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.     

New generation of fire retardant polyester resins

Smoke evolution [in a smoke chamber (750 x 750 x 1000) ± 5 mm, Polish Standard PN-91/K-02501 equivalent to UIC 561-OR (1991)] was studied in, and the oxygen index flammability test (Polish Standard PN-76/C-89020) was carried out for, glass-reinforced polyester (GRP) laminates obtained with unsaturated polyester (UP) resins containing chlorine and bromine in the chain. In these studies, the effect on these properties of such additives as ZnSnO₃ (ZS), ZnSn(OH)₆ (ZHS), Al(OH)₃ or Mg(OH)₂ and Sb₂O₃ in an amount of up to 30 mass-% was determined. The most efficient ignition and smoke-evolution retarder from among the investigated compounds was ZS and ZHS, whereas an essential reduction in smoke evolution was observed also with Sb₂O₃. GRP laminates with these additives meet the fire-safety recommendations concerning smoke evolution from materials used in transportation means and in the building industry.     

Base Metal-terpyridine Complex Immobilized on Stationary Phase Aimed as Reusable Hydrosilylation Catalyst

The catalytic activity of a base metal-terpyridine complex immobilized on silica gel ( M(tpy)X₂@SiO₂/H₂O : M=Mn, Fe, Co, Ni, Cu; X=Cl, Br) for hydrosilylation was investigated. Co(tpy)Br₂@SiO₂/H₂O in the presence of NaBHEt₃ exhibited the highest catalytic activity for hydrosilylation of 1-octene with diphenylsilane (Ph₂SiH₂) to form the anti-Markovnikov-type hydrosilylation compound as the main product. The reusability of Co(tpy)Br₂@SiO₂/H₂O activated by NaBHEt₃ was examined. It was found that the catalytic activity decreased with repeated use because of the peeling off of the Co complex anchor portion from the silica gel surface upon the attack of NaBHEt₃. The introduction of Co(OAc)₂ instead of CoBr₂ to silica gel formed Co(tpy)(OAc)₂- and Co(tpy)(OH)₂-immobilized silica gel, which exhibited catalytic activity for the hydrosilylation in the absence of an activator such as NaBHEt₃. The glassware in which Co(tpy)(OH)₂ was immobilized on the inner wall was prepared. It was found that the hydrosilylation catalytically occurred on the surface of a pretreated glassware and that the catalytic activity did not decrease even after 10 repeated uses.     

Magnetic properties of composite materials based on plant- or mineral-derived amorphous silica

Fe _x (O, OH) _y –SiO₂ composite samples are prepared. The composite matrix is amorphous silica prepared by controlled precipitation from silicate solutions or silica derived from rice husks. The iron is shown to exist in the form of acagenite β-FeO(OH) or hematite α-Fe₂O₃. The magnetic properties of the composites are studied at temperatures in the range 2–300 K and fields in the range ±5 T. The composite samples exhibit superparamagnetic properties.     

Raman study of structural defects in SiO2 aerogels

The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups.The typical bands due to ring breathing also called defect bands D ₁ and D ₂ located at 490 and 610 cm^–1 are present. However, the evolution of the D ₂ band compared to that of OH band (980 cm^–1) seems apparently, in contradiction with the results previously reported in the literature. During heat treatments between 25 and 300°C the D ₂ and the OH bands increase simultaneously. Generally, in silica glass the defect band D ₂ grows at the expense of the OH groups.This result is explained by the oxidation of the organic compounds which, in this temperature range, leads to the formation of the both species (OH) and those related to siloxane rings. ²⁹Si MAS NMR results are in agreement with the Raman study.     

