Silicate Network Research Articles

Dissolution of silica component of glass network at early stage of corrosion in initially silica‐saturated solution

AbstractCorrosion of glass in silica‐saturated solution has been performed with the assumption that dissolution of silicate species from the glass network would not occur. Using surface‐sensitive analytical techniques, we report experimental evidence suggesting the dissolution of silicate network species from a model nuclear waste glass, called international simple glass (ISG), in an aqueous solution initially saturated with soluble silica species. Results from low energy ion scattering and X‐ray photoelectron spectroscopy reveal a complete depletion of mobile element species (B, Na) from the ISG surface and an enrichment of Zr on the outmost surface. In support of spectroscopic analyses, results from topographic imaging with atomic force microscopy show a stochastic dissolution of glass surface resulting in a higher surface roughness with increasing corrosion time in aqueous solution. This study shows that a true equilibrium between soluble silica species in the solution phase and silicate species in the glass network could not be warranted by performing corrosion experiments in the solution where dissolved silica species are initially equilibrated with amorphous silica in the presence of KOH. The leaching of mobile species (B, Na) could affect the saturation level of aqueous solution and induce further dissolution of the glass surface.

Structural characterization of bioactive glasses containing rare earth elements (Gd and/or Yb)

Rare earth-containing bioactive glasses are promising materials for biomedical applications like brachytherapy, luminescence-based imaging, magnetic resonance imaging, among others, due to the electronic configuration of rare earth. Although studies of such glasses have continuously been increasing, they still have been poorly studied as biomaterials. In this work, we studied the influence of gadolinium and ytterbium on the structure of bioactive glasses and iron-based bioactive glasses. The glasses were obtained by melt quenching, and their structures were characterized by X-ray diffraction, nuclear magnetic resonance, X-ray photoelectron spectroscopy, electron paramagnetic resonance and scanning electron microscopy. The results showed that the addition of rare earth elements in the glass structure creates more non-bridging oxygen bonds in the silicate network, to satisfy the condition of octahedral coordination of the rare earth ions. An observed Q3 → Q2 + Q1 depolymerization of the glass network is a factor that could favor bioactivity. In conclusion, our experimental data address the bioactive behavior of rare earth-containing glasses to an increased concentration of non-bridging oxygen bonds and a more fragmented network.

Alkali-activation of CaO-FeOx-SiO2 slag: Formation mechanism from in-situ X-ray total scattering

The pursuit of low-CO2 technologies has led to a surge in research on alternative cementitious materials, of which alkali-activated materials are a large family. In recent years alkali-activated materials have expanded to encompass Fe-rich precursors in addition to the more commonly employed aluminosilicate precursors. The formation mechanism of alkali-activated materials from two Fe-rich synthetic slags has been assessed by employing in-situ X-ray total scattering and subsequent pair distribution function analysis. The evolution of the local atom-atom correlations reveals three reaction stages. After the dissolution of Fe-silicate clusters from the slag, a binder phase is formed with Fe in both Fe2+ and Fe3+ oxidation states. The Fe2+ state is present in the form of trioctahedral layers, similar to those in Fe(OH)2, while the Fe3+ is likely located in the polymerized silicate network. Exposure to air causes the Fe2+ species to transition to the Fe3+ state.

Preparation of mesoporous silica by the rapid gelation of Na2SiO3 and H2SiF6 in aqueous surfactant solution

Abstract Microporous and mesoporous materials are used as catalyst carriers, adsorbents, and ion exchangers. In this study, mesoporous molecular sieves were prepared through the rapid reaction of Na2SiO3 and H2SiF6 in a water solution containing surfactants. Mesoporous silica (MS) precipitates were produced within 5 s and X-ray diffraction (XRD) analysis of the MS samples indicated the formation of mesoporous molecular sieves owing to the appearance of well-defined peaks at intervals of 3.8–5.2 nm. The specific surface area was 371 m2 g−1 when using a cationic surfactant and in the range of 959–1135 m2 g−1 in nonionic surfactants. The pore-size distribution of MS samples showed a constant value of 2.5–3.1 nm. The shape of the silica particles observed via scanning electron microscopy was spherical with a uniform size of ∼0.7 μm. Transmission electron microscopy images of the samples obtained using the nonionic surfactant showed worm-hole-shaped pores, whereas those obtained using the cationic surfactant had regular honeycomb-shaped pores. MS samples synthesized using nonionic surfactants were thermally very stable in the light of their XRD peaks being maintained at 900 °C. The intensity of Q3 and Q4 signals for the MS obtained by nonionic surfactant is double than that of cationic surfactant, proving that silicate network of MS-PL15 is lots thicker than that of MS-CTAB. MS synthesized by nonionic surfactant can be used as a catalyst support at high temperatures because they has a large specific surface area and excellent thermal stability.

