Study of fluoride treatment of silica-containing raw material

An effect of ammonium hydrofluoride treatment of silica-containing raw material was examined. We described thermodynamics and kinetics of caking raw materials and their crushed materials, ammonium hexafluorosilicate sublimation, and amorphous silica formation. Constants of rate and activation energy of the chemical reactions were calculated.     

Characterization of Silica-Containing Aluminum Hydroxide and Oxide Aerogels

Pure and silica-containing Al hydroxide aerogels were prepared by the supercritical drying method. The samples were later calcined, giving rise to alumina and Si–Al mixed oxides. The materials were characterized from the points of view of their bulk and surface structures. The Si-free material before calcination is well-crystallized boehmite that converts to γ-alumina by calcination. The silica-containing hydroxides are composed of boehmite layers with silicates in the interlayer region. The resulting mixed oxides present silica essentially in the bulk. The surface structure of alumina seems poorly sensitive to silica addition. Surface silanol groups appear only for SiO₂more than 4%. No Brønsted acidity appears. Silica addition allows mixed oxides with higher surface areas to be obtained.     

含硅磷杂化物环氧树脂固化物性能研究

首先用γ-环氧丙氧基三甲氧基硅烷(KH-560)和亚磷酸二乙酯(DEP)反应的中间产物进行水解缩合反应,合成了一种含磷低聚硅氧烷杂化物.并用FTIR,NMR,GPC对其结构及分子量进行了表征.然后将含磷低聚硅氧烷引入到双酚A环氧树脂(E-54)制备硅磷杂化物环氧树脂的固化物.对这种含硅磷杂化物环氧树脂固化物的性能研究发现其极限氧指数为23～29,DSC分析结果玻璃化转变温度(Tg)可以达到204℃,失重5%的温度(Td)5%比纯E-54提高近20℃.该固化物具有阻燃性能,同时具有较好的热性能。     

State of silicon in silicate and silica-containing solutions and their binding properties

Relationship between the distribution of silicon atoms over connectivities in concentrated silicate and silica-containing alkaline solutions differing in chemical composition and preparation methods, on the one hand, and the binding properties of these solutions, on the other, was studied by ²⁹Si NMR spectroscopy.     

Heat-insulating material on the basis of silica-containing wastes formed in crude ore recovery in Kola Peninsula

The possibility was demonstrated for obtaining a heat-insulating material from silica-containing product formed in acid treatment of nepheline produced at the Open Joint Stock Company Apatit. Granular porous material based on silica fume was prepared. The heat conductivity of the bulk material was 0.075?C0.08 W m^?1 deg^?1.     

A study of the effect of nepheline acid processing conditions on structural-surface properties of silica products formed

A study of the physicochemical properties of silica products formed in acid processing of the nepheline concentrate is reported. It was found that amorphous silica produced in precipitation of silicon dioxide from solutions obtained in sulfuric acid decomposition of nepheline occupies an intermediate position between white carbon and silica gel, whereas silica produced from gelatinized silica-containing solutions close in properties to silica gel. The morphology of silicon dioxide samples formed by various methods was studied and a comparative analysis of their structural-surface properties was made.     

Adsorption Characteristics of Organic Dyes In Aqueous Solutions On Mixed-Oxide Gels. Silica-Containing Mixed-Oxide Gels

Abstract

Adsorption characteristics of four types of organic dyes in aqueous solutions on seven silica-containing mixed-oxide gels were investigated. C.I. Basic Red 18 was adsorbed well on all the gels. Silica-magnesia, which was prepared by the homogeneous precipitation, showed higher adsorptive ability for all the dyes than the other adsorbents.

It was proved from the examinations that the initial pH of dye solution, the composition of gel, and the precipitation method of gels affected the adsorptive ability.     

