Glass sintering with concurrent crystallization

Concurrent Crystallization Mechanism Leading to Low Temperature Percolation of LAGP Glass-Ceramic Electrolyte

Sintering of ceramic electrolytes (CE) is the most efficient way to obtain a dense, all ceramic solid-state battery with oxide-based materials. However, the high temperature required for this process leads to detrimental reactivity between CE and the active material. Crystalline ceramics are necessary for highly conductive oxide materials. Still, thermomechanical properties of glass-phase materials can be used to obtain a denser and more conductive CE. Glass-phase CE can be produced with Nasicon-type CE. Here, Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass is used as a model to investigate the formability, densification, and conduction properties upon crystallization. A complete study of the crystallization mechanism is first performed to fully understand how a high conductivity of 6.3 × 10-5 S·cm-1 at 30 °C with 92% relative density is obtained at a sintering temperature of only 550 °C without pressure. This is approximately 200 °C below the usual sintering temperature of LAGP. X-ray diffraction is then used to calculate the amount of crystalline phase as a function of time. A combined study of reaction kinetics and conductivity evolution reveals an autocatalytic nucleation effect, which produces an early crystallization pathway. Density is studied to quantify the ability of the glass to flow during the crystallization process.

Fast Surface Dynamics on a Metallic Glass Nanowire

The dynamics near the surface of glasses can be much faster than in the bulk. We studied the surface dynamics of a Pt-based metallic glass using electron correlation microscopy with sub-nanometer resolution. Our studies show an ∼20 K suppression of the glass transition temperature at the surface. The enhancement in surface dynamics is suppressed by coating the metallic glass with a thin layer of amorphous carbon. Parallel molecular dynamics simulations on Ni₈₀P₂₀ show a similar temperature suppression of the surface glass transition temperature and that the enhanced surface dynamics are arrested by a capping layer that chemically binds to the glass surface. Mobility in the near-surface region occurs via atomic caging and hopping, with a strong correlation between slow dynamics and high cage-breaking barriers and stringlike cooperative motion. Surface and bulk dynamics collapse together as a function of temperature rescaled by their respective glass transition temperatures.

Structural, Thermal and Dielectric Properties of Low Dielectric Permittivity Cordierite-Mullite-Glass Substrates at Terahertz Frequencies

Glass-ceramic composites containing cordierite, mullite, SiO₂ glass and SiO₂-B₂O₃-Al₂O₃-BaO-ZrO₂ glass were fabricated in a process comprising solid state synthesis, milling, pressing and sintering. Thermal behavior, microstructure, composition and dielectric properties in the Hz-MHz, GHz and THz ranges were examined using a heating microscope, differential thermal analysis, thermogravimetry, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis, impedance spectroscopy, transmission method and time domain spectroscopy (TDS). The obtained substrates exhibited a low dielectric permittivity of 4.0-4.8. Spontaneously formed closed porosity dependent on the sintering conditions was considered as a factor that decreased the effective dielectric permittivity.

Ultrafast consolidation of bulk nanocrystalline titanium alloy through ultrasonic vibration

Nanocrystalline (NC) materials have fascinating physical and chemical properties, thereby they exhibit great prospects in academic and industrial fields. Highly efficient approaches for fabricating bulk NC materials have been pursued extensively over past decades. However, the instability of nanograin, which is sensitive to processing parameters (such as temperature and time), is always a challenging issue to be solved and remains to date. Herein, we report an ultrafast nanostructuring strategy, namely ultrasonic vibration consolidation (UVC). The strategy utilizes internal friction heat, generated from mutually rubbing between Ti-based metallic glass powders, to heat the glassy alloy rapidly through its supercooled liquid regime, and accelerated viscous flow bonds the powders together. Consequently, bulk NC-Ti alloy with grain size ranging from 10 to 70 nm and nearly full density is consolidated in 2 seconds. The novel consolidation approach proposed here offers a general and highly efficient pathway for manufacturing bulk nanomaterials.

Oriented surface nucleation and crystal growth in a 18BaO·22CaO·60SiO2 mol% glass used for SOFC seals

Oriented nucleation of walstromite as well as an unknown phase of the composition BaCaSi₃O₈ is detected after crystallizing a 37BaO·16CaO·47SiO₂ (wt%) glass.

