Margit Fabian

In this study, the influences of WO₃ on the structure, thermal behavior and luminescent characteristics of Eu³⁺-doped borosilicate glasses with compositions (35 − x/2)B₂O₃:(35 − x/2)SiO₂:25La₂O₃:5CaO:0.5Eu₂O₃:xWO₃, x = 0, 5, 10, and 15 mol% have been studied via X-ray and neutron diffraction (XRD, ND) combined with reverse Monte Carlo (RMC) modeling, infrared spectroscopy (IR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy and density measurements. IR and RMC structural modeling reveal that the glass network consists of SiO₄ tetrahedra with non-bridging oxygen (Q²); diborate, pyroborate and metaborate units; [WO₄]²⁻ and WO₆ groups; and Si-O-W, Si-O-B, B-O-B and W-O-W linkages. Structural and density analyses show that incorporating up to 10 mol% WO₃ increases structural disorder, depolymerizes the silicate matrix, and creates non-bridging oxygens (NBOs). In contrast, at 15 mol% WO₃, the network exhibits crosslinking due to the development of interconnected, polymerized WO₆ octahedra. Thermal investigations demonstrate exceptionally high glass transition temperatures (T_g > 700 °C) and notable thermal stability, as no crystallization occurred up to 800 °C in any sample. The slight decrease in T_g to 718 °C at 15 mol% WO₃ validates network “softening” driven by the formation of polymerized WO₆ octahedral structural units. Photoluminescence spectra showed a strong red emission at 612 nm from the ⁵D₀→⁷F₂ transition of Eu³⁺ under near-UV (392 nm) excitation. It was established that the addition of WO₃ to borosilicate glasses leads to improvement of the emission properties of the active ion through structural modification. These results demonstrate that the optimized glass compositions hold potential for use as red phosphor materials.

Borosilicate glass is a potential candidate for high-level radioactive waste conditioning, thus understanding the effects caused by the combined presence of uranium and actinides within these matrices is of great importance. The glass matrix was simultaneously loaded with UO₃ and lanthanide oxides (CeO₂, Nd₂O₃, and Eu₂O₃) as chemical surrogates for actinides. Neutron diffraction in combination with Reverse Monte Carlo simulation confirmed that the basic glass structure is comprised of tetrahedral SiO₄, and BO₃/BO₄ units. X-ray absorption spectroscopy indicated the presence of Ce mainly as Ce^III and the co-existence of U^V and U^VI. U acts as an intermediate oxide and reduces the number of four-coordinated B, lanthanide ions serve as modifiers, with their increasing concentration shifting the B-O coordination from 3 to 4. X-ray photoelectron spectroscopy revealed a depth-dependent variation in the U^IV/U^VI ratio. Leaching tests showed increased dissolution of Si, B, and Na, compared to the glass matrix.

Since plans for a future deep geological repository (DGR) site have been published in Hungary, further study of their material characteristics has become essential to understand how to operate and design them properly fully. The main goal of this study is to understand the retention of cations (Ni(II) and Co(II)) by the B75 bentonite through adsorption and desorption experiments and the interactions between materials of the glass/copper/bentonite model system under repository conditions. The obtained adsorption and desorption isotherms show irreversible sorption of both ions at higher concentrations (above 10^-5 M), where the difference is higher in the case of the Ni(II) ions than for Co(II) ions. The surface study of the borosilicate glass shows an increasing trend in the concentration of Zr and O, and a decrease in the case of Si, Ba, Na, and B, showing an equilibrium state from the beginning. The surface of different physical shapes of copper (rod, tape, sliver) shows differences in the case of the rod; higher C and lower O amounts were found, which indicates the formation of Cu₂O; however, the difference between the samples was not influential. Based on the inductively coupled plasma-optical emission spectrometry, the concentration of elements in the pore water solutions was determined. The release of B, K, Na, and Si increased throughout the experiment; in contrast, the concentrations of divalent cations (Ca and Mg) decreased throughout the measurement. No copper dissolution was detected.

