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Oral hygiene and regular maintenance are crucial for preserving good peri-implant health. However, available prophylaxis products and toothpastes, which are optimized for cleaning teeth, tend to contaminate and abrade implant surfaces due to their organic components and silica microparticles, respectively. This study aims to develop an organic-free implant-paste based on two-dimensional nanocrystalline magnesium phosphate gel and hydrated silica nanoparticles (20-30% w/w) for cleaning oral biofilm on titanium dental implants. The surface chemistry, morphology, and bacterial load of contaminated Ti disks before and after decontamination using prophylaxis brushing with toothpaste and implant-paste were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and fluorescence spectroscopy. Both commercial toothpastes and implant-paste remove bacteria, however, only implant-paste protects Ti metal from abrasion and removes organic contaminants. XPS showed a significant decrease of carbon contamination from 73% ± 2 to 20% ± 2 after mechanical brushing with implant-paste compared to 41% ± 11 when brushing with commercial toothpastes (p

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re‐evaluating the safety of silicon dioxide (E 551) when used as a food additive. The forms of synthetic amorphous silica (SAS) used as E 551 include fumed silica and hydrated silica (precipitated silica, silica gel and hydrous silica). The Scientific Committee on Food (SCF) established a group acceptable daily intake (ADI) ‘not specified’ for silicon dioxide and silicates. SAS materials used in the available biological and toxicological studies were different in their physicochemical properties; their characteristics were not always described in sufficient detail. Silicon dioxide appears to be poorly absorbed. However, silicon‐containing material (in some cases presumed to be silicon dioxide) was found in some tissues. Despite the limitations in the subchronic, reproductive and developmental toxicological studies, including studies with nano silicon dioxide, there was no indication of adverse effects. E 551 does not raise a concern with respect to genotoxicity. In the absence of a long‐term study with nano silicon dioxide, the Panel could not extrapolate the results from the available chronic study with a material, which does not cover the full‐size range of the nanoparticles that could be present in the food additive E 551, to a material complying with the current specifications for E 551. These specifications do not exclude the presence of nanoparticles. The highest exposure estimates were at least one order of magnitude lower than the no observed adverse effect levels (NOAELs) identified (the highest doses tested). The Panel concluded that the EU specifications are insufficient to adequately characterise the food additive E 551. Clear characterisation of particle size distribution is required. Based on the available database, there was no indication for toxicity of E 551 at the reported uses and use levels. Because of the limitations in the available database, the Panel was unable to confirm the current ADI ‘not specified’. The Panel recommended some modifications of the EU specifications for E 551.

Experimental studies reveal complex dissolution behavior of quartz in aqueous NaCl solutions at high temperature and pressure, involving variation from salting-in to salting-out that changes with temperature, pressure, and salt concentration. The behavior is not explainable by traditional electrostatic theory. An alternative hypothesis appeals to complexing of SiO2 with NaCl and can explain the observations. However, the hypothesis of complexing, as previously applied, is inadequate in several respects: it neglects polymerization of solute silica, regards the SiO2-NaCl hybrid complex(es) as anhydrous, which seems unlikely, and invokes an incorrect stoichiometry of the hydrated silica monomer, now known to be Si(OH)42H2O. These neglected features can be incorporated into the complexing model in a revised formulation based on a simple thermodynamic analysis using existing quartz solubility data. The analysis leads to a quasi-ideal solution model with silica monomers, dimers, and two distinct hydrous SiO2-NaCl hybrid complexes with overall NaCl:H2O = 1:6, one Na-bearing and one Cl-bearing. Their (equal) molar concentrations (Xhc) are governed by a pressure- and temperature-dependent equilibrium constant, Khc ¼ X 2=ðaNacla 62OÞ, where aNacl and aH2O are the respective activities of the solvent components. The stability of the hybrid complexes (i.e., their concentration) is very sensitive to H2O activity. The entire set of experimental quartz-solubility data at 700°C, 1–15 kbar, is reproduced with high fidelity by the expression logKhc ¼� 4:585 þ 0:2691P � 2:023 � 10 � 3 P 2 (P is pressure in kbar), including the transition from low-pressure salting-in to high pressure salting-out. The results indicate that hybrid SiO2-NaCl complexes are the main hosts for dissolved silica at NaCl concentrations greater than 6 wt%, which are likely common in crustal fluids. At higher temperatures, approaching the critical end point in the system SiO2-H2O, the model becomes progressively inaccurate, probably because polymers higher than the dimer become significant as SiO2 concentration

