Formation Of Silica Research Articles

Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica

AbstractTo understand the effects of H2O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg2SiO4 with 1.1 wt% H2O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2 (mStv), containing 1 wt% H2O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering the lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming the phase assembly Brd + Pc + Stv. The results may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds.

Fluid dynamic simulations of EG-W (ethylene glycol–water)​ mixtures to predict nanofluid heat transfer coefficients

In previous scholarly studies, the water and ethylene glycol mixtures as base liquids have been considered in the ratio of 40:60 (60EGW), with specific investigations focusing on a nanofluid in the form of Silicon dioxide (SiO 2 ) in relation to its thermo-physical properties, besides its nature of the heat transfer coefficients (HTC). In this study, the main aim lies in SiO 2 heat transfer coefficient prediction. With the approach of computational fluid dynamics (CFD) considered, the experimental conditions constitute 40EGW. For SiO 2 nanoparticles, their viscosity and thermal conductivity are experimentally assessed, having been dispersed in 60EGW and 40EGW. Also, the existing literature and experimental values are used to conduct regression analysis. With thermal features on the focus, there is also the formulation of correlations. Furthermore, there is the invocation of correlations in heat transfer coefficients and CFD simulations that target Al 2 O 3 and SiO 2 nanoparticles, with predictions entailing their dispersion in 40EGW and 60EGW base fluids. The inlet temperature is set at 60 to 80 °C, and it is at this stage that there is CFD simulation implementation. For the volume concentration, the ranges include 0.0 percent to 1.5 percent. The existing literature is relied upon relative to the validation of the coefficients of heat transfer, besides previously predicted nanofluids. From the results, compared to the case of 40EGW base fluid, there is 51 percent and 53 percent enhancement when the experimental conditions are set at 1.0 percent volume concentration, with temperatures being 80 °C. From the computational outcomes, Al 2 O 3 /40EGW nanofluids tend to be associated with significant heat transfer coefficients. Specifically, the enhancement of heat transfer for these materials stands at 52.9%. On the other hand, the enhancement of heat transfer when the base fluid of SiO 2 /40EGW is considered stands at 51.0%. These values are obtained when the experimental conditions are considered at 80 °C, as well as a volume concentration of 1.0%. Therefore, when aspects of heat transfer coefficients and thermal conductivity are considered, the superiority of 40EGW is confirmed. As such, the study confirms the impact of the base nanofluids set at 40EGW relative to the coefficients of heat transfer and also the thermal properties of materials.

Biomimetic core–shell silica nanoparticles using a dual-functional peptide

Biomimetic nanomaterials have attracted tremendous research interest in the past decade. We recently developed biomimetic core–shell nanoparticles – silica nanocapsules, using a designer dual-functional peptide SurSi under room temperature, neutral pH and without use of any toxic reagents or chemicals. The SurSi peptide is designed capable of not only stabilizing nanoemulsions because of its excellent surface activity, but also inducing the formation of silica through biosilicification at an oil–water interface. However, it remains challenging to precisely control the peptide-induced nucleation and biosilicification specifically at the oil–water interface, thus forming oil-core silica-shell nanocapsules with uniform size and monodispersity. In this study, the fundamental mechanism of silica formation through a peptide catalyzed biosilicification was systematically investigated, so that the formation of oil-core silica-shell nanocapsules can be precisely controlled. The SurSi peptide induced hydrolysis and nucleation of biomineralized silica particles were monitored to study the biosilicification kinetics. Effects of pH, SurSi peptide concentration and pre-hydrolysis of silica precursors were also studied to optimize the formation of biomimetic silica nanocapsules. The fundamental understanding achieved through these systematic studies provides valuable insights for making core–shell nanoparticles via controlling nucleation and reaction at interfaces.

