Search

Hydrated silica (SiO2·nH2O) aggregates in the root endodermis of grasses. Application of soluble silicates (Si) to roots is associated with variations in the balance of reactive oxygen species (ROS), increased tolerance to a broad range of stresses affecting ROS concentrations, and early lignin deposition. In sorghum (Sorghum bicolor L.), silica aggregation is patterned in an active silicification zone (ASZ) by a special type of aromatic material forming a spotted pattern. The deposition has a signature typical of lignin. Since lignin polymerization is mediated by ROS, we studied the formation of root lignin and silica controlled by ROS via modulating hydrogen peroxide (H2O2) concentrations in the growth medium. Sorghum seedlings were grown hydroponically and supplemented with Si, H2O2, and KI, an ionic compound that catalyses H2O2 decomposition. Lignin and silica deposits in the endodermis were studied by histology, scanning electron and Raman microscopies. Cell wall composition was quantified by thermal gravimetric analysis. Endodermal H2O2 concentration correlated to the extent of lignin-like deposition along the root, but did not affect its patterning in spots. Our results show that the ASZ spots were necessary for root silica aggregation, and suggest that silicification is intensified under oxidative stress as a result of increased ASZ lignin-like deposition.

Quantum chemical simulation of the adsorption of N acetylneuraminic acid (NANA) on the surface of silica with the participation of the fructose molecule by the method of density functional theory B3LYP, 6-31G (d, p) was done. The influence of the solvent was taken into account in the supermolecular and continuum approximations, and a cluster approach was used for the adsorption complexes. NANA adsorption of the hydrated silica surface was considered as a process of replacement of water molecules on the silica surface by adsorbate molecules. Two schemes of influence of fructose molecule on NANA adsorption are considered. According to the first scheme, the hydrated NANA molecule interacts with the hydrated silicon-fructose adsorption complex. According to the second scheme, the cluster of hydrated silica interacts with the hydrated NANA-fructose complex. The energy of intermolecular interaction according to the scheme 1 is -9.2 kJ / mol, which is significantly lower compared to the same value with the participation of glucose or sucrose (-20.5 and -86.2 kJ / mol). Scheme 2 proved to be a thermodynamically unfavorable process, as its energy effect is +6.9 kJ / mol, in contrast to similar processes for glucose (-21.8) and sucrose (-87.7 kJ / mol). This confirms the experimental fact of the interaction of substances in a mixture of NANA with carbohydrates in relation to the interaction with silica in comparison with the interaction of substances with silica separately.

The formation of a composite system based on equal amounts of hydrophobic, porous polymethylsiloxane and hydrophilic nanosilicon A-300 was studied. It is shown that during the formation of a composite system the specific surface of the material is significantly reduced, which is due to the close contact between hydrophobic and hydrophilic particles. When water is added to the composite system, in the process of homogenization under conditions of dosed mechanical loading, the effect of nanocoagulation is manifested – the formation of nanosized particles of hydrated silica inside the polymethylsiloxane matrix, recorded on TEM microphotographs. When measuring the value of the interfacial energy of PMS and PMS/A-300 composite by low-temperature 1H NMR spectroscopy, it was found that the effect of nanocoagulation is manifested in a decrease (compared to the original PMS) energy of water interaction with the surface of the composite obtained under small mechanical conditions. its growth when using high mechanical loads. In the process, the binding of water in heterogeneous systems containing PMS, pyrogenic nanosilica (A-300), water and surfactants – decamethoxine (DMT) was studied. Composite systems were created using metered mechanical loads. It is shown that when filling the interparticle gaps of PMS by the method of hydrosealing, the interphase energy of water in the interparticle gaps of hydrophobic PMS with the same hydration is twice the interfacial energy of water in hydrophilic silica A-300. This is due to the smaller linear dimensions of the interparticle gaps in PMS compared to A-300. In the composite system, A-300/PMS/DMT/H2O there are non-additive growth of binding energy of water, which is probably due to the formation, under the influence of mechanical stress in the presence of water, microheterogeneous areas consisting mainly of hydrophobic and hydrophilic components (microcoagulation). Thus, with the help of mechanical loads, you can control the adsorption properties of composite systems and create new materials with unique adsorption properties.

surface characteristics and color Stability of two aesthetic restorative materials. Materials and Methods: A total of 180 specimen were prepared from two tested materials (Filtek Z350 resin composite and Equia forte glass ionomer with nano filled coat).The specimen were divided into three groups (n=60). Group 1: hydrated silica containing tooth paste Group 2: calcium carbonate containing tooth paste, Group 3: trisodium phosphate containing tooth paste, each group was subdivided into two subgroups according to number of brushing duration (1120, 2240) cycles (n=15).Each subgroup was further subdivided into three divisions according to the type of test performed (micro hardness, surface roughness, color stability) (n=5). All tests were done before and after brushing then the data were statistically analysed. Results: Baseline results revealed that resin composite has higher micro hardness, lower surface roughness and more color stability compared to glass ionomer. Regarding the effect of tooth paste; trisodium phosphate containing tooth paste recorded the higher micro hardness, lower surface roughness and more color stability among all tested groups. On other hand, brushing for eight weeks (2240cycles) showed significant decrease in micro hardness, increase in both surfaces roughness and color instability. Conclusion: Abrasive containing whitening dentifrices and number of brushing cycles have an influential effect on surface characteristics and color stability of composite and glass ionomer.

