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Phase separation was observed in silica glass following low‐temperature heat treatment in high water vapor pressure through the formation of bubbles. Although the 6 day diffusion treatment in saturated water vapor pressure at 250°C does not normally cause phase separation, the reactive fracture surface and subsurface damage caused by polishing with cerium oxide (CeO2) allowed for an increase in water absorption during treatment and heterogeneous nucleation of the bubbles at damaged sites. The sub‐surface damage, characteristic of blunt contact damage, was only revealed when the polished sample was etched. The formation of bubbles and polishing damage were observed in two silica glasses—one containing chlorine impurities and the other containing OH impurities. Raman spectra collected after fracture or polishing and water diffusion treatment demonstrated an increase in the abundance of –OH species including silanol (SiOH) groups and an evolution in the glass structure in the bubble regions compared with the bubble‐free regions. These results indicate an increase in the reactivity between water and glass fracture surfaces relative to the bulk. [ABSTRACT FROM AUTHOR]

Maintaining high surface area and porosity at high temperatures is important when considering aerogels for use in thermal management systems. The mesoporous structure of aerogels results in extremely low thermal conductivity, making them lightweight, high performance insulating materials. Maintaining these properties requires innovative routes to suppress sintering and pore collapse as use temperatures rise. The current work aims to improve the pore structure stability of yttria‐stabilized zirconia aerogels by the addition of a SiO2 coating. The functionalization of surface hydroxyl groups by the addition of SiO2 is hypothesized to mitigate condensation reactions, which are a driving force for shrinkage and pore structure collapse. Zirconia aerogels with 0, 10, and 30 mol% yttria (YO1.5) additions were coated in a tetraethyl orthosilicate (TEOS) solution and exposed to temperatures up to 1200°C. Crystal structure, pore structure, and aerogel morphology were investigated to understand changes in aerogel thermal stability. The SiO2 coating exhibited a greater influence on pore stability over yttria concentration, with specific surface area of the coated aerogels being twice that of the uncoated aerogels up to 1000°C. However, the presence of the SiO2 coating promoted rapid sintering and densification at 1200°C, establishing an upper use temperature for SiO2 and a need to develop other coating chemistries. [ABSTRACT FROM AUTHOR]

A recent study showed that generating local crystalline paths within a glassy matrix provides only a moderate increase in thermal conductivity until the path fills most of the total volume. It was indicated that percolation theory governs the thermal conductivity in such crystalline‐implanted glass composites. In this study, we use computer simulations to investigate the effect of partial vitrification by breaking structural order of silica crystals by local vitrification. Such locally vitrified crystal structures are made by the bond‐transposition method, where the extent of vitrification can be tuned. Also, we test melt‐quenching of three SiO2 crystalline structures (α‐quartz, coesite, and stishovite) to make silica glasses with different densities. The cooling rates and pressures were varied during the melting process in order to obtain glass structures with varied degrees of order. Our results show that the thermal conductivity of silica glasses calculated using Green–Kubo relation decreases rapidly as soon as the crystallinity is disturbed by bond transition or generated local glassy phase. This implies the phonon mean free path rapidly shrinks with even a small number of scatterers, regardless of the original polymorph. Through the investigation of the pressure effect, a strong proportional relation between the thermal conductivity and the density is found among all silica samples. Such correlation can be accounted by assuming a constant integral term in the Green–Kubo relation without the volume scaling, which is reasonable based on a weak dependence of κV on the density of silica glass except with a slight increase at low quench pressures. We hypothesize that when the quench pressure increases moderately, an increase of characteristic ring size tends to generate a more flexible SiO2 structure which results more phonon scattering. Green–Kubo modal analysis further shows that the contribution from modes at low frequencies is suppressed when SiO2 is melt‐quenched at higher pressure and vice versa. [ABSTRACT FROM AUTHOR]

As demand for customized specialty fibers grows, standardized production methods face challenges. This article reviews industry standards and discusses potentially disruptive techniques that enable rapid prototyping and fabrication of optical fiber devices. Furthermore, we showcase laser powder deposition's (LPD) potential for additive manufacturing (AM) of customized glass structures. In the case of, for example, fiber preforms, although the feasible size is smaller than the industry standard, utilizing laser‐based manufacturing techniques for a small batch production presents an attractive avenue for rapid prototyping and expedites material and design optimization. In the realm of AM of glass, LPD offers numerous benefits, including minimal shrinkage, high densification, and the ability to tailor glass composition to achieve desired optical properties. The article reviews the latest achievements and highlights future directions in this technology. [ABSTRACT FROM AUTHOR]

As an environment‐friendly powder with good coloring performance, rare earth sulfide is one kind of the important choices to replace cadmium and lead colorants. In particular, γ‐Ce2S3 belongs to rare earth sesquisulfide, which has a bright red color. However, the uncoated γ‐Ce2S3 is easy to decompose and release H2S in a humid or acidic environment, and its air thermal stability is limited to 350°C. In this work, γ‐Ce2S3 powders coated with zinc oxide were prepared by heterogeneous precipitation method, and a dense protective layer was formed by ZnO to improve chemical and thermal stability. Moreover, silicon dioxide was deposited on the surface of the zinc oxide coating using the microemulsion process to strengthen the powder's acid resistance. The double shells structure greatly promoted thermal stability and acid resistance of γ‐Ce2S3 powders. The results showed that rare earth sulfide powders with double shells have good stability for coloring applications. [ABSTRACT FROM AUTHOR]

An integrated experimental and thermodynamic modeling investigation of the phase equilibria in the PbO–NiO–SiO2 system in air and also in equilibrium with liquid metal has been undertaken to better characterize the chemical reactions taking place in the Ni‐containing Pb processing slags. New experimental phase equilibria data at 720°C–1740°C were obtained for this system using high‐temperature equilibration of synthetic mixtures with predetermined compositions in sealed silica ampoules or in Au/Pt–Ir foils, a rapid quenching technique, and electron probe x‐ray microanalysis of the equilibrated phase compositions. Phase equilibria and liquidus isotherms in the quartz/tridymite/cristobalite (SiO2), olivine (Ni2SiO4), monoxide (NiO), Ni‐barysilite (Pb8NiSi6O21), massicot (PbO), and di‐lead silicate (Pb2SiO4) primary phase fields were revealed and the extent of the high‐SiO2 two‐liquid immiscibility gap in equilibrium with cristobalite was determined. New experimental data were used in the development of a thermodynamic database describing this ternary system. Also, modeling revision of the NiO–SiO2 binary system was conducted, resulting in a smaller miscibility gap in ternary systems that was closer to the experimental results. [ABSTRACT FROM AUTHOR]

