Si-O Bonds Research Articles

Formation of Bio-based Derived Dicalcium Silicate Ceramics via Mechanochemical Treatment: Physical, XRD, SEM and FTIR Analyses

Beta-dicalcium silicate plays an important role in modern technology, but its tendency for polymorphic transformation results in the dusting phenomenon, is a major challenge. Therefore, mechanochemical treatment is used to reduce the particle size to retain the stability of the polymorph. In this study, pure dicalcium silicate ceramics of β-monoclinic structure with P 121/c1 space group were synthesized using calcium oxide and silicate powders derived from calcined eggshells and rice husks, respectively. The powders were mixed in a 2:1 molar ratio by mechanochemical treatment and heat-treated in the air at temperatures ranging from 900°C to 1100°C for 2 h. The results reveal that pure betadicalciumsilicate formed at 1100°C without adding stabilizers. The properties of the pristine and sintered bodies were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). SEM revealed that the grain and pore sizes increase with rising sintering temperatures. FTIR spectra indicate the existence of Si-O bonds in -4 4 SiO tetrahedrons on all the samples. The sample sintered at 1000°C attains the lowest bulk density (1.2463 g/cm3), whereas the apparent porosity is the highest (62.5%). The reason for this trend is due to the decomposition of carbonate into CO2 gas. The densification onset for the sample sintered at 1100°C as the bulk density rises and grain size achieves 6.06 μm. This study further explains the effect of sintering temperatures on the physical, structural, and morphological properties of Ca2SiO4 which would also be useful for further optimization of its use.

Silicate Derived from Phaeodactylum tricornutum for Removal of Polystyrene: Interfacial Effects of Living Organism and Its Derivatives with Nanoplastics.

The deposition of nanoplastics in the environment poses a direct threat to human health through the food chain. There is an urgent need to investigate how they can be effectively removed from water. In this work, the toxic effects of nanopolystyrene (PS) at different concentrations on Phaeodactylum tricornutum (PT) were investigated. The results show that PS affects the cell activity of PT through cell wall adhesion and shading effect and hinders the transmission of light energy, thus inhibiting the growth of PT. Considering that living PT is not suitable for the removal of heterogeneous aggregation of PS, magnesium silicate (MS) was obtained by calcination of PT biomass based on retaining salt. The maximum adsorption capacity of PS by MS was 40.85 mg g-1, which was 10 times higher than that of conventional adsorbents. The presence of competitive anions significantly affects the removal of PS. The application in real water bodies and the reusability of the adsorbents were also verified. By characterizing the materials before and after adsorption, it is found that the adsorption mechanism mainly includes electrostatic attraction, hydrogen bonding, π-π interaction, and complexation between Si-O bond and PS. This study explains the toxic effect of nano-PS on PT and innovatively develops a biomass derivative from diatoms, which provides a novel and feasible strategy for environmental remediation.

Temperature-Dependent Oxidation Behavior of Silicon Carbide Surface: Reactive Molecular Dynamics Simulations.

The high-temperature oxidation mechanism of silicon carbide (SiC) is crucial for designing thermal protection systems in aircraft. This study explored the oxidative chemical reaction processes and mechanism on SiC surface and interfaces within the temperature range of 300-2300 K by using reactive molecular dynamics simulation. The oxygen impact on the silica (SiOx) growth of the SiC surface was analyzed, which shows a progressive increase of silica thickness. The simulation results indicated that the oxidation process of SiC was a typical passive oxidation mechanism. With the environmental temperature rising and oxygen impact, the increase of oxidation thickness on the SiC surface undergoes three oxidizing reaction processes: little chemical adsorption of oxygen molecules on the initial surface, rapid oxidation of silicon and carbon, and dramatic oxidation of the interface between the oxidation layer and SiC. Additionally, this work studied the mechanism of oxidation thickness growth and chemical diffusion of oxygen. The oxidation rate is weakened according to the oxygen atom diffusion barrier effect of silica repulsion. Moreover, the kinetic parameters were statistically calculated by fitting the growth of Si-O bonds and their reaction rate constants. Subsequently, the activation energy and pre-exponential factors were derived by using the Arrhenius equation to model the chemical reaction kinetics of the thermal oxidation process. The chemical reaction behaviors of the two stages could be concluded as follows: (i) in stage I, the initial oxidation is reaction rate limiting; (ii) in stage II, SiC oxidation is limited by both the oxidation reaction rate and the oxygen diffusion coefficient of the oxidation layer. The activation energy of stage II increased compared with stage I due to the oxygen atoms diffusion barrier between the oxidation layers. This study on the oxidation and ablation mechanism of the SiC surface at the atomic scale would provide insight into understanding thermal oxidation behavior and the design of ceramic materials.