Certain martian hydrated silica deposits have been hypothesized to represent ancient hot spring environments, but many environments can produce hydrated silica on Earth. This study compares the mineral assemblages produced in terrestrial hot springs to those observed in silica-producing volcanic fumarolic environments to determine which diagnostic features of hot springs could be remotely sensed on Mars. We find that hot spring environments are more likely to produce geochemically mature silica (

Silica deposition in roots of sorghum is highly controlled. Modified lignin is deposited in a spotted pattern along the cell walls of endodermis cells. These spots act as silica nucleation sites, leading to the formation of silica aggregates., Silicon dioxide in the form of hydrated silica is a component of plant tissues that can constitute several percent by dry weight in certain taxa. Nonetheless, the mechanism of plant silica formation is mostly unknown. Silicon (Si) is taken up from the soil by roots in the form of monosilicic acid molecules. The silicic acid is carried in the xylem and subsequently polymerizes in target sites to silica. In roots of sorghum (Sorghum bicolor), silica aggregates form in an orderly pattern along the inner tangential cell walls of endodermis cells. Using Raman microspectroscopy, autofluorescence, and scanning electron microscopy, we investigated the structure and composition of developing aggregates in roots of sorghum seedlings. Putative silica aggregation loci were identified in roots grown under Si starvation. These micrometer-scale spots were constructed of tightly packed modified lignin, and nucleated trace concentrations of silicic acid. Substantial variation in cell wall autofluorescence between Si+ and Si– roots demonstrated the impact of Si on cell wall chemistry. We propose that in Si– roots, the modified lignin cross-linked into the cell wall and lost its ability to nucleate silica. In Si+ roots, silica polymerized on the modified lignin and altered its structure. Our work demonstrates a high degree of control over lignin and silica deposition in cell walls.

In this work, an interfacially active PPA@SiO2 microsphere for ASP flooding-produced water treatment was synthesized by grafting polyether–polyquaternium (PPA) copolymer onto mesoporous hydrated silica (SiO2). This PPA@SiO2 microsphere integrates both demulsification and adsorption functionalities. The physicochemical properties of the SiO2 variants were monitored via SEM, BET, XPS, contact angle and zeta potential tests. When disposing of a simulated alkali–surfactant–polymer flooding produced water that contained 500 mg L−1 oil, this functional PPA@SiO2 microsphere exhibited an oil removal efficiency of 78.0% at 1.0 g L−1 dosage, which is higher than that of pristine SiO2 (39.1%) and hydrophobic modified SiO2 (54.2%). This remarkable oil removal efficiency was attributed to its abilities to destabilize and aggregate the emulsified oil droplets. Oil micromorphology test results indicated that PPA@SiO2 could aggregate the fine oil droplets into oil clusters, which significantly favors the oil–water separation efficiency. An adsorption kinetics and thermodynamics study manifested that oil adsorption onto PPA@SiO2 was an exothermic process, mainly dominated by external surface adsorption, which agreed with the BET and micromorphology study. Furthermore, the oil adsorption mechanism has been explored and confirmed according to all the experimental results. This modification protocol significantly reduced the PPA consumption and it was also found that the loaded oil onto PPA@SiO2 could be effectively separated through a petroleum ether extraction process, so as to recycle the carrier particles. This novel PPA@SiO2 microsphere with its high oil removal efficiency offers technical promise and huge potential for oily wastewater treatment.

Silica has the highest demonstrated potential of any phase to preserve microfossils on Earth and therefore may host potential biosignatures on Mars. We detected hydrated silica in Jezero crater, the landing site of the National Aeronautics and Space Administration's Mars 2020 rover mission, by applying Dynamic Aperture Factor Analysis/Target Transformation to images from the Compact Reconnaissance Imaging Spectrometer for Mars. Hydrated silica detections with Dynamic Aperture Factor Analysis/Target Transformation were verified using commonly accepted Compact Reconnaissance Imaging Spectrometer for Mars analysis methods. The morphology of geologic units associated with silica was characterized with high‐resolution imaging. Several hypotheses are presented for the formation environment of hydrated silica. All are testable via in situ investigation. We assess the likelihood of silica to preserve biosignatures in these different scenarios based on habitability considerations and biosignature preservation in Earth analog environments and materials. Also reported are possible detections of hydrated silica in the Nili Fossae basement and olivine‐rich units, as well as Al‐phyllosilicate within Jezero crater.

