Improvement in colloidal sol-gel SiO2 glass by attrition of aggregates in sols

The two-step colloidal sol-gel process for forming SiO₂ glasses has been improved by the use of attrition in ball mills consisting of borosilicate glass jars with fused SiO₂ cylinders as milling media. The average size of aggregates was reduced from more than 40 μm to less than 3 μm by milling up to 64 h depending on the hardness of the dried gel. Data on pore size distribution in the twice dispersed and dried gels show that 24 to 30 vol% of the pores are due to interaggregate spaces (pores whose sizes are larger than those represented by the average 16 nm pores between primary SiO₂ particles). These large pores cause a bimodal size distribution with the secondary peak at 3 to 4 μm with no milling and the position of the secondary peak decreases with milling until it is no longer resolved from the primary peak. The average size of the interaggregate pores is more than an order of magnitude smaller than the average size of the aggregates due to the efficiency of packing the aggregates of a broad size distribution. Milling is shown to markedly improve the transparency of the SiO₂ glass after sintering.     

Enhancing the performance of pre-cast concrete blocks by incorporating waste glass – ASR consideration

There is a growing interest of using recycled crushed glass (RCG) as an aggregate in construction materials especially for non-structural applications. Although the recycled crushed glass is able to reduce the water absorption and drying shrinkage in concrete products due to its near to zero water absorption characteristics, the potential detrimental effect of using glass due to alkali–silica reaction (ASR) in cementitious materials is a real concern. The extent of ASR and its effect on concrete paving blocks produced with partial replacement of natural aggregates by crushed glass cullet are investigated in this study. This study is comprised of two parts. The first part quantified the extent of the ASR expansion and determined the adequate amount of mineral admixtures that was needed to reduce the ASR expansion for concrete paving blocks prepared with different recycled crushed glass contents using an accelerated mortar bar test in accordance with ASTM C 1260 (80 °C, 1 N NaOH solution). In the second part, concrete paving blocks were produced using the optimal mix proportion derived in the first part of this study and the corresponding mechanical properties were determined.It was found from the mortar bar test that the incorporation of 25% or less RCG induced negligible ASR expansion after a testing period of 28 days. For mixes with a glass content of higher than 25%, the incorporation of mineral admixtures such as pulverized fuel ash and metakaolin was able to suppress the ASR expansion within the stipulated limit but the results need to be confirmed by other test methods such as the concrete prism test.The study concluded that the optimal mix formulation for utilizing crushed waste glass in concrete paving blocks should contain at least 10% PFA by weight of the total aggregates used.     

Macroscopic and microstructural properties of engineered cementitious composites incorporating recycled concrete fines

Recycled concrete fines (RCF) are fine aggregates and particles from the demolition waste of old concrete. Unlike recycled coarse aggregates, RCF is seldom used to replace sands in concrete due to its high surface area and attached old mortar on the surface of RCF. This study investigated potential use of RCF as microsilica sand substitute in the production of engineered cementitious composites (ECC), a unique high performance fiber-reinforced cementitious composites featuring extreme tensile strain capacity of several percent. The results showed that it is viable to use RCF as microsilica sand substitute in the production of ECC and the resulting RCF-ECCs possess decent compressive strength and strain capacity. Microstructure investigation on the component level revealed that RCF size and content modify matrix toughness and fiber/matrix interface properties. The influence of RCF size and content on ECC properties was clearly revealed and explained by the resulting fiber bridging σ(δ) curves of RCF-ECCs calculated from the micromechanical model. Micromechanics-based design principle can therefore be used for ingredients selection and component tailoring of RCF-ECCs.     

Crystallization of sol-gel derived glass ceramic powders in the CaO-MgO-Al2O3-SiO2 system

Samples in the cordierite primary crystallization field were prepared in the CaO-MgO-Al₂O₃-SiO₂ quaternary system by sol-gel techniques, using both polymeric and colloidal gels. Dried gels were characterized by infrared spectroscopy, thermal analysis and electron microscopy. The crystallization of gel-like glass from both kinds of gels, as a function of temperature was followed by X-ray diffraction. Cordierite was detected as the only final crystalline phase, although some other crystalline phases, different for each kind of gel, were observed in the pathway reaction. The polymorphic modification of cordierite detected was pseudohexagonal, because no evidence of splitting was observed.     

