Characterisation of porous glasses prepared from Cathode Ray Tube (CRT)

Display tubes such as those used in TV receivers and computer monitors have an evacuated glass envelope, which consists mainly of a screen (front component) and a funnel (back component hidden inside the TV set or monitor). These two components have different compositions: the screen is composed of lead-free glass with strontium and barium oxides, whereas the funnel is composed of glass with lead oxides. In order to comply with future government measures, a method is required for the recycling or re-utilisation of CRT (Cathode Ray Tube) glasses in end-of-life electronic goods. One open-loop recycling method is to create foam glasses from CRTs using a reducing agent. The results for the chemical compositions of these glasses and their physical properties showed that foam glasses can be prepared from glasses from various CRT glassmakers. In this paper, we use several methods to determine the structures of these foam glasses. We use helium pycnometry, Hg porosimetry, specific surface area measurements and scanning electron microscopy as direct methods for determining foam glass structure. These methods provide information about the morphologies and reactivities of these porous materials. Densities, porosities and pore size distributions were measured, which enable us to suggest some potential applications for the fabricated foam glasses.     

Optimisation of low temperature sinter crystallisation of waste derived glass

Abstract

Abstract

Mixtures of inorganic waste materials are commonly converted into glasses, in turn to be transformed into glass ceramics. Specific composition designs may lead to glasses with a low crystallisation temperature, useful for low cost ceramisation by bulk nucleation. This feature, however, may be disadvantageous if the same glasses are subjected to sintering, since intensive crystallisation hinders the viscous flow. This paper illustrates the optimisation of simultaneous sintering and crystallisation of a waste derived glass, originally intended for bulk nucleation, when coupled with recycled glasses, at a very low temperature (800°C). The mixing with secondary glasses did not merely enhance the densification (residual porosity of ～3%) but modified the crystallisation. Owing to the mechanical properties (e.g. Young’s modulus and bending strength exceeding 80 GPa and 90 MPa respectively), the obtained sintered glass ceramics may find profitable applications in the building industry.     

Integrated utilization of high alumina fly ash for synthesis of foam glass ceramic

Due to the numerous increase of the building energy consumption and huge volume of industrial wastes produced in China, the development of thermal insulation materials is quite needed. Herein, foam glass ceramic, a kind of thermal insulation materials, was fabricated by using solid wastes high alumina fly ash and waste glass as the main raw materials. First, in this study the proportion scheme of this research was designed by using Factsage 7.1 and the foaming agent was CaSO₄. Secondly, the decomposition of calcium sulfate and the influence of process parameters, namely the sintering temperature and the foaming agent additive amount, on the microstructure and mechanical properties of foam glass ceramic were investigated. The experimental results showed that when the proposed foam glass ceramic was sintered at between 1180 and 1220?°C, it exerted excellent macro and micro properties. The optimum parameters were 2% CaSO₄ addition and sintering temperature of 1200?°C, and the corresponding bulk density and compress strength values were 0.98?g/cm³ and 9.84?MPa, respectively. Overall these results indicated that the preparation of foam glass ceramic made up a promising strategy for recycling industrial waste into new kind of building insulation materials.     

镍渣基泡沫玻璃的制备及其性能研究

以镍渣和废玻璃作为主要原料,使用Na2CO3为发泡剂,采用模具装填法来烧制泡沫玻璃.研究了镍渣的掺量、发泡剂掺量、发泡温度和发泡时间对泡沫玻璃的气孔结构和相关力学性能的影响.研究表明:镍渣掺量减少,Na2CO3掺量增加和发泡温度的升高,均会降低泡沫玻璃的体积密度,提高样品的平均气孔直径;镍渣掺量对泡沫玻璃的组成成分和晶体种类没有明显的影响;以20%镍渣和80%玻璃粉为主料,5%~7%Na2CO3为发泡剂,在发泡温度870 ℃下保温60 min,可以制备出气孔率为85.14%,体积密度为0.3715 g/cm3,抗折强度为2.062 MPa,平均气孔直径在3.13 mm的镍渣基泡沫玻璃.     