Combined treatments of fiber surface etching/silane-coupling for enhanced mechanical strength of aramid fiber-reinforced rubber blends

This study sought to improve the interfacial bonding force between aramid fiber (AF) and a rubber matrix. We pretreated the aramid fiber with anhydrous calcium chloride (CaCl2) and sodium hydroxide (NaOH) solutions. We then performed a separate modification using two different methods, first, grafting the aramid fiber with silane coupling agent γ-Methacryloxypropyl trimethoxy silane (KH570) and secondly in situ formation of silica on the surface of aramid fiber. In addition, mechanical blending was adopted to prepare natural rubber/cis-1,4-polybutadiene rubber/aramid fiber (NR/BR/AF) composites. Finally, aramid fibers were characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM), then the mechanical properties of the corresponding composites analyzed. Results revealed that the synergistic action of anhydrous CaCl2 and NaOH solutions caused an increase in surface roughness and the contact area of the aramid fiber. The Sol-gel method allowed successful coating of the secondary modified aramid fiber surface with a layer of in situ-generated silica. Consequently, this improved surface reactivity of the fiber and the rubber matrix, thus promoting their combination. Moreover, we successfully grafted KH570 onto the surface of the aramid fiber through an oxygen-containing group on the surface of the pretreated aramid fiber. Tensile properties of AF composites exhibited a 31.9% increase after secondary modification with KH570 whereas their DIN abrasion performance increased by 16.2%. Notably, a significant improvement in interfacial adhesion was recorded in modified AF prepared NR/BR composites, which further improved the mechanical properties of NR/BR composites.

Study on the tribological properties of graphene oxide composite films by self-assembly

A series of graphene oxide composite lubricating films were fabricated in virtue of self-assembly technique driven by chemical bonds, which could strongly enhance interfacial interaction. The composite lubricating film Si-APS-GO-HOAF composed of GO and HFPO oligomer acid fluorides (HOAF) exhibited excellent tribological properties even immersed in 0.15 M NaCl solution for one month, attributing to strong interfacial interaction of chemical bonds and the synergistic effect of GO and HOAF. Furthermore, the outermost layer HOAF was partly adsorbed on the surface of the friction pair during the friction process and gradually formed a layer of transferred lubricating film. Surface analysis demonstrated that the formation of carbon oxide fragments and silicon oxides led to the damage of assembled layers, causing lubrication failure.

Titanium white modification with silica nanoparticles and formation of structured clusters on vibrating screen

The behaviour of titanium white (TiO2) particles with particle size smaller than 45 μm during the modification with nanoparticles (5–50 nm) of hydrophobic silica powder on the vibrating screen and following examination of the newly formed particle clusters is described. Using the vibrating screen aerated in certain places using loudspeaker the subsequent fluidization of the titania particles via simultaneous modification with silica was achieved. The particles of titania are being less cohesively bounded, the van der Walls are weaker and flowability of the system is radically improved. By the targeted fluidization of regions on the screen, was possible to experiment with resulting shapes of particle clusters from the nanoparticles of silica and titanium white in this research. Resulting structure can appear at approximately 2 s of 222.32 Hz excitation using loudspeaker acoustic waves. Methyl groups of hydrophobic nanoparticles of silica can be source for advanced surface applications.

Development of recoverable magnetic mesoporous carbon adsorbent for removal of methyl blue and methyl orange from wastewater

Abstract The novel magnetic mesoporous activated carbon (MMAC) was prepared from activated carbon (AC), produced from rice husk through ZnCl2 chemical activation. Meso-structure was induced via Korea Advanced Institute of Science and Technology-6 (KIT-6) silica formation and magnetic behavior was incorporated by magnetite by wetness impregnation method. KIT-6 silica enhances the porosity and provides a 3D structure to improve the adsorption process. The adsorption of methyl blue (MB) and methyl orange (MO) dyes on MMAC, mesoporous activated carbon (MAC) and AC was investigated and compared. The adsorbents were characterized by SEM, XRD, BET and FTIR analysis techniques. The effect of different process parameters on the adsorption efficiency such as pH of the dye solution, initial dye concentration and dosing of adsorbents were studied. The adsorption efficiency was evaluated by testing aliquot in UV–vis spectroscopy. The experimental data for the MMAC shows that MB followed the Freundlich isotherm while MO was well suited with the Langmuir model. The MMAC removed 82 % MB and 98.5 % MO dye solution in 30 min. The adsorbent was regenerated and reused for MB and MO for 4 cycles without a significant decrease in the adsorption efficiency. The MMAC was found to be the most efficient adsorbent than MAC and AC because of its high surface area and high pore volume. The magnetic behavior of MMAC separates the adsorbent after the adsorption process, making it potential adsorbent for water treatment.