Conversion of monolithic gels to glasses in a multicomponent silicate glass system

Multicomponent silicate glasses of composition (wt%) 66SiO₂-18B₂O₃-7Al₂O₃-6Na₂O-3BaO were prepared by three sol-gel processes which differed primarily in the extent of hydrolysis of the metal alkoxide precursors. Gels which were prepared from solutions in which a stoichiometric excess of water was added, causing extensive replacement of OR groups (R (C _x H(_2x+1))^s–1 by hydroxyl groups, were converted to fully dense, organic-free, monolithic glasses at temperatures near the glass transition temperature. Gels containing large numbers of OR groups showed enhanced densification at lower temperatures due to condensation reactions, but these gels could not be converted to fully dense, organic-free glasses. This investigation has shown that at least three possible densification mechanisms might be operative during the gel to glass conversion: volume relaxation, condensation reactions and viscous sintering.A US Department of Energy Facility.     

Dielectric behavior of perovskite glass ceramics

The recent developments of energy storage devices are concerned with larger energy storage ability, low loss and good temperature stability. It has a great technological importance in engineering science. The dielectric materials like ceramics and glass ceramics have great interest in electronic ceramic industry due to above concern. The ceramic dielectrics are used as a capacitive element in electronic circuits. The perovskite glass ceramics have very high dielectric constant and low dielectric loss. The high dielectric constant in glass ceramics is attributed to space charge polarization. In order to produce glass ceramics of high dielectric constant, barium titanate glass ceramics is the first discovered ferroelectric perovskite. In this review article, we are summarizing the dielectric behavior of perovskite glass ceramics such as BaTiO₃, SrTiO₃, PbTiO₃, (Ba,Sr)TiO₃ and (Pb,Sr)TiO₃.     

The role of residual cracks on alkali silica reactivity of recycled glass aggregates

Despite its environmental and economical advantages, crushed recycled glass has limited application as concrete aggregates due to its deleterious alkali-silica reaction. To offer feasible mitigation strategies, the mechanism of ASR should be well understood. Recent research showed that unlike some natural aggregates, soda-lime glass undergoes ASR within cracks in the interior of glass particles and not at glass-paste interface. These cracks originate during bottle crushing and propagate further by ASR. This paper examines whether glass aggregates could become innocuous if these cracks are healed by annealing or when the crack widths are smaller than a critical size. The results confirm that glass annealed at 650 °C for 40 min or particles containing cracks smaller than approximately 2.5 μm can be considered innocuous based on ASTM C1260. Also larger glass particles contain significantly higher percentages of reactive microcracks which may explain why ASR expansions are lowered by reducing the size of glass aggregates.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

Effect of addition of Ag on the microstructures and electrical properties of sol-gel derived SnO2 glass composites

The effect of addition of Ag on the microstructure and electrical properties of sol-gel derived SnO₂-glass composites was examined. Comparisons of the microstructures and electrical properties were carried out between glass composites prepared by a sol-gel method and a conventional one using glass frit. The glass composite gels and the SnO₂-glass powder mixtures containing AgNO₃ were calcined at 500 °C in order to decompose AgNO₃ into Ag and then fired at 900 °C. In the sol-gel derived glass composites, the grain growth of Ag was suppressed and Ag particles connected mutually at the boundaries of aggregated gel particles to form three-dimensional networks. Thus, the glass composite derived by the sol-gel method showed a high electrical conductivity and a positive temperature coefficient of resistance (TCR). The highly electrical conductive paths of Ag in the glass composite were effectively formed when powder compacts were formed at a higher pressure. On the other hand, in the glass composites prepared using SnO₂-glass powder mixtures, coarse-grained Ag particles were isolated in closed pores regardless of the forming pressure, and therefore did not contribute to electrical conduction in the glass composite.     

