Ionic salt permeability through phase‐separated membranes composed of amphoteric polymers

Amphoteric copolymers composed of hydrophilic poly(dimethyl acrylamide) and hydrophobic poly(dimethyl siloxane) formed phase‐separated membranes. The hydrophilic and hydrophobic components formed continuous phase‐separated domains in the membranes. The hydrated poly(dimethyl acrylamide) domains formed membrane‐spanning pathways, which permitted an ionic salt to permeate the membranes. The permeability of the ionic salt through the amphoteric copolymer membranes was studied. On the basis of the results, the mechanism of salt transport could be explained by the free‐volume theory, which was used for the analysis of diffusive transport in the hydrated, homogeneous membranes. The diffusion coefficient of the ionic salt increased exponentially as the volume ratio of the hydrophilic polymer to water [(1 − H)/H, where H is the degree of hydration] decreased in the membrane. It was possible to postulate that the diffusion of the ionic salt through the membranes was dependent on the free‐volume fractions of water and hydrophilic poly(dimethyl acrylamide) domains in the membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Physiochemical Characterization of Iodine(V) Oxide,Part 1: Hydration Rates

In the first of a series of papers on the iodine(V) oxide system, the chemical and physical properties associated with iodine(V) oxide in its anhydride (I₂O₅) and hydrated states (HI₃O₈ and HIO₃) are examined. The three forms of the oxide have been investigated utilizing differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and powder X‐ray diffraction (PXRD). Furthermore, the hydration rates governing the conversion of the anhydride (I₂O₅) to the initial hydrate (HI₃O₈) and later to the final hydrated state (HIO₃) are reported and discussed. Results from this study suggest that the hydration mechanism for I₂O₅→HI₃O₈ begins with an accelerating period described as a nucleation and growth phase followed by a decelerating period that is diffusion limited. The initial rate of hydration was observed to be governed by a nucleation and growth mechanism, which was inhibited by covering the surface of the particle with an inert metal. Based on this investigation the initial rate of hydration appears to be strongly dependent on the anhydride’s available surface area which facilitates nucleation and growth of HI₃O₈. The final step, HI₃O₈→HIO₃, proceeds through an initial induction period followed by a continuous acceleratory period unlike the first hydration step.     

Some physical properties of anhydrous and hydrated Brownmillerite doped with NaF

Different samples of Brownmillerite (the ferrite phase of cement clinker) doped with 0, 1 or 3 wt.% NaF were prepared. At first, the oxide mixture of Brownmillerite was prepared according to the following composition: 4 mol CaO, 1 mol Al₂O₃ and 1 mol Fe₂O₃ in addition to 1 or 3 wt.% NaF. Each mixture was mixed very well, introduced into an electric furnace at 1300 °C for 1 h in a platinum crucible, and then quenched in air. The product was divided into four portions mixed with 40 wt.% distilled water to form Brownmillerite paste, except for one portion which was left dry. Each paste was molded into two molds; after 24 h, they were immersed in a distilled water and withdrawn after 1 or 3 days of hydration, respectively. The pastes were ground again. The anhydrous powders of Brownmillerites and the hydrated samples were prepared for a.c. conduction measurements by pressing it to be in pellets form. The two surfaces of each pellet were coated with silver paste. The a.c. conductivity and dielectric constant for different samples were measured using four-probe method. The data was collected from 320 up to 670 K. Mössbauer spectra and X-ray diffraction patterns were measured for each sample (anhydrous and hydrated) to confirm the formation of Brownmillerite, identify the iron states and the magnetic properties. The results showed that NaF addition to Brownmillerite expedites the hydration reaction rate. The superparamagnetic relaxation, which appeared in the anhydrous Brownmillerite spectra due to the small particle size, decreases with increasing the hydration time. Also, the Fe³⁺(Oh) state increases while Fe³⁺(Td) decreases with the time of hydration. The a.c. conductivity value at fixed frequency for anhydrous and hydrated samples was found to increase with NaF addition. The a.c. conductivity and Mössbauer measurements can be used as good tools to verify the purity of Brownmillerite phase and, accordingly, the purity of cement.     

Irradiation Grafted Polymeric Films. II. Gas Transport Properties of Hydrated Potassium Acrylate-Grafted Polyethylene Films

Abstract

The permeability constants of oxygen and carbon dioxide through hydrated potassium acrylate-grafted polyethylene films increase rapidly as the degree of hydration of the films increases above about 28 wt %. Below about 28 wt %, the carbon dioxide permeability constant increases with the degree of hydration. In the case of oxygen, the opposite is true.

