Surface Sintering of Porous Glass Plates under Laser Radiation

The kinetics of surface sintering of flat plates of the 96SiO₂ · 3.8B₂O₃ · 0.2Na₂O (mol %) porous glass exposed to CO₂ laser radiation is investigated under conditions when either the irradiation time is varied at a constant radiation power density or the radiation power density is varied at a constant irradiation time. It is established that the irradiation time is the most appropriate controlled parameter in the process of sintering. A decrease in the thickness of the porous layer sintered on the plate surface is accompanied by an increase in the radii of curvature of the interfaces of this layer.     

Organization of silver nanoclusters in porous glass bulk by laser irradiation

The structure modification in the bulk of plates of photochromic porous glass (PCPG) containing 0.28 wt % Ag₂O under the action of laser irradiation of a near IR-range with a power density of 0.6–1.9 MW/cm² and irradiation duration of 5–20 s is carried out. Locally modified structure regions are composed of the central and edge parts with a different content of silver nanoclusters and different density of the porous matrix. It is found that the size of the modified regions is much larger than the size of the focused laser beam, which can be associated with the thermophysical peculiarities of the material and the conditions of its laser-induced heating. The dynamics of the variation in the size of the modified region and its parts depending on the duration of the irradiation are studied.     

Spectral properties of Er<Superscript>3+</Superscript> in alkali-zinc-tellurite,barium-tellurite-molybdate,and fluoride glasses

Glasses of three compositions—TeO₂ · ZnO · N₂O (TZN), where N is Li, Na, or K; TeO₂ · MoO₃ · BaO (TMB); and ZrF₄ · BaF₂ · LaF₃ · AlF₃ · NaF (ZBLAN)—activated by Er³⁺ or Yb³⁺ and Er³⁺ ions were synthesized and investigated. For the ZBLAN glass, the brightest luminescence of Er³⁺ ions in the visible range was observed under excitation by the irradiation of a diode laser with the generation wavelength 0.98 μm. The TZN glass is not inferior in the intensity of luminescence with the wavelength 1.55 μm to the TMB glass, having phonons of higher energy than those for the TZN glass (940 and 740 cm⁻¹, respectively). A glass was prepared with a high content of molybdenum oxide. The possibility to increase the up-conversion efficiency in tellurite glasses is considered.     

Reduction of crystallization ability of sodium zinc phosphate glass under X-ray radiation

The effect of X-ray radiation on the crystallization ability of maximally homogenized sodium zinc phosphate glass with a minimal light scattering value of V _v = 4 × 10^?6 cm^?1 has been investigated. The crystallization kinetics of the sodium zinc phosphate glass of the 33.9P₂O₅ · 56.6ZnO · 9.5Na₂O (mol % from analysis) composition under the conditions of homogeneous nucleation and X-ray radiation have been studied. It has been demonstrated that the crystallization properties of phosphate glasses are more sensitive to the synthesis method than those of silicate glasses. It has been established that sodium zinc phosphate glass crystals represent the main crystalline phase precipitated in the glass of the above composition. The main parameters of nucleation have been determined in glass without preliminary radiation, including stationary nucleation rate I _st, nonstationary nucleation time ??, and nucleation activation energy E _??. It have been found that the effect of the CuK _?? X-ray radiation leads to the slowing down or even cessation of the nucleation of crystals in glass (the result depends on the change in the radiation intensity along the sample depth) in the case when radiation takes place immediately during the nucleation thermal treatment of the sample in a high-temperature chamber of the X-ray device. The kinetics of sodium zinc phosphate crystallization in the samples upon their pretreatment by CuK _?? X-ray irradiation has been investigated. It has been shown that the rate of crystal nucleation in glasses exposed to X-ray radiation is lower than that in glasses without preliminary irradiation.     