Spectroscopic properties of CuO, SnO, and Dy2O3 co-doped phosphate glass: from luminescent material to plasmonic nanocomposite

Prospective applications of noble metal and rare-earth co-doped dielectrics in optical devices demand for a comprehensive understanding of the influence of material composition and processing on resulting properties. In this study, we report on the spectroscopic properties of a 50P₂O₅:50BaO glass matrix containing copper, tin, and dysprosium prepared by melting and subsequently subjected to heat treatment (HT). An achievement in terms of material preparation is that addition of stoichiometric amounts of CuO and SnO dopants along with the source of Dy³⁺ ions (Dy₂O₃) is shown effective for the precipitation of Cu nanoparticles (NPs) during HT. Optical absorption and photoluminescence (PL) spectroscopy including emission decay dynamics are employed in the characterization of the co-doped material as prepared, and as a function of HT. The basic structure of the phosphate host is assessed by ³¹P nuclear magnetic resonance spectroscopy. The optical data suggests the presence of both Cu²⁺ and Cu⁺ ions in the melt-quenched co-doped glass together with the Dy³⁺ ions. Thermal processing is indicated to result in the chemical reduction of ionic copper species via Sn²⁺ and ultimately produces the non-luminescent plasmonic Cu particles. The presence of such NPs is also observed to produce a quenching effect on Dy³⁺ PL, interpreted in terms of an ion-to-particle excitation energy transfer operating via interband transitions in the nanoscale metal. Thus, the glass may act as either a luminescent material or a plasmonic nanocomposite desirable for nonlinear optics dependent upon its thermal history.     

Expansion behaviour of glass aggregates in different testing for alkali-silica reactivity

The potential for reaction between amorphous silica in recycled glass used as aggregate in concrete and alkalis in cement is the subject of debate in current concrete literature. Whilst the ASTM C1260 accelerated mortar bar method is conventionally used for rapid ASR assessment, there is doubt about its suitability for glass aggregates. This paper reports upon a comparison of the relative ASR reactivity of various colours of recycled glass aggregates using the ASTM C1260 and C227 test methodologies. The results show that with limited exception the ASTM C1260 method does not cause glass aggregates to react by the end of the prescribed test period. In contrast, the ASTM C227 method causes all glass aggregates to react within 2 weeks, despite the test being designed for 12 months or even longer if necessary. This paper compares and contrasts the results of the two methods over a wide range of glass aggregate and cementitious systems made with two sizes of mortar bar, draws conclusions about the reasons for the differences observed and makes remarks on the expansion behaviour of glass aggregates in cementitious systems.     

Feasible use of large volumes of GGBS in 100% recycled glass architectural mortar

The use of 100% recycled glass as aggregates in architectural mortar is regarded as an environmentally friendly, cost-effective and attractive feature for construction applications due to the natural characteristics of glass (e.g. aesthetic pleasing, impermeability, chemical resistance properties). However, the need to use large quantities of white cement for architectural products may increase the overall cost of production. Therefore, the possibility of using a near-white coloured ground granulated blast furnace slag (GGBS) to replace white cement for architectural mortar production is an attractive option. This paper reports a study which is an extension of our previous work aiming to investigate the feasibility of using large volumes of GGBS (ranging from 15% to 75% white cement replacements) to produce self-compacting-based architectural mortars. To improve the appearance (whiteness) of the mortar, a small quantity of titanium dioxide (TiO₂) was added to the selected mixes for comparison purposes. Fresh and hardened properties of the mortar including mini-slump flow, density, water absorption, flexural strength, equivalent compressive strength, drying shrinkage, alkali silica reaction (ASR) and acid attack resistance were investigated. The overall performance showed that it is feasible to use GGBS for the production of architectural mortar and 60% replacement of white cement by GGBS was determined to be optimal. The replacement significantly increased the flexural strength, and reduced the drying shrinkage and risk of ASR expansion, as well as improved the ability to resist acid attack of the mortar produced.     

