Vapor hydration of SON68 glass from 90 °C to 200 °C: A kinetic study and corrosion products investigation

Corrosion of nuclear waste glass in unsaturated conditions is expected to occur upon the closure of the repository galleries during disposal cell saturation in the proposed French disposal site. The objectives of the present work were to determine the alteration kinetics of the SON68 reference in such conditions. Vapor hydration tests were conducted using thin, polished SON68 glass coupons contained in stainless steel autoclaves. Temperatures ranged between 90 °C and 200 °C and the relative humidity (RH) was maintained at 91 ± 1%. Additional experiments at 175 °C and 80, 85, 90 and 95% RH were also conducted to assess the role of RH on the glass corrosion rate. The nature and extent of corrosion have been determined by characterizing the reacted glass surface with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Elemental profiling of the glass hydrated at 90 °C was studied by TOF-SIMS. The chemical composition of the external layer depends on experimental conditions. The hydration rate at 90 °C (TOF-SIMS analysis) is 10 × higher than the generally accepted final rate of SON68 in water at 90 °C (~ 10^? 4 g m^? 2 d^? 1). This may indicate that the glass hydration process cannot be simulated by experiments in aqueous solution with a high S/V ratio. Subsequent leaching (corrosion in an aqueous solution) of samples weathered in water vapor showed dissolution rate values higher than those of pristine glass. This result indicates that mobile elements are trapped within the alteration products during the hydration step and it gives insight into mobility variations of the considered elements.     

IBA and SIMS coupling to study glass alteration mechanisms

Alkali-alumino-borosilicate glasses have been synthesized by melting the stoichiometric corresponding powder mixtures and heating at 1100 °C in a platinum crucible. Electron microprobe analyses were then carried out in order to determine their initial composition. Glass samples were submitted to static aqueous leaching tests in deionized water during 1 month (surface/ratio = 0.3 cm⁻¹) at temperature of 96 °C. The leachates were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The leached samples were then characterized by ion beam analytical (IBA) methods: Rutherford backscattering and elastic recoil spectrometries (RBS and ERDA), proton-induced X-ray or gamma ray emission (PIXE and PIGE) and secondary ion mass spectrometry (SIMS). The role of the presence of one or several contained transition elements (Fe, Mo, and Nd) and the effect of their respective contents on the chemical durability of alkali-borosilicate glasses were investigated. This work outlines the fact that a competition may occur between congruent and selective dissolution. Both surface hydration thickness and mobile element depletion amplitude cannot be considered as the unique reliable glass durability indicators.     

Facile synthesis of ordered large-pore mesoporous silica thin film with Im3m symmetry using n-butanol as the cosurfactant

A facile synthesis route to ordered large-pore (10.7 nm) mesoporous silica film with the cubic Im3m mesostructure is reported in a TEOS–F127–BuOH–HCl–H₂O system through dip-coating method. Characterization by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption reveals that the obtain mesoporous silica material possessed high surface area and large pore diameter. A relative comparison between the mesoporous silica films synthesized with and without BuOH is also presented. A reasonable formation mechanism of the large-pore mesoporous silica film is depicted in this work.     

Atomic layer deposition of TiO2 on mesoporous silica

Ultra-thin layers of titanium dioxide are conformally grown within the pores of an ordered mesoporous silica, SBA-15, using atomic layer deposition, reducing the pore size from the original value of 67 Å to a final value of 32 Å. Analysis of the nitrogen isotherms indicated a conformal growth process in which both the internal surface area of the mesoporous material and the external surface was coated.     

Design and synthesis of large-pore p6mm mesoporus zirconia thin films templated by a novel block copolymer

A novel poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymer was employed as the structure-directing agent for the preparation of large-pore, mesoporous for zirconia with two-dimensional (2D) hexagonal (p6mm) mesostructure through evaporation-induced self-assembly (EISA) approach. The presented materials, calcined at 400 °C and 500 °C, were characterized in detail by X-ray diffraction, transmission electron microscopy, and nitrogen sorption. The results showed that the mesoporous zirconia possesses a large-pore diameter, high BET surface area, and large-porosity. A probable formation mechanism was also presented in this work.     