The Boda Claystone Formation (BCF) is considered to serve as a natural barrier to the potential high-level radioactive waste repository in Hungary. In order to evaluate the radionuclide retention capacity of the albitic claystone of the BCF, the adsorption and diffusion properties of the rock for Ni²⁺ and Co²⁺ cations (activation products) were investigated separately and in competitive conditions when the two ions were simultaneously added. Batch sorption experiments were performed with powdered and conditioned albitic claystone samples in synthetic pore water to obtain adsorption isotherms. In addition, adsorption tests were performed on petrographic thin sections to check the transferability between dispersed and compact systems. Correlation analysis of microscopic X-ray fluorescence elemental maps recorded on thin sections suggested that nickel is primarily bound to clay minerals (mainly illite and chlorite), which was confirmed by (scanning) transmission electron microscopy measurements. Around illite particles, a newly formed nickel-rich few atomic layer thick phyllosilicate phase was identified. The discrepancy between the experimental and modeled adsorption isotherm at high concentrations could be explained with this nickel-rich new phase. Apart from C_in = 10⁻³ M and only Ni²⁺ or Co²⁺ in the source, the apparent diffusion coefficients of Ni²⁺ and Co²⁺ (C_in = 10⁻³–10⁻² M) were found to be similar. Overall, the BCF shows promising capabilities to retain the studied radionuclides.

Broad band transmitting glasses from visible to mid-infrared with good mechanical strength, chemical durability, glass-forming ability, and thermal stability are preferred for optics and laser technology applications. Generally, low phonon energy glasses possess an extended transmission cutoff toward mid-infrared, but at the same time, retention of other desired properties is challenging for the researchers. In this work, we have shown that mixed alkaline earth (Ba/Sr) would have the potential to improve overall glass properties while retaining its low phonon energy when CaO is partially substituted by BaO/SrO in calcium magnesium zinc silica-aluminate (CMZSA) glass. Quantitative structure analysis of its role in glass properties has been carried out using molecular dynamics (MD) simulation and experimental techniques. This study reveals that Al and Si mainly attained fourfold coordination, while Zn and Mg majorly existed in Al-O-Zn/Mg triclusters. The Ba²⁺ ions play almost equal roles as charge compensators and network modifiers, while Sr²⁺ ions play a larger role in charge compensation. As a result, the SrO-added glass leads to the highest bridging oxygens as compared to others and corroborates with improved optical, thermal, and mechanical properties. Hence, the SrO-added glass shows the most stable network connection and improved overall glass properties.

Silicate glasses containing silicon, sodium, phosphorous, and calcium have the ability to promote bone regeneration and biodegrade as new tissue is generated. Recently, it has been suggested that adding SrO can benefit tissue growth and silicate glass dissolution. Motivated by these recent developments, the effect of SrO/CaO–CaO/SrO substitution on the local structure and dynamics of Si-Na-P-Ca-O oxide glasses has been studied in this work. Differential thermal analysis has been performed to determine the thermal stability of the glasses after the addition of strontium. The local structure has been studied by neutron diffraction augmented by Reverse Monte Carlo simulation, and the local dynamics by neutron Compton scattering and Raman spectroscopy. Differential thermal analysis has shown that SrO-containing glasses have lower glass transition, melting, and crystallisation temperatures. Moreover, the addition of the Sr²⁺ ions decreased the thermal stability of the glass structure. The total neutron diffraction augmented by the RMC simulation revealed that Sr played a similar role as Ca in the glass structure when substituted on a molar basis. The bond length and the coordination number distributions of the network modifiers and network formers did not change when SrO (x = 0.125, 0.25) was substituted for CaO (25-x). However, the network connectivity increased in glass with 12.5 mol% CaO due to the increased length of the Si-O-Si interconnected chain. The analysis of Raman spectra revealed that substituting CaO with SrO in the glass structure dramatically enhances the intensity of the high-frequency band of 1110–2000 cm⁻¹. For all glasses under investigation, the changes in the relative intensities of Raman bands and the distributions of the bond lengths and coordination numbers upon the SrO substitution were correlated with the values of the widths of nuclear momentum distributions of Si, Na, P, Ca, O, and Sr. The widths of nuclear momentum distributions were observed to soften compared to the values observed and simulated in their parent metal-oxide crystals. The widths of nuclear momentum distributions, obtained from fitting the experimental data to neutron Compton spectra, were related to the amount of disorder of effective force constants acting on individual atomic species in the glasses.

