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Langgemach, Wiebke; Baumann, Andreas; Ehrhardt, Manuela; Preußner, Thomas; Rädlein, Edda
The strength of uncoated and coated ultra-thin flexible glass under cyclic load. - In: AIMS Materials Science, ISSN 2372-0484, Bd. 11 (2024), 2, S. 343-368

Ultra-thin flexible glass with thicknesses of 100 µm or below is a substrate in the fields of optics, electronics, and semiconductors. Its brittleness is challenging in production processes like physical vapor deposition processes, especially in roll-to-roll production. In many cases, multiple geometric deformations take place and each step, like coating or cutting, influences the glass strength. By now, the relation between the strength of ultra-thin glass under quasi-static conditions and its strength under cyclic load has not been studied. Moreover, the effect of coatings has not been investigated. Both aspects are crucial to design reliable production processes. Therefore, the strength of ultra-thin glass under cyclic load was studied for uncoated and coated substrates. Two coating types were investigated: a single indium tin oxide film and a seven-layer antireflective layer stack. The coatings significantly influence the strength of the underlying glass in both test modes. The barrier properties, thin film stress, and the morphology/crystalline structure are identified as the major characteristics influencing the strength.
Charfi, Bilel; Herrmann, Andreas; Zekri, Mohamed; Qasymeh, Montasir; Damak, Kamel; Maâlej, Ramzi
Correlation of rare earth coordination and spectral properties in Er3+ doped Na2O-Al2O3-SiO2 glasses with different Al2O3 concentrations by molecular dynamics simulations. - In: Journal of luminescence, ISSN 0022-2313, Bd. 273 (2024), 120676, S. 1-9

The molecular structure of Er2O3 doped Na2O-Al2O3-SiO2 glasses with varying Na2O/Al2O3 ratios is explored via molecular dynamics (MD) simulations using the so-called inherent structure sampling method, which allows the calculation of a large number of local structures of low concentration, as needed to determine the surrounding of low concentration dopants. General structural parameters, including radial distribution functions, coordination numbers and interatomic distances of all network forming and network modifying ions are reported. However, in this work, special attention is devoted to the effect of Al2O3 concentration on the local surrounding of the doped Er3+ ions. It is shown that the Er atoms coordinate 5-6 oxygen ions in their first coordination sphere in the investigated glasses. The Er-O coordination number increases monotonically with increasing Al2O3 concentration and decreasing Na2O/Al2O3 ratio. It is found that the Er atoms are preferably connected to non-bridging oxygen atoms (NBO) in all glasses, even in the peraluminous composition. Additionally, the MD simulation results are compared to the glasses spectral properties that were already investigated in detail by Tanabe and Hanada. The increasing Er-NBO coordination number derived by MD simulations could be correlated with the increased peak splitting of the Er3+ absorption peaks reported by Tanabe and Hanada. Furthermore, a correlation between the Judd-Ofelt parameters published by Tanabe and Hanada and the Er3+ coordination in the glass structure is discussed. It is shown that the Er-O coordination increases with increasing Ω2 parameter as the Al2O3 concentration increases in the glass composition. A correlation of the average overall Er-O coordination number with the symmetry of the local Er site is proposed.
Langgemach, Wiebke; Rädlein, Edda
A new method for evaluating the influence of coatings on the strength and fatigue behavior of flexible glass. - In: Journal of electronic materials, ISSN 1543-186X, Bd. 0 (2024), 0, insges. 11 S.

Flexible glass is an interesting substrate for a variety of displays, especially bendable or foldable ones, as it shows excellent surface properties and appealing haptics. With the necessary skill, flexible glass can be coated with thin films of different functionality, such as electrical or optical thin films, using plasma processes. In displays, thin film coatings such as transparent conductive electrodes and/or antireflective layer stacks are of major importance. Despite its attractive surface properties, however, flexible glass is still brittle, and its strength must be examined and monitored during any functionalization process, especially with regard to the fatigue behaviour. Currently, specific setups for cyclic fatigue testing of coated flexible glass are not available. Therefore, a new test method is presented herein for easy-to-handle rapid strength and fatigue testing using an endurance testing machine. This method overcomes two issues with the commonly used two-point bending test: the correct insertion of specimens is much easier, and both strength and fatigue testing using the same setup are now possible. Finite element method (FEM) simulation outcomes and first experimental simple fracture tests show that results comparable to those with a two-point bending test setup can be achieved with less effort. This makes it possible to analyze the fracture behaviour of flexible glass under cyclic loading and to evaluate the influence of thin film stress and other coating properties on its performance.
Rädlein, Edda;
Strategies towards circular economy for glass materials and products. - In: European journal of glass science and technology, ISSN 1753-3554, Bd. 64 (2023), 4, S. 108-119

