Reactivity Of Glasses Research Articles

Influence of humidity in the alteration of unstable glasses

AbstractThe control of humidity between certain limits is essential to avoid the alteration of historical objects, such as unstable historical glasses. However, the usual limits can be altered due to the presence of volatile organic compounds. This work presents the results of the exposure of soda, potash, and mixed‐alkali silicate glasses to neutral and acidic (formic) atmospheres with ∼30%, ∼70%, and ∼100% relative humidity. The hygroscopic capacity of the glass was analyzed by gravimetry, and the surface alteration was evaluated by infrared spectroscopy, optical microscopy, and ion chromatography. In all glasses, the alteration begins with alkali ions’ lixiviation followed by the silica network's hydrolytic attack. The results showed that soda and mixed‐alkali silicate glasses exhibit similar behavior, while the potash‐lime one experienced the fastest degradation due to its composition. Results also confirmed that high humidity increased the alteration rate causing a higher hygroscopicity and reactivity of glasses. Finally, acidic environments promoted the ion‐exchange reaction at high humidity, accelerating the lixiviation of alkaline ions and promoting the diffusion of water into the glass network.

Elucidating the impact of chemical variability on the nano-structure of Fe-rich slags

Fe-rich silicate slags are promising resources in the production of alternative cementitious materials. In this investigation, molecular dynamics simulations have been employed to provide a comprehensive structural description of a range of binary FeO-SiO2 and ternary CaO-FeO-SiO2 glasses, which are the basis of the slag systems that are observed in the non-ferrous metallurgy. The impact of the chemical variations on the structure of the glasses is assessed. Fe atoms have a slightly more profound role as network modifiers, and Ca as charge compensators for lower SiO2 content. There is a preference of Fe atoms to be associated with free oxygens, as compared to Ca atoms, forming small scale clusters. The obtained results enrich our understanding of the relationship between the composition, the structure and the reactivity of such complex glasses.

Mechanism of dissolution reactivity and reactions of various calcium borate glasses and glass-ceramics

This study investigated the effect of calcium addition on boron coordination and ion release in deionized water (DIW) of five melt-quench-derived compositions: xCaO-(100-x)B2O3 (x=25, 27, 33, 38 and 48 mol%) and one sol-gel-derived 48CaO-52B2O3 glass. The mechanism of hydration and hydrolysis reactions was elaborated based on ionic release and structural change pre- and post- ageing in DIW. For melt-quench-derived glasses, within 8 h ageing, the hydration reactions were more rapid than the hydrolysis reactions, resulting in solution pH increase, where ionic release was more dependent on composition than boron coordination. At longer ageing times, hydration and hydrolysis reactions occurred simultaneously, leading to solution pH stabilization, and calcium and boron release decreased with an increase in the boron tetrahedral fraction (N4) in glasses. Non-bridging-oxygens in the melt-quench-derived 48CaO-52B2O3 glass-ceramic and hydroxyl groups in the equivalent sol-gel-derived glass fostered calcium and boron release. All glass formulations demonstrated higher N4 post DIW exposure.

Role of Zn in aluminosilicate glasses used as supplementary cementitious materials

The cement industry relies on the use of supplementary cementitious materials (SCM) to lower the related CO2 emission. SCM are often amorphous materials containing minor elements, which is why it is important to study the impact of these materials on cement reactivity. Two calcium aluminosilicate glass series as model substances of SCM were synthesized and investigated. In both series Ca was partially replaced by Zn, Sr and Mg in different ratios. Moreover, four cement blends made with CEM I 52.5 R and aqueous solutions of Mg(NO3)2·6H2O, Zn(NO3)2·6H2O and Sr(NO3)2 were investigated. Zn retards the reactivity of both glasses and cements system. This retardation effect is suggested to be related both to the formation of the calcium hydroxozincate hydrate, which affects the portlandite formation and, thus, the pH of the system, and to the formation of surface complexes which retards the dissolution and so the reactivity of the glasses.

