Natural corrosion of the uranium-colored historical glasses

The historical uranium-colored glasses have been collected from the dumps of former glassworks. Buried in the soil the glasses have been exposed to natural weathering for approximately 150 years. Uranium content ranges from 0.089 to 0.556 wt% depending on the particular glass type. Two types of natural corrosion crusts were distinguished: (1) The leached glass that is hydrated and depleted of alkalies: Affected layer is up to 0.56 mm thick. The corrosion involves leaching of alkali ions from the glass. In comparison with the primary glass the corroded part shows higher uranium content. Uranium concentration in the leached layer increases because (UO₂)²⁺ sorption on the residual glass. (2) Laminated outer layer of residual glass and newly formed aluminosilicate along with calcite: The surface layer system of newly formed phases and leached relics of glass is at most 30 μm thick. With respect to the glass composition the research suggests that the Ca²⁺ and Al³⁺ ions forming new phases have been provided by the natural leaching solution. The uranium concentration in the corrosion crust is significantly lower. Alpha spectroscopy demonstrated the isotopes ²³⁸U and ²³⁴U in the products of the glass corrosion are at the radioactive disequilibrium.     

A comparison of natural and experimental long-term corrosion of uranium-colored glass

The alteration features of historical U-colored glasses exposed to natural weathering for over 150 years were compared with the experimental alteration of similar glass with ～0.3 wt% of uranium using a long-term (up to 426 days) kinetic laboratory batch leaching test in deionized water. Two types of natural corrosion crusts were identified by a combination of SEM/EDS, HRTEM/SAED, EPMA and XRD: (i) formation of a leached layer (up to ～600 μm thick) depleted in alkalis and enriched in Si with stable concentration of U and Al and (ii) formation of lamellae depleted in alkalis, Si and U and enriched in Al. The presence of newly formed gibbsite (Al(OH)₃) and kaolinite (Al₂Si₂O₅(OH)₄) were confirmed in the second type of corrosion crust by HRTEM. Dissolution of the glass components including uranium was determined during the laboratory leaching test. Several μm thick alkali-depleted alteration zones with stable U content relatively enriched in Si and Al were formed on the glass surface. The PHREEQC-2 modeling also predicted the precipitation of secondary gibbsite and kaolinite in the late stages of the leaching. These phases may form especially when sufficient amounts of Al are available from the environment (e.g., soil). Furthermore, they provide surfaces for sorption and may, in some cases, affect the mobility of U ions released from the glass in dependence on pH and U speciation.     

Chemical diffusion and crystalline nucleation during oxidation of ferrous iron-bearing magnesium aluminosilicate glass

Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM) have been used to evaluate the mechanism and kinetics of oxidation of a Fe²⁺-doped MgO---Al₂O₃---SiO₂ glass (with nominal composition along the enstatite-cordierite-liquid divariant) which was heat treated in air under the time and temperature ranges 10–150 h and 700–800°C, respectively. The results clearly demonstrate that oxidation occurs by a cation diffusion process: specifically, the divalent cations diffuse from the interior of the glass to the free surface where they subsequently react with environmental oxygen to form a two-phase, MgO---(Mg, Fe)₃O₄ crystalline layer which covers the (divalent cation-depleted) glass. Oxidation of some Fe²⁺ within the glass occurs via the inward flux of electron holes (a counterflux to the divalent cation diffusion required to maintain charge neutrality of the glass); this internal oxidation results in the fine-scale ( 1–5 nm), homogeneous nucleation of crystalline (Mg, Fe)₃O₄ within the divalent cation-depleted layer of the glass. Chemical diffusion of an oxygen species is thus demonstrated to be a slower, parallel kinetic process which is not required for oxidation to occur in this material. A first-order analysis of oxidation kinetics in the glass is presented.     

Aqueous alteration of five-oxide silicate glasses: Experimental approach and Monte Carlo modeling

The alteration behavior of glass comprising five oxides (61 ? x)SiO₂–17B₂O₃–18Na₂O–4CaO–xZrO₂ was studied during static leach tests in a buffer solution at 90 °C and with a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm^?1. The morphological evolution of altered glasses investigated by small-angle X-ray scattering (SAXS) exhibits a strong dependence with the zirconium content in the glass. The experiments were compared with modeling results using Monte Carlo simulation. The model has been improved to simulate the alteration kinetics and alteration layer morphology, considering zirconium atoms at coordination number 6. The simulations exhibit very good agreement with experimental results, showing relations between the alteration rate and the restructuring altered layer. The model is used to interpret experimental observations by proposing a porosity closure mechanism in the altered layer to account for the diminishing alteration rate. For high zirconium concentrations, the simulation highlights the existence of percolation pathways responsible for a complete alteration of the glass. Zirconium has a hardening effect that limits the dissolution of neighboring atoms; this effect is favorable in terms of the glass alteration kinetics, but by inhibiting silicon recondensation it prevents complete closure of the porosity and the glass is completely altered.     

