the w/c ratio and chloride concentration but decreases by using silica fume. A general equation was also developed correlating the total and bound chloride in order to obtain more accurate service life prediction.     

Viscous and elastic properties of poly(methyl methacrylate) melts filled with silica nanoparticles

In this paper it is shown that elastic properties of a poly(methyl methacrylate) melt in the linear range of deformation are more significantly influenced by the addition of silica nanoparticles than viscous ones. The effect is the strongest in the steady-state which is reached at several thousand seconds. That is the reason why the often used dynamic-mechanical experiments are not a very suitable method for investigations of that kind. Therefore, creep and creep-recovery tests were applied for the characterisation of the filled materials. The linear steady-state recoverable compliances following from the recovery experiments increase by a factor of 6 at the highest measured volume content of 2.1%. This finding is explained by the existence of long retardation times in the filled materials resulting from interactions between the fillers and matrix molecules attached to their surfaces which reduce their molecular mobility. Retardation spectra calculated from the recovery curves quantify these assumptions. The model is supported by the experimental finding that the recoverable compliance becomes smaller above a certain stress applied and approaches that of the matrix as such a behaviour could be explained by a detachment of the molecules from the particle surface. The paper demonstrates that investigations of elastic properties of nanoparticle filled polymers in the molten state at long experimental times are a very sensitive tool to get an insight into interactions between particles and macromolecules of such systems.