Initial Dissolution Rate of the International Simple Glass as a Function of pH and Temperature Measured Using Microchannel Flow-Through Test Method

International simple glass (ISG) is a six-component alumino-borosilicate glass developed as a reference benchmark glass for six nations collaborating study on high-level nuclear waste glass dissolution/corrosion mechanism. In this study, aqueous dissolution tests were performed for the ISG using microchannel flow-through (MCFT) method to evaluate the initial dissolution rate of glass matrix, r₀, precisely and systematically as a function of solution pH and temperature. The test results indicated that the r₀ shows a “V-shaped” pH dependence with a bottom at around pH4 at each temperature. Compared with Japanese reference glass of P0798, for which the r₀ showed a “U-shaped” pH dependence with a bottom at around pH6 in our previous study, the ISG shows the higher dissolution rate at basic pH, and lower dissolution rate at neutral to acidic pH. The results also indicated that the r₀ increases with temperature according to an Arrhenius law, and the apparent activation energy evaluated from Arrhenius relation is 62–77 [kJ/mol] at any pH from 3 to 10, which suggests the initial dissolution of ISG proceeds controlled by a surface-reaction mechanism in this pH range.     

The dissolution behavior in alkaline solutions of a borosilicate glass with and without P2O5

There are a variety of applications for glasses in alkaline environments, including glass fibers and glass‐coated steel to reinforce concrete structures. To understand how a simple glass reacts in such environments, the dissolution behavior of a 25Na₂O–25B₂O₃–50SiO₂ (mol%) glass, doped with and without 3 mol% P₂O₅, in pH 12 KOH and pH 12 KOH saturated with Ca²⁺ ions was studied. Ca²⁺ ions in the solution significantly reduce the glass dissolution rate by forming a passivating calcium silicate hydrate (C–S–H) gel layer on the glass surface. When these corroded glasses were then exposed to Ca‐free KOH, the C–S–H layer redissolves into the undersaturated solution and the glass dissolution rate increases. For phosphate‐doped borosilicate glass, PO₄^3? units released from the dissolving glass react with Ca²⁺ ions in saturated solutions to form crystalline hydroxylapatite on the glass surface, but this layer does not protect the glass from corrosion as well as the C–S–H does. The nature of the C–S–H layer was characterized by Raman spectroscopy, which reveals a gel layer constituted mainly of silicate anions.     

Fracture behaviour of ceramic–metallic glass gradient transition coating

A new composite coating material of ceramic (Al₂O₃-40?wt% TiO₂)–metallic glass (Fe₅₆Cr₂₃Mo₁₃B₈) gradient transition coating was successfully prepared by atmospheric plasma spraying technology, and a new theory of laminar–columnar structure gradient transition synergistic enhancement effect was proposed. The microstructure and element distribution of the composite coating were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA). The fracture toughness and fracture behaviour of the composite coating were analysed via micro-hardness and three-point bending (3PB) tests. The results showed that the stress release of the ceramic–metallic glass gradient transition coating was stable compared with that of the conventional gradient coating in the stage of acute deformation, and the coating exhibited better fracture toughness. Different areas of the ceramic–metallic glass gradient transition coating exhibited different fracture behaviours. Additionally, the ceramic layer was made of columnar crystals, and the metal–glass layer was lamellar. The laminar–columnar structure gradient transition synergistic enhancement effect improved the anti-crack growth and fracture toughness. This study provides a new and viable option for the improvement of thermal spraying ceramic composite coatings.     

