Rapid Conversion of Perhydropolysilazane into Thin Silica Coating at Low Temperature

The conversion of perhydropolysilazane(PHPS)to silica at low temperature is beneficial for its application on thermally vulnerable substrates.In this work,it is demonstrated that(3-aminopropyl)triethoxysilane(APTES)has high catalytic efficiency for the low temperature conversion of PHPS and the catalytic mechanism of APTES was suggested.The influence of temperatu re and humidity on the catalytic conversion process was investigated,and it was found that PHPS can be rapidly converted to silica in 10 min at 80℃with relative humidity of 90%.The achieved silica is mainly composed of SiNO_(3)/SiO_(3)OH and SiO_(4)structure with O/Si of 1.74 and N content of 1%.As an approach to prepare inorganic coating,the low-temperature conversion method achieves a silica coating with low volume shrinkage of 0.86%,low roughness of R_(a)=0.293 nm,high nanoindentation hardness of 3.62 GPa and modulus of 30.06 GPa,which exhibits high potentials as protective coating for va rious materials even those vulnerable to high temperature.

Enhancement of Heat-Resistance of Carbonyl Iron Particles by Coating with Silica and Consequent Changes in Electromagnetic Properties

Silica-coated carbonyl iron particles （CIPs） are fabricated with the Stober method to improve their heat-resistance and wave-aSsorption properties. The morphology, heat-resistance, electromagnetic properties and microwave absorption of raw-CIPs and silica-coated CIPs are investigated using a scanning electron microscope, an energy dispersive spectrometer, a thermal-gravimetric analyzer, and a network analyzer. The results show that the heat-resistance of silica-coated CIPs is better than that of raw CIFs. The reflection losses exceeding -lOdB of silica-coated CIPs are obtained in the frequency range 9.5-12.4 GHz for the absorber thickness of 2.3 mm, and the same reflection losses of uncoated CIPs reach the data in the lower frequency range for the same thickness. The enhanced microwave absorption of silica-coated CIPs can be ascribed to the combination of proper electromagnetic impedance match and the decrease of dielectric permittivity.

Hexagonal boron nitride nanosheets incorporated antireflective silica coating with enhanced laser-induced damage threshold

Boron nitride(BN) nanosheets incorporated silica antireflective(AR) coating was successfully prepared on fused silica substrate to improve the antilaser-damage ability of transmissive optics used in high-power laser systems. The BN nanosheets were obtained by urea assisted solid exfoliation, and then incorporated into basic-catalyzed silica sols without any further treatment. The transmission electron microscope(TEM) images indicated that the BN nanosheets generally consisted of 2–10 layers. The antireflective BN/SiO_2 coating exhibited excellent transmittance as high as 99.89% at351 nm wavelength on fused silica substrate. The thermal conductivity 0.135 W · m^(-1)· K^(-1) of the BN/SiO_2 coating with 10% BN addition was about 23% higher than 0.11 W · m^(-1)· K^(-1) of the pure SiO_2 AR coating. The laser-induced damage threshold(LIDT) of that BN/SiO_2 coating is also 23.1% higher than that of pure SiO_2 AR coating. This research provides a potential application of BN/SiO_2 coatings in high-power laser systems.

The Effect of Gelatin on the Preparation of Silica Coated Iron Particles

A method is described for coating fine iron particles(~1 μm) with a uniform silica layer, produced by the hydrolysis of tetraethyl orthosilicate. The presence of a small amount of gelatin on the surface of the iron particles facilitates this process. The X ray photoelectron measurements indicated that the gelatin interacted with the surface of the iron particles by means of both nitrogen(in —NH 2 groups) and oxygen(in —COOH groups) and then bound to the silica. The silica coating increases the resistance of the iron particles to oxidation on heating in air, which makes the temperature at which an observable oxidization occurs from 330 ℃ to 400 ℃ raised.

