Seasonal Dynamics of Amorphous Silica in Vantaa River Estuary

In order to understand the importance of amorphous silica (ASi) in transport of bio-reactive Si from catchment areas to the seas in northern anthropogenically influenced catchments, we investigated the seasonal evolution of ASi concentrations and load patterns together with environmental variables along the Vantaa River estuary in southern Finland during one year. A clear seasonal variation was observed in the ASi dynamics of the river with highest loads during spring, when 79% of the yearly ASi load was discharged. The main reason for this appeared to be the high discharge of the river and concomitant high load of ASi. About 38% of the annual bio-reactive Si load of the river consisted of ASi. The ASi concentration in the river varied from 11 to 192  $\upmu $ mol L. About 3% of the ASi load accumulated in the sediments of the estuary. The role of ASi in the riverine transport of bio-reactive can be very important in northern agricultural catchments and phytoliths probably play a significant role in the transport of ASi from catchment areas to the sea.     

The Vegetation Silica Pool in a Developing Tidal Freshwater Marsh

Tidal marshes play an important role in the estuarine Si cycle. Dissolved silicon (DSi) is taken up by marsh diatom communities and by tidal marsh vegetation. Delivery of DSi back to the estuary after biogenic silica dissolution potentially increases the resilience of the estuary against harmful effects of DSi depletion events. Tidal freshwater marsh vegetation, often dominated by reed (Phragmites australis) has previously been hypothesized to contribute to the Si buffering function of tidal marshes, by dissolution of reed biogenic Si (BSi) into the soil pore water and consequent seepage of DSi to the estuary. In this study the Si pool in the vegetation of a restored tidal freshwater marsh was quantified using species-based cover-biomass relationships and Si analyses. The Si pool in the aboveground biomass increased from 1.2 to 6.5 t km^?2 during the first 6 years of colonization by tidal freshwater marsh species. Our results indicate that young tidal freshwater marshes have a high potential to build up a large vegetation Si pool quickly, mostly due to colonization by species that have both high Si concentrations and high biomass production (e. g. P. australis). This Si pool in vegetation could act both as a long-term sink for Si along estuaries (should Si remain buried in the sediments) or as a short-term source for DSi (should Si be dissolved to DSi).     

Ab initio Molecular Dynamics Simulations of the Hydroxylation of Nanoporous Silica

Accurate information on the interactions between water and silica is critical to the understanding of its properties including mechanical strength under stress and long‐term chemical durability of silica and silicate glasses. In this study, interactions between water and nanoporous amorphous silica models were investigated using density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations which accurately describe bond breakage and formation as well as chemical reactions. AIMD simulations up to 30 ps were performed for systems containing water and nanoporous silica with a wide range of porosities (31%–67%). Partial removal of defects, such as two‐membered rings, was observed during the AIMD runs whereas more reactive coordination defects were removed during the initial geometry optimization. The limited two‐membered ring removal can be attributed to restricted water‐defect movement or the increased stability of rings located on concave surfaces. Two‐membered ring removal mechanisms included the formation of an overcoordinated silicon (Si⁵) intermediate defect from the dynamic simulations. Si⁵ defects continued to develop throughout the simulations, indicating a thermodynamic drive for two‐membered ring removal which is kinetically limited. Changes in the electronic structures, such as atomic charges, and bond length‐bond angle correlation functions were monitored during the hydroxylation process.     

Molecular Dynamics Simulation of the Structure and Hydroxylation of Silica Glass Surfaces

The surface structure of silica glasses has been simulated using molecular dynamics. The surface hydroxyl concentration was estimated to be 4.5/nm², based on surface defect statistics. Hydroxyl-silica potentials were developed and used to study the hydroxylation of silica surface. It is found that the energy of chemisorption of water declines in the sequence: three coordinated silicon (Si³) and non-bridging oxygen (NBO) on separate sites, Si³ and NBO on combined sites, two- and three-membered rings. Partial hydroxylation of the most reactive sites, which leads to an OH coverage of 2.5/nm², was studied. Structural relaxation after hydroxylation was observed.     

Molecular Dynamics Simulations of the Structure and Properties of Low Silica Yttrium Aluminosilicate Glasses

Yttrium aluminosilicate glasses are of technological importance in photonics, nuclear waste disposal, and as a delivery vehicle for radiation therapy. Their structures are also of great interest in glass science to elucidate the principles of glass formation and structures. We provide classical molecular dynamics simulation results of a series of yttrium aluminosilicate glasses with low silica concentration. Detailed structure analyses including coordination number, pair and bond angle distributions, Si–O and Al–O network structures, and primitive ring statistics are reported. It is found that the average aluminum coordination number decreases from 4.7 to 4.2 with increasing silica content from 5 to 20 mol%, while maintaining alumina at 55 mol%. Four-coordinated aluminum ions increase from 40% to 84% in the series and the fraction of edge-sharing alumino-oxygen polyhedra decreases, indicating an increased network former role of aluminum ions with increasing silica content. Physical properties such as elastic constant, bulk modulus, Young's modulus, and Possion's ratio were calculated. The results show a decrease of bulk, Young's, and shear moduli with increasing silica and decreasing yttria contents that is in good agreement with experimental data.     