Preparation and characterization of binary Mg-silicate glasses via Sol-Gel route

Sol-gel processing allows synthesis of low-energy glasses. In this work, binary magnesium silicate glasses with various MgO contents are synthesized using a modified sol-gel route. TGA and XRD analyses indicate that amorphous glasses with up to 50 mol% MgO can be obtained at 500°C. The reactivity of the glasses is evaluated to assess the use of the sol-gel technique in the large-scale synthesis of alternative cementitious materials. Reactivity tests show that, as MgO content increases, reactivity of glasses increases, reaches an optimum and then declines. This trend doesn't agree with the theoretical one estimated by NBO/T value, which is generally used for the evaluation of glass reactivity. Mg2+ ions play a role as the network modifier when first introduced to silicate glasses. This leads to the depolymerization of the networks, causing an increase in reactivity. Then the magnesium partly behaves as a network former, bonding with oxygens to form MgOx polyhedron when there are insufficient primary glass-forming oxide SiO2, resulting in the polymerization of networks, hence the decrease in reactivity.

Metal Organic Framework Glasses: A New Platform for Electrocatalysis?

Metal organic framework (MOF) glasses are a coordination network of metal nodes and organic ligands as an undercooled frozen-in liquid, and have therefore broadened the potential of MOF materials in the fundamental research and application scenarios. On the road to deploying MOF glasses as electrocatalysts, it remains several basic scientific hurdles although MOF glasses not only inherit the structural merits of MOFs but also endow with active catalytic features including concentrated defects, metal centers and disorder structure etc. The research on the ionic conductivity, catalytic stability and reactivity of MOF glasses has yielded scientific insights towards its electrocatalytic applications. Here, we first comb the history, definition and basic properties of MOF glasses. Then, we identify the main synthetic methods and characterization techniques. Finally, we advance the potentials and challenges of MOF glasses as electrocatalysts in furthering the understanding of these themes.

Experiments on the reactivity of basaltic minerals and glasses in Venus surface conditions using the Glenn Extreme Environment Rig

AbstractClimate models for Venus rely heavily on theoretical modeling and laboratory experimentation due to the extreme surface conditions of the planet and limited in situ surface data. To better explore the relative importance of reactions between the surface and the atmosphere on Venus, we exposed representative volcanic glasses and basaltic minerals to a large‐scale simulation of Venus surface conditions with a realistic atmospheric composition. This study consistend of two experiments of 42 and 80 days that replicated both physical conditions and atmosphere composition derived from available in situ near‐surface data using the Glenn Extreme Environment Rig (GEER) at the NASA Glenn Research Center. These experiments revealed significant reactivity of common Ca‐bearing pyroxenes (diopside and augite) to form anhydrite. Olivine and labradorite showed minimal reactivity. Volcanic glasses, including both natural and synthetic samples, were exceptionally reactive, rapidly forming both anhydrite and thénardite (Na2SO4), as well as transition metal sulfates (i.e., Cu, Cr), halite (NaCl), and sylvite (KCl). Our results document chemical and textural alteration of sample surfaces and provide sufficient evidence for an active sulfur sink on multiple samples, with sulfates as the dominant secondary mineralogy. These experiments suggest likely surface mineralogies and solid phases present on Venus' surface with significant implications for upcoming missions and provide new data for comparison to high‐temperature mineral–gas reactions prevalent on Venus, Earth, and Io.

Dissolution-precipitation reactions of silicate mineral fibers at alkaline pH

Silicate mineral fibers – stone (Sw) and glass wool (Gw) – are promising resources for cementitious binders. Insights gained from their dissolution kinetics under alkaline conditions can help to control the release of elements, formation of cementitious phases, and understand reactivity of similar type glasses (soda-lime and basalt). Decreasing the liquid-to-solid ratio (L/S) affects the dissolution rate of Sw, whereas the effect was lower for Gw. Residual rate observed for Sw was due to approaching equilibrium between the surface precipitates and solution chemistry. Two types of precipitation products were observed for both fibers at high pH: Mg-Al-Fe LDH and a C-N-(A-)S-H phase with a small concentration of Al. Dissolved Al was observed to incorporate more in LDH at a high L/S, whereas at a low L/S, Al incorporates more into C-N-(A-)S-H gel, altering its morphology. In addition, Ca-Ti-Si-rich globular domes, and Ca-Fe-Ti-rich nano-dome like hydrogarnets on the Sw fiber surfaces were observed.