Effect of Al2O3 on the structure–property relationship of sodium aluminophosphate glasses: A combined study of experiments,MD simulations,and QSPR analysis

Aluminophosphate glasses have found wide applications in various fields, such as biomedical materials, optical components, sealing materials, and nuclear waste forms. In spite of their well-investigated short-range ordered structures, the relationship between the properties and the medium-range structural features is far from being understood. In this paper, atomistic structures of sodium aluminophosphate (SAP) glasses were reproduced by molecular dynamics simulations. In addition, experimental methods, including Raman, differential scanning calorimetry, and synchrotron X-ray total scattering, have been applied to characterize the structures of these glasses, together with the measurements of various glass properties, such as the density, glass transition temperature (T_g), coefficient of thermal expansion (CTE), and hardness. Moreover, the quantitative structure–property relationship (QSPR) analysis was performed to correlate the simulated glass structures with the experimentally measured properties. The simulation results reveal that the P–O–P linkages in the glass network are gradually replaced by the P–O–Al linkages with additional alumina to the compositions, which contributes to the property changes of the SAP glass systems. Meanwhile, the long chains in the SAP glasses tend to form ring structures, and the primitive rings are concentrated in the range between 4- and 20-membered rings. Furthermore, QSPR analysis shows that the simulated structures have good correlations with the experimental properties, and the established structure–property model is promising in predicting certain properties of aluminophosphate glass systems.     

粉煤灰泡沫玻璃的试验研究

以粉煤灰和玻璃粉为主要原料,添加适量的发泡剂、稳泡剂等助剂,可制得粉煤灰泡沫玻璃。通过对制品体积密度、表观密度、开口孔孔隙率、吸水率等性能的测定,分析了发泡剂、粉煤灰掺量对泡沫玻璃性能的影响。实验表明,适量添加粉煤灰和玻璃粉,可制得性能较好的粉煤灰泡沫玻璃。     

Effect of doping by transitional elements on properties of chalcogenide glasses

In present work, the results on the influence of doping by transitional elements on thermal, optical, structural and magnetic properties of chalcogenide glasses are presented.Thermal properties (T_g values for undoped and doped glasses) were studied using differential scanning calorimetry technique. Activation energy of glass transition was estimated with the use of Kissinger’s expression. Structural studies were carried with the use of Raman and infrared spectroscopy and X-ray diffraction. Radial electron distribution functions in doped and undoped bulk glasses were obtained and analyzed. In Raman spectra, main observed effect under the introduction of dopants was the change of relative concentration of main and non-stoichiometric structural units characteristic for As₂S₃ glasses. Investigation of influence of transition metals Mn-dopants on the optical properties of As₂S₃ glass was studied in mid-IR region. Pure chalcogenide glasses are diamagnetics. Introduction of transitional and rare earth impurities changes the magnetic properties of investigated chalcogenide glasses.     

Tailored waste based glasses as secondary raw materials for porcelain stoneware

Abstract

The high temperature processing of porcelain stoneware products is attractive for the possibility to incorporate several inorganic wastes. However, even if recycling is an environmental benefit, it can be disadvantageous for the overall properties of the ceramic product, if wastes are not selected in terms of their chemical and physical characteristics. In the present work several kind of industrial and urban wastes, such as mining residues, lime, glass from dismantled cathode ray tubes and soda lime glass were used, after their vitrification. These newly formed glasses were used as partial substitution for natural feldspar sands (the glass content being from 5 to 7 wt-% of the total mix). Owing to the specific ('tailored') chemical formulation of the newly formed glasses, the modified products exhibited higher crystallisation, with a more homogeneous microstructure, leading to significant improvements in reliability and indentation fracture toughness.     

Alkaline and alkaline-earth silicate glasses and glass-ceramics from municipal and industrial wastes

Municipal (bottom ash and glass cullet coming from the municipal solid waste incineration and a community glass recycling program, respectively) and industrial (steel fly ash) wastes are particularly suitable to be subjected to a vitrification/devitrification process, leading to the production of alkaline and alkaline-earth silicate differently colored glasses with good chemical properties, capable to be transformed into surface nucleated basaltic glass-ceramics. These materials were investigated by means of differential thermal analysis, durability and release tests, X-ray diffraction and scanning electron microscopy.     

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part I: Physical properties

Understanding composition-structure-property relationships of high-alumina nuclear waste glasses are important for vitrification of nuclear waste at the Hanford Site. Two series of glasses were designed, one with varying Al:Si ratios and the other with (Al + Na):Si ratios based on the international simple glass (ISG, a simplified nuclear waste model glass), with Al₂O₃ ranging from 0 to 23 mol% (0 to 32 wt%). The glasses were synthesized and characterized using electron probe microanalysis, X-ray photoelectron spectroscopy, small angle X-ray scattering, high-temperature oxide melt solution calorimetry, and infrared spectroscopy. Glasses were crystal free, and the lowest Na₂O and Al₂O₃ glass formed an immiscible glass phase. Evolution of various properties—glass-transition temperature, percentage of 4-coordinated B, enthalpy of glass formation—and infrared spectroscopy results indicate that structural effects differ based on the glass series.     