Effect of Trichoderma reesei Proteinases on the Affinity of an Inorganic-Binding Peptide

An inorganic-binding peptide sequence with high affinity to silica-containing materials was fused to a glycoside hydrolase GH26 mannanase, ManA, from the extremely thermophilic bacterium Dictyoglomus thermophilum. The resulting recombinant enzyme produced in Escherichia coli, ManA-Linker, displayed high binding affinity towards synthetic zeolite while retaining its catalytic activity at 80 °C. ManA-Linker was able to bind to the zeolite at different pH levels, indicating a true pH-independent binding. However, complete degradation of the peptide linker was observed when the recombinant ManA-Linker was exposed to the supernatant from the filamentous fungus Trichoderma reesei. This degradation was caused by extracellular proteinases produced by T. reesei during its growth phase. Several derivatives of ManA-Linker were designed and expressed in E. coli. All the derivatives carrying a single sequence of the linker were still susceptible to T. reesei proteinase degradation. Complete substitution of the linker sequence by (GGGGS)₁₆ resulted in a proteinase-resistant ManA derivative, ManA-Linker-(GGGGS)₁₆, which was able to bind to zeolite in a pH-dependent manner.     

Synthesis of Alumina and Silica-Containing Alumina Xerogel Hosts

Using the sol-gel process, we prepared two types of xerogels. Thin, transparent, crack-free alumina disks were prepared from aluminum tri-secondary butoxide (ASB). Addition of partially hydrolyzed tetraethylortho-silicate (TEOS) to such alumina sols produced translucent, warped silica-containing alumina xerogels. While the pure alumina xerogels were water soluble, addition of silica improved their durability. To understand the change in water solubility, we investigated the chemical and structural changes that occurred when silica was added. Characterization was performed using X-ray diffraction analysis, thermal analysis, nitrogen sorption analysis and ²⁷Al NMR spectroscopy.     

Growth behavior and kinetics of self-assembled silica-carbonate biomorphs

Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates--previously supposed to be involved in the growth mechanism--originate from secondary precipitation after growth is already terminated.     

Silica - Titania Support for HVOC's Combustion Catalysts

Preparation of support series for catalysts of combustion of halogenated volatile organic compounds (H-VOC's) was carried out. It was stated that all they allow preparing active catalysts however their main drawback is the lack of hardness against products of H-VOC's combustion e.g. hydrogen chloride and chlorine. Laboratory tests showed that titania and silica - titania supports were characterized by the highest hardness against chlorine derivatives. In comparison to the titania supports, low content (ca. 10 wt.%) silica-containing supports have better mechanical properties, i.e. mechanical strength and attrition resistance. In this paper the method of preparation, composition and physicochemical properties of silica - titania support are presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heterophase Polymerization as Synthetic Tool in Polymer Chemistry for Making Nanocomposites

Summary: The paper considers various possibilities to produce inorganic – polymeric nanocomposites via aqueous heterophase polymerization. Special emphasis is placed on strategies to synthesize nanocomposite particles via joint nucleation or joint polymerization. The former strategy is used to make composite particles with CaCO₃ as inorganic component. The strategy of joint polymerization takes advantage from the condition that aqueous heterophase polymerization is a convenient possibility to synthesize amphiphilic block copolymers. This method relies on the fact that polymeric radicals can survive in isolated latex particles that are stabilized by hydrophilic blocks. This strategy can be successfully applied to produce silica-containing block copolymer particles in a one-step procedure.     

Anchoring of polyacrylate onto silica and formation of polyacrylate/silica nanocomposite particles via in situ emulsion polymerization

Polyacrylate/silica nanocomposite latex particles were prepared by in situ emulsion polymerization of acrylate monomers initiated by 2,2′-azobis(2-amidinopropane)dihydrochloride (AIBA) adsorbed by silica nanoparticles. The anchoring of polyacrylate (ACR) onto silica nanoparticles was achieved through the physical absorption and chemical grafting reaction. The elution and HF etching experiments showed that most silica nanoparticles were encapsulated by ACR to form the raspberry-like ACR/silica nanocomposite latex particles. The silica nanoparticles with a greater grafting degree of ACR tended to locate in the bulk of the polymer, and the silica particle with a lower grafting degree would not be combined with polymer latex particles and always remained in water phase. The formation of the final ACR/silica nanocomposite latex particles included the anchoring of ACR onto silica primary particles, aggregation of silica primary particles to form the silica-containing latex particles, and the growth of latex particles.     

