Untersuchungen zum Ionenaustausch in ionenleitenden Gläsern unter Verwendung eines elektrischen Feldes
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Philipps-Universität Marburg
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Abstract
In this paper, ion exchange experiments were presented on selected cationic-conducting
glasses. The exchange experiments include experiments with ionic-blocking electrodes and ionic-non-blocking electrodes. The former includes electropoling, the latter includes alkali-proton/deuteron substitution (APS/ADS) and electric field assisted ion exchange. What all experiments have in common is that an electric field is applied to a glass sample on which sputtered metal electrodes are placed. Depending on the chemical nature of the electrode and the gas atmosphere used, the electrodes either block ions or allow ions to pass through. In classic electropoling, platinum electrodes are used in a vacuum. The native cations of the glass are displaced at the positive electrode. However, the platinum electrodes are ion-blocking under these conditions, so that a cationic depletion zone forms below the surface of the glass, in which a negative excess charge remains. This excess charge leads to high electric fields, which act on the remaining cations and are characteristic of electropoling. If the experiment is carried out under otherwise identical conditions in a hydrogen atmosphere instead of a vacuum, hydrogen molecules are oxidized to protons at the positive platinum electrode (anode). These H+ ions can now displace the native alkali ions in the glass. In this alkali-proton substitution (APS), the platinum electrode behaves in an ion-permeable manner for protons. If a deuterium atmosphere is used, the substitution of native alkali ions by deuterons takes place under the same mechanism (ADS). If silver or copper electrodes are used instead of platinum electrodes, these are oxidized on the anodic side and the resulting metal ions can displace the native alkali ions (EFAIE). In all cases, characteristic ionic displacement profiles are generated on the positive anode side of the glass sample, which can be analyzed qualitatively and quantitatively using secondary ion time-of-flight mass spectrometry (ToF-SIMS). The experimentally generated displacement profiles can be described quantitatively using Nernst-Planck-Poisson theory (NPP theory). NPP theory can be used to describe the transport of charged carriers in glass. The driving forces for ion transport are the particle number gradient and the electric field. Both driving forces are explicitly taken into account in NPP simulations. The free parameters in NPP simulations that are not determined by the experiment are the diffusion coefficients of the mobile species. The diffusion coefficients
of the ions can exhibit a pronounced concentration dependence. This variation of the diffusion coefficient can be correlated with the burst energy distribution of a solid. In highly amorphous systems, the diffusion coefficient varies more with concentration than in crystalline systems. With ion exchange experiments and NPP analysis it is possible to obtain information about the potential energy landscapes in the form of the width of the burst energy distribution (SED) in glasses.
The dissertation includes a part of method development of the ion exchange experiments and the
application on selected glass systems. The electropoling, the APS and the EFAIE experiments were already known in the literature before the dissertation and were experimentally adapted so that the diffusion parameters of the glasses can be determined using ToF-SIMS and NPP theory. The ADS was developed as an in-house creation, a variant of the APS technique with deuterons in place of protons. The application of the APS technique was outlined using self-synthesized alkali-aluminium-germanium-phosphate (AAGP) glasses. In the LAGP (lithium), NAGP (sodium) and KAGP (KAGP) glasses, the native alkali ions could be displaced by external protons to a depth of several micrometers. The steepness of the diffusion front in the three different concentration depth profiles already gave an indication of the ratio of the diffusion coefficients of the external protons to the native alkali ions. In addition to the absolute values of the respective diffusion coefficients, the result of the NPP analysis is the width of the SEDs. The widths of the determined SEDs are identical in all three glasses with 120 meV (FWHM). This result clearly implies that the width of the potential energy landscape
in a glass framework is not dependent on the alkali ion species that later
populates these lattice sites. The potential energy landscape is thus primarily influenced by the glass framework
. ADS experiments on AAGP glasses with mixed alkali ions have shown the successful displacement of native alkali ions by deuterons. Interestingly, in Li-Na-AGP both Li+ and Na+ can be displaced by D+, whereas in Li-K-AGP glass the K+ ions appear immobile. EFAIE experiments on LAGP and NAGP showed that the respective native alkali ions are successfully displaced by the silver and copper ions. However, the introduction of noble metal ions into the glass leads to chemical material changes visible in the ToF-SIMS, which are particularly visible with Cu2+ ions. S53P4 bioglass is a medically relevant glass that is used as a bone replacement material in the human body. Despite a large number of publications on the bioactivity of the glass, the electrochemical properties and in particular the transport parameters of the Na+ and Ca2+ ions