First application of the depth profile of silica species as a tracer by fast‐atom bombardment mass spectrometry: investigation of the circulation of seawater and silica uptake by diatoms

Silica, represented by SiO₂, is the general name for the compounds composed of Si, O and H with their derivative complexes. Silica forms various chemical species in aquatic solutions, such as a monomer (Si(OH)₃O⁻), dimer (Si₂(OH)₅O), and others. These species are known to vary in their relative abundances in solution depending on the chemical and physical conditions. Silica species dissolved in seawater have been examined by fast-atom bombardment mass spectrometry (FAB-MS) to elucidate the behavior of silica and its circulation as a novel tracer reflecting the chemical and physical conditions of seawater and the bioactivity of diatoms, which take up silica. In the seawater of Tokyo Bay, silica species such as [Si(OH)₂O₂Na]⁻ ([monomer–Na]⁻), [Si₂(OH)₅O₂]⁻ ([dimer]⁻), [Si₂(OH)₄O₃Na]⁻ ([dimer–Na]⁻), [Si₄(OH)₇O₅]⁻ ([cyclic tetramer]⁻), [Si₄(OH)₆O₆Na]⁻ ([cyclic tetramer–Na]⁻), [Si₄(OH)₉O₄]⁻ ([linear tetramer]⁻) and [Si₄(OH)₈O₅Na]⁻ ([linear tetramer–Na]⁻) were observed and assigned by FAB-MS. To investigate the suitability of silica species as a tracer, the relative peak intensity ratios of silica species observed in the mass spectra, i.e. the profiles of the ratio of the linear tetramer to the cyclic tetramer (m/z 329/311) and the ratio of the dimer to the cyclic tetramer (m/z 173/311) against depth, were examined to determine the annual changes and reproducibility of the depth profiles. In particular, the depth profile of the relative ratio of the linear tetramer to the cyclic tetramer, 329/311, exhibits critical changes depending on the seawater budget. These changes in the relative ratios were identified by an experiment involving a simple sodium chloride solution system. Our measurement is expected to elucidate the dynamics of silica and its role as ‘food’ for diatoms, and we showed that speciation using mass spectrometry is a powerful tool for examining elemental behavior in nature and environmental changes. Our results suggest that a silica tracer is useful for investigating the behavior of seawater in small coastal regions and the uptake of silica by diatoms. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal analysis and microstructure of Portland cement-fly ash-silica fume pastes

Thermal analysis (thermogravimetry and differential thermal analysis) was used with scanning electron microscopy technique to investigate the hydration mechanisms and the microstructure of Portland cement-Fly ash-silica fume mixes. Calcium silicate hydrate (C–S–H), ettringite, gehlenite hydrate (C₂ASH₈), calcium hydroxide (Ca(OH)₂) and calcium carbonate (CaCO₃) phases were detected in all mixes. In the mixes with the use of silica fume addition, there is a decrease in Ca(OH)₂ with increasing silica fume content at 5 and 10% compared to that of the reference Portland-fly ash cement paste and a corresponding increase in calcium silicate hydrate (C–S–H).     

Thermogravimetric studies of the tricalcium silicate hydration in the presence of solid additives

The calcium hydroxide content in the tricalcium silicate pastes hydrating with the amorphous silica and solid calcium hydroxide addition were determined using the TG method. The effect of the accelerated Ca(OH)₂ growth at the lower silica contents was proved. The significant hydration rate increase at higher silica contents was also confirmed.

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Zusammenfassung Unter Anwendung von TG wurde der Calciumhydroxidgehalt bei der Hydratation von Tricalciumsilikat mit Zusätzen von amorphem Siliziumdioxid und festem Calciumhydroxid ermittelt. Der Einfluß des beschleunigten Ca(OH)₂ Wachstumes bei niedrigeren Siliziumdioxidgehalten wurde erwiesen. Eine eindeutige Erhöhung der Hydratationsgeschwindigkeit bei höheren Siliziumdioxidgehalten wurde ebenfalls bestätigt.

