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185 cracks were initiated in a soda-lime-silica glass by Vickers indentation and grown under controlled dry nitrogen atmosphere. Direct observation of subcritical crack growth (SCCG) upon indentation was performed using a video camera with an image acquisition rate of 3 ms. The results show that the validity of K(c) relations used to determine the indentation fracture toughness from a single imprint is questionable. It seems that correlation of crack length to stress intensity necessitate the use of statistical significant data of multiple crack events.
Electric contacts based on silver-glass dispersions are key components in optoelectronic microsystems and control modules for medical, information & communication and energy technology in our networked society. Driven by the complexity of modern production processes and ever shorter time-to-market requirements, the fast and specific development of tailored silver-glass dispersions has become a bottleneck of technology development. Nevertheless, the underlying mechanisms of silver dissolution, transport, and reprecipitation, and the resulting micro structure evolution during firing are poorly understood. The broad literature on the precipitation of colloidal silver particles and the related processes of silver dissolution and diffusion mostly refer to very small volume fractions of silver. Transferring these results to the sintering of glass-containing silver dispersions, is therefore highly questionable. In this case, silver dissolution, electrical contact between silver particles, transport and reprecipitation take place under special conditions. This includes short diffusion lengths (particle size < 10 μm), the presence of three-phase contacts silver - glass - sintering atmosphere, as well as silver reprecipitation at the sintering contacts as the driving force of silver transport. Here, a dynamic balance of the silver concentration can be expected to result from the ratio between silver dissolution and reprecipitation. The aim of the project is to gain basic insight into the mechanisms of dissolution, transport and reprecipitation of silver in sintering silver glass dispersions. In this context, the main focus is on gaining basic knowledge about the dissolution of metallic silver in low melting oxide glasses as the limiting factor of the sintering of silver-glass composites. In particular, we will strive to gain insight into the effect of the oxygen content of the sintering atmosphere, of the oxygen dissolved in the silver particles, of silver oxide on the surface of the silver powder, of the electric contact between the silver particles, as well as the basicity of the glass. Furthermore, we strive for insights into the silver mobility and the silver concentration that can be attained (silver solubility) in oxide glasses with a low melting point. Summing up all these aspects, a closed explanatory model for silver dissolution, transport and reprecipitation during the sintering of glass silver dispersions will be introduced.
Comparison of fluorescence measurements performed on different fluorescence instruments, analyte quantification from fluorescence intensities as well as the determination of fluorescence quantum yields require instrument calibration and consideration of the wavelength-dependent instrument-specific quantities spectral photon flux reaching the sample and spectral responsivity. Here, we present guidelines and recommendations for the qualification of fluorescence instruments and introduce suitable chromophore-based reference materials. Moreover, the design concepts of the different BAM fluorescence standards are discussed.
Development of durable transparent enamel colors for the manufacture of decorate glass panels
(2017)
Today glass is broadly used in modern architecture. For applications indoor it is possible to produce decor glass by using enamel colors and glass painting techniques without any problems. However, this is more limited for applications outdoor. Humidity and environmental pollution attack the surface of the coating and damage it strongly. There are only few colors on the market which are resistant towards acids and bases until now. Additionally, most of those colors are opaque. In order to extend the color palette, chemically resistant colored glasses are being developed which are transparent, relatively low melting and intensively toned even in thin coat thickness. To achieve such ambitious aim, many parameters have to match which act in complex manner. Metal oxides were used to color the glasses. A lead-free glass composition was developed to avoid an exposition of heavy metals to the environment. The glasses were characterized, in particular in terms of their thermal properties, their crystallization behavior and their chemical durability. Different practical applications will be shown.
Fundamental understanding of crack healing in glassy crystalline materials is very important for solid oxide fuel cell (SOFC) sealants, since cracks caused by sealing or thermal cycling still remain a substantial bottleneck in developing durable SOFC.
Previous studies on soda lime silicate glass [Sin14] showed that crack healing is driven by viscous flow and that healing progress is proportional to time t and inverse viscosity η. This finding would allow to present healing data of a given glass for different temperatures in a master curve healing progress versus t/η. Such master curves would be a helpful tool in understanding crack healing kinetics.
Against this background, crack healing in non-crystallizing sodium calcium silicate (NCS) and sodium borosilicate glasses (NBS) have been studied. Moreover, to evaluate the influence of micro structure in crystallized glass on crack healing process, glass matrix composites (GMC) were prepared from NCS and zirconia as inert ceramic filler material mimicking a partially crystalline micro structure. By this way, the micro structure can be kept constant during crack healing. Cracks were generated by Vickers indention and healed isothermally at different temperatures. Crack healing progress was monitored by optical and electron microscopy. Results show that the above mentioned proportionality actually applies for the studied glasses for which such a master curve could be obtained. In comparison to a non-crystallized glass, the effective viscosity of GMC is increased by the rigid filler content. This effect substantially retards crack broadening during later healing stages, which often ends up in large pores. On the other hand, local viscous crack healing is still possible in larger glassy regions. This behavior seems to be very interesting for crack healing optimized micro structures.
Fundamental understanding of crack healing in glassy crystalline materials is very important for many applications, especially for sealing solid oxide fuel cells (SOFC) since cracks caused by sealing or thermal cycling still remain a substantial bottleneck in developing durable SOFC.
Previous studies on soda lime silicate glass [Sin14] showed that crack healing is driven by viscous flow and that healing progress is proportional to time t and inverse viscosity η. This finding would allow to present healing data of a given glass for different temperatures in a master curve healing progress versus t/η. Such master curves would be a helpful tool in understanding crack healing kinetics.
Against this background, crack healing in non-crystallizing sodium calcium silicate (NCS) and sodium borosilicate glasses (NBS) have been studied. Moreover, to evaluate the influence of micros structure in crystallized glass on crack healing process, glass matrix composites (GMC) where prepared out of NCS and zirconia as inert ceramic filler material mimicking a partially crystalline micro structure. Cracks were generated by Vickers indention and healed isothermally at different temperatures. Crack healing progress was monitored by optical and electron microscopy. Results show that the above mentioned proportionality actually applies for the studied glasses for which such a master curve could be obtained. In comparison to a non-crystallized glass, the effective viscosity of GMC is increased by rigid filler content. This effect substantially retards crack broadening during later healing stages, which often ends up in large pores. On the other hand, local viscous crack healing is still possible in larger glassy regions. This behavior seems to be very interesting for crack healing optimized sealants.