A novel green nanocomposite for EOR: Experimental Investigation of IFT Reduction, wettability Shift, and nanofluid stability

A stable nanofluid (NF) is crucial for success of nano-enhanced oil recovery (nEOR) processes. However, this represents a significant challenge as nanoparticles (NPs) tend to agglomerate under high salinity and NP concentration adversely affecting the oil recovery. New nanomaterials including functionalized nanoparticles also known as nanocomposites (NC) can help to overcome these issues. In this paper, first, we reported synthesis, characterization, and performance evaluation of a novel hydrophobic CuO-SiO2-Montmorillonite-K+-Thiazine NC for the first time. The NC was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), X-Ray Diffraction (XRD), Thermogravimetry Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR). SEM analysis showed that the NC is composed of uniformly distributed NPs. EDAX results confirmed presence of Cu, SiO2, O2, and Cl in the NC. XRD analysis indicated that SiO2 is the dominant phase in the crystal lattice and responsible for adsorption capacity of the NC. TGA analysis showed that the NC will be thermally stable in typical reservoir temperatures (∼80°C). FTIR results confirmed presence of Si-O, Cu-O, Si-O-Si, Al-O-Si, Al-OH, and OH bonds in the NC. In the second phase of this research work, the novel NC was used to investigate recovery of a Kazakhstani paraffinic heavy crude oil from Berea sandstone with focus on IFT reduction, oil recovery, wettability alteration, and stability analysis of the NFs. NFs were prepared with NC concentrations of 250, 500, and 1,000 ppm using moderate salinity (MS), low salinity (LS), and distilled water (DW). The results showed that the optimal NF (250 ppm LS) exhibited a high zeta potential value (−65.5 mV) indicating a high stability which is superior to all of the previously reported NCs. This high stability is attributed to use of thaizine as a source of natural surfactant. The optimum NF also altered the wettability of the sandstone by 77.6% and the contact angle (CA) was reduced from 117.9° to 26.4° making the system strongly water wet. The nanoclay has significantly facilitated the wettability alteration. The optimum NF also reduced the IFT by 92.3% from 27.42 mN/m to 2.11 mN/m. An incremental oil recovery of 20% was also achieved in the tertiary or EOR stage of oil. A comparison with the NCs reported in the literature confirmed the excellent performance of this novel NC in terms of NF stability, IFT reduction, and wettability alteration. The novel NC has a great potential for nEOR and other oilfield and environmental applications.

Crystal growth of hydrated calcium silicate synthesized from fly ash and lime milk at 100 °C

To maximize the high-value application of fly ash, this study investigates the incorporation of amorphous silica derived from fly ash as a silicon source and lime milk as a calcium source into microporous calcium silicate powders through dynamic hydrothermal synthesis at 100 °C for a duration of 2 h or less. The products were collected at various synthesis intervals and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric differential scanning calorimetry (TG-DSC). Results indicate that microporous calcium silicate forms through a dynamic reaction that disrupts Si-O bonds, enhancing the mobility of silica-oxygen tetrahedra and generating H2SiO42−groups. Ca2+ ions also interact with these bonds, resulting in Q1 and Q2 forms of silica-oxygen tetrahedra. Phase transformation of calcium silicate at various intervals was noted, beginning with 3CaO·2SiO2·3H2O, shifting to 2CaO·3SiO2·2.5H2O, and finally to CaO·2SiO2·2H2O at 90 min. Thus, microporous calcium silicate evolves from an amorphous C-S-H gel into a crystalline form, featuring diverse calcium silicate minerals with calcium-silicon ratios and particle sizes between 10 and 20 μm, with sizes increasing until the 80-min.

