Silicate Surface Research Articles

Effects of chemical etching on surface structure and tribological behavior of silicate substrates

Abstract This study investigated the effect of chemical etching on the surface structure and tribological behavior of silicate substrates. Silicate surfaces were etched using a mixture of nitric acid (HNO3) and ammonium bifluoride (NH4HF2) for durations ranging from 1 to 60 min. The etched surfaces were characterized using optical microscopy, scanning electron microscopy, surface profilometry, water contact angle measurements, and UV–vis spectroscopy to evaluate the changes in surface morphology, roughness, wettability, and optical properties. Tribological performance was assessed using reciprocating ball-on-plate friction tests. The results showed that increasing the etching time resulted in the formation of microscale surface features, increased surface roughness, enhanced hydrophilicity, and reduced optical transmittance. The average friction coefficient decreased with an increase in the etching time up to 30 min, beyond which a slight increase was observed. The 1-minute etched specimen exhibited the best wear resistance with the narrowest wear track and the least material removal. The improved tribological performance was attributed to the formation of a stable transfer film, reduced real contact area, and entrapment of wear debris. This study highlights the potential of chemical etching as a technique to tailor the surface structure and tribological properties of silicate materials for various applications.

Obtaining granular adsorbents based on biopolymers and clay minerals

The development of granular, low-cost adsorbents represents an important environmental challenge. Natural clay minerals show promise in this area, as they exhibit adsorption capacity a range of pollutants. Nevertheless, the high dispersion of aluminosilicates limits their widespread use. To enhance the processability of these materials, they are subjected to granulation using natural biopolymers, such as sodium alginates. Concurrently, the adsorption capacity of the granules can be increased by the application of modifiers to the surface of natural silicates, in particular iron oxyhydroxides, which are efficacious in the removal of heavy metals from water. The aim of this study is to obtain granular adsorbents based on saponite and biopolymer that are stable in water and capable of removing heavy metal ions from the water environment. The rheological behavior of the suspensions was investigated in order to ascertain the optimal conditions for high-quality granulation. The phase composition of the modified saponite was determined by X-ray diffraction analysis. The structural-sorption characteristics of the samples were investigated using the method of low-temperature nitrogen adsorption-desorption, and their thermal properties were studied by differential thermal and thermal gravimetric analyses. The present study demonstrates that the viscosity of saponite and sodium alginate-based suspensions with varying mass ratios is dependent on the clay mineral content of the mixture, at a fixed polymer quantity. The conditions for granulation were determined, and it was established that the stability of the granules in the aqueous medium is influenced by the quantity of sodium alginate incorporated into the mixture. It was established that the specific surface area of the modified sample decreases during the granulation process. This value is 109 m2/g, which is less than the 173 m2/g that observed for the powdered adsorbent. The processes and phase transformations occurring in granular materials during heating were studied. As a result of the study of the rheological characteristics of suspensions based on saponite and sodium alginate, it was found that these systems are thixotropic. It was also discovered that the stability of the granules in an aqueous medium is significantly affected by the amount of sodium alginate added to the suspension. The potential applications of the obtained adsorbents in the purification of water from heavy metal ion contamination are shown.

Understanding the Impact of H2 Diffusion Energy on the Formation Efficiency of H2 on the Interstellar Dust Grain Surface

We use microscopic Monte Carlo simulation techniques to investigate the impact of H2 diffusion energy on the recombination efficiency of H2 on interstellar dust grain surfaces under diffuse and translucent cloud conditions. We constructed five models representing different possible conditions encountered by adsorbed H and H2 on interstellar dust grains. We implemented adsorption sites with multiple binding energies for surface species; the Encounter-Desorption mechanism was also included. The study focused on silicate surfaces in diffuse clouds and water ice surfaces in translucent clouds. The results show that the recombination efficiency of H2 on dust surfaces decreases as H2 diffusion energy increases. An interesting finding of this work is that considering different binding sites for H and H2 gives rise to multiple steady phases, during which the recombination efficiency remains constant with a change in H2 diffusion energy.