Suites of hydrous and hydrated minerals have been detected on Mars through space-borne remote-sensing instruments. These minerals are often found associated with impact craters, where their origin is attributed to (1) exhumation of pre-existing ancient hydrothermal systems, and (2) impact-related hydrothermal activity. This paper provides a review of the latter, that is, impact-induced hydrothermalism on Mars detected and mapped using orbital imaging spectroscopic as well as high-resolution panchromatic and digital elevation data. The major alteration mineral assemblages that have been detected include phyllosilicates such as smectites, kaolinites, prehnites, chlorites, and mica, and some tectosilicates such as hydrated silica. The most common minerals are chlorites, Fe/Mg smectites, with a few instances of prehnite, which indicate sub-surface alteration. Al-phyllosilicates are also commonly observed suggesting near-surface liquid water activity for extended periods. The observed hydrothermal alteration assemblages are used to get insights into the nature of circulating hydrothermal fluids, including the fluid/rock ratios and pH. Spatial patterns in the distribution of the minerals is not discernible and these impact-induced hydrothermal systems may suggest local events, which are limited within individual craters.

An electrocoagulation (EC) process to remove fluoride and arsenic from groundwater (fluoride 5.5 mg L−1, arsenic 50.4 µg L−1, hydrated silica 132 mg L−1, sulfate 40 mg L−1, nitrate 6.7 mg L−1, phosphate 0.55 mg L−1, hardness 23 mg L−1, alkalinity 59.0 mg L−1, pH 8.5 and conductivity 824.5 µS cm−1) was investigated. The EC was carried out in a filter-press flow reactor, containing a three-cell stack equipped with aluminum electrodes. The influence of current density (j), mean linear flow rate in the EC reactor (ur) and the co-existing ions on the fluoride and arsenic removal efficiencies was analyzed. All EC tests, performed at 0.23 ≤ ur ≤ 0.93 cm s−1 and 5 ≤ j ≤ 7 mA cm−2, satisfied the World Health Organization (WHO) standard for fluoride (CF- ≤ 1.5 mg L−1). The EC tests that satisfied the WHO standard for arsenic (CAs ≤ 10 µg L−1) were at 0.23 cm s−1 and 6 ≤ j ≤ 7 mA cm−2. Spectroscopic analyses on aluminum flocs showed that these are mainly composed of aluminum silicates. Fluoride replaces a hydroxyl group from aluminum flocs and arsenates adsorb on aluminum aggregates. The best EC test in terms of energy consumption (6.7 kWh m−3) was obtained at 0.23 cm s−1 and 6 mA cm−2.

A facile process to synthesize polydopamine (PDA) coated silver nanoparticles (AgNPs) dispersed onto hydrated silica support has been reported here. The nanoparticles were evaluated by X-ray diffraction, FTIR and EDX study. The AgNPs size was found to be around ∼19.0 nm obtained from DLS, FESEM and TEM analysis. The UV–vis spectra of the prepared catalyst nanoparticles support the generation of AgNPs over PDA coated hydrated silica (SiO2) surface. The broadening at UV–vis spectra near ∼400 nm has a prominent evidence of AgNPs. The nanoparticles were employed as catalyst against 4-nitrophenol reduction, Congo red degradation and potassium hexacyanoferrate (III) reduction. The catalytic reaction was monitored in UV–vis spectrophotometer. The catalytic effect was observed as of minimal duration with respect to other reported values. The catalyst also has sufficient reusability upto six numbers of cycles without deterioration of its catalytic activity.

Silicone rubber (SR) is an insulating material widely used in DC cable accessories. Its interface is a weak area of insulation and there is a problem of charge accumulation. Hydrated silica (SiO 2 •nH 2 O) is a reinforcing agent commonly used in SR, and its main component is SiO 2 . This article is based on polymethylvinylsiloxane, doped with SiO 2 particles of different mass fractions. The attenuation of the isothermal surface potential of the sample was tested. Combined with the isothermal surface potential attenuation model, the trap characteristics of the sample are obtained. The results show that the doped SiO 2 introduces a large number of traps on the surface of the SR, among which deep traps are the main ones. Based on the principle of molecular dynamics, simulation calculations of related molecules were carried out, and the results were consistent with the experimental results. The Si-O-Si bond formed by SiO 2 and SR and the hydroxyl group on the surface of SiO 2 introduce impurity trap energy levels between the original forbidden band and conduction band, thereby affecting the surface charge transfer. The results of the research provide help for the design of DC cable accessories.