The effect of substitution of Bi2O3 for alkali oxides on thermal properties, structure and wetting behavior of the borosilicate glass

The effect of substitution of Bi₂O₃ for alkali oxides in the borosilicate sealing glass on thermal properties, structure and wetting behavior of the borosilicate glass was studied. The thermal expansion coefficient (TEC) decreased with the substitution, however, the TEC varied little while the alkali oxides were completely consumed. The variation in glass transition temperature (T_g) and the FTIR results of the glasses indicated significant effect of Bi₂O₃ substitution on the glass structure, which caused a progressive conversion of BO₃ to BO₄ unit in the glass. The appropriate amount of Bi₂O₃ obviously improved the wetting performance of the borosilicate glass on Al₂O₃ substrate due to the high polarizability of Bi³⁺ ion.     

Effect of barrier layers on the properties of indium tin oxide thin films on soda lime glass substrates

In this paper, the electrical, structural and optical properties of indium tin oxide (ITO) films deposited on soda lime glass (SLG) haven been investigated, along with high strain point glass (HSPG) substrate, through radio frequency magnetron sputtering using a ceramic target (In₂O₃:SnO₂, 90:10 wt.%). The ITO films deposited on the SLG show a high electrical resistivity and structural defects compared with those deposited on HSPG due to the Na ions from the SLG diffusing to the ITO film by annealing. However, these properties can be improved by intercalating a barrier layer of SiO₂ or Al₂O₃ between the ITO film and the SLG substrate. SIMS analysis has confirmed that the barrier layer inhibits the Na ion's diffusion from the SLG. In particular, the ITO films deposited on the Al₂O₃ barrier layer, show better properties than those deposited on the SiO₂ barrier layer.     

Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system

65(SrO·TiO₂)−35(2SiO₂·B₂O₃) wt% glass was synthesized. Differential thermal analysis study shows one exothermic peak which shifts towards higher temperature with increasing heating rate. Glass ceramics prepared by controlled crystallization of strontium titanate borosilicate glass produce uniform distribution of crystallites in a glassy matrix. Attempt was made to crystallize strontium titanate phase in this glass ceramic. Different phases precipitated out during ceramization have been identified by X-ray diffraction. It appears that due to high reactivity of SrO with B₂O₃, strontium borate crystallizes as principal phase followed by TiO₂ (rutile) and Sr₃Ti₂O₇ phases. Dielectric constant of these glass ceramics was observed to be more or less temperature independent over wide range of temperatures with low values of dielectric constant and dissipation factor.     

Alkali-silica reaction in concrete containing glass

The use of surplus waste glass in concrete has been avoided on the grounds that it is known to undergo harmful alkali-silica reaction (ASR). As part of a research project to develop draft specifications for glass in concrete, a major ASR testing programme was undertaken to establish appropriate use of glass in concrete which avoided harmful ASR. The British Standard for assessing ASR reactivity of aggregate—BS 812-123—was used. Testing was conducted on concrete mixes containing glass as either fine aggregate, filler aggregate, or as a Type II addition. Glass used as fine aggregate was found to produce significant expansion for both green and amber glass. GGBS and metakaolin had the effect of reducing this expansion considerably. Concrete containing powdered glass displayed much less expansion. A simple schematic model for the alkali-silica reaction of glass, based on glass dissolution mechanisms is proposed, and related to the test results.     

Properties of self-compacting concrete prepared with recycled glass aggregate

The effects of recycled glass (RG) cullet on fresh and hardened properties of self-compacting concrete (SCC) were investigated. RG was used to replace river sand (in proportions of 10%, 20% and 30%), and 10 mm granite (5%, 10% and 15%) in making the SCC concrete mixes. Fly ash was used in the concrete mixes to suppress the potential alkali-silica reaction. The experimental results showed that the slump flow, blocking ratio, air content of the RG–SCC mixes increased with increasing recycled glass content. The compressive strength, tensile splitting strength and static modulus of elasticity of the RG–SCC mixes were decreased with an increase in recycled glass aggregate content. Moreover, the resistance to chloride ion penetration increased and the drying shrinkage of the RG–SCC mixes decreased when the recycled glass content increased. The results showed that it is feasible to produce SCC with recycled glass cullet.     