Understanding the change in electrical resistance of TiO2 thin film irradiated with YVO4 third-harmonic generation pulse laser

To selectively control the electrical resistance, thin films of TiO₂ were irradiated with a YVO₄ third-harmonic generation pulse laser in various power conditions. It was observed that when the laser power was less than 0.26 W, the electrical resistance of thin films decreased with the increase in laser power, whereas when the laser power was more than 0.26 W, the electrical resistance increased as the laser power increases. The minimum electrical resistance of the irradiated thin film was found to be four orders of magnitude lower than that of the unirradiated thin film. X-ray absorption fine structure analysis revealed that the valence of Ti ions in the thin films was reduced after laser irradiation, indicating the formation of oxygen vacancies with electron doping. The cross-sectional observation by a scanning electron microscope revealed that high laser power irradiation caused the thin films to become porous, and the percolation theory explains the origin of the increase in electrical resistance with developing porous structure. We propose a phase diagram to completely explain the relationship between electrical resistance and laser power, which supply a guideline on laser modification in TiO₂ electrical resistance.     

Hydrogen Permeation Properties and Hydrothermal Stability of Sol–Gel‐Derived Amorphous Silica Membranes Fabricated at High Temperatures

The sol–gel method was applied to the fabrication of amorphous silica membranes for use in hydrogen separation at high temperatures. The effects of fabrication temperature on the hydrogen permeation properties and the hydrothermal stability of amorphous silica membranes were evaluated. A thin continuous silica separation layer (thickness = <300 nm) was successfully formed on the top of a deposited colloidal silica layer in a porous glass support. After heat treatment at 800°C for an amorphous silica membrane fabricated at 550°C, however, it was quite difficult to distinguish the active separation layer from the deposited colloidal silica layer in a porous glass support, due to the adhesion of colloidal silica caused by sintering at high temperatures. The amorphous silica membranes fabricated at 700°C were relatively stable under steam atmosphere (500°C, steam = 70 kPa), and showed steady He and H₂ permeance values of 4.0 × 10^?7 and 1.0 × 10^?7 mol·m^?2·s^?1·Pa^?1 with H₂/CH₄ and H₂/H₂O permeance ratios of ~110 and 22, respectively. The permeance ratios of H₂/H₂O for membranes fired at 700°C increased drastically over the range of He/H₂ permeance ratios by factors of ~3–4, and showed a value of ~30, which was higher than those fired at 500°C. Less permeation of water vapor through amorphous silica membranes fabricated at high temperatures can be ascribed to the dense amorphous silica structure caused by the condensation reaction of silanol groups.     

Heating of Energetic Materials by Continuous-Wave Near-IR Laser Radiation

The heating of energetic materials by the radiation of fiber-coupled continuously-pumped lasers at near IR-wavelengths of 0.98, 1.56, and 1.94 μm was studied. Samples of pressed secondary explosives and loose gunpowder were used. The length of the linear portion of the temperature rise and the rate of its rise immediately after exposure to laser radiation were measured. It was established that the rate of temperature rise at the initial time was proportional to the laser radiation power aP. For a 600 μm diameter of the laser beam emerging from the fiber, the coefficient of proportionality a for secondary explosives was 6–250 K/(s · W) at a wavelength of 0.98 μm and 40–2000 K/(s · W) at wavelengths of 1.56 and 1.94 μm. For gunpowder, a = 7000–15 000 K/(s · W), which is an order of magnitude or more higher than that for most of the secondary explosives we studied. The possibility of increasing the efficiency of laser heating of secondary explosives by applying an absorbing thin film on the surface of the samples was studied. The heating dynamics and the initial stage of ignition of energetic materials by laser radiation were investigated.     

Fabrication of fluorocarbon terminated DLC thin film using soft X-ray

The control of wettability on a diamond-like carbon (DLC) thin film was carried out by exposing the film to synchrotron radiation (SR) ranging 50–1000 e V under perfluorohexane (C₆F₁₄) gas atmosphere. The contact angle of the DLC surface with a water droplet was found to increase from 73° to 114° by the SR irradiation under C₆F₁₄ gas atmosphere. The chemical components variations of the DLC surface were studied using X-ray photoelectron spectroscopy and the modified DLC film with F was studied using near-edge X-ray absorption fine structure spectroscopy. By mounting the new sample holder for the parallel SR irradiation, we succeeded in preventing secondary reaction of deposited material and controlling the contact angle of the fluorocarbon modified DLC surface.     