Experimental verification of the effect of lithium silicate surface treatment on concrete durability

Abstract This paper presents the results of a research focused on the behaviour of lithium silicate sealer as an additional protection of concrete structures against environmental degradation effects. The results are compared with the behaviour of siloxane sealer – an agent commonly used for the protection of concrete structures against environmental effects in practice. The paper presents the results of several tests: contact angle, porosity change and carbonation depth that was determined by accelerated test method. All the mentioned tests lead to a conclusion that siloxane sealer is significantly more efficient in increasing the durability of structures than lithium silicate sealer.

Enhancing bonding of zirconia lithium silicate ceramics to dentin: The effect of surface treatment and resin cement

This laboratory study evaluated the influence of surface treatments on surface topography, and the bonding of CAD/CAM (computer-aided design computer-aided manufacturing) zirconia-containing lithium silicate (ZLS) surfaces to human dentin using various contemporary resin cements. Specimens from ZLS CAD/CAM blocks (Celtra™ Duo and Vita™ Suprinity) underwent three surface pretreatments: grinding only; 5 % hydrofluoric acid etching followed by application of a silane coupling agent, and a self-etching ceramic primer. The specimens were bonded to a flat exposed dentin surface using two etch-and-rinse and two self-adhesive resin cements, and then sectioned into microspecimens for microtensile bond strength (μTBS) testing. Failure modes of bonded surfaces, and ceramic surface roughness and topography were assessed. Results indicated that surface treatment was essential for ZLS-dentin bonding. Hydrofluoric acid and silane, along with the self-etching primer resulted in comparable strengths and outperformed the control group. Etch-and-rinse cements yielded significantly higher μTBS than self-adhesive cements. Significant differences in surface roughness and topography were observed among the treatment groups. Hydrofluoric acid exhibited the highest roughness parameters and most prominent surface changes. These findings highlight the importance of surface treatment for enhancing zirconia-containing lithium silicate bonding to dentin, and emphasize the critical role of the resin cement choice in optimizing dental restorative outcomes.

Search for Chirality in Hydrogenated Magnesium Nanosilicates: A DFT and TD-DFT Investigation.

The formation of silicate grains in the interstellar medium (ISM), especially those containing chiral surfaces such as clinopyroxenes, is poorly understood. Moreover, silicate interactions with various forms of hydrogen-proton (H+), neutral H (HI), and molecular hydrogen (H2) are of high importance as hydrogen comprises >90% of the ISM gas budget, and these species play important roles in the formation of new molecules in space. Furthermore, silicate surfaces catalyze the formation of H2 in the interstellar medium formed on dust grain surfaces by H-H association. The technical difficulty of in situ laboratory investigations of nanosilicate nucleation using astrophysically relevant environmental conditions makes computational chemistry a useful tool for studying potential nanosilicate structures. Furthermore, chiral surfaces interacting with chiral organic molecules could serve as templates that lead to the enantiomeric excess of l-amino acids and d-polyols detected in carbonaceous meteorites. However, in order for this effect to take place, an excess of one chiral form of a mineral is required to break the symmetry. This symmetry-breaking event could have been due to the asymmetric absorption of circularly polarized light by the nanosilicate as it traverses star-forming regions. We investigate this possibility using a metastable chiral form of an enstatite dimer as an input for density functional theory (DFT) and time-dependent (TD)-DFT calculations to obtain various properties and circular dichroism spectra. All in all, twenty-six magnesium nanosilicate structures were studied using varying degrees of hydrogenation: none, with HI, with H+, and with H2. The HSE06/aug-cc-pVQZ level of theory was used for the DFT calculations. TD-DFT calculations utilized the CAM-B3LYP/cc-pVQZ and ωB97X-D3/cc-pVQZ functional and basic set pairings. Results show that (1) all twenty-six structures have absorption bands that fall within the 0.6-28.3 μm range available with the newly launched James Webb Space Telescope and (2) there is a small enantioselective effect by UV-CPL on the eight chiral enstatite dimers (predicted g-values of up to 0.007). While the observed effect is small, it opens up the possibility that it is the inorganic material that becomes enantiomerically biased by UV-CPL, driving chiral enhancements in meteoric organic molecules.