OBJECTIVE The aim of this study was to evaluate the effect of brushing with whitening toothpaste on the colour change of composite resins discoloured with coffee. METHODS Disc-shaped samples were prepared using one nano-hybrid (Clearfil Majesty Esthetic), one micro-hybrid (GC G-aenial Anterior) and one nano-ceramic composite (Zenit) (n = 6). After initial colour measurements, the samples were coloured in the coffee solution for 5 days. Colour measurements were made again after the colouring process, and brushing simulation was applied for 7, 15 and 30 days with two different whitening toothpastes containing calcium carbonate+perlite (Signal whitening system, SWN) and hydrated silica+hydrogen peroxide (Colgate optic White, COW) and a conventional non-whitening toothpaste containing hydrated silica (Sensodyne pronamel, SPN). Colour change (∆E00 ) after brushing was calculated using the CIEDE2000 system. Repeated measures variance analysis was used for the analysis of data. RESULTS G-aenial anterior and Zenit showed significant coloration compared to Majesty esthetic after coloration with coffee (p 1.8). Colour change over time after brushing with both whitening toothpastes differed significantly (p 0.05), there was a significant difference between Majesty esthetic, G-aenial anterior and Zenit in groups brushed with COW (p

Diatoms are unicellular eukaryotic microalgae widely distributed in aquatic environments, possessing a porous silica cell wall known as frustule. Diatom frustules are considered as a sustainable source for several industrial applications because of their high biocompatibility and the easiness of surface functionalisation, which make frustules suitable for regenerative medicine and as drug carriers. Frustules are made of hydrated silica, and can be extracted and purified both from living and fossil diatoms using acid treatments or high temperatures. Biosilica frustules have proved to be suitable for biomedical applications, but, unfortunately, they are not officially recognised as safe by governmental food and medical agencies yet. In the present review, we highlight the frustule formation process, the most common purification techniques, as well as advantages and bottlenecks related to the employment of diatom-derived silica for medical purposes, suggesting possible solutions for a large-scale biosilica production.

Mars’ transition from an early “warm and wet” to a “cold and dry” environment left fingerprints on the geological record of fluvial activity on Mars. The morphological and mineralogical observations of aqueous activity provided varying constraints on the condition and duration of liquid water on the Martian surface. In this study, we surveyed the mineralogy of Martian alluvial fans and deltas and investigated the hydrated silica-bearing deposits associated with some of these landforms. Using CRISM data, we identified 35 locations across Mars with hydrated silica in proximity to fans/deltas, where the spectral characteristics are consistent with immature or dehydrated opal-A. In a few stepped fans/deltas, we find hydrated silica occurs within the bulk fan deposits and form sedimentary layers correlated with elevation. Meanwhile, in the older fans/deltas, silica mostly occurs at distal locations, and the relation to primary sedimentary deposits is more complex. We propose that the hydrated silica-bearing deposits in stepped fans/deltas likely formed authigenically from Martian surface waters, mainly during the Late Hesperian and Early Amazonian. These silica-bearing deposits could be a tracer for the temperature or duration of water involved in the formation of these deposits, given more precise and detailed observations of the sedimentary context, accessory minerals, the concentration of hydrated silica, and sediment-to-water ratio. Therefore, we consider that silica-bearing deposits should be among the most critical samples to investigate for future Mars missions, which are accessible in the landing sites of Mars 2020 and ExoMars 2022 missions.

Acid-based geopolymers are interesting materials, as they usually present higher mechanical and thermal properties than their alkali-based counterparts do, but they are difficult to use for complex shapes due to the high viscosity of their reactive mixture. This can be overcome by the addition of water in the formulation. In this study, geopolymers have been synthesized from metakaolin and phosphoric acid with variable [P] concentration (by a modification of either the water content or Al/P ratio). Measurements of the viscosity, density and consolidation times have been performed on reactive mixtures differentiated by their water content. Furthermore, a study of the geopolymers’ microstructure and mechanical properties confirmed their evolution with [P]. Finally, a characterization by thermal and structural analyzes of their structure (Fourier transform infrared spectroscopy and X-ray diffraction), have been carried out in order to assess the influence of the water content on the different amorphous networks. It appears that the addition of water influences the structure of the material, as it leads to the formation of new amorphous networks. More specifically, for Al/P = 1 and variable water amounts, the networks are mainly based on the coexistence of Al–O–P with an hydrated silica network, while for variable Al/P, the Al–O–P network coexists with the unreacted metakaolin. In addition, it seems that all the properties are governed by the parameter nP/nAl + nH2O.

Diatoms—unicellular photosynthetic algae—are promising natural sources of nanostructured silica. These microorganisms produce in their membrane approximately a highly ordered porous cell wall called a frustule as protection from environmental stress. Diatom frustules consist of hydrated silica that show peculiar properties including biocompatibility, tailorable surface chemistry, chemical inertness, and thermal stability. Frustules harvested from aquatic ecosystems or diatomaceous fossil sediments represent an excellent cost-effective source of biosilica for a broad range of biomedical applications. The porous ultrastructure of the frustules displays a large surface area available for coating with various biomolecules through different functionalization methods. In this review article, we highlight the main features of diatom biosilica and present some of the most advantageous properties that support the employment of frustules in the field of drug delivery, biosensing, and regenerative medicine. In particular, it is offered an insight into the most common functionalization strategies through which diatom physicochemical properties can be modified and tailored according to the described field of application.

