Tetraethyl Orthosilicate Concentration Research Articles

Controlling Diameter and Morphology of Colloidal-Silica-Abrasives Via Designing Surfactant Functional Group

As the design rule of logic semiconductor has been scaled down toward 5, 3, 2.1, 1.5, and 1.0 nm, the line width of Cu-film as interconnect line of logic semiconductor has been rapidly scaled down toward 36, 32, 24, 20 and 16 nm. The CMP of the Cu-lines is essential fabrication process, challenging an achievement of dishing and erosion during Cu-film CMP. In particular, the dishing and erosion of the Cu-film CMP has been principally affected by the diameter and morphology of colloidal-silica-abrasives in a CMP slurry. In a conventional synthesis method synthesis of colloidal-silica-abrasives, ethoxysilanol was formed via the hydrolysis reaction by Tetraethyl orthosilicate(TEOS) and H2O producing ethoxysilanol, following the condensation reaction between two ethoxysilanol. The diameter of colloidal-silica-abrasives could be obtained by adjusting the concentrations of TEOS, alcohol, and alkali catalyst, but the solid loading of colloidal-silica-abrasives could be varied. Thus, in our study, a novel synthesis method of the colloidal-silica-abrasives was designed by adding a charged functional group surfactant during the conventional colloidal-silica-abrasives synthesis method. The effect of the surfactant having negative charged carboxyl functional group (i.e. Ethylenediaminetetraacetic acid: EDTA) on the diameter and morphology of the colloidal-silica-abrasives were investigated as function of the EDTA concentration; i.e. when the concentration of EDTA increased from 0 to 0.03 wt%, the diameter of colloidal-silica-abrasives increased from 47.0 to 103.8 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.36 wt%, as shown in Fig. 1. In addition, when the ETDA concentration increased above 0.0025 wt%, the morphology of colloidal-silica-abrasives was transformed from cocoon shape to spherical shape. Furthermore, the effect of the surfactant having the positive charged amine functional group (i.e. Triethanolamine: Tri-ETA, Ethylenediamine: EDA, Diethylenetriamine: DETA, Triethylenetetramine: TETA) were estimated as function of the number of amine functional group in the surfactant, as shown in Fig. 2. When the number of positive charged amine functional groups increased 0 to 4, the diameter of colloidal-silica-abrasives increased from 67.2 to 143.86 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.2 wt%. In addition, the synthesis with positive charged amine functional group was transformed from cocoon shape to spherical shape. The synthesis mechanism, the enhanced polishing rate of Cu-film surface, dishing and erosion after Cu-film will be presented in detail. Acknowledgement This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (1415180388) and KSRC(Korea Semiconductor Research Consortium) (20019474) support program for the development of the future semiconductor device. Figure 1

Silicon application enhances wheat defence against Sitobion avenae F. by regulating plant physiological-biochemical responses

Sitobion avenae F. is a highly prevalent and devastating pest in wheat crops, leading to significant yield losses. Silicon (Si) has been widely recognized as an effective inducer of plant resistance against aphids. Nevertheless, the underlying mechanisms governing the physiological and biochemical responses of plants induced by Si defense against S. avenae F. remain incompletely understood. In this study, we conducted experiments by treating wheat leaves with varying concentrations of Tetraethyl orthosilicate (TEOS) spray under aphid infestation. We meticulously observed and recorded the life cycle of S. avenae F. and measured the content of plant hormones, secondary metabolites, and the activity of defense enzymes in wheat leaves. Furthermore, we utilized structural equation modeling to discern the causal correlation between aphid performance and the physiological-biochemical responses of wheat under TEOS sprays. Our findings revealed that a concentration of 3 mmol/L TEOS significantly shortened the net reproductive rate, intrinsic rate and finite rate of increase, and mean generation time of S. avenae F., while simultaneously prolonging the population doubling time. Additionally, the content of lignin, total phenolics, flavonoids, alkaloids, tannin, jasmonic acid (JA), and salicylic acid in wheat leaves exhibited a substantial increase. Furthermore, the activity of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), catalase, and lipoxygenase in wheat leaves was significantly enhanced. Our results suggest that TEOS spray reduced the survival and population growth of S. avenae F. while enhancing the defense response of wheat against aphids by activating the activity of PAL and PPO in wheat, and increasing the content of total phenolic and JA. This work provides valuable insights for the development of appropriate Si fertilizers for effective pest management and offers robust theoretical support for wheat aphid control through agricultural fertilization strategies.