New BST–silica suspension coating material for dielectric thin films fabricated at low temperatures

Abstract

A new Ba_0·7Sr_0·3TiO₃ (BST)–silica suspension has been developed as a coating material for dielectric thin films. Using a spin on glass (SOG) wet process, a thin layer consisting of nanoparticles of BST and silica was formed on an Al/SiO₂/Si wafer. The BST–silica suspension was made by mixing a BST nanoparticle dispersion with methyl siloxane oligomer. A silicon wafer was coated with the BST–silica suspension using a spin coater and heat treated. The sample was then coated with methyl siloxane oligomer and heat treated again, and finally, a top electrode was applied. The Al/SiO₂/BST–SiO₂/Al/SiO₂/Si stack thus prepared is a metal insulator metal (MIM) capacitor. The electrical properties of the MIM capacitor were evaluated and its capacitance, dissipation factor and voltage coefficient of capacitance were determined to be 1054 pF mm^?2, <0·1 and <100 ppm V^?1 respectively.     

Synthesis and characterisation of porous luminescent glass ceramic scaffolds containing europium for bone tissue engineering

Eu₂O₃ was added to bioactive glass ceramic in the system CaO–SiO₂–P₂O₅–MgO–CaF₂ to prepare porous luminescent scaffold with high mechanical property. The crystal structure, compressive strength, in vitro bioactivity, cell affinity and luminescent property under ultraviolet of samples was evaluated. According to results, Eu₂O₃ improved the crystallisation behaviour but inhibited fluorapatite formation in the glass ceramics. Although scaffolds had connective porous structure, the compressive strength could be improved to as high as 3·6 MPa with the addition of Eu₂O₃. The in vitro bioactivity test showed a decrease in Ca release ability and a retardation of apatite forming on the samples with increasing substitution of Eu₂O₃ for CaO. The 3-(4,5-dimethylthiazol-2-yl)-2,5-dipheyltetrazolium bromide assay and SEM observation results displayed that ROS17/2·8 cells could attach and differentiate on all the scaffolds. Moreover, the Eu₂O₃ doped scaffolds fluoresced well a red colour under ultraviolet, and a decrease in the emission intensities could be observed after the cell coculturing process.     

MnO2 Thin Film Electrodes for Enhanced Reliability of Thin Glass Capacitors

Many dielectric thin films for energy storage capacitors fail by thermal breakdown events under high‐field drive conditions. The lifetime of the device can be improved under conditions where the current path within the defect regions in dielectrics is eliminated. Self‐healing electrodes were developed by depositing a manganese dioxide (MnO₂) thin film between the glass substrate and an aluminum film. For this purpose, thin films of MnO₂ on boroaluminosilicate glass were fabricated via chemical solution deposition and heat‐treated at temperatures in the range 500°C–900°C. The α‐MnO₂ structure was stabilized by Ba²⁺ insertion to form the hollandite structure. The phase transition temperature of α‐MnO₂ to Mn₂O₃ is strongly dependent on the Ba concentration, with transition temperatures of 600°C and 675°C with Ba concentrations of [Ba]/[Mn] = 0.04 and 0.1, respectively. The electrical resistivity increased from 4.5 Ω·cm for MnO₂ to 10⁵ Ω·cm for Mn₂O₃. Both dielectric breakdown strength and the associated cleared aluminum electrode area increased with an MnO₂ interlayer between Al electrodes and the borosilicate glass. The enhancement in dielectric strength was related with self‐healing. The associated redox reaction between MnO₂ and Mn₂O₃ was also proved by RAMAN spectroscopy following dielectric breakdown.     

Study on porous silk fibroin materials. I. Fine structure of freeze dried silk fibroin

Silk fibroin solution was prepared by dissolving the silk fibroin in triad solvent CaCl₂ · CH₃CH₂OH · H₂O. In this article we tested and analyzed the state of frozen silk fibroin solution and fine structure of freeze dried porous silk fibroin materials. The results indicated that the glass transition temperature of frozen silk fibroin solution ranges from −34 to −20°C, and the initial melting temperature of ice in frozen solution is about −8.5°C. When porous silk fibroin materials are prepared by means of freeze drying, if freezing temperature is below −20°C, the structure of silk fibroin is mainly amorphous with a little silk II crystal structure, and if freezing temperature is above −20°C, quite a lot of silk I crystal structure forms. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2185–2191, 2001     

Antibacterial and photocatalytic active transparent TiO2 crystallized CaO–BaO–B2O3–Al2O3–TiO2–ZnO glass nanocomposites

