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PubMed1999

Adsorptive Deformation of Organo-Substituted Laminar Silicates.

Deformations of organo-substituted laminar silicates (Pyzhevsk montmorillonite and synthetic fluorohectorite) upon water, hexane, and benzene vapor sorption have been studied. To solve this problem a dilatometer was used. Its main part was a line differential transformer, the core of which was connected to the sorbent by means of a rod. Any changes of the sorbent height caused a change in the core position in the transformer, which influenced the signal recorded from its secondary winding. The calibrated dilatometer was located in a liquid thermostat with a given temperature and was connected with the measurement unit (frequency meter, voltmeter, generator). Montmorillonite and synthetic fluorohectorite were modified by cetylpyridinium bromide and used in the form of tablets. As a result of the sample preparation conditions, the modified clay silicates swelled isotropically. These results were compared with the adsorption isotherms obtained gravimetrically. High sensitivity of the dilatometric method to the structural changes of the organo-substituted laminar silicates has been shown. The dilatometer used allowed the measurement of absolute deformations in the range 1 x 10(-4) to 3 mm. Copyright 1999 Academic Press.

Journal Article↗

PubMed2003

Is there a feedback between N availability in siliceous and calcareous soils and Cistus albidus leaf chemical composition?

The effects of the Mediterranean shrub Cistus albidus on N cycling were studied in two siliceous (granitic-derived and schistic-derived) and one calcareous soil differentiated by their texture and acidity. We aimed to find out whether soils under C. albidus were affected by the release of C compounds from the canopy, and whether phenolic compound production in C. albidus changed depending on the soil N availability. Calcareous soils, with higher clay content and polyvalent cations, had a higher organic matter content but lower net N mineralization rates than siliceous soils, and C. albidus growing therein were characterized by lower foliar N and phenolic compound concentrations. Under C. albidus, all types of soils had higher phenolic compound concentrations and polyphenol oxidase activity. C. albidus presence and leachate addition decreased net N mineralization and increased soil respiration in siliceous soils, and these changes were related to a higher soil C/N ratio under the canopy. In calcareous soils, however, no significant effects of plant presence on N cycling were found. In the studied plant-soil system it is not likely that higher phenolic compound concentrations were selected during evolution to enhance nutrient conservation in soil because (1) higher phenolic compound concentrations were not associated with lower soil fertilities, (2) C compounds released from C. albidus accelerated N cycling by increasing N immobilization and no evidence was found for decreased gross N mineralization, and (3) soil organic N content was more related to soil chemical and physical properties than to the effects of the C. albidus canopy.

Biological Availability↗

PubMed2000

Ab initio calculations on the five-membered alumino-silicate framework rings model: implications for dissolution in alkaline solutions

An ab initio restricted Hartree-Fock calculation utilising the standard 6-31G basis set was used to calculate total energies after PM3 calculations of energy-optimised geometries for the five-membered alumino-silicate framework rings cluster for a total of ten T sites. Calculations have shown that in the absence of protons or other ions, the most favourable sites for 1A1, 2A1 and 3A1 substitution of Si are the T6, T1 and T9 sites respectively. With more Al atoms replacing Si in a cluster, T-O bond lengths and T-O-T angles show lengthening and sharpening trends respectively, which indicates that the structure is distorted to a more relaxed symmetry with Obr atoms moving outwards. The calculated bond lengths and angles have been shown to match the values observed in previous studies, including those for a four-membered alumino-silicate single ring cluster. Based on the optimised five-membered alumino-silicate framework rings model, a further ab initio HF calculation has been conducted on ring breakage for releasing Al(Q3) and Si(Q3) centres to form T(OH)4 and HOT(OM)3 tetrahedra under local and highly alkaline environment. The obtained results suggest that Al(Q3) compared with Si(Q3) breaks more readily with the exothermal reaction enthalpy being in excess of -244.4 kJ/mol, while the most reactive Si(Q3) centre shows an exothermal reaction enthalpy of only -33.8 kJ/mol. This indicates that Al dissolves in preference to Si in local environment. The dissolution mechanism of the five-membered Al-Si framework rings model in highly alkaline solutions has been suggested to be composed of an ion-pairing reaction and an interaction between the remaining broken ring cluster triple bond TOH and MOH.