NH3 adsorption and competition with H2O on a hydroxylated aluminosilicate surface.

The interaction between ammonia (NH3) and (alumino)silicates is of fundamental and applied importance, yet the specifics of NH3 adsorption on silicate surfaces remain largely unexplored, mainly because of experimental challenges related to their electrically insulating nature. An example of this knowledge gap is evident in the context of ice nucleation on silicate dust, wherein the role of NH3 for ice nucleation remains debated. This study explores the fundamentals of the interaction between NH3 and microcline feldspar (KAlSi3O8), a common aluminosilicate with outstanding ice nucleation abilities. Atomically resolved non-contact atomic force microscopy, x-ray photoelectron spectroscopy, and density functional theory-based calculations elucidate the adsorption geometry of NH3 on the lowest-energy surface of microcline, the (001) facet, and its interplay with surface hydroxyls and molecular water. NH3 and H2O are found to adsorb molecularly in the same adsorption sites, creating H-bonds with the proximate surface silanol (Si-OH) and aluminol (Al-OH) groups. Despite the closely matched adsorption energies of the two molecules, NH3 readily yields to replacement by H2O, challenging the notion that ice nucleation on microcline proceeds via the creation of an ordered H2O layer atop pre-adsorbed NH3 molecules.

Trapped Water on Silicates in the Laboratory and in Astrophysical Environments

The existence of strongly bound water molecules on silicate surfaces, above the desorption temperature of water ice, was first predicted by computational studies and has recently been demonstrated by laboratory experiments. Such trapped water may be present in various astrophysical environments and there is now evidence for its presence in the diffuse interstellar medium (ISM) and in extraterrestrial particles. We present here new results of a laboratory study of the phenomenon of trapping (strong bonding) of water molecules by silicates. We show that the efficiency of the trapping is strongly dependent on the properties and composition of the surface. Our results point out that the presence of trapped water should be due to the hydrophilic properties of the silicate surface and that the nature of the trapping is physical (physisorption rather than chemisorption). We demonstrate that water can be trapped on silicates up to temperatures of about 470 K, which speaks for the presence of wet silicate grains in the terrestrial planet formation zone in planet-forming disks. Studying the thermal and UV stability of trapped water, we conclude that the detection of trapped water in the diffuse ISM speaks for its efficient continuous formation. We discuss our results as relevant to fundamental scientific questions, such as the oxygen depletion problem, the origin of water on Earth, and the formation of rocky planets.

Study on structure-performance relationship and action mechanism of organic chemicals in cement grinding aids

Grinding aids (GAs) are an important addtive in the cement production process. However, the relationship between the molecular structure of GAs and its grinding efficiency has not been clearly revealed. In this study, the influence of GAs with different structures, including glycols and alkanolamines, on the grinding efficiency of pure clinker was systematically investigated. The working mechanism from their adsorption and dispersion configurations on tricalcium silicate (C3S) surface was investigated by first-principles method. As the structural parameters of GAs, number of polar groups is found to affect the grinding efficiency of cement clinker. The grinding performance of alkanolamines is better than that of glycols at the same dosage, when the number of hydroxyl groups is the same. The tertiary alkanolamines are adsorbed through the double-ended hydroxyl group to form larger molecular projection areas than the glycols with single-ended hydroxyl group, thus resulting in higher dispersion efficiency. Further, with the growth of the number of methyl groups in the molecular structure of the tertiary alkanolamines, the thickness of the adsorbed molecular layer grows from 9.25 Å to 9.87 Å, and the ability to shield the electrostatic forces between cement particles is enhanced and result in a better grinding aid performance.