The separation factor (CO₂/O₂) increases rapidly with film hydration up to about 28 wt %. Above this degree of hydration, the separation factor gradually approaches the value for pure water. An explanation for the results obtained is presented.     

Properties and mechanism of a poly(ionic liquid) inhibitor contained bi-functional groups for bentonite hydration

Present polymer inhibitors depend on a major inhibitory group to restrain bentonite hydration, and monomer design is concerned to improve the inhibition and stability through complex copolymerization. Conveniently, a homopolymer (PIL-NH₂) that contained primary amine and cationic imidazolium as bi-functional groups was proposed, aiming to provide two synergistic inhibitory modes. Comprehensive methods were conducted to characterize the chemical structure and inhibitory performance of PIL-NH₂. The ζ potential absolute value of bentonite suspension was decreased by PIL-NH₂ from 28.7–33.3 mV to 4–7 mV, and the increment of bentonite particle size d₅₀ was observable from 1.83892 μm to over 200 μm. With water squeezed out, the lattice spacing d₀₀₁ of hydrated bentonite was reduced from 1.9070 to 1.2683 nm due to PIL-NH₂ intercalation. The ESEM images revealed that inhibited bentonite showed a tight structure with classical dehydration phenomenon, and the hydrogen bond between PIL-NH₂ and bentonite was further confirmed according to the FT-IR result. In mechanism analysis, the electrostatic attraction and hydrogen bond existed simultaneously for PIL-NH₂ to adsorb bentonite. The two adsorption modes from bi-functional groups were synergistic to improve inhibition remarkably. PIL-NH₂ maintained high performance during the whole hydration process, including crystalline hydration, osmotic hydration, and hydrated dispersion.     

A core-shell structured diffusion-bubbling membrane for efficient oxygen separation: Formation and transport properties

The newly developed core-shell structured molten oxide membranes with fast combined diffusion-bubbling oxygen mass transfer and theoretically infinite selectivity are of technological interest because of their high separation efficiency. In this article, a core-shell structured molten V₂O₅–Cu₂O- based diffusion-bubbling membrane was prepared by one-step thermal treatment of initial CuO–25 wt.% Cu₅V₂O₁₀ ceramic composite in a chemical field (under an oxygen partial pressure difference across the composite) above copper vanadate peritectic transformation temperature (816°C). Oxygen fluxes through the membrane were measured at 830°C, using either gas mixtures (O₂ + N₂) with different oxygen concentrations or air as feed gas at the shell of the membrane and helium (He) as sweep gas. Oxygen flux through the membrane with a shell thickness of 0.15–0.61 mm was 3.8·10^–8–1.4·10^–7 mol/cm²/s under an oxygen partial pressure difference of 0.1 –0.75 atm, respectively. The effect of oxygen partial pressure on the thickness of the membrane shell is found. The relationship between membrane shell thickness, oxygen partial pressure difference across the membrane, and oxygen permeation flux through the membrane is established. Oxygen permeation flux through the dual-phase MIEC membrane shell is described in terms of the diffusion model. Oxygen permeation flux through the membrane core is described both within the framework of the stationary model and nonstationary model for uniform (the membrane thickness is much larger than the characteristic distance of bubble dynamic relaxation) and accelerated (the membrane thickness is comparable to the characteristic distance of bubble dynamic relaxation) bubble motion in a viscous oxide melt, respectively.     

An Extended Empirical Valence Bond Model for Describing Proton Mobility in Water

In order to study the microscopic nature of the hydrated proton and its transport mechanism, we have introduced a multistate empirical valence bond model, fitted to ab initio results. This model was applied to the study, at low computational cost, of the structure and dynamics of an excess proton in liquid water. The quantum character of the proton is included by means of an effective parametrization of the model using preliminary path-integral calculations. The mechanism of proton transfer is interpreted as the translocation of a special O–H⁺–O bond along the hydrogen network, i.e., a series of reactions of the form H₅O₂⁺ + H₂O ⇌ H₂O + H₅O₂⁺, rather than H₃O⁺ + H₂O → H₂O + H₃O⁺ as usually described. The translocation of the special bond can be described as a diffusion process with a jump time of 1 ps. A time-dependent correlation function analysis of the special pair relaxation yields two timescales, 0.3 and 3.5 ps. The first time is attributed to the interconversion between a delocalized (H₅O₂⁺-like) and a localized (H₉O₄⁺-like) form of the hydrated proton within a given special pair. The second one is the relaxation time of the special pair, including return trajectories. The computed diffusion constant, as well as the isotopic substitution effect, are in good agreement with experiment. The hydration structure around the excess proton is discussed in terms of various radial distribution functions around the water molecules involved in the special pair and those in the first solvation shell. The hydrogen-bond-dynamics which accompanies the translocation process is studied statistically. The “Moses mechanism” proposed by Noam Agmon for proton mobility in water is partially verified by our simulations.     