Journal Article↗

PubMed2001

Effect of some amino acids and peptides on silicic acid polymerization.

The polymerization of silicic acid in aqueous solutions at different pH was followed by the colorimetric molybdosilicate method. The role of four amino acids (serine, lysine, proline and aspartic acid) and the corresponding homopeptides was studied. All four amino acids behave the same way and favor the condensation of silicic acid. Peptides exhibit a stronger catalytic effect than amino acids but they appear to behave in very different ways depending on the nature of side-groups and pH. Poly-lysine and poly-proline for instance lead to the precipitation of solid phases containing both silica and peptides. The role of these biomolecules on the polymerization of silicic acid is discussed in terms of electrostatic interactions, hydrogen bonds and solubility.

Journal Article↗

PubMed2005

Hydration of tricalcium and dicalcium silicate mixtures studied using quasielastic neutron scattering.

Quasielastic neutron scattering was used to study the hydration reaction of tricalcium and dicalcium silicate mixtures by following the fixation of hydrogen into the reaction products, and by applying hydration models to the data. The reaction kinetics were well-described by an Avrami-derived model for the nucleation and growth regime during early hydration times and a diffusion-limited model for later periods. This study showed that the hydration reaction is not a simple linear combination of the reactions for the individual components. Compressive strength tests correlated with the neutron scattering data, suggesting that the details of the interaction affect the microstructure and therefore the strength of the product. Results suggest that favorable reaction mechanics provide optimal strength when an 80-95% tricalcium silicate and 20-5% dicalcium silicate mixture is used.

Journal Article↗

PubMed2006

Revisiting the identification of structural units in aqueous silicate solutions by two-dimensional silicon-29 INADEQUATE.

(29)Si-(29)Si INADEQUATE experiments have been successfully used on sodium aqueous silicate partially enriched (19% of (29)Si isotope) solutions in order to gain connectivity information and to help in spectral assignments. The structures of almost all known species from the literature were confirmed by this technique. Moreover, accurate scalar J couplings were extracted. The two-dimensional (2D) spectra demonstrated additional cross correlations for some Si-Si bonds never reported before, representing additional oligomeric species. They reveal five silicate cages with the following connectivity sets: Q(2)-Q(2)-Q(3) or Q(3Delta)-Q(3Delta)-Q(3) for one species, Q(2)-Q(2) or Q(3Delta)-Q(3Delta) for three species (Q(3Delta) indicates a three-connected silicon in a three-membered cycle), and Q(3)-Q(3) for one species. All possible molecular graphs for anions containing silicon up to 11 atoms, matching these sequential connnectivities, were enumerated. Additionally, a direct comparison between resonances observed in the 2D experiments with that obtained in the 1D spectrum allows us to assign single-sited silicate anions. Only a few species reported before were not detected, most probably due to their too low concentration in our solutions.

Journal Article↗

PubMed2006

A new self-consistent empirical interatomic potential model for oxides, silicates, and silica-based glasses.

A new empirical pairwise potential model for ionic and semi-ionic oxides has been developed. Its transferability and reliability have been demonstrated by testing the potentials toward the prediction of structural and mechanical properties of a wide range of silicates of technological and geological importance. The partial ionic charge model with a Morse function is used, and it allows the modeling of the quenching of melts, silicate glasses, and inorganic crystals at high-pressure and high-temperature conditions. The results obtained by molecular dynamics and free energy calculations are discussed in relation to the prediction of structural and mechanical properties of a series of soda lime silicate glasses.

Journal Article↗

PubMed2006

Si-O bonded interactions in silicate crystals and molecules: a comparison.