Effect of calcium on dissolution and precipitation reactions of amorphous silica at high alkalinity

A better understanding of silica dissolution–precipitation reactions at high pH aqueous solutions allows for promotion of favorable (e.g., pozzolanic) reactions and mitigation of deleterious (e.g., alkali-silica) reactions in concrete. In this paper, the kinetics and products of silica glass dissolution are studied as a function of solution pH, temperature, and availability of calcium. It was observed that dissolution rate versus time increases linearly with pH and reaches a maximum at pH = 14, with slower dissolution at higher alkalinities. In solutions with similarly high pH, but saturated with portlandite, glass dissolution is significantly slower. This is due to formation of a dense, low porosity, and strongly bonded C–S–H layer on the surface of glass, which serves as a barrier against diffusion of OH⁻ and alkali ions towards the substrate glass. This protective layer forms only when Ca is abundant and portlandite saturation can be maintained on a local scale.     

Glass forming region and bonding mechanism of low-melting V2O5–TeO2–Bi2O3 glass applied in vacuum glazing sealing

As a new kind of energy-saving glass, vacuum glazing has excellent thermal and sound insulation properties and is widely used in building, household appliances and solar photovoltaic. The edge sealing material, along with sealing method, is key to the fabrication of vacuum glazing. Low transition temperature (T_g) and good fluidity at sealing temperature (T_s) make low-melting glass of V₂O₅–TeO₂–Bi₂O₃ (VTB) system perfect to be the edge sealing material for vacuum glazing. The glass forming region of VTB ternary system was mapped for the first time in this work. Low-melting VTB glass of 40V₂O₅–50TeO₂–5Bi₂O₃–3ZnO–2Na₂O (wt%) was optimized to be the sealing material. Glass powder of this composition could be used to seal the edges of vacuum glazing at an extremely low temperature of 360°C. With the assistance of anodic-bonding method, the bonding strength of vacuum glazing was dramatically enhanced. Vacuum glazing fabricated under the optimized process parameters of 420°C, 600 V, and 60 min possesses a highest bonding strength of 4.31 MPa. Furthermore, anodic-bonding mechanism of low-melting VTB glass applied in vacuum glazing sealing has been thoroughly researched.     

Corrosion and Infrared Study of Some γ-Irradiated Lead-Phosphate Glasses Doped with MoO3

In this study we compared the effect of three different concentrations of MoO₃ on the corrosion of sodium phosphate glass containing lead and aluminum oxides to develop its durability. The corrosion was studied in deionized water and acidic solution of 0.1 N HCl. The dissolution mechanism is interpreted depending on the glass weight loss versus time and change in the glass surface. MoO₃ had a stabilizing effect on the glass, causing a decrease in the glass dissolution rate. Acidic medium was found to strongly enhance the glass dissolution. The pH decrease in water with increase in acidic solution gives evidence of the release of some phosphorous ions to form phosphoric acid. The consequent enhancement of the glass durability was influenced by the presence of MoO₃ and showed a remarkable advance by doping with 3 wt% of MoO₃. FT-infrared absorption spectra of the studied glasses show IR vibrational bands due to phosphate groups mainly of the metaphosphate and pyrophosphate units together with the sharing and interference of IR vibrations due to Pb–O bonds. Gamma irradiation produces a minor effect on the IR spectra, and enhances the base glass durability at the beginning of the corrosion process, which can be related to the shielding behavior of the high lead glass. However, glass containing 3% MoO₃ has the best durability and is the least affected by irradiation. The glass durability corresponding to its structure is verified by IR spectroscopy.

     

Effect of surface properties of MgO on its dissolution and spinel growth in CaO–SiO2–Al2O3 slag

The dissolution behavior of MgO in CaO–SiO₂–Al₂O₃ ternary slag at the interface of single-crystal, dense poly-crystal, and porous poly-crystal MgO was investigated to evaluate the effect of the surface properties of the MgO. The experimental results revealed that a detached spinel layer formed at the MgO interface due to the change in thermodynamic condition of the slag, which was independent of the surface properties. On the other hand, it was also confirmed that the growth rate and morphology of the detached spinel layer strongly depended on the surface properties, such as porosity and curvature of MgO. During the formation of the spinel layer at the interface during MgO dissolution, a kinetic approach adopting parabolic relation theory was employed to determine the correlation between the surface properties and the spinel growth mechanism.     

