| 1. |
- Druenert, Ferdinand, et al.
(författare)
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Ancient Roman nano-technology : Insight into the manufacture of mosaic tesserae opacified by calcium antimonate
- 2018
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 38:14, s. 4799-4805
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Tidskriftsartikel (refereegranskat)abstract
- Opaque mosaic glass tesserae containing calcium antimonates from Ancient Messene, Greece (1st-4th century CE) were investigated by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Both trigonal CaSb2O6 and cubic Ca2Sb2O2, with crystallite diameters below 1 pm, were identified as opacifying agents. To better understand ancient technologies, we prepared model glasses that were opacified by crystallisation via a secondary heat treatment, by direct crystallisation during the melting process, or by the addition of pre-reacted calcium antimonate to a base glass. We found that direct crystallisation replicated the antique glass artefacts most accurately. We demonstrated that 0.2 wt% of nucleating agents like TiO2 and SnO2 already exert significant influence on the crystallisation behaviour of calcium antimonates. Secondary scattering centres such as silica and carbonates contribute to the optical appearance. Concurrently, we reproduced opaque white glass ceramics in a reconstructed, wood-fired, Roman-type glass furnace built by Wiesenberg (2014).
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| 2. |
- Druenert, F., et al.
(författare)
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Copper-based opaque red glasses - Understanding the colouring mechanism of copper nanoparticles in archaeological glass samples
- 2018
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 76, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashutten, Taunus Mountains, and an early modern glassworks in Wieda, Harz Mountains, were analysed with regard to their optical appearance. By scanning electron microscopy and X-ray diffraction, metallic copper nanoparticles were identified as a conspicuous constituent in these glasses. In addition, similar opaque red glasses were reproduced in the laboratory in order to better understand the manufacturing process. Detailed analysis of the optical scattering was conducted in order to evaluate the role of Cu-0 nanoparticles in the colouring mechanism relative to other possible reasons of colouration. We find clear differences between the possible contributions of Cu2O (cuprite) particles and metallic copper (Cu-0) nanoparticles. Through simulated backscattering spectra we were able to calculate an average copper particle radius in the archaeological glass samples resulting in a value of up to 95 nm, which matches well the results of SEM investigation (minimum 65 nm). Using the methods we applied in this study, it becomes possible to reconstruct various processing conditions as they were applied in medieval manufacture of these particular materials. (C) 2018 Elsevier B.V. All rights reserved.
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| 3. |
- Efthimiopoulos, I., et al.
(författare)
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Femtosecond laser-induced transformations in ultra-low expansion glass : Microstructure and local density variations by vibrational spectroscopy
- 2018
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 123:23
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Tidskriftsartikel (refereegranskat)abstract
- We report X-ray diffraction, resonance Raman, and infrared (IR) results on pristine ultra-low expansion (ULE) glass, a binary titanosilicate glass with 5.67 mol. % TiO2. ULE processing by femtosecond (fs) laser radiation leads to nanograting writing and photo-darkening for imaging and data storage. We investigate here the vibrational/structural changes induced by fs laser irradiation of ULE at 515 nm. Optical imaging revealed the formation of micro-cavities, and Raman mapping showed molecular oxygen trapped in such cavities of laser-irradiated ULE glass. While titanium in the pristine glass was found predominantly in tetrahedral Ti4+ sites highly dispersed in the silicate matrix, Raman and IR reflectance spectroscopy on laser-irradiated ULE indicated the formation of Ti3+ sites; Ti3+ octahedral sites are formed in the shells of cavities and aggregate in amorphous Ti2O3-type clusters, while the glass around and below cavities contains Ti3+ tetrahedral sites dispersed in the silicate network. Laser-processed ULE glass was found to also exhibit local restructuring of the silicate matrix. Shifts of the strong IR band at about 1080-1100 cm(-1) were translated into changes of the average Si-O-Si bond angle in the laser-transformed areas and found to reflect local density variations; the average local density increases relative to silica glass up to about 8% in the shells of micro-cavities and decreases by about 0.5% in the surrounding material. Chemical processes were proposed to account for photo-darkening and the local structural transformation effect in the probed areas of the fs laser-processed ULE glasses. Published by AIP Publishing.
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| 4. |
- Möncke, Doris, et al.
(författare)
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IR and Raman study of oxy-nitride glasses
- 2018
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Ingår i: Presented at Glass and the Meeting of Minds (SGT18), Cambridge, UK (2nd -5th September 2018). ; , s. 54-
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Konferensbidrag (refereegranskat)
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| 5. |
- Möncke, Doris, et al.
(författare)
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Long-term stability of laser-induced defects in (fluoride-)phosphate glasses doped with W, Mo, Ta, Nb and Zr ions
- 2018
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 498, s. 401-414
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced defects in glasses are of considerable interest for many applications from optics to photonics. The importance of low-level impurities of polyvalent ions in aiding defect formation has been identified early on. (Fluoride-)phosphate glasses are used today as laser materials, waveguides, amplifiers and luminescing materials, all sensitive to a change of the materials transmission by the interaction with light during application. To better understand the processes of defect generation and recovery, a systematic comparison of defect formation in various glasses and for various radiation sources and dopants has been conducted over the last decades. Here we will focus on (fluoride-) phosphate glasses doped with 50 to 5000 ppm of the 4d and 5d ions Zr, Nb, Ta, Mo and W. Glasses were melted under air or under reducing conditions in order to shift the redox equilibrium of the dopants before irradiation with either the 193 nm or 248 nm excimer laser. Only for W, Mo and Nb reduced ion species were confirmed by optical and/or ESR spectroscopy in the pre-irradiated glasses. However, irradiation showed for all metaphosphates the presence of reduced dopant species (W5+, Mo5+, Ta4+, Nb4+, Zr3+), acting as extrinsic hole centers (HC) after being photo-oxidized by laser irradiation to the fully oxidized d ions (Mn+)(+)-HC. Only for Ta5+ with its (Ta5+)(-)-electron center (EC), photo-reduction to the tetravalent ion was observed. Defect recovery was followed up to 16 years after the irradiation experiments, showing that most (Mn+)(+)-HC were very stable, while intrinsic HC either recombined with EC or converted into extrinsic (Mn+)(+)-HC. Due to ubiquitous iron impurities, even these high purity glasses with iron levels of 5-10 ppm or less, showed the formation of (Fe2+)(+)-HC.
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| 6. |
- Wójcik, Natalia A., et al.
(författare)
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Influence of synthesis conditions on glass formation, structure and thermal properties in the Na2O-CaO-P2O5 system doped with Si3N4 and Mg
- 2018
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 494, s. 66-77
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Tidskriftsartikel (refereegranskat)abstract
- Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-0 with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000-1500 degrees C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 degrees C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 degrees C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 degrees C to 640 degrees C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.
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| 7. |
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