Study on Synthesis of CSH Gel and Its Immobilization of Heavy Metals

Calcium silicate hydrate (CSH) gel is the most important hydration product of cement. It influences the mechanical properties of resulting materials and plays an important role in the adsorption and immobilization of heavy metal ions. Research in the structure of CSH gel and its ability for heavy metal immobilization enables the development of tailored cement-based materials, a feature that holds significant future potential. In this study, CSH gel was synthesized under different pH and Ca/Si conditions. Structural and morphological changes in CSH gel were investigated using modern technologies. The results revealed that both pH and Ca/Si ratios were important factors influencing the structure of CSH gel. During the formation of CSH, both Cr3+ and Pb2+ can be incorporated into CSH gel, and promoting the formation of calcium hydroxide Cr3+ can also replace Si4+ in the Si-O bond.

Substitution of blast furnace slag by melting furnace slag as active component in green concrete application

Blast furnace slag (BFS), a commonly used substitute for cement clinker, is in large demand and gradually increasing in price. Melting furnace slag (MFS), a by-product of the co-disposal of waste incineration fly ash and metallurgical dust sludge, has potential hydration properties, and its large accumulation also poses a serious threat to the environment. In this study, we focus on the effect of MFS replacing BFS on concrete properties and its hydration mechanism. Results showed that MFS significantly enhanced the compressive strength at the later stage of hydration, and the 28-d compressive strength of MSD concrete was 15.15 % higher than BSD concrete. MFS enriched with a large amount of amorphous silica and alumina played a key role in the hydration process. This is mainly shown as the increase in the fluctuation of Si-O and Al-O bond strengths and the decrease in the energy separation between Ca 2p and Si 2p levels. In addition, the increased substitution of aluminum for silicon in MSD results in the formation of C-A-S-H gels, which are tightly bonded with ettringite to form a composite structure. Subsequent durability assessments indicate that the incorporation of MFS diminishes the permeability to chlorides and sulfates, while also bolstering the concrete’s resistance to carbonation. These findings imply a positive impact on the concrete’s enduring service life.

A self-assembled layer on titanium surface via silane coupling of chlorogenic acid and strontium chelate improves the osteogenic potential in a high-glucose environment

Bioactive coatings on titanium surfaces represent a crucial strategy to enhance the success rate of titanium implants in diabetic patients. In this study, a chelate comprising chlorogenic acid (CGA) and strontium (Sr) was synthesized and subsequently immobilized onto titanium surface through aminoethyl-aminopropyltrimethoxysilane (AEAPTMS) coupling, wherein AEAPTMS was selected from four silanes based on quantum chemistry analysis. This novel coating was characterized by XPS, SEM, contact angle measurements, and friction experiments, and its effects on cell adhesion, proliferation, osteogenic differentiation, and mitochondrial function in a high-glucose environment were evaluated by comparison with the surface treatments of none, alkali thermal treatment, and physically immersed CGA&Sr solution. It was proven that CGA&Sr could be grafted onto the titanium surface by AEAPTMS coupling, via Si-O bonds and -NH-C = O- bonds at the two ends of AEAPTMS. Furthermore, it provided satisfactory friction resistance and hydrophilicity, as well as improvement in proliferation, adhesion, and osteogenic mineralization of MC3T3-E1 cells in a high-glucose environment. The AEAPTMS-CGA&Sr coating significantly enhanced the osteogenic potential of cells by upregulating the expression levels of key osteogenesis-related genes such as—OCN, OSX, ALP, Runx2, and COL-1 and promoted the secretion of osteogenesis-related proteins. Mitochondrial dynamics analysis showed that CGA&Sr effectively restored hyperglycemia-induced alterations in mitochondrial dynamics and function by modulating the downregulation of mitochondrial fission genes Fis1 and Drp1, upregulating fusion genes Mfn1 and Mfn2, promoting recovery of mitochondrial membrane potential, and eliminating reactive oxygen species. The study results suggested that the AEAPTMS-CGA&Sr coating might be a promising strategy for modifying titanium implants for tolerance to a high-glucose environment.