The atomic scale solid–liquid interfacial process dominates the macro‐dissolution of silica, yet its direct experimental observation is challenging. Here we employed the reactive molecular dynamics to model this process in alkaline condition. An elevated temperature strategy under canonical ensemble (NVT) was applied to accelerate the process for sufficient sampling at temporal domain. A stepwise transformation from fully linked SiO4 network (Q3 and Q4) to reduced linkage and eventually aqueous species (Q0) was revealed. The simulated dissolution rate agrees well with the value predicted by empirical model. By tracing hydrogen atoms, we found that the dehydroxylated silica surfaces in alkaline electrolyte solutions underwent a transition from Si–O–Si bond cleavage‐dominated (mainly reacted with OH−) to hydroxylation‐dominated surface reactions. The free‐energy reconstruction of well‐tempered metadynamics reveals that 1500 K accelerates dissolution without altering the reaction pathways. These findings offer novel insights into the evolution of atomic‐scale surface configurations during the dissolution kinetics of silica. [ABSTRACT FROM AUTHOR]

In this work, we develop and employ an accelerated design strategy using a machine learning algorithm to overcome the challenges for designing a new machinable glass ceramic. The trained machine learning model predicts the specific hardness value for numerous possibilities of processing conditions such as growth temperature and time. We report that the optimized growth parameters of 1200°C and 5 h achieve the highest machinability of 0.4 in the glass ceramic. Furthermore, we predicted the eight most promising candidates containing specific ratios of silicon, magnesium, aluminum, lithium, boron, potassium, barium, and oxygen. Combining machine learning with experimental data enables a systemic and rapid design of a ceramic material while capturing the underlying physics represented in the experimental data. [ABSTRACT FROM AUTHOR]

It is essential to etch SiO2 for producing silica glass components, semiconductor devices, and so on. Although wet‐etching with hydrogen fluoride (HF) solutions is usually employed for this purpose, it faces a drawback that microstructures stick during the drying of the solution. To overcome this problem, we have developed a dry‐etching technique with gaseous HF at high temperatures. In the present study, an interesting phenomenon was found that silicon thermal oxides were much less etched than vitreous silica by gaseous HF. Such difference had not been found in wet‐ or humid HF gas etching. Because their bulk chemical formulae are the same (SiO2), it was suggested that the surface species affected the reaction rate. In fact, preprocessing with water vapor plasma remarkably increased the etching rate on the thermal oxides layer, and vacuum heating almost completely suppressed the reaction on the vitreous silica and the plasma‐treated thermal oxides. These results indicate that the surface silanol groups enhance the reaction between SiO2 and gaseous HF. Based on the results, a model of chain reaction for SiO2 and gaseous HF was proposed, where the surface silanol groups act as the reaction center. [ABSTRACT FROM AUTHOR]

To investigate the possible structural differences between silica glass fibers and bulk silica glasses, electron energy loss spectroscopy (EELS) has been used to study the short-range and medium-range structures of both forms of silica glasses. The short-range structure of silica glass, such as the coordination and symmetry, was investigated by the energy loss near edge structure (ELNES) of Si L2,3-edges. The ordering structure in the medium-range was analyzed by the exponential optical absorption edge also known as the Urbach edge of the glasses. The optical absorption data were obtained from the low energy loss spectrum of EELS through Kramers-Kronig analysis. The results show that silica fiber has the same short-range structure as the bulk specimen, but is significantly more disordered than the bulk glasses.

Residual stress profiles in silica glass were measured after water diffusion treatment under 47.33 kPa (355 Torr) water vapor at 350°C and 650°C. Earlier, it was found that water solubility in silica glass exhibited peculiar time dependence: Solubility increased with time exceeding the normal water solubility expected from higher temperatures. Then, the water solubility decreased with time. It was hypothesized that the stress induced by water diffusion and its subsequent relaxation is responsible for the phenomenon. Residual surface stress generation in silica glass was found to correlate closely with surface hydroxyl concentration, systematically increasing until eventual surface stress relaxation results in stress decrease for treatments beyond 265 hours at 650°C. This observation validates previous theories of time dependent diffusivity in silica glass. [ABSTRACT FROM AUTHOR]

Mesoporous silica has been applied in catalysis, separations, and drug delivery. It has generally been made using organosilicon precursors such as tetraethyl orthosilicate. For sustainability, it is necessary to find readily accessible mineral sources for making mesoporous silica. In this work, we demonstrate the successful synthesis of mesoporous silica with 10 nm average pore size using the mineral forsterite (Mg2SiO4) as a silica source, providing a potentially cheaper and more Earth‐friendly route to making technologically important porous silica materials. Pure forsterite was synthesized by a solid‐state chemistry route at 1000°C and underwent dissolution–reprecipitation in aqueous hydrochloric acid containing the soft template surfactant, Pluronic P123. Variations of initial reaction pH (−0.2 to 0.6), reaction time (12–24 h), reaction temperature (50 to 90°C), and silica precursor (forsterite and fumed silica) were performed. The mesoporous silica aged at 70°C for 24 h had the highest porosity, with a surface area of 735 m2/g and a pore volume of 1.4 ml/g, comparable to mesoporous silica made using conventional starting materials. This novel geomimetic synthesis route supports the possibility of analogous formation of structured (mesoporous or zeolitic) silica in nature under abiotic or prebiotic conditions. [ABSTRACT FROM AUTHOR]

Porous silica is widely used as antireflection films in inertial confinement fusion facilities and be irradiated by high fluence neutron. To date, the neutron irradiation effect of amorphous porous silica is still unclear. In this paper, we give a comprehensive insight into neutron irradiation effect on microstructure, mechanical, and optical properties of porous silica under 14 MeV neutron irradiation by using molecular dynamics and density‐functional theory‐based methods. We find that, for microstructure, neutron irradiation elongates Si–O bond distance, obviously reduces the max value of Si–O–Si bond angle, coordination number distribution, and increases Si3+ and non‐bridging oxygen defects. The bulk modulus, shear modulus, and Young's modulus are all obviously reduced due to neutron irradiation, but Poisson's ratio changes relatively small. The light transmittance is reduced, and the optical absorption coefficient is increased after neutron irradiation, especially in the photon energy range of 3–4 eV, which is detrimental to the resistance of laser‐induced damage. Moreover, we find that neutron irradiation has more influence on high‐porosity porous silica than low‐porosity porous silica, which is mainly due to the higher defect percentage in high porosity. Present work is expected to be valuable in the study of degradation mechanism of nuclear material under neutron radiation. [ABSTRACT FROM AUTHOR]

