Multicomponent Optical Glasses with High Refractive Index

Glass and Ceramics - The effect of the modifying oxides Nb2O5, BaO, Ga2O3, and TiO2 on the glass-forming ability, the thermal, physical, and optical properties of glasses in the four-component...     

Crystallization Behavior of Potassium Niobium Silicate Glasses

Crystallization behavior of potassium niobium silicate (KNS) glasses having compositions expressed by the general formula x K₂O· x Nb₂O₅·(1 - 2 x )SiO₂, with x = 0.167, 0.182, 0.200, 0.220, and 0.250, has been studied by DTA, X-ray diffraction, second harmonic optical generation (SHG), and electron microscopy. Bulk crystallization of potassium niobates in glasses with compositions near K₂O·Nb₂O₅·2SiO₂, as well as surface crystallization of KNbSi₂O₇ phase, has been established. Transparent glass-ceramics, based on potassium niobates with remarkable SHG signal values, can be obtained from glasses with the lowest silica content, by heat treatment at temperatures just above T _g, while at higher temperatures from all of the glasses under investigation the main crystallizing phase is KNbSi₂O₇ ferroelectric. Applying a dc electric field, grain-oriented crystallization is produced in KNS glasses with development of significantly anisotropic arrangements of KNbSi₂O₇ crystallites.     

Nickel-doped gallium-containing glasses luminescent in the near-infrared spectral range

The heat treatment of glasses synthesized in the M ₂O-Ga₂O₃-GeO₂-SiO₂ (M = Li, Na, K) system results in bulk precipitation of Ga₂O₃ and LiGa₅O₈ nanocrystals and, consequently, in luminescence within the bands with maxima at wavelengths of 1500 and 1300 nm, respectively, with the half-width exceeding 300 nm. In their spectral luminescence properties, the gallium germanium silicate glasses synthesized are similar to the gallium silicate glasses. However, the melting temperature of the former glasses is approximately 100°C lower, which considerably facilitates the preparation of glasses of high optical quality.     

Development of a Cyclone-Based Aerosol Sampler with Recirculating Liquid Film: Theory and Experiment

This article describes the theoretical considerations, design criteria, and experimental performance of a cyclone-based, liquid-film, bioaerosol sampler. Different from conventional cyclones, this novel sampler draws air tangentially into the bottom of a swirling cyclone, creating a negative pressure differential which causes continuous suction of sorption liquid from its reservoir into the cyclone. The liquid swirls with the air vortex and rises spirally along the sampler wall in the form of a thin film. In the presence of an excess pressure differential, the liquid goes over the upper edge of the cyclone (overflow mode) and flows back to the bottom of the sampler. As a result, there is a continuous circulation of the sorption liquid in the sampler, which enhances the efficacy of capturing viable aerosol particles from incoming air. In this study, mathematical models using simplified Navier-Stokes equations are developed to describe the behavior of the airflow, the formation of the liquid film, and the precipitation process of the aerosol particles. Numerical solutions are presented as an approximation to these complex air and liquid flow streams in the whirlwind cyclone. Based on the theoretical assessment, practical design criteria for a novel sampler were formulated and a series of prototype samplers were fabricated and evaluated. In this report, experimental findings concerning the thickness of the air vortex, the pressure profile in the cyclone, and the apex height of the liquid film are presented. The results are in good agreement with theoretical prediction. However, the theory seems to overestimate the capturing efficiency for particles around the cutoff size (in the study, 1–2 μm) when comparing with data obtained from the experiments.     

Polarization-Dependent Birefringence in Lithium Aluminosilicate Glass

Glass and Ceramics - The formation of polarization-dependent birefringence, apparently due to the formation of nanogratings, in the bulk of lithium silicate and lithium aluminosilicate glasses...     

Influence of Calcium Oxide Additive on the Properties and Structure of Building Geopolymers Based on Fly Ash from CHPP-22

Glass and Ceramics - The physicomechanical properties and microstructure of geopolymer building materials, based on low-calcium fly ash from CHPP-22, were investigated as functions of the type of...     

Nickel-assisted growth and selective doping of spinel-like gallium oxide nanocrystals in germano-silicate glasses for infrared broadband light emission

The target of taking advantage of the near-infrared light-emission properties of nickel ions in crystals for the design of novel broadband optical amplifiers requires the identification of suitable nanostructured glasses able to embed Ni-doped nanocrystals and to preserve the workability of a glass. Here we show that Ni doping of Li(2)O-Na(2)O-Ga(2)O(3)-GeO(2)-SiO(2) glass (with composition 7.5:2.5:20:35:35 and melting temperature 1480 °C, sensibly lower than in Ge-free silicates) enables the selective embedding of nickel ions in thermally grown nanocrystals of spinel-like gallium oxide. The analysis of transmission electron microscopy and x-ray diffraction data as a function of Ni-content (from 0.01 to 1 mol%) indicates that Ni ions promote the nanophase crystallization without affecting nanoparticle size (~6 nm) and concentration (~4 × 10(18) cm(-3)). Importantly, as shown by optical absorption spectra, all nickel ions enter into the nanophase, with a number of ions per nanocrystal that depends on the nanocrystal concentration and ranges from 1 to 10(2). Photoluminescence data indicate that fast non-radiative decay processes become relevant only at mean ion-ion distances shorter than 1.4 nm, which enables the incorporation of a few Ni ions per nanoparticle without too large a worsening of the light-emission efficiency. Indeed, at 0.1 mol% nickel, the room temperature quantum yield is 9%, with an effective bandwidth of 320 nm.