From biowaste to BioPave: Biological pathways for sequestration of anthropogenic CO2 and enhancing durability of roadway infrastructures

Biomass-derived bio-oils are emerging as sustainable, low-carbon alternatives for construction materials, particularly in innovative pavement applications, 'BioPave'. This study evaluates bio-oils from various sources, including algae and wastewater biomass, revealing variations in carbon, nitrogen, and sulfur contents, along with viscosity. We focused on their application in outdoor construction, assessing their resistance to thermal and solar radiation, and moisture. The study also examines their interaction with siliceous surfaces and their influence on asphalt adhesion in BioPave systems under moisture conditions. Laboratory experiments and computational modeling demonstrated molecular composition significantly influenced bio-oils' responses to thermal and UV exposure. Bio-oils rich in polar groups showed hardening upon thermal treatment, while those with higher concentrations of saturated aliphatics remained more stable. Furthermore, our findings highlight the significance of dosage control in maximizing beneficial effects of bio-oils in intermolecular interactions at bitumen-aggregate interface in BioPave applications. These findings offer insights into the potential of bio-oils in sustainable construction and the need for dosage control to optimize pavement performance.

Structural Transformation of Azonia[5]helicene Photoproduct via Reaction Field Function of Layered Inorganic Material.

In an attempt to generalize "on surface synthesis", which has unique potential in the area of organic synthesis, the focus was placed on layered silicates having a highly flat surface. The photoreaction of (±)-13-bromo-6a-azonia[5]helicene (AHHBr) and (±)-2-bromo-13-methyl-6a-azonia[5]helicene (AHBrMe) in solution and within the layers was examined. In the case of AHBrMe, the photoproduct was different from that in solution. 1H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), and electrospray ionization-mass spectrometry (ESI-MS) measurements revealed that the photoproduct obtained within the layers was a benzo-perylene molecule with a completely flat lactone structure (AL). This study is the first example of the successful conversion of a chemical reaction path due to the steric effect of the flat surface of layered silicate.

The Effects of Various Silicate Coatings on the Durability of Concrete: Mechanisms and Implications

Silicate solutions can improve the durability of concrete conveniently and effectively. To horizontally compare the enhancement effects of different composite silicate solutions, three types of silicate surface treatment agents were prepared by using sodium silicate, potassium silicate, and lithium silicate as the main agents, along with urea, sodium polyacrylate, catalysts, and fluoro-carbon surfactants as the adjuvants. Furthermore, their effects on the durability of concrete were compared. The results showed that silicate surface treatment could reduce the content of Ca(OH)2, increase the content of hydrated calcium silicate (C-S-H), and improve the compactness and hydrophobicity of the hardened cement surface. Although the three surface treatments enhanced the durability of concrete, the effects differed based on the complexities and mixtures. The sodium silicate compounded with potassium silicate performed the best of all three, wherein the content of the C-S-H gel increased by 389.8%, the permeability decreased by 60.6%, the water contact angle improved to 83.5° and the chloride ion resistance and freeze–thaw resistance of concrete increased by 36.7% and 37.34%, respectively, compared with the control sample.

Switching Product Selectivity in Immobilized Tungstate Catalysts by Control of Hydrophobicity of Mesoporous Silicate Supports