The Effect of Heavy Ion Irradiation on the Forward Dissolution Rate of Borosilicate Glasses Studied in Situ and Real Time by Fluid-Cell Raman Spectroscopy.

Borosilicate glasses are the favored material for immobilization of high-level nuclear waste (HLW) from the reprocessing of spent fuel used in nuclear power plants. To assess the long-term stability of nuclear waste glasses, it is crucial to understand how self-irradiation affects the structural state of the glass and influences its dissolution behavior. In this study, we focus on the effect of heavy ion irradiation on the forward dissolution rate of a non-radioactive ternary borosilicate glass. To create extended radiation defects, the glass was subjected to heavy ion irradiation using 197Au ions that penetrated ~50 µm deep into the glass. The structural damage was characterized by Raman spectroscopy, revealing a significant depolymerization of the silicate and borate network in the irradiated glass and a reduction of the average boron coordination number. Real time, in situ fluid-cell Raman spectroscopic corrosion experiments were performed with the irradiated glass in a silica-undersaturated, 0.5 M NaHCO3 solution at temperatures between 80 and 85 °C (initial pH = 7.1). The time- and space-resolved in situ Raman data revealed a 3.7 ± 0.5 times increased forward dissolution rate for the irradiated glass compared to the non-irradiated glass, demonstrating a significant impact of irradiation-induced structural damage on the dissolution kinetics.

Difference in radiation effects of sodium borosilicate glass and vitreous silica with ions

Borosilicate glass is used to vitrify high-level radioactive waste. Radiation effects on borosilicate glass have been studied extensively. Sodium borosilicate glass samples with compositions of 67.3% SiO2, 16.7% B2O3 and 16% Na2O in molar percent and vitreous silica were irradiated with multi-energy and single-energy Xe ions. After irradiation, hardness and modulus of both materials were accessed by nanoindentation. Volume change in two materials was evaluated using AFM. The hardness, modulus and volume change of both sodium borosilicate glass and vitreous silica varied fast and then saturated with the dose. The trends of both modulus and volume change with the dose for sodium borosilicate glass were respectively opposite to those for vitreous silica. The relative hardness variation of sodium borosilicate glass was −35%, and that of vitreous silica was about −10%. Difference in radiation effects between the sodium borosilicate glass and vitreous silica suggested that hardness decrease in sodium borosilicate glass irradiated with ion might be induced not only by transformation of silicate network but also by the transformation of boron network.

ToF-SIMS depth profiling of altered glass

Glass and mineral corrosion usually leads to the formation of morphologically and compositionally complex surface layers that can be characterized by various analytical techniques to infer rate control mechanisms. In this study, we investigate the capabilities and limitations of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to better understand chemical processes of glass corrosion. In particular, we focus on the potential impact of the ToF-SIMS ion beam on the distribution of several elements of interest in alteration layers formed on International Simple Glass, a six-oxide reference glass altered in a solution enriched in alkalis and spiked with H218O. A thin flake of glass partially altered on both sides is analyzed entirely from one side to the other to determine whether atoms weakly bonded to the solid are displaced by the beams. We highlight the beam effect on cations weakly bonded to the silicate network (Li, Na, K, and B, Ca, Cs to a lesser extent) affecting the profile shape of these elements. No impact is observed on 18O and H, but it is demonstrated that quantification of isotopic ratios is possible only for a limited range of isotopic enrichment.