Impact on electrochemical performance of SiO2/Polyaniline@Carbon nanofibers composite electrode by biosilicification with different tetraethyl orthosilicate concentration

To overcome the drawback of carbon nanofibers (CNFs) such as the low energy density and low specific capacitance as electrode for supercapacitors, SiO2/PANI@CNFs composite was prepared by layer-by-layer (LbL) assembly technique, in which the SiO2 served as a component for improving capacitive behavior. Polyaniline (PANI) is used as nucleation site for synthesizing SiO2 particles as well as active material for improving capacitance. In this study, SiO2 particles were synthesized using biosilicification process as a bioinspired, rapid, and facile synthetic route for SiO2 particles at ambient temperature and pressure, etc. To elucidate effect of SiO2 on the electrochemical properties, SiO2/PANI@CNFs samples were prepared by varying concentration ratio of tetraethyl orthosilicate (TEOS) to CNFs. It was observed that the specific surface area and the capacitance are highly dependent on the TEOS concentration. The capacitance of the composite prepared at the TEOS concentration of 0.19 mmol reaches 412 F g−1 at the current density of 1 A g−1. These results are attributed to increased specific surface area from interstitial voids between SiO2 particles and hydrophilic nature of SiO2 particles, which offers sufficient channels for rapid ion diffusion and leads easy accessibility to the active sites for the electrochemical reaction between electrode and aqueous electrolyte. Due to its excellent electrochemical and biocompatible properties, bioinspired SiO2 inorganic material will promote the development of energy storage devices in biomedical and environmental electronics.

Dielectric Performance of Forsterite-Coated Titanium Substrate-Based Medical Implant

Forsterite solutions with variable concentrations of tetra ethyl ortho-silicate (TEOS) and magnesium nitrate hexahydrate (MNH) are prepared using the sol-gel method. The dip coating method is applied to coat forsterite solution on a titanium (Ti) substrate. Forsterite coated Ti substrates are subjected to structural analysis and phase identification using the X-ray Diffraction (XRD) technique. Surface morphology and elemental composition of coated Ti substrates are also investigated using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. An extensive study is also conducted with the help of a vector network analyzer (VNA) assembly to determine the dielectric properties (dielectric constant, dielectric loss, alternating current conductivity, and loss tangent) and their relationship with frequency at room temperature in the frequency range of 200 MHz - 20 GHz. Furthermore, focusing on their use in medical implants, the impact of TEOS and MNH on the surface morphology and dielectric characteristics of forsterite coated Ti substrate is also examined in detail. Results proved that forsterite coated Ti substrate with a higher composition of TEOS and MNH performs better than others.

Concentration-dependent construction of raspberry-like SiO2 shell on spherical FeNi towards improved electromagnetic performance from kHz to GHz

Constructing resistive layer with novel structure holds great potential in upgrading electromagnetic properties of soft magnetic materials in a wide frequency range. In this work, FeNi@SiO2 composites with controllable core–shell structures, including 2D-type laminar shell and 3D-type raspberry-like shell, were fabricated by modified Stöber method. The structure of SiO2 shell depends highly on the concentration of tetraethyl orthosilicate (TEOS). In detail, a laminar shell can be formed at low TEOS concentration, owing to slow condensation. While at high TEOS concentration, heterogeneous growth on powder surface and homogeneous growth in solution of silica networks are significantly accelerated, resulting in the formation of the raspberry-like shell. Improved electromagnetic performance of FeNi@SiO2 cores at 2 MHz, including high resistivity, low eddy current loss, and low loss factor, should be ascribed to the unique raspberry-like shell structure. Meanwhile, raspberry-like shell also contributes to enhanced attenuation and acceptable impedance matching in GHz range. Consequently, a wide effective absorption bandwidth of 8.92 GHz can be achieved at a thin thickness of 1.85 mm. This work provides deep insights into the growth mechanism of different SiO2 shells and sheds new light on the design of high-performance soft magnetic composites working in different frequency bands.