This paper presents the results of measurements performed on &alpha, quartz subjected to shear stress in dry conditions, to understand the relationship between the shear intensity and the resulting physical and chemical effects. If a shear stress of intensity higher than 100 MPa is applied continuously to alpha quartz crystals, they will tend to lose their crystallinity, progressively reduce their friction coefficient (Cof) and change into a low-order material, apparently amorphous under X-ray diffraction, but with a structure different from silica glass. Raman and Pair Distribution Function analyses suggested a structure like cristobalite, a silica polymorph well-known for its auxetic behavior, i.e., having a negative Poisson ratio. This elastic parameter pre-eminently controls the friction coefficient of the material and, if it is negative, the Cof lowering. As a result, the increase in low crystallinity cristobalite is sufficientto explain the lowering of the quartz friction coefficient up to values able to contribute, in principle, to the triggering processes of active faults. This allows hypothesizing a slip induction mechanism that does not include the need to have the interposition of layers of hydrated silica, as invoked by many authors, to justify the low friction coefficients that are achieved in shear stress tests on rocks abundant in quartz.

This paper shows the elimination of arsenic (As) and hydrated silica from natural groundwater (48.63 µg L−1 arsenic, 77.5 mg L−1 hydrated silica, 0.33 mg L−1 phosphate, 5 mg L−1 sulfate, 240 mg L−1 alkalinity, 89.5 mg L−1 hardness, pH 8.44 and 450 µS cm−1 conductivity) by electrocoagulation (EC). The flow plant employed a parallel plates EC reactor in series with a flocculator-settler. Aluminum was used as the sacrificial electrode. Before the electrolysis in the flow plant, a systematic study of the aluminum dose was carried using the EC reactor adapted to a jar test. The influence of the mean linear flow velocity (1.2–4.8 cm s−1) and current density (6–9 mA cm−2) on the removal of As and hydrated silica was addressed. The residual concentration of As and hydrated silica in the flow plant was CAs = 4.2 µg L−1 and Chs = 4.5 mg L−1, respectively, at 9 mA cm−2 and 1.2 cm s−1, which agree well with that obtained in the jar test array. The residual As concentration fulfills the World Health Organization (WHO) recommendation (

The simultaneous removal of hydrated silica, fluoride and arsenic from deep well water (hydrated silica 72 mg L − 1 , fluoride 4.4 mg L − 1 , arsenic 106.2 μg L − 1 , sulfate 50 mg L − 1 , phosphate 0.99 mg L − 1 , pH = 8.2 and conductivity 659 μS cm − 1 ) by electrocoagulation (EC) was investigated. The EC was performed in a continuous electrochemical reactor using aluminum plates as sacrificial anodes coupled directly to a jar test device. The effect of current density (4 ≤ j ≤ 8 mA cm−2) and mean linear flow rates in the EC reactor (0.057 ≤ u ≤ 0.57 cm s−1) on the hydrated silica, fluoride, and arsenic removal efficiencies was analyzed. The abatement of hydrated silica was obtained at 8 mA cm−2 and 0.057 cm s−1, while the residual concentrations of F− and As after the same electrolysis were 0.19 mg L − 1 and 9.8 μg L − 1 , satisfying the WHO guidelines for F− (≤1.5 mg L − 1 ) and As (≤10 μg L − 1 ). Spectroscopic analyses on aluminum flocs revealed that they are predominantly composed of aluminum silicates. Arsenates adsorb on aluminum flocs and fluoride replaces a hydroxyl group from aluminum aggregates.

Immobilizing nanoscale zero-valent iron (NZVI) particles on silica-based supports is an effective way to overcome the NZVI aggregation. The pH value and calcium hardness can change the aggregation kinetics and alter the stability of the suspensions of NZVI-silica based materials, thus change the reactivity of these NZVI-silica based materials to remove chlorinated aliphatic hydrocarbons (CAHs). The removal of CAHs by these NZVI-silica based materials includes adsorption by silica based supports and degradation by NZVI particles. Using 1,1,1-TCA and mesoporous hydrated silica (mHS) as model chlorinated aliphatic hydrocarbon (CAH) and silica based support, the effects of pH value and Ca2+ concentration on both the adsorption and adsorption-degradation processes of CAHs by NZVI-silica based materials were studied. The structural and textural features, suspension stability, particle size distribution, and Zeta potential of the materials under various conditions were characterized by different techniques. Both decreasing initial pH value and increasing Ca2+ concentration can reduce the Zeta potential of mHS and lead to the aggregation of mHS particles, thus inhibiting the removal of 1,1,1-TCA via adsorption by mHS through decreasing the number of sites for adsorption. Low initial pH value can accelerate the corrosion of NZVI core and remove the passivation layer, thus promoting the removal of 1,1,1-TCA via adsorption-degradation by NZVI@mHS. Ca2+ can decrease the sites for adsorption and form precipitates which can block mesoporous channels, thus hinder the 1,1,1-TCA removal via adsorption-degradation by NZVI@mHS.