Porous ceramics offer unique properties that can bring advances to many application areas. The freeze‐casting process has a strong potential for fabricating porous ceramics; however, the effects of process parameters on part porosity must be well understood for scalable manufacturing via freeze casting. This paper presents an experimental analysis of the freeze‐casting process that correlates the freeze‐casting parameters with pore characteristics. A full‐factorial design of experiments is conducted on a unidirectional freeze‐casting testbed using silica as the ceramic material and camphene as the solvent. The effects of solid loading, particle size, cooling temperature, and the distance from the cooling surface on porosity characteristics are evaluated. The fabricated samples are cross‐sectioned vertically and horizontally and imaged using scanning electron microscopy. Image processing is used to obtain the porosity characteristics of areal porosity, pore size, pore shape, and pore orientation. The capability to steer the pore orientation is also demonstrated through bidirectional freezing experiments supported by a finite‐element model. As a result, a quantitative understanding of the effects of freeze‐casting process parameters on porosity characteristics is gained for the silica–camphene system. These results and the presented approach can be used for reproducible manufacture of porous ceramics with controlled porosity. [ABSTRACT FROM AUTHOR]

The mass transport mechanisms of Ti in TiO2:SiO2 and Ge in GeO2:SiO2 direct ink write, additively manufactured glasses were studied. Due to the low solubility of Ti in SiO2 and high melting point of TiO2 relative to SiO2, Ti transport was found to occur via solid state interdiffusion between adjoining SiO2 and TiO2 precursor particles. The diffusivity of titanium in SiO2 measured over typical sintering temperatures (1000–1300°C) using Rutherford backscattering spectrometry was D=9.1×10−7[m2/s]exp(378[kJmol]RT)$D\ = \ 9.1{\rm{\ }} \times {10^{ - 7}}{\rm{\ }}[ {{\rm{m}}^2/{\rm{s}}} ]{\text{\ exp\ }}({\frac{{378[ {\frac{{{\rm{kJ}}}}{{{\rm{mol}}}}} ]}}{{RT}}})$. This provides an estimate of ∼30 nm for the diffusion length under typical sintering conditions (2 h at 1200°C). Although Ti and Ge have similar diffusivities in SiO2 glass at low concentrations, GeO2 was found to be much more mobile during the sintering of printed GeO2:SiO2 green bodies. This was evident in glasses with phase separated GeO2 regions over length scales of ∼10 µm and in experiments involving binary xerogel films in which GeO2 migrated over ∼10 µm through cracked, porous SiO2 layers. Large phase separated regions and long transport lengths in GeO2:SiO2 suggest that the transport of GeO2 occurs prior to the densification of the SiO2 matrix via an alternative mechanism such as capillary flow. These results inform important considerations in the design of index modifying inks for the direct ink write process, namely initial precursor phase, mutual solubility with the base SiO2 glass, and mass transport throughout the sintering process. [ABSTRACT FROM AUTHOR]

The modification of basic oxygen furnace (BOF) slag by adding silica can improve the properties of BOF slag for applications in the cement industry. The rapid dissolution of silica is essential to hot slag modification. In this work, the dissolution behavior of silica in the molten CaO–SiO2–Fe2O3–MgO–MnO system as synthetic BOF slag was investigated by using the traditional rotating cylinder technique. Effects of rotation speed, temperature, immersion time, and slag basicity on the silica dissolution were studied. Scanning electron microscopy equipped with energy dispersive spectrometer (SEM‐EDS) and FactSage simulations were employed to reveal the dissolution mechanism. It was found that the dissolution of the silica rod was affected by both the thermodynamic driving force and the slag viscosity. The silica dissolution rate in molten CaO–SiO2–Fe2O3–MgO–MnO slag increased with increasing the rotation speed and temperature, but first increased and then decreased when decreasing the slag basicity from 2.5 to 1.5. A linear correlation between the logarithm of the dissolution rate and the logarithm of cylinder periphery velocity with a slope of 0.44 was observed, indicating the mass transfer within the boundary layer as the dissolution rate determining step. A direct dissolution way was found during the dissolution of silica in molten CaO–SiO2–Fe2O3–MgO–MnO slag. [ABSTRACT FROM AUTHOR]

Taking silica as an exemplary material system, we studied water‐assisted densification behaviors of different crystallinities (quartz, glass, and vitreous silica). To avoid the complexity in data interpretation, we adopted a simple procedure similar to those used for pressing salt pellets for IR: compressing silica powders in a mold with pure water under ambient conditions. It is discovered that crystalline silica is compacted through liquid lubrication, while amorphous silica's densification behaviors contradict the widely regarded dissolution‐reprecipitation mechanism. Another mechanism is thus proposed: stress‐driven water incorporation into the solid structures produces hydrated silica of considerable plasticity for deformation and fusion. Inspired by this water‐assisted mechanism, a more effective sintering method is developed via repetitive stressing/destressing treatments at room temperature, enabling dramatically boosted densities (e.g., over 90% with transparent appearance for silica glass) and enhanced mechanical performance. This generic strategy may apply to a wide range of materials. Furthermore, the hydration‐enabled deformation/sintering mechanism proposed in this work offers fresh insights into the biomineralization puzzles, particularly those on how life accomplishes some of the most challenging tasks faced by humans in modern ceramic technology, for example, to fuse, mend or reshape the rigid brittle ceramic objects in aqueous environments under ambient conditions. This purely inorganic biomineralization mechanism may be particularly important for life at its early stage of evolution on earth. [ABSTRACT FROM AUTHOR]

Silica glass exhibits rate‐dependent and irreversible processes during deformation and failure, resulting in inelastic effects. To explore this phenomena, molecular dynamics simulations of structural relaxation surrounding a crack tip in silica glass were performed at four different temperatures (100, 300, 600, 900 K) using a reactive force field. Per‐atom stresses were found to relax during the simulation, with the highest stress relaxation occurring at 900 K. Stress relaxation was radially dependent relative to the crack tip, with stress dissipation occurring primarily within a 25–30 Å inelastic region. Within 10 Å of the crack tip, the defect concentration decreased from 0.18 to 0.09 #/nm2 during inelastic relaxation at 900 K. Conversely, the defect concentration 20 Å from the crack tip increased from 0.105 to 0.118 #/nm2 at 300 K, and from 0.113 to 0.126 #/nm2 at 600 K, which formed a defect‐enriched region ahead of the crack tip. The difference in defect concentrations suggests the possibility of a stress mediated defect migration mechanism, where defects move away from the crack tip during inelastic relaxation. Additionally, defect speciation indicated that undercoordinated silica defects, such as non‐bridging oxygen, were removed through the formation of higher coordination defects during relaxation. Overall, stress relaxation causes changes in the defect concentration profile near the crack tip, which has the potential to alter the properties of silica glass in the inelastic region during relaxation. [ABSTRACT FROM AUTHOR]

