Filtern
Dokumenttyp
- Zeitschriftenartikel (6)
- Vortrag (4)
- Posterpräsentation (3)
Sprache
- Englisch (13) (entfernen)
Schlagworte
- Vickers (5)
- Crack growth (4)
- Soda-lime silicate glass (4)
- Water speciation (4)
- Glass (3)
- Water content (3)
- Elastic constants (2)
- Glass transition (2)
- Indentation fracture toughness (2)
- Internal friction (2)
Organisationseinheit der BAM
- 5 Werkstofftechnik (11)
- 5.6 Glas (11)
Eingeladener Vortrag
- nein (4)
The presence of water in the surrounding atmosphere of a propagating crack has a major influence on the subcritical crack growth. While these external phenomena are well understood, there is still a lack of knowledge on the influence of structurally bound water on crack propagation. Thus, our recent study aims on the analysis of crack propagation in water bearing soda-lime silicate glasses with up to 8 wt.% water. The samples were synthesized in an internally heated pressure vessel at 0.5 GPa. Since this preparation route limits the sample sizes, standard test geometries allowing for the determination of stress intensity factors, such as double cantilever beam, are not feasible. Thus, radial cracks in the hydrous glasses were initiated by Vickers indentation and crack growth was simultaneously captured with a camera system. An automated image analysis algorithm was used for the analysis of the crack length of each single video frame. To minimize influences by atmospheric water, all experiments were conducted in a glovebox purged with dry N2. About 150 cracks per glass composition were analyzed to provide statistical significance of the Vickers-induced SCCG. The results show that structurally bound water has a major influence on SCCG by means of crack lengths, growth rates and time of crack initiation.
Water has a strong impact on the viscosity and the transition temperature of oxide glasses. It acts as a fluxing agent, reducing viscosity particularly in the glass transition range, and by that flattening the viscosity-temperature curve and decreasing the fragility of hydrous glass melts. This general behavior is found for silicate and borate as well as in borosilicate compositions. However, there is still a lack of data with respect to hydrous phosphate glasses. Here, we study the influence of structural water on the viscosity of Li2O-MgO-(Al2O3-)P2O5 glasses. The glasses were synthesized in an internally heated pressure vessel (IHPV) at a pressure of 0.5 GPa. The selected pressure allows for the synthesis of glass specimens with water contents of several wt.%. The viscosity measurements were carried out in the glass transition range, i.e. log η ≈ 10-13 (η in Pa s), using a sphere penetration viscometer. The measured data agree with glass transition temperatures measured by differential thermo analysis. First results further suggest that the fragility of the analyzed phosphates decreases with increasing water content.