     

Molecularly imprinted polymers on a silica surface for the adsorption of tobacco‐specific nitrosamines in mainstream cigarette smoke

Tobacco‐specific nitrosamines are one of the most important groups of carcinogens in tobacco products. Using adsorbents as filter additives is an effective way to reduce tobacco‐specific nitrosamines in cigarette smoke. Molecularly imprinted polymers (MIPs) using nicotinamide as template were grafted on the silica gel surface to obtain MIP@SiO₂ and employed as filter additives to absorb tobacco‐specific nitrosamines in mainstream cigarette smoke. Four milligrams of MIP@SiO₂ per cigarette was added to the interface between filter and tobacco rod to prepare a binary filter system. The mainstream smoke was collected on an industry‐standard Cambridge filter pad and extracted with ammonium acetate aqueous solution before analysis. Compared to the cigarette smoke of the control group, the levels of tobacco‐specific nitrosamines with silica gel and with MIP@SiO₂ were both reduced, and the adsorption rates of N‐nitrosonornicotine, N‐nitrosoanabasine, N‐nitrosoanatabine, and 4‐(methylnitrosamino)‐1‐(3‐pyridine)‐1‐butanone with silica gel and with MIP@SiO₂ were 20.76, 15.32, 18.79, and 18.01%, and 41.33, 34.04, 37.86, and 35.53%, respectively. Furthermore the content of total particle materials in cigarette smoke with silica gel was decreased evidently but showed no observable change with MIP@SiO₂. It indicated MIP@SiO₂ could selectively reduce tobacco‐specific nitrosamines in the mainstream cigarette smoke with no change to the cigarette flavor.     

Photocatalytic properties of [polymerized n-butyl-o-titanate + hydrogen peroxide] complex on the decomposition of water

The electronic structure of the [pol-Ti(OBu)₄ + H₂O₂] complex, which is formed during the photolysis of water over [pol-Ti(OBu)₄ + CH₃OH] complex on silica gel, is elucidated in detail from the photocatalytic standpoint by DV-Xα cluster calculations. The numerical results reveal the appearance of a localized state (active site) similar to that of the [pol-Ti(OBu)₄ + CH₃OH] complex. The [TiOBu)(OH)(OH)₄]²⁻ cluster, which substitutes a hydroxyl group for the (OOH) group, exhibits an electronic structure very close to that of the [Ti(OBu)(OMe)(OH)₄]²⁻ cluster (A₁ or A₂), which was studied previously. A reduction in photocatalytic activity for the water decomposition is discussed.     

Performance improvement of EPDM and EPDM/Silicone rubber composites using modified fumed silica,titanium dioxide and graphene additives

In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO₂) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO_2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.     

Solid-state Al and Si NMR characterization of hydrates formed in calcium aluminate-silica fume mixtures

Partially deuterated Ca₃Al₂(SiO₄)_y(OH)_12−4y-Al(OH)₃ mixtures, prepared by hydration of Ca₃Al₂O₆ (C₃A), Ca₁₂Al₁₄O₃₃ (C₁₂A₇) and CaAl₂O₄ (CA) phases in the presence of silica fume, have been characterized by ²⁹Si and ²⁷Al magic-angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca₃Al₂(OH)₁₂ and Al(OH)₃ phases were detected. From the quantitative analysis of ²⁷Al NMR signals, the Al(OH)₃/Ca₃Al₂(OH)₁₂ ratio was deduced. The incorporation of Si into the katoite structure, Ca₃Al₂(SiO₄)_3−x(OH)_4x, was followed by ²⁷Al and ²⁹Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of ²⁷Al MAS-NMR components associated with Al(OH)₆ and Al(OSi)(OH)₅ environments. The ²⁹Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C-S-H and C-A-S-H for short. From ²⁹Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures.     