Bond critical point, local kinetic energy density, G(rc), and local potential energy density, V(rc), properties of the electron density distributions, rho(r), calculated for silicates such as quartz and gas-phase molecules such as disiloxane are similar, indicating that the forces that govern the Si-O bonded interactions in silica are short-ranged and molecular-like. Using the G(rc)/rho(rc) ratio as a measure of bond character, the ratio increases as the Si-O bond length, the local electronic energy density, H(rc)= G(rc) + V(rc), and the coordination number of the Si atom decrease and as the accumulation of the electron density at the bond critical point, rho(rc), and the Laplacian, inverted Delta2 rho(rc), increase. The G(rc)/rho(rc) and H(rc)/rho(rc) ratios categorize the bonded interaction as observed for other second row atom M-O bonds into discrete categories with the covalent character of each of the M-O bonds increasing with the H(rc)/rho(rc) ratio. The character of the bond is examined in terms of the large net atomic charges conferred on the Si atoms comprising disiloxane, stishovite, quartz, and forsterite and the domains of localized electron density along the Si-O bond vectors and on the reflex side of the Si-O-Si angle together with the close similarity of the Si-O bonded interactions observed for a variety of hydroxyacid silicate molecules and a large number of silicate crystals. The bond critical point and local energy density properties of the electron density distribution indicate that the bond is an intermediate interaction between Al-O and P-O bonded interactions rather than being a closed-shell or a shared interaction.

Journal Article↗

PubMed2005

Interlayer esterification of layered silicic acid-alcohol nanostructured materials derived from alkoxytrichlorosilane.

Layered silicic acid-organic nanohybrid materials consisting of long-chain alkoxy groups attached to thin silica layers have been prepared via esterification of a layered silicic acid-alcohol nanostructured material derived from hexadecoxytrichlorosilane (C(16)H(33)OSiCl(3)). The esterification reaction was performed by heating the layered composite. The detailed characterization of the product heated at 80 degrees C revealed that the interlayer alcohol molecules partly ( approximately 50%) reacted with the interlayer surface silanol groups to form alkoxy groups. Unreacted alcohol molecules were removed by tetrahydrofuran (THF) treatment to form a novel alkoxylated layered silica material. This product retains its structure up to 120 degrees C and has a higher stability in organic solvents if compared with the layered silicic acid-alcohol nanocomposite before esterification, whose structure collapsed over 100 degrees C. Furthermore, various alcohols can be adsorbed into the esterified nanohybrid with the expansion of the interlayer spacing.

Journal Article↗

PubMed2005

Gaining insight into the nanoscale properties of sol-gel-derived silicate thin films by single-molecule spectroscopy.

The application of single-molecule spectroscopic methods in studies of individual nanoscale environments within sol-gel-derived silicate thin films is reviewed. Representative examples of the experiments performed and results obtained in several studies from the authors' laboratories are given. Included are investigations of the static and dynamic polarity properties of organically modified silicate (ORMOSIL) films. The results of these studies point to nonrandom variations in the film properties, providing strong evidence for the formation of phase-separated organic- and inorganic-rich domains. Studies of single-molecule diffusion through the same films yield important evidence for the formation of liquidlike silicate oligomers that facilitate probe molecule diffusion. Finally, single-molecule studies of the local pH within individual film environments are discussed. Valuable information on the contributions of local materials' acidity variations to overall sample heterogeneity is obtained. The results of immersion studies indicate that certain molecular environments are inaccessible to external solutions over periods as long as a few hours. The article concludes with a discussion of possible future challenges in this research that may be addressed by new and existing single-molecule methods.

Journal Article↗

PubMed2006

Surface characteristics of layered silicates: Influence on the properties of clay/polymer nanocomposites.

A sodium montmorillonite and six organophilic montmorillonites coated with different surfactants were characterized in various ways in the study. Particle and surface characteristics were determined by nitrogen adsorption and inverse gas chromatography, respectively. The gallery structure of organophilic montmorillonite, the orientation of surfactants in the galleries, and surface coverage were estimated by X-ray diffraction measurements and model calculations. The effect of organophilization on the properties of polypropylene/clay composites was determined by the measurement of tensile properties. The results showed that the surface energy of uncoated layered silicates is large; thus, the forces keeping the layers together are very strong. The long chain surfactants used for the coating of montmorillonite orientate more or less parallel to the surface and usually cover the platelets in a single layer in commercial silicates. Surplus surfactant is not located in the galleries, but among the particles, and might influence the properties of composites negatively. Organophilization leads to the drastic decrease of surface free energy. Surface tension of all coated clays is practically the same, irrespective of the type of the surfactant used for treatment. Low surface energy leads to weaker forces between the layers, which might facilitate exfoliation. This effect can be further enhanced by the use of surfactants with two long aliphatic chains, one of which orientates vertically to the surface, leading to larger gallery distance. Polymer/silicate interaction also decreases as an effect of decreasing surface tension proved by the decrease of tensile yield stress of polypropylene/montmorillonite composites. Besides surface tension, the exfoliation of layered silicates is influenced by several other factors as well, like gallery distance, mutual solubility of the components, competitive adsorption, or possible chemical reactions.