The Effect of Ultrasound on the Dissolution of Pyrite Ores in Acidic and Fe2(SO4)3 Solutions

This paper deals with the investigation of the effect of ultrasonic energy on the dissolution of pyrite ores in acidic and Fe₂(SO₄)₃ solution. In the effect of ultrasound on the dissolution at various temperatures was experimentally investigated, while keeping the particle size and the solution concentration constant. The same experimental runs, without using ultrasound, were performed and the results were compared. According to these results, it was observed that ultrasound increased the conversion fraction by approximately 30 % compared with the experimental results without ultrasound.     

Structural impact of nitrogen incorporation on properties of alkali germanophosphate glasses

The structure, atomic packing density, calorimetric glass transition, and hardness of mixed sodium–lithium germanophosphate oxynitride glasses with varying Ge/P and N/P ratios were investigated. The combined influences of nitridation and mixed network former effect (MNFE) on the glass structure were analyzed using Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and ³¹P nuclear magnetic resonance (NMR) spectroscopy. Evidence for the existence of germanium in a higher coordination state, i.e., five‐ or sixfold coordination, was obtained by performing XPS analysis of the oxide glasses, with indication of conversion to tetrahedral coordination upon nitridation. Raman spectroscopy measurements implied that the germanate network was modified upon nitridation, including the removal of ring‐like germanate structures and P–O–Ge mixed linkages. The partial anionic N‐for‐O substitution gave rise to the linear dependence of the glass transition temperature (T_g) and hardness (H_V) on nitrogen content (expressed as N/P ratio), especially for lower Ge/P ratio. However, nitridation also caused an unexpected increase in liquid fragility and decrease in density. This suggests that the governing structural parameter for property evolution in such LiNaGePON glasses is not only the increased degree of cross‐linking of the phosphate chains, but rather the short‐ and intermediate‐range structural modifications within the germanate component of the oxynitride glasses.     

Dissolution of Plutonium Metal Using Nitric Acid Solutions Containing Potassium Fluoride

Abstract

The deinventory and deactivation of the Department of Energy's (DOE's) FB-Line facility at the Savannah River Site (SRS) required the disposition of approximately 2000 items from the facility's vaults. Plutonium (Pu) scraps and residues which do not meet criteria for conversion to a mixed oxide fuel will be dissolved and the solution stored for subsequent disposition. Some of the items scheduled for dissolution are composite materials containing Pu and tantalum (Ta) metals. The preferred approach for handling this material is to dissolve the Pu metal, rinse the Ta metal with water to remove residual acid, and burn the Ta metal. The use of a 4 M nitric acid (HNO₃) solution containing 0.2 M potassium fluoride (KF) was initially recommended for the dissolution of approximately 500 g of Pu metal. However, prior to the use of the flowsheet in the SRS facility, a new processing plan was proposed in which the feed to the dissolver could contain up to 1250 g of Pu metal. To evaluate the use of a larger batch size and subsequent issues associated with the precipitation of plutonium-containing solids from the dissolving solution, scaled experiments were performed using Pu metal and samples of the composite material.

In the initial experiment, incomplete dissolution of a Pu metal sample demonstrated that a 1250 g batch size was not feasible in the HB-Line dissolver. Approximately 45% of the Pu was solubilized in 4 h. The remaining Pu metal was converted to plutonium oxide (PuO₂). Based on this work, the dissolution of 500 g of Pu metal using a 4–6 h cycle time was recommended for the HB-Line facility. Three dissolution experiments were subsequently performed using samples of the Pu/Ta composite material to demonstrate conditions which reduced the risk of precipitating a double fluoride salt containing Pu and K from the dissolving solution. In these experiments, the KF concentration was reduced from 0.2 M to either 0.15 or 0.175 M. With the use of 4 M HNO₃ and a reduction in the KF concentration to 0.175 M, the dissolution of 300 g of Pu metal is expected to be essentially complete in 6 h. The dissolution of larger batch sizes would result in the formation of PuO₂ solids. Incomplete dissolution of the PuO₂ formed from the metal is not a solubility limitation, but can be attributed to a combination of reduced acidity and complexation of fluoride which slows the dissolution kinetics and effectively limits the mass of Pu dissolved.     