Gallium colloid formation during ion implantation of glass

Data are reported on the size and depth distribution of gallium colloids formed by gallium ion implantation at energies of 50 and 60 keV, and nominal doses up to 1.1 × 10¹⁷ ions/cm² into coverlip glass, float glass and white crown glass. Measurement techniques used to reveal colloid-induced changes include the wavelength dependence of optical reflectivity, transmission electron microscopy (TEM) and Rutherford backscattering (RBS). The reflectivity can be controlled by variations in ion dose, implant temperature and ion beam energy. The highest reflectivity is found after implants near 50°C and the level is extremely sensitive to the implant temperature. For controlled beam conditions, the reflectivity data are reproducible, despite there being variations in the colloid size and depth distributions as seen by TEM and RBS. The TEM data reveal that the depth distribution develops in two distinct regions, which at high concentration can precipitate into two layers of large colloids. Subsidiary experiments are reported to attempt to separate the effects of variations in the implant temperature and surface charging which influence the reflectivity, RBS and colloid formation.     

Water penetration mechanisms in nuclear glasses by X-ray and neutron reflectometry

To determine the water diffusion at the early stage of the alteration, X-ray and neutron reflectometry have been performed on altered simplified glasses and the SON68 glass (an inactive R7T7-type French nuclear glass). For the first experiment, the simplified and SON68 glasses were altered at pH 3 and pH 6 and characterized by X-ray reflectometry as a function of the alteration duration. The evolutions of the electron density profile obtained from the reflectivity curves simulations have allowed the determination of the layers compositions. At the beginning of the alteration and for pH 3, the altered surface layer is constituted of a dealkalized zone. Upon alteration progress, the water diffuses inside the layer and hydrolyzes the Si–O–B bonds. For the second experiment, glasses were altered in D₂O (pD 3) and analyzed in D₂O saturated cell. After a D₂O/H₂O substitution, the samples were characterized one more time in H₂O saturated cell. The evolution of the scattering length density shows that in the first stage of the alteration, the layer is constituted of two parts: a dealkalized glass and a dealkalized and boron depleted glass where water has diffused. According to the glass composition and after few hours of alteration, this dealkalized glass part can disappear.     

Alteration of soda silicate glasses by organic pollutants in museums: Mechanisms and kinetics

The role of the organic pollutants formic acid, acetic acid and formaldehyde in the alteration of unstable soda silicate glasses is examined through SIMS depth profiling of replica glass aged in polluted and non-polluted atmospheres under ambient conditions. The effect of different controlled atmospheres is compared to the polluted atmosphere encountered in museum storage. The results show that formic acid rather than formaldehyde is responsible for the increased alteration in the National Museums of Scotland glass collection. Formic acid caused sodium formate crystals to form at the glass surface and increased the leaching of alkali. Acid pollutants increased both the alteration depth and the amount of sodium extracted from the altered layer, which fell to a concentration ～1 at.%, compared to 4–5 at.% in the non-acidic atmospheres. The research highlights the gap existing between alteration models obtained from controlled laboratory experiments, predicting an eventual slowing down of the alteration, and the reaction process taking place in real environments (as found in museums), where the environmental fluctuations maintain a roughly linear progression of the alteration. The storage of unstable glasses in wooden cabinets or showcases emitting organic pollutants must be avoided and glasses should be kept in stable environmental conditions.     