Aiming at circular economy we must provide strategies for reuse of EoL (end of life) glass products, for maintenance and increase high material recycling quotas and be open for new technologies. The well-established returnable bottle system in Germany is an almost perfect example for product recycling, albeit in a confined market segment for certain beverages. On the other hand, recycling nonpackaging glass is tremendously far from closed cycles. The glass packaging market has grown slowly but successfully in spite of the competition from PET and other plastics. Glass producers struggle with even higher energy prices and will focus more and more on renewable energies. Consumers are aware that glass offers an alternative to increasing packaging waste. Which future tasks result from this situation? Three main topics arise for container glass: less one-way packaging, more returnable packaging, and innovative strategies for collection and sort- ing. Knowledge on the best practice examples is expected to be transferred to non-container glasses. An overview on the current status of demands is being documented with the goal of more ideas being generated to assist in glass recycling.
Henkel, Sebastian; Schulze, Christian; Frank, Samson; Bliedtner, Jens; Rädlein, Edda
Experimental investigations on the manufacturing of fused silica freeform surfaces by means of fine and ultra-fine grinding. - In: Tenth European Seminar on Precision Optics Manufacturing, (2023), 1275502, S. 1275502-1-1275502-9

The manufacturing of optical freeform surfaces offers a high potential for optical approaches in the future, since they can make new optical systems lighter and more compact or even enable completely new functions, compared to conventional optics. However, the expanded possibilities go hand in hand with higher complexity in production of freeforms for precision optical applications. This leads to high prices and long delivery times. This paper shows an approach to improve manufacturing of freeforms in small batch sizes with a high degree of customization, by a process chain consisting of (ultrasonic-assisted) pre- and fine grinding combined with ultra-fine grinding using resin bond tools. The process chain is suited for efficient fabrication of optical surfaces. A main focus of the experiments is on reduction of low- and mid-spatial frequency surface deviations, as well as surface roughness. Several different influencing factors in a 5-axis CNC grinding process of fused silica freeforms are investigated and their effects on the resulting surface topography (from the low to the high frequency range of surface deviations) are observed using white light interferometry measurement principles. Various optimization approaches can be concluded.
Brokmann, Ulrike; Weigel, Christoph; Altendorf, Luisa-Marie; Strehle, Steffen; Rädlein, Edda
Wet chemical and plasma etching of photosensitive glass. - In: Solids, ISSN 2673-6497, Bd. 4 (2023), 3, S. 213-234

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF4/H2 etching gas mixture with a constant volumetric flow of 30 sccm and a variable H2 concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ cHF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements.
Herrmann, Andreas; Assadi, Achraf Amir; Lachheb, Raoula; Zekri, Mohamed; Erlebach, Andreas; Damak, Kamel; Maâlej, Ramzi; Sierka, Marek; Rüssel, Christian
The effect of glass structure and local rare earth site symmetry on the optical properties of rare earth doped alkaline earth aluminosilicate glasses. - In: Acta materialia, ISSN 1873-2453, Bd. 249 (2023), 118811

Understanding the connection of molecular structure and optical properties of rare earth doped luminescent materials is essential for fabrication of state-of-the-art active laser media. On the other hand, rare earth ions can be used as a probe ion for the molecular structure of the host material if the structure-property correlations are known. Therefore, this work combines molecular dynamics simulations, Judd-Ofelt theory and UV-vis-NIR absorption spectroscopy including the behavior of the structure-sensitive hypersensitive absorption transitions of Er3+ to expand the knowledge on the local molecular structure in the immediate vicinity of the doped rare earth ions in dependence of glass composition. For this purpose, glasses of the compositions (35-x) BaO &hahog; x MgO &hahog; 10 Al2O3 &hahog; 55 SiO2 (mol%) (x = 0, 7.5, 15, 25, 35) and (20-x) BaO &hahog; x MgO &hahog; 20 Al2O3 &hahog; 60 SiO2 (mol%) (x = 0, 10, 20), doped with 2 × 10^20 ions/cm^3 Er3+ were prepared and analyzed. Clear differences in the absorption spectra between glasses of different BaO/MgO ratios, i.e. different network modifier field strengths, and different network modifier oxide to Al2O3 ratios are found and discussed in detail. Glasses with high BaO concentrations and high network modifier oxide to Al2O3 ratios provide lower rare earth coordination numbers with oxygen in general but higher coordination probabilities with non-bridging oxygen, which results in notably increased splitting of the optical transitions of the doped rare earth ions and higher hypersensitivity / lower local site symmetry for the doped rare earth ions in the investigated compositions. Based on our results and results from other publications the local rare earth site symmetry in glasses can in general be correlated with the rare earth coordination number.
Kazak, Oleg; Halbedel, Bernd
Correlation of the vector gradient of a magnetic field with the kinetic energy of hard magnetic milling beads in electromechanical mills. - In: Chemie - Ingenieur - Technik, ISSN 1522-2640, Bd. 95 (2023), 10, S. 1615-1622