Isobutylene–isoprene rubber (IIR)/nanoclay composites were prepared by solution intercalation method. Cloisite Na+ montmorillonite and organo-modified montmorillonite (OMMT) nanoclays, namely, cloisite 10 A, cloisite 15 A, and cloisite 20 A were used in this study. The effect of in situ bonding system HRH (hexametylene tetramine: resorcinol: hydrated silica) on the dispersion of used nanoclays in the rubber matrix were examined by X-ray diffraction and scanning electron microscope (SEM). Both techniques showed complete exfoliation of the clays silicate layers in IIR/OMMT/HRH nanocomposites (NCs). Rheometeric and mechanical properties (tensile strength, elongation at break%, and E-modulus) of the NCs were studied. The addition of HRH system to IIR/OMMT NCs improves their mechanical properties. Moreover, IIR/clays/HRH NCs showed a decrease in the scorch time (tS2) and the cure time (tC90), which is an industrial privilege for saving time and energy. Swelling measurements were used to determine the filler–rubber interaction (Qf/Qg), the molar mass between cross-links (Mc) and the cross-linking density (ν) for each composite. The presence of HRH system enhances the rubber–filler interaction; in addition to an increase in the cross-link density values. POLYM. COMPOS., 34:1559–1565, 2013. © 2013 Society of Plastics Engineers

Hexactinellid sponges are known for their ability to synthesize unusually long and highly flexible fibrous spicules, which serve as the building blocks of their skeletal systems. The spicules consist of a central core of monolithic hydrated silica, surrounded by alternating layers of hydrated silica and proteinaceous material. The principal objective of the present study is to ascertain the role of the latter laminate architecture in the material's resistance to both crack initiation and subsequent crack growth. This has been accomplished through indentation testing on the giant anchor spicule of Monorhaphis chuni, both in the laminated region and in the monolithic core, along with a theoretical analysis of deformation and cracking at indents. The latter suggests that the threshold load for crack initiation is proportional to Kc4/E2H where Kc is fracture toughness, E is Young's modulus, and H is hardness. Two key experimental results emerge. First, the load required to form well-defined radial cracks from a sharp indent in the laminated region is two orders of magnitude greater than that for the monolithic material. Secondly, its fracture toughness is about 2.5 times that of the monolith, whereas the modulus and hardness are about 20% lower. Combining the latter property values with the theoretical analysis, the predicted increase in the threshold load is a factor of about 80, broadly consistent with the experimental measurements.

A novel method for the preparation of short nylon fiber–natural rubber composites was developed in which short fibers chopped to approximately 6 mm were incorporated in the latex stage and processed into sheet form. By this method, mixing cycle time was reduced without compromising the fiber dispersion. Fiber breakage during mixing was reduced. The new composites when compounded with a dry bonding system based on hexamethylenetetramine, resorcinol and hydrated silica (HRH) showed improved modulus, tensile strength and abrasion resistance compared to conventional composites. Tear strength, resilience, and compression set were similar to the conventional composites. SEM analysis indicated better interaction between matrix and fibers in the case of latex master batch. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

It is shown that the high-solubility layer previously demonstrated (Clelland, Cumming & Ritchie, 1951) on silicious dust-particle surfaces is not a surface layer of hydrated silica; and evidence is adduced that it is a vitreous silica layer of the Beilby type, formed during the production of the dust by crushing and grinding. An important part of the evidence is the demonstration that prolonged grinding of quartz leads to a reduction in density. This reduction is attributed to partial conversion of the dust particles to vitreous silica: no conversion to other crystalline modifications of silica could be detected. Further, when the high-solubility layer has been removed from silicious dust particles by solvents, it can be regenerated by a purely mechanical polishing process. The regenerated layer yields silica into aqueous media very largely in colloidal form.