Corrosion resistance of multicomponent disilicate (Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)2Si2O7 against CMAS and volcanic ash

With the increasing operating temperature of gas turbine engines, calcium-magnesium-aluminosilicate (CMAS) poses a serious threat on environmental barrier coatings (EBCs) applied on hot-sections of aero-engines. Here, we have synthesized a novel multicomponent disilicate—(Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)2Si2O7 (brief to (5RE0.2)2Si2O7), and comparatively studied its performance in the presence of synthesized CMAS and natural volcanic ash at 1400ºC. In comparison with Yb2Si2O7, (5RE0.2)2Si2O7 has a shorter Si-O bond length and a larger RE-O bond length because of the larger average RE3+ radius. After CMAS corrosion, some apatite grains precipitate at the CMAS/(5RE0.2)2Si2O7 interface to develop a loose reaction layer, exhibiting a higher corrosion resistance than Yb2Si2O7. Meanwhile, the consumption of CaO and release of SiO2 during the chemical reaction process increase the viscosity of CMAS to some extent and thus weaken its infiltration propensity. For the volcanic ash case, it directly infiltrates into the interior of (5RE0.2)2Si2O7 along grain boundaries without any reaction due to the relatively low CaO content, exhibiting a more serious attacking behavior. In addition, (5RE0.2)2Si2O7 effectively increases the contact angle of molten volcanic ash due to its lower surface energy. These finds here provide a better understanding for the design and application of next-generation EBC material.

Thermal stability of MDM and oxidative decomposition mechanism under the condition of air infiltration: A combined experimental, ReaxFF-MD and DFT study

When siloxanes are used as the working fluids of organic Rankine cycle systems, there is a possibility of air infiltration due to the large vacuum present in the condenser. To address this issue, experimental and simulation studies were conducted on the thermal stability and pyrolysis product characteristics of octamethyltrisiloxane (MDM) in the presence of air. The results indicated that air significantly promotes the decomposition of MDM at the temperatures above 250 °C. Air was helpful in increasing the formation of CH2O, CO, and CO2, and also enhanced polymerization of decomposition product of siloxane, leading to higher yields of MD2M, MD3M, MD4M, D3, D4, and D5. By combining reactive force field molecular dynamics (ReaxFF-MD) simulations with density functional theory (DFT) calculations, the microscopic mechanisms of MDM's oxidative decomposition by O2 in air and H2O under humid conditions were elucidated. O2 can easily combine with unsaturated Si atoms to form Si-O bonds, combine with CH3 radicals to form C-O bonds, and undergoes hydrogen extraction reactions to initiate decomposition. H2O mainly undergoes initial decomposition through CH3 radical hydrogenation and binding with unsaturated Si atoms. The generated O2H, O, and OH radicals tend to bind with Si atoms in molecules and radicals, facilitating polymerization reactions.

Novel single-phase Li2SiO3 microwave dielectric ceramic with low permittivity

Novel low-permittivity lithium metasilicate (Li2SiO3) ceramics were synthesized to explore the relationships between crystal structure parameters and dielectric properties. X-ray diffraction and Rietveld refinement indicated that the Li2SiO3 ceramics formed a single orthorhombic structure with a Cmc21 space group. Optimal microwave dielectric properties of εr = 6.20 ± 0.02, Q×f = 30,550 ± 250 GHz (f0 = 15.5 GHz), and τf = −40.95 ± 0.56 ppm/℃ were achieved through sintering at 1025 ℃. Raman spectroscopy analysis showed that the values of εr and Q×f were negatively correlated with the Raman shift and full width at half maximum of the strongest peak at 982 cm−1, respectively. Meanwhile, the Phillips–Vechten–Levine theory revealed that the εr values and the Q×f values were closely related to the average bond ionicity and the lattice energy of the Si-O bonds, respectively. Moreover, the increase in τf values depended on the increase in oxygen bond valence and the distortion of the [LiO4] tetrahedron. These results on the Li2SiO3 ceramics could provide some theoretical information for developing high-performance microwave dielectric ceramics.

Amine-functionalized cellulose-silica composites for the remediation of hexavalent chromium (Cr IV) in contaminated water