Influence of Accelerating Admixtures on the Reactivity of Synthetic Aluminosilicate Glasses.

This research aims at gaining a further understanding of the impact of accelerating admixtures on the reactivity of supplementary cementitious materials (SCMs), which are widely used as a clinker replacement in blended cements. This was done on synthetic glasses with controlled composition and structure that mimic two types of real SCMs (slag and calcium-rich fly ash). The effects of DEIPA, TIPA, NaSCN and Na2S2O3 on the glass dissolution, hydration kinetics and reaction products were investigated. The obtained results concluded that the pH of the NaOH solution and the composition of the synthetic glass play a key role on the effect of the admixtures. In 0.1 M NaOH (pH = 13.0), all the studied admixtures inhibited the dissolution of slag-like glasses while they enhanced the dissolution of Ca-rich fly ash-like glasses, being Na2S2O3 the admixture that led to the highest increase of the dissolution rate of the Ca-rich fly ash-type glasses. In 1 M NaOH solutions (pH = 13.8), only the alkali admixtures (NaSCN and Na2S2O3) enhanced the degree of reaction of both glasses. In slag-type glasses pastes mixed with 1 M NaOH, the addition of 2% Na2S2O3 induced the highest increase of their reactivity as inferred by the total heat release and the amount of bound water. This is related to the formation of a high amount of S(II)-AFm, in addition to C-A-S-H, that would increase the aluminium undersaturation of the pore solution and consequently the further dissolution of the glass.

Alpha dose rate and decay dose impacts on the long-term alteration of HLW nuclear glasses

In the prospect of deep geological disposal, the long-term behavior of high-level nuclear glasses has to be investigated regarding alpha radiation induced by long-life minor actinides. The present study focuses on the effects of alpha radiation on the long-term chemical reactivity of R7T7-type glasses, by separately considering the alpha dose rate and the alpha decay dose. Old SON68 glasses doped with 238/239PuO2 or 244CmO2 were studied to simulate high alpha dose rates corresponding to an early water ingress and a high level of alpha decay doses corresponding to long-term disposal conditions. A part of the 238/239Pu-doped glass block was annealed to fully recover the irradiation-induced damage accumulated since the glass was fabricated and to dissociate the effect of the alpha dose rate from that of the alpha decay dose. The glasses were then leached under static conditions at 90 °C for several years. The results showed that the residual alteration rate is not affected by the alpha dose rate over a wide range of dose rate values expected under disposal conditions: this glass remained relatively insensitive to the alpha radiolysis phenomena at the glass–water interface. However, over the duration of the experiments, the residual alteration rate of the damaged 238/239Pu-doped glass was enhanced compared to that of the annealed glass. This result is in agreement with those obtained on the 244Cm-doped glass and with reported values in the literature on simplified externally irradiated glasses, indicating that the ballistic effects of the recoil nuclei are responsible for this increase in the residual alteration rate.

Toward the understanding of crystallization, mechanical properties and reactivity of multicomponent bioactive glasses

In this study, we have applied Molecular Dynamics (MD) simulations to obtain reliable structural models of the bulk and surfaces of the 45S5 Bioglass® and three recently designed glasses in the system Na2O-K2O-CaO-MgO-SrO-P2O5-SiO2 and to interpret their different behaviour and properties. In fact, the substitution of sodium oxide with alkaline earth oxides (Ca, Mg and Sr) in the traditional 45S5 Bioglass® has been shown to be beneficial for improving the sinterability and mechanical properties of the glass maintaining optimal biocompatibility.The reduced tendency of crystallization has been associated to the increased chemical disorder around network former cations, the reduced mobility of alkaline earth cations with respect to sodium and the reduced coordination number of magnesium, which hamper the large structural re-organization necessary to the precipitation of the Na2Ca2Si3O9 crystal phase. In all the compositions, fragmented chains dominate the silica network and the network connectivity is similar. However, the increased interconnection of such chains by Mg, Ca and Sr cations makes the substituted glasses stiffer and harder than the 45S5 Bioglass®. The different reactivity of the glasses is due to the different amount of alkali cations and undercoordinated species at the glass surfaces.The approach presented provides deeper insights on the structure-properties relationships in bioactive glasses, and can be used to find precious guidelines for compositional tuning and designing innovative bioactive glass compositions with desired behaviour or property for a specific application.