Investigation of alkali borosilicate glass durability using tritium tracing, β-autoradiography, scanning electron microscopy and ion beam analysis

A Li-Na-containing borosilicate glass was submitted to aqueous corrosion in static mode in tritiated solutions of various pH at room temperature and 90 °C. Tritium counting, β-autoradiography, scanning electron microscopy (SEM) and ion beam analysis (IBA) techniques have been used to investigate the composition variations of the leached glass surfaces. In an acidic medium, the glass surface is covered by a thick hydrated silica layer; mobile elements like Li, Na and B and transition elements like Fe and Mo are strongly depleted. Near pH 7, relative enrichments of aluminium and iron are shown together with strong Li, Na and B depletions. In a basic medium, the glass surface exhibits iron and molybdenum enrichments whereas mobile elements seem to be kept at their nominal concentration level at the glass surface. The tritium activity and distribution on the leached glass surface is shown to depend strongly on the pH of the tritiated solutions. These observations are correlated with the observed changes of the surface morphology and chemistry characterized by IBA and SEM analysis. Elemental solubility versus pH of various chemical species have been calculated for comparison purpose with the experimental observations.     

Surface modification of SiO2 glass by laser processing

Various oxide films on SiO₂ glass substrates were irradiated by a laser beam. A continuous CO₂ laser source (wavelength 10.6 μm) was used for this purpose; the composition change at the surface layer was determined by Rutherford backscattering spectrometry (RBS). All the alkaline-earth oxides as well as those of lanthanum and yttrium, entered the glass after treatment. ZrO₂ and CeO₂, however, did not enter the SiO₂ glass due to laser irradiation. It is interesting, however, that a film of ZrO₂ + Al₂O mixture easily entered into the SiO₂ glass by laser processing. The conditions and mechanism of laser-enhanced interaction of ZrO₂ or other oxide films with SiO₂ glass surfaces are discussed especially in view of their structural behaviour in glass.     

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.     

Aging of alkali-resistant glass and basalt fibers in alkaline solutions: Evaluation of the failure stress by Weibull distribution function

In alkaline solutions, the reaction of hydroxyl ions with Si–O–Si-groups of the glass network leads to the formation of hydrated surfaces and dissolved silicate. The rate of this corrosion depends on the chemical constitution of the fiber and the alkaline solution as well as on time and temperature. The investigation of the aging of glass and basalt fibers with different chemical constitutions in NaOH and cement solutions shows that the corrosion mechanism changes due to the inhibiting effect of calcium ions. The strength distributions have been evaluated using a Weibull distribution function. The mechanical behavior strongly depends on the chemistry of the solution and determines the parameters of the Weibull distribution function in terms of either single or mixed distributions. The corrosion in NaOH solution leads to a strong dissolution of the outer layer of the glass and basalt fibers, whereas during aging in cement solution at the same pH-value a limited, local attack was revealed.     

Effect of organic acid vapors on the alteration of soda silicate glass

Organic acids were previously shown to be involved in the alteration of historic soda silicate glasses in humid atmospheres under museum storage conditions. The present study investigates the role of these pollutants on the visual, compositional and structural modification of soda silicate glasses. Replica glasses aged in humid or humid/acidic atmospheres under accelerated conditions were examined and compared using light microscopy, electron microprobe and Raman spectroscopy. The characteristic modifications induced by each atmosphere are described. In the acid polluted atmosphere the leaching process created a layer that retained the transparency of the glass but with a chemical structure hydrated and more polymerized following the loss of alkali and the associated non-bridging oxygens, and the formation of new bridging bonds. In an unpolluted humid atmosphere, the dissolution process caused disruption of the silicate network at the glass surface and formation of an opaque gel layer. The hydrated silicate species and the cations in this gel layer subsequently polymerized to form a new amorphous material, hydrated and more depolymerized than the original glass. This investigation confirms that organic acid pollutants are responsible for the modifications observed on altered historic soda silicate glasses in the collections of the National Museums of Scotland.     

Use of FTIR reflectance spectroscopy to monitor corrosion mechanisms on glass surfaces

Fourier transform infrared (FTIR) reflectance spectroscopy was used to monitor corrosion mechanisms on the surface of lithium disilicate (Li₂O-2SiO₂) glass samples exposed to an aqueous solution for short times. The traditional mechanisms of glass corrosion were observed but a spectral feature was resolved that was previously unreported. This feature consisted of a peak suspected to result partially from a silanol (Si-OH) vibration in the region 800-1050 cm⁻¹ that shifted and reappeared in a cyclic fashion throughout the corrosion process. The behavior of this peak tends to suggest that the creation and condensation of Si-OH groups is the reaction responsible for causing the shift of the main Si-O-Si and Si-O⁻ peaks, a phenomenon which has previously lacked a detailed explanation.     