Correlated surface perturbation in stressed foil made of amorphous alloy

A foil strip made of amorphous alloy Fe₇₀Cr₁₅B₁₅ was loaded with the tensile stress ～500 MPa and remained with the ends kept fixed during 2 h. The statistical characterization of the temporal transformation of the sample surface relief was performed using the autocorrelation functions computed for one-dimensional profiles measured along the axis of loading. The profiles were recorded with the help of the scanning tunneling profilometer. The acquisition time of a single scan was about 0.5 min. The calculated autocorrelation function of the profile depths in the original foil shows a long-range (～2 × 10³ nm) correlation between relief components. The application of the tensile stress causes an immediate, significant increase of the roughness depth from ～40–50 nm to 100–200 nm with a corresponding drop of the correlation length to 0.7 × 10³ nm. The surface relief does not remain stable during loading but varies as a result of the competitive processes, such as microcrack growth, stress-induced flattening, and shearing. The variability of the deformation process in the ‘structureless’ amorphous alloy is due to the dynamical non-uniformity of the multi-focal damage nucleation.     

Influences of chemical aging on the surface morphology and crystallization behavior of basaltic glass fibers

The impact of aging in high humidity and water on the surface morphology and crystallization behavior of basaltic glass fibers has been studied using scanning electron microscopy, transmission electron microscopy, calorimetry and X-ray diffraction. The results show that interaction between the fibers and the surrounding media (high humidity or water at 70 °C) leads to chemical changes strongly affecting the surface morphology. The crystallization peak temperature of the basaltic glass fibers are increased without changing the onset temperature, this may be caused by a chemical depletion of network modifying elements.     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

Dielectric properties of non-swelling bentonite: The effect of temperature and water saturation

In the present work, dielectric and conductivity measurements in the frequency range of 10 mHz–1 MHz were carried out by means of a high-resolution broadband spectrometer on non-swelling bentonite samples, at various low levels of hydration. The evolution of dielectric response was also examined after annealing of the samples up to 260 °C. Conductivity results in conjunction with the electric modulus representation (M1) is proved to be the most suitable for the analysis of the dielectric data. Dielectric response is dominated by ionic (surface and bulk) conductivity as well as by grain polarization due to migration of ions along the clay layers. Both mechanisms are strongly affected by the concentration of bound water and the thermodielectric effect. Havrilliak–Negami dielectric relaxation functions were used to model the observed relaxations mechanisms in modulus formalism and the fitting parameters were evaluated at various water contents of the measured samples.     

The comparisons of growth mechanisms for Si thin films with different deposition rates in CVD process by the description of the roughness evolution

The roughness evolutions of micro-crystalline silicon thin films (μc-Si:H) with different growth rates prepared by chemical vapor depositions have been investigated by atomic force microscopy. The growth exponent β was measured as 0.8 ± 0.03, 1.1 ± 0.07 and 0.75 ± 0.02 for three sets of samples prepared by PECVD with and without hydrogen dilution ratio modulation and by HWCVD, respectively, and does not correlated with the deposition rate in a set. However, the root-mean-square roughness and lateral correlation length decrease with increasing the deposition rate for both PECVD and HWCVD process. We suggested that the nonstationary growth with large β is correlated with the shadowing effect. The influence of the deposition rate on the surface roughness could be related to the diminishing of the shadowing effect by surface species diffusion with higher mobility on an H-covered surface. The initial surface and nucleation condition play an important role in the surface roughness evolution.     

Vitrification of wastes and preparation of chemically stable sintered glass-ceramic products

The present work illustrates the conversion of wastes, such as panel glass from dismantled cathode ray tubes, mining residues from feldspar excavation and lime from fume abatement systems in the glass industry, into two glasses which were subjected to a sinter-crystallization process. The surface mechanism of nucleation, starting from finely ground powders (<37 μm), allowed a rapid crystallization at a relatively low temperature (2 h at 880 °C). This resulted in with the preparation of glass-ceramics possessing a mechanical properties (bending strength and microhardness exceeding 60 MPa and 6.3 GPa, respectively) comparable to that of commercial glass-ceramics and natural stones for building applications, coupled with a good chemical durability. This feature, together with the type of crystals developed, was correlated to the fluorine content of the parent glasses.     

