Mária Chromčíková

Thermodynamic model and structure of CaO–P2O5 glasses

The distribution of Q-units of CaO–P2O5 glasses was described by the thermodynamic model of Shakhmatkin and Vedishcheva. The glass was considered as the ideal solution of CaO, P2O5, CaP2O6, Ca2P2O7, and Ca3P2O8. In the first step, molar Gibbs energies of considered species were taken from the FACT thermodynamic database. The obtained result was compared with 31P solid-state NMR study of Roiland. It was shown that the calculated values were in fairly good agreement with the experimental values. After that, the nonlinear regression treatment was used for optimization of molar Gibbs energies by minimizing the sum of squares of deviations between experimental and calculated Q-distribution. In such a manner, the non-ideality of the system was reflected. In the studied case, no significant improvement of obtained results was achieved by this procedure—thus, the ideal solution assumption included in the thermodynamic model of Shakhmatkin and Vedishcheva holds very well for the studied binary glasses.

Thermal Properties and Related Structural Study of Oxide Glasses

Glass is accompanying people from the early times of mankind. First it was the natural glass generated by the volcanic processes and the glass “produced” by the impact of meteors on the earth. During formation of the earth, highly siliceous melts of rocks froze to natural glasses such as obsidians. After some time the people start the glass melting. Glass was first produced by man about 4,000 years ago in ancient Egypt. From this time the need of the knowledge of glass composition, structure and properties is dated. These are the typical questions answered by the glass chemistry [1–6].

Structure and Properties of Selected Zirconia Silicate Glasses

Viscosity, density, thermal expansion, glass transition temperature, refractive index, molar refraction, and chemical durability of selected compositional series of Na2O-K2O-ZnO-CaOZrO2- SiO2 glasses containing 1 and 3 mol. % ZrO2 were measured and interpreted according to the network-forming / -modifying activities of particular oxides. The influence of ZrO2 / SiO2, ZnO / CaO, and K2O / Na2O substitution on measured physical and chemical properties was discussed.

Parameterization and Validation of Thermochemical Models of Glass by Advanced Statistical Analysis of Spectral Data

Shakhmatkin and Vedishcheva proposed the associated solutions’ thermodynamic model (SVTDM) of glasses and glass-forming melts. This model considers glasses and melts as an ideal solution formed from saltlike products of chemical reactions between the oxide components and the original (unreacted) oxides. The model does not use adjustable parameters; only the standard Gibbs energies of the formation of crystalline compounds and the analytical composition of the system considered are used as input parameters. A nonlinear regression treatment with the help of a genetic algorithm is used for the optimization of molar Gibbs energies by minimizing the sum of squares of deviations between experimental and calculated structure units’ distributions. In such a manner, the non-ideality of glass systems is reflected. The proposed method of using the optimized effective parameters (i.e., reaction Gibbs energies) within the SVTDM copes with most frequently met weak points of this method, i.e., missing of thermodynamic data for some components of SVTDM; missing of some components in the SVTDM because of insufficient knowledge of particular phase diagram or because of taking into account only the stable crystalline phases (and ignoring, e.g., the metastable ones); the assumption of zero mixing enthalpy connected with the supposed ideality of the studied glass system; the assumption of regular mixing entropy connected with the supposed ideality of the studied glass system; and the uncertainty in the mixing entropy originating in the uncertainty of molecular weight of individual components.

Chemical Durability of Gamma-Irradiated Glass Fibrous Insulation

Abstract The chemical durability of gamma-irradiated glass fibrous insulation commonly used in the reactor containment of nuclear power plants was tested by static leaching tests at 90°C. Distilled water and borate coolant solution were used as corrosive media. Two radiation doses, 2 and 4 MGy, were applied, the higher one roughly corresponding to 30 years of irradiation in reactor containment. The glass insulation was irradiated at low (70°C) and increased (450°C) temperatures. The results of the static leaching tests were compared with those obtained for nonirradiated native glass fibers. In distilled water, higher normalized leached amounts of calcium were found for low-temperature-irradiated glass fibers and in the initial stage of leaching of high-temperature-irradiated glass fibers; the lower normalized leached amounts were found for boron for glasses irradiated at both temperatures. In the borate coolant solution, higher normalized leached amounts of calcium and lower leached amounts of aluminum were observed for glasses irradiated at both temperatures. In all cases, the results were comparable for both applied radiation doses. Moreover, extraordinary brittleness of the glass fibers irradiated at high temperature was observed. This principally new finding needs further experimental and theoretical investigation.