Radio-frequency-heating capability of silica-coated manganese ferrite nanoparticles

MnFe204 nanoparticles （NPs） with various sizes and tight size-distribution were synthesized by a chemical solution- phase method. The as-synthesized NPs were coated with a silica shell of 4 nm-5 nm in thickness, enabling the water- solubility and biocompatibility of the NPs. The MnFe204 NPs with a size of less than 18 nm exhibit superparamagnetic behavior with high saturated magnetization. The capacity of the heat production was enhanced by increasing particle sizes and radio frequency （RF） field strengths. MnFe204/SiO2 NPs with 18-nm magnetic cores showed the highest heat- generation ability under an RF field. These MnFe204/SiO2 NPs have great potentiality to cancer treatments, controlled drug releases, and remote controls of single cell functions.

Synthesis of Nanoscale Shell-core Titania Coated Silica Particles in the Presence of Polyether Polyamine and the Phase Transition

The nanoscale titania coated silica was prepared via a two-step precipitating approach, where the nanoscale silica nuclei were first prepared by passing an aqueous solution of sodium silicate through an ion-exchange resin bed, then coated with the precipitation from hydrolyzed butyl titanate in an ethanol-hexane mixture at a low pH value in the presence of poly(ethylene oxide) polyamine salt(PPA) at a high temperature of 90 ℃. In the second-step precipitating process, the spontaneously precipitated titania shell on the silica nuclei was stabilized in the suspension solution with the help of the adsorption of PPA on the particles. A possible precipitating mechanism was suggested. Furthermore, the amorphous titania shell could undergo crystallization from the amorphous to the anatase structure at a high temperature of 650 ℃, and a further phase transition from the anatase to the rutile structure in the different sintering processes at a rising temperature of 750 ℃.

Effect of Self-adhesive Resin Cement and Tribochemical Treatment on Bond Strength to Zirconia

Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconia blocks were evaluated： Maxcem （MA）, Smartcem （SM）, Rely X Unicem Aplicap （UN）, Breeze （BR）, Biscem （BI）, Set （SE）, and Clearfil SA luting （CL）. The specimens were grouped according to conditioning as follows： Group 1, polishing with 600 grit polishing paper; Group 2, silica coating with 110 μm Al2O3 particles which modified with silica; and, Group 3, tribochemical treatment - silica coating ＋ silanization. Specimens were stored in distilled water at 37℃ for 24 hours before testing shear bond strength. Results Silica coating and tribochemical treatment significantly increased the bond strength of the MA, UN, BR, B1, SE and CL to zirconia compared to #600 polishing. For both #600 polished and silica coating treatments, MDP- containing self-adhesive resin cement CL had the highest bond strengths to zirconia. Conclusion Applying silica coating and tribochemical treatment improved the bond strength of self-adhesive resin cement to zirconia, especially for CL.

Silica-coating-assisted nitridation of TiO_(2) nanoparticles and their photothermal property

Nanoparticles of refractory compounds represent a class of stable materials showing a great promise to support localized surface plasmon resonances(LSPRs)in both visible and near infrared(NIR)spectral regions.It is still challenging to rationally tune the LSPR band because of the difficulty to control the density of charge carriers in individual refractory nanoparticles and maintain the dispersity of nanoparticles in the processes of synthesis and applications.In this work,controlled chemical transformation of titanium dioxide(TiO_(2))nanoparticles encapsulated with mesoporous silica(SiO_(2))shells to titanium nitride(TiN)via nitridation reaction at elevated temperatures is developed to tune the density of free electrons in the resulting titanium-oxide-nitride(TiO_(x)N_(y))nanoparticles.Such tunability enables a flexibility to support LSPR-based optical absorption in the synthesized TiO_(x)N_(y)@SiO_(2) core-shell nanoparticles across both the visible and NIR regions.The silica shells play a crucial role in preventing the sintering of TiO_(x)N_(y) nanoparticles in the nitridation reaction and maintaining the stability of TiOxNy nanoparticles in applications.The LSPR-based broadband absorption of light in the TiO_(x)N_(y)@SiO_(2) nanoparticles exhibits strong photothermal effect with photo-to-thermal conversion efficiency as high as〜76%.