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron® modified tin oxide layer prepared by the sol–gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO₂ layer was deposited by the sol–gel dip-coating process in the presence of Tiron^® as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO₂-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time.     

Preparation and characterization of electrodeposited indium selenide thin films

Indium Selenide (InSe) thin films were deposited from a mixture of Indium chloride and selenium dioxide in aqueous solution by electrodeposition technique on Indium Tin oxide coated glass substrates. The effects of the parameters during deposition such as current density, deposition potential versus saturated calomel electrode, pH value and concentration of source material were studied. X‐ray diffraction studies were carried out on the films to analyze the microstructure using an x‐ray diffractometer and were examined by RAMAN spectroscopy. The Raman peak position did not change much with chemical concentrations. Raman scattering due to the (LO) phonon was observed at 211 cm^–1. Optical absorption studies were performed with a double beam ultra violet‐visible –NIR spectrophotometer in the wavelength 300–1100 nm. The surface morphology of the layer was examined using a scanning electron micrograph. The composition of the films was studied using an Energy Dispersive Analysis by X‐Rays (EDAX).     

Water diffusion in silicate glasses under natural weathering conditions: evidence from buried medieval stained glasses

In this study, ion-microprobe analyses of four samples of buried medieval stained-glasses are used to demonstrate that water penetrates into the matrix of pristine glasses at low temperatures, thereby showing that glass alteration is not only a surface process. The diffusion coefficients of water determined from concentration profiles of hydrogen are found to be correlated with the bulk polymerization state of the glass. This observation is discussed with respect to glass structure and implies that ionic exchange between hydrogen and network modifying metal cations is the major process responsible for glass hydration.     

Acetic acid derived mesoporous bioactive glasses with an enhanced in vitro bioactivity

In this paper, a novel mesoporous bioactive glass (MBG) with a nanoscale surface feature in the SiO₂–CaO–P₂O₅ system has been synthesized by means of the acetic acid-assisted sol–gel process. As a comparison, the normal sol–gel derived bioactive glass (NBG) with the same composition was also synthesized. The structure and in vitro bioactivity of as-prepared samples were characterized using various methods. The results indicated that using acetic acid as a structure-assisted agent and hydrolysis catalyst is in favor of preparing the bioactive glass with nanoscale surface morphology, larger specific surface area, relatively homogeneous sized mesopore distribution. Depending on this novel structure, MBG presented an enhanced formation of hydroxyl-carbonate apatite layer and high in vitro bioactivity.     

Formation of nanoparticles in soda-lime glasses by single and double ion implantation

Structural characteristics and optical properties of monometallic and bimetallic Ag and Au nanoparticles in the surface region of soda-lime glass fabricated by ion implantation have been studied by transmission electron microscopy and optical spectroscopy. As a result it has been found that both, implantation dose and process temperature, strongly influence the metal nanoparticle formation governed by ion diffusion and metal precipitation as well as the involved stress generation around the particles. Thus, the mean size of metal nanoparticles and the width of the particle containing region beneath the glass surface increase with increasing temperature as well as implanted dose. Upon sequential high-dose double implantation to form bimetallic Ag–Au nanoparticles a rather complex configuration has been obtained. Particles of sizes above a threshold of 5–10 nm exhibit distinct image contrast features indicating the development of central voids whose sizes are proportional to the outer particle diameter.     

PbO–B2O3–SiO2 glass powders with spherical shape prepared by spray pyrolysis

PbO–B₂O₃–SiO₂ glass powders were directly prepared using spray pyrolysis. The powders were spherical and fine-sized. One glass particle was obtained from one droplet by melting the precursors inside a hot wall tubular reactor. The characteristics of these powders were compared with those of the commercial product, which was prepared using the conventional melting process. The spherical powders, which were prepared using spray pyrolysis at 1000 °C, had broad peaks at around 28° in the XRD spectrum. The glass phase was formed during the spray pyrolysis process even within a short residence time of the powders inside the hot wall tubular reactor. The mean size of the prepared glass powders was 1 μm. The dielectric layers formed from the spherical, fine-sized glass powders had a high transparency at firing temperatures above 520 °C. The maximum transparency of the dielectric layer formed from the glass powders obtained from spray pyrolysis was 95.3% at the firing temperature of 560 °C. The dielectric layer formed from the spherical, fine-sized glass powders had a smooth surface and no void inside the dielectric layer.