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The aim of this work is to analyse and understand the densification process of silica glasses at the micrometer scale under micro-indentation. The density evolution at micro-scale of silica glass following a micro-indentation exhibits a high maximum density change, up to 21% in contrast to normal glasses such as float glass, which have a low densification change. In the case of silica glass, it is observed that the evolution of the densification in the lateral dimension is gradual, as for high Poisson's ratio glasses. However, we find that along the central axis, the evolution with depth is quite different : It presents two regions. In the area immediately below the indenter, the densification is high and almost constant. Just under this imprint, there is a relatively sharp transition to the purely elastic region. Our present study, based on Brillouin diffusion measurements, allows us to improve the description of the imprint for normal/anomalous glass and to explain the location of median cracks in the silica imprint: in the transition zone between densified and undensified regions. • The imprint of microindented silica shows a quasi-uniform densification area. • Brillouin spectrometry allows localization of compacted and non-compacted glass in the sample. • With a density evolution inside the glass, the theoretical Brillouin spectrum can be calculated. [ABSTRACT FROM AUTHOR]

To design ultralight nanocomposite aerogels with good compatibility of different components, excellent thermostability, flame retardancy and strength is an urgent issue to be addressed. In this work, we fabricated a lightweight, compressible aramid nanofiber/silicon dioxide (ANF/SiO 2) composite aerogel by sol-gel method. The homogeneous SiO 2 knots were formed in-situ among the nanofibers resulting a semi-interpenetrating network structure. Due to the supporting effect of the ANF on the overall skeleton and the inhibiting effect of SiO 2 the compression properties of the ANF/SiO 2 aerogels were significantly improved. In addition, the aerogel shows low thermal conductivity, excellent thermal stability and flame retardancy meanwhile advanced self-extinguishing properties even after two minutes combustion. The design does not rely on any toxic or corrosive substances and provides a new insight into the preparation of composite aerogels with green, compressibility, thermal insulation and excellent flame retardancy. [Display omitted] [ABSTRACT FROM AUTHOR]

• Molecular dynamics simulations are used to study the surface of amorphous silica. • The average electrical charge of oxygen and silicon is determined. • The microstructure of the most external faces is analyzed. • The effects of temperature between 300 and 3400 K are discussed. Through classical molecular dynamics computational simulations, the surface of amorphous silica (vitreous silica) was generated for a system comprising 64 SiO 2 molecules (192 atoms) via the classical three-body glass potential. Starting from the liquid state of silica at 3400 K, it was cooled in three different ways at intervals of 200, 400, and 2000 K, with a cooling rate of 4.4 K/ps and establishing relaxation at intermediate temperatures, yielding three groups of surfaces from 3400 to 1400 K. Subsequently, these systems underwent sudden cooling from 1400 to 300 K via the Andersen and Nosé‒Hoover thermostats, followed by relaxation at 300 K via a microcanonical ensemble (NVE constant). Each surface that underwent relaxation was analyzed through ab initio molecular dynamics for the following three physical properties, which are temperature dependent. The average electric charges of oxygen and silicon. Microstructures on the outermost part of the surface were observed and comprised nonbridging oxygen atoms, undercoordinated silicon, and N-membered rings (3 ≤ N ≤ 5). The radial distribution functions were analyzed for all surfaces. Below 2000 K, a type of freezing is observed in all the structures because of the glass transition. All analyses were performed at zero pressure. [ABSTRACT FROM AUTHOR]

Gas bubble is a common defect in high-purity fused silica materials, but the formation of the second phase particles related to gas bubble and its mechanism remain unclear till now. In this work, we have presented a method for characterization of colored gas bubbles in high-purity fused silica crucibles for Czochralski silicon by the means of TEM and EDX. Based on it, the origin of the coloring of the gas bubbles is demonstrated to be induced by the gathering of Fe impurity and then, the formation of high-density second phase—ferric oxide (Fe 2 O 3) crystals around the gas bubbles. Moreover, our results provide insight into the formation mechanism of second phase crystals which can be induced by stress field variations around gas bubbles during the cooling process that probably promoted by volume shrinkage effect and increasing solubility of gas from gas bubbles into fused silica substrate. The understanding of the second phase particle formation mechanism in high-purity fused silica materials is valuable for its further controlling. [ABSTRACT FROM AUTHOR]

• Mechanical properties and fracture are analyzed using three different potentials. • A critical length along the deformation axis causes a brittle to ductile transition. • An energetic condition, valid for the three potentials, explains fracture behavior. In this work, the role of structure size and interaction potential on the ductility and mechanical properties of bulk glasses are extensively analyzed using molecular dynamics (MD) simulations. Elastic moduli and mechanical properties for bulk silica structures were calculated from the MD trajectories using three different force fields - diffusive charge reactive potential (DCRP), Teter and Vashishta potentials. These results from MD simulations were compared to experimental measurements and the overall results reassert that, while the elastic moduli show a neglectable variation with structure size, the fracture behavior is considerably affected. Specifically, it is found that the length along the deformation axis is the driver for the brittle to ductile transition. The fracture results, combined with an energy analysis, reveal that the energetic condition for brittle fracture, where elastic strain energy should overcome the fracture surface energy, remains valid for the three potentials. [ABSTRACT FROM AUTHOR]

Silica aerogels are considered as promising porous thermal insulation materials. However, the macropores between skeletons in the microstructure prevent further improvement of the thermal insulation performance. Therefore, it is feasible to decrease the macropores content between skeletons to enhance the thermal insulation performance. In this work, we employed Al 2 O 3 nanoparticles as fillers and utilized high-temperature treatment to shrink the skeletons and reduce the macropores content. The experimental results demonstrate that the Al 2 O 3 nanoparticles are well-dispersion within the skeletons and the diameters of macropores dramatically decrease from 7.55 μm to 0.78 μm. The thermal conductivity declines from 0.0821 to 0.0673 W/ (m K). Furthermore, the silica aerogel is treated at high-temperature environment to further reduce the macropores diameters. As a result, the skeleton structure undergoes significant shrinkage. The micropore volume increases from 0.013 to 0.102 cm3 g−1, and the specific surface area increases from 9.828 to 294.4 m2 g−1. The thermal conductivity decreases from 0.0727 to 0.0368 W/ (m K) with the temperature increasing. Theoretical calculations indicate that the attribution of the thermal conductivity reduction is primarily the weakening of gaseous heat transfer below 400 °C. Above 400 °C, the effect of solid heat transfer becomes stronger than the limitation of gaseous heat transfer, which aligns with the experimental results. This study presents novel strategy for enhancing the thermal insulation performance of silica aerogels. [ABSTRACT FROM AUTHOR]

• Effects of cationic surfactants on the tunable characteristics of PSMs were studied. • A mechanism for regulating PSMs by cationic surfactants was proposed. • The effect of micelles on particle size and pore size was revealed. • The importance of cationic surfactants for the PSM spherization process was proved. In this study, amorphous porous silica microspheres (PSMs) were synthesized by the micelle templating method. The effects of cationic surfactants with different alkyl chain lengths and molar masses on the tunable characteristics of PSMs were systematically investigated under alkaline and mild conditions. By increasing the alkyl chain length and the molar mass of the cationic surfactant, PSMs with sizes adjustable from 930 to 158 nm and average pore sizes tunable from 1.8 to 3.3 nm were obtained, and the inter-particle dispersity was also improved. This study provides a mechanism for regulating PSMs by cationic surfactants, suggesting that the particle size and pore size are related to the silica-surfactant micelle concentration and micelle size, respectively. In addition, it visually confirms the key role of cationic surfactants in the spherization process by comparing the morphology of the products before and after adding cationic surfactants. [ABSTRACT FROM AUTHOR]