Molecular modeling studies of polymer electrolytes for power sources

Density functional theory and classical molecular dynamics simulations permit us to elucidate details of ionic and molecular transport useful for the design of polymer electrolyte membranes. We consider two systems of current interest: (a) ionic transport in polyethylene-oxide compared to that in a polyphosphazene membrane targeted to be a good ionic carrier but a bad water carrier and (b) transport of oxygen and protons through hydrated nafion in the vicinity of a catalyst phase.It is shown that in polyphosphazene membranes, nitrogen atoms interact more strongly with lithium ions than ether oxygens do. As a result of the different complexation of Li⁺ with the polymer sites, Li⁺ has a much higher diffusion coefficient in polyphosphazene than in polyethylene oxide electrolyte membranes, with the consequent relevance to lithium-water battery technology.For the hydrated membrane/catalyst interface, our simulations show that the Nafion membrane used in low-temperature fuel cells interacts strongly with the catalytic metal nanoparticles directing the side chain towards the catalyst surface. Results at various degrees of hydration of the membrane illustrate the formation of water clusters surrounding the polymer hydrophilic sites, and reveal how the connectivity of these clusters may determine the transport mechanism of protons and molecular species.     

Structural Origin of the Thermal and Diffusion Behaviors of Lithium Aluminosilicate Crystal Polymorphs and Glasses

Lithium aluminosilicate polymorphs α–LiAlSi₂O₆, β–LiAlSi₂O₆, and the LiAlSi₂O₆ glass have been studied comparatively using classical molecular dynamics (MD) simulations with an aim to better understand the structural origin of the different thermomechanical behaviors and lithium ion diffusion properties. The melting behaviors and structural evolution were investigated for the three phases using MD simulations. The structural features of the three simulated samples were analyzed using coordination number, pair and bond angle distributions. The results showed that β‐LiAlSi₂O₆ and the LiAlSi₂O₆ glass had similar melting behavior, had more random short‐range atomic structures, and lower densities as compared to the α‐LiAlSi₂O₆ phase, which has a more ordered and compact structure. The lithium ion diffusion behavior in α–LiAlSi₂O₆, β–LiAlSi₂O₆, and LiAlSi₂O₆ glass and their melts are determined and compared by calculating the mean square displacements. It was found that at high temperatures, the melts of α–LiAlSi₂O₆, β–LiAlSi₂O₆, and LiAlSi₂O₆ glass had similar diffusion properties. While at low temperatures, α–LiAlSi₂O₆ had the lowest diffusion coefficient and highest diffusion energy barrier due to its more close‐packed structure and lacking of defects to facilitate lithium ion diffusion. Both the β–LiAlSi₂O₆ and glass show high ionic conductivity even at low temperatures. This originates from their lower density and thus relatively open structures, but slightly different diffusion mechanisms. Lithium ion diffusion in β–LiAlSi₂O₆ is through the large available interstitial sites while that in the glass is through vacancies due to high free volume. The glass phase had slightly lower lithium ion diffusion energy barrier and higher lithium ion diffusion coefficients as compared to the β–LiAlSi₂O₆ phase, indicating the glass phase can achieve high ionic diffusion and, in some cases, even higher than the crystalline phases with similar densities and short‐range structures.     