Production of low-energy fragment-ion beams from hexamethyldisiloxane and the irradiation of SiO+ ion beam to substrates with supplemental oxygen gas for SiO2 film formation

In this work, low-energy fragment-ion beams were produced from hexamethyldisiloxane (HMDSO) used as a source material and substrates were irradiated by these beams with supplemental oxygen gas for the formation of silicon dioxide (SiO2) film. During this process, SiO+ ions having an energy of 50 eV were mass-selected from various fragments derived from the decomposition of HMDSO. These ions were subsequently transferred to a Si substrate at room temperature in conjunction with a supplemental oxygen flow. The resulting film was assessed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to confirm SiO2 deposition. The bonding of incident SiO+ ions with a quartz crystal microbalance (QCM) was assessed at ion energies of 50, 100 and 200 eV, and the sticking probability of incident SiO+ ions to the QCM crystal substrate was found to decrease monotonically with increasing energy.

Biological Route to Fabricate Silica on Cellulose Using Immobilized Silicatein Fused with a Carbohydrate-Binding Module.

Silicatein is an enzyme capable of catalyzing silica formation under mild conditions and is a promising catalyst for the fabrication of biohybrid materials. However, unfavorable aggregation of silicatein makes it unsuitable for use in material fabrication. In this study, a soluble protein tag (ProS2) and a carbohydrate-binding module (CBM) were used to develop a soluble and cellulose-binding fusion silicatein, ProS2-Sil-CBM, which can be efficiently immobilized on cellulose to form silica on it. ProS2-Sil-CBM was soluble in aqueous media and strongly bound to cellulose. ProS2-Sil-CBM bound on cellulose catalyzed the formation of a silica layer on the cellulose in the presence of tetraethyl orthosilicate as the substrate. Scanning electron microscopy (SEM) and surface elemental analysis confirmed the formation of silica on cellulose. This technique can be used to fabricate inorganic-organic hybrid materials to immobilize biomolecules and can be applied to develop novel biocatalytic systems, biosensors, and tissue culture scaffolds.

Experimental and theoretical study of deactivated HDT catalysts by Si species deposited on their surfaces: Models proposition, structural and thermodynamic analysis

It is known that silicon species originate from the thermal degradation of the polydimethylsiloxane, adsorb on the catalysts surface used for hydrotreatment in the oil refining industry. This severely affects the performance of these catalysts and considerably reduce their lifetime. Combining 29Si and 13C CP/MAS NMR experiments and DFT calculations, we investigated the poisoning process of these catalysts by silicon species in order to obtain a better understanding of this process. Two structural models (mono and bilayer) for amorphous silica deposited on the γ-Al2O3 surface and some intermediates that can be formed during this process were proposed. From the calculated 29Si chemical shifts, it was possible to identify chemical shifts variations due to different structural elements for each species, thereby, it was possible to make a more appropriate assignment of the resonances found in 29Si CP/MAS NMR spectra in the literature. Besides that, through of the good agreements obtained between the experimental and simulated 29Si CP/MAS NMR spectra, we identified that probably the D4, T1, T3, T4, Q1 and Q2 species are present in the initial stage of the contamination and that the amorphous silica bilayer model deposited on the γ-Al2O3 surface best characterizes the final stage of the contamination. Moreover, the thermodynamic analysis revealed that the chemisorption reaction of the Hexamethylcyclotrisiloxane (D3) compound is much more stable than the Octamethylcyclotetrasiloxane (D4) compound and of a fragment (corresponding to 13 or 14 of the D3 and D4compounds, respectively), and the chemisorption reaction of the fragment presented the highest values of ΔG°. This leads us to deduce that the D3 and D4 compounds chemisorb preferentially without breaking. Besides, it also showed that the amorphous silica formation process on the γ-Al2O3 surface is spontaneous and the bilayer formation reaction is more stable than the monolayer.