Fractal behavior of amorphous metal structure under the action of tensile stress

We report a series of time-separated topograms of the stressed surface of a foil made of metallic glass Fe₇₀Cr₁₅B₁₅. The numerical analysis of the tortuosity of both normal profiles and horizontal sections of the surface relief demonstrates a fractal/self-affine geometry as beginning from the nanoscopic scale level. Unlike the foils made of convention metals whose surface profile do not exhibit any features of fractality, in the original metallic glass foil the scaling character of the profile depth distribution was revealed. This is a statistical representation of non-equilibrium nanoscopic structure resulting from the highly critical glass forming process in the amorphous alloy. The temporal variation of fractal dimension after applying the 500 MPa tensile stress includes a rise to 1.46 ± 0.06 at the initial stage of loading, dramatic drop to 1.12 + 0.03, and gradual increase to 1.22 ± 0.02 just before the formation of regular shear bands, that is in ∼1.5 h after the stress application. The mechanism of formation of the transient fractal structures is discussed in terms of mid-range order dynamics in disordered media.     

Sintering of nanoparticles of α-Fe2O3 using gelatin

We have demonstrated in this work that single phase of α-Fe₂O₃ nanoparticle can be prepared using gelatin. It was characterized by X-ray powder diffraction (XRPD) technique, gas sorption technique (BET), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The nanoparticle was obtained from an aqueous solution of gelatin and FeCl₃ · 6H₂O, as Fe source, annealed in the temperature range of 200–600 °C for 12 h. The mean particle size of this powder measured with XRPD is about 100 nm and this size agrees well with TEM experiments. Also, the TEM result shows agglomeration that was confirmed by BET technique. These results show that gelatin could be an alternative organic precursor to produce metal oxide powders with nanometer dimensions.     

Thickness-dependent structural transition in GaAs nanocrystals grown on Si (1 1 1) surface

Structural stabilities in GaAs nanocrystals grown on the Si (1 1 1) substrate have been studied by transmission electron microscopy in order to see the structure and growth mechanism. The GaAs nanocrystals grown epitaxially on the Si (1 1 1) surface kept at 573 K have thin shapes consisting of a flat surface which is parallel to the Si (1 1 1) surface. The crystalline structure of the initial growth layer approximately below 5 nm in thickness is the zincblend structure, but with increasing thickness the structure changes to the wurtzite structure by formation of orderly-arranged stacking faults. The small difference in the driving force between the wurtzite structure and the zincblende structure could bring about a situation, where the kinetic rate of nucleus formation is high for the wurtzite structure than for the zincblende structure. It would highly increase the probability that the wurtzite structure is formed as a non-equilibrium state.     

Processing optimization and optical properties of 3-D photonic crystals

The synthesis optimization of three-dimensional photonic crystals (direct and inverse opals) is discussed in terms of the influence of processing parameters on the final optical quality. A colloidal/sol–gel route, starting with the self-organization of polystyrene microspheres into opal structures by convective self-assembly, followed by infiltration with a dielectric matrix precursor sol and heat treatment, has been followed. Several substrate hydrophilization methods have been tested and different substrates. Sol–gel infiltration of the opal template interstices with silica was achieved by dip-coating or micro-syringe application and it was followed by removal of the polymeric template. The concentration of the colloidal sol, containing polystyrene spheres of 235 or 460 nm in diameter, was optimized. The structural and optical properties of the opals and inverse opals have been studied by field emission scanning electron microscopy and optical reflectivity spectroscopy, in order to assess the relationship between their structure and the photonic properties obtained. By using borosilicate glass substrates hydrophilized with hydrochloric acid, colloidal photonic crystals of good quality have been obtained, with well ordered regions up to ～100 μm². By monitoring the effective refractive index change with relative humidity of the surrounding atmosphere, using spectroscopic ellipsometry with an environmental chamber, it was concluded that the present photonic crystals are suitable for humidity sensing applications.     

The effect of Mn,Fe and Cu ions on potash-glass corrosion

The corrosion products of potash-glass with manganese, iron and copper ions were studied by analysing the glass surfaces after being in contact with static water or using a stirrer for different periods. Glass samples with 56 mol.% SiO₂, 24 mol.% CaO and 20 mol.% K₂O were prepared, with 1 mol% of the different metal oxides. The basic composition of these glasses is analogous to the composition of the medieval stained glasses of the XV century from the Monastery of Batalha. The corrosion products were characterized using Ion Beam Analysis, Optical Microscopy and Fourier Transform Infrared spectroscopy. The experimental conditions used reproduced well the corrosion processes found in ancient glasses of similar composition weathered through five centuries. A silica-rich-layer and calcium carbonate were identified on the surface. It was also detected that more than one silica-rich-layer has developed during the longer immersion periods. The elemental profiles for Si, K, Ca, Cu, Mn and Fe were obtained by means of Rutherford Backscattering Spectrometry in the attacked surface region of the glass, while hydrogen profiles were obtained by Elastic Recoil Detection. It is shown that a layer forms that is richer in the transition elements and that copper containing glasses displayed faster initial glass corrosion.     