Characteristics of poly(vinyl pyrrolidone)/poly(acrylic acid) interpolymer complex prepared by template polymerization of acrylic acid: Effect of reaction solvent and molecular weight of template

Poly(vinyl pyrrolidone) (PVP)/poly(acrylic acid) (PAA) interpolymer complexes were prepared, in ethanol or dimethylformamide (DMF), by template polymerization of acrylic acid in the presence of PVP (MW: 42.5 or 1100 K) used as the template. FTIR analysis showed that the complexes were formed through hydrogen bonding between the carboxyl groups of the PAA and the carbonyl groups of the PVP. The glass‐transition temperature (T_g) of the complex, prepared in ethanol, was higher than that of the component polymers, whereas the T_g of the complex, prepared in DMF, was located between that of the component polymers. The dissolution rate of the complex was affected by the molecular weight of the PVP and the reaction solvent. The release rate of ketoprofen from the complexes showed a pH dependency, and was slower at a lower pH. The ketoprofen release rate from the complex was controlled mainly by the dissolution rate of the complex above the pK_a of PAA (4.75) and by the diffusion rate below the pK_a. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2390–2394, 2004     

Glass‐transition temperature–conversion relationship for an epoxy–hexahydro‐4‐methylphthalic anhydride system

The DGEBA–MHHPA epoxy system has found increasing applications in microelectronics packaging, making crucial the ability to understand and model the cure kinetics mechanism accurately. The present article reports on work done to elucidate an appropriate model, modified from the empirical DiBenedetto's equation, to relate the glass‐transition temperature (T_g) to the degree of conversion for a DGEBA–MHHPA epoxy system. This model employs the ratio of segmental mobility for crosslinked and uncrosslinked polymers, λ, to fit the model curve to the data obtained. A higher ratio value was shown to indicate a more consistent rate of increase of T_g in relation to the degree of conversion, while a lower value indicated that the rate of T_g increase was disproportionately higher at higher degrees of conversion. The best fit value of λ determined by regression analysis for the DGEBA–MHHPA epoxy system was 0.64, which appeared to be higher than for those previously obtained for other epoxy systems, which ranged from 0.43–0.58. The highest T_g value obtained experimentally, T_{g max}, was 146°C, which is significantly below the derived theoretical maximum T_g∞ value of 170. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 511–516, 2000     

Synthesis of poly(methyl methacrylate) nanoparticles initiated by azobisisobutyronitrile using a differential microemulsion polymerization technique

Nanosized poly(methyl methacrylate) (PMMA) particles with a high molecular weight of 10⁶ g mol^?1 and a polydispersity index of about 1–2 were synthesized, for which 2,2′‐azobisisobutyronitrile was used as the initiator and a differential microemulsion polymerization technique was employed. The kinetics of the polymerization, the glass transition temperature, tacticity, the particle size distribution, and the morphology of the nanosized PMMA synthesized were investigated. The dependence of the number of the polymer particles (N_p) and the number of the micelles (N_m) on the concentration of the surfactant was discussed. The molecular weight distribution was found to be nearly constant over the polymerization time, which was attributed to the significance of micellar polymerization. The resultant nanosized PMMA has a rich syndiotactic configuration (53–57% rr triads) with a glass transition temperature of about 125°C. A beneficial operation condition was discovered where the conversion reached a maximum at a high monomer‐to‐water ratio. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Corrosion of ISG fibers in alkaline solutions