Comparative Study on Optical Properties and Scratch Resistance of Nanocomposite Coatings Incorporated with Flame Spray Pyrolyzed Silica Modified via in-situ Route and ex-situ Route

A new type of transparent scratch resistant coatings including in-situ modified SiO2 （g-SiO2） in flame spray pyrolysis （FSP） process was prepared. The maximum content of g-SiO2 in the coating was 15 wt%, which is higher than that of SiO2 modified by traditional wet chemical route （I-SiO2, only 10 wt%）. The results of transmission electron microscopy have demonstrated that in-situ surface modified g-SiO2 particles dispersed well with smaller agglomerates in the final coating, which was much better than the particles modified via wet chemical route. Visible light transmittance and haze tests were introduced to characterize the optical quality of the films. All coatings were highly transparent with the visible light transmittance of above 80%, especially for coatings containing g-SiO2, which exhibited slightly higher visible light transmittance than l-SiO2 embedded one. The haze value of coatings incorporated with 15 wt% g-SiO2 was 1.85%, even lower than the coating with 5 wt% I-SiO2 （haze value of 2.09%）, indicating much better clarity of g-SiO2. The excellent optical property of g-SiO2 filled coatings was attributed to the good dispersion and distribution of particles. Nano-indention and nano-scratch tests were con- ducted to investigate the scratch resistance of coatings on nano-scale. The surface hardness of the coatings rose by 18% and 14%, and the average friction coefficient decreased by 15% and 11%, respectively, compared to the neat coat due to the addition of 10 wt% g-SiO2 and I-SiO2. The pencil hardness of the coating with 15 wt% g-SiO2 increased from 2B for the neat coating to 2H. However, the pencil hardness of coating with 10 wt% I-SiO2 was only H. The results showed that the g-SiO2 embedded coatings exhibited higher scratch resistance and better optical properties.

Sol-gel preparation of a silica antireflective coating with enhanced hydrophobicity and optical stability in vacuum

A new silica antireflective coating with improved hydrophobicity and optical stability in a vacuum is obtained by a two-step route. Firstly, silica sols are prepared with a sol-gel process, in which tetraethyl orthosilicate is utilized as a precursor. And by introduction of fluorine containing glycol into the sols, the porosity of silica particles and surface polarity of the coatings are decreased. Afterward, coatings are constructed with low surface roughness by modification of PMBA-PMMA. The coatings retain transmission of up to 99.6%, and laser damage threshold of about 50 J/cm^2 at a wavelenth of 532 nm （1-on-1. 10 ns）

Postprocessing treatments to improve the laser damage resistance of fused silica optical surfaces and SiO_2 coatings

The combination of deep wet etching and a magneto-rheological finishing （MRF） process is investigated to simultaneously improve laser damage resistance of a fused-silica surface at 355 nm. The subsequently deposited SiO2 coatings are researched to clarify the impact of substrate finishing technology on the coatings. It is revealed that a deep removal proceeding from the single side or double side had a significant impact on the laser-induced damage threshold （LIDT） of the fused silica, especially for the rear surface. After the deep etching, the MRF process that followed does not actually increase the LIDT, but it does ameliorate the surface qualities without additional LIDT degradation. The combination guarantee both the integrity of the surface＇s finish and the laser damage resistance of the fused silica and subsequent SiO2 coatings.