Transparent TiO₂ crystallized 5CaO–10BaO–65B₂O₃–Al₂O₃–20TiO₂–10ZnO (CBBATZ) glass nanocomposites were fabricated using melt-quenching technique followed by specific heat treatments. As-quenched glass samples were provided three different heat treatments at 630°C for 3, 5, and 10 hours in order to obtain different amounts of TiO₂ nanocrystals in the glass. The presence of rutile phase of TiO₂ nanocrystals in glass was confirmed by X-ray diffraction. The glass nanocomposite heat treated for 10 hours showed a hydrophobic nature with contact angle of 90.90°. Contact angle decreased from 90.90 to 22.20°, when irradiated under ultraviolet (UV) radiation for 45 minutes. This photoinduced hydrophilicity showed a photocatalytic and self-cleaning properties of glass nanocomposite. During photocatalytic ink test, the maximum change in color of Resurin (Rz) ink and 60% degradation in absorbance of ink within 150 minutes under UV radiation were found for glass nanocomposite heat treated at 10 hours. Also, 78% degradation in absorbance of methylene blue dye (pollutant) within 180 minutes under UV irradiation was found for glass naocomposite heat-treated at 10 hours. Antibacterial performance of transparent glass nanocomposite against Escherichia coli was evaluated as well. More than 95% of the bacterial cells were degraded with glass nanocomposite heat-treated at 10 hours. CBBATZ glass nanocomposite found to impart the antibacterial effect through generation of reactive oxygen species (ROS) in aqueous medium. ROS species which was confirmed in the bacterial cell through intracellular ROS generation kit. During evaluation of mechanical properties using nanoindentation technique, the values of hardness and reduced modulus increased by ~26% and 10%, respectively, for glass nanocomposite heat-treated at 10 hours as compared to as-quenched glass.     

Sol-gel synthesis of photostructured gold-containing lithium silicate glasses

A sol-gel method has been proposed for preparing the batch used in the synthesis of a photostructured gold-containing glass of the composition 33.56Li₂O · 66.5SiO₂. It has been found that the main crystalline phase in the glass of this composition is lithium disilicate Li₂O · 2SiO₂. The temperature-time dependences of the nucleation rate of lithium disilicate crystals with a gold impurity have been investigated under conditions of X-ray irradiation of the initial glass and without irradiation. It has been shown that, in the absence of X-ray irradiation, the gold impurities do not affect the nucleation of lithium disilicate crystals. It has been established that the use of the sol-gel method for the preparation of the batch for synthesizing photostructured gold-containing glasses leads to a more uniform spatial distribution of gold microimpurities in the bulk of the glass.     

Vacuum-Deposited Thin Film of Aniline–Formaldehyde Condensate/WO3·nH2O Nanocomposite for NO2 Gas Sensor

A hydrated tungsten oxide (WO₃·nH₂O)-embedded aniline–formaldehyde condensate (AFC/WO₃·nH₂O) nanocomposite thin film was prepared on an indium tin oxide (ITO)-coated glass surface via vacuum-deposition technique. The resulting AFC/WO₃·nH₂O/ITO thin film was characterized using ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and electron microscopy (SEM). The composite thin film exhibited a crystalline surface morphology containing nanocrystals of WO₃·nH₂O with a diameter ranging from 15 to 20 nm. The AFC/WO₃·nH₂O/ITO film allowed for the low potential detection of NO₂ gas at a concentration range from 0 to 9000 ppm. The NO₂ gas sensing characteristics were studied by measuring the change in the current with respect to concentration and time. The current of the AFC/WO₃·nH₂O/ITO film linearly increased with an increase in concentration of NO₂ gas with a response of ~20 s.     