essential for bioactivity remain unexplored. All ion exchange experiments presented in this work were carried out on self-synthesized S53P4 bioglass samples. In APS/ADS experiments it could be shown that the mobile native Na+ ions can be displaced by H+ or D+ ions. The Na+ ion is thus the dominant mobile charge carrier in S53P4. In the NPP analyses of the APS and ADS experiments, the same diffusion parameters for the native Na+ ions were obtained independently of each other. The width of the SED in the S53P4 bioglass is 103.7 meV (FWHM). This value was confirmed by further independent EFAIE experiments with silver electrodes and subsequent NPP analysis. The silver ions of the oxidized electrode enter the material and displace the native Na+ ions. The same diffusion parameters of the native glass could thus be determined for the S53P4 bioglass by three independent experiments (APS, ADS, EFAIE). The results of the experiments and the theoretical simulations are therefore self-consistent. An electropolishing experiment on the bioglass also shows no contradiction to the previous experiments. However, the Ca2+ ions of the glass scaffold become mobile due to the particularly high electric fields during poling. This creates a zone below the anode in which
both the Na+ ions and the Ca2+ ions are depleted. This is therefore direct evidence of the
mobility of the Ca2+ ions in the S53P4 bioglass. Theoretical analysis of the diffusion coefficients showed that the diffusion coefficient of Ca2+ ions is at least 3 orders of magnitude lower than that of Na+ ions. Therefore, Ca2+ appears immobile in the APS/ADS/EFAIE experiments.
The ion transport on the technical glass D263T from Schott has already been investigated in previous work [42]. An APS experiment was carried out to determine the burst energy distribution in this glass more precisely. Since the protons have a particularly small diffusion coefficient in the D263T borosilicate framework, they almost completely displace both native alkali ions Na+ and K+ to a depth of approx. one micrometer. The chemical composition of the sample surface was thus changed. The NPP analysis revealed a strong concentration dependence of the diffusion coefficient of the Na+ ions and a constant diffusion coefficient for the native K+ and externalH+ ions. A justification for the constant diffusion coefficient of the K+ ions cannot be given based on the current state of knowledge. The width of the SED in D263T is 235.7 meV (FWHM). The particularly low diffusion coefficient of the H+ ions in the D263T glass leads to a strong potential drop of the experimentally applied potential in the zone exchanged with H+, which has been described in detail. The relevance of the Poisson equation and the effect of the
diffusion coefficients on the electric fields occurring in the sample were discussed.
Further EFAIE experiments on D263T glasses showed that the native Na+ ions can be displaced by the noble metal ions, but not the native K+ ions. The latter appear immobile during the EFAIE experiments, but not during the APS experiments. Using the ADS technique, deuterium zones of different thicknesses were created below the anode of three D263T glasses. The thickness of the deuterium zone depends on the experimentally applied voltage and the amount of charge. These samples are important for cooperative research projects in which, for example, the change in the hardness of the surface due to ion exchange can be analyzed. The results of this work have shown that various techniques can be used for ion exchange and that these can be described quantitatively using NPP theory. The APS and ADS techniques in particular provide access to the targeted chemical modification of glass compositions. The focus of the work was on expanding the understanding of the burst energy distributions in some selected glass systems. The burst energy distributions were determined for the three glass systems AAGP, S53P4 and D263T. Although the work comprehensively analyzed the mechanisms of ion exchange and the resulting diffusion profiles, the effect of these changes on the macroscopic properties of the glasses was not explicitly
investigated. Future studies could, for example, focus on the biocompatibility changes of S53P4 after an APS experiment. However, the high reproducibility of the experiments performed and the precise determination of the diffusion coefficients provide a solid basis for potential industrial applications. Future studies could, for example, focus on the biocompatibility changes of S53P4 after an APS experiment. However, the high reproducibility of the experiments performed and the precise determination of the diffusion coefficients lay a solid foundation for potential industrial applications of these ion exchange techniques.
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Created: 2025Issued: 2025-08-11Updated: 2025-08-12
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Fachbereich Chemie
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Philipps-Universität Marburg
Language
ger
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DoctoralThesis
DFG-subjects
ToF-SIMS KonzentrationstiefenprofileAlkali-Protonen-Susbstitution (APS)DeuteronensubstitutionFeldassistierter IonenaustauschIonenaustausch
DDC-Numbers
540
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Rein, Kevin: Untersuchungen zum Ionenaustausch in ionenleitenden Gläsern unter Verwendung eines elektrischen Feldes. : Philipps-Universität Marburg 2025-08-11. DOI: https://doi.org/10.17192/z2025.0500.
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