Recycling of inorganic waste in monolithic and cellular glass-based materials for structural and functional applications

The stabilization of inorganic waste of various nature and origin, in glasses, has been a key strategy for environmental protection for the last decades. When properly formulated, glasses may retain many inorganic contaminants permanently, but it must be acknowledged that some criticism remains, mainly concerning costs and energy use. As a consequence, the sustainability of vitrification largely relies on the conversion of waste glasses into new, usable and marketable glass-based materials, in the form of monolithic and cellular glass-ceramics. The effective conversion in turn depends on the simultaneous control of both starting materials and manufacturing processes. While silica-rich waste favours the obtainment of glass, iron-rich wastes affect the functionalities, influencing the porosity in cellular glass-based materials as well as catalytic, magnetic, optical and electrical properties. Engineered formulations may lead to important reductions of processing times and temperatures, in the transformation of waste-derived glasses into glass-ceramics, or even bring interesting shortcuts. Direct sintering of wastes, combined with recycled glasses, as an example, has been proven as a valid low-cost alternative for glass-ceramic manufacturing, for wastes with limited hazardousness. The present paper is aimed at providing an up-to-date overview of the correlation between formulations, manufacturing technologies and properties of most recent waste-derived, glass-based materials. © 2016 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phase composition and in vitro bioactivity of porous implants made of bioactive glass S53P4

This work studied the influence of sintering temperature on the phase composition, compression strength and in vitro properties of implants made of bioactive glass S53P4. The implants were sintered within the temperature range 600-1000°C. Over the whole temperature range studied, consolidation took place mainly via viscous flow sintering, even though there was partial surface crystallization. The mechanical strength of the implants was low but increased with the sintering temperature, from 0.7 MPa at 635°C to 10 MPa at 1000°C. Changes in the composition of simulated body fluid (SBF), the immersion solution, were evaluated by pH measurements and ion analysis using inductively coupled plasma optical emission spectrometry. The development of a calcium phosphate layer on the implant surfaces was verified using scanning electron microscopy-electron-dispersive X-ray analysis. When immersed in SBF, a calcium phosphate layer formed on all the samples, but the structure of this layer was affected by the surface crystalline phases. Hydroxyapatite formed more readily on amorphous and partially crystalline implants containing both primary Na(2)O·CaO·2SiO(2) and secondary Na(2)Ca(4)(PO(4))(2)SiO(4) crystals than on implants containing only primary crystals.

Sintering behaviour of 45S5 bioactive glass

In this study, we report on the effect of Bioglass structural transformations on its sintering behaviour. While heating up to 1000 degrees C, five successive transformations occur: glass transition, glass-in-glass phase separation, two crystallization processes and a second glass transition. The sintering of the material exhibits two main shrinkage stages associated with the two glass transitions at 550 and 850 degrees C. At 580 degrees C, the glass-in-glass phase separation induces a decrease in the sintering rate immediately followed by the major crystalline phase crystallization (Na(2)CaSi(2)O(6)) between 600 and 700 degrees C, from the surface to the bulk of the particles. A complete inhibition of sintering takes place followed by a minor shrinkage effect due to crystallization. A plateau is then observed until the second glass transition temperature is reached. A modification of Frenkel's model allows the determination of the glass-in-glass phase separation kinetics and the identification of the structural transformations effects on sintering behaviour.

A two-scale model for simultaneous sintering and crystallization of glass-ceramic scaffolds for tissue engineering

Bioglass-based glass-ceramic foams have been developed recently as highly porous, mechanically competent, bioactive and degradable scaffolds for bone tissue engineering. However, the development of the material so far has been based on a trial-and-error approach, and the existing materials are far from being optimized. In this paper, a mechanism-based model is presented for sintering deformation of Bioglass foams. The porous foams consist of struts which, in turn, consist of Bioglass particles. A corresponding two-scale model is developed based on existing viscous sintering models. Crystallization plays a key role in the sintering deformation of Bioglass foams and is taken into account in the model. Qualitative comparison between the model predictions and experimental observations is presented, showing that the model is able to capture the complicated interplay between crystallization and viscous flow during the sintering process.