Low-Temperature Synthesis of Nanosize Zn2SiO4:Mn2+ Phosphor from the Precursor Sol in Supercritical Ethanol and its Photoluminescent Properties

Acetylcellulose (AC)/silica and polyvinylpyrrolidone (PVP)/silica composites were prepared by the sol–gel method from Si(OCH₃)₄-AC-HNO₃-H₂O-tetrahydrofuran-CH₃OC₂H₄OH and Si(OCH₃)₄-PVP-(CH₃COOH or NH₃)-H₂O-CH₃OH-CH₃OC₂H₄OH solutions. AC/silica composites were composed of micrometer-sized particles rich in silica and a matrix rich in AC, while PVP/silica composites were single-phase on the SEM length scale. The AC/silica composites exhibited elastic-plastic behavior, and had excellent machinability without chipping on cutting with an electric saw while the PVP/silica composites showed less plasticity and machinability. Youngs modulus and bending strength were increased by post-drying, 1.8–2.8 GPa and 49–88 MPa, respectively, for the AC/silica composites, and 1.0–3.9 GPa and 17–79 MPa, respectively, for the PVP/silica composites.     

Preparation and stability of strongly luminescent CdSe/Cd(OH)<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> nanocomposite particles in aqueous solution

Cadmium hydroxide-deposited cadmium selenide nanoparticles were prepared by the addition of cadmium sulfate solution to cadmium selenide nanoparticles in a weak alkaline solution at room temperature. The photoluminescence measurements displayed that the luminescence intensity was greatly increased by the addition of cadmium ions due to the formation of cadmium hydroxide on the surfaces of the cadmium selenide nanoparticles. Then, CdSe/Cd(OH)₂/SiO₂ nanocomposite particles were synthesized using 3-mercatopropyl trimethoxysilane by Stöber method. After the formation of CdSe/Cd(OH)₂/SiO₂ nanocomposite particles, the emission ability was mostly stabilized. Additionally, the stabilization of the composite particles against dilution with the physiological saline was checked. The results showed that the photoluminescence stability was promoted after the deposition of silica on the surfaces of the CdSe/Cd(OH)₂ nanoparticles. Comparison of the stability of CdSe/SiO₂ nanoparticles with that of CdSe/Cd(OH)₂/SiO₂ ones showed that Cd(OH)₂ shell could enhance the photoluminescence effectively.     

Determination of the changes of the basic structures of silica species in dependence on the concentration of sodium chloride by FAB-MS

The chemical species of silica in NaCl solutions of different concentrations were identified by FAB-MS (fast atom bombardment mass spectrometry). The basic structures of silica species, such as cyclic pentamer (Si₅¶(OH)₉O₆ ^–), linear pentamer (Si₅(OH)₁₁O₅ ^–), cyclic hexamer (Si₆(OH)₉O₈ ^–, Si₆(OH)₁₁O₇ ^–) and linear hexamer (Si₆(OH)₁₄O₆ ^–), were identified, in addition to dimer (Si₂(OH)₅O₂ ^–), trimer (Si₃(OH)₇O₃ ^–) and cyclic tetramer (Si₄(OH)₇O₅ ^–). The patterns of changes of the peak intensities of the silicate complexes relative to the dimer with increasing NaCl concentration were classified into two types: that represented by linear silicate complexes and the other by cyclic silicate complexes. The differences in the type of chemical species and their changes according to the NaCl concentration reflect the number of bonds necessary for polymerization and hydrolysis of the silica complexes. The differences between the linear and the cyclic silicate type have some implications on the dissolution mechanism of silicate complexes, the hydration of the molecules and the equilibrium between solubility, hydrolysis, polymerization and the salting-out effect in NaCl solution.     

Effect of Chiral Additives in the Preparation of Cellulose-Based Chiral Stationary Phases in HPLC, and Effect on Enantiomer Resolution

Chiral stationary phases (CSPs) for high-performance liquid chromatographic (HPLC) have been prepared by coating silica gel with cellulose tribenzoate or cellulose trisphenylcarbamate. The effect of chiral additives on preparation of the CSPs was studied with (+)-l-mandelic acid, (−)-2-phenyl-1-propanol, (+)-1-phenyl-1,2-ethanediol and (−)-1-(1-naphthyl)ethanol as chiral additives for cellulose tribenzoate and (−)-2-phenyl-1-propanol and (+)-phenylsuccinic acid as chiral additives for cellulose trisphenylcarbamate. The results showed that chiral recognition by these stationary phases was increased in comparison with the original CSPs, especially the resolution (R _S) obtained. The method can be used to improve the efficiency of enantiomer separation by silica gel stationary phases coated with polymers.     