SBA-15分子筛形成过程的介观动力学模拟及实验研究

为了研究三嵌段共聚物的自组装过程和SBA-15的形成机理,采用介观动力学(MesoDyn)方法模拟介孔分子筛SBA-15形成过程中模板剂P123与硅源试剂TEOS的协同自组装过程,并通过向体系引入稳恒剪切力来代替实际外力模拟了SBA-15六角介观相的形成过程,直观地展现了P123/硅酸物种超分子聚集体在SBA-15结构形成过程中的作用。模拟结果表明,P123与TEOS在水溶液中通过协同作用能够自组装形成尺寸均一的球状超分子聚集体,这是硅基有序介孔分子筛SBA-15形成过程中的前驱体:疏水的PPO嵌段团缩在该超分子聚集体的内部,在SBA-15分子筛形成中起决定性的致孔作用;亲水的PEO嵌段与包裹在胶束外部的TEOS相互交织在一起,其使得SBA-15在制备后期脱除模板剂后形成一些与主介孔相互连接的无规则微孔。在引入剪切力作用后,该P123/TEOS超分子聚集体不再自组装形成球状胶束,而是被拉扯成圆柱状的胶束,并且最终排列成为具有规则的六角形状的聚集结构,这一六角介观相则是介孔分子筛SBA-15的结构基础。今采用模拟条件,用水热法合成了高质量的SBA-15分子筛,通过XRD和高分辨透射电镜分析表明,模拟SBA-15形成过程的结果与实验合成的SBA-15具有相互吻合的完美二维六方结构。     

SiC模具高温模压石英玻璃物相接触角的分子动力学模拟

针对高温下石英玻璃纳米液滴在SiC模具表面接触角难以测量的问题,采用分子动力学方法,模拟研究了不同温度和粗糙表面面向模压的SiO2/SiC高温接触角以及SiO2熔体的界面结构.应用压力张量法发现了MS-Q势函数模拟的SiO2熔体表面张力较接近实际值,即SiO2高温表面特性模拟可优先采用MS-Q势函数.针对SiC模具纳米级表面的粗糙度,发现当粗糙度因子r>1.5时润湿模式由Wenzel变为Cassie-Baxter,此时Ra的变化对接触角值无明显影响,Rmr值减小使得接触面积分数f减小,接触角值随之增大.因此,保持r大于1.5的同时适当减小Rmr值有利于减小固液摩擦,降低石英玻璃工件和SiC模具界面上的脱模力.随着温度升高SiO2表面结构变得松散,导致其在SiC表面接触角减小.在超过2300K时接触角值的变化率增大,为减小工件-模具界面的粘附,模压温度应选择2300K以下.     

Self-Diffusion in Confined Water: A Comparison between the Dynamics of Supercooled Water in Hydrophobic Carbon Nanotubes and Hydrophilic Porous Silica

Confined liquids are model systems for the study of the metastable supercooled state, especially for bulk water, in which the onset of crystallization below 230 K hinders the application of experimental techniques. Nevertheless, in addition to suppressing crystallization, confinement at the nanoscale drastically alters the properties of water. Evidently, the behavior of confined water depends critically on the nature of the confining environment and the interactions of confined water molecules with the confining matrix. A comparative study of the dynamics of water under hydrophobic and hydrophilic confinement could therefore help to clarify the underlying interactions. As we demonstrate in this work using a few representative results from the relevant literature, the accurate assessment of the translational mobility of water molecules, especially in the supercooled state, can unmistakably distinguish between the hydrophilic and hydrophobic nature of the confining environments. Among the numerous experimental methods currently available, we selected nuclear magnetic resonance (NMR) in a field gradient, which directly measures the macroscopic translational self-diffusion coefficient, and quasi-elastic neutron scattering (QENS), which can determine the microscopic translational dynamics of the water molecules. Dielectric relaxation, which probes the re-orientational degrees of freedom, are also discussed.     