Towards designing reactive glasses for alkali activation: Understanding the origins of alkaline reactivity of Na-Mg aluminosilicate glasses.

Alkali-activated materials (AAMs), sometimes called geopolymers, are eco-friendly cementitious materials with reduced carbon emissions when compared to ordinary Portland cement. However, the availability of most precursors used for AAM production may decline in the future because of changes in industrial sectors. Thus, new precursors must be developed. Recently there has been increased interest in synthetic glass precursors. One major concern with using synthetic glasses is ensuring that they react sufficiently under alkaline conditions. Reactivity is a necessary, although not sufficient, requirement for a suitable precursor for AAMs. This work involves the synthesis, characterization, and estimation of alkaline reactivity of Na-Mg aluminosilicate glasses. Structural characterization showed that replacing Na with Mg led to more depolymerization. Alkaline reactivity studies indicated that, as Mg replaced Na, reactivity of glasses increased at first, reached an optimal value, and then declined. This trend in reactivity could not be explained by the conventional parameters used for estimating glass reactivity: the non-bridging oxygen fraction (which predicts similar reactivity for all glasses) and optical basicity (which predicts a decrease in reactivity with an increase in Mg replacement). The reactivity of the studied glasses was found to depend on two main factors: depolymerization (as indicated by structural characterization) and optical basicity. Depolymerization dominated initially, which led to an increase in reactivity, while the effect of optical basicity dominated later, leading to a decrease in reactivity. Hence, while designing reactive synthetic glasses for alkali activation, structural study of glasses should be given due consideration in addition to the conventional factors.

Pozzolanic reactivity of natural pozzolans, ground glasses and coal bottom ashes and implication of their incorporation on the chloride permeability of concrete

It is well understood that the partial replacement of portland cement with pozzolans in sufficient proportions results in improved long-term performance of concrete. However, dwindling availability of the most widely used pozzolan in the construction industry, fly ash, is forecast due to the termination of coal-fired electricity power stations around the world, necessitating the exploration of alternative pozzolans. Experimental investigations are conducted to study the performance of traditional pozzolans such as fly ash, silica fume and natural pozzolans (metakaolin, pumice, perlite and lassenite) together with novel pozzolans, including ground glasses (high-alkali and low-alkali), and ground bottom ash. Twenty-one concrete mixtures are examined for compressive strength, electrical conductivity, electrical resistivity, chloride permeability, and chloride migration coefficient. The reactivity of pozzolans studied is also determined in terms of compressive strength in lime-pozzolan mortar using a modified lime-reactivity test method. Many of the materials tested demonstrate the potential to be used in place of fly ash. However, a wide variation in the performance of these materials is evident which highlights the need for a reliable test to determine the level of reactivity of a pozzolan. The results indicate that the 7-day strength in the modified lime-reactivity test provides a good indication of the pozzolanic reactivity of the material and of how the material can be expected to contribute to the strength and permeability of concrete. The use of electrical resistivity as an indicator of the performance of pozzolans in terms of strength development and chloride penetration resistance when used to partially replace portland cement in concrete is also discussed.

Surface Reactivity and Dissolution Properties of Alumina-Silica Glasses and Fibers.