Graphene Based Membrane Modified Silica Nanoparticles for Seawater Desalination and Wastewater Treatment: Salt Rejection and Dyes

The clean water crisis in Indonesia is increasing every year, and waste from the textile industry sector can also add to this problem. There are various water treatment processes to deal with the clean water crisis, one of which is the desalination process using graphene oxide. With the addition of hydrophilic nanoparticles, graphene oxide (GO) membranes can increase roughness and have good mechanical strength. SiO2 nanoparticles also have a high specific surface to absorb water or are hydrophilic. This study aims to determine the ability of the GO-SiO2/Psf membrane to reject salt (NaCl solution) and filtering of methylene blue solutions. Membrane prepared by variations of Tetraethyl orthosilicate (TEOS) 0.6; 0.8; 1.0; and 1.2 ml for GO/SiO2 composite synthesis. The results showed that the GO-SiO2/Psf membrane could absorb methylene blue solution. The most optimum absorption value occurred at a TEOS concentration of 0.8 ml and had the most effective salt rejection value for NaCl solution equal to 67.22%.

Structural, Optical, and Morphological Characterization of Silica Nanoparticles Prepared by Sol-Gel Process

In the current years, silica nanoparticles have become more favorable in various disciplines like medicine, nano-biotechnology, the food industry, and drug delivery due to their tunable physicochemical characteristics. In this paper, the silica nanoparticles were synthesized by hydrolysis and condensation of tetra-ethyl-ortho-silicate (TEOS) in an ethanolic medium using ammonia as a stimulator in the reaction. The chemical bond structures of silica nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) which confirmed the existence of the Si-O bonds according to the different absorption peaks of the samples. The amorphous structure of these nanoparticles was certified by finding the board peaks in the X-Ray Diffraction (XRD) patterns. The elemental chemical composition of silica nanoparticles was investigated by Energy Dispersive X-Ray Spectroscopy (EDX) where 61.48wt % of silicon and 23.48wt% of oxygen were found. Almost round-shaped spherical and uniform silica nanoparticles with smooth surfaces were investigated by Scanning Electron Microscopy (SEM) measurement. The different particle sizes of silica nanoparticles within the range of 95±5.59 to 280±7.8 nm were found by controlling the concentration of TEOS. The optical absorption spectra and band gap calculations were also analyzed by Ultraviolet-Visible (UV-Vis) spectrophotometry for the different concentrations of TEOS. The results revealed that with increasing the concentration of TEOS, the absorption spectra of silica nanoparticles increased and their optical bandgap decreased from 3.92 eV to 3.79 eV.

Silicon dioxide nanoparticles decorated on graphene oxide nanosheets and their application in poly(l-lactic acid) scaffold

IntroductionThe aggregation of graphene oxide (GO) is considered as main challenge, although GO possesses excellent mechanical properties which arouses widespread attention as reinforcement for polymers. ObjectivesIn this study, silicon dioxide (SiO2) nanoparticles were decorated onto surface of GO nanosheets through in situ growth method for promoting dispersion of GO in poly(l-lactic acid) (PLLA) bone scaffold. MethodsHydroxyl and carboxyl functional groups of GO provided sites for SiO2 nucleation, and SiO2 grew with hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) and finally formed nanoparticles onto surface of GO with covalent bonds. Then, the GO@ SiO2 nanocomposite was blended with PLLA for the fabrication of bone scaffold by selective laser sintering (SLS). ResultThe results indicated that the obtained SiO2 were distributed relatively uniformly on surface of GO under TEOS concentration of 0.10 mol/L (GO@SiO2-10), and the covering of SiO2 on GO could increase interlayer distance of GO nanosheets from 0.799 nm to 0.894 nm, thus reducing van der Waals forces between GO nanosheets and facilitating the dispersion. Tensile and compressive strength of scaffold containing GO@SiO2 hybrids were significantly enhanced, especially for the scaffold containing GO@SiO2-10 hybrids with enhancement of 30.95 % in tensile strength and 66.33 % in compressive strength compared with the scaffold containing GO. Additionally, cell adhesion and fluorescence experiments demonstrated excellent cytocompatibility of the scaffold. ConclusionsThe good dispersion of GO@SiO2 enhances the mechanical properties and cytocompatibility of scaffold, making it a potential candidate for bone tissue engineering applications.