Intensive and overuse of antibiotics during the last years has triggered a distinct rise in antibiotic resistance worldwide. In addition to the newly developed antimicrobials, there is a high demand for alternative treatment options against persistent bacterial infections. The biocidal impact of metal ions like copper (Cu2+), silver (Ag+), and zinc (Zn2+), also known as the oligodynamic effect has been used for ages to kill or inhibit the growth of microorganisms and to employ long‐term prevention strategies against their biological antagonists. Herein, we report on the synthesis of Cu, Ag, and Zn metal and corresponding oxide nanoparticles immobilized on hollow mesoporous silica capsules (HMSCs) obtained by a hard‐template assisted sol‐gel synthesis followed by reduction of appropriate metal salts in the presence of HMSCs. Compartmentalization of nanosized metal and oxide clusters in Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles prevented their agglomeration and offered high release kinetics of metal ions between 2.0 and 3.7 mM during 24 h, as monitored by UV‐vis analyses. The distribution and morphology of pristine and metal functionalized HMSCs were evaluated by transmission electron microscopy analysis revealing the successful synthesis of Ag, Cu, and ZnO nanoparticles supported on HMSCs. X‐ray photoelectron spectroscopy revealed that mainly Cu(II), Ag(0), and Zn(II) species were present in the modified HMSCs. In addition to the surface attachment of preformed metal (Ag and Cu) and metal oxide (ZnO) cluster, nucleation of metal nanoparticles inside the void of HMSCs provided an internal reservoir which allowed for a time‐dependent release of metal ions through slower dissolution rates leading to a long‐term and sustained bacterial inhibition over several hours. The high antimicrobial efficiency of Ag@HMSCs, Cu@HMSCs, and ZnO@HMSCs particles was investigated toward both Gram‐positive (Bacillus subtilis) and Gram‐negative (Escherichia coli) bacteria by INT assays showing a complete growth inhibition for both bacteria types after 24 h. While Ag@HMSCs and Cu@HMSCs showed a higher susceptibility against Gram‐negative bacteria, ZnO@HMSCs showed a higher susceptibility against Gram‐positive bacteria. This demonstrates the promise of metal‐loaded capsules as antibacterial delivery vehicles with dual‐mode time‐release profiles being potential alternatives for antibiotic drugs. [ABSTRACT FROM AUTHOR]

Silica is known as the archetypal strong liquid, exhibiting an Arrhenius viscosity curve with a high glass transition temperature and constant activation energy. However, given the ideally isostatic nature of the silica network, the presence of even a small concentration of defects can lead to a significant decrease in both the glass transition temperature and activation energy for viscous flow. To understand the impact of trace level dopants on the viscosity of silica, we measure the viscosity‐temperature curves for seven silica glass samples having different impurities, including four natural and three synthetic samples. Depending on the type of dopant, the glass transition temperature can vary by nearly 300 K. A common crossover is found for all viscosity curves around ~2200–2500 K, which we attribute to a change of the transport mechanism in the melt from being dominated by intrinsic defects at high temperature to dopant‐induced defects at low temperatures. [ABSTRACT FROM AUTHOR]

Hi Nicalon, Hi Nicalon S, Sylramic, and Sylramic iBN SiC fibers were exposed to ~60 μg/cm2 of Na2SO4 in a 0.1% SO2/O2 gaseous environment for times between 0.75 and 24 h at 1000°C. After exposure, the corrosion products were characterized using SEM, EDS, ICP‐OES, TEM, and EFTEM to determine their high‐temperature resistance to Na2SO4 and key reaction mechanisms. All SiC fiber types tested in this work exhibited little resistance to Na2SO4 deposit‐induced attack relative to their behavior in dry O2 environments. It was found that Hi‐Nicalon displayed the least resistance to Na2SO4 deposit‐induced attack due to excess carbon content resulting in the formation of a highly porous crystalline oxide and promotion of basic corrosion conditions. All fiber types formed a crystalline SiO2 reaction product, either cristobalite or tridymite. Sylramic and Sylramic iBN formed a crystalline SiO2 reaction layer containing TiO2 needles due oxidation of TiB2 particles. Additionally, Na2SO4 deposits resulted in pitting of all fiber surfaces. [ABSTRACT FROM AUTHOR]

Further attenuation of Rayleigh scattering of silica glass is required to extend the capacity of long‐distance optical fiber communication. To theoretically examine the effect of aluminum and fluorine co‐doping on the density fluctuations of silica glass, which is related to Rayleigh scattering, a set of force‐matching potentials (FMP) for simulating F‐doped aluminosilicates was developed using Bayesian optimization based on density functional theory calculations. Molecular dynamics (MD) simulations with the new FMP could evaluate the densities of silica glasses to which a small amount of fluorine was doped and those of aluminosilicate glasses with a wide range of aluminum contents within reasonable accuracy. The FMP successfully represents the changing role of aluminum from a network former without a compensating cation (threefold coordination) to that with a compensating cation and a charge compensator in the aluminosilicates. Indeed, relative concentrations of four, five, and sixfold‐coordinated aluminum observed by NMR measurements were reproduced better than the original Teter potential at a high aluminum content. At an aluminum content lower than 1 mol%, threefold‐coordinated aluminum was observed, which is consistent with ESR measurements. After careful validations of the FMP, the effect of the co‐doping of alumina and fluorine on the density fluctuations of silica glass was computationally examined. Consequently, it was expected that the co‐doping might not sufficiently attenuate the Rayleigh scattering, even though 1 wt% fluorine would be able to reduce the density fluctuations of aluminosilicate glasses for some extent. This is because more alumina‐doping increases density fluctuations of silica glass if the drawing temperature and procedure are the same with those for silica glass fiber. Thereby, a possible fabrication process to sufficiently attenuate the Rayleigh scattering of the F‐doped aluminosilicate glass was proposed, according to the density fluctuation analysis at high temperature. [ABSTRACT FROM AUTHOR]

We use low‐temperature heat capacity, low‐frequency Raman scattering, and THz time domain spectroscopy in order to scale the vibrational density of states and the Boson peak in SiO2‐Al2O3‐B2O3 Yb‐laser host glasses. When substituting B2O3 for SiO2 at constant Al2O3 dopant level, we find an optimal value for the ratio of B/Al in terms of mixture stability, at which the excess in the electron donor capability of Al2O3 (relative to the SiO2 backbone) is compensated by the more acidic B2O3. At this composition, Al2O3 plays a mediating role in the structure of aluminoborosilicate glasses, facilitating dissolution of Yb2O3 and admixture of B2O3 into the SiO2 network. [ABSTRACT FROM AUTHOR]