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

Bone cements are often used for bone repair and fixation. The main objective of formulating a bone cement is to achieve structure and properties similarity to bone. In addition, bioactivity of a bone cement provides a major advantage that helps achieving better binding and interaction with the surrounding tissues. In the current study, gypsum was used as a matrix for a composite that comprises highly crystalline prestine and acid-treated wollastonite (CaSiO3) fibers. Composites made by mixing their powder precursors with deionized water at room temperature, were investigated for their composition using X-ray diffraction (XRD) and Thermogravimetric Analysis (TGA), for their microstructure using Scanning Electron Microscopy (SEM), for their compressive strengths and modulus of elasticity, and for setting time measurements. In addition, cement composites were evaluated for their preliminary bioactivity in a protein-free Simulated Body Fluid (SBF) for up to 14 days. Results show the improvement of mechanical properties and bioactivity of the composites using acid-treated wollastonite fibers. This was attributed to the formation of hydrated silica layer on the surface of the acid-treated fibers which improved the binding with the gypsum matrix and provided nucleating sites for the deposition of bone-like apatite spherolites from SBF media.

Raw kaolinite (kaol) was experimentally transformed to P-type hydrated silica aluminate (HSA-P). After treated by LaCl 3 ·7H 2 O solution, the final product of La-loaded for P-type hydrated silica aluminate (HSA-P-La) was obtained. The middle and final products were characterized using fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM). Kaol, HSA-P, HSA-P-La was introduced into PP with intumescent flame retardants (IFR), respectively. And their effect on the flame retardant and thermal properties of PP composites was studied by limiting oxygen index (LOI), vertical burning test, cone calorimeter test (CCT) and thermogravimetric analysis (TGA). The LOI increases from 18.0% of neat PP to 31.2 in composite of 75 wt% PP/25 wt % IFR, further increases to 32.5, 35.1, 37.5 in 75 wt% PP/23.5 wt % IFR/1.5 wt% Kaol, HSA-P or HSA-P-La, respectively. CCT results show heat release content and rate is best controlled in PP/IFR/HSA-P-La composite. Morphology observation indicates the char layer of PP/IFR/HSA-P-La composite is most compact and thick, which guarantees excellent fire resistance. At same time the effect of HSA-P/HSA-P-La was also compared with generally used A-type hydrated silica aluminate (HSA-A)/HSA-A-La. Anyway HSA-P/HSA-P-La exhibited higher efficiency than HSA-A/HSA-A-La in both flame retardancy and thermostability.

Nanoscale zero-valent iron@mesoporous hydrated silica core-shell particles (NZVI@mHS CSP) with improved dispersibility, transportability and dechlorination strength were successfully synthesized and tested for the removal of chlorinated aliphatic hydrocarbons from groundwater. The structural, electronic and textural features of the NZVI@mHS CSP were characterized by different techniques. The NZVI@mHS CSP depicted a specific surface area of 71 m2·g−1, significantly higher, compare to NZVI (12 m2·g−1), with a mesoporous network due to the formation of a hydrated silica shell surrounding the NZVI particle. NZVI@mHS CSP showed an enhanced transportability in sand column compared with NZVI, related to the suspension stability, small aggregated particle size (

Bayer red mud (RM) was produced from aluminum ore according to Bayer process. In order to study the feasibility of stabilized Bayer RM for use in road construction, strength properties of RM stabilized by lime-fly ash using orthogonal experimental method were evaluated. In test design, the normalized orthogonal table of L9 (34) was adopted. The influence of ratio of lime-ash, the dosage of lime and fly ash, and the type of Bayer RM (Two kinds of Bayer RM from different producers) on the unconfined compressive strengths (UCS) of 7-day and 28-day curing age were studied. The experimental results showed that these factors significantly influenced the UCS. The principal factors influencing 7-day UCS was ratio of lime-ash, followed by chemical compositions of Bayer RM and the dosage of lime and fly ash in last. The principal influencing factor of 28-day UCS was chemical compositions of RM, followed by ratio of lime-ash and the dosage of lime and fly ash in last. Then the optimum proportion for the UCS was determined through the orthogonal analysis. The X-ray fluorescence (XRF) showed that chemical compositions and contents of two types of RM were significantly different in iron, silicon and calcium. The microscopic analysis of the raw material and stabilized material employed X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) showed that C3A(Ca3Al2O6), C2S, and calcium carbonate increased under the optimal conditions of lime-fly ash stabilization, and hydrated silica aluminate and CSH were gradually generated. The stabilization mechanism of Bayer RM by lime-fly ash is related to hydration like aluminate cement. There is no essential difference in reaction mechanism for two kinds of Bayer RM and the difference in the strength properties is essentially originates from the active material content.

Promising nanocomposites (EPDM-nRHP) were prepared from EPDM/ nanosized rice husk powder (nRHP) in the presence of HRH system as modifying dry bonding agent. HRH system comprised hydrated silica, r...