Oxygen transport kinetics of MIEC membranes coated with different catalysts

Oxygen permeation through mixed ionic‐electronic conducting membrane may be controlled by oxygen bulk diffusion and/or oxygen interfacial exchange kinetics. In this article, we chose BaCe_0.05Fe_0.95O_3‐δ (BCF) as a representative to study the oxygen transport resistances of the membrane coated with different porous catalysts, including BCF itself, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ (BSCF) and Sm_0.5Sr_0.5CoO_3‐δ (SSC). The oxygen transport resistances of bulk, gas‐solid interfaces of feed‐side and sweep‐side of the catalyst‐coated membranes can be separately obtained through a linear regression of experimental data according to an oxygen permeation model. The three resistances of the membrane coated with BCF catalyst are smaller than those of the membrane coated with BSCF and SSC catalysts, although BSCF catalyst itself has the fastest bulk diffusion and interfacial exchange kinetics. The catalytic activities of BSCF and SSC catalysts on BCF membranes are impacted by the transport kinetics of catalysts, microstructure of catalyst layers, and cationic inter‐diffusion between the membrane and catalysts. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2803–2812, 2016     

Review in Applied Electrochemistry. Number 54 Recent Developments in Polymer Electrolyte Fuel Cell Electrodes

Since the 1980s there has been a significant lowering of the platinum loading of polymer electrolyte fuel cell electrodes from about 4–10 mg cm^–2(platinum black) to about 0.4 mg cm^–2 or even less (carbon supported platinum), by the introduction of ionomer (liquid Nafion^®) impregnated gas diffusion electrodes, extending the three-dimensional reaction zone. From the 1990s to the present studies have been carried out to decrease the loss of performance during cell operation due both to the presence of liquid water causing flooding of the catalyst layer and mass transport limitations and to the poisoning of platinum by the use of reformed fuels. This review deals with the developments in electrode configuration going from dual layer to three layer electrodes. The preparation methods, the characteristics and the optimal composition of both diffusion and reactive layers of these electrodes are described. The improvement in the performance of both CO tolerant anodes and cathodes with enhanced oxygen reduction by Pt alloying is also discussed.     

Thermodynamics of Nafion™-vapor interactions. I. Water vapor

Interaction between water vapor and Nafion™ perfluorosulfonate ionomer has been investigated via combined flow microcalorimetry and isothermal sorption over a wide range of water relative pressure. The molar enthalpy of sorption was determined for the untreated polymer, the residual polymer after extraction by aqueous propanol, and the extracted fraction. The extract appears to be low molecular weight Nafion™ but with an equivalent weight more than double that of the unextracted polymer. The equivalent weight of the residual polymer is slightly lower than that of the original Nafion™, apparently due to partial alkylation. Molar enthalpy for formation of the sulfonic acid monohydrate is about the same for the residual and unextracted polymers, but much greater for the extracted fraction. For untreated Nafion™, the magnitude and concentration dependence of the molar enthalpy indicates that sorption of water exhibits a clear progression from hydronium ion formation (≤1 H₂O/SO₃H) through growth of isolated hydrated clusters (≤6 H₂O/SO₃H) to a continuous internal water phase. A more complicated process occurs for the extract and residual polymer fractions in that an endotherm associated with elastic compression of the polymer matrix surrounding isolated water clusters is superimposed on the hydration exotherm over the concentration range of cluster growth. There is only a minor indication of this endotherm for unextracted Nafion™ because of more facile relaxation of the polymer structure due to plasticization by the low molecular weight fraction.     

Identification of the reaction mechanism of the Pt,O2/La(Sr)Ga(Mg)O3−α electrode system

By means of impedance spectroscopic measurements, the electrode conductivity near the equilibrium potential was determined for the Pt,O₂/La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 electrode system as a function of the oxygen partial pressure (3-105 Pa) and temperature (816-1147 K). A model of two parallel processes proceeding in the electrode system is proposed. It is assumed that one of the reaction routes is localized at the platinum-gas interface and is limited by the diffusion of adsorbed oxygen on the platinum surface towards the three-phase “electrode-electrolyte-gas” boundary. The other route is localized at the “electrolyte-gas” interface and its rate is determined by the diffusion of electron holes in the electrolyte. The results of a calculation based on the proposed model are in accordance with the experimental data. The calculated values of the enthalpy and entropy of oxygen adsorption on platinum, the activation energy of oxygen diffusion along the platinum surface, and the activation energy of the hole transport in the electrolyte agree with literature data.     