As one of the most abundant materials on Earth, silica has been widely studied in various crystal structures and glassy states. However, in terms of molecular structure and the corresponding mechanical properties between those of ordered and disordered states, partially ordered silica states are not well‐explored in the relevant literature owing to a low probability of appearance in experiments and simulations. The lack of this knowledge significantly hinders the understanding of the inherent mechanism of mechanical properties and limits the applications in many engineering fields. In this study, we present an exploration of the complex interdependent relations of the structural properties of silica over a wide range of free energy surfaces and establish a machine learning‐based prediction model via high‐throughput molecular dynamics simulations coupling with an enhanced sampling method. Each scale of structure information of samples with varying crystallinity is analyzed. First, descriptors of silica structures were identified and selected as inputs to a deep neural network (DNN). The results indicate that our DNN‐based approach can provide an accurate prediction of bulk modulus, shear modulus, and tensile strength of silica samples. Furthermore, the generalizability of the machine learning model is verified on the prediction tasks for much larger silica systems, as well as silica quenched at varying cooling rates. Overall, the enhanced sampling method can reliably accelerate the exploration of free energy surfaces and collection of training samples, and machine learning methods are effective in generating accurate and reliable predictions of mechanical properties of materials over the free energy surface. [ABSTRACT FROM AUTHOR]

Silica glass samples were given various heat treatments under stress at low temperatures and subsequently their residual stress distributions in terms of retardance were observed using a polarized light microscope, confirming previously reported fast surface stress relaxation while providing more detailed characterization. Retardance profiles of silica glass fibers heat‐treated under a constant bending strain in the presence of atmospheric water vapor were measured and fit to a previously developed diffusion‐based relaxation model. The retardance of a cross‐section of a silica glass rod heat‐treated at 650°C in lab air under applied torsional shear strain was also measured to confirm the presence of residual surface shear stress which was predicted by the decrease of torque with time for the rod. Together, these results confirm the low‐temperature fast surface stress relaxation which occurs when water vapor is present for both bending and shear stresses. [ABSTRACT FROM AUTHOR]

BN coated α‐SiC was exposed to ~2.5 mg/cm2 of Na2SO4 for 0.75‐144 hours between 700°C and 1100°C in a 0.1% SO2‐O2 gaseous environment. A combination of SEM, EDS, ICP‐OES, XRD, and optical profilometry was used to determine that BN induced a previously unobserved form of Na2SO4 deposit‐induced hot corrosion of SiC below the melting temperature of Na2SO4 (Tm = 884°C). Above the melting temperature of Na2SO4 BN did little to alter the hot corrosion behavior of SiC, due to B2O3 volatility. Substrate attack below the melting temperature of Na2SO4 was found to result in rivulet recession features, whereas deep, localized pitting occurred above the melting temperature of Na2SO4. Initially, the mixture of Na2SO4 and BN led to the formation of a Na2O‐ and B2O3‐containing liquid silicate and accelerated corrosion which after prolonged exposure, resulted in the partial crystallization into a lath‐like tridymite and cristobalite mixture. Prolonged exposure resulted in a flattening of SiC consumption rates after exposure for several hours at 1000°C and after several days at 800°C, resulting in decreased SiC oxidation/corrosion kinetics. [ABSTRACT FROM AUTHOR]

Nanostructured silicon carbide (SiC) is an exceptional material with numerous applications, for example, in catalysis, biomedicine, high‐performance composites, and sensing. In this study, a fast and scalable method of producing nanostructured SiC from plant materials by magnesiothermic reduction via self‐propagating high‐temperature synthesis (SHS) route was developed. The produced biogenic material possessed a high surface area above 200 m2/g with a SiC crystallite size below 10 nm, which has not been done previously by SHS. This method enables affordable synthesis of the material plant‐based precursors in a reaction that only takes a few seconds, thereby paving a way for nanostructured SiC production in high volumes using renewable resources. The material was also functionalized with carboxylic acid and bisphosphonate moieties, and its use as metal adsorbent in applications such as wastewater remediation was demonstrated. [ABSTRACT FROM AUTHOR]

Silica, sharing the same tetrahedral order and many structural, thermodynamic and dynamic anomalies with water, has been speculated to have a density increase upon melting similar to water. In this work, an increase in density upon melting cristobalite silica and a shallow density maximum followed by a density minimum during cooling of silica liquid are observed in classical molecular dynamics simulations. The density maximum gradually diminishes with the increase in alkali size/content in alkali silicate glasses. The structural origin of the anomalous density maximum in silica is revealed by detailed structural analysis. During the cooling process, a range of rings with different sizes form in liquid silica, with 6‐member rings being the most dominant, which cause the silica network to open up and compensate the regular volume shrinkage upon cooling. These two competing factors lead to a density maximum, but to a less extent than that observed in melting of cristobalite silica. With the increase in modifier size/content in the alkali silicate glasses, the connectivity of silica network gradually breaks down; the population of 6‐member rings decrease with the increase in smaller or larger rings, therefore the density maximum becomes less obvious and eventually disappears. [ABSTRACT FROM AUTHOR]

Understanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear‐induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF‐MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF‐MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Sisubstrate–O–Sicounter_surface bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water‐producing hydroxyl groups and their key role in the hydrolysis reaction is discussed. [ABSTRACT FROM AUTHOR]

Fused silica optics used in lasing systems requires a high laser‐induced damage resistance. Processes typically used to polish fused silica lenses induce subsurface and surface damage that collect ceria abrasive, creating a layer of contamination. The contamination can be a precursor to laser damage during use. A preliminary study showed the feasibility of magnetic field‐assisted finishing (MAF) for polishing fused silica and suggested possible beneficial effects of the MAF‐polished surface on the laser‐induced damage threshold (LIDT). This paper proposes a method to examine the fundamental polishing characteristics of MAF for fused silica. Using the proposed method, this paper explores the material removal characteristics of the MAF process and improves the understanding of the MAF polishing mechanism. The 45% improvement of LIDT shows the efficacy of MAF for removing the contamination layer of fused silica surfaces with minimal changes in the surface roughness. [ABSTRACT FROM AUTHOR]