Despite its importance for many applications (such as catalysis and structure ripening), adsorption on amorphous silica remains poorly understood as most studies focus on crystalline surfaces. Here, we investigate the adsorption of carbon dioxide, CO 2 , on hydroxylated silica nanopores by means of molecular dynamics (MD) simulations that compare amorphous and crystalline surfaces. We find that adsorption onto amorphous surfaces is enhanced by the heterogeneity of the structure and by the presence of under-coordinated defects (non-bridging oxygen and threefold coordinated silicon). We identify two classes of adsorption features: (i) a continuous region characterized by an intermediate density of adsorbed CO 2 molecules, which is generated by weak interactions with hydroxyl groups and forms a network that allows molecules to diffuse through the surface adsorption layer; (ii) high-density cage-like features (embedded into the network and induced by the presence of defects) in which CO 2 molecules form multiple short- and long-lived bonds with surrounding atoms and remain adsorbed for a longer time. The rich variety of adsorption features enhances physisorption and leads to longer mean adsorption time than onto the crystalline surfaces. The adsorption time onto amorphous surfaces deviates from the exponential distribution observed in silica crystals and displays a characteristic fat tail. Our findings support the experimental discovery of the potential of defected silica surfaces for CO 2 adsorption and subsequent catalytic conversion to methane, suggesting the possibility of designing and manufacturing specific adsorption features for tailored heterogeneous catalysis. • In fully hydroxylated crystal pore CO 2 -desorption times are exponential distributed. • Amorphous surfaces are characterized by hydroxyl groups and under-coordinated defects. • Variability of adsorption features at the amorphous surfaces enhances physisorption. [ABSTRACT FROM AUTHOR]

Understanding the kinetic balance between reversible and irreversible photon-absorption (IPA/RPA) in amorphous-SiO 2 (a-SiO 2) is crucial for mitigating optical damage and assessing the lifetime of irradiated optics. Experimental work has placed some thermodynamic bounds on the formation of defects from damage precursor, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing deep neural network potential, we find that the formation of defects are temperature-dependent and density-dependent, where competitions between IPA and RPA take place. The IPA prevails in the early formation of E'-center, and the ratio of IPA/RPA is related to the strained bonds, Si Si bonds and 5-coordinated silicon (Si 5). Furthermore, the Si 5 is critical to the propagation of E'-center and densification of a-SiO 2. Additionally, we develop quantitative models of defects in regard with irradiation temperature of specified temperature and irradiation photon-energy, respectively. • Machine learning-based deep potentials were developed for a-SiO 2 with different dangling bonds. • It was demonstrated that deep potentials can achieve DFT accuracy. • The creation of E'-center/NBOHC pair is not sensitive to heating rates but sensitive to temperature, and the pair begin to explosively increase after T d 1720 K. • We implies the creation and propagation mechanism of defects during reversible and irreversible photon-absorption from damage precursors, where 5-coordinated Si plays an important role in RPA and Si Si bonds plays an important role in IPA. • We build the quantitative model for the creation of E'-center with photon-energy and temperature during PA, respectively. [ABSTRACT FROM AUTHOR]

• Reinforcement of the P 2 O 5 bioglass network with incorporation of SiO 2. • Confirmation of rich HAP layer by XRD, FTIR, and SEM-EDS. • Controlled degradation and rise in pH as a function of silica content & incubation time. • Ca-P molar ratio is close to 1.67 suggested for bone regeneration efficacy of ZNCPS. • Samples exhibited superior antibacterial activity against E. coli. Biomaterials development is currently the main active research area in the field of bone tissue engineering. In the present study, the bioactive glasses with different chemical compositions (mol %) of zinc oxide, silica, calcium oxide, sodium oxide, and phosphates were synthesized by the melt-quench technique. We studied the thermal, physical, and other structural characteristics of the glasses to know the structural stability and potentiality to use as implant material. The in-vitro studies were performed to test the apatite forming ability and biocompatible nature of the prepared bioglass samples by immersing in simulated body fluid (SBF) solution with ion concentrations nearly equal to those in human blood plasma (pH =7.4 at 37 °C). All glass samples showed the formation of a clear layer of hydroxyapatite (HAP) on their surfaces after 14, and 21 days of immersion in SBF and the crystallization phases, morphology and functional groups of the hydroxyapatite layer (HAP) were confirmed by the characterizations of X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared (FTIR) analyses respectively. The antimicrobial studies of the silica containing phosphate bioglasses against Escherichia coli (E. coli) , carried out for 24 h confirmed their potential antibacterial activity. The overall obtained results of the as developed silica containing phosphate bioglasses with enhanced properties suggested to use as potential bone regenerative implant material in the field of biomedicine. [Display omitted] [ABSTRACT FROM AUTHOR]

We compute the thermal conductivity of amorphous SiO 2 combining density functional theory calculations and lifetime models. The supercell we use to represent amorphous SiO 2 is small, 78 atoms. We show that this rudimentary model is nevertheless sufficient to reproduce the temperature dependence of the thermal conductivity from 0.1 K to 1000 K if we use a lifetime model at low frequencies accounting for Rayleigh scattering, the absorption of phonons by two levels systems and structural relaxations. The necessary conditions needed to observe the plateau in the thermal conductivity around 10 K are also discussed according to this model. • Ab initio calculation of the thermal conductivity of amorphous silica. • Intraband and interband contributions to the thermal conductivity. • The calculations are performed using small sample of amorphous silica. [ABSTRACT FROM AUTHOR]

The ion-implantation of silica is widely used in optoelectronics and neighboring areas. Si + ions serve for formation of clusters/nanocrystals in components of microelectronic devices; Ge+, P+, and B+ are used for controlling refraction index in lightguides. All enumerated ions interact chemically with oxygen atoms in SiO 2 , thus shading the stoichiometric distortions caused by direct impact interactions of particles with a host. In this research, the optically-active defects in the silica network were induced by embedding of chemically inert Ar + ions and thermal neutrons. A set of bands belonging to neutral oxygen vacancies (≡Si-Si≡), non-bridging oxygen hole centers (NBOHC) and some other point defects were detected in the photoluminescence spectra of implanted/irradiated samples. The intensity variation of the bands at the Ar + fluence increase was found to be caused by a competition between defect nucleation and their annealing or/and concentration quenching at high fluence. The ionization of atoms by charged particles resulted in the multivariant spectral manifestation of the defects of the same type due to their arrangement in differently distorted host localities. The diversification of defects produced by neutrons was lesser, because the neutron impact on the silica host was limited by the interactions with nuclei. • Amorphous SiO 2 was implanted with Ar + ions and irradiated by thermal neutrons. • Photoluminescence spectra were recorded before and after the treatment. • Charged ions enable to produce ionization of atoms and molecules. • Thermal neutrons interact only with nuclei (without ionization of matrix). • This difference in particle embedding manifested itself in diversity of point defects. [ABSTRACT FROM AUTHOR]