The ability of bulk glass and fibers to react in aqueous solution, with organic polymers and coupling agents, depends on the surface charge, reactivity, and adsorption properties of the glass surface, i.e. the character and density of surface -OH groups, whereas glass and fiber chemical stability and biosolubility depend on the resistance to dissolution. If glass dissolution products are accumulated in a media, they can change the surface properties by specific adsorption. We determined the -OH surface concentration, reactivity, adsorption, and dissolution properties of aluminosilicate glasses containing various modifiers and compared the results with the behavior of complex mineral wool fibers. Using proton consumption and element release from batch surface titration experiments, over the range 5 < pH < 10, surface -OH adsorption properties were modeled with the FITEQL program. During titration, network modifiers in the glass subsurface are preferentially replaced by protons, resulting in cation accumulation in the solution and formation of a leached layer enriched with Si on the solid. The behavior of Al was different. At 5 < pH < 9, only very small amounts of Al were found in the leachates, which can be explained by almost complete Al adsorption as stable surface complexes, i.e. >XOAl(OH)2 (where X = Si or Al and > represents the surface). At pH > 9, divalent cations adsorbed specifically, as >XOMe+ complexes (Me = Ca or Mg). This deeper understanding of the surface behavior of glasses and fibers is important for the design of composite materials, for applications in biology and medicine and in materials production in general, as well as for understanding natural processes, such as global uptake estimates of CO2 during rock weathering.

The Significant Impact of Carbon Nanotubes on the Electrochemical Reactivity of Mg-Bearing Metallic Glasses with High Compressive Strength.

Here, we elucidate the significant impact of carbon nanotubes (CNTs) on the electrochemical behavior of Mg-based amorphous composite materials that were reinforced with CNTs while using pressure die casting. The addition of 3 vol % CNTs led to an increase in the compressive strength of Mg-based amorphous material from 812 MPa to 1007 MPa, and the fracture strain from 1.91% to 2.67% in the composite. Interestingly, the addition of CNTs significantly contributed to the enhancement of corrosion resistance of Mg-based glass by ~30%. The superior mechanical properties are primarily related to the fact that the addition of CNTs hindered the growth of shear bands (cracks), while the high corrosion resistance is related to inferior wettability and the bridging effect between adherent corrosive oxide film and the matrix that provided enhanced corrosion resistance.

The relationship between local structure and photo-Fenton catalytic ability of glasses and glass-ceramics prepared from Japanese slag

Local structure and the photo-Fenton reactivity of iron-containing glasses and glass-ceramics prepared from Japanese domestic waste slag were investigated. The largest rate constant (k) of (2.8 ± 0.08) × 10−2 min−1 was recorded for the methylene blue degradation test by using H2O2 with a heat-treated ‘model slag’. The 57Fe Mossbauer spectrum was composed of a paramagnetic doublet with isomer shift of 0.18 ± 0.01 mm s−1 attributed to distorted FeIIIO4 tetrahedra. These results indicate that the paramagnetic Fe3+ provided strong photo-Fenton catalytic ability, and that waste slag can thus be recycled as an effective visible-light activated photocatalyst.

Topological Control of Water Reactivity on Glass Surfaces: Evidence of a Chemically Stable Intermediate Phase

Glass surfaces are of considerable interest due to their disproportionately large influence on the performance of glass articles in many applications. However, the behavior of glass surfaces has proven difficult to model and predict due to their complex structure and interactions with the environment. Here, the effects of glass network topology on the surface reactivity of glasses have been investigated using reactive and nonreactive force field-based molecular dynamics simulations as well as density functional theory. A topological constraint-based description for surface reactivity is developed, allowing for improved understanding of the physical and chemical origins of surface reactivity. Results show evidence for the existence of a chemically stable intermediate phase on the surface of the glass where the glass network is mechanically isostatic.