The static fatigue limit, or the threshold stress intensity factor, Ko, for first subcritical crack growth has been measured directly in silica glass for T ≥ 600°C using the double cantilever beam (DCB) crack growth technique. Values measured ranged from 0.48 to 0.61 MPa·m1/2 for a temperature range of 600°C‐850°C, respectively. Cracks growing near the static fatigue limit had a time‐dependence, where the crack growth decreased and appeared to stop at K ≈ Ko. Slow crack growth curves (K‐v) have been measured from room temperature, 50% RH, up to 850°C with subcritical crack growth not measurable for T > 900°C. Increasing temperature was found to first increase, and then decrease the slope of Region I, and a peak in fatigue resistance was found around 150°C‐300°C. At T > 600°C subcritical crack growth was observed for K higher than previously measured KIC values. This observation and the static fatigue limit in silica are explained by a water‐assisted stress relaxation mechanism at the crack tip. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations show that the expansion of silica glass occurs by the presence of the hydroxyl (SiOH) groups present in the glass as opposed to intact water (H2O) molecules, providing an accurate molecular description of the experimentally observed volume changes in silica glass exposed to water. Using a robust and accurate reactive potential, the simulations show that the expansion is caused by the rupture of siloxane (Si–O–Si) linkages in the glass via reactions with water molecules, forming SiOHs. Such reactions remove smaller rings and form larger rings, with a decrease in the overall number of rings smaller than a prescribed large ring size in comparison to dry glasses. This change in ring structure overcomes the inherently stronger hydrogen bonding in the glasses containing SiOH in comparison to the glasses containing predominantly intact H2O molecules. This stronger H‐bonding of the SiOH also causes a shift to lower frequencies in the high‐frequency OH vibrational spectrum for the silanols, as shown in previous ab‐initio calculations. This introduces a question about assuming the lower frequency part of the high‐frequency peak is only due to intact H2O molecules. A slight decrease in volume occurred in the glasses containing the largest concentration of intact H2O molecules. There is no change in the ring size distribution between the H2O glasses and dry glasses. Rather, the slight decrease in volume in the H2O system is caused by a decrease in siloxane bond angles caused by the formation of H‐bonds between the H2O molecules and the glass O in the siloxane cages surrounding the H2O molecules. [ABSTRACT FROM AUTHOR]

SiOC/HfO2‐based ceramic nanocomposites with in situ formed HfO2 nanoparticles were prepared via a single‐source precursor (SSP) approach starting from a polymethylsilsesquioxane (PMS) modified by Hf‐ and Ti‐alkoxides. By varying the alkyl‐group of the employed Hf‐alkoxides, SiOC/HfO2‐based ceramic nanocomposites with different HfO2 polymorphs formed via thermal decomposition of the SSP under the same heat‐treatment conditions. Using PMS chemically modified by Hf(OnBu)4, tetragonal HfO2 phase was formed after the synthesis at 1100°C in Ar, whereas both, tetragonal and monoclinic HfO2 nanocrystals, were analyzed when replacing Hf(OnBu)4 by Hf(OiPr)4. After oxidation of the synthesized nanocomposites in air at 1500°C, a facile formation of oxidation‐resistant HfSiO4 (hafnon) phase occurred by the reaction of HfO2 nanocrystals with silica present in the SiOC nanocomposite matrix derived from Hf(OiPr)4‐modified SSPs. Moreover the amount of hafnon is dramatically increased by the additional modification of the polysiloxane with Ti‐alkoxides. In contrast, ceramic nanocomposites derived from Hf(OnBu)4‐modified SSPs, almost no HfSiO4 is detected after oxidation at 1500°C even though in the case of Ti‐alkoxide‐modified single‐source precursor. [ABSTRACT FROM AUTHOR]

Combining sol‐gel processing and laser sintering is a promising way for fabricating functional ceramic deposition with high dimensional resolution. In this work, crack‐free silica tracks on a silica substrate with a thickness from ~360 nm to ~950 nm, have been obtained by direct exposure to a CO2 laser beam. At a fixed scanning speed, the density and microstructures of the silica deposition can be precisely controlled by varying the laser output power. The porosity of the laser‐sintered silica tracks ranged from close to 0% to ~60%. When the thickness of the silica deposition exceeded the critical thickness (eg, ~2.2 µm before firing), cracks occurred in both laser‐sintered and furnace‐sintered samples. Cracks propagated along the edge of the laser‐sintered track, resulting in the crack‐free track. However, for the furnace heat‐treated counterpart, the cracks spread randomly. To understand the laser sintering effect, we established a finite element model (FEM) to calculate the temperature profile of the substrate during laser scanning, which agreed well with the one‐dimensional analytical model. The FEM model confirmed that laser sintering was the main thermal effect and the calculated temperature profile can be used to predict the microstructure of the laser‐sintered tracks. Combining these results, we were able to fabricate, predesigned patterned (Clemson tiger paw) silica films with high density using a galvo scanner. [ABSTRACT FROM AUTHOR]

The decomposition of sulfur trioxide to produce sulfur dioxide and oxygen using a catalytic membrane reactor is technology that promises to improve the economic viability of the thermochemical water‐splitting Iodine‐Sulfur (IS) process for large‐scale CO2‐free hydrogen production. The chemical stability of membrane materials under SO3, however, is a significant challenge for this strategy. In this study, microporous membranes with a layered structure that consisted of a membrane support prepared from α‐Al2O3, an intermediate layer prepared from silica‐zirconia, and a top layer prepared from bis (triethoxysilyl)ethane‐derived organosilica sols, were examined for stability under SO3 and for use in SO3/O2 separation. An α‐Al2O3 support that features SiO2–ZrO2 intermediate layers with large pore sizes and a high Si/Zr molar ratio showed excellent resistance to SO3, which was confirmed by N2 adsorption, Energy Dispersive X‐ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). These membranes also demonstrated a negligible change in gas permeance before and after SO3 exposure. Subsequently, in binary‐component gas separation at 550°C, microporous organosilica‐derived membranes achieved an O2/SO3 selectivity of 10 (much higher than the Knudsen selectivity of 1.6) while maintaining a high O2 permeance of 2.5 × 10−8 mol m–2 s–1 Pa–1. [ABSTRACT FROM AUTHOR]

The present work explores the preparation of fayalite α‐Fe2SiO4, the iron‐rich end‐member of the olivine solid‐solution series, as a tar removal catalyst for biomass gasification. The synthetic procedure was developed starting from the stoichiometric mixture of hematite and micrometer size silicon carbide and employing thermal treatments in controlled atmospheres at 1000‐1100°C supported by thermodynamic modeling to assess the required redox conditions. The treatments in dry and humidified inert gas yielded phase mixtures containing metallic Fe as one of the main phases, thus emphasizing a shortage of oxygen supply. XRD and TGA studies of precursor mixtures on heating in dry CO2 demonstrated a multistep mechanism of the overall reaction including (a) fast reactivity between silicon carbide and hematite at ~920°C with formation of metallic Fe and amorphous silica followed by (b) formation of fayalite involving oxygen supplied in the form of CO2 and competing with (c) over‐oxidation to thermodynamically favorable Fe3O4+SiO2 mixture. Comparative studies of reactivity in powdered and pelletized samples emphasized the importance of the kinetic factor in the formation of Fe2SiO4 while preventing further oxidation. The preferential formation of fayalite in the CO2 atmosphere is shown to be favored by shorter treatments of compacted samples at higher temperatures. The procedure was designed (2‐step heating to 1100°C in CO2 followed by fast cooling) for the preparation of pelletized fayalite α‐Fe2SiO4 catalyst with only minor traces of surface over‐oxidation which can be suppressed by adding 10 vol.% of forming gas to CO2 flow. [ABSTRACT FROM AUTHOR]