Photoluminescence of Amorphous SiO2 with Implanted Ar+ Ions

Implantation of ions into amorphous silicon dioxide (a-SiO2) is widely used in microelectronics (mainly, using Si ions) and in the production of light-guiding components of optical fibers (Ge, P, B ions). All of these elements interact with the matrix oxygen, so the point defects that occur during implantation are not only the result of the displacement of the silicon–oxygen frame atoms from their equilibrium positions, but also reflect the specific chemical interaction in the material. In this study, inert argon ions were implanted into silicon dioxide plates, which excluded chemical reactions. It is demonstrated using photoluminescence (PL) that the highest concentration of point defects in the damaged silicate network belongs to neutral oxygen vacancies (NOVs). The concentration of these and some other induced defects increased with an increase in fluence up to 5 × 1015 Ar+/cm2, and, with a further increase in dose, the concentration dropped due to annealing of defects in the layer heated by the introduction of ions. The NOV defects appeared in the photoluminescence spectrum in the form of doublets, that is, pairs of bands belonging to the same optical transition. The appearance of doublets is explained by the dependence of the optical transition energy on the localization of identical point defects in zones of different distortions of the matrix structure.

Transformation of Vanadium-Bearing Titanomagnetite Concentrate in Additive-Free Roasting and Alkaline-Pressure Leaching for Extracting Vanadium (V)

With a view to satisfying the requirements of environmental protest and efficient usage of resources, a novel process for efficiently extracting vanadium (V), titanium (Ti), and iron (Fe) from vanadium-bearing titanomagnetite concentrate was developed. In the new process, vanadium is pre-extracted by additive-free roasting under the air atmosphere and alkaline leaching technologies. In this paper, transformation of vanadium-bearing titanomagnetite concentrate in the roasting is investigated based on thermodynamic analyses and experimental discussion. Thermodynamic analyses show that oxidation of V(III) into V(V) would happen in the roasting experiment over the range of 327–1327 °C and vanadium-iron spinel phase (FeV2O4) can be oxidized more easily than magnetite (Fe3O4) when the temperature is higher than 861 °C. Experimental results show that some compounds (V2O5, Fe2Al4Si5O18, and Fe2SiO4) with low melting temperature were obtained by solid reactions at low temperature and melted as a binding phase at elevated temperature. Liquids were generated due to some chemical reactions or phase transformation reaction (Fe2V2O4(s) → Fe2O3(s) + liquid) at elevated temperature. Main phases of Fe2O3 and Fe2TiO5 are connected and sintered with the binding phases of the compounds with low melting temperature or the mixtures with low liquidus temperature. In addition, higher roasting temperature leads to higher vanadium leaching efficiency over the range of 800–1200 °C. However, over-burning would happen at 1250 °C, some of vanadium oxide was wrapped by silicate network, and the conversion of V(III) into V(V) was prevented from occurring. Therefore, the vanadium leaching efficiency decreased from 59.1% (Troa. = 1200 °C) to 57% (Troa. = 1250 °C).

Effect of Calcium Precursor on the Bioactivity and Biocompatibility of Sol-Gel-Derived Glasses.

This study investigated the impact of different calcium reagents on the morphology, composition, bioactivity and biocompatibility of two-component (CaO-SiO2) glasses produced by the Stöber process with respect to their potential application in guided tissue regeneration (GTR) membranes for periodontal repair. The properties of the binary glasses were compared with those of pure silica Stöber particles. The direct addition of calcium chloride (CC), calcium nitrate (CN), calcium methoxide (CM) or calcium ethoxide (CE) at 5 mol % with respect to tetraethyl orthosilicate in the reagent mixture gave rise to textured, micron-sized aggregates rather than monodispersed ~500 nm spheres obtained from the pure silica Stöber synthesis. The broadening of the Si-O-Si band at ~1100 cm−1 in the infrared spectra of the calcium-doped glasses indicated that the silicate network was depolymerised by the incorporation of Ca2+ ions and energy dispersive X-ray analysis revealed that, in all cases, the Ca:Si ratios were significantly lower than the nominal value of 0.05. The distribution of Ca2+ ions was also found to be highly inhomogeneous in the methoxide-derived glass. All samples released soluble silica species on exposure to simulated body fluid, although only calcium-doped glasses exhibited in vitro bioactivity via the formation of hydroxyapatite. The biocompatibilities of model chitosan-glass GTR membranes were assessed using human MG63 osteosarcoma cells and were found to be of the order: CN < pure silica ≈ CC << CM ≈ CE. Calcium nitrate is the most commonly reported precursor for the sol-gel synthesis of bioactive glasses; however, the incomplete removal of nitrate ions during washing compromised the cytocompatibility of the resulting glass. The superior bioactivity and biocompatibility of the alkoxide-derived glasses is attributed to their ease of dissolution and lack of residual toxic anions. Overall, calcium ethoxide was found to be the preferred precursor with respect to extent of calcium-incorporation, homogeneity, bioactivity and biocompatibility.