Processing and Characterization of Bulk Chalcogenide Glasses Used for Waveguide Applications

Chalcogenide glasses (ChG) are of interest due to their optical and electronic properties for use in waveguide applications. To assess expected uniformity in films deposited from bulk glass starting materials, the extent of parent bulk glass property variation was evaluated. Resulting structural and optical properties of melt-derived ChG's were investigated using X-ray diffraction (XRD), Raman spectroscopy, differential thermal analysis and spectrophotometric analysis. The influence of melt size, purification, and other melting conditions on sample homogeneity were quantified and within-melt property variation of bulk glass samples was found to be less than 5% for all parameters examined.     

Electron energy loss spectra from silica glass optical fibers

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 L_2,3-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.     

Structural Investigation of the Surface of Bioglass 45S5 Enriched with Calcium Ions

In this article the changes on the surface of the 45S5 bioglass submitted to an enrichment with calcium ions were investigated. The method employed was the immersion of bioglass in calcium molten salt bath at 450°C. Changes in composition were probed by different techniques of chemical analysis. The use of SEM‐EDS allowed estimating the thickness modified, as being about 10 μm. X‐ray photoelectron spectroscopy enabled to infer over the structural changes on the surface of 45S5 bioactive glass. The entry of calcium in the vitreous network promoted the phase separation of microdomains rich in silica and phosphate on the surface of the glass. The formation of immiscibility region was attributed a depolymerization of silica network and also, to a possible migration of phosphate species from the bulk. The results of this study indicate a great change in the surface properties of this biomaterial. In addition, the method proposed in this study proved to be very promising in the possibility of designing the surface of bioactive glasses, to modulate the desired properties, keeping the bulk unchanged.     

Preparation and characterization of foam glass from waste container glasses and water glass for application in thermal insulations

Glass foams are modern developed building materials which are now favorably competing with conventional materials for applications in thermal insulation. In this study, glass foams are synthesized solely from waste container glasses of mixed colors using sodium silicate (water glass) as foaming agent. Several glass foams of 150 × 150 × 30 mm were prepared from waste glasses of 75 μm, 150 μm and 250 μm size with addition of 15 wt % sodium silicate respectively and pressed uniaxially under a pressure of 10 MPa. The prepared glass foams were then sintered at temperatures of 800 °C and 850 °C respectively. Tests such as bulk density, estimated porosity, flexural strength, compressive strength and microstructure evaluation were used to assess the performance of the developed glass foams. The results showed that with increasing temperature and grain sizes, the percent porosity of the developed foams increased while the bulk density decreased. The microstructure evaluation showed that the finer the grain sizes used, the more homogenized are the pores formed and the higher the temperature, the larger the pores but are mostly closed. Both compressive and flexural strength were found to decrease with grain sizes and higher temperatures. The thermal conductivities of all the developed foam glasses satisfy the standard requirement to be used as an insulating material as their thermal conductivities did not exceed 0.25 W/m.K.     

The use of egg shells to produce Cathode Ray Tube (CRT) glass foams

Cleaned Cathode Ray Tube (CRT) (panel and funnel) waste glasses produced from dismantling TV and PC colour kinescopes were used to prepare glass foams by a simple and economic processing route, consisting of a direct heating of glass powders at relatively low temperatures (600–800 °C). This study reports on the feasibility of producing glass foams using waste egg shells as an alternative calcium carbonate-based (95 wt%) foaming agent derived from food industry. The foaming process was found to depend on a combination of composition, processing temperature and mixture of raw materials (glass wastes). Hot stage microscopy (HSM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize foams and evaluate the foaming ability and the sintering process. The experimental compositions allowed producing well sintered glass foams with suitable properties for some functional applications with environmental benefits such as: (1) reduced energy consumption because of the low heat treatment temperatures used; and (2) materials produced exclusively from residues.     

Physical and Mechanical Behavior of Polymer Glasses. VI. the Role of Free Volume

Abstract

For various polymer glasses, the temperature-induced recovery of residual deformation was studied. The ratio between the low-temperature and high-temperature recovery components is controlled by the difference between deformation temperature and glass transition temperature T _g of polymer samples independently of their chemical structure. This ratio correlates with polymer macroscopic mechanical characteristics such as elastic modulus and yield stress. Experimental results were treated in terms of the dynamics of segmental mobility within different structural sublevels with different packing densities. To correlate this mechanical response with the structural state of glassy polymers, positron annihilation lifetime spectroscopy (PALS) was used. For different polymer glasses, the microscopic segmental mobility and resultant macroscopic mechanical properties were shown to be controlled only by the development of the adequate free volume content which depends on the difference between testing temperature and T _g . These results allowed us to propose the general correlation between microstructure, microscopic molecular mobility, and Macroscopic mechanical behavior of polymer glasses.     