This paper evaluated mechanical and thermal stability of alkali‐activated materials obtained from metakaolin and alternative silica sources, such as rice husk ash (RHA) and silica fume (SF), and were reinforced with recycled ceramic particles (RP) obtained by grinding bricks. Specimens were produced, and after 7 days of curing, they were exposed to temperatures between 300 and 1200°C to determine the influence that different percentages of RP had on the mechanical behavior and microstructure of the produced composites. The results showed a reduction in the linear contraction by 10.22% with 20 wt% RP and that the reinforcing materials improved the mechanical performance of the geopolymers after exposure to high temperatures; the compressive strengths reached 137.7 (±11.4)  MPa after being exposed to 1200°C for the matrix based on RHA and 180.6 (±19.15) MPa after being reinforced with 20 wt% RP. The improvement was mainly due to densification and the formation of crystalline products such as leucite, kalsilite, and mullite. [ABSTRACT FROM AUTHOR]

Coloration of amorphous silica powder containing titania was investigated by nitridation in an ammonia flow. The oxide precursors were obtained by the hydrolysis of a mixture of tetraethyl orthosilicate (TEOS) and tetrabutoxy titanium (TBT). The color changed with the amount of TBT in the mixture, the hydrolysis pH and the ammonolysis temperature. The original white color of the 8 mol% TBT powder hydrolyzed under basic pH conditions changed to pale goldenrod at 700°C, then to dark olive green at 800°C, and further darkened with increasing ammonolysis temperature. A steel‐blue color appeared at 900°C for the powder obtained with 3 mol% TBT, and increased in darkness at 1000°C. A similar bluish color was observed for powders obtained by acidic hydrolysis after ammonolysis above 900°C, and this was independent of the amount of titania, although the chroma decreased with increasing firing temperature for the powder with 3 mol% TBT. The ammonolysis powder products were characterized using X‐ray diffraction (XRD), electron probe micro analysis (EPMA), transmission electron microscopy‐electron energy‐loss spectroscopy (TEM‐EELS), scanning transmission electron microscopy‐high‐angle annular dark‐field imaging (STEM‐HAADF) and Ti–K edge X‐ray absorption fine structure (XAFS). The color change was related to both precipitated TiN nanocrystals and residual titanium in the amorphous silica matrix. The TiN exhibited a goldish reflection and also plasmonic absorption from light blue to gray depending on the TiN crystallite size. The plasmonic absorption and resonance of nanocrystalline TiN will be useful similarly to that of gold in nanotechnology for various kinds of energy application. Ammonolysis changes the white color of amorphous titania‐silica to greenish brown to bluish color depending the preparation condition. [ABSTRACT FROM AUTHOR]

Abstract: The fictive temperature of glass is a consequence of its thermal history (cooling rate, primarily) and has a direct effect on physical and chemical properties of the glass. But, it is not easy to measure. The ability to nondestructively and spectroscopically measure it at room temperature would be of great benefit. Although empirical correlations have been established between fictive temperature and selected absorption peaks in the infrared spectra of silica glass, the fundamental understanding for this correlation has not been reported. Here, we use molecular dynamics simulations to show that the blue shift in the Si–O–Si asymmetric stretching peak of pure silica glass, which is known to correlate with a decrease in fictive temperature, can be attributed to a decrease in the average length of the Si–O bond in the silica network, not changes in the density or the Si–O–Si bond angle. The decrease in density at higher fictive temperatures of silica is associated with a decreased population of 5‐ and 6‐membered rings and broadening of the ring‐size distribution, and an increase in the average Si–O–Si bond angle. [ABSTRACT FROM AUTHOR]

Abstract: In this work, silica powders and transparent glass‐ceramic materials containing LaF3:Eu3+ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu3+‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λem = 611 nm) and emission (PL: λexc = 393 nm, λexc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f6‐4f6 transitions originated from Eu3+ optically active ions (5D0 → 7FJ, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu3+ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ1(5D0) = 2.07 ms, τ2(5D0) = 8.07 ms and τ1(5D0) = 0.79 ms, τ2(5D0) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu3+ ions from amorphous silica framework to low phonon energy LaF3 nanocrystal phase. [ABSTRACT FROM AUTHOR]

Abstract: In order to increase the oxidation resistance of carbon/carbon (C/C) composites at long‐term high temperature, C/C‐Ultra High Temperature Ceramics composites (UHTCs) with a dual‐layer UHTCs oxidation coating was successfully designed and fabricated. The microstructure and ablation resistance were investigated and discussed. After ablation in arc‐heated wind tunnel with temperature being 2200°C for 1000s, the mass ablation rate and linear ablation rate were −1.9 × 10−2 mg/cm2s and 2.9 × 10−5 mm/s, respectively. The formation of thermodynamically compatible oxide scale including ZrO2 skeleton and SiO2 or Zr–Si–O glass on the surface were mainly contributed to the excellent ablation resistance of the composite. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports a novel fluorinated micro‐nano hierarchical Pd‐decorated SiO2 structure (hereafter called Pd/SiO2), which was formed by the deposition of Pd nanoparticles (NPs) on SiO2 microspheres. The SiO2 layers with microscale roughness were fabricated by electrospraying a solution prepared using the sol‐gel process. Subsequently, the Pd NPs were deposited using an ultraviolet reduction process. The resulting surfaces exhibited a micro‐nano hierarchical morphology. After fluorination, the micro‐nano hierarchical surface exhibited outstanding water repellency with a water contact angle (WCA) of 170° and a sliding angle <5°, indicating excellent superhydrophobic properties. The layers exhibited good long‐term durability and excellent ultraviolet resistance. Interestingly, the surface was oleophilic (CA of oil ~10°). These results show the potential of employing superhydrophobic fluorinated Pd/SiO2 layers in smart devices, such as self‐cleanable surfaces and intelligent water/oil separation systems. [ABSTRACT FROM AUTHOR]

