13 Zentrale Universitätseinrichtungen

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14

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Institute: search.filters.UBSInstitut.Fakultätsübergreifend / Sonstige EinrichtungAuthor: search.filters.author.Urbanek, Matea

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    Chemo-mineralogical changes in six european monumental stones caused by cyclic isothermal treatment at 600 °C
    (2025) Urbanek, Matea; Wriessnig, Karin; Artner, Werner; Pintér, Farkas; Ottner, Franz
    This experimental study analyses the extent of chemo-mineralogical changes that occur when a building stone encounters a cycling isothermal treatment at 600 °C. Four carbonate and two silicate European building stones were analysed in their fresh quarried and thermally treated conditions by means of colour measurements, in situ X-ray diffraction (XRD), and optical microscopy. Furthermore, powdered samples were characterised by Fourier-transform infrared spectroscopy, simultaneous thermal analysis, and cycling thermogravimetry (TG). The in situ XRD spectra revealed a surface-limited phase transformation of solid calcite and dolomite under isothermal conditions during the first 10 min at 600 °C and 500 °C, respectively. The onset of thermal decomposition and extent of phase transformation were governed by the microstructure of the solid samples. Inter- and intragranular microcracks are induced to varying degrees, and their incidence depended on the stone’s microstructure. Discolouration indicated a transformation of minor elements across the entire analysed sample volumes. Kaolinite was preserved even after three hours of thermal treatment at its dehydroxylation temperature due to its sheltering in confined pore spaces. Mass loss was more pronounced when cyclic treatment was employed compared to a non-periodic treatment, as determined by a TG analysis performed at same time intervals. Examining the chemo-mineralogical and microstructural changes caused by heat treatment allows us to study how and if regaining mechanical strength and restoring physical properties are possible for purposes of heritage restoration after fire damage.
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    Nano-zirconia as a protective and consolidant material for marble in architectural surfaces
    (2025) Urbanek, Matea; Gil-Díaz, Teba; Lützenkirchen, Johannes; Castelvetro, Valter
    Natural weathering of carbonate building surfaces exposed to outdoor conditions can be effectively tackled by appropriate products. The aim of this experimental study was to evaluate the effectiveness of nano-zirconia (n-ZrO2) as a consolidant for calcite surfaces. Sorption kinetics were investigated in batch experiments by applying aqueous dispersions of n-ZrO2 onto model, crushed Apuan marble samples of different bead sizes. Adsorption and desorption by the action of simulated rainwater as an environmentally relevant leaching solution were investigated. Adsorption studies revealed a good chemical affinity between n-ZrO2 and calcite, while desorption resulted in <6% release of n-ZrO2 and 100-fold lower solubility for 1 mm-sized beads compared to controls. These results suggest that n-ZrO2 may adsorb efficiently to calcite and protect the surface from dissolution. The results of further tests performed on artificially aged and consolidated samples of Apuan marble indicate that the application of n-ZrO2 only moderately affects water vapor permeability, water absorption coefficient, and drying behaviour. Therefore, no harmful effects are expected from the treatment. Micromechanical tests showed slightly increased mechanical strength after treatment. The obtained results highlight the effectiveness of n-ZrO2 as a surface consolidant and protective agent for calcite.