Coal gasification coarse slag (CGCS) is solid waste generated during coal gasification. The mainly treatment method of CGCS is storage and landfill, which causes severe environmental pollution and waste of land resources. Sodium silicate can be synthesized using CGCS after impurities are removed for the high content of amorphous silica. In this work, a novel method of acid activation depolymerization-dilute alkali dissociation is proposed to synthesize high-modulus, low-impurity sodium silicate using CGCS under mild conditions. In the acid activation depolymerization process, the content of impurities such as CaO and Fe2O3 can be reduced from over 30% to below 3%. SiO2 composition can be enriched from 35.75% to 60.60%. The SiOAl bond is broken, the coordination structures of Q4(2Al) and Q4(3Al) are depolymerized, and the reactive Q4(0Al) and Q3(0Al) coordination structures of amorphous silica are formed. Numerous defects appear in the aluminosilicate structure, exposing a large number of active SiOH bonds. Efficient desilicated ratio is increased from 7.59% to 73.45%. During the process of dilute alkali dissociation, a large number of reactive SiOSi bonds with network structure defects are broken with the destruction of hydroxyl groups, while SiO and SiOH bonds are formed. Amorphous silica is leached into the liquid phase in the form of oligomers, and high-modulus sodium silicate can be obtained. Under optimal conditions, the removal ratio of amorphous silica and modulus of sodium silicate can reach 80% and 3.53, respectively. The synthesized sodium silicate can be used to produce hydrated silica, adhesives and surface coatings. This process not only reduces pollution, but also alleviates the shortage of high-purity quartz sand resources and promotes the clean development of coal chemical enterprises.

This work investigates chemical stability of Mg-silicates and silica in aqueous systems in order to gain in-depth understanding of their dissolution and precipitation behaviour under different conditions. The aim was to utilise the knowledge gained to develop an engineered carbon mineralisation technology for an efficient and cost competitive CO2 capture and utilisation. The results, based firmly on 29Si solid-state MAS NMR spectroscopy, and complementary techniques, demonstrate the influence of Si coordination (Qn) on the extent of Mg-silicates dissolution, as the increase in the number of neighbouring Si atoms in the structure of Mg-silicates reduced dissolution of Mg-silicates. While 100 and 80% of Q1(3 Mg) Mg-silicate dissolved in pH = 5 and 6.5, the extent of dissolution for Q2(2 Mg) was lower at values of 90 and 65% under the same conditions, while Q3(1 Mg) did not actually dissolve in solutions with pH = 5 and 6.5. The results of precipitation studies indicated the effect of Mg solubility on the structure and Mg content of the precipitated phases. While Mg-silicates with all three structures of Q1(3 Mg), Q2(2 Mg) and Q3(1 Mg) precipitated in the mildly alkaline environment (pH = 8.5) with the ratios of 20, 40 and 40% respectively, in concentrated acidic solutions of pH = 0, only pure silica (no Mg content) with Q3(1H)/Q4(0H, 0 Mg) having a ratio of 35 and 65% precipitated. The results of direct and indirect carbon mineralisation experiments showed that only 40 and 57 wt% of Mg content of thermally treated Mg-silicate was extracted respectively, consistent with 29Si NMR analyses, indicating that only intermediate Mg-silicate phases I and II with Q1(3 Mg) and Q2(2 Mg) structures were reactive, while other Mg-silicate phases remained inert. Another reason for limited Mg extraction in direct and indirect carbon mineralisation experiments is related to precipitation of a silica-rich phase/s on the surface of the reacting particles leading to passivation, again consistent with 29Si NMR analyses. This confirmed precipitation of Mg-silicate with a Q3(1 Mg) structure as well as hydrated silica Q3(1H) and silica Q4(0H, 0 Mg) in aqueous environments, similar to carbonation processes.

The influence of proton-donor properties and concentration of dopant nanoparticles introduced into Nafion and MF-4SС perfluorosulfonic cation-exchange membranes on the characteristics of cross-sensitive DP-sensors (sensors whose analytical signal is the Donnan potential) in alkaline solutions of sulfur-containing organic compounds were studied. The dopants were acid salts of heteropoly acids (HPAs) and hydrated silica SiO2 and zirconia ZrO2 surface-modified with sulfur-containing groups and an acid HPA salt. A correlation was revealed between the DP-sensor sensitivity to anions (and zwitter-ions) in alkaline solutions, size and proton-donor ability of the added particles, and diffusion permeability of hybrid membranes. Optimum compositions of membranes for arrays of cross-sensitive DP-sensors ensuring the simultaneous determination of cations and anions (and zwitter-ions) in the test solutions with an error of less than 18% were selected.