Abstract: This study employed thermal poling at 200°C as a means to modify the surface mechanical properties of soda lime silica (SLS) glass. SLS float glass panels were allowed to react with molecules constituting ambient air (H2O, O2, N2) while sodium ions were depleted from the surface region through diffusion into the bulk under an anodic potential. A sample poled in inert gas (Ar) was used for comparison. Systematic analyses of the chemical composition, thickness, silicate network, trapped molecular species, and hydrous species in the sodium‐depleted layers revealed correlations between subsurface structural changes and mechanical properties such as hardness, elastic modulus, and fracture toughness. A silica‐like structure was created in the inert gas environment through restructuring of Si–O–Si bonds at 200°C in the Na‐depleted zone; this occurred far below Tg. This silica‐like surface also showed enhancement of hardness comparable to that of pure silica glass. The anodic thermal poling condition was found so reactive that O2 and N2 species can be incorporated into the glass, which also alters the glass structure and mechanical properties. In the case of the anodic surfaces prepared in a humid environment, the glass showed an improved resistance against crack formation, which implies that abundant hydrous species incorporated during thermal poling could be beneficial to improve the toughness. [ABSTRACT FROM AUTHOR]

Abstract: Silica sol is one of the frequently used binders in high‐temperature resisting fibrous porous ceramics, but in the drying process, it can diffuse with water and influence the uniformity of ceramics. To solve this diffusion problem and fabricate homogeneous fibrous porous ceramics, cationic starch was firstly introduced in mullite fibrous system. The effects of starch content and high‐temperature binder content on microstructure, physical, and mechanical properties were also investigated. The results indicate that starch consolidated mullite fibrous ceramics owned a homogeneous 3D skeleton structure, since the introduced starch can absorb both water and silica particles by gelatinization and ensure the even distribution of binders. Compared with the mullite fibrous ceramics fabricated without starch addition, starch consolidated ceramics owned better microstructure and higher interior compression strength. Furthermore, both the starch and silica sol content had great impact on the microstructure, density, porosity, thermal conductivity, and compressive strength of the fibrous ceramic. [ABSTRACT FROM AUTHOR]

Abstract: Multicomponent epoxy micro/nano‐composites containing micro‐alumina, micro‐quartz, and nano‐silica were fabricated to develop electrical insulation materials with high thermal conductivity. Simply changing the ratio between the alumina and quartz microparticles caused a trade‐off relationship between the thermal conductivity and electrical insulation. Increasing the alumina content in the epoxy‐alumina/quartz micro‐composites enhanced the thermal conductivity but deteriorated the dielectric strength. An increase in the thermal conductivity without incurring a loss in the dielectric strength was achieved by incorporating silica nanoparticles in the epoxy micro‐composites. Adding silica nanoparticles to the epoxy micro‐composites was found to be more efficient in improving the thermal conductivity compared to increasing the alumina ratio, especially at low alumina/quartz ratios. This behavior corresponded to theoretical models. Therefore, we provide a useful insight, both practical and theoretical, into the more advanced optimization of designing multicomponent epoxy composites for electrical insulation with high thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Interdiffusion processes between aluminum enriched PVD‐sputtered silica thin films and industrial float soda‐lime silicate glass substrates are quantitatively studied using SIMS analysis. Heat treatments are performed at temperatures close or above the glass transition temperature of the float glass. Aluminum doping of the film is shown to strongly increase the migration of alkali from the glass substrate to the silica thin film. In particular the final alkali content in the film exhibits a linear scaling with the aluminum concentration. An interdiffusion process is evidenced between bulk alkali ions and protons originating from a significant water content in the as‐deposited silica film. Experimental measurements of sodium concentration are shown to be consistent with a simple thermodynamic model based on the equilibration of the activity of sodium between the film and the glass substrate. [ABSTRACT FROM AUTHOR]

Abstract: Mechanistic insight into the process of crack growth can be obtained through molecular dynamics (MD) simulations. In this investigation of fracture propagation, a slit crack was introduced into an atomistic amorphous silica model and mode I stress was applied through far‐field loading until the crack propagates. Atomic displacements and forces and an Irving–Kirkwood method with a Lagrangian kernel estimator were used to calculate the J‐integral of classical fracture mechanics around the crack tip. The resulting fracture toughness (KIC), 0.76 ± 0.16 MPa√m, agrees with experimental values. In addition, the stress fields and dissipation energies around the slit crack indicate the development of an inelastic region ~30Å in diameter. This is one of the first reports of KIC values obtained from up‐scaled atomic‐level energies and stresses through the J‐integral. The application of the ReaxFF classical MD force field in this study provides the basis for future research into crack growth in multicomponent oxides in a variety of environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: A coupled key phase diagram study and critical evaluation and optimization of all available experimental data of the Li2O–MgO–SiO2 system was performed to obtain a set of Gibbs energy functions to reproduce all the reliable phase equilibria and thermodynamic data. Differential scanning calorimetry measurements and equilibration/quenching experiments were performed in the Li2SiO3–MgO and Li4SiO4–Mg2SiO4 sections, respectively, using sealed Pt capsules to prevent the volatile loss of Li. According to the present experimental results, Li2MgSiO4 is the only compound present in the Li4SiO4–Mg2SiO4 isopleth, which shows a peritectic melting at 1465 ± 6°C (1738 ± 6 K). The Modified Quasichemical Model, which considers short‐range ordering in the melt, was employed to describe the thermodynamic properties of the liquid phase. The Li4SiO4–Li2MgSiO4 and Mg2SiO4‐rich solid solutions were modeled using the Compound Energy Formalism. [ABSTRACT FROM AUTHOR]

Here we study the diffusive transfer of water into silica glass in the presence of externally applied stresses, and stresses caused by water induced swelling of the glass. By considering the simultaneous action of water penetration into the surface of silica glass and the development of swelling stresses in the water-penetrated zone, several experimental findings previously published in the literature can be interpreted quantitatively. These include an apparent decrease of the diffusivity with time, an increase of water solubility in the surface region under compressive loading, the opposite effect under tensile loading and a reversal of these two effects deeper within the glass. These expectations are fully met in published experiments carried out to date. [ABSTRACT FROM AUTHOR]

In the IR spectra of the silica and silicate glasses, the shifts of the maximum intensity position of the νSi-O-Si,as band upon heating or applying mechanical stress could be attributed to changes in the distribution of bond parameters such as bond length and bond angle. Upon heating, isotropic expansion occurs and the density changes; upon applying mechanical stress, anisotropic strain is induced and a significant change in the Si-O-Si bond angle is observed. From molecular dynamics simulations of a silica glass, we show that the peak position shift correlates better with the asymmetric change in the Si-O bond length distribution, rather than the Si-O-Si bridge angle, the O-Si-O tetrahedral angle, or the density change. This new finding provides an insight into how and why the νSi-O-Si,as IR peak of soda lime silica ( SLS) glass shifts upon chemical strengthening via ion exchange and thermal tempering. [ABSTRACT FROM AUTHOR]