Viscosity‐structure relationship of alkaline earth silicate melts containing manganese oxide and calcium fluoride

AbstractThe effect of CaF2 on the viscosities of the MO‐SiO2‐xMnO‐yCaF2 melts (M[=Ca or Ba]O/SiO2 = 0.4‐0.5, x = 10[±1] or 40[±2] mol%, y = 0‐15 mol%) have been studied at high temperatures. At MnO = 40[±2] mol%, the viscosity of Ba‐Mn‐silicate melts is lower than that of Ca‐Mn‐silicate melts because Mn2+ is a strong network modifier in the former system. However, the viscosities of both alkaline earth silicate melts with MnO = 10[±1] mol% are not affected by cation type because MnO activity is too low to affect the viscosity of the melts. The CaF2 addition decreases the viscosities of the Ba‐Mn‐silicate melts with low‐MnO contents, while it has less impact on the viscosities of the melts with high‐MnO contents. The effect of CaF2 on the relationship between viscosity and the structure of the silicate melts is quantitatively analyzed using the micro‐Raman spectra of quenched glass samples. The NBO/Si ratio of alkaline earth silicate melts, which indicates the degree of polymerization of the silicate networks, has a linear relationship with the activation energy for the viscous flow of the melts.

Quantification of boron in aluminoborosilicate glasses using Raman and 11B NMR

Bulk methods and 11B Nuclear Magnetic Resonance were used to propose a calibration curve to determine the total B2O3 and the boron speciation using the non-destructive and the non-quantitative nature of Raman spectroscopy. The calibration was established from the analyses of 21 aluminoborosilicate glasses synthesised at 1 atm. and 1150 °C and an additional standard aluminoborosilicate glass. The studied glasses have composition in the Na2O-CaO-Al2O3-SiO2-B2O3 system with total B2O3 from 4.7 to 46.6 mol%.Raman spectra exhibit signatures in the 800–1200 and 1200–1600 cm−1 region corresponding to the symmetric stretches of silicate (HF) and borate networks (BO), respectively. The integrated area ratio (AB-O−/AHF) is correlated to the total mol.% B2O3. The mol.% B2O3 data are reproduced within 15% from the Raman spectra.Boron speciation from 11B NMR is correlated to the AB-O−/AHF determined by Raman; however, the mol.% BO4 appears also dependent on the Al2O3 content. We derived a multiple linear regression estimating the mol.% BO4 as a function of AB-O−/AHF and mol.% Al2O3. Results are valid for the investigated glasses and additional work is needed to better constrain the speciation model.

Design of Refining Slag Based on Raman and NMR Spectroscopy Study for Removing Phosphorus for SoG-Si

In present study, Nuclear magnetic resonance (NMR), Raman vibrational spectroscopy were used to investigate in detail the behavior and state of phosphorus (P) in a system SiO2–CaO–Na2O–P2O5 slag. The role of the degree of P–Silicon (Si) cross linking on the P removal from silicon using slag treatment was highlighted by comparing the dephosphorization data. The results show that adding Na2O into acidity slag (CaO/SiO2 = 0.5) from 0 to 30 wt% results in the first increase and then decrease of the removal ratio of P from silicon. When Na2O content is near 15 wt%, the removal ratio of P is above 60%. P2O5 oxidized of P from silicon can be incorporated into the silicate network through P–BO–Si bonds and be stabilized in slag in the form of Q3 (Si and P) species. The removal ratio of P presents a same trend as the relative amount of P–BO–Si bonds and Q3 (Si and P) species, demonstrating fixing P in slag could promote the P removal. Q2 (Si) species of the silicate network as primary intermediate structure could capture P to form Q3 (Si and P) species. When Na2O is less than 15 wt%, Q3 (Si and P) species is promoted to be formed by increasing Na2O, Conversely, it will be depolymerized as Na2O is added to more than 15 wt% to release P by the preferred break of P–BO–Si bonds.