Microorganism-Templated Nanoarchitectonics of Hollow TiO2-SiO2 Microspheres with Enhanced Photocatalytic Activity for Degradation of Methyl Orange.

In this study, hollow SiO2 microspheres were synthesized by the hydrolysis of tetraethyl orthosilicate (TEOS) according to the Stober process, in which Pichia pastoris GS 115 cells were served as biological templates. The influence of the preprocessing method, the TEOS concentration, the ratio of water to ethanol, and the aging time on the morphology of microspheres was investigated and the optimal conditions were identified. Based on this, TiO2-SiO2 microspheres were prepared by the hydrothermal process. The structures and physicochemical properties of TiO2-SiO2 photocatalysts were systematically characterized and discussed. The photocatalytic activity for the degradation of methyl orange (MO) at room temperature under Xe arc lamp acting as simulated sunlight was explored. The result showed that the as-prepared TiO2-SiO2 microspheres exhibited a good photocatalytic performance.

Controlled oxidation of metallic copper nanoparticles by a silica coating

The development of a simple method that perfectly controls the oxidation and aggregation of metallic copper (Cu) nanoparticles has been anticipated. In the present work, silica-coated metallic Cu nanoparticles were used as a control. Metallic Cu nanoparticles were synthesized from Cu(CH3COO)2, hydrazine, citric acid, and cetyltrimethylammonium bromide in water exposed to air. The metallic Cu nanoparticles were silica-coated by adding ethanol, (3-aminopropyl) trimethoxysilane (APMS)/ethanol, tetraethylorthosilicate (TEOS)/ethanol, and NaOH aqueous solution to the metallic Cu nanoparticle colloid solution. The morphology of silica-coated metallic Cu nanoparticles was dependent on the presence or absence of APMS and the TEOS concentration. Oxidation of the metallic Cu nanoparticles even with annealing in air was controlled by the silica shells due to their function as a physical barrier.

SYNTHESIS OF BIOACTIVE MEMBRANES FOR GUIDED TISSUE REGENERATION (GTR): A COMPARATIVE STUDY OF THE EFFECT SILANE-BASED CROSS-LINKER

Membranes for GTR (Guided Tissue Regeneration) are a promising method for treating periodontitis cases. The manufacture of membranes for GTR based on chitosan, gelatin, and carbonated hydroxyapatite (CHA) by crosslinker tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) using the freeze-drying method has been successfully carried out. This research is intended to obtain the optimum synthesis method in the manufacture of membranes with the addition of TEOS and APTES cross-linkers. The membrane was synthesized using a ratio of chitosan (CH) and gelatin (G) = 1:2 with a concentration of TEOS and APTES of 1 mol. Membrane synthesis was carried out using 4 (four) different methods, namely G/CH/CHA, G/CH/CHA+TEOS, G/CH/CHA+APTES, and G/CH/CHA+TEOS-APTES. The addition of silane crosslinking agents was intended to increase the stability of the membrane so that it has high mechanical strength. The synthesized membranes were characterized using SEM-EDX, FTIR, XRD, tensile strength test, and water absorption test. The results of SEMEDX characterization show that the G/CH/CHA+TEOS samples have a higher number of pores, this is supported by higher absorption capacity data compared to the G/CH/CHA+APTES and G/CH/CHA+TEOS-APTES. The tensile strength test shows that the G/CH/CHA+TEOS sample has the highest tensile strength, while XRD data showed insignificant differences in crystallinity between synthesis methods. FTIR spectra all show the typical adsorption bands of gelatin and chitosan the formation of hydrogen bonds and silica networks in the membrane. The synthesis G/CH/CHA+TEOS method is proven to be more effective in obtaining the membrane with the highest tensile strength 2.6 ± 0.15 MPa, and absorption capacity of 451.4 ± 135.24%.