Structural relaxation of lead and barium-free crystal glasses

The structural relaxation of Na2O–K2O–CaO–ZrO2–SiO2 (NKCZ), Na2O–K2O–ZnO–ZrO2–SiO2 (NKzZ), Na2O–CaO–ZnO–ZrO2–SiO2 (NCzZ), K2O–CaO–ZnO–ZrO2–SiO2 (KCzZ), and Na2O–K2O–CaO–ZnO–ZrO2–SiO2 (NKCzZ) glasses were studied by thermomechanical analysis. The structural relaxation was described by the Tool–Narayanaswamy–Mazurin model (TNMa). The relaxation function of Kohlrausch, Williams, and Watts (KWW) was used. The parameters of relaxation model were calculated by nonlinear regression analysis of thermodilatometric curves measured under cyclic time–temperature regime by thermomechanical analyzer under the constant load. The values of the exponent b of the KWW equation, modulus K, limit dynamic viscosity η0 of the Mazurin’s expression for relaxation time, and constant B of the Vogel–Fulcher–Tammann viscosity equation were optimized. It was found that TNMa relaxation model very well describes the experimental data. A more detailed analysis of the obtained results showed that the equimolar substitution of SiO2 by ZrO2 (i.e., the increase of the ZrO2 content in the glass) decreases the parameter b, therefore the continuous distribution of the relaxation times spectrum is widening. A wider spectrum of relaxation times was obtained even in the case of substitution of ZnO for CaO and K2O for Na2O. Substitution of ZrO2 for SiO2 decreases the dynamic viscosity limit η0 that corresponds to an activation energy increase of temperature dependence of isostructural viscosity. Increased content of ZrO2 in the glass caused the increase of the value of the modulus K.

Stress Strain Testing of the Strand of E-Glass Fibers

The mathematical model of the stress-strain curve of the strand of glass fibers was proposed and applied on the experimental data obtained for E glass fibers. The model reflects the lognormal continuous distribution of the unstrained lengths of glass fibers and the Weibull distribution of the fibers strength. The regression treatment of experimental data provided the statistically robust estimates of the parameters of the lognormal length distribution, of the Young modulus, and of the parameters of the Weibull glass fibers strength distribution. It was shown that neglecting of the continuous unstrained length distribution leads to serious errors in estimates of the fiber strength distribution.

Chemical Durability of Glass Thermal Insulation Fibers in Borate and Phosphate Water Solutions

Glass fiber is commonly used as thermal insulation for the equipment in nuclear power plants. In case of LOCA (Loss Of Coolant Accident), the insulation can be damaged by the jet impact and carried to the screens of the emergency systems needed to cool the reactor. In this case, the fibers can be strongly corroded by particular cooler solutions and their behavior under this environment can modify the head loss of the screens. The pH value of coolant solution can be stabilized respectively by borate or phosphate buffering systems depending of the plants. A new type of small scale laboratory equipment allowing simultaneous study of the chemical durability of glass fibers and hydrodynamic conditions on the glass fiber bed placed on the screen was developed and tested. The results obtained for leaching of glass fibers in sodium borate and sodium phosphate solutions show the significant difference between the saturation levels of Ca, Al, and Si in tested leaching solutions. The observed difference in leaching chemistry caused significant differences in the head loss value and its time development. This preliminary conclusion opens a new research field to improve the NPPs but it has to be substantiated by additional records and sensitivity studies including uncertainties analysis.