AbstractNovel mesoporous silicates modified with imidazolium cation were applied as the support for peroxotungstate. Stepwise introduction of multiple functional groups to SBA‐15 was achieved by the combination of the direct and post‐synthesis procedures. The co‐condensation of tetraethoxysilane and 3‐(imidazolyl‐1‐yl)‐propyltriethoxysilane in the presence of the micelles of an amphiphilic surfactant yields the hydrophilic SBA‐15 type silicate support with the imidazole modifier locating into the mesopores. The hydrophobic environment of the supports was imparted by capping the residual silanols on the silicate surface with trimethylsilyl groups. The fluoroalkyl‐ or alkyl‐imidazolium cation‐anchored supports were derived from the corresponding imidazole‐functionalized precursors. The anion‐exchanging reaction between peroxytungstate and the imidazolium cation‐anchored supports yielded the corresponding tungstate‐immobilized catalysts. The hydrophilic catalyst with the fluoroalkyl‐imidazolium mediated alkene epoxidation with H2O2 in less polar solvents. The hydrophobic one, in contrast, produced diol through the epoxidation and following hydration in an aqueous solvent by the action of the highly Lewis acidic tungsten. The hydrophobic catalysts had the advantage of being more tolerant than hydrophilic catalysts, as evidenced by reusability tests. The activities of the alkyl‐imidazolium catalysts were lower than those of the corresponding fluoroalkyl‐imidazolium catalysts, indicating that the local structures surrounding the tungstate site affected the catalytic performance.

Selective fluorination of the interlayer surface of layered silicates

Neutral fluoride substances were intercalated into layered silicates, facilitating the selective fluorination of inner surfaces.

A Study on Surface Modification Characteristics and Charge–Discharge Mechanism of Natural Serpentinite Ore Secondary Battery

This study conducts low-vacuum sulfidation to form a sulfidation layer on the serpentinite-derived magnesium iron silicate, thereby enhancing its electrochemical properties. Results show (Mg,Fe)2SiO4 calcined at 900 °C has the best crystallinity, and the cubic FeS2 is synthesized on the surface of the orthorhombic magnesium iron silicate (MFS). Two distinct charge plateaus can be distinguished during the first charge process, and the discharge capacities increased significantly. This study confirms that the surface FeS2 layer provides extra ion pathways, allowing more lithium/magnesium ions to be extracted and inserted in the serpentinite-derived magnesium iron silicate. Accordingly, the serpentinite electrode boasts straightforward exploitation with low-cost advantages and potential.

Study on selective emitter fabrication through an innovative pre‐diffusion process for enhanced efficiency in TOPCon solar cells

AbstractTOPCon (tunnel oxide passivated contact) solar cell is the mainstream high‐efficiency crystalline silicon solar cell structure. However, the lack of efficient passivation contact mechanisms on the front surface restricts the electrical performance ability to improve further. Selective emitter (SE) technology, considered a potential solution, needs to be more mature. This work provides a unique thermal pre‐diffusion approach combined with laser treatment and post‐oxidation annealing to create SE structures in TOPCon solar cells. Times for the high‐temperature process are equivalent to those for a traditional homogenous emitter. The innovative thermal pre‐diffusion process created a unique boron doping profile, achieving a high surface concentration of nearly 1 × 1020 cm−3 with a shallow junction depth of approximately 0.25 μm. Laser treatment further activated boron and facilitated its diffusion, influenced by the boron silicate glass layer and surface boron atoms. Adjustments were made to improve the pre‐diffusion recipe, including an additional boron deposition step, increasing non‐activated boron atoms. Introducing larger pyramidal microstructures also improved the junction depth and surface concentration in the heavily doped region. Compared to homogeneous emitters, the SE structures exhibited lower surface concentration in the lightly doped region, reducing the recombination current density in the passivation region J0,pass values. The SE structures achieved higher junction depths, limiting metal atom diffusion and reducing the current recombination density in the metal contact region J0,metal values. The contact resistivity between metal and silicon was also decreased. Overall, introducing SE structures resulted in a batch‐average efficiency improvement of 0.26%, reaching an average efficiency of 25.22% for TOPCon solar cells, and has industrial mass‐producible.