The diatom biosilica was produced by cultivation of the selected species of diatoms (Pseudostaurosira trainorii) under laboratory conditions. The morphological and structural features, elemental composition, surface area and pore structure, photoluminescence properties, structural bonds and thermal stability of the obtained biosilica were examined using a set of techniques comprising scanning electron microscopy, transmission electron microscopy, UV/vis photoluminescence spectroscopy, IR spectroscopy, X-ray powder diffraction, thermogravimetry, elemental analysis, and porosimetry. The study results demonstrated that diatom frustules possess a three-dimensional structure with silica walls perforated by spatially periodic porous network. Biosilica is composed (98%) of amorphous hydrated silica like opal-A and strong bonded organic residual (about 2%) of biosilica associated proteins and can be considered as naturally organic functionalized 3D silica composite. The diatom biosilica is characterized by three main types of photoluminescence activity: the excitation and emission in the broad mid-ultraviolet range (250–300 nm), the strong photoluminescence in the green region (523 nm) at excitation in mid-ultraviolet region (260 nm), and the excitation-emission in the very narrow blue region (480–493 nm). Keywords: Diatom biosilica, Three-dimensional structure, Organic functionalized biosilica, Photoluminescent material

© 2017 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart. Opal-A, opal-CT and chalcedony develop in various geological environments mainly through continental weathering and hydrothermal processes. Although some spectroscopic criteria already differentiate the structural varieties of silica, no criterion distinguishes the formation process of opaline silica. The originality of this study is based on a unique collection of 38 hydrous silica samples of different structures formed in various geological contexts and lithologies. This large and diverse sampling of silica emphasizes that several new spectroscopic criteria distinguish opal-A, opal-CT and chalcedony: the apparent maximum of the absorption at 5200 cm-1, the area of the absorption of silanol groups as well as the area ratio of the 5200 and 4500 cm-1 bands. Moreover, we observed that the shape of the molecular-water band, quantified by a new criterion developed here (concavity-ratio criterion, CRC), differentiates opals formed by weathering (CRC0.82), regardless of their structure (-A or-CT). This new method quickly assesses the geological conditions of opal formation (on Earth or other terrestrial planets) for which data are unclear or missing.

Hybrid ion-exchange membranes of MF-4SK brand containing hydrated silica and zirconia nanoparticles with sulfonic acid-functionalized surface have been synthesized. The effect of modification on the properties of materials in the proton and potassium forms and the characteristics of potentiometric sensors based on these materials have been studied. It has been found that membrane modification leads to an increase in the ionic conductivity compared with that of the unmodified MF-4SK sample and, in some cases, to a decrease in diffusion permeability. Variations in the cation transport selectivity provided by the modification of MF-4SK membrane have made it possible to decrease the sensitivity of sensors to interfering hydronium cations in an acid medium and increase the sensitivity to amino acid anions and zwitterions in an alkaline medium. Optimum membrane compositions for the determination of histidine cations at pH 7 have been selected.

It is of great importance to deeply understand the crystallization mechanism of zeolite in both fundamental research and industrial applications. Here we have systemically investigated the crystallization of zeolite NaA using hydrated silica (SiO 2 ·3H 2 O) and sodium aluminate solids in the absence of water solvent, which is well characterized by X-ray diffraction (XRD), scanning electron micrography (SEM), UV-Raman, and 27 Al MQMAS and 29 Si MAS NMR techniques. The XRD patterns show that the complete crystallization requires for 5 h at 80 °C. The SEM images suggest that the nucleation mainly occurs on the surface of solid particles. The UV-Raman spectra exhibit that a large amount of the zeolite building units of four-membered rings (4R) formed in the starting solid particles, which even occurs before the crystallization, while crystal growth is always along with the formation of zeolite building units of six-membered rings (6R). The 27 Al 2DMQMAS NMR spectra show that the D4R species are dominant in the precursors for crystallization of NaA. According to these results, we believe that the rearrangement of zeolite building units such as aluminosilicate D4R plays a critical role for the crystallization of zeolite NaA in the absence of water solvent.

This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08 mg L−1 fluoride, 90 mg L−1 hydrated silica, 50 mg L−1 sulfate, 0.23 mg L−1 phosphate, pH 7.38 and 450 μS cm−1 conductivity) by electrocoagulation (EC), using an up-flow EC reactor, with a six-cell stack in a serpentine array, opened at the top of the cell to favor gas release. Aluminum plates were used as sacrificial electrodes. The effect of current density (4 ≤ j ≤ 7 mA cm−2) and mean linear flow rate (1.2 ≤ u ≤ 4.8 cm s−1), applied to the EC reactor, on the elimination of fluoride and hydrated silica was analyzed. The removal of fluoride followed the WHO guideline (

Silica can take many forms, and its interaction with water can change dramatically at the interface. Silica based systems offer a rich tapestry to probe the confinement of water as size and volume can be controlled by various templating strategies and synthetic procedures. To this end, microporous silica nanoparticles have been developed by a reverse microemulsion method utilizing zinc nanoclusters encapsulated in hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimers as a soft template. These nanoparticles were made tunable within the outer diameter range of 20-50 nm with a core mesopore of 2-15 nm. Synthesized nanoparticles were used to study the effects of surface area and microporous volumes on the vibrational spectroscopy of water. These spectra reveal contributions from bulk interfacial/interparticle water, ice-like surface water, liquid-like water, and hydrated silica surfaces suggesting that microporous silica nanoparticles allow a way to probe silica water interactions at the molecular scale.