Molecular dynamics simulations to compute diffusion coefficients of gases into polydimethylsiloxane and poly{(1,5‐ naphthalene)‐co‐[1,4‐durene‐2,2′‐bis(3,4‐dicarboxyl phenyl)hexafluoropropane diimide]}

Diffusion coefficients of N₂, O₂, CO₂ and CH₄ at 298 K in polydimethylsiloxane (PDMS) and poly{[(1,5‐naphthalene)‐co‐[1,4‐durene‐2,2′‐bis(3,4‐dicarboxyl phenyl)hexafluoropropane diimide]} (6FDA‐1,5‐NDA) polymers have been estimated using molecular dynamics (MD) simulations. Estimated diffusion coefficients in PDMS decrease systematically with increasing size of the penetrant gas molecules following the experimental observations. For 6FDA‐1,5‐NDA polymer, diffusion coefficients decrease in the same order of magnitude, but differ in their sequential order, due to varying side group interactions of the polymer with the gaseous molecules. Cohesive energy density, solubility parameter and free volume of the polymers were determined using MD simulations. Reliability and accuracy of the simulations have been tested typically with the computed values of the diffusion coefficient of O₂ in PDMS polymer, which compare well with the literature data. X‐ray scattering profiles of 6FDA‐1,5‐NDA have been generated to understand the interrelationship between the morphology and diffusion coefficients. The radial distribution function was evaluated to find the contribution of atoms that are important in understanding the molecular interactions during gas diffusion in polymers. Copyright © 2007 Society of Chemical Industry     

Kinetics of release of particulate solutes incorporated in cellulosic polymer matrices as a function of solute solubility and polymer swellability. I. Sparingly soluble solutes

A comparative study has been made of the kinetics of release into water of simple hydrophilic, but sparingly soluble, solutes (exemplified by CaSO₄ or SrSO₄) incorporated in varying amounts in cellulosic polymer matrices of low or high water swellability. Hydrophobic cellulose acetate films (cast from an acetone dope containing a dispersion of the appropriate salt particles occupying a fractional volume ϵ_N = 0.1–0.4 in the loaded hydrated matrix) were found to be particularly useful for this purpose because they could be easily hydrolyzed to cellulose, thus producing hydrophilic polymer matrices containing identical amounts and distributions of solute particles. The kinetic behavior observed exhibited the same main features as previously noted in drug release studies. Thus, a √t kinetic law was obeyed in all cases (apart from a relatively short initial period), while the diffusion coefficient calculated by application of the Higuchi model tended to rise with increasing solute load. This tendency was very strong in the case of the hydrophobic weakly swollen matrix and much weaker in the case of the hydrophilic one. On the reasonable assumption that the diffusion of solute in the salt-depleted matrix (which controls the release rate) occurs via aqueous pathways, the tortuosity τ of these pathways was calculated and found to attain extremely high values in the case of lightly loaded (ϵ_N = 0.1) matrices. These high τ values were drastically reduced upon either (1) increase of the salt load or (2) hydrolysis to cellulose. This behavior is shown to result from the fact that at ϵ_N = 0.1, the salt particles were fully coated with cellulose acetate so that water taken up to fill the space vacated by released salt is in the form of globules dispersed in a weakly hydrated polymer matrix and, hence, is ineffective in providing continuous aqueous pathways. In (1), these globules are increasingly bridged by gaps left in the original loaded matrix, as a result of incomplete coating of the solute particles with polymer. In (2), bridging is similarly effected by the formation of aqueous pathways through the polymer when its degree of hydration is sufficiently increased. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 277–287, 1998     

High Diffusion Permeability of Anion-Exchange Membranes for Ammonium Chloride: Experiment and Modeling

It is known that ammonium has a higher permeability through anion exchange and bipolar membranes compared to K⁺ cation that has the same mobility in water. However, the mechanism of this high permeability is not clear enough. In this study, we develop a mathematical model based on the Nernst–Planck and Poisson’s equations for the diffusion of ammonium chloride through an anion-exchange membrane; proton-exchange reactions between ammonium, water and ammonia are taken into account. It is assumed that ammonium, chloride and OH⁻ ions can only pass through membrane hydrophilic pores, while ammonia can also dissolve in membrane matrix fragments not containing water and diffuse through these fragments. It is found that due to the Donnan exclusion of H⁺ ions as coions, the pH in the membrane internal solution increases when approaching the membrane side facing distilled water. Consequently, there is a change in the principal nitrogen-atom carrier in the membrane: in the part close to the side facing the feed NH₄Cl solution (pH < 8.8), it is the NH₄⁺ cation, and in the part close to distilled water, NH₃ molecules. The concentration of NH₄⁺ reaches almost zero at a point close to the middle of the membrane cross-section, which approximately halves the effective thickness of the diffusion layer for the transport of this ion. When NH₃ takes over the nitrogen transport, it only needs to pass through the other half of the membrane. Leaving the membrane, it captures an H+ ion from water, and the released OH⁻ moves towards the membrane side facing the feed solution to meet the NH₄⁺ ions. The comparison of the simulation with experiment shows a satisfactory agreement.     

