Papers by Author: Františka Dorčáková

Abstract: The indentation creep of free-standing Y-ZrO2 layer and 20Sc-60Si-20Mg-80O-20N oxynitride glass has been investigated. Creep experiment has been performed with flat cylindrical indenter (hot pressed SiC) in the temperature range from 860 °C to 1300 °C at the loads from 20 to 100 MPa. The strain-time relationship was registered and the creep exponent and activation energy of creep have been calculated. The microstructure changes have been observed and documented. Viscosity as a function of temperature and the glass transition temperature (Tg) were determined in oxynitride glass and compared with values from compressive creep.

Abstract: Thermal shock resistance of the RE-Si-Mg-O-N glasses (RE = La, Nd, Yb, Lu) with 0 and 20 eq.% of nitrogen was investigated by the indentation-quench method based on propagation of Vickers cracks. Crack growth was measured on the same sample for a test series of different quenching temperatures. Thermal shock resistance of the studied materials was determined as a temperature difference resulting in 10 % growth of the initial cracks (∆T10) and by the thermal shock parameter R calculated from the material properties. Although the comparison of ∆T10 and R values as a function of glass composition revealed some differences between these two approaches, also a common trend was observed. Thermal shock resistance increased with the fractional glass compactness resulting from RE type and N content increase.

Abstract: Effects of the rare-earth additives (RE = Sc, Y, La, Nd, Gd, Sm, Yb and Lu) and nitrogen on contact strength of the oxide and oxynitride glasses were investigated at room temperature. The advantage of this relatively new technique is its experimental simplicity and using of miniature samples, however, a relatively complex stress distribution around the contact points reduces Weibull parameter in comparison with the conventional bending strength. Contact strength of the tested glasses is also strongly influenced by surface finish. The differences in the effects of REmodifiers in oxide and oxynitride glasses suggest that the contributions from RE and nitrogen may not be simply additive, as observed earlier for various thermo-mechanical properties. However, additional study is necessary to eliminate the effects of surface defects to support this assumption.