Alkali silica reaction in concrete - Revealing the expansion mechanism by surface force measurements

Alkali-silica reaction (ASR) is a major cause for concrete deterioration worldwide. However, the mechanism leading to cracking has not been identified yet. In this study, the extended Surface Force Apparatus (eSFA) has been used to determine the surface forces of alkali-silica solutions between two atomically smooth mica surfaces. The setup imitates the situation present in reactive concrete aggregates with negatively charged silicate surfaces and negatively charged polynuclear silica in solution. The distance of strong electrostatic repulsion increases with increasing concentration of dissolved silica, leading to the buildup of pressure up to 6 MPa. When the precipitation of ASR products in confined conditions is triggered by the addition of CaCl2 to the alkali-silica solution, the resulting solidification pressure forces the mica platelets apart and reaches 6–13 MPa. The eSFA experiments shows that solidification pressure is the mechanism leading to aggregate cracking and expansion of ASR-affected concrete.

The exosomal secretomes of mesenchymal stem cells extracted via 3D-printed lithium-doped calcium silicate scaffolds promote osteochondral regeneration.

The development of surface modification techniques has brought about a major paradigm shift in the clinical applications of bone tissue regeneration. Biofabrication strategies enable the creation of scaffolds with specific microstructural environments and biological components. Lithium (Li) has been reported to exhibit anti-inflammatory, osteogenic, and chondrogenic properties by promoting several intracellular signaling pathways. Currently, research focuses on fabricating scaffolds with simultaneous dual bioactivities to enhance osteochondral regeneration. In this study, we modified the surface of calcium silicate (CS) scaffolds with Li using a simple immersion technique and evaluated their capabilities for bone regeneration. The results showed that Li ions could be easily coated onto the surfaces of CS scaffolds without affecting the microstructural properties of CS itself. Furthermore, the modifications did not affect the printing capabilities of the CS, and porous scaffolds could be fabricated via extrusion. Moreover, the presence of Li improved the surface roughness and hydrophilicity, thus leading to enhanced secretion of osteochondral-related regeneration factors, such as alkaline phosphatase (ALP), bone sialoprotein (BSP), and collagen II (Col II) proteins. Subsequent in vivo studies, including histological and micro-CT analyses, confirmed that the Li-modified CS scaffolds promoted osteochondral regeneration. The transcriptome analysis suggested that the enhanced osteochondrogenic capabilities of our scaffolds were influenced by paracrine exosomes. We hope this study will inspire further research on osteochondral regeneration.

High-Density Coordinatively Unsaturated Zn Catalyst for Efficient Alkane Dehydrogenation.

The exploration of non-noble metal catalysts for alkane dehydrogenation and their catalytic mechanisms is the priority in catalysis research. Here, we report a high-density coordinatively unsaturated Zn cation (Zncus) catalyst for the direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). The catalyst demonstrated good catalytic performance (∼40% initial EB conversion rate and >98% ST selectivity) and excellent regeneration ability in the reaction, which is attributed to the high-density (HD) distribution and high-stability structure of Zncus active sites on the surface of zinc silicate (HD-Zncus@ZS). Density functional theory (DFT) calculations further illustrated the reaction pathway and intermediates, supporting that the Zncus sites can efficiently activate the C-H bond of ethyl on ethylbenzene. Developing the high-density Zncus catalyst and exploring the catalytic mechanism laid a good foundation for designing practical non-noble metal catalysts.

A computational and experimental investigation of the anchoring of organosilanes on the halloysite silicic surface

In this work, the effect of halloysite nanotubes alkali activation on its grafting efficiency with organosilanes was studied by Density Functional Theory and experimental investigations. In particular, computational analysis allowed to enlight the structural properties of the organic molecules attached to the silanol groups on halloysite outer surface. The energetics of the reactions showed that the pretreatment with a base is crucial for the modification of the surface due to the appearance of a high number of active sites which lead to thermodynamically favored exothermic processes. Experimental evidences are in good agreement with calculation hypothesis. For instance, the coating efficiency is higher after the alkali activation of the inorganic counterpart for both the investigated organosilanes. The findings here reported are important in order to improve any functionalization protocols for aluminosilicates without variations or loss of the hollow nanotubular morphological features and it paves the ground to halloysite based technological applications in many fields, from nanotechnology to catalysis.