Adsorption method for Hexavalent chromium (Cr(VI) removal from domestic and industrial wastewater is widely desirable due to public health concern of the heavy metal. The purpose of this study was to investigate the evaluation of Cr(VI) adsorption using a novel adsorbent: amine-functionalized cellulose-silica composite derived from banana fibers. We employed the in-situ sol–gel method to create cellulose-silica silane functionalized composites, analyzing them through different characterization techniques such as Attenuated total reflectance- Fourier transform infrared spectroscopy (ATR-FTIR), X-ray Diffraction Analysis (XRD), Thermo gravimetric analysis (TGA)/differential thermogravimetric (DTG), Brunauer–Emmett–Teller (BET), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques. ATR-FTIR depicted key organic constituents in raw banana pseudo stem fibers (BF) and the formation of SiO bonds in BCSiO2 composite, and further enhanced by the grafting of N-[3-(trimethoxysilyl)propyl ethylenediamine (DAPTMS) onto the BC-SiO2 surface in BC-SiO2-DAPTMS. XRD and TGA/DTG analyses revealed changes in crystallinity and thermal stability, while BET analysis showcased altered surface area and pore characteristics in BC-SiO2-DAPTMS (2 %). SEM and TEM imaging provided visual evidence of structural modifications and improved dispersion in BC-SiO2-DAPTMS composites. The impact of composite weight, contact time, and pH on Cr(VI) removal rates was examined, revealing optimal performance at slightly acidic pH 4 value (80.7 %) and enhanced efficiency with increased contact time of 65 min (86.66 %), composite weight of 1 g (82.62 %), and initial concentration was for 0.8 mg/l (80 %). The kinetics and isotherms analyzed using pseudo second order (PSO) and pseudo first order (PFO) models, highlight the composite’s efficiency. The Freundlich model was found to better fit the adsorption isotherm data, while the PSO model described the kinetics more accurately. These insights contribute to optimizing the BC-SiO2-DAPTMS (2 %) composite for efficient Cr(VI) ion removal in water treatment applications.

Synergistic hydration mechanism of steel slag-metakaolin based on ionic dissolution properties combined with industrial CT analysis

Replacing cement with solid waste materials is a key approach to preserving natural resources and mitigating carbon dioxide emissions. In this research, we explored elemental complementation as an eco-friendly and low-carbon approach to develop composite cementitious materials (CCMs) by partially substituting cement with steel slag (SS) and metakaolin (MK), thereby overcoming the low reactivity of SS and facilitating its broader application. We scrutinized the synergistic effects of SS-MK CCMs on parameters such as solubility, water demand, setting time, compressive strength, the formation of hydration products, and microstructure. Employing a suite of analytical techniques, including Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), measurement of hydration heat, and X-ray computed tomography. The findings revealed that the alkaline environment produced by SS-cement powder promoted the breakdown of Si-O and Al-O bonds within MK, facilitating both the early hydration process and the development of strength.MK compensates for the lack of strength caused by the slow hydration of SS in the early stage, while the SS accelerated a pozzolanic reaction of MK, leading to a 28d compressive strength of 54.77 MPa for the composite, while the 28d strength of SS20 was 39.74 MPa; MK effectively utilized portlandite, enhancing the hydration of SS and increasing the production of calcium silicate hydrate, which optimized the pore structure and improved sphericity. Furthermore, the SS-MK CCMs addressed the issues of f-CaO excess and prolonged setting times in the SS-cement system, while also ameliorating the high calcium demand and reduced fluidity in the MK-cement system. Additionally, its lower cumulative heat release from hydration enhances the material’s volumetric stability. This study presents a strategy for the large-scale application of SS and contributes to the value-added, eco-friendly use of industrial solid wastes.

Reinvigorating Photo-Activated R-Alkoxysilanes Containing 2-Nitrobenzyl Protecting Groups as Stable Precursors for Photo-Driven Si-O Bond Formation in Polymerization and Surface Modification.

This study aimed to revitalize silicon-based sol-gel chemistry methodologies utilizing photoprotected R-alkoxysilanes to control the synthesis of unique silicon-based materials. We have investigated the synthesis, characterization, light-induced deprotection, and subsequent polymerization/surface functionalization through the use of 2-nitrobenzyloxy-based photoremovable protecting groups (PPGs) as alkoxy reactive groups on ethyl and phenyl (R x -(alkoxy) y silanes, with x = 0-3 and y = 1-3). The photochemical dynamics, relative efficiencies, and kinetics of the novel alkoxysilane-based PPGs were thoroughly investigated using UV light irradiation by NMR and UV/vis methods. We then explored the tin-catalyzed coupling of photodeprotected products (R x -silanols) to form polymers/oligomers. We have found that photoenabled removal of PPGs and conversion to silanols from all silane systems studied is achieved. Furthermore, these deprotected species are polymerizable into siloxanes and effectively used as light-controlled surface modifiers with masking techniques of which proof-of-concept examples are given, enabling promising application as photolithographic reagents.