Formation of closed pore structure in CaO-MgO-Al2O3-SiO2 (CMAS) porous glass-ceramics via Fe2O3 modified foaming for thermal insulation

Due to the low density, low thermal conductivity and low water absorption, porous glass-ceramics have demonstrated excellent performance for thermal insulation. Closed pore structure can greatly reduce the thermal conductivity and convection as well as achieve high mechanical strength. However, yet it is difficult to realize closed pore structure due to the critical preparation condition. Here we use Fe₂O₃, which is the by-product of copper tailings, to optimize the pores structures of the porous glass-ceramics and facilitate the formation of uniform closed pore structure. The porous glass-ceramics were prepared by melting-quenching method, followed by sufficiently foaming through powder sintering route with SiC powders as foaming agent. The foaming process, micro structure, pore structure and thermal insulation performance were directly observed by heating microscope, scanning electron microscope (SEM), X-ray computed tomography and infrared thermal imager. The results show that the addition of Fe₂O₃ modified the depolymerization degree of the glass network and increased the numbers of non-bridged oxygen, decreasing the foaming temperature. The resultant closed pore structure showed a better thermal insulating performance than open pore structure. Accordingly, we achieved a low thermal conductivity of 0.19 W·m^?1·K^?1 with the highest specific strength of 19.55 MPa·g^?1·cm^?3 based on closed pore structure.     

Laser-Induced Formation of Molecular Barriers in Porous Glass

The possibility of creating physical barriers with various degrees of permeability in porous glass (PG) plates by local variation in the density of the porous structure of the matrix is demonstrated. The compaction of PG in the volume is provided by exposure to femtosecond laser pulses, while the surface impermeability of the compaction areas is provided by exposure to radiation of the CO₂ laser. This approach to control the density of the PG structure makes it possible to create molecular barriers that represent a physical and/or chemical boundary for molecules located in a porous matrix (with controlled permeability). The discussed technology of the local porosity control opens the way to designing integral photon, fluid, and other types of devices based on PG plates.     

Time of hot-spot formation in shock compression of microballoons in a condensed medium

The optical thermal radiation arising from the shock collapse of glass or polymer microballoons in a transparent condensed medium (water or polymerized epoxy resin) was detected. The temporal characteristics of the detected radiation in the pressure range 0.5–29 GPa at different viscosities of the material surrounding the pore were determined. The brightness temperature of hot spots was estimated to be 1600–3200 K at a pressure of 2–29 GPa. The length of the leading edge of the radiation pulse corresponding to the time of hot-spot formation increases from 2 · 10^?8 to 30 · 10^?8 s, depending on the shock-wave intensity and the viscosity of the material surrounding the pore. Analysis of the data shows that in the pressure range 5–29 GPa, hot-spot formation is dominated by the hydrodynamic mechanism of collapse and in the range 0.5–5 GPa, by the viscoplastic mechanism.     

Energy aggregation properties of TiO2-silica composite aerogel under ultra-high-energy (7 kW·cm-2) continuous-wave laser irradiation

TiO₂, a light-shielding agent for silica aerogels, is widely used in optical limiting and photocatalysis, but its application in high-energy lasers is extremely limited. We added TiO₂ to silica aerogel in three different ways to get the best resistance to high energy laser. Through microstructure analysis and high energy laser irradiation test results, it is concluded that direct deposition of TiO₂ nanoparticles can achieve the best laser resistance synergistic effect with silica aerogel. A thermal barrier temperature difference of 1275 °C was generated with a material thickness of 7.5 mm. Comparing the microscopic pore structure before and after high-energy laser irradiation, it was observed that the phase transition destruction of the TiO₂–silica composite aerogel was completely different from that of pure silica aerogel. The TiO₂–silica composite aerogel showed no signs of breakdown within 2 min of continuous-wave (CW) laser irradiation with power of 7 kW·cm^-2. By changing the amount of TiO₂ added, we also obtained the general trend of this synergistic effect, extended the mathematical model “maximum energy transfer radius (METR)”, and advanced the application of this material in the field of high energy laser protection.     

Non-isothermal crystallisation behaviour of fluorophlogopite/nepheline glass ceramics

Abstract

Fluorophlogopite/nepheline glass ceramics were formed from the system of SiO₂–Al₂O₃–MgO–K₂O–Na₂O–F, and the thermodynamic, crystallisation behaviour and microstructure were investigated using differential thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that fluorophlogopite crystals and nepheline crystals crystallised simultaneously, and bulk nucleation was the main crystallisation mechanism. Crystal growth was prone to follow the two-dimensional direction and controlled by diffusion. Activation energy for glass transition was 797·43 kJ mol^?1, and crystallisation activation energy was 433·16 kJ mol^?1.