Hydrolysis and Condensation of Tetraethyl Orthosilicate at the Air–Aqueous Interface: Implications for Silica Nanoparticle Formation

The silica (SiO2) nanoparticles of a well-known silica precursor tetraethyl orthosilicate (TEOS) are generally synthesized via a promising solution-gelation inorganic polymerization process. The monodisperse silica nanoparticles have potential applications ranging from the formation of dental nanocomposites to antireflective coatings. In the present study, we have systematically investigated the in situ interfacial molecular structure of TEOS and its impact on the interfacial water structure during the processes of hydrolysis and condensation at the air–aqueous interface using sum-frequency generation (SFG) vibrational spectroscopy. With the presence of water, a gradual decrease in the SFG intensity in the CH-stretch region for each concentration of TEOS with time reflects the elimination of ethoxy groups, which is a signature of the hydrolysis process. Further, the impact of the hydrolysis process is revealed from the significant enhancement in the SFG signal in the OH-stretch region. The hydrolysis of TEOS is then followed by condensation in which the ≡Si─O– charged species are replaced by forming the ≡Si─O─Si≡ bridging network. The signature of the condensation process is reflected with the gradual decrease in the observed enhanced SFG signal in the OH-stretch region. The formation of monodispersed silica nanoparticles as an end product of size variation from 1.75 to 4.67 nm with the increase in TEOS concentration is confirmed with the DLS measurements. We have also probed the pH-dependent SFG studies at three different pH values (2.0, 5.8, and 9.0). The dominant pH-dependent hydrolysis process is revealed from the observed molecular structure of TEOS at the air–aqueous interface.

Water Purification through a Novel Electrospun Carbon Nanofiber Membrane.

Here, we report water purification through novel polyvinyl alcohol (PVA)-based carbon nanofibers synthesized through the electrospinning technique. In our novel approach, we mix PVA and tetraethyl orthosilicate (TEOS) with green tea solutions with different concentrations to synthesize carbon-based nanofibers (CNFs) and further calcine at 280 °C for carbonization. The scanning electron microscopy (SEM) results show the diameter of the nanofibers to be ∼500 nm, which decreases by about 50% after carbonization, making them more suitable candidates for the filtration process. Next, using these carbon nanofibers, we prepare filters for water purification. The synthesized CNF filters show excellent performance and successful removal of contaminants from the water by analyzing the CNF-based filters before and after the filtration of water through SEM and energy-dispersive X-ray (EDX) spectroscopy. Our SEM and EDX results indicate the presence of various nanoparticles consisting of different elements such as Mg, Na, Ti, S, Si, and Fe on the filters, after the filtration of water. Additionally, the SEM results show that PVA and TEOS concentrations play an important role in the formation, uniformity, homogeneity, and particularly in the reduction of the nanofiber diameter.

Effect of SiO2 nanoparticle addition on growth of interfacial Ag3Sn intermetallic compound layers between lead-free solder and silver conductor

This study investigated the effects of silver powder modification on intermetallic compound (IMC) formation and silver leaching during soldering at high temperatures. Silica nanoparticles (NPs) were deposited onto a silver powder surface to inhibit silver leaching, which can lead to soldering joint failure during high-temperature soldering. The NPs were deposited through hydrolysis and a condensation reaction of tetraethyl orthosilicate (TEOS) based on the Stöber method. Fourier transform infrared spectroscopy and scanning electron microscopy were used to observe the microstructures of silver powders after the deposition of silica NPs with various TEOS concentrations and various deposition times. As the deposition time increased, the amount of silica NPs on the surface of the silver powder increased. The transmission electron microscopy results show that silica NPs were located at the IMC grain boundaries, which can hinder the dissolution of IMCs by lead-free solder melt along grain boundaries during soldering, retarding silver leaching. The growth kinetics and mechanism of IMCs during soldering were investigated. The results show that the growth of IMCs is mainly dominated by bulk diffusion. The activation energy for IMC growth increased and the growth rate decreased with increasing silica NP addition and deposition time.