A novel technology for lithium extraction through low-temperature synergistic roasting of α-spodumene with lepidolite

α-Spodumene and lepidolite have garnered significant attention because of the booming market of lithium (Li) salts. However, α-spodumene requires a high-temperature phase transition step at ≥1050 °C, and lepidolite needs a large amount of sulfate to extract Li. The economic and environmental benefits of these processes need to be improved. Herein, an innovative scheme, low-temperature synergistic roasting of α-spodumene with lepidolite, was proposed to efficiently extract Li. The conditions for phase transition roasting, acid baking, and water leaching were sequentially optimized. The mechanisms underlying the synchronous phase transition of α-spodumene and lepidolite were studied using various characterization methods. Results indicated that lepidolite lowers the transition temperature of spodumene from the α-phase to the β-phase by 150 °C. During the synergistic roasting, fluorine escapes from the lepidolite lattice and attacks SiO, AlO, and LiO bonds within the α-spodumene lattice. Under optimal conditions, 97.60 % of the Li was extracted, while the leaching ratios of Na, K, Al, and Si were only 50.96 %, 10.96 %, 5.75 %, and 0.30 %, respectively. Current scheme is a promising low-carbon technology that synchronously achieves the low-temperature phase transition of α-spodumene and additive-free Li extraction from lepidolite, offering superior economics, environmental benefits, and practicality compared with the existing methods.

Low-cost dealkalization of bauxite residue by gypsum coordinated with industrial iron salt: Mineralogical mechanisms and field practice

The sustained-release of alkalinity in bauxite residue hinders the soil formation and ecological restoration processes in disposal areas. Ferric salts (Fe3+), known for their rapid neutralization reaction process and straightforward operational simplicity, showed a synergistic advantage with gypsum (CaSO4) in the alkaline regulation of bauxite residue. Nevertheless, the mineralogical mechanisms of the reaction between Fe3+ and Ca2+ and alkaline minerals in bauxite residue remained unclear. The present study aimed to elucidate the geochemical stability mechanisms of sodalite and cancrinite, major alkaline minerals in bauxite residue, driven by Fe3+ and Ca2+ from a mineral structural perspective and the integrated restoration effect was demonstrated by the field experiment. Unreacted shrinking core model (USCM) calculations demonstrated that Fe3+ was able to enter the lattice structure of sodalite and cancrinite to replace Na+ and assisted Ca2+ in successfully replacing Na+ in cancrinite. Moreover, Fe3+ and Ca2+ facilitated the formation of insoluble coating layers on their surface. In the lattice structure of sodalite and cancrinite, the replacement reaction for Na+ was influenced by the competition between Fe3+ and Ca2+. The Ca2+ preferentially replaced Na+, while Fe3+ accumulated near the Si-O bonds, balancing the negative charges of the Si-O and Al-O tetrahedra structure and further inhibited alkaline mineral dissolution. The pH and EC of bauxite residue decreased from 10.52 to 7.60 and 712 μS/cm to 501 μS/cm, respectively, after a one-year field-scale amelioration by the integration of Fe3+ and Ca2+. These findings highlighted the synergistic roles of Fe3+ and Ca2+ in regulating the alkalinity of bauxite residue and provided a practical strategy for ecological restoration in disposal areas.

Spectroscopic insights on defects in self-irradiated natural Zircon: A natural analogue for slag host matrix for Zr-metallic wasteform

Zircon is a proposed slag host matrix associated with the metallic wasteform route developed for Zr-hull management. This study de-alienates the nature of radiation damage in Zr- and Si- sublattice in self-irradiated zircon matrices under long term of geological times using a natural analogue approach. To address this, self-irradiated reddish-brown zircon from Tamil Nadu, India was characterized using spectroscopic techniques such as X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and Photoluminescence (PL) combined with Monte Carlo Based SRIM calculations. The observations revealed that the “as-received” zircon showed significant radiation damage primarily in the Si-sublattice (Si-O-Si linkages) while retaining its crystallinity, indicating a high degree of radiation resistance. The accumulated alpha-dose and displacements per atom (dpa) were evaluated to be 0.59 × 1018 decays/g and 0.019, respectively using RAMAN and SRIM calculations. Photoluminescence studies reveal that after annealing at 1673 K for 96 h, there was a partial recovery of radiation defects and a decrease in Si-O-Si bonds, although defects from dopant atoms remained unchanged. The damage observed is correlated with the nature of atomic bonding in Si-O and Zr-O bonds. The conclusions drawn suggest that zircon demonstrates considerable durability and selective recovery from radiation damage, making it a promising candidate for radioactive waste management.