The low density (smaller than 10% of the bulk density) and the nanostructured porosity of silica aerogels provide their extremely low thermal conductivities but also impact their poor mechanical properties. Atomic scale simulation is the appropriate tool to predict the thermal and mechanical properties of such materials. For such simulations, the interatomic potential should be carefully chosen to ensure result validity but also reasonable computational times. A truncated BKS potential has been used for aerogels as it fairly reproduces the nanostructure. It allows reducing the computational time by a 3000 gain factor on the CPU time per atom per step compared to the original BKS interatomic potential while predicting correctly the mechanical properties. However, when it comes to skeletal thermal conductivity of nanoporous silica, the associated computation times are too large for a representative volume. This is due to the low thermal diffusivity of the material. Here, a new method that takes advantage of the amorphous structure of silica and the diffusive nature of phonon heat transfer at the scale of an aerogel aggregate is proposed. The time dependent temperature profile in the system obtained from Non-Equilibrium Molecular Dynamics simulations is compared to the classical solution of the thermal diffusion equation and an identification procedure is used to determine the thermal conductivity of silica aerogels. [ABSTRACT FROM AUTHOR]

Local re-fusion of damaged sites on fused silica surface by using CO 2 laser is an effective and commonly used method for mitigating their growth to resist subsequent UV laser irradiations. However, residual stress will be introduced in or around the mitigated sites during or after a rapid cooling process of a heated material, which is detrimental for the re-use of the fused silica element. Thus, controlling the temperature during the heating process is a critical issue. Unfortunately, the temperature and the corresponding stress evolution within irradiation time are still unclear at present. In this article, a thermo-mechanical model based on finite element was developed to investigate these issues, and experiments were performed to validate the simulated results. The surface morphology evolution of damaged sites during the re-fusion processes was elaborated. The residual stresses were quantified by using photoelastic technique and chemical etching methods, which were also compared with the simulated data. Results showed that the theoretical simulation data fits well with experimental results, which will provide a significant contribution on understanding the melting process and explaining the mitigation process of damaged sites irradiated by CO 2 laser. • The evolution of temperature and residual stress during the re-fusion process by CO2 laser is studied. • Two stress affected zone will be formed during the cooling process, only one will be solidified at last. • The tensile and compressive stresses will exchange once the temperature exceeds the strain point. • The stress changes exponentially in depth direction. • The morphology evolution of damage site during the re-fusion process is elaborated. [ABSTRACT FROM AUTHOR]

Here, for the first time, europium was incorporated into the open-structure three-dimensional mesoporous siliceous material. Samples with different loadings of europium were synthesized through one-step hydrothermal treatment based on sol-gel technique. The prepared samples were characterized by different characterization techniques and the results showed the formation of isolated trivalent europium ions in silica matric at low loading samples. However, at high loading samples, nanoparticles of europium III oxide, with an average size of 5–10 nm size, were detected inside the pores of mesoporous silica matrix. The photoluminescence property of the prepared samples was investigated at two different excitation wavelengths of 393 nm and 466 nm. The maximum photoluminescence emission intensity peaks was observed at approximately 614 nm at the two-excitation wavelength. The intensity of emission peak for the 614 nm was also found to be enhanced with increasing the loading of europium ions, this signify that europium acts as a good luminescent activator for red phosphor. • Eu3+ ions were incorporated for the first time in 3D mesoporous siliceous material • The synthesis was carried out in one-step solvent-free, surfactant-free procedure • At small loading, Eu3+ was incorporated in the framework of silica matrix, however, at high loading Eu3+ was incorporated as Eu 2 O 3 nanoparticles • PL property was very much similar either under the excitation wavelengths of 394 nm and 466 nm [ABSTRACT FROM AUTHOR]

The barrier properties of the technologically attractive amorphous silica films depend on their structural characteristics at the atomic level, which, in turn are strongly influenced by the deposition conditions. In this paper, we propose an investigation of the poorly investigated densification mechanism of amorphous SiO 2 films processed by CVD from TEOS and O 2 between 400 and 550 °C. Based on literature survey and our original experimental results, we show that the densification process of these films, occurring with increasing the deposition temperature, is highlighted by a decrease of the water and silanol content, probed by transmission FTIR. We discuss the evolution of Si-O-Si related vibration signatures and we use the central force model to correlate the LO 2 and LO 3 shifts with the decrease of the Si-O-Si bond force constant, when the deposition temperature increases. Nuclear analysis reveals that films processed below 525 °C present hydrogen content between 5 ± 0.3 and 7 ± 0.3%at. Ellipsometry measurements attest that films processed at 550 °C are close to O/Si silica stoichiometry and hydrogen free. We show that application of the P-etch test results in particularly low erosion rate of 10 Å.s−1 for dense films processed at 550 °C. • CVD processed amorphous silica films from TEOS+O2 become denser with increasing deposition temperature from 400 to 550 °C. • The LO 3 FTIR vibration mode presents a blue shift with increasing process temperature corresponding to film densification. • The densification corresponds to a decrease and ultimately elimination of water and silanol groups. • The resistance to P-etch test of amorphous silica films increases with increasing deposition temperature • Annealing CVD silica films at 800°C in dry atmosphere provides them with state of the art P-etch corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract The silica aerogel was synthesized by simple and cost-effective sol-gel process under ambient pressure drying. The wet gel was modified by using trimethylchlorosilane (TMCS) as silylating agent. The prepared aerogel was characterized by X-ray diffractometer (XRD), thermogravimetric and differential thermal analyzer (TG-DTA), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET) analyzer, field emission scanning electron microscope (FE-SEM) and Ultraviolet-Visible (UV–Vis) spectrophotometer for structural, thermal, functional, surface, morphological and optical properties. The presence of hump in X-ray diffraction pattern revealed the amorphous nature of prepared silica aerogel. Thermal stability of silica aerogel investigated by TG-DTA show a hydrophobic nature up to 478 °C. FE-SEM images confirmed the porous nature of silica aerogel. The surface area and pore radius measured by BET analyzer disclosed as 792.308 m2/g and 5.779 nm respectively while the total pore volume is 2.289 cc/g. Superhydrophobic nature of silica aerogel sample was affirmed by contact angle measurements. The energy band gap calculated from UV–Vis spectra was found to be 4.25 eV confirming the insulating nature of prepared silica aerogel. The resulting silica aerogel possesses high thermal stability, Superhydrophobicity and large specific surface area which can be useful in various applications such as catalysis, coating materials, oil spill cleanup processes and insulating materials. Graphical abstract Unlabelled Image Highlights • Synthesis of silica aerogel by simple and economic ambient pressure drying method. • Trimethylchlorosilane (TMCS) used as a silylating agent for surface modifications. • Prepared aerogels shown high thermal stability with respect to hydrophobicity. • Brunauer-Emmett-Teller analysis disclosed large surface area of prepared aerogel. • High contact angle value affirmed the superhydrophobic nature of the aerogel. [ABSTRACT FROM AUTHOR]