Functionalization of silica nanoparticles for nucleic acid delivery

Silica nanoparticles （SiNPs） have been widely engineered for biomedical applications, such as bioimaging and drug delivery, because of their high tunability, which allows them to perform specific functions. In this review, we discuss the functionalization and performance of SiNPs for nucleic acid delivery. Nucleic acids, including plasmid DNA （pDNA） and small interfering RNA （siRNA）, constitute the next generation molecular drugs for the treatment of intractable diseases. However, their low bioavailability requires delivery systems that can circumvent nuclease attack and kidney filtration to ensure efficient access to the target cell cytoplasm or nucleus. First, we discussed the biological significance of nucleic acids and the parameters required for their successful delivery. Next, we reviewed SiNP designing for nucleic acid delivery with respect to nucleic acid loading and release, cellular uptake, endosomal escape, and biocompatibility. In addition, we discussed the co-delivery potential of SiNPs. Finally, we analyzed the current challenges and future directions of SiNPs for advanced nucleic acid delivery.

Fabrication and ultraviolet-shielding properties of silica-coated titania-doped ceria nanoparticles

A series of well-dispersed titania-doped ceria nanoparticles Ce1–xTixO2 were rapidly prepared by a novel salt-assisted solution combustion process using correspondent metal nitrates as oxidizers and ethyl glycol as fuel, and then coated with amorphous silica by seeded polymerization using tetraethyl orthoslicate （TEOS）. The as-prepared samples were characterized by transmission electron microscopy （TEM）, X-ray diffraction （XRD）, Fourier-transform infrared spectroscopy （FTIR）, and ultraviolet-visible light （UV-Vis） diffuse reflectance spectroscopy. The results indicated that compared with the as-prepared pure ceria nanoparticles, the red-shift phenomenon occurred for Ti-doped ceria nanoparticles with Ti incorporation. Meanwhile, the absorption intensity in the UV light region slightly decreased and transmission rate in visible light region was somewhat enhanced. In comparison with the silica-coated CeO2 nanopowders, the silica-coated Ce0.95Ti0.05O2 nanopowders displayed the same absorption intensity in the UV light region, broader UV absorption band and higher transmission rate in visible light region.

Preparation and upconversion luminescence of monodisperse Y_2O_2S:Yb/ Ho-silica/aminosilane core-shell nanoparticles

Y2O2S:Yb/Ho-silica/aminosilane core-shell nanoparticles were prepared by a solid-gas method in combination with polyvinylpyr-rolidone assisted one-step ammoniating method. The core was a single Y2O2S:Yb/Ho with 80 nm in diameter and the shell was silica/aminosilane with around 5 nm in thickness. The results of sedimentation experiment indicated that the nanoparticles could be well-dispersed in ethanol and water to form stable colloids. Since the coating weakened lattice vibration energies of the Y2O2S:Yb/Ho...

Solution-processable precursor route for fabricating ultrathin silica film for high performance and low voltage organic transistors

Silica is one of the most commonly used materials for dielectric layer in organic thin-film transistors due to its excellent stability, excellent electrical properties, mature preparation process, and good compatibility with organic semiconductors. However, most of conventional preparation methods for silica film are generally performed at high temperature and/or high vacuum. In this paper, we introduce a simple solution spin-coating method to fabricate silica thin film from precursor route, which possesses a low leakage current, high capacitance, and low surface roughness. The silica thin film can be produced in the condition of low temperature and atmospheric environment. To meet various demands, the thickness of film can be adjusted by means of preparation conditions such as the speed of spin-coating and the concentration of solution. The p-type and n-type organic field effect transistors fabricated by using this film as gate electrodes exhibit excellent electrical performance including low voltage and high performance. This method shows great potential for industrialization owing to its characteristic of low consumption and energy saving, time-saving and easy to operate.

Effect of Temperature on Thermal Treatment of Silica Coated Magnetic Nanoparticles

In the quest for developing a catalyst with as many desired characteristics, a facile synthetic route was designed for the preparation of mesoporous silica coated magnetic nanoparticles（MSMNP） employing a colloid mill reactor. The composite particles were characterized by the techniques, such as nitrogen adsorption-desorption isotherms, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction patterns （XRD）, thermo-gravimetric analysis（TGA）, Fourier transform infrared spectroscopy（FTIR） and vibrating sample magnetometer（VSM）, etc. The analysis showed that the resulted MSMNP composites were composed of silica shell layers with open pores connecting channels and NiFe204 with spinel structure, so the thermal treatment temperature did not show significant effect on pore textural properties, and its specific surface areas were in the range of 443-- 474 m2/g, while pore volume of about 0.8 cm3/g with an average pore size of around 9.5 nm. The composites with super paramagnetic nature were encapsulated entirely with amorphous silica layers contributing to optimum porosity and abundant surface hydroxyl groups.