甲基丙烯酸甲酯/纳米SiO_2粒子分散液的细乳化和细乳液聚合

对包含纳米SiO2粒子的甲基丙烯酸甲酯(MMA)的细乳化和细乳液聚合行为进行了研究.发现在超声细乳化过程中,90%以上的分散于MMA相的纳米SiO2粒子将从油相逃逸到水相.采用甲基丙烯酸3-(三甲氧基甲硅烷基)丙酯(MPS)偶联剂处理SiO2粒子,可以增加其表面亲油性,抑止这种逃逸,经测定几乎全部SiO2粒子在超声细乳化后仍稳定停留在细乳化亚微液滴中.通过进一步细乳液聚合,得到了分散稳定、界面清晰的包裹有纳米SiO2粒子的聚甲基丙烯酸甲酯复合粒子乳液.     

Conversion of silica-containing additives upon testing of cement compositions for alkali expansion

The peculiar features of the conversion processes proceeding upon the mortar-bar tests [GOST(State Standard) 8269.0] of high-dispersion silica-containing additives (silica fume, metakaolin, and precipitated silica) in the composition of a cement stone and sand-cement mortars at 20 and 80°C were studied. According to the solid-state NMR spectroscopy at 80°C, the additives rapidly loss phase individuality by reacting with Ca(OH)₂ to form calcium silica hydrogel (C-S-H), with Portland cement hydration in the presence of mineral additives proceeding slower than in the initial stone. Compared to Portland cement gel, the C-S-H product formed by the additives is characterized by lower Ca/Si ratio, longer aluminum-silicon-oxygen structural chains, and by higher content of aluminum in them.     

Room-temperature decomposition of 2,2'-azobis(isobutyronitrile) in emulsion gels with and without silica

The decomposition of 2,2'-azobis(isobutyronitrile) (AIBN) at room temperature was studied in emulsion gels, with and without silica, using UV/visible spectroscopy. The emulsion gels consisted of toluene, AIBN, an aqueous solution of a surfactant (either hexadecyltrimethylammonium bromide, CTAB, or sodium dodecyl sulfate, SDS), and, in some cases, fumed silica. The AIBN compositions were determined in the opaque emulsion gels by converting them to transparent microemulsions. The decomposition rate constants for AIBN were determined to be 3.7 x 10(-8) s(-1) (+/-0.6 x 10(-8) s(-1)) for the emulsion gels and 10.2 x 10(-8) s(-1) (+/-1.3 x 10(-8) s(-1)) for the silica-containing emulsion gels. These rate constants were significantly greater than that in toluene solution, which, by our technique, is below our measurement threshold (effectively 0).     

In-vitro protein interactions with a bioactive gel-glass

Recent theories suggest that the local adsorption of biologically active peptide growth factors onto the surface of an implant may contribute to the unique osteogenic nature of silica-containing bioactive ceramics. A sol-gel derived glass is used as a model of the in-vivo reaction product of 45S5 bioactive glass at relatively short times (<48 hrs.) to investigate protein adsorption/desorption behavior. The adsorption kinetics of three heme-class proteins (cytochrome c, myoglobin, and hemoglobin) are measured spectroscopically. The rate of adsorption is shown to increase with average pore size, which is determined by the silica content of the gel. Adsorption rate decreases as protein size is increased and as solution pH is decreased. Biological function of an adsorbed peroxidase enzyme on pre-reacted Bioglass^® is shown to be retained. Desorption during physiologic conditions is shown to be linear with time and pH dependant, while independent of gel bioactivity.     