The corrosion behavior of glass fibers synthesized from the International Simple Glass (ISG) reference ingot, an international High‐Level Waste (HLW) borosilicate glass standard, is reported. Bundles of glass fibers were submerged in 120 mL of four different solutions of initial pH values (pH_i) of 9.5, 10.5, 11.5, and 12.5 for static corrosion testing. While all the experiments reached a residual corrosion rate after ~50 days, which remained approximately constant for the duration of the pH_i 9.5‐11.5 experiments, the pH_i 12.5 experiment underwent a Stage II→III dissolution transition after 57 days. This transition was preceded by a decrease in the Al concentration in solution followed by an increase in B and Si concentration in the leachate. Zeolite NaP2 was observed to form on these fibers via scanning electron microscopy and X‐ray diffraction—the crystallinity of the fibers was estimated to be ~40%‐45% (relative to amorphous component) after the Stage II→III transition. Transmission electron microscopy cross‐sectional imaging of sampled fibers revealed several porous layers on the pH_i 9.5‐11.5 samples, and a more aggressive alteration mechanism in the pH_i 12.5 fibers. Potential markers that indicate a transition from Stage II→Stage III corrosion are shown to occur based on experimental observations.     

Rotating disc electrode study of the electropolishing mechanism of NiTi in methanolic sulfuric acid

The mechanism during electropolishing of NiTi in methanolic 3 M sulfuric acid is elucidated based on the investigations carried out using a rotating disc electrode (RDE). The influence of the rotation rate, temperature and the addition of Ni and Ti ions in solution on the dissolution kinetics are investigated and analysed. The dissolution of NiTi during electropolishing exhibits Levich behaviour confirming mass transport as the rate-limiting step. The temperature dependence shows a typical Arrhenius behaviour and the activation energy for dissolution is E_a = 19.2 (±1.33) kJ mol⁻¹. The addition of metal ions to the electropolishing solution results in a lower limiting current density for both, Ni²⁺ and Ti⁴⁺ addition. This confirms the mass transport of dissolved species from the anode surface to the bulk of the solution as the rate-determining step.     

FTIR Spectral Analysis of Corrosion Mechanisms in Soda Lime Silica Glasses Doped with Transition Metal Oxides

Hydrolysis kinetics of soda lime silicate glass (SLS) with 75 mol% SiO₂ in different pH solutions was investigated. Fourier Transform Infrared (FTIR) spectroscopy was used to monitor and confirm the proposed corrosion mechanisms on the surfaces of prepared undoped (SLS) glass together with samples doped with one of the first 3d-transition metal oxides (TMO) (TiO₂→CuO) when exposed to an aqueous solution for a short time period. The traditional proposed mechanism of silicate glass corrosion through ion exchange is analyzed in correlation with infrared reflectance vibrational spectra to confirm the suggested mechanism. The effects of transition metal oxides are followed and interpreted.     

Dissolution of MgO based refractories in CaO-Al2O3-MgO-SiO2 slag

Dissolution of different types of MgO based refractories into molten CaO-Al₂O₃-MgO-SiO₂ slag was studied. Formation of micro spinel particles by addition of either colloidal alumina or micro alumina powder in the MgO matrix efficiently reduced the dissolution. The dissolution of MgO was found to be controlled by the slag penetration into the MgO matrix. In the case of stagnant slag, the slag-penetration would lead to the final dissociation of the decarbonized commercial MgO-carbon cube in less than 6 min. The major dissolution took place between the MgO grains and the liquid in this penetrated layer. The increase of the thickness slowed down the dissolution. In the case of stagnant slag and slag stirred at low speed, the internal mass transfer in the slag-penetrated layer is the controlling step. At higher stirring speeds, the slag-penetrated layer was removed. The removal of the penetrated layer would enhance the dissolution process.     

