G. Della Mea

Hydrated-layer formation during dissolution of complex silicate glasses and minerals

Abstract The characteristics of aqueous dissolution of three complex silicate glasses (rhyolitic, basaltic, and simulated nuclear-waste glass) have been investigated by analytical techniques based on energetic ion beams, which provide depth profiles of various elements including hydrogen, on the altered surface of the materials. The two main corrosion features of this type of glass have been extensively documented: the build-up of a hydrated layer and the surficial accumulation of transition and heavy elements. Comparison with the corrosion behavior of ion-bombarded silicate minerals and study of the influence of solution temperature (in the range 60–200°C) and chemistry (effect of high sodium concentration) allow a better understanding of the corrosion mechanism. It is shown that hydration involves two different processes simultaneously, namely ion exchange between hydrogen and glass network modifiers and permeation of molecular water, their respective importance depending markedly on temperature and solution chemistry. Heavy element accumulation is explained by the precipitation of hydroxides or complex hydrosilicates, the latter possibly resulting also from ion exchange with major cations of primary hydrosilicates.

Structural characterization of proton exchanged LiNbO3 optical waveguides

This paper reports the results of structural analysis of proton‐exchanged lithium niobate optical waveguides fabricated in Z‐, X‐, and Y‐cut substrates immersed in pure benzoic acid. Rutherford backscattering spectrometry, nuclear reactions, secondary ion mass spectrometry, scanning electron microscopy, and x‐ray diffraction were used to measure atomic composition profiles and the marked lattice distortion induced by the proton exchange process in the waveguiding layer. H and Li concentration measurements indicate an exchange of about 70% of the Li atoms are present in the virgin LiNbO3 crystal.

Structure and optical properties of Au-polyimide nanocomposite films prepared by ion implantation

Au-polyimide nanocomposites have been synthesized by implanting different doses of Au+ ions in 100nm thick films of pyromellitic dianhydride-4,4′ oxydianiline polyimide, prepared by glow discharge vapor deposition polymerization. Unambiguous evidence of Au nanoclusters growth is found only at the highest implantation doses (5×1016Au+∕cm2). Structural, compositional, and optical characterizations show that the implantation induces the compactation of the initial film due to H and C loss. The resulting structure is a composite containing 2–3nm gold nanoparticles arranged in a layer of about 40nm and, just beneath the sample surface, a 15nm thick carbon-rich layer. Optical simulations suggest the presence of a gold-carbon core-shell structure in the nanoparticles.

Optimal crystal surface for efficient channeling in the new generation of hadron machines

The new generation of hadron machines may profitably take advantage of channeling for steering and collimation of high-energy particle beams. In that case, the requirements on the quality of the crystal surface are rather stringent in terms of both lattice perfection and roughness. Here, the authors show the structural and morphological characterizations of crystals fabricated through a method to achieve a surface that fulfills all needed specifications for application in hadron machines.

Sodium surface concentration analysis on glass by 23Na(p,α)20Ne nuclear reaction

Abstract The 23Na(p, α)20Ne nuclear reaction has been used to investigate the depth profile of Na near the surface of commercial soda-lime-silicate glasses. The depth profile of Na has been quantitatively determined (with a depth resolution of about 120 A) without migration effects due to the measurement method. Such perturbations, which make other analysis techniques difficult to use, appear only with very high current densities of the incident beam. A brief review of the principles of nuclear reaction used to analyse the concentration profile near the surface of samples is presented. A comparison with the traditional methods is discussed.

Use of ion beam techniques for studying the leaching properties of lead implanted silicates

Abstract Na and H depth profiling has been performed on samples of soda-lime glass and albite subjected to Pb ion implantation and leaching, by means of resonant nuclear reactions. Before leaching, the implanted albite samples show a particular Na depth profile with a marked depletion at the range of the incident Pb ions but an unchanged surface concentration. For soda-lime glass, a Na surface depletion has been noted, which increases with the ion dose. After leaching, the compositional change in albite is limited to the implanted layer, whereas in soda-lime glass it proceeds at much larger depths and exhibits a linear time dependence for short leach times. In addition Pb implantation is found to drastically increase H penetration in vitreous silica. Such ion induced effects are discussed with reference to the use of ion implantation to simulate internal irradiation due to α-decay.

Modifications of sodium concentration profiles after electron and proton irradiation of glasses

Abstract In this work we studied the effect of electron and proton irradiation on the depth distribution of sodium in commercial soda-lime glasses. Samples have been irradiated at different energies and fluences. The 23Na (ρ, α) 20Ne nuclear reaction has been used to determine the sodium profiles. No detectable changes in the sodium concentration profiles have been introduced during the measurements, the proton fluences and doses needed in this type of analysis being very low. The obtained results support the hypothesis that the driving force for Na diffusion is mainly connected to the build-up of an electric field whose direction is determined by the projectile charge, while Na mobility changes because of the local temperature increase due to the beam power dissipation.

Chemical durability of zinc-containing glasses

Abstract The effect of different amounts of ZnO on the chemical durability of a borosilicate glass is discussed. Up to 16% of ZnO the leaching rate is constantly depleted and related to the zinc content. For this powdered sample the weight loss after 24 days of leaching at 70°C is only 8%, which is a very low value. The altered surface was studied by means of RBS and NRA techniques and it was possible to find a layer poor in zinc and rich in silicon, which peels off in different times depending on the glass composition. The thickness of this layer is also related to the zinc content. Because of the poor zinc content of the surface layers the improved durability of the zinc glasses is not attributed to a surface layer effect, but to the bulk structure of the glass in which the role of the zinc becomes very important.

XPS and nuclear analysis of compositional changes occurring in glass on electron beam irradiation

X-ray photoelectron spectrometry and nuclear microanalysis have been utilized to study the compositional changes occurring in a commercial soda-lime-silica glass after electron beam irradiation. Samples were irradiated with electron energies between 2.5 and 4.5 keV and current densities of 1.2 and 4.0 μA/cm2. After electron bombardment a reduction in the Na and O surface concentration appears. Na has been observed to migrate towards the inside of the sample. It accumulates at depths comparable to the maximum electron ranges. The accumulation rate has been observed to depend on the beam power. For a beam energy of 4.5 keV the amount of Na accumulated at depth is nearly twice its surface depletion, supporting the hypothesis that the irradiation influences the glass composition at depths greater than the maximum electron ranges.

Alkali migration in ion irradiated glasses

Abstract Ion implantation into alkali silicate glasses induces an alkali ion migration which modifies the glass composition in the implanted region. The alkali migration can be correlated to different mechanisms, clearly connected to the different stopping power regimes of incident particles. In the nuclear stopping power regime (heavy-ion irradiation) the observed alkali depletion at the surface has been interpreted on the basis of a phenomenological model, which takes into account a preferential ejection of alkali atoms from the surface and of an enhanced diffusion over the range of implanted ions. Glasses with different alkali contents have been irradiated by using Ar ions at different energies, currents and doses. Theoretical models are presented to explain the experimental results. The alkali depth profiles, before and after irradiation, have been determined by using Rutherford backscattering spectrometry and resonant nuclear reactions.