Structural Engineering in the Self-Assembly of Amphiphilic Block Copolymers with Reactive Additives: Micelles, Vesicles, and Beyond.

Control of polymer assemblies in solution is of great importance to determine the properties and applications of these polymer nanostructures. We report a novel co-self-assembly strategy to control the self-assembly outcomes of a micelle-forming amphiphilic block copolymer (BCP) of poly(ethylene oxide) (PEO) and poly[3-(trimethoxysilyl)propyl methacrylate] (PTMSPMA), PEO114-b-PTMSPMA228. With a reactive and hydrophobic additive tetraethyl orthosilicate (TEOS), the assembly nanostructures of PEO114-b-PTMSPMA228 are tunable. The swelling of the PTMSPMA block by hydrophobic TEOS increases the hydrophobic-to-hydrophilic ratio that enables a continuous morphological evolution from spherical micelles to vesicles and eventually to large compound vesicles. TEOS that co-hydrolyzes with the PTMSPMA block can further stabilize and fix these hybrid nanostructures. With high TEOS concentrations, these polymer assemblies can be further converted through thermal annealing into unique silica nanomaterials, including nanospheres, hollow nanoparticles with dual shells, and mesoporous silica frameworks that cannot be synthesized through conventional syntheses otherwise.

The Separation of Oily Water Mixture Using Membrane

The increment of oil discharge in the water system gives a great impact to the environments. Membrane separation has been widely used to treat the oily water mixture due to its environmentally process, low operating cost and has better efficiency. Polysulfone (PSF) is widely used in the membrane fabrication due to its good physico-chemical, mechanical and hydraulic stability, but its hydrophobicity limits its application in the separation of oily mixture due to the fouling. The blend of PSF with poly (vinyl alcohol) (PVA) could compensate this limitation where the covalent bonding between PSF/PVA could form a protective layer to prevent the deposition of organic foulants on the membrane surface. Furthermore, PVA has been studied intensively for membrane applications because of its good chemical stability, film-forming ability and high hydrophilicity. To ensure the compatibility and high stability of the resultant membrane, the cross linking of the polymer blend (PSF/PVA) with tetraethylorthosilicate as silica nano precursor through sol-gel reaction was conducted in this study. Polyethylene glycol 400 was added as an additive to improve the properties of the integral membrane. The concentration of tetraethylorthosilicate was varied at 0wt.%, 0.5wt.%, and 1wt.% while the concentrations of other polymers are remained constant. Performance testing on the fabricated membrane through pure water flux and rejection of oil particles were conducted. The results exhibited that higher concentration of tetraethylorthosilicate led to higher water flux and higher rejection of oil particles respectively for the fabricated membrane. The crosslinked membranes achieved l00% of oil rejection after 45 minutes filtration time, meanwhile membrane from pure polymer blend only achieved 60.2% of oil rejection. This finding shows the potential of the fabricated membrane to be further explored in the area of oily water mixture treatment process.

Impacts of Green Synthesis Process on Asymmetric Hybrid PDMS Membrane for Efficient CO2/N2 Separation.

The effects of green processes in hybrid polydimethylsiloxane (PDMS) membranes on CO2 separation have received little attention to date. The effective CO2 separation of the membranes is believed to be controlled by the reaction and curing process. In this study, hybrid PDMS membranes were fabricated on ceramic substrates using the water-in-emulsion method and evaluated for their gas transport properties. The effects of the tetraethylorthosilicate (TEOS) concentration and curing temperature on the morphology and CO2 separation performance were investigated. The viscosity measurement showed that, at specific reaction times, it is benefit beneficial to fabricate the symmetric hybrid PDMS membranes with a uniform and dense selective layer on the substrate. Moreover, the a high TEOS concentration can decrease the reaction time and obtain create the a fully crosslinked structure, allowing more efficient CO2/N2 separation. The separation performance was furtherly improved with in the membrane prepared at a high curing temperature of 120 °C. The developed membrane shows excellent CO2/N2 separation with a CO2 permeance of 27.7 ± 1.3 GPU and a CO2/N2 selectivity of 10.3 ± 0.3. Moreover, the membrane shows a stable gas separation performance of up to 5 bar of pressure.