Interfacial structures of spinel crystals with borosilicate nuclear waste glasses from molecular dynamics simulations

Spinel crystal formation presents a critical issue and glass formulation in nuclear waste glass processing. In this paper, the interfacial structures of the model borosilicate nuclear waste glasses, the international simple glass (ISG), with two types of spinel crystals, namely the MgAl₂O₄ and NiFe₂O₄, were studied using classical molecular dynamics simulations with effective partial charge potentials and recently developed composition-dependent boron-related parameters. The simulation results revealed the structural features of the borosilicate nuclear waste glasses and their interfaces with the two types of spinel crystals. It was found that there exist notable structural changes of glasses close to the interfacial region, affected by the adjacent crystal structures, terms of preferential segregation and ordering of cations, as well as ctaion coordination numbers. Specifically, the fraction of fourfold coordinated boron (B³) in glass near the interface decreases as compared to the bulk glass. In addition, the amount of fourfold coordinated Al decreases while fivefold Al increases in the glass region close to the glass-crystal interface, which suggests indication of initial stage of crystal growth as Al adopts higher (sixfold) coordination like in the crystal as compared to majority of fourfold coordination in the glass. These interfacial structure changes obtained from MD simulations provide evidence of the influence of the precipitated crystals on the surrounding melt and glass and the initial stage of crystal growth.     

Corrosion behavior of some glasses immobilized with REE in simulated mineralized solutions

Bentonite clay is the most promising material with great waterproof properties, which is considered to hold a great potential as an engineering sealing barrier in deep geological repository use. However, the other properties of the said material after contact with groundwater may be of a huge concern in terms of longterm disposal of radioactive waste in a number of circumstances. This article analyses possible results of such interactions and their consequences. Samples of borosilicate, aluminophosphate, and iron phosphate glass, containing rare earth elements (REE) of the composition Ce_0,12La_0,19Nd_0,31O as simulators of radioactive waste, were synthesized. Solutions of model underground water, imitating the water of the Nizhnekansky granitoid massif that passed through clay engineering barriers, were investigated. The analysis of the structure of glasses after contact with model bentonite, zeolite, and kaolin contact solutions at 120 °C, simulating the heat release of alpha-emitters immobilized in glass, was carried out. It was shown that glasses, upon contact with model solutions, were subject to the formation of a corrosion layer as well as depletion of the glass phase in structure-forming elements. Significant structural rearrangement after leaching in all samples was determined by IR spectrometry, while the smallest changes were typical for samples leached in bidistilled water and kaolin contact solution. This information could be crucial for modeling the long-term behavior of nuclear glass in various scenarios of geological repository degradation or accidents.     

Crystallization of Rhenium Salts in a Simulated Low‐Activity Waste Borosilicate Glass

This study presents the characterization of salt phases that formed on simulated low‐activity waste glass melts during a rhenium solubility study. This study with rhenium salts is also applicable to real applications involving radioactive technetium salts. In this synthesis method, oxide glass powder is mixed with the volatile species, vacuum‐sealed in a fused quartz ampoule, and then heated in a furnace. This technique restricts the volatile species to the headspace above the melt but still within the sealed ampoule, thus maximizing the concentration of these species that are in contact with the glass. Above the previously determined solubility of Re⁷⁺ in this glass, a molten salt phase segregated to the top of the melt and crystallized into a solid layer. This salt was analyzed with X‐ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, as well as wavelength dispersive spectroscopy and was found to be composed of alkali perrhenates (NaReO₄, KReO₄) and alkali sulfates. Similar crystalline inclusions were found in the bulk of some glasses as well.     

Controllable competitive nanocrystallization of La3+-based fluorides in aluminosilicate glasses and optical spectroscopy

Glass ceramic has been regarded as an alternative to traditional bulk materials such as single crystal and transparent ceramic. The nucleation/growth behavior of glass ceramic via crystallization is an important topic but is seldom studied so far. In the present work, a series of La³⁺-based oxyfluoride aluminosilicate glasses are designed to understand their nanocrystallization processes upon heating. Impressively, controllable LaF₃, α-NaLaF₄ and β-NaLaF₄ phase-competitive crystallization in glasses is achieved and structural/spectroscopic characterizations confirm the key role of Al/Si ratio to determine the release of Na⁺ ions from glass network to participate in crystallization and phase transformation. Furthermore, the developed glass ceramics are evidenced to be ideal hosts for lanthanide dopants (such as Eu³⁺ and Yb³⁺/Er³⁺), which can effectively incorporate into the precipitated fluoride crystal lattices by substituting La³⁺ ions. As a consequence, incoherent LED-excitable upconverting devices are constructed to demonstrate their promising application as emitting media in display.