Abstract The photoelectric response of pure silica glasses excited by excimer lasers has been studied. The samples were made under various conditions. Photoelectric polarization of samples due to the Dember effect has been registered. The signal was recorded under the conditions of a space charge limited current. The space charge resulting from the capture of electrons and holes creates a static electric field that prevents diffusion of released charge carriers. The current registration in the external circuit stops, despite the continuation of photoexcitation. This effect was used as a fact of measuring the photocurrent in the sample volume instead of the parasitic current that is not associated with the sample. The screen has been chosen to prevent the influence of a spurious signal. It has been found that charge carriers are released when excited in the spectral absorption range of localized states of silica. Based on the Dember effect, the sign of the photoelectric response shows the type of charge carriers - an electron or a hole is mobile. Thus, a sample containing aluminum without alkali ions gives a negative signal, which indicates the diffusion of electrons at 290 K, since aluminum is an effective hole trap. An oxygen-deficient sample at 290 K provides a positive signal indicating the diffusion of holes, because the center of oxygen deficiency is an effective electron trap. This sample at 100 K provides a negative signal due to the effective self-trapping of holes. Highlights • Photoelectric response of pure silica was studied. • Excited localized states liberate charge carriers. • Electrons and holes diffusion provide current. • Electrons and holes trapping provides space charge. • Space charge prevents diffusion of carriers and stops current. [ABSTRACT FROM AUTHOR]

Abstract Bulk samples of single Ag-, Dy-doped and Ag-Dy-codoped silica matrices were synthesized using the sol-gel processing. These matrices were characterized using X-ray diffractometry, ultraviolet-visible-near infrared (UV-VIS-NIR), Fourier transform infrared, photoluminescence (PL) excitation and emission spectroscopic techniques. High resolution transmission electron microscope confirmed the presence of fine spherical Ag nanoparticles (NPs), whose average size is approximately 10–15 nm, in the Ag-doped and Ag-Dy-codoped silica matrices. UV-VIS-NIR spectra revealed absorption peaks due to Dy3+ active centers in addition to the surface plasmon resonance bands of Ag NPs centered at 410 and 452 nm in these matrices, respectively. UV-excited PL of the materials was studied and compared. Near-white light emission, which was assessed by the calculated CIE chromaticity coordinates, could be observed under UV excitation at 365 nm in the Ag-Dy-codoped silica matrix. This white light was realized by appropriate combination of prominent yellow and blue emissions. Electron spin resonance spectra revealed paramagnetic spin states for Ag which can be attributed to the quantum size effect of very fine Ag NPs dispersed in the silica network. The obtained results indicate that the Ag-Dy-codoped silica phosphor could be a promising candidate for application as white light emitting phosphor for UV LED chips. Highlights • Ag-, Dy-doped and Ag-Dy-codoped silica glasses were synthesized by sol-gel method. • TEM confirmed formation of fine spherical Ag-nanoparticles having size of 10–15 nm. • UV-VIS showed absorptions due to surface plasmon resonance of Ag at 410 and 452 nm. • Ag-Dy-codoped silica produced white light emission under UV excitation at 365 nm. • This white light arose from appropriate combination of yellow and blue emissions. [ABSTRACT FROM AUTHOR]

Abstract A low-cost and high-performance quartz fiber/Al 2 O 3 -SiO 2 aerogel (QF/ASA) composite insulation material has been successfully prepared by vacuum filtration molding and sol-gel impregnation following surface-modified ambient pressure drying (APD). The macroporous in the quartz fiber perform are filled by Al 2 O 3 -SiO 2 aerogels with a large amount of mesoporous. The morphology, microstructure, thermal conductivity and thermal stability of the QF/ASA composite were investigated. Compared to the fiber/aerogel materials dried by supercritical drying, the composite exhibits similar low density (0.36 g·cm−3), high specific surface area (580.5 m2·g−1), low thermal conductivity (0.049 W·m−1·K−1) at room temperature. The compressive strength of the composite up to 0.85 MPa which is approximately triple as much as that of fiber perform. After being heated at 600 to 1100 °C, the specific surface area of composite aerogel decrease from 578.0 to 113.6 m2·g−1 and the linear shrinkage is almost zero. The XRD patterns show that mullite (3Al 2 O 3 ·2SiO 2) appeared in the Al 2 O 3 -SiO 2 aerogel after heat-treatment at 1100 °C, which is consistent with the molar ratio of silica and alumina of 2:3. [ABSTRACT FROM AUTHOR]

Abstract The effect of temperature on multicomponent chemical diffusion in liquids of the quaternary system CaO – Na 2 O – Al 2 O 3 – SiO 2 has been studied. Diffusion-couple experiments were performed around a central composition of 64.5 wt % SiO 2 , 13.3 wt % Na 2 O, 10.8 wt % CaO, 11.4 wt % Al 2 O 3. Experiments were performed for three temperatures far above the glass transition (1200, 1280 and 1360 °C), as well as 30°C above the glass transition. Strong multidiffusive effects were observed for all temperatures, with significant uphill diffusion of calcium, demonstrating that uphill diffusion happens close to the glass transition as well as at high temperature. For each temperature, we determined the diffusion matrix of the system and quantified its eigenvectors and eigenvalues, which correspond formally to (respectively) exchanges between ions, and associated diffusion coefficients. Little variation of the eigenvectors of the diffusion matrix was observed as a function of temperature, with a dominant eigenvector corresponding to the exchange of sodium with calcium, the two other eigenvectors corresponding to the exchange of calcium with network formers. For the temperature range 1200–1360 °C, the eigenvalues of the diffusion matrix have an Arrhenian temperature dependence, with an activation energy consistent with electrical conductivity for the exchange of sodium and calcium, and an activation energy consistent with viscosity for eigenvectors involving network formers. Multicomponent diffusion close to the glass transition is characterized by the same eigenvectors as at higher temperature, but some diffusion profiles are asymmetric due to strong viscosity contrasts resulting in concentration-dependent eigenvalues. Moreover, we observe some departure from Eyring relation close to the glass transition, with diffusion eigenvalues several orders of magnitude greater than the Eyring prediction. Highlights • Diffusion matrices were determined for one sodium and calcium aluminosilicate composition at four temperatures • Eigenvalues of the diffusion matrix were found to be Arrhenian down to 30 degrees above the glass transition. • We verified Eyring's law at superliquidus temperatures, but observed a departure from it close to the glass transition. [ABSTRACT FROM AUTHOR]

Abstract Glasses based on SiO 2 -PbO-CdO-Ga 2 O 3 system have been studied for the first time for fabrication of mid-infrared optical elements. Gallium oxide concentration was gradually increased, replacing silicon dioxide, for different cadmium and lead oxide content. The thermal and optical properties were investigated for different compositions. It was observed that the thermal stability, refractive index, and the transmission in the infrared range increased with increase of gallium and lead concentrations. The most thermally stable glass composition was selected for fabrication of optical elements such as optical fibers. We also successfully fabricated mid-infrared lenses by hot embossing for potential application in compact gas detectors. Highlights • Thermal and optical properties of SiO 2 -PbO-CdO-Ga 2 O 3 glass system were investigated. • Substitution of silicon dioxide with gallium oxide decreases glass susceptibility to crystallization. • Thermally stable glass composition of 28SiO 2 -45PbO-15CdO-12Ga 2 O 3 is suitable for fabrication of lenses and optical fibers. [ABSTRACT FROM AUTHOR]