Journal Article↗

PubMedDate not supplied

Histological investigation of organisms with hard skeletons: a case study of siliceous sponges.

Siliceous and calcareous sponges commonly are treated with acid to remove the spicules prior to embedding and cutting for histological investigations. Histology of spiculated sponge tissue represents a challenging problem in sponge histotechnology. Furthermore, fluorescence in situ hybridization (FISH), a key method for studying sponge-associated microbes, is not possible after acid treatment. For a broad range of siliceous sponge species, we developed and evaluated methods for embedding in paraffin, methylmethacrylate resins, LR White resin and cryomatrix. Different methods for cutting tissue blocks as well as mounting and staining sections also were tested. Our aim was to enable histological investigations and FISH without prior removal of the spicules. To obtain an overview of tissue and skeleton arrangement, we recommend embedding tissue blocks with LR White resin combined with en bloc staining techniques for large specimens with thick and numerous spicules, but paraffin embedding and subsequent staining for whole small specimens. For FISH on siliceous sponges, we recommend Histocryl embedding if the spicule content is high, but paraffin embedding if it is low. Classical histological techniques are used for detailed tissue examinations.

Animals↗

PubMed2006

Properties and coagulation performance of coagulant poly-aluminum-ferric-silicate-chloride in water and wastewater treatment.

An efficient inorganic polymer coagulant, poly-aluminum-ferric-silicate-chloride (PAFSC), was developed using two approaches: (i) hydroxylation of the mixture of AlCl3, FeCl3 and fresh polysilicic acid in different Al/Fe/Si molar ratios to obtain PAFSCc and (ii) hydroxylated poly-aluminum-iron-chloride (PAFC) combined with aged polysilicic acid in different Al/Fe/Si ratios to produce PAFSCm. The properties of PAFSC in comparison with polyaluminum silicate chloride (PASC) and polyferric silicate chloride (PAFC) were characterized by various experimental methods. The effect of Al/Fe/Si molar ratio on the hydrolysis-polymerization process of Al (III) and Fe (III) in PAFSC solutions was examined by pH titration, and the effect of Al/Fe/Si molar ratio on electrokinetic mobility of PAFSC was studied by Zeta potential measurement. The laboratory experiments were performed to evaluate the PAFSC in comparison with polyaluminum chloride (PAC) for the coagulation of synthetic water samples, actual surface water and wastewater. The results show that interactions exist among aluminum species, ferric species and polysilicic acid, and the Al/Fe/Si molar ratio affects the Zeta potential of the hydrolyzate and the coagulating performance. PAFSC achieved a better water treatment result than PAC. At the same basicity (B) value and Al/Fe/Si ratio, PAFSCc has better coagulation performance than PAFSCm. PAFSC is a new type and high efficiency composite inorganic polymer coagulant.

China↗

PubMed2001

Clinical Effects of a Dietary Antioxidant Silicate Supplement, Microhydrin((R)), on Cardiovascular Responses to Exercise.