This paper describes the experimental investigation and numerical simulation of a novel electromechanical milling principle: the direct transformation of energy into the movement of milling beads with special magnetic properties. The experimental results show that this principle is ideally suited for the finest grinding of organic agents. Anthraquinone particles with a median size of 25.5 µm were electromechanically ground to 1 µm and the magnetic field strength in the process chamber has the greatest influence on milling results. The developed model reveals that the distribution of the time- and location-dependent vector gradient of the magnetic field in the process chamber determines the energy transfer from the exciter systems to the milling beads and hence the grinding results. With a suitable characterization of the vector gradient distribution, it is possible to establish a correlation between the vector gradient and specific milling beads power. This correlation is fundamental for the design of electromechanical milling machines.
Herrmann, Andreas; Zekri, Mohamed; Maâlej, Ramzi; Rüssel, Christian
The effect of glass structure on the luminescence spectra of Sm3+-doped aluminosilicate glasses. - In: Materials, ISSN 1996-1944, Bd. 16 (2023), 2, 564, S. 1-12

Peralkaline Sm3+-doped aluminosilicate glasses with different network modifier ions (Mg2+, Ca2+, Sr2+, Ba2+, Zn2+) were investigated to clarify the effect of glass composition and glass structure on the optical properties of the doped Sm3+ ions. For this purpose, the Sm3+ luminescence emission spectra were correlated with the molecular structure of the glasses derived by molecular dynamics (MD) simulations. The different network modifier ions have a clear and systematic effect on the peak area ratio of the Sm3+ emission peaks which correlates with the average rare earth site symmetry in the glasses. The highest site symmetry is found for the calcium aluminosilicate glass. Glasses with network modifier ions of lower and higher ionic radii show a notably lower average site symmetry. The symmetry could be correlated to the rare earth coordination number with oxygen atoms derived by MD simulations. A coordination number of 6 seems to offer the highest average site symmetry. Higher rare earth coordination probabilities with non-bridging oxygen result in an increased splitting of the emission peaks and a notable broadening of the peaks. The zinc containing glass seems to play a special role. The Zn2+ ions notably modify the glass structure and especially the rare earth coordination in comparison to the other network modifier ions in the other investigated glasses. The knowledge on how glass structure affects the optical properties of doped rare earth ions can be used to tailor the rare earth absorption and emission spectra for specific applications.
Charfi, Bilel; Zekri, Mohamed; Herrmann, Andreas; Damak, Kamel; Maâlej, Ramzi
Atomic scale network structure of a barium aluminosilicate glass doped with different concentrations of rare-earth ions explored by molecular dynamics simulations. - In: Computational materials science, Bd. 218 (2023), 111965

Molecular dynamics (MD) simulation is employed for exploring the coordination of atoms in peralkaline BaO-Al2O3-SiO2 glasses of variable Gd3+ doping concentrations between 1 and 3.8 mol% Gd2O3. For this the MD simulation procedure of inherent structure sampling was used which provides statistically robust information on the local atomic surrounding of the doped rare earth ions. Distributions of Si/Al/Ba/Gd cations in the first, second and third coordination spheres are investigated. Special focus is laid on the effect of Gd3+ doping concentration on the local surrounding of the Gd3+ ions, i. e. rare earth clustering, and general glass structure. The simulations show that SiOAl bonds are preferred in comparison to SiOSi and AlOAl connections with respect to the random model predictions. Deviations from a statistical Si/Al distribution around the BaOp and GdOq polyhedra are observed. The network modifier ions are preferably surrounded by other network modifier ions, rather than by network formers. It is shown that the incorporation of Gd does not affect radial distribution functions, cumulative radial distribution function curves and the coordination sphere of Gd for Gd2O3 doping concentrations of up to 3.8 mol%, i.e. no rare earth clustering is observed. However, increasing Gd2O3 concentrations decrease the number of bridging oxygen and increase the number of non-bridging oxygen (NBO) species in the glass structure. Charge compensation of the additional non-bridging oxygen species is achieved by increasing NBO coordination numbers with Ba2+.