• Phenyl-modified, hybrid silica aerogels were prepared via in-situ sol-gel method. • The aerogels show superhydrophobicity with self-cleaning and water-bounce ability. • The hydrophobicity can retain as high as 500 °C via adjusting the modifier dosage. • Hot steam resistance and excellent thermal insulating ability are achieved. Silica aerogels tend to be employed as thermal insulating materials, however their properties are inevitable to deteriorate in humid conditions owing to the hydrophilic nature, especially above 200 °C. Herein, phenyl modified silica aerogels with superhydrophobicity, self-cleaning capacity, and ultra thermal insulation are prepared. Phenyltriethoxysilane (PTES) working as the modifier condenses with tetraethyl orthosilicate (TEOS), forming a three-dimension network containing ladder polyphenylsilsesquioxane structure, where the introduction of bulk phenyl groups decreases free energy and fabricates hierarchical regime, leading to distinctive water repellency. The water contact angles are larger than 150° with low hysteresis (less than 2°), rendering droplet bouncing and self-cleaning capacities. As the molar ratio of PTES to TEOS rises to 1, the superhydrophobicity can be preserved at temperatures as high as 500 °C. In addition, hot-steam resistance and excellent thermal insulation are achieved. When subjected to a direct impact of 200 °C steam for 5 h, the hybrid aerogel demonstrates a reversible rise of thermal conductivity around 34%. The maximum back-surface temperature keeps 55.9 °C after exposure to hot steam for 10 min. The modification can broaden the application area of silica aerogels in high-temperature thermal insulation. [Display omitted] [ABSTRACT FROM AUTHOR]

• Densified and irradiated silica glass relaxation pathways and relationship with local density indicators probed via activation energy distribution analysis. • Observed non monotonous evolution of D 2 band intensity during early annealing stage. • Existence of high-density amorphous (HDA) and low-density amorphous (LDA) phases in silica indicated through non monotonous behavior of D 2 band. • Discovery of HAD-LDA phases transition in silica glass post electron irradiation, influencing thermal stability and structural properties. We investigated thermal stability of silica glass that underwent high-temperature (HT), high-pressure (HP) densification followed with electron irradiations. We performed isothermal annealing and in situ Raman spectroscopy to observe changes in the silica structure. By determining the activation energy distributions at the root of the densification process, we aimed to gain insights into the relaxation pathway of densified silica and its relationship with the structural properties. Of particular interest we observed a non monotonous behavior of D 2 band in Raman spectra in HP-HT samples exposed at low dose ≤107 Gy, which we attribute to presence of a specific phase of silica glass known as the high-density amorphous phase. Our study highlights the impact of irradiation on the ratio between high-density amorphous and low-density amorphous phases, and on relative activation energy distributions. These findings have important implications for development of high-performance optical devices based on silica densification for a wide range of applications. [ABSTRACT FROM AUTHOR]

Abstract Initial Al-100 and hydro-compacted amorphous/crystalline nanoalumina cAl-100 alone or in blends with hydrophobic amorphous nanosilica AM1 were characterized using low-temperature 1H NMR and IR spectroscopies, adsorption, XRD, DSC, microscopy, and cryoporometry. Mechanical treatment of weakly hydrated (0.5 g/g) nanooxides results in their hydro-compaction changing many of the material characteristics. There is overlapping of confined space effects for water bound in voids between nanoparticles with effects caused by the colligative properties of aqueous solution of trifluoroacetic acid in a chloroform medium. The interfacial phenomena determine the temperature behavior of bound water/ice depending on dispersion media features. Contact area between unfrozen water and nanooxide surface is smaller than the specific surface area due incomplete water filling of voids between hydrophilic/hydrophobic nanoparticles. In composites with cAl-100/AM1, there is a tendency of diminution of the contact area of water with hydrophobic nanosilica AM1 and hydrophobic chloroform immiscible with water. This effect changes the temperature behavior of water, which becomes more strongly bound to hydrophilic alumina. The observed effects can be of importance upon practical applications of nanooxide based composites. Highlights • Mechanical treatment of wetted hydrophilic alumina and hydrophobic silica gives a specifically structured composite • Confined space effects are enhanced in treated Al-100/AM1 blend but the chloroform medium effect on bound water decreases • Weak and strong grinding of wet Al-100/AM1 blend enhances or reduces dispersion media effect on bound water, respectively [ABSTRACT FROM AUTHOR]

Abstract Similar to normal indentation studies, structural compaction and shear flow occur also in the lateral deformation of glass surfaces through scratching. Here, we apply instrumented indentation with tangential displacement in order to study the elastic-plastic regime of scratch-deformation on silica, borosilicate and soda lime silicate glasses. We adopt the protocol of volume recovery analysis by high-temperature annealing to determine variations in geometry and volume of the scratch groove before and after the release of scratch-induced densification. While very similar relative recovery behavior is found for both normal indentation and scratch testing, inherent differences occur in the absolute presence of deformation modes across all three types of glass. In particular, caused by shear deformation at the apex of the employed Berkovich scratch tip, pronounced material pile-up occurs in scratching for normal loads which are about one order of magnitude below reference experiments of normal indentation. This leads to an increase in the effective friction coefficient and a non-trivial correlation between the scratch hardness and the normal hardness of glasses. [ABSTRACT FROM AUTHOR]

Abstract Thermal stabilization of carrot juice components, mainly β-carotene, has been studied when they are embedded in a silica matrix. The organic components induce structural changes on the inorganic matrix, decreasing the sintering temperature at which stable forms of amorphous silica such as β-tridymite, and crystalline structures like α / β-cristobalite can be obtained, they also induce the formation of stishovite traces at ambient pressure. We made use of the sol-gel method with a water/TEOS molar ratio of 11 to prepare the silica composite. The characterization of the samples was carried out using X-ray diffraction, IR spectroscopy, emission fluorescence, thermogravimetric analysis and scanning electron microscopy. Results indicate high thermostability of the composite as a result of the protective function of the photosystem II carotenoids, which tend to delay the gel-glass transition removing water at higher temperature than other chlorophyll species embedded in a silica matrix. Highlights • Thermal stabilization of carotenoids embedded in a silica matrix • Structural behavior of silica composite with embedded carrot juice elements • Fluorescence emission of organic/inorganic composite • Optical characterization of β-carotene stabilized in a silica matrix [ABSTRACT FROM AUTHOR]

In previous study, it was found that the fractal dimension of the silica aerogel could be only controlled by adjusting the catalysts. In this work, we used the aging process investigated by Hæreid et al. to continuously adjust the fractal dimension of silica aerogel. The fractal structure of the silica aerogels were analyzed by small angle x-ray scattering (SAXS). The SAXS measurements show linear increases in the volume fractal dimension (2.32–2.64) of the secondary particles with aging time (0–72 h). This linear behavior is due to the silica precipitated from the aging solution to the secondary particles is at a constant rate. In the meantime, the light transmittances was obtained by ultraviolet–Visible–infrared spectrophotometer, extinction coefficient were obtained by fitting the curve of light transmittances. We developed a new model to build a connection between the extinction coefficient and the fractal dimension of the silica aerogel obtained by SAXS. From new model, it was found it is due to the increases in volume fractal dimension ( D f ) that result in increases of extinction coefficient and decreases of light transmittances. The optical transparency of silica aerogel is strongly affected by the volume fractal dimension ( D f ) of the secondary particles of silica aerogel. [ABSTRACT FROM AUTHOR]