A high-purity CVD β-SiC showed a relatively low corrosion rate in deoxygenated supercritical water at 500°C. The corrosion rate was lower than that previously reported for CVD SiC in 360°C water and much lower than that reported for sintered and reaction-bonded SiC. The present study confirmed that CVD SiC was preferentially attacked at the grain boundaries. Analytical examinations did not reveal the presence of a measurable oxide scale. As a result, it is believed that corrosion of the high-purity SiC occurred via hydrolysis to hydrated silica species at the surface that were rapidly dissolved into the supercritical water.

A novel procedure is presented for precipitation of highly dispersed silica from sodium metasilicate solution using sodium hydrogencarbonate. In the course of silica precipitation, hydrophobicity-inducing agents were introduced to the reactor, including derivatives of saturated and unsaturated higher fatty alcohols and nonylphenylpolyoxyethyleneglycol ethers. Silicas of variable physicochemical characteristics were obtained. Analysis of the principal physicochemical properties of the silicas was performed, their surface morphology was examined using scanning electron microscopy while particle size distribution, polydispersity and tendency to form the agglomerate structures were estimated by the dynamic light scattering technique. The zeta potential was also measured by estimation of electrophoretic mobility. Sodium hydrogencarbonate solution was found to be a very good silica-precipitating agent in solutions of sodium metasilicate. The hydrated silica obtained demonstrated low bulk density and a high capacity to absorb paraffin oil. © 2002 Society of Chemical Industry

This work examines a polymerisation catalyst based on zirconocene with methylaluminoxane (MAO) as a cocatalyst on silica surfaces, Calculations were carried out using the Atom Superposition and Electron Delocalisation method (ASED-MO) considering the (111) and (100) silica planes, both completely and partially hydrated. Our results suggest the production of a cationic zirconocene as a final step for the active site formation for (111) silica plane, occurring preferentially on partially hydrated silica. On the contrary this may not be possible for the (100) plane, resulting in this case in the formation of a MAO-zirconocene complex as a final and most stable state.

— A number of martian meteorite samples contain secondary alteration minerals such as Ca-Mg-Fe carbonates, Fe oxides, and clay minerals. These mineral assemblages hint at hydrothermal processes occurring in the martian crust, but the alteration conditions are poorly constrained. This study presents the results of experiments that examined the alteration of a high-Fe basalt by CO2-saturated aqueous fluids at 23 and 75 °C and by mixed H2O-CO2 vapors at 200 and 400 °C and water-rock ratios of 1:1 and 1:10. Results indicate that observable alteration of the basalt takes place after runs of only seven days. This alteration includes mobilization of silica into phases such as opal-CT and quartz, as well as the formation of carbonates, oxides, and at some conditions, zeolites and hydrous silicates. The degree of alteration increases with run temperature and, in high-temperature vapor experiments, with increasing water content of the vapor. The degree of alteration and the mineralogy observed in the martian meteorites suggests that none of these samples were exposed to aqueous fluids for long periods of time. Nakhla and Lafayette probably interacted with water for relatively brief periods of time; if so, silica may have been leached from the parent rocks by the altering fluids. Allan Hills 84001 shows possible evidence for very limited interaction with an aqueous fluid, but the overall slight degree of alteration described for this meteorite strongly suggests that it never interacted extensively or at high temperature with any water-bearing fluid. Elephant Moraine A79001 may not have been altered by aqueous fluids at all. The results of this study best support models wherein the meteorite parent rocks were wetted intermittently or for brief periods of time rather than models that invoke long-term reaction with large volumes of water. Our experiments studied alteration of a high-Fe basalt by dilute, CO2-saturated, aqueous solutions at 23 and 75 °C and by mixed H2O-CO2 vapors at 200 and 400 °C. The results suggest that alteration of the parent rock takes place even after very short reaction times of seven days. All experiments produced carbonate minerals, including calcite, and in some cases, magnesite, siderite, and ankerite. A free silica phase, either opal, quartz, or hydrated silica, formed in most experiments. More altered experiments also contained minerals such as zeolites and hydrous phyllosilicates. Clay minerals were not observed to form in any experiments. In aqueous fluids, higher temperature corresponded with a higher degree of alteration, whereas changing fluid composition had no observable effect. In high-temperature vapors, the degree of alteration was controlled by temperature and the proportion of H2O to CO2, with water-rock ratio also playing a role in transport of silica. Application of these results to martian meteorites that contain secondary alteration minerals suggests that none of the martian rocks underwent extensive interaction with aqueous fluids. Nakhla and Lafayette contain clay minerals, which suggests that they interacted with water to some extent, possibly at elevated temperatures. Although ALH84001 shows possible evidence of very limited interaction with aqueous fluids, EETA79001 does not. These results support models for the alteration of these meteorites that do not invoke long-term interaction with water or reaction with large volumes of water. Except for some models for alteration of ALH84001, this conclusion agrees with most of the literature on alteration of martian meteorites.