Effects of deicers on the performance of concrete pavements containing air-cooled blast furnace slag and supplementary cementitious materials

This study investigates the effects of continuous deicer exposure on the performance of pavement concretes. For this purpose, the differences in the compressive strength, the changes in the dynamic modulus of elasticity (DME) and the depth of chloride ingress were evaluated during and after the exposure period. Eight different concrete mixtures containing two types of coarse aggregates (i.e. air-cooled blast furnace slag (ACBFS) and natural dolomite) and four types of binder systems (i.e. plain Type I ordinary portland cement (OPC) and three combinations of OPC with fly ash (FA) and/or slag cement (SC)) were examined. These mixtures were exposed to three types of deicers (i.e. MgCl₂, CaCl₂, and NaCl) combined with two different exposure conditions (i.e. freezing-thawing (FT) and wetting-drying (WD)). In cold climates, these exposure conditions are the primary durability challenges that promote the physical deterioration of concrete pavements. The results indicated that among the studied deicers, CaCl₂ had the most destructive effect on the tested concretes while NaCl was found to promote the deepest level of chloride ingress yet was shown to have the least damaging impact on concretes. The microstructure evaluation revealed that the mechanism of concrete deterioration due to the deicer exposure involved chemical reactions between the deicers and concrete hydration products. The use of FA or SC as partial replacements for OPC can offset the detrimental effects of both deicers and FT/WD cycles.     

UV–vis spectroscopic studies of CaF2 photo-thermo-refractive glass

A photo-thermo-refractive glass based on the system Na₂O/K₂O/CaO/CaF₂/Al₂O₃/ZnO/SiO₂ doped with Ag₂O, CeO₂, SnO₂, Sb₂O₃ and KBr was investigated. This glass undergoes a permanent refractive index change after UV irradiation and subsequent two step heat treatment at temperatures above Tg. This is due to the formation of Ag metal clusters which act as nucleation centers for CaF₂ crystallization. Oxidation of Ce³⁺ by UV light is the initial reaction and acts as photosensitizer in the glass. The UV–vis absorption spectra during this photo-induced crystallization process were measured. The spectral components that form the absorption spectra of cerium were studied in detail by a band separation with Gaussian functions. Deconvolution of the cerium absorption bands shows an envelope of five spectral components for the trivalent cerium due to the 4f-5d transitions and two spectral components for the tetravalent cerium caused by charge transfer transitions. The effect of different dopants and melting conditions on the photo-thermal process were studied to investigate the influence of glass technology on the photoprocess.     

Investigation on adhesion, interphases, and failure behaviour of cyclic butylene terephthalate (CBT)/glass fiber composites

Interphases exist in hybrid materials and significantly influence their mechanical performance. To find a bridge between the microscopic and macroscopic mechanical properties, this work investigates the microscopic nature of glass fiber surfaces and glass/CBT interphases in terms of topography, fractography, and adhesion properties. The variations in glass fiber surface properties result from the different sizings. Using the single fiber pull-out test, AFM, and ζ potential tests, it is shown that the interfacial bond strengths in CBT resin composites can vary depending on the kind of sizing formulation and properties. The greatest adhesion strength is achieved by aminosilane sizings with epoxy resin film former. The surface roughness of the fibers can be varied by sizings with different content and ζ potential values, which has no significant contribution to interphase adhesion strength from ‘mechanical interlocking’. For the systems with film formers, cohesive failure occurs and similar values of both interfacial adhesion strength, τ_d, and fracture energy release rate, G_ic, are obtained, in which τ_d approaches the shear yield strength of CBT matrix. A further enhancement of interfacial adhesion is limited by the mechanical properties and the non-homogeneous microstructure of CBT resin due to the less-than-perfect CBT polymerization.