Decay of H<Subscript>2</Subscript>O<Subscript>2</Subscript> under the action of the colloidal catalyst based on iron(III) oxides in a neutral medium

The catalytic activity of the colloidal catalyst based on iron(III) hydroxide was studied in the decomposition of H₂O₂ in a neutral medium (pH 6.7). A colloidal micellar solution of iron(III) hydroxide after preparation was kept at 19–20 °С for 2 or 20 h without additives or with C₂H₅OH additives. The decomposition of H₂O₂ under the action of the colloidal catalyst (20 h) proceeds via the first-order reaction with the decay rate constant k_d = 1.26?10^–4 s^–1, whereas the decay rate of the first-order reaction is k_d = 0.77?10^–4 s^–1 for the colloidal catalyst (2 h) prepared in the presence of C₂H₅OH.     

TG-MS analysis of nitrile butadiene rubber blends (NBR/PVC)

Blends of nitrile butadiene rubber (NBR) with polyvinyl chloride (PVC) are widely used in products such as hoses and seals. As part of a project that uses NBR/PVC blends for manufacturing forest fire hoses, blends of NBR/PVC with various inorganic fillers, such as Mg(OH)₂, china clay (organic modified kaolin) and nano clay (organic modified bentonite) were studied by TG-MS. No significant changes were observed to the type of the polymers’ decomposition products, compared to that of NBR/PVC blend without additives. The most remarkable change was the absence of HCl from decomposition products in the presence of the Mg(OH)₂ additive.     

Formation of variable-composition iron(III) hydrosilicates with the сhrysotile structure

The process of formation of iron hydrosilicates (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was studied. It was shown that the stage of coprecipitation of magnesium and iron hydroxides in the presence of silica nanoparticles forms poorly crystallized layered Mg–Fe double hydroxides having Fe³⁺ ions in the octahedral sites. Hydrothermal treatment of the mixtures of coprecipitated hydroxides and silica nanoparticles gives rise to layered hydrosilicates, where Fe³⁺ ions occupy both the octahedral (preferentially) and tetrahedral sires. The possibility of the formation and a fairly stable existence of the variable-composition layered hydrosilicate (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was shown to correlate with the stability range of its precursor brucite-like Mg–Fe layered double hydroxide.     

Unconventional Assembly of Bimetallic Au–Ni Janus Nanoparticles on Chemically Modified Silica Spheres

This paper reports that Janus Au?Ni nanoparticles (JANNPs) can self‐assemble onto silica spheres in a novel way, which is different from that of single‐component isotropic nanoparticles. JANNPs modified with octadecylamine (ODA) assemble onto catechol‐modified silica spheres (SiO₂?OH) to form a very special core–loop complex structure and finally the core–loop assemblies link each other to form large assemblies through capillary force and the hydrophobic interaction of the alkyl chains of ODA. The nanocomposites disassemble in the presence of vanillin and oleic acid because of the breakage of the catechol–metal link. Vanillin‐induced disassembly enables the JANNPs to reassemble into a core–loop structure upon ODA addition. The assembly of SiO₂?OH and isotropic Ni or Fe₃O₄ particles generates traditional core–satellite structures. This unconventional self‐assembly can be attributed to the synergistic effect of Janus specificity and capillary force, which is also confirmed by the assembly of thiol‐terminated silica spheres (SH?SiO₂) with anisotropic JANNPs, isotropic Au, and Ni nanoparticles. These results can guide the development of novel composite materials using Janus nanoparticles as the primary building blocks.