Study on photoelectric properties of Si supported ZnO

The ZnO films were deposited on p-Si(100) substrate to show the stoichiometric coefficient ratio of Zn and O is greater than 1:1, indicating the existence of oxygen vacancies in ZnO films, moreover, the oxidation state of Si2p shows the formation of silicon oxide in the vicinity of Si/ZnO interface (ZnO side), which result from Si diffusion into ZnO film. Different models of Si supported ZnO were constructed based on experimental results to study its photoelectric properties, the numerical investigations reveal that Fermi level of ZnO:Si, ZnO:Si-int, and ZnO-V O all move to conduction band minimum, which means they are beneficial to n type semiconductor. The dielectric function of ZnO–Si-int moves to the lower energy direction (red shift), the conductivity of which is higher in the range of 3eV∼7eV, and its absorption and reflectivity both are higher with wavelength more than 300 nm; however, the optical properties of ZnO:Si are poor, implying that the degradation of photoelectrical properties of Si/ZnO heterojunction result from Si diffusion in ZnO films. • We perform a test on photoelectric property of Si supported ZnO nanofilm. • We perform a numerical approach on photoelectric property of Si supported ZnO nanofilm. • We detected the fantastic change on optical properties of Si supported ZnO nanofilm. • It implies a potential method for design photovoltaic devices.

Silicon isotope variations in hydrothermal systems at Yellowstone National Park, Wyoming, U.S.A.

Silicon (Si) isotopic compositions of authigenic Si-bearing materials can be powerful tracers of geological Si cycling and reconstruction of Earth’s climate. Interpretations of Si isotope data, however, are complicated by an inadequate understanding of natural Si isotopic fractionation pathways. This study investigated Si isotope fractionation between hydrothermal fluids and amorphous silica sinters of Cistern Spring and Deerbone Spring at Yellowstone National Park, USA, with a particular focus on spatial variations along spring flowpaths. Modeling of geochemical data indicate that the fluids at Cistern Spring were supersaturated with respect to amorphous silica whereas the fluids at Deerbone Spring were undersaturated due to lower SiO2 content and a more alkaline pH. The δ30Si values of the spring waters for both sites exhibit small variations, whereas the associated amorphous silica sinters displayed a considerable range and generally decreased downflow (from − 2.25 to −5.04‰ for Cistern and from −0.11 to −0.81‰ for Deerbone). The magnitude of apparent isotopic fractionation between solid and aqueous silica (Δ30Sisolid-fluid) was significantly larger for the samples from Cistern Spring than for Deerbone Spring or similar hot spring systems at Geysir geothermal field in Iceland. The Δ30Sisolid-fluid values for Cistern Spring ranged from −2.40 to −5.49‰ along the flowpath and correlated inversely with the rate of silica precipitation, indicating a process dominated by kinetic isotope fractionation. In contrast, the magnitude of Si isotopic fractionation was significantly smaller at Deerbone Spring (+0.21 to −0.64‰). A portion of the opaline sinters at Deerbone may have formed cryogenically under freezing winter conditions that altered silica saturation and formation pathway. Rapid isotope exchange with silica undersaturated hydrothermal fluids may have erased initial kinetic isotope effects. Re-equilibration between opal-A and fluids was strongly affected by isotopic fractionation between aqueous silica species and fluid ionic strengths. These results document both kinetic and equilibrium Si isotope fractionation from field observations and highlight the pivotal role of fluid-rock interaction on the preservation of Si isotope signatures in the rock record.

On the Potential of Silicon as a Building Block for Life.

Despite more than one hundred years of work on organosilicon chemistry, the basis for the plausibility of silicon-based life has never been systematically addressed nor objectively reviewed. We provide a comprehensive assessment of the possibility of silicon-based biochemistry, based on a review of what is known and what has been modeled, even including speculative work. We assess whether or not silicon chemistry meets the requirements for chemical diversity and reactivity as compared to carbon. To expand the possibility of plausible silicon biochemistry, we explore silicon’s chemical complexity in diverse solvents found in planetary environments, including water, cryosolvents, and sulfuric acid. In no environment is a life based primarily around silicon chemistry a plausible option. We find that in a water-rich environment silicon’s chemical capacity is highly limited due to ubiquitous silica formation; silicon can likely only be used as a rare and specialized heteroatom. Cryosolvents (e.g., liquid N2) provide extremely low solubility of all molecules, including organosilicons. Sulfuric acid, surprisingly, appears to be able to support a much larger diversity of organosilicon chemistry than water.