Effect of soluble Cr2O3 on the silicate network, crystallization kinetics, mineral phase, microstructure of CaO-MgO-SiO2-(Na2O) glass ceramics with different CaO/MgO ratio

Cr2O3 is often used as a glass additive to prepare glass ceramics. Chromium element exists mainly in two parts in the glass ceramics: chromium-containing spinel and soluble chromium in glass matrix. Herein, effect of soluble chromium on the CaO-MgO-SiO2-(Na2O) glass system is researched. Glass and glass ceramics were characterized by Raman spectrum, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry. It is found that the addition of Cr2O3 increased the Q2si structure unit in glass networks, especially in glass systems with high MgO content. The crystallization temperatures of the systems were increased with the addition of Cr2O3. Soluble chromium reduced the crystallization activation energy of the glass system slightly, but did not alter its crystallization behavior (surface crystallization). With the increase of MgO content, the mineral phases of the glass ceramics gradually changed from wollastonite to diopside. Cr2O3 reduced the lattice parameters of the mineral phases. The addition of Cr2O3 has a significant effect on grain refinement and structural compactness of the glass ceramics system with high MgO content.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Eu3+ Luminescence in High Charge Mica: An In Situ Probe for the Encapsulation of Radioactive Waste in Geological Repositories.

Isolation of high-level radioactive waste (HLW) in deep geological repositories (DGR) through a multibarrier concept is the most accepted approach to ensure long-term safety. Clay minerals are one of the most promising materials to be used as engineered barriers. In particular, high charge micas, as components of the engineered barrier, show superselectivity for some radioactive isotopes and a large adsorption capacity, which is almost twice that of the other low charge aluminosilicates. In addition, high charge micas are optimum candidates for decontamination of nuclear waste through two different mechanisms; namely an ion exchange reaction and a nonreversible mechanism involving the formation of new stable crystalline phases under hydrothermal conditions. In this work, we report a new in situ optical sensor based on the incorporation of Eu3+ in these high charge micas for tracking the long-term physical-chemical behavior of HLW contaminants in DRG under mild hydrothermal conditions. The incorporation of Eu3+ into the interlayer space of the mica originates a well resolved green and red luminescence, from both the 5D1 and 5D0 excited states, respectively. The formation of new crystalline phases under hydrothermal conditions involves important changes in the Eu3+ emission spectra and lifetime. The most interesting features of Eu3+ luminescence to be used as an optical sensor are (1) the presence or absence of the Eu3+ green emission from the 5D1 excited state, (2) the energy shift of the 5D0 → 7F0 transition, (3) the crystal-field splitting of the 7F1 Eu3+ level, and (4) the observed luminescence lifetimes, which are directly related to the interaction mechanisms between the lanthanide ions and the silicate network.

Magnesium substitution in calcium and strontium fluoro-phospho-aluminosilicate glasses by multinuclear 19F, 31P, 27Al, and 29Si MAS-NMR spectroscopy

Abstract Two series of glasses were produced by systematically substituting magnesium for calcium and strontium in the glass compositions, 4.5SiO2. 3Al2O3. 1.5P2O5. (3-x)CaO/SrO. xMgO. (2-y)CaF2/SrF2. yMgF2, 0 ≥ x ≥ 3, 0 ≥ y ≥ 2 and these glasses were characterised by 19F, 31P, 27Al, and 29Si MAS-NMR spectroscopy. The substitution of magnesium for calcium and strontium resulted in the gradual formation of F-Mg(n) species over the F-Ca(n) and F-Sr(n) with additional loss of Al F species. The 31P and 27Al MAS-NMR spectra showed the presence of Al-O-PO33− species charge balanced by a mixture of Ca2+ and Mg2+ or Sr2+ and Mg2+. In addition to that, the 31P MAS-NMR spectrum of the fully magnesium substituted glass showed the presence of amorphous magnesium pyrophosphate, Mg2P2O7. Al(IV) was the major Al species with small amount of Al(V) and Al(VI), but the amount of Al(V) increased with increase in magnesium substitution. Moreover, the fully magnesium substituted fluoro-phospho-aluminosilicate glass resulted in the more polymerised silicate network with increased number of the bridging oxygen on SiO4 tetrahedra.