不含锌白炭黑分散剂在白炭黑填充胶料中的应用

研究了不含锌白炭黑分散剂对白炭黑填充胶料性能的影响。结果表明：白炭黑分散剂FNS-924不含锌,主要成分为脂肪酸和酯类的混合物;随着白炭黑分散剂FNS-924用量的增大,混炼胶流动性提高,加工性能改善;随着白炭黑分散剂FNS-924用量的增大,白炭黑分散性改善,硫化胶的硬度、定伸应力和拉伸强度降低,拉断伸长率提高,滚动阻力和生热降低。     

二氧化硅种子在硅溶胶粒径增长中的行为研究

文章描述了粒子在利用单质硅粉制备硅溶胶反应中的一般生长过程,分析表明采用种子生长法制备可控粒径的硅溶胶,其关键是通过反应条件的控制促使种子生长并抑制次生粒子的形成,通过次生粒子的定量计算可反映出体系的粒径分布情况。实验发现当二氧化硅种子浓度为1．5wt％时对硅溶胶粒径增长最为有利。同时利用水溶液中二氧化硅粒子的核／壳模型对种子生长过程的行为做出了合理解释。     

Indentation Behavior of Soda-Lime Silica Glass, Fused Silica, and Single-Crystal Quartz at Liquid Nitrogen Temperature

In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K. The hardness of all three materials increases by a factor of ∼2.5 on cooling to liquid nitrogen temperature. High-magnification SEM photographs revealed that the deformation and cracking patterns of the glasses changed strikingly: no shear lines were observed within the indentations, and ring cracking occurred instead of radial/median cracking. In addition, cracking occurs at much higher loads than at room temperature. The hardness results have been explained in terms of volume flow (densification) rather than shear flow (viscous or plastic) for the glasses at low temperature. The quartz crystal, on the other hand, deformed plastically at both room temperature and 77 K. Cracking differences result from changes in both flow and water activity     

Strength, Degradation, and Coating of Silica Lightguides

Silica and germania–silica glasses are most appropriate for use in making lightguide fibers because of their special optical and mechanical properties. They can be prepared easily in a highly pure state and thus exhibit very low optical absorption losses. In addition, because of their high bond strength and complete three-dimensional bonding, they have a very high theoretical (and practical) mechanical strength. The two most serious drawbacks from a mechanical point of view are brittleness and reactivity with water. Their brittleness allows them to be easily damaged, while their reactivity with water gives rise to stress-accelerated reaction or inhomogeneous corrosion in the presence (fatigue) and absence (aging) of stress. By the development of suitable polymeric and metallic coatings, both problems can be largely overcome.     

Influence of Mesoporous Silica and Butyral Content on the Mechanical,Water Absorption,and Permeability Properties of in situ Synthesized Silica/PVB Nanocomposite Films

Poly(vinyl butyral)–silica nanocomposites were synthesized in situ with three different degrees of butyral and with varying silica content for each vinyl butyral polymer ratio. The glass transition temperatures of the polymer nanocomposites were found to be ～40–46 and ～52°C for the neat polymer, respectively. The 4 wt% silica loaded film showed higher strength and lower strain to failure compared with the neat polymer. The matrix with 0.5 and 0.75 butyral:alcohol for 2.5–4 wt% silica exhibited good water vapor transmission and the efficiencies of these films were 50% higher than their encapsulated pristine polymer films.     

Tidal turbines harness the power of the sea

Just as there were once 10?000 windmills across Europe, countless water mills helped power the rural economy and then the industrial revolution. And, just as reinforced plastics have supported the 21st century reincarnation of windmills as wind turbines, so they are beginning to contribute to the next likely large-scale commercial renewable energy source - water current power. George Marsh reports.     

成核阶段对沉淀法白炭黑团聚程度的影响

白炭黑制备过程中发生的团聚会影响其分散性,研究影响白炭黑制备过程中团聚程度的主要因素有助于制备高分散的白炭黑。本文采用正交实验法研究了沉淀法白炭黑制备过程中成核阶段各个因素对白炭黑团聚程度的影响,采用透射电镜表征白炭黑一次粒子大小和团聚程度,采用激光粒度仪表征白炭黑的平均粒径。结果表明,反应温度、硅酸钠浓度及加酸速度是影响白炭黑二次粒子平均粒径及团聚程度的主要因素;高温下,白炭黑一次粒子约为50 nm,团聚程度较高,但二次粒子平均粒径较小;低温下,白炭黑一次粒子约为10 nm,团聚程度略小。随着低温反应时间的增长,白炭黑一次粒子团聚程度增加。     

硅溶胶的性质、制法及应用

硅溶胶(silicasol)是二氧化硅胶体微粒在水中均匀扩散形成的胶体溶液,具有许多优良性质和特点,作为一种精细化工产品,被广泛应用于化工、材料、纺织、造纸、电子等工业。概括介绍硅溶胶的种类、特性、制造工艺及其主要应用,并对其制造及应用前景进行了展望。