Comparing the reactivity of glasses with their crystalline equivalents: The case study of plagioclase feldspar

Abstract To evaluate the impact of atomic short- and long-range orders on silicate dissolution kinetics, the dissolution of amorphous and crystalline oligoclase was investigated at pH 1.5 and 10 at 90 °C. Experiments in solution saturated with respect to SiO2 am were additionally performed to constrain the effect of Si-rich surface layer formation on dissolution rates. The face-specific dissolution rates of the crystalline oligoclase and of the oligoclase glass were determined from element budget in solution and surface retreat measured by vertical scanning interferometry. The results show that atomic ordering primarily impacts solid reactivity, irrespective to the pH of the solution. A strong relation between the crystal surface orientation, the evolution of its topography and its dissolution rate was observed. The ( 0 0 1 ), ( 0 1 0 ) and ( 1 0 1 ¯ ) flat faces containing the strongest bonds dissolved the most slowly and their dissolution rates remained constant throughout the experiments. In contrast, the stepped ( 1 1 ¯ 1 ) face was characterized by the highest initial dissolution rate, but progressively decreased, suggesting that the preferential dissolution of stepped sites expose afterwards more stable planes. The differences in terms of etch pit density from one surface to another also explained the difference in dissolution rates for the ( 0 0 1 ) and ( 0 1 0 ) faces. The fluid chemistry suggested the formation of very thin (100–200 nm) Si-rich surface layers in acidic conditions, which weakly affected the dissolution rate of the pristine crystal. At pH 1.5, oligoclase glass dissolves at a rate similar to that of the fastest studied faces of the crystal, suggesting the absence of structural effect on oligoclase dissolution. Whereas Si-rich surface layers likely formed by interfacial dissolution-reprecipitation for oligoclase crystal, molecular dynamic calculations suggest that the slightly more open structure of the glass could also allow ion-exchange following water diffusion into the solid. This mechanism could explain why the surface layer of the glass is characterized by a different chemical composition. Results at pH 10 are strikingly different, as the oligoclase glass dissolves up to 20 times faster than its crystalline equivalent. This non-linear response of the material upon pH was linked to the density of critical bonds in oligoclase that is indeed pH-dependent. In acidic pH, the preferential dissolution of Al leaves a highly polymerized and relaxed Si-rich surface, whereas in basic pH the preferential dissolution of Si leads to a complete destructuration of the network because of the lack of Si O Al bonds.

Structure and reactivity of synthetic CaO-Al2O3-SiO2 glasses

Reactivity of glasses is predominantly linked to the degree of depolymerization of the glass structure. In this work, eight calcium aluminosilicate glasses were synthesized with compositions reflecting the glassy phases of industrial fly ashes and slags. The chosen composition ranges allow for isolation and identification of the roles of Ca and Al. The reactivity of the glasses is found to be mainly dependent on the CaO content as calcium depolymerizes the glass structure and increases the rate of reaction of the glasses. The effect of Al2O3 on glass reactivity is less pronounced and relies on chemical weakening of the glass structure. However, an increasing alumina content has a pronounced effect on the hydrate phase assemblage, bound water content, portlandite consumption and the heat of reaction. The resulting compressive strength of composite cement mortars incorporating the synthesized CaO-Al2O3-SiO2 glasses is found to be a function of both the degree of glass reaction and the actual phase assemblage.

Deciphering the atomic genome of glasses by topological constraint theory and molecular dynamics: A review

From telescope lenses to optical fibers and smartphone screens, glasses have been key enablers in human history. Unlike crystalline materials, glasses can virtually feature any composition and stoichiometry, which creates limitless opportunities to develop new glass formulations with unusual properties. However, this large compositional space renders traditional Edisonian trial-and-error discovery approaches poorly efficient. Accelerating the discovery of new glasses requires the genome of glass to be decoded, that is, to identify and decipher how the basic structural building blocks of glasses control their engineering properties—in the same way as the human genome offers information that serves as a blueprint for an individual’s growth and development. Here, we review some of our recent effort in that direction. Our approach combines molecular dynamics simulations with topological constraint theory—a simple, yet powerful framework that can be used to predict the compositional dependence of glass properties or pinpoint promising compositions with tailored functionalities. In this review, we report how we used this approach to understand the origin of glass-forming ability as a balance between atomic flexibility and internal stress, predict the mechanical properties of glasses, and tune the chemical reactivity of silicate glasses.