Biologically mediated silicification of marine cyanobacteria and implications for the Proterozoic fossil record

Abstract Silicification was a major mode of fossilization in Proterozoic peritidal environments, but marine silica concentrations and the chemical and biological mechanisms that drove microbial silicification and formation of early diagenetic chert in these environments remain poorly constrained. Here, we use taphonomy experiments to demonstrate that photosynthetically active cyanobacteria that are morphologically analogous to the oldest cyanobacterial fossil, Eoentophysalis, mediate the formation of magnesium-rich amorphous silica in seawater that is undersaturated with respect to silica. These results show that microbes in Proterozoic tidal environments may have mediated their own silicification at lower silica concentrations than previously assumed.

All‐Solution Processed Multicolor Patterning Technique of Perovskite Nanocrystal for Color Pixel Array and Flexible Optoelectronic Devices

AbstractIn the present study, a new patterning method is introduced through the surface modification and stabilization of perovskite nanocrystals, which is compatible with conventional photolithography process based on all‐solution processes. Chemically designed gel‐type silica‐coated CsPbX3 (X = Br, I, etc.) perovskite nanocrystals combined with dip coating method are introduced to form stable and uniform films. Analyses of the physical and chemical states of nanocrystals and investigation of the kinetics in silica formation are conducted. In an optimized condition, physically uniform and chemically stable perovskite thin films are deposited on various substrates such as flexible, stretchable substrates, or even nonflat objects. By adopting these advantages and developing stable photolithographic chemicals, the high resolution patterns are successfully patterned with green and red emitting CsPbBr3 and CsPbBr3I3−x perovskites with the size down to 5 µm of radius and even a multicolor pixel array which can be used for the color filter, light converting or detecting applications. Flexible white light emitting diode is also fabricated with a large color gamut coverage. This work provides a fundamental understanding of perovskite nanocrystals, and also offers a technological breakthrough enabling various optoelectronic applications.

Aplicação de boro na produção e qualidade de sementes de couve-flor

Estudos sobre o efeito da adubação via foliar na produção e qualidade de sementes de hortaliças ainda são escassos e observa-se carência de informações referente recomendações que proporcionem aumento na produção de sementes com elevado potencial fisiológico. Assim, objetivou-se avaliar o efeito da aplicação de boro via foliar em distintos estádios fenológicos da couve-flor na produção e qualidade fenológica de sementes. O experimento foi desenvolvido no período de janeiro de 2017 a março de 2018. A espécie estudada foi a couve-flor cultivar Piracicaba Precoce com 16 tratamentos, resultantes da combinação de número de aplicações (1, 2, 3, 4, 5) de boro via foliar a 1,0 g L-¹ em cinco estádios fenológicos: haste floral com 30 cm; abertura das primeiras flores; formação das primeiras síliquas; 50% de síliquas formadas e 100% de síliquas formadas, além do controle sem aplicação de boro. O delineamento experimental foi em blocos casualizados com quatro repetições. De acordo com os resultados observou-se que a aplicação de boro via foliar em diferentes estádios fenológicos da couve-flor ‘Piracicaba Precoce’ não diferiu do controle (sem boro) para produção de sementes. Realizar uma aplicação de boro via foliar para produção de sementes de couve-flor nos estádios: de abertura das primeiras flores (média: 96%); na formação das primeiras síliquas (média: 94%), e no momento em que há 100% de síliquas formadas (ainda verdes) (média: 93%), há aumento de vigor em média de 16% a mais quando comparado a plantas com 30 cm de haste floral (estádio mais jovem, média: 78% de vigor)

Identification of the Domains Involved in Promotion of Silica Formation in Glassin, a Protein Occluded in Hexactinellid Sponge Biosilica, for Development of a Tag for Purification and Immobilization of Recombinant Proteins.

Glassin, a protein occluded in biosilica of the hexactinellid sponge Euplectela, promotes silica formation from silicic acid at room temperature and neutral pH and is characterized by its primary structure which consists of a tandem repeat carrying three distinct domains, histidine and aspartic acid-rich (HD) domain, proline-rich (P) domain, and histidine and threonine-rich (HT) domain. The present study aims to clarify the domain responsible for the promotion of silica formation and to demonstrate usefulness of glassin and its domain as a tag for purification and immobilization of recombinant proteins. When each domain was mixed with silicic acid at neutral pH, silica was formed with HD domain as well as glassin, or a single repeat, but not with P or HT domain. Neither of amino or carboxy-terminal half of HD domain induced silica formation. The amount of silica formed with HD domain was significantly lower than that of glassin or a single repeat. HD domain fused with HT domain raised the amount of silica formed, while a HD domain fused with P domain, a mixture of HD and P domains, or a mixture of HD and HT domains has little effect on the promotion of silica formation. Collectively, a minimum sequence for promotion of silica formation is HD domain, whose activity can be enhanced by HT domain through a topological effect. In addition, practicality of glassin and HD domain was demonstrated by fusion of these sequences to green fluorescent protein which was successfully purified with Ni affinity chromatography and immobilized on silica.

