Intrinsically functionalized alumo-silicat glass-ceramic
Synthesis and Properties of Functional Materials
Final Report Abstract
A two-stage process was successfully developed with which it is possible to change the surface chemistry, structure and properties of LZAS glass-ceramics by means of thermal poling. For this purpose, a special furnace was planned, designed and built, with which such a "thermal poling" process was successfully transferred to glass ceramics for the first time. A lithium aluminosilicate glass with zinc and magnesium was selected as basic system. This glass formed the main crystal phases high quartz solid solution (HQMK) and, at higher temperatures, keatite solid solution (KMK) during ceramization. During the thermal poling treatment, cation migration towards the cathode was achieved by applying a voltage (50 to 2500 V) at an elevated temperature (200 to 500 °C). Under the anode-side surface, a depletion of lithium cations and a resulting strong internal electric field was generated, which allowed the discharge of electrons into the anode. As a result, the neutral, non-bridging oxygen compounds reacted with each other to form bridging oxygen, polymerizing the network. Depth profiles showed complete lithium depletion down to a depth of 18.7 μm. In addition, Raman spectra in this region indicated an increase in the mean order and polymerization of the network. The second charge equalization mechanism identified was the formation of oxygen tri-clusters based on atomic pair distribution functions. The treated glasses were partially crystallized following the thermal poling treatment. By measuring thermally stimulated depolarization currents, a thermally activated relaxation of cations could be observed, which was, however, interrupted by the crystallization of the high quartz solid solution phase. A layered structure (crystalline surface and glassy intermediate layer) was detected below the surface facing the anode. The surface has a lower crystallinity compared to the volume, as only 25 % of the lithium cations can migrate back during relaxation. Lithium relaxation is hindered by the fact that sodium and potassium cations occupy the interstitial sites of the charge balancing positions on the non-bridging oxygen anions and aluminum deficit tetrahedra. SEM images and Raman investigations have shown that the surface of the glass-ceramics has been altered far beyond the thickness of the depleted zone. The structural changes and the layer structure generate compressive stresses (-600 MPa) below the surface in the crystal phase due to different thermal expansion coefficients. The thickness of the depleted zone is in first approximation a state function of the electrical stress and temperature. Although only one glass-ceramic system has been investigated so far, it is assumed that the two-stage process can also be applied to other alkali-aluminosilicate glasses and glass-ceramics based on the relationships developed and the results obtained. In summary, a new method for functionalizing the surfaces of glass-ceramics has been successfully developed during this work.
Publications
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New in situ method for the determination of the crystallization kinetics of glass‐ceramics. Journal of the American Ceramic Society, 103(12), 6746-6754.
Sander, Malte; Jacobs, Philipp & Roos, Christian
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Controlled surface crystallization of lithium‐zinc‐alumosilicate glass‐ceramics using thermal poling. Journal of the American Ceramic Society, 105(5), 3279-3290.
Sander, Malte; Engelmann, Pawel; Jacobs, Philipp & Roos, Christian
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Functionalization of glass-ceramics by gas discharge treatments; ICG Conference, Berlin, 2022
Hildebrand, J. & Roos, C.
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Properties of thermally poled lithium alumosilicate glasses and glass-ceramics, ICG Conference, Berlin, 2022
Sander, M., Mense, M. & Roos, C.
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Struktur von thermisch gepolten Lithiumalumosilikatgläsern und Glaskeramiken; DGG-DKG Arbeitskreis „Glasig-kristalline Multifunktionswerkstoffe“, Aachen, 2022
Sander, M. & Roos, C.
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Structure and properties of thermally poled lithium alumosilicate glasses and glass-ceramics, Dissertation, Fakultät für Georessourcen und Materialtechnik der Rheinisch- Westfälischen Technischen Hochschule Aachen
Sander, M.