The by-product silicon tetrachloride (SiCl 4 ) was usually obtained from polysilicon industry and was a cheaper alternative precursor. An economic method to produce silica aerogel using silicon tetrachloride under ambient pressure drying was presented in this work, which can also solve the pollution problem during the by-product silicon tetrachloride treatment process. The prepared aerogel samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller analysis, thermal conductivity analysis, contact angle test, Fourier transform infrared spectroscopy and thermogravimetric analysis. It was found that the molar ratio of H 2 O/SiCl 4 could affect the properties of aerogels seriously. The density and thermal conductivity first decreased and then increased as the molar ratio increased from 13 to 32. The porosity showed an opposite trend with the density. Silica aerogel with high specific surface area (856.7 m 2 /g), low density (0.077 m 3 /g) and low thermal conductivity (0.0213 W/m·k) were obtained at the optimal conditions when the molar ratio was 25. The resulting aerogel is also mesoporous material with super hydrophobicity and have a huge application in thermal insulation field. [ABSTRACT FROM AUTHOR]

The growth rates of Na 2 O⋅2CaO⋅3SiO 2 crystals on a polished surface, u s , and in the volume, u v u v , of the soda-lime-silica glass of the same composition were measured in a temperature range spanning from 873 to 1023 K ( T 12  = 845 K corresponds to a viscosity η = 10 12  Pa·s). We found that u s is significantly higher than u v and this difference progressively increases with decreasing temperature reaching in our experiment more than two orders of magnitude. This fact indicates that at low temperatures the effective diffusion coefficient of the structural units determining the growth kinetics along the glass surface is significantly higher than that in the bulk of glass, and gradually approaches the latter with increasing temperature. We also showed that the temperature at which the decoupling between the surface and volume diffusion coefficients occurs is higher than the decoupling temperature between diffusion coefficients estimated from viscosity via Stokes–Einstein−Eyring equation and by crystal rates in the bulk of glass. Our main conclusion about relation between surface and volume diffusion based on the analysis of surface and volume crystal growth for silicate glass combines the measurements performed for some molecular glasses, which proved that surface diffusion is much faster than volume diffusion. [ABSTRACT FROM AUTHOR]

Vitreous silica is modelled by Molecular dynamics. Glass structure is transferred into undirected graph and decomposed into disjoint structural units that are ideally mixed to calculate configuration entropy. A good agreement of the approach with experimental heat capacity drop at T g is demonstrated. Entropy is related with structural evolution of the obtained units; among them dangling oxygen dominantly effects low-temperature course of entropy. Configuration entropy is fitted by two parabolas; the one, corresponding to lower temperatures, introduces temperature T ⁎ , at which structure is completely frozen. It is proposed T ⁎ is a counterpart of Vogel temperature in Vogel-Fulcher-Tammann (VFT) equation. A new model of viscosity is introduced as the combination of the quadratic dependence of configuration entropy and Adam and Gibbs equation. The model removes the singularity at Vogel temperature, predicts existence of strong and fragile glasses, and provides a base for fitting viscosities of real glasses. Fragility is associated with quickness of structural response to temperature changes and the distance between T g and T ⁎ . The validity of the model is demonstrated on experimental data of viscosity for SiO 2 and B 2 O 3 glasses. [ABSTRACT FROM AUTHOR]

In this work, SiO 2 -CaO-P 2 O 5 based bioactive glasses were synthesized by the sol-gel method using calcium l -lactate pentahydrate and calcium nitrate tetrahydrate (CaNT) as calcium oxide precursors in order to achieve an improvement of the material bioactivity. The obtained samples were characterized by X-ray diffraction (XRD), FT-IR spectroscopy and scanning electron microscopy, then they were assessed from the perspective of their bioactive properties, while the textural properties were evaluated by Brunauer-Emmett-Teller method. The XRD pattern confirms the amorphous structure for all samples, except the glass synthesized with CaNT, where few crystallization centres associated with apatite phase were identified. A higher specific surface area and pore volume were obtained for the glasses prepared with calcium l -lactate pentahydrate in comparison with those obtained by using CaNT, result that was expected to be favorable in terms of bioactivity. The in vitro bioactivity assessment revealed the occurrence of a more pronounced apatite layer onto the glass' surfaces prepared with calcium l -lactate pentahydrate than as for the samples obtained with CaNT. [ABSTRACT FROM AUTHOR]

Silica aerogels are highly nano-porous and fragile solids, which exhibit brittle properties under tensile loading. In this work, molecular dynamics simulations with a model size up to 5.07 million atoms have been performed to investigate the effect of the crack length to height ratio on the fracture strength, fracture toughness and strain energy release rate. For a wide range of densities from 295 to 1155 kg m −3 , we demonstrate that the fracture toughness and the strain energy release rate at the onset of the crack propagation increase with the crack length to height ratio. Moreover, these fracture properties were found to exhibit a power law dependence on the aerogel density with exponent values of 2.02 ± 0.05 for the fracture toughness and 1.16 ± 0.04 for the strain energy release rate. The investigations presented grant a more comprehensive understanding of the fracture behavior and provide a mechanistic basis for reliable applications of silica aerogels. [ABSTRACT FROM AUTHOR]

The present work explores the potential of B 2 O 3 substituted bioactive glasses towards improvement in surface apatite formation along with better cell proliferation and improved antibacterial properties. While the base glass was selected from SiO 2 -Na 2 O-CaO-P 2 O 5 system (commercially available S53P4 glass), four B 2 O 3 modified glass compositions were formulated by replacing SiO 2 in the base glass composition by B 2 O 3 with 25, 50, 75 and 100%. To understand the amorphous nature of the glasses as well as the structural changes in the glasses, X-ray diffraction (XRD) analysis and Fourier transform infrared (FTIR) spectroscopy were performed, respectively. The thermal behaviour of the glasses were analysed using differential scanning calorimetry (DSC) and an improvement in the glass stability factor ( ∆T ), was observed at optimized B 2 O 3 concentration. The apatite formation on the surfaces of glasses after bioactivity study for various time periods was analysed using XRD and FTIR. A gradual increase in the pH value and ion concentration ( e.g. Ca 2+ , B 3+ ) in simulated body fluid (SBF) was observed along with faster apatite formation with gradual increase in B 2 O 3 substitution. The in vitro cell proliferation studies using MTT assay demonstrate that the cell proliferation was better on the glasses (BG1B, BG2B and BG3B) compared to base glass (BG0B). Antibacterial study was performed using broth microdilution method against Escherichia coli (E. coli) bacteria exploring the antibacterial effects of these glasses from which B 2 O 3 substituted glasses were observed to exhibit improved antibacterial properties compared to base glass (BG0B). [ABSTRACT FROM AUTHOR]

We present first principles calculations on conversion of a peroxy linkage (POL, Si   O   O   Si ) defect. GW and Bethe-Salpeter equation methods are introduced. POL defect has different reaction paths when interacts with H 2 . It will convert into silanol (Si OH+Si OH) at the ground state (S 0 ) and likely to transfer into Si OOH + Si H at the triplet state (T 1 ). Optical absorption strength of hydrogen-induced defects is higher than the POL defect between 6 and 8 eV and would be more easily lead to a laser-induced damage phenomenon. Our results not only display a better understanding of how H 2 molecular interacts with the POL defect, but also provide a guidance to figure out these defects in silica fiber. [ABSTRACT FROM AUTHOR]