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels. © 1996 John Wiley & Sons, Inc.

To prepare supported catalyst for ethylene polymerization, silica was treated with trialkylaluminum (AIR3) followed by supporting Cp2ZrCl2. Partially hydrated silica (H-SiO2) was chosen for reaction with AIR3 to prepare catalyst precursor. The H-SiO2/ AIR3 / Metallocene catalyst system could effectively catalyse ethylene polymerization even with common alkylaluminums as cocatalyst. The catalytic activity of supported catalyst depended on H2O content of silica. H2O/(CH3) 3Al ratio, metallocene and cocatalyst. The analysis data of silica surface by BET and CP MAS 13C NMR revealed that the catalyst precursor prepared from the reaction between H-SiO2 and (CH3) 3Al was methylaluminoxane (PMAO) supported on silica with high surface area and reduced pore size.

Pure soluble silica prepared by a sol-gel method induced bone-like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel-derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bone-bonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel-derived silica and titania are important for hydroxyapatite induction. material which possesses and/or develops both a negatively charged surface and abundant OH groups in a physiologically-related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone-bonding biomaterials.

The properties of natural rubber vulcanizates reinforced with nylon 6 short fibers were studied. It was found that the stress of vulcanizates decreased with initial fiber loading, followed by an increase with increasing the amount of fiber. The effect of reinforcing carbon black HAF on the physicomechanical properties was studied in the presence and absence of hydrated silica.

It has been confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body. It has been proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer, but this has not yet been proved. In the present study, it is shown experimentally that a pure hydrated silica gel can induce apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.

An intumescnt material has been developed, based on alkali silicates, which can be used in fire protection in the form of sheets or boards which can be joined to various materials, ranging from wood and wood products to metal. The swelling of the material on heating to over 100°C or on contact with a flame is due to and endothermic process and is associated with the emission of water vapour. The solid foam formed is rigid and consists of hydrated silica. The phenomena observed during the preparation of the boards and their behaviour on heating can be explained in terms of silicate chemistry.

Rice husk ash (RHA) obtained from rice mill and hydrated silica from RHA were used as a filler in vulcanized SBR 1502 and the dielectric properties were measured at a frequency of 1592 Hz at room temperature. The optimum hydrated silica content giving a good dielectric constant and conductivity was 125 parts/100 parts rubber and the dielectric loss was also high so that it could be a good insulater. There was no significant change in dielectric constant, dielectric loss and conductivity of SBR 1502 filled with RHA which could be used as high frequency dielectric due to low dielectric loss.

Samples of ancient Roman glass taken from burial vaults on the Island of Cyprus have been examined. Analysis shows the glass to be of the soda-lime type characteristic that period. The heavy incrustation produced by weathering has been studied spectroscopically and microscopically and is shown to consist, for the most part, of hydrated silica, formed by the slow hydrolytic decomposition of the glass. The beautiful iridescence exhibited by the glass is due to the selective destructive interference of light the thin films of transparent incrustation on the surface of the glass.

The three major factors which affect bleaching performance are type of clay, bleaching method, and oil quality. These are discussed in order. Under the first are such topics as purpose of clay in industry, source of raw material, clay types, physical structure, effect of activation on structure, variation in effectiveness of clays produced from different raw materials, and mechanism of the clay’s action. Also covered is the effect of the clay’s properties-moisture, apparent bulk density, specific gravity, acidity, pH, hydrated silica, particle-size distribution, and the theory of variability. Under the second are effect of bleaching conditions, such as temperature, time, agitation, temperature of clay addition, vacuum versus atmospheric bleaching; commercial methods including atmospheric batch, vacuum batch, vacuum continuous; and effect of oil quality. Under the third are response of different color pigments to bleaching, effect of moisture, oxidation, and organic impurities in the oil. Of the three factors, oil quality has the greatest influence upon bleaching performance.