Improvement on the onset voltage for electroluminescent devices based in a SiOx/SiOy bilayer obtained by sputtering

Abstract This work is focused on the composition, optical and electroluminescent properties of silicon rich oxide (SiOx, x < 2) films monolayers and bilayers (SiOx/SiOy) deposited by Sputtering with silicon excess between 6.2 to 10.7 at.% were deposited on p-type (100) silicon substrates. As-deposited SiOx films emit a broad photoluminescence (PL) band where the maximum peak shifts from 420 to 540 nm as the Si-excess increases from 6.2 to 10.7 at.%, respectively. The PL intensity strongly increases and the main PL peak shifts to the red region when the SiOx films are thermally annealed. The PL emission band was dependent on silicon excess and the presence of Si-O bonds defects working as emission centers. MOS-like devices were fabricated (N+ polysilicon was used as top contact and aluminum as bottom contact) to study the EL of SiOx monolayers and SiOx/SiOy bilayers. It was found that the required voltage to obtain EL was reduced when SiOx/SiOy bilayers were used in light emitting capacitors (BLECs) as compared to those with SiOx monolayers.

Phosphorus doped hydrogenated silicon oxycarbide: Film formation, properties and its application on silicon heterojunction solar cell

An ultrathin phosphorus doped hydrogenated microcrystalline silicon oxycarbide (n-μc-SiCO:H) layer deposited by plasma enhanced chemical vapor deposition (PECVD) method can be used as a window layer for silicon heterojunction solar cells. The optical and electrical properties of n-μc-SiCO:H films were controlled by PECVD deposition conditions. The interplay effects of H2, CO2 and PH3 to SiH4 gas ratio on the chemical composition, material structure and properties of n-μc-SiCO:H film were systematically determined. O, H, C and P atoms were observed to incorporate into the silicon network of n-μc-SiCO:H layer, while most of the atoms bond directly to Si atoms. Incorporation of oxygen and carbon atoms into n-μc-SiCO:H film, confirmed by XPS as formation of Si-O and Si-C bonds, enlarged the optical absorption band gap (Eg) value. Both film crystallinity and phosphorus concentration in n-μc-SiCO:H layer were observed to be controlled by the H2, CO2 and PH3 to SiH4 gas ratio. The electric performance of HJT solar cell was depended on the optical and electrical properties of n-μc-SiCO:H layer. An average efficiency (across ∼ 120 cells) of 26.32 % was achieved in cells with optimized deposition parameters for the n-μc-SiCO:H layer. The reaction gas ratio was also the dominant factor in determining the number and size of nanoscale Si crystallites embedded in the n-μc-SiCO:H layer. The conductivity of n-μc-SiCO:H layer was determined by the activated phosphorus concentration but independent of the total phosphorus concentration. It was also found that large concentrations of small Si crystallites of size less than 3 nm improved film conductivity.

In-depth insights into transformation mechanism of synthetic saponite to amorphous silica under acid attack

Amorphous mesoporous materials derived from synthetic saponite (Sap) by acid treatment have been used in catalysis for several decades. Uncovering the transformation process of Sap from layered to amorphous structure under acid attack is beneficial to optimize the structure of Sap-derived mesoporous materials, yet such transformation process remains unclear. Herein, a magnesium-Sap was synthesized by hydrothermal method and then treated with sulfuric acid. By studying the changes in phase composition, morphology, chemical state of elements and surface area of the synthetic Sap after acid attack, a specified transformation mechanism of synthetic Sap to amorphous silica is clarified. The experimental results indicate that after leaching of Mg and Al cations from the Mg/AlO6 octahedral sheets of Sap during acid attack, the retained SiO4 tetrahedral sheets of Sap were transformed into amorphous short-range ordered silica phases and nanoscrolls with pseudohexagonal side pores. The transformation process of synthetic Sap under acid attack can be divided into leaching of metal ions from octahedral sheets of Sap to form layered silica particles, splitting and crimping of surface nano-silica layers from the formed silica particles, and completely amorphous transformation. The distortion of SiO bonds in SiO4 tetrahedral sheets during acid attack might be the driving force for such transformation. This work provides specific transformation process of synthetic Sap under acid attack which is conductive to the controllable preparation of acid-treated Sap derivates, and has certain significance for understanding of structural transformation of clay minerals with MgO6 octahedral structure.