Synthesis, structural and spectroscopic studies on GdBO_3:Yb^(3+)/Tb^(3+)@SiO_2 core-shell nanostructures

The presented study concerned up-converting core/shell type nanomaterials based on lanthanide（Ⅲ） ions, Ln（Ⅲ）, doped orthoborates. The system studied composed of the GdBO3 doped with Yb^3＋/Tb^3＋ luminescent core ensured an effective cooperative sensitization up-conversion, resulting in a bright green luminescence. The silica coating process was performed by a modified St？ber method, which resulted in the formation of core-shell nanostructures, making them suitable for bioapplications. The nanophosphors and nanocomposites were obtained by various methods, such as co-precipitation in the presence of Triton X-100 and micelle synthesis with ethylenediaminetetraacetic acid（EDTA） as organic modifiers/surfactants. The synthesized nanomaterials were characterized with the use of powder X-ray diffraction（XRD）, infrared light absorption with Fourier transform FT-IR spectra, transmission electron microscopy（TEM）, up-conversion emission spectra under IR light, as well as excitation spectra, emission spectra and fluorescence lifetimes under UV light, and their photophysical properties were compared.

SiO2-coated pure anatase TiO2 catalysts for enhanced photo-oxidation of naphthalene and anthracene

Our current efforts reveal the preparation of SiO2@TiO2 nanocomposites having different thicknesses of silica shell and the relationship to photocatalytic activity （PCA） for the photo-oxidation of naph-thalene and anthracene. The presence of SiO2 coating over TiO2 surface was demonstrated by FT-IR analysis, with peaks corresponding to Si-O-Si （1081 cm 1） and Si-O-Ti （950 cm-1） bonds observed. High-resolution transmission electron microscopy analysis confirmed the presence of SiO2 in the as- prepared nanocomposites and the amount of Si, Ti, and O was determined by energy dispersive X-ray spectroscopy analysis. Increasing the Si02 shell thickness increases the surface area of the nanocompos- ites （69-235 m2/g）, which enhances naphthalene/anthracene adsorption. However, the observed PCA trend presents an inverse correlation to the adsorption studies, where the as-prepared samples possess- ing the highest surface areas exhibited the least PCA, while catalysts having lower surface areas （among silica coated samples） displayed the highest PCA in the degradation of naphthalene and anthracene to CO2. Despite complete degradation of naphthalene and anthracene, incomplete mineralization occurred, ascribed to the formation of various intermediates, identified by GC-MS analysis.

SiO_2@C hollow sphere anodes for lithium-ion batteries

As anode materials for lithium-ion batteries, SiO2 is of great interest because of its high capacity, low cost and environmental affinity. A facile approach has been developed to fabricate SiO2@C hollow spheres by hydrolysis of tetraethyl orthosilicate（TEOS） to form SiO2 shells on organic sphere templates followed by calcinations in air to remove the templates, and then the SiO2 shells are covered by carbon layers.Electron microscopy investigations confirm hollow structure of the SiO2@C. The SiO2@C hollow spheres with different SiO2 contents display gradual increase in specific capacity with discharge/charge cycling,among which the SiO2@C with SiO2 content of 67 wt% exhibits discharge/charge capacities of 653.4/649.6 mAh g^（-1） over 160 cycles at current density of 0.11 mA cm^（-2）. The impedance fitting of the electrochemical impedance spectroscopy shows that the SiO2@C with SiO2 content of 67 wt% has the lowest charge transfer resistance, which indicates that the SiO2@C hollow spheres is promising anode candidate for lithium-ion batteries.