Deep geological storage is the accepted solution for the final disposal of high-level radioactive waste therefore, it is necessary to study the host rock of the planned Hungarian waste repository and the materials involved in the engineered barriers. The main goal was to understand the characteristics and stability of the glass/steel/claystone system, from the structural properties of the vitrified waste (borosilicate glasses) to the clay response in the repository. Repository conditions were applied during the experiments to understand the chemical evolution of the system. A triplicate setup was kept at 80 °C for 3, 7 and 12 months and post-mortem characterization was performed. No alteration products were observed with scanning electron microscopy energy dispersive X-ray spectroscopy measurements on the surface of the glass and Fe or in the clay after the end of the experimental period. Based on the elemental analysis of the liquid phase, the released amount of B, K, Si and Na increased, while that of Ca and Mg decreased compared to the baseline. The concentrations of Cl⁻ and SO₄²⁻ did not change significantly. Ca- and Mg-silicate precipitation was observed by X-ray photoelectron spectroscopy at the surface range of the borosilicate glasses because of the synthetic porewater treatment.

In this study, we investigated the influence of Bi₂O₃ and WO₃ on both structure and optical properties of 50ZnO:(49 − x)B₂O₃:1Bi₂O₃:xWO₃; x = 1, 5, 10 glasses doped with 0.5 mol% Eu₂O₃. IR spectroscopy revealed the presence of trigonal BØ₃ units connecting superstructural groups, [BØ₂O]⁻ metaborate groups, tetrahedral BØ₄⁻ units in superstructural groupings (Ø = bridging oxygen atom), borate triangles with nonbridging oxygen atoms, [WO₄]²⁻ tetrahedral, and octahedral WO₆ species. Neutron diffraction experimental data were simulated by reverse Monte Carlo modeling. The atomic distances and coordination numbers were established, confirming the short-range order found by IR spectra. The synthesized glasses were characterized by red emission at 612 nm. All findings suggest that Eu³⁺ doped zinc borate glasses containing both WO₃ and Bi₂O₃ have the potential to serve as a substitute for red phosphor with high color purity.

Deep geological repository is widely considered as the preferred solution for the final disposal of high-level radioactive waste. Investigation representative of the Hungarian disposal concept was conducted using mock-up diffusion cells to study the chemical changes of S235JR carbon steel canister and CEM II/B concrete of the Public Limited Company for Radioactive Waste Management under anerobic and water saturated conditions at 80 °C. Micro-Raman, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy, fluid and potentiometric analysis were performed over a period of 12 months. The analysis was supported by thermodynamic and reactive transport modeling using the HYTEC code. The findings revealed that a uniform corrosion process occurred, leading to rapid passivation of the C-steel with magnetite as the primary corrosion product. Modeling demonstrated that the increase in temperature to 80 °C and the chemical evolution of the concrete did not significantly affect the corrosion passivation process. Although the formation of Fe-siliceous hydrogarnets is thermodynamically possible at 80 °C, it did not jeopardize magnetite passivation. The results show that the passivation of the containers occurred under the test conditions and this is a promising result for further investigations.

Deep geological repository is widely considered as the preferred solution for the final disposal of high-level radioactive waste. Investigation representative of the Hungarian disposal concept was conducted using mock-up diffusion cells to study the chemical changes of S235JR carbon canister and CEM II/B PURAM concrete under anerobic and water saturated conditions at 80°C. Micro-Raman, SEM-EDX, fluid and potentiometric analysis were performed over a period of 12 months. The discussion was supported by thermodynamic and reactive transport modeling. The findings revealed that a uniform corrosion process occurred, leading to rapid passivation of the C-steel with magnetite as the primary corrosion product. Modeling demonstrated that the increase in temperature to 80°C and the chemical evolution of the concrete did not significantly affect the corrosion passivation process. Although the formation of Fe-siliceous hydrogarnets is thermodynamically possible at 80°C, it did not jeopardize magnetite passivation. Overall, the results suggest that the containers would have a long lifespan under the studied disposal conditions.