Evaluation of structural, optical and physical properties of polyurethane composites doped with metal alkoxides

Abstract In this research, polyurethane (PU)/tetraethyl orthosilicate (TEOS) composite was prepared via one-step polymerization method using different concentrations of TEOS in PU. The structural, optical and physical properties of PU composite were characterized by SEM imaging, FT-IR spectroscopy, water uptake, Raman spectroscopy and optical microscopy imaging of synthesized samples. The SEM results showed that by adding TEOS to the PU, the cell and window size of synthesized samples decreased. This result was also observed in the optical micrographs. The bonding characteristics of PU/TEOS composites were analyzed using Raman and FT-IR spectra. According to the FT-IR spectra, the degree of phase separation (DPS) and hydrogen bonding index, R, in 800 μl TEOS/PU had the highest R and DPS factors. By adding different concentrations of TEOS to PU, the apparent density decreased but the real density increased. The total, open and closed porosity of the synthesized samples were calculated. At low loading of TEOS in PU, the open porosity of the samples increased. The PU/TEOS composites may be promising candidates for absorbing sound.

Hierarchical silica monolith prepared using cellulose monolith as template

Silica monoliths with a continuous porous structure have received much attention in biomedical and environmental applications owing to their high-performance separation/adsorption behaviors. However, it is difficult to maintain a porous structure in silica monoliths because their synthesis often involves complicated phase separation in sol-gel reactions. Herein, for the first time, we used an ecofriendly cellulose material as a template to prepare a hydrophilic and hierarchically porous silica monolith. The cellulose monolith template was prepared from cellulose acetate by a thermally induced phase separation method. The silica was then prepared in the presence of the cellulose monolith by a typical sol-gel reaction of tetraethyl orthosilicate (TEOS) to form the composite monolith, which was converted to the silica monolith by burning in air to remove the cellulose monolith. Owing to the hierarchically porous structure of the cellulose monolith template, the obtained silica monolith showed a similar hierarchically porous structure, as confirmed by scanning electron microscopy and nitrogen adsorption-desorption analyses. The pore structure could be controlled by changing the fabrication parameters, such as the kind of cellulose monolith and TEOS concentration. The surface-modified silica monolith was developed for further applications.

Fe-based amorphous soft magnetic composites with SiO2 insulation coatings: A study on coatings thickness, microstructure and magnetic properties

Core-shell structured FeSiBCCr@SiO2 amorphous soft magnetic composites (ASMCs) with tunable insulating layer thicknesses have been designed and fabricated by the powder metallurgy method. The growth process of the coatings obtained via the sol-gel method has been systematically studied based on the analysis of the growth mechanism and the insulating layer thicknesses calculated by a modified method. In the powder-coating process using small quantities of tetraethyl orthosilicate (TEOS) (0.025–0.1 mL/g), a relatively uniform insulating layer is formed on the surface of the powders. Increasing the TEOS concentration further (0.25–1 mL/g) greatly enhances the reaction kinetics of the hydrolysis and condensation reactions. Consequently, the SiO2 shells of the amorphous powder rapidly grow in thickness and also generate aggregates. The evolution of the thickness of the coatings under different growth conditions also corresponds to the variation of the magnetic performance of the ASMCs. The ASMCs with an appropriate SiO2 insulating layer exhibit stability at high frequencies and significantly lower the contribution of eddy current to the total loss. Conversely, a thick insulation layer results in a high fraction of the non-magnetic phase and consequently enhances the hysteresis loss. Thus, an enhanced magnetic performance of the FeSiBCCr ASMCs can be achieved by adjusting the TEOS concentration (0.025–0.1 mL/g) or the thickness of the SiO2 insulating layer.