Ozone and Oxygen permeation behavior of silicone capillary membranes employed in membrane ozonators

The permeabilities and selectivities of O₃, O₂, and N₂ through silicone capillary membranes employed to degrade organic pollutants in water or air have been experimentally determined. These characteristics have been studied for silicone membranes used in membrane reactors having the following conditions: O₃ in O₂ on one side of the membrane, and either water containing pollutants or a perfluorocarbon (FC) phase containing pollutants on the other side. The permeability of O₃ (8.8 e-13 kgmol · m/m² · s · kPa) is four times that of O₂ through virgin silicone rubber. Exposure to O₃ modifies the polymer and alters the permeabilities of O₃ and O₂. The presence of water with O₃ leads to an increase in O₃ and O₂ permeability (∼ 30%) and an increase in the selectivity, (∼ 10%). The increased permeabilities are likely to be due to the formation of peroxides on the surface and possibly in the polymer. When the silicone capillary membranes were exposed to a perfluorocarbon (FC), the permeabilities of O₃ and O₂ decreased (∼ 9%) due to an increase in crosslinking in the polymer matrix; there was also a slight increase in (∼ 2%), which can be ascribed to the smaller molecular sieving radius of O₂ compared to N₂. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1263–1273, 1998     

A Trend to the Production of Calcium Hydroxide and Precipitated Calcium Carbonate with Defined Properties

In this paper, production of precipitated calcium carbonate (PCC) with required particle size and morphological structure, along with its dependence on technological parameters and the properties of Ca(OH)₂, is discussed. The effect of the reaction environment on the kinetics of CaO hydration and the formation of crystals in water suspension was established. A remarkable difference in the system's restoration ability after stirring was observed. The hydration process is initially controlled by a kinetic mechanism, followed by a diffusion‐controlled process. The dissolution speed of lime hydrated to suspension is eight times higher than that of lime hydrated to powder. Particles of hydrated lime appeared in various forms.     

Kinetics of diffusion of water and dimethylmethylphosphonate through poly(dimethylsiloxane) membrane using coated quartz piezoelectric sensor

The mass sensing principle of quartz crystal has successfully been employed to study the diffusion of dimethylmethylphosphonate (DMMP) and water through a poly(dimethylsiloxane) (PDMS) membrane. For this study a new permeation cell has been fabricated which houses a Cu(II) butyrate ethylenediamine-coated quartz crystal sensor. This development was motivated by the desire to measure the diffusion coefficients rapidly, precisely, and at different temperatures. Temperature dependence diffusion coefficients of DMMP and water are also evaluated using the same cell, which enables calculation of the activation energies for the diffusion process. From the diffusion and solubility data permeability coefficients of DMMP and water have been calculated. It is observed that PDMS membrane offers a selectivity for DMMP over water roughly by 13 : 1 (i.e., P_DMMP/P_water > 13). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1789–1794, 1997     

A Preliminary Investigation of the ISG Glass Vapor Hydration

During the geological disposal of high-level waste, the nuclear glass is expected to be first hydrated in water vapor prior to liquid alteration. In the present work, we investigated the vapor hydration of the International simple glass (ISG) at 175°C and different relative humidities (60%, 80% and 98%). The glass hydration was investigated by nuclear reaction analysis (NRA) and Fourier transform infra-red spectroscopy. The chemical and mineralogical compositions of the alteration products were studied using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) and μ-Raman spectroscopy, respectively. The NRA results gave water diffusion coefficients of 2.31–7.34 × 10⁻²¹ m²/s_, in good agreement with the literature data on borosilicate glasses altered in aqueous media. The glass hydration increased with relative humidity percentage and the SEM-EDS analysis showed a slight enrichment in Si and loss of Na in the hydrated glass layer compared with the pristine glass. The hydration rate of the ISG glass was little higher than that of the French SON68 glass hydrated using water vapor. The corrosion products were analcime, tobermorite, and calcite, which were typical of the SON68 glass hydrated in similar conditions.