Amorphous silicate minerals, often described as rock flour, were once common in natural water sources and abundant in glacial stream waters. Not only do the silica mineral particles bond water and other elements for transport; they also can be adsorbed with reduced hydrogen, which releases electrons, providing antioxidant or reducing potential to surrounding fluids. The purpose of this investigation was to examine the cardiovascular responses during exercise after consumption of a dietary silicate mineral antioxidant supplement, Microhydrin((R)) (Royal BodyCare, Inc., Irving, TX). A clinical trial incorporating a double-blind, placebo-controlled, crossover experimental design was employed. Subjects received either active agent or placebo, four capsules per day, for 7 days before the trial. The trial evaluated six exercise bicycle-trained subjects performing a 40-km bicycling time trial. Ratings of perceived exertion and measurements of oxygen uptake, heart rate, performance workload, and preexercise and postexercise blood lactate concentrations were obtained. Although there were no differences (P >/=.05) in work performed, heart rate, oxygen uptake, and ratings of perceived exertion during the time trial, the postexercise blood lactate concentrations were significantly lower (P </=.05) when the silicate mineral supplement was used, compared with placebo. These data suggest a beneficial effect of Microhydrin on lactate metabolism.

Journal Article↗

PubMed2001

Systematic ab initio study of the compressibility of silicate garnets.

The structural properties of the silicate garnets andradite, Ca(3)Fe(2)Si(3)O(12), uvarovite, Ca(3)Cr(2)Si(3)O(12), knorringite, Mg(3)Cr(2)Si(3)O(12), goldmanite, Ca(3)V(2)Si(3)O(12), blythite, Mn(2+)(3)Mn(3+)(2)Si(3)O(12), skiagite, Fe(2+)(3)Fe(3+)(2)Si(3)O(12), calderite, Mn(2+)(3)Fe(3+)(2)Si(3)O(12), and khoharite, Mg(3)Fe(3+)(2)Si(3)O(12), have been investigated with a quantum-mechanical model as a function of applied pressure. The study has been performed with the density functional theory code CASTEP, which uses pseudopotentials and a plane-wave basis set. All structural parameters have been optimized. The calculated static geometries (cell parameters, internal coordinates of atoms and bond lengths), bulk moduli and their pressure derivatives are in good agreement with the experimental data available. Predictions are made for those cases where no experimental data have been reported. The data clearly indicate that the elastic properties of all silicate garnets are dominated by the compressibility of the dodecahedral site. The compression mechanism is found to be based on a bending of the angle between the centers of the SiO(4) tetrahedra and the adjacent octahedra, as in the aluminosilicate garnets. An analysis of the relationship between ionic radii of the cations and the compressibility of silicate garnets is presented.

Journal Article↗

PubMed2001

Newly developed aminopropyl-silicate immunoisolation membrane for a microcapsule-shaped bioartificial pancreas.

An aminopropyl-silicate membrane, synthesized from tetramethoxysilane (TMOS) and 3-aminopropyltrimethoxysilane (APTrMOS) by the sol-gel method, was formed onto Ca-alginate gel beads via electrostatic interactions. The permeability of the membrane could be controlled easily by changing the molar ratio of both the precursors ([APTrMOS]/[TMOS]). The aminopropyl-silicate membrane prepared at a molar ratio of 2.40 rejected gamma-globulin and BSA successfully, whereas it permeated ovalbumin. This result indicates that the molecular weight cutoff point of this newly developed aminopropyl-silicate membrane is approximately 60 kDa.

Bioartificial Organs↗

PubMed1993

Remobilization of Heavy Metals Retained as Oxyhydroxides or Silicates by Bacillus subtilis Cells.

The stability of heavy metals bound as either silicates or oxyhydroxides by the surfaces of Bacillus subtilis with changes in pH and presence of competing cations and EDTA was studied. Wall-bound silicate was very stable. Of all conditions, a pH of 3.0 (by HNO(3)) promoted the greatest release of Cd (87% [wt/wt]), Pb (77%), or Cu (54%). Bacterial Pb resisted extraction by EDTA, and Cd that was included in bacterial-silicates proved difficult to remobilize.

Journal Article↗

PubMed1993

A study of siliceous pneumoconiosis in a desert area of Sunan County, Gansu Province, China.

Three hundred and ninety five residents in a desert area were examined with chest radiographs and 28 cases with siliceous pneumoconiosis were found. The prevalence of siliceous pneumoconiosis was 7.09%, and that over 40 years of age was 21%. The histological findings of lungs from a camel living in that area for 20 years also confirmed to have siliceous pneumoconiosis.

Adult↗