Short-range atomic order in the surface layer of sputter-deposited Al0.6W0.4 thin film investigated using directional elastic peak electron spectroscopy

A mechanism of creating maxima in directional elastic peak electron spectroscopy (DEPES) polar profiles for textured polycrystalline samples and for amorphous samples with a short-range atomic order is proposed and discussed. DEPES was used in investigating the atomic order in Al and W polycrystalline samples. The maxima found in DEPES polar profiles correspond with the texture expected for these samples on the basis of literature data. A method of processing DEPES data of amorphous metallic alloy with a short-range atomic order is proposed and successfully used for an Al_0.6W_0.4 alloy. The results obtained indicate that nanocrystals with an average linear size in the range of 1 nm and with a particular orientation with respect to the sample surface are present in the surface layer of the sample investigated. A concentration of nanocrystals with such orientation equal to 1.9 × 10¹⁹/cm³ was found when using of the contrast obtained for the maximum in the DEPES polar profile, corresponding to an incidence angle of zero. The contrast of DEPES profiles for the Al_0.6W_0.4 sample increases remarkably during annealing at 373 K. An increase in the amount of preferentially-oriented nanocrystals is suggested as the probable reason for this increase.     

Physical-chemistry of silica/alkaline silicate interactions during consolidation. Part 1: Effect of cation size

The purpose of this work is to identify the effect of the cation nature on mechanisms of the sand consolidation with alkaline silicate solution at low temperature (70 °C). Three diluted lithium, sodium and potassium silicate solutions with [Si] = 2.8 mol/l were used to agglomerate sand composed of grains which mean diameter is 340 μm. According to the cation, different behaviors were observed in terms of the drying time and the material cohesion. Essentially, the drying time increases with decreasing cation size. In contrast, the compressive strength raises when the cation size increases inducing intra-granular rupture highlighted by SEM observations. This could find an explanation in the cation hydration sphere of cations. The strength of the cation–water electrostatic interaction becomes less important as the size of the cations increase leading to more ionic bonds. Despite their strong consolidation, potassium-based materials have a high solubility in water. This result is consistent with the ionic nature of bonds.     

Derivation of the near-surface dielectric function of amorphous silicon from photoelectron loss spectra

The near-surface dielectric function ε(?ω) of hydrogenated amorphous silicon (a-Si:H) films has been derived from X-ray photoelectron energy-loss spectra, over the energy range 0–40 eV. Removal of low lying single-electron excitations is a prerequisite step to proceed to the derivation of the single plasmon energy loss function Im[? 1/ε(?ω)] due to collective electron oscillations. Several methods are compared to separate interband transitions from bulk or surface plasmons excitation. The shape of interband excitation loss in the range 1–10 eV can be described by a Henke function; alternatively, its removal using a sigmoid weighting function is a low-noise and reliable method. After deconvolution of multiple plasmon losses and self-consistent elimination of surface plasmon excitation, the single plasmon loss distribution allows recovery of optical (ellipsometry) data measured in the near-UV to visible range.     

Protein–solvent interaction in urea–water systems studied by dielectric spectroscopy

Dielectric spectroscopy measurements were performed at 298 K for bovine serum albumin (BSA) dissolved in aqueous solutions of urea (0–9  M with steps of 1 M). It was shown that unfolding of BSA molecules by urea influenced the dynamic structures of water and urea molecules, and consequently changed their dielectric responses. At low urea concentrations (0–5 M), unfolding of BSA molecules is not very significant and mainly the globular surface of the BSA interacts with the solvent molecules. In comparison with urea solutions without BSA, the high frequency dielectric spectrum (γ-dispersion) was significantly broadened with addition of the BSA, although the characteristic frequency was not affected much. Such behavior is similar to that reported for aqueous solutions of synthetic polyelectrolytes. At high urea concentrations (6–9 M), significant unfolding of the BSA molecules occurred, exposing the hydrophobic side chains to the solvent and likely increasing the effects of hydrophobic hydration. As a result, the dielectric response of the solvent molecules was found to be more complicated.