The glasses of composition (35–x) Li 2 O–5ZrO 2 –10Y 2 O 3 –50SiO 2 : x NiO (0 < x < 0.5) have been synthesized. The amorphous nature of the samples is verified by XRD studies and DTA studies. The information on of various structural vibrational units (viz., zirconate, silicate) and their compositional dependence of is evaluated by FT–IR and Raman studies. The results of these studies have indicated that there is a growth of asymmetrical bands at the expense of symmetrical bands of silicate units with increasing concentration of NiO. The optical absorption (OA) and photoluminescence (PL) spectral of Li 2 O–ZrO 2 –Y 2 O 3 –SiO 2 : NiO glasses indicated gradual increase of octahedral occupancy of Ni 2+ ions in the glass network with the increase in the concentration of NiO in the glass network. [ABSTRACT FROM AUTHOR]

In this paper, we clarify the gel-to-glass (G-G) transformation behavior of the sol-gel derived xAl 2 O 3 -(100 − x)SiO 2 (x = 0, 10, 20 and 30 mol) systems by differential scanning calorimetry, X-ray diffraction, infrared (IR) spectroscopy and transmission electron microscopy. The SiO 2 -Al 2 O 3 gels exhibit lower G-G transition temperature than the pure SiO 2 reference gel. Adding Al 2 O 3 to the SiO 2 gel can suppress the dependence of glass transition temperature ( T g ) on hydroxyl concentration, and this effect is attributed to the highly cross-linked structure in alumina-silica gels. In addition, the Al-rich phase separates from the Si-rich matrix phase, and such immiscibility increases with increasing Al 2 O 3 content. This behavior is similar to that of the melt-quenched alumina-silica glasses. [ABSTRACT FROM AUTHOR]

The quaternary glass system tellurium dioxide, boron trioxide, silicon dioxide and manganese dioxide where x = 0.00 to 0.05 M fraction has been successfully prepared via conventional melt and quench-casting technique. The density was determined by Archimedes method with distilled water as buoyant liquid. The results showed that the density decreases and molar volume increases with respect to manganese concentration. FTIR spectral studies suggest that glass network is mainly built up of boron trioxide, tetrahedral boron, tellurium trioxide, trioxotellurate and silicon dioxide structural units. The ultrasonic velocities and elastic moduli were recorded using a pulse-echo method at frequency 5 MHz at room temperature. Some other physical properties such as Debye temperature, softening temperature, microhardness, Poisson's ratio, fugacity, fractal bond connectivity and Cauchy relation were determined. Results indicate that these parameters depend upon the composition of the glass system and the dopant concentration, MnO 2 inside the glass system. [ABSTRACT FROM AUTHOR]

At present synchrotron and neutron sources are the preferred choices for the Pair Distribution Function (PDF) analysis, but there is a need to explore PDF in a laboratory XRD system for quick feedback about the short range structure of the amorphous materials. Present work considered both crystalline (quartz) and amorphous silica to study the structural differences in silica by PDF analysis using Ag radiations in laboratory XRD. The structural information about short range ordering of the oxygen (O) atoms around silicon (Si) atoms as obtained by the PDF were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments. The PDF studies showed that the amorphous silica possessed short range periodicity within the basic unit of (SiO4) 4− tetrahedra with a Si O & O O distance are of about 1.622 Å and 2.713 Å while the short range as well as long range ordered structure present in quartz with Si O & O O distance are 1.562 Å and 2.661 Å respectively. Raman spectra showed some asymmetry in amorphous silica which corresponds to the defects present in the lattice and thus forming the n-fold ring structure with Si and O resulting in the wide variation of bridging bond angle Si O Si in amorphous silica. NEXAFS studies revealed the structure of amorphous silica and quartz in the intermediate range (3–5 Å) at the Si L and O K edges. The structural information about short range ordering of the O around Si atoms as obtained by these methods were found to be in good match with the results as obtained by PDF, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials. [ABSTRACT FROM AUTHOR]

Human interaction with multimedia devices occurs predominantly over inorganic glass surfaces. Scratch-induced damage is a primary limitation in the suitability of brittle glasses for this purpose. However, neither truly quantitative data nor a topo-chemical understanding of the underlying deformation process which would allow for the development of improved materials is presently available. Here, we present lateral nano-indentation experiments for determining the work of deformation which is involved in the process of glass scratching. Using a series of hot-compressed vitreous silica with mild degrees of structural densification, we derive relations between quantitative scratch hardness and the underlying glass structure. We show that Young's modulus provides a clear rational for the observed variations in scratching hardness. In the specific case of silica, the energy needed to generate a certain scratch volume corresponds to roughly one tenth of Young's modulus. This relationship formally indicates that only about one tenth of the bonds which are involved in the deformation process are broken in its course. However, comparison with a more complex glass material with a certain fraction of two dimensional structural units and a strong ability for topological adaption to local stress clearly indicates a deviation from this behavior. This opens a pathway to topo-chemical engineering of scratch-resistant glasses. [ABSTRACT FROM AUTHOR]

Amorphous micro silica (MS) is used as a raw material in the production of porous calcium silicate. MS is a by-product from the silicon and silicon-alloy production, and strongly influences the properties of porous calcium silicate products. We investigate the kinetics of the formation of calcium silicate hydrate (C-S-H) gel from the reaction between quicklime and MS based on two types of MS (MS97.5 and MS92.8, which have 97.5 and 92.8 wt% SiO 2 , respectively). The C-S-H gel is found to be amorphous, but with short- and medium range order similar to tobermorite for the two types of MS. MS97.5 is found to react faster than MS92.8. The activation energy is determined to be 76 kJ/mol for MS97.5 and 103 kJ/mol for MS92.8. For comparable surface area of MS, the C-S-H formation mechanism is strongly affected by metallic or metal oxide impurities in two ways. First, the positively charged metal ions are attached to the negatively charged hydroxyl groups at the MS surface, resulting in less available hydroxyl groups for MS-quicklime reaction, and in lower solubility of MS. Second, impurities react with the calcium silicate network, making less raw material available for the reaction. [ABSTRACT FROM AUTHOR]

Silica aerogel is one of the most attractive insulation materials but has not been broadly applied yet because of limitation of its fragile nature. In this work, we synthesized a compressible bacterial cellulose/silica aerogel composite from the co-precursor of tetraethylorthosilicate and methyltrimethoxylsilane by a two-step acid-base catalyzed sol-gel method followed by supercritical CO 2 drying. This aerogel composite possessed a series of excellent properties: standing the considerable strain, high resilience, dust-free, low density of 0.066 g/cm 3 and low thermal conductivity of 0.0292 W/(m·K) along with hydrophobicity with a water contact angle of 147°. Weight loss analysis indicated that the thermal stability of the as-prepared composites was about 270 °C which primarily depended on the thermal stability of the bacterial cellulose. These outstanding properties were attributed to the Interpenetration Polymer Network structure formed via the co-precursors and the bacterial cellulose and the excellent fabric of the aerogel retained by the supercritical CO 2 drying. The results suggest that the as-prepared aerogel composite has potential applications as a suitable insulation material with dust-free and resilience. [ABSTRACT FROM AUTHOR]