Viscosity and related structure transformation of fluorine bearing silicate melt under ultrasonic field

The fluorine bearing and free silicate melts of Na2O-K2O-SiO2-CaF2 system were treated under ultrasonic field, and the melt structure and viscosity were measured. The results showed that the fluorine bearing silicate melt can be depolymerized and the polymerization decreased with the ultrasonic intensity. The viscosity of the fluorine bearing silicate melt decreased more quickly to the dynamic balance point between the dissociation and reconnection of the species, and reverted more slowly to the natural state than the fluorine free silicate melt, because fluorine ions join the silicate network via the formation of new Si-F bonds. The formation of SiF bonds can intensify the reduction of the viscosity, but the consumption of fluorine ions may lead to an increasing of the viscosity, which resulted in the weak decreasing trend in the viscosity as the ultrasonic intensity increased. The method may be helpful in assisting the synthesis of fluorine bearing bioactive glass.

Insight into the atomic scale structure of CaF2-CaO-SiO2 glasses using a combination of neutron diffraction, 29Si solid state NMR, high energy X-ray diffraction, FTIR, and XPS

Abstract Bioactive glasses are important for biomedical and dental applications. The controlled release of key ions, which elicit favourable biological responses, is known to be the first key step in the bioactivity of these materials. Properties such as bioactivity and solubility can be tailored for specific applications. The addition of fluoride ions is particularly interesting for dental applications as it promotes the formation of fluoro-apatite. To date there have been mixed reports in the literature on how fluorine is structurally incorporated into bioactive glasses. To optimize the design and subsequent bioactivity of these glasses, it is important to understand the connections between the glass composition, structure and relevant macroscopic properties such as apatite formation and glass degradation in aqueous media. Using neutron diffraction, high energy X-ray diffraction, 29Si NMR, FTIR and XPS we have investigated the atomic scale structure of mixed calcium oxide / calcium fluoride silicate based bioactive glasses. No evidence of direct Si-F bonding was observed, instead fluorine was found to bond directly to calcium resulting in mixed oxygen/fluoride polyhedra. It was therefore concluded that the addition of fluorine does not depolymerise the silicate network and that the widely used network connectivity models are valid in these oxyfluoride systems.

Фотолюминесценция аморфного SiO-=SUB=-2-=/SUB=-, подвергнутого имплантации ионов Ar-=SUP=-+-=/SUP=-

AbstractImplantation of ions into amorphous silicon dioxide ( a -SiO_2) is widely used in microelectronics (mainly, using Si ions) and in the production of light-guiding components of optical fibers (Ge, P, B ions). All of these elements interact with the matrix oxygen, so the point defects that occur during implantation are not only the result of the displacement of the silicon–oxygen frame atoms from their equilibrium positions, but also reflect the specific chemical interaction in the material. In this study, inert argon ions were implanted into silicon dioxide plates, which excluded chemical reactions. It is demonstrated using photoluminescence (PL) that the highest concentration of point defects in the damaged silicate network belongs to neutral oxygen vacancies (NOVs). The concentration of these and some other induced defects increased with an increase in fluence up to 5 × 10^15 Ar^+/cm^2, and, with a further increase in dose, the concentration dropped due to annealing of defects in the layer heated by the introduction of ions. The NOV defects appeared in the photoluminescence spectrum in the form of doublets, that is, pairs of bands belonging to the same optical transition. The appearance of doublets is explained by the dependence of the optical transition energy on the localization of identical point defects in zones of different distortions of the matrix structure.