Evaluation of novel composition (SiO2–CaO–Na2O–P2O5, SrO–CuO) degradable amorphous silicate glasses properties and comprehensive characterization of the thermal features

The current work presents and discusses the findings of a comprehensive study on the structural, chemical and thermal properties of SrO and CuO incorporated SiO₂–CaO–Na₂O–P₂O₅ amorphous silicate glass with a novel composition. Here, fundamental features (experimental density, oxygen density, and hardness) of all glasses were determined and chemical as well as phase composition of the glasses was verified with XRF and XRD, respectively. Moreover, the thermal behavior (viscos flow and crystallization kinetics) of amorphous silicate glass was investigated by non-isothermal methods using DTA analysis. The activation energies of glass transition (E_g) were calculated in the range of 546–1115 kJ/mol by Kissinger method, whereas the activation energies of crystallization (E_c) were calculated in the range of 164–270 kJ/mol by three different methods (Kissinger, Ozawa, Yinnon and Uhlmann). Avrami exponent (n) values ranged from 1.17 to 3.28 demonstrated that amorphous silicate glasses have different crystallization mechanism. Working temperature, which is one of the parameters indicating glass stability, increased with the incorporation of Sr and Cu from 187 °C to 245 °C. The initial dissolution measurement has been applied to study the degradability behavior of Sr and Cu incorporated amorphous glasses in vitro. Quantitative evaluation of Si⁴⁺ (0.156–0.373 kV), Ca²⁺ (0.043–0.332 kV), Na⁺ (0.044–0.329 kV), P⁵⁺ (0.057–0.289 kV), Sr²⁺ (0.134–0.385 kV), and Cu²⁺ (0.090–0.203 kV) depending on the ion activation energy (E_a-ion) and ion concentration at different temperature values (24, 37 and 55 °C) was performed in contact with Tris-HCl solution by ICP-OES analysis. The results revealed that investigated glasses were degradable and incorporation of Sr and Cu affected the glass initial dissolution. Overall, investigated glasses are suitable for various application such as hot-working production, glass-ceramic manufacturing, and glass or glass-ceramic scaffolds fabrication, due to wide working temperature ranges and high crystallization tendencies of the developed glasses.     

Chemical durability of borosilicate pharmaceutical glasses: Mixed alkaline earth effect with varying [MgO]/[CaO] ratio

Glass for pharmaceutical packaging requires high chemical durability for the safe storage and distribution of newly developed medicines. In borosilicate pharmaceutical glasses which typically contain a mixture of different modifier ions (alkali or alkaline earth), the dependence of the chemical durability on alkaline earth oxide concentrations is not well understood. Here, we have designed a series of borosilicate glasses with systematic substitutions of CaO with MgO while keeping their total concentrations at 13 mol% and a fixed Na₂O concentration of 12.7 mol%. We used these glasses to investigate the influence of R = [MgO]/([MgO] + [CaO]) on the resistance to aqueous corrosion at 80°C for 40 days. It was found that this type of borosilicate glass undergoes both leaching of modifier ions through an ion exchange process and etching of the glass network, leading to dissolution of the glass surface. Based on the concentration analysis of the Si and B species dissolved into the solution phase, the dissolved layer thickness was found to increase from ~100 to ~170 nm as R increases from 0 to 1. The depth profiling analysis of the glasses retrieved from the solution showed that the concentration of modifier ions (Na⁺, Ca²⁺, and Mg²⁺) at the interface between the solution and the corroded glass surface decreased to around 40%–60% of the corresponding bulk concentrations, regardless of R and the leaching of modifier cations resulted in a silica-rich layer in the surface. The leaching of Ca²⁺ and Mg²⁺ ions occurred within ~50 and <25 nm, respectively, from the glass surface and this thickness was not a strong function of R. The leaching of Na⁺ ions varied monotonically; the thickness of the Na⁺ depletion layer increased from ~100 nm at R = 0 to ~200 nm at R = 1. Vibrational spectroscopy analysis suggested that the partial depletion of the ions may have caused some degree of the network re-arrangement or re-polymerization in the corroded layer. Overall, these results suggested that for the borosilicate glass, replacing [CaO] with [MgO] deteriorates the chemical durability in aqueous solution.