Available data of density, molar volume, refractive index and molar refraction of Al 2 O 3 –SiO 2 glasses have been analyzed. The analysis shows that any of these properties can be expressed in terms of a factor of SiO 4 tetrahedron and another one related to a structural species of AlO 3/2 formula. These factors, together with previously found factors of the modified AlO 4 tetrahedra, are useful to calculate the properties of Li 2 O–Al 2 O 3 –SiO 2 and CaO–Al 2 O 3 –SiO 2 glasses with [Al 2 O 3 /(Li 2 O or CaO)] > 1. Structural forms of AlO 4 , AlO 5 and AlO 6 groupings are proposed, in which the charge compensation is attained through various distributions of 2-, 3- and 4- coordinated O 2– ions. Any of these groupings is equivalent to the AlO 3/2 formula. It is concluded that the studied properties are not sensitive to coordination of Al 3+ ions. [ABSTRACT FROM AUTHOR]

Charge trapping in amorphous silica (a-Si O 2) dielectric layer can degrade electrical performances of semiconductor devices. Earlier studies demonstrate that a SiO 4 tetrahedra unit with a wide O-Si-O angle (≥ 132. 0 ∘ ) can act as an electron trapping site in unstrained a-Si O 2 cells. With first-principle calculations, in conjunction with molecular dynamic calculations, this work investigates the impacts of uniaxial tensile strain on one-electron trapping behaviors of a-Si O 2 , including atomic configurations and electronic properties. Stable states of strained a-Si O 2 cells with an extra electron indicate that a SiO 4 with a wide O-Si-O angle (≥ 132. 0 ∘ ) and a long Si-O bond (≥ 1. 660 Å) making up the angle can act as a novel intrinsic electron tap. An electron trapping on this trap can generate a stable defect complex with two components: a negatively charged non-bridging oxygen hole center and a neutral oxygen vacancy with an unpaired electron. [ABSTRACT FROM AUTHOR]

• Open-celled materials called aerogels are made up of linked nanostructures. • An overview of silica-based aerogels' traditional chemistry and synthesis processes is provided. • A review of the literature is provided on techniques for silica-based aerogels' multifunctionality and mechanical improvement. • Application of aerogels: state of the art. Silica aerogels have piqued the interest of researchers because of their distinct nanoporous networks, composed of interconnected silica nanoparticles and high-volume nanosized pores. They are produced using the "sol-gel" process, which involves precursor preparation, gelation, aging, and drying and is a reliable process for making silica aerogels. The hydrophobicity or hydrophilicity of silica aerogels can be attributed to either the synthesis process or the surface silanol groups. Silica aerogels used in marketable and high-tech engineering applications such thermal insulation, separation, coatings, sensing, and catalysis due to their unique features. This article highlights silica aerogels' intrinsic properties, potential applications, and recent scientific advances. Moreover, it provides an overview of the synthesis, processing, and recent applications of aerogels in air purification, such as CO 2 capture and VOC removal, and in water treatment, including the removal of oil and toxic organic compounds and heavy metal ions. Significant features of the science behind these applications are described, and when relevant, critical issues affecting aerogel application are noted. [Display omitted] [ABSTRACT FROM AUTHOR]

This study presents a simple sol-gel synthesis of silica using Tetraethylorthosilicate, water, and three alcoholic solvents. The gelation was carried out in autoclave between temperatures from ambient to 180 °C. The FTIR analyses showed that the chemical bonds of the synthesized silicas do not depend on the autoclave temperature and solvent used. Then, for both ethanol and isopropanol solvents, it was found that the higher the gelation temperature, the larger the mean diameter and specific pore volume in the prepared samples. The same trend was observed for water vapor adsorption. Such behavior seems to result from a faster network gelation entrapping more residual molecules, which leads to a more porous adsorbent after their removal, despite a stronger structural densification probably occurring for higher hydrothermal temperatures. Besides, such a densification process decreasing the porosity proved to be more significant when using an alcoholic solvent with a higher boiling point. [Display omitted] [ABSTRACT FROM AUTHOR]

• The electrostatic repulsion and Debye radius of the sol-gel particles were affected by the addition of N-hexane. • Modulation of gelation time and microstructure of silica aerogels by addition N-hexane to solvent. • Thermal conductivity of silica aerogel is as low as 0.012 W/m·K by modulating microstructure. • The variation of thermal conductivity in the experiment is verified by introducing theoretical calculations. In this work, a kind of superhydrophobic silica aerogels was prepared at ambient pressure using tetraethoxysilane (TEOS) as precursor. Particularly, N-hexane was added in the solvent to modulation pore microstructure and effect on the insulation properties of samples were analyzed. It is discovered that when the volume ratio of N-hexane to TEOS is 1:2.24 the thermal conductivity of samples can reach the lowest of 0.012 W/m·K. Compared with that of samples no addition of N-hexane, the density is decreased, the theoretical average pore size increases and the total pore volume increases. Due to N-hexane it leads cross-linking between the sol particles stronger and inhomogeneous. Thus gelation process is speeded up resulting in a change in pore structure. Low density can reduce the solid-phase heat transfer, perfect pore microstructure reduces the contribution of gas-phase heat transfer, and only when the two aspects forms a suitable combination it can exhibit optimal thermal insulation performance. [Display omitted] [ABSTRACT FROM AUTHOR]

We used a resonance wavelength shift of a whispering gallery mode to monitor volume relaxation at room temperature in cylindrical and spherical resonators fabricated by quenching the molten tip of a pure silica optical fiber. The high sensitivity of the method allowed measurement of the linear dimension at sub-ppm resolution. All the resonators registered a volume increase in the first few hours, in agreement with the volume-temperature equilibrium curve of type IV silica below the glass transition temperature. When heating of the fiber was insufficient, the volume increase was greater, ascribed to a larger volume of strained silica. We also formulated thermodynamics to estimate the temperature coefficients of polarizability at constant pressure and at constant density from resonance shift data obtained in experiments performed on relaxed silica resonators. [ABSTRACT FROM AUTHOR]

Silica glass doped with silver was synthesized using the sol-gel method. The formation of the silica network and the purity of samples were confirmed by Fourier transform infrared spectroscopy. The nature of silver as a function of annealing temperature was investigated using X-ray diffraction (XRD), UV–Vis spectrophotometry, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) techniques. The obtained results from XRD and UV–Vis absorption showed similar information which both confirmed the formation of Ag nanoparticles (NPs) in the samples annealed at high temperature, but revealed nothing about the nature of Ag in the as-prepared samples and those annealed at low temperature. The images and diffraction patterns from HRTEM showed the interesting result that even for the as-prepared sample some of the Ag ions were converted to Ag NPs. This result was further confirmed by XPS data. Moreover, the HRTEM images showed that an increase in the annealing temperature increases the size of the Ag NPs, although the shape of the NPs remains almost unchanged. The quantitative information extracted from XPS results revealed that the ratio of Ag NPs to Ag ions increases with increasing annealing temperature. [ABSTRACT FROM AUTHOR]