Development and Evaluation of a New Fluorinated Double-Wall Carbon Nanotube HPLC Stationary Phase

A novel column based on silica-containing immobilized fluorinated double-wall carbon nanotubes (F-DWCNTs) was developed. This F-DWCNT stationary phase was synthesized to combine the analytical performance of carbon nanotubes and the fluorine-based unique selectivity for polar compounds. First, the chromatographic support was coated with DWCNTs in a noncovalent way to preserve the sp² internal nanotube structure. Second, the DWCNT silica particles were functionalized with fluorine atoms via a solution of Br₂ and BrF₃ at room temperature. This F-DWCNT stationary phase was applied for a variety of separations. The solute retention behaviour was particularly studied under isocratic conditions with a high fraction of ACN in the ACN/water (v/v) mobile phase. The retention factors of the solute molecule do not depend linearly on the ACN fraction, but follow a quadratic relationship. This fluorinated stationary phase separated compounds based upon a combination of hydrophobic and polar selective stationary phase interactions. This F-DWCNT appeared to work best when fluorinated or halogenated compounds were encountered. They have longer retention time, better selectivity and work well with high fraction of organic modifiers. This novel stationary phase could thus be a good choice for LC–MS experiments.     

Electron energy loss spectroscopy (EELS) of iron Fischer-Tropsch catalysts.

Electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy have been used to study iron catalysts for Fischer-Tropsch synthesis. When silica-containing iron oxide precursors are activated in flowing CO, the iron phase segregates into iron carbide crystallites, leaving behind some unreduced iron oxide in an amorphous state coexisting with the silica binder. The iron carbide crystallites are found covered by characteristic amorphous carbonaceous surface layers. These amorphous species are difficult to analyze by traditional catalyst characterization techniques, which lack spatial resolution. Even a surface-sensitive technique such as XPS shows only broad carbon or iron peaks in these catalysts. As we show in this work, EELS allows us to distinguish three different carbonaceous species: reactive amorphous carbon, graphitic carbon, and carbidic carbon in the bulk of the iron carbide particles. The carbidic carbon K edge shows an intense "pi*" peak with an edge shift of about 1 eV to higher energy loss compared to that of the pi* of amorphous carbon film or graphitic carbon. EELS analysis of the oxygen K edge allows us to distinguish the amorphous unreduced iron phase from the silica binder, indicating these are two separate phases. These results shed light onto the complex phase transformations that accompany the activation of iron catalysts for Fischer-Tropsch synthesis.     

Cone calorimeter analysis of flame retardant poly (methyl methacrylate)-silica nanocomposites

Nanocomposite is a promising method to reduce fire hazards of polymers. Specifically due to increased interfacial area between polymer and nanofillers, polymer nanocomposites have an advantage in reducing fire hazards efficiently even when the flame retardant additives are at a concentration of 5 mass% or less. In theory, crosslinking between the polymer chains can create a carbon-dense structure to enhance char formation, which can further promote the flame retardancy. However, little research has been done to explore the flammability of crosslinking polymer nanocomposites with a low concentration of nanosilica particles. In this study, crosslinked and non-crosslinked poly (methyl methacrylate) (PMMA) nanocomposites of a low concentration of nanosilica particles have been prepared via an in situ method. Their fire properties were tested by using the cone calorimeter at the heat flux of 50 kW m^?2. Although silica-containing flame retardants tend to negatively affect the ignitability and soot production especially at a high concentration, through the condensed phase mechanism, the samples of high loading rate of nanosilica particles show better fire retardancy performance in the aspect of flammability, including decreased heat release rate, mass loss rate, and total heat release. Additionally, crosslinking indeed attributes to the less intensive combustion of crosslinked PMMA samples, especially at a low concentration of nanosilica. The combination of nanosilica particles with the modification of the internal structure of the polymer nanocomposites might be a good strategy to improve fire retardancy.