微波水热法合成硅酸钇纳米晶

以硝酸钇、硅酸钠和氢氧化钠为主要原料,采用一种新方法-微波水热法可控合成了硅酸钇纳米晶.研究了起始溶液配比,合成温度及退火温度对硅酸钇的影响.采用X射线衍射仪(XRD)和透射电子显微镜(TEM)对粉体进行了表征.结果表明:随着合成温度的升高,Y_2SiO_5的含量增加.低温退火处理有助于提高硅酸钇微晶的结晶程度.选不同配比的溶液体系,经微波水热150 ℃作用10 min后,得到的前驱体于900 ℃下保温2 h,最终可获颗粒尺寸分别为400~600 nm、200~400 nm和400~600 nm的Y_2SiO_5、Y_(4.67)(SiO_4)_3O和Y_2Si_2O_7三种晶型的纳米晶,且其晶型最佳.     

Zusammenhänge zwischen Struktur und Ladungstransport verschiedener Silbersilicate

On Relations between Structural and Electrochemical Properties of Various Silver Silicates The structures of the explored silver silicates are dominated by anionic lattice, within the Ag⁺ iones are able to move and transport electrical charge. This transport is disturbed mainly by the grain boundaries. Impedance spectroscopic measurements verify this matter because of the capacitance related to the single spectra.     

Organically modified xerogels as supports for solid-phase chemistry

Organically modified xerogels (OMX_NH2) can be used as an easy to handle and chemically stable support in solid-phase chemistry and are compatible with enzymatic transformations.     

The thermochemical reactivity of silicate minerals in hydrogen and methane

The thermochemical reduction of transition metal silicates, i.e. garnierite (Ni,Mg)₆[(OH)₈(Si₂O₇)], chrysocolla (Cu,Al)₂H₂Si₂O₅(OH₄)·nH₂O, dioptase CuSiO₃·H₂O, willemite Zn₂SiO₄, and hemimorphite Zn₄Si₂O₇(OH)₂·H₂O has been studied. By means of combined thermogravimetric/mass spectrometric measurements, X-ray diffraction and analytical scanning electron microscopy it is shown that in a 5% H₂/95% N₂ or in a methane atmosphere the transition metals are selectively reduced at temperatures qualitatively corresponding to their electrochemical potential. Mixtures of elemental transition metals and quartz, SiO₂, are obtained as solid products. Depending on the nature of the parent mineral, different mixtures of volatile products are obtained. Principal volatile product, however, is water vapour. The reduction in methane leads to the formation of syngas.The authors acknowledge the financial support of the Schweizerisches Bundesamt für Energiewirtschaft as well as the Fonds der Chemischen Industrie.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Polyurethane‐nanocomposite materials via in situ polymerization into organoclay interlayers

New nanocomposite materials based on polyurethane intercalated into organoclay layers have been synthesized via in situ polymerization. The syntheses of polyurethane–organoclay hybrid films were carried out by swelling the organoclay [12‐aminododecanoic acid montmorillonite] into different kinds of diols followed by addition of diisocyanate then casting in a film. The homogeneous dispersion of MMT in the polymer matrix is evidenced by scanning electron microscope and x‐ray diffraction, which showed the disappearance of the peak characteristic to d₀₀₁ spacing. It was found that the presence of organoclay has improved the thermal, solvent resistance and mechanical properties. Also, the tensile strength is increased with increasing the organoclay contents to 20% by the ratio 182% related to the PU with 0% organoclay. On the contrary, the elongation has decreased with increasing the organoclay contents. Copyright © 2007 John Wiley & Sons, Ltd.     

聚合物/层状硅酸盐纳米复合材料的性能

取合物／层状硅酸盐纳米复合材料是近十年发展起来的一类新型材料，即使硅酸盐纳米填料的含量很低，一般在5％（wt）以下，就使该类材料具有许多优良的性能，如杨氏模量，储能模量，热稳定性，气体阻隔性及阻燃性等均有较大的提高。本文综述了该类材料的性能。     

Biocatalytic Gelation of Silica in the Presence of a Lipase

The effect of the lipase from Burkholderia cepacia (previously known as Pseudomonas cepacia) on the gelation kinetics and gel structure was examined on a type of silica aerogel made from a mixture of methyltrimethoxysilane and tetramethoxysilane. For this purpose, gels were made with increasing concentrations of lipase in otherwise constant other conditions (pH, water and Si precursors concentrations). It was found that the enzyme accelerated the gelation kinetics, hence was participating in some way to the hydrolysis of the silica precursor. The structure of the gel was simultaneously modified to produce an increasing proportion of Q⁴ silicon sites.     

Strain-eliminating chemical bonding self-organizations within intermediate phase (IP) windows in chalcogenide, oxide and nitride non-crystalline bulk glasses and deposited thin film binary, ternary and quaternary alloys

Transitions into, and out of intermediate phases (IPs) with minimal strain have been identified to date by Boolchand and co-workers, in bulk glasses, primarily by the extraordinary low values of the change in enthalpy, ΔH_nr, associated with non-reversible heat flow, and by Lucovsky and coworkers in deposited thin films, and at dielectric–semiconductor interfaces by combining spectrographic characterizations, primarily synchrotron X-ray absorption and X-ray photoemission, and electrical measurements. This paper emphasizes chemical bonding self-organizations that minimize macroscopic strain within the IP windows, and identifies for the first time the necessary and sufficient conditions for IP windows to open, and to close, as a function of changes in the alloy composition. Percolation theory, and in particular competitive and synergistic double percolation provide a quantification of IP window first and second transition compositions that account for many of the experimentally determined IP window threshold transitions and IP window widths identified to date.