Alternating silicon oxy-nitride and silicon oxide stripe formation by nitric oxide (NO+) ion implantation

We report nitric oxide ion (NO+) beam induced nanoscale pattern formation on Si (100) surface. The patterns are found to be structurally as well as chemically periodic. A highly reactive 14 keV NO+ beam is developed in an Electron Cyclotron Resonance ion beam system and implanted on Si (100) surface at oblique angles to form a periodic nano-ripple pattern with specific silicon oxide and silicon oxy-nitride enriched sectors with different dielectric constants. Well-defined ripple patterns start to form at comparatively lower ion fluences due to an additional instability generation by the chemical reaction of NO+ ions with silicon. The chemical shift of the Si 2p peak in the x-ray photoelectron spectroscopy study of an ion irradiated sample confirms the formation of silicon oxide and silicon oxy-nitride, whereas the local chemical nature of the ion induced ripple patterns, probed by electron energy loss spectroscopy, approves spatially resolved silicon oxide and silicon oxy-nitride stripe pattern formation. The ion modified layer thickness measured by cross-sectional transmission electron microscopy has an excellent agreement with Monte Carlo simulations. The optical sensitivity of an NO+ bombarded chemically patterned Si surface is also studied by UV–Visible spectroscopy. Formation mechanisms and potential applications of such nano-scale spatially graded materials are discussed.

Extraction of nano‐porous silica from hydrosodalite produced via modification of low‐grade kaolin for removal of methylene blue from wastewater

AbstractBACKGROUND: This work employs low‐grade kaolin as raw material in the economical production of nano‐porous silica with extended surface area via the hydrothermal acidification of intermediate zeolite composite to remove methylene blue from wastewater. Hydrosodalite fabricated through the modification of meta‐kaolin (MK) with sodium aluminate (NaAlO2) was used as a precursor in the hydrothermal acidification step.RESULTS: The direct conversion of MK to zeolite composite generating a low crystalline phase, containing quartz which was eliminated in the acidification step, exhibited a strong affinity towards dye adsorption. It was indicated that the NaAlO2/MK ratio could influence the hydrosodalite crystallization as well as adsorption efficiency of the nano‐porous silica obtained from acidification of zeolite composite. The nano‐porous silica formation involved the ion extraction from hydrosodalite cabbage‐like particles, depending on crystallinity of intermediate zeolite composite.CONCLUSION: The mesoporous silica represented the appropriate adsorptive behavior when produced from precursor modified with lower NaAlO2 content, NaAlO2/MK = 0.24, attributed to superior specific surface area, 420 m2 g−1, with average pore diameter about 3.3 nm. The equilibrium data was better correlated by Redlich–Peterson isotherm. Compared to the surface area of silica powders fabricated from high grade kaolins, Al2O3/SiO2, > 0.83, by the acid‐etched strategy, the mesoporous silica produced from the low‐grade kaolin by the template free method indicates higher value. © 2020 Society of Chemical Industry

An Unexpected Role of H During SiC Corrosion in Water

During aqueous corrosion, atoms in the solid react chemically with oxygen, leading either to the formation of an oxide film or to the dissolution of the host material. Commonly, the first step in corrosion involves an oxygen atom from the dissociated water that reacts with the surface atoms and breaks near surface bonds. In contrast, hydrogen on the surface often functions as a passivating species. Here, we discovered that the roles of O and H are reversed in the early corrosion stages on a Si terminated SiC surface. O forms stable species on the surface, and chemical attack occurs by H that breaks the Si-C bonds. This so-called hydrogen scission reaction is enabled by a newly discovered metastable bridging hydroxyl group that can form during water dissociation. The Si atom that is displaced from the surface during water attack subsequently forms H2SiO3, which is a known precursor to the formation of silica and